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-rw-r--r--compiler/rustc_ast/src/ast.rs348
-rw-r--r--compiler/rustc_ast/src/ast_traits.rs11
-rw-r--r--compiler/rustc_ast/src/attr/mod.rs5
-rw-r--r--compiler/rustc_ast/src/expand/autodiff_attrs.rs3
-rw-r--r--compiler/rustc_ast/src/format.rs3
-rw-r--r--compiler/rustc_ast/src/lib.rs1
-rw-r--r--compiler/rustc_ast/src/mut_visit.rs19
-rw-r--r--compiler/rustc_ast/src/ptr.rs11
-rw-r--r--compiler/rustc_ast/src/visit.rs38
-rw-r--r--compiler/rustc_ast_lowering/src/asm.rs1
-rw-r--r--compiler/rustc_ast_lowering/src/block.rs3
-rw-r--r--compiler/rustc_ast_lowering/src/expr.rs34
-rw-r--r--compiler/rustc_ast_lowering/src/item.rs126
-rw-r--r--compiler/rustc_ast_lowering/src/lib.rs24
-rw-r--r--compiler/rustc_ast_lowering/src/pat.rs9
-rw-r--r--compiler/rustc_ast_lowering/src/path.rs2
-rw-r--r--compiler/rustc_ast_passes/messages.ftl16
-rw-r--r--compiler/rustc_ast_passes/src/ast_validation.rs104
-rw-r--r--compiler/rustc_ast_passes/src/errors.rs45
-rw-r--r--compiler/rustc_ast_passes/src/feature_gate.rs8
-rw-r--r--compiler/rustc_ast_pretty/src/pprust/state.rs3
-rw-r--r--compiler/rustc_ast_pretty/src/pprust/state/expr.rs13
-rw-r--r--compiler/rustc_ast_pretty/src/pprust/state/item.rs61
-rw-r--r--compiler/rustc_attr_parsing/Cargo.toml1
-rw-r--r--compiler/rustc_attr_parsing/messages.ftl7
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/allow_unstable.rs28
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/body.rs5
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/cfg.rs5
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs83
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/confusables.rs9
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/deprecation.rs31
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/dummy.rs4
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/inline.rs28
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/link_attrs.rs123
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/lint_helpers.rs27
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/loop_match.rs7
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/macro_attrs.rs32
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/mod.rs21
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/must_use.rs9
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/no_implicit_prelude.rs7
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/non_exhaustive.rs13
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/path.rs12
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/proc_macro_attrs.rs20
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/repr.rs25
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs12
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/semantics.rs4
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/stability.rs101
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/test_attrs.rs68
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/traits.rs28
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/transparency.rs8
-rw-r--r--compiler/rustc_attr_parsing/src/context.rs254
-rw-r--r--compiler/rustc_attr_parsing/src/lints.rs23
-rw-r--r--compiler/rustc_attr_parsing/src/session_diagnostics.rs27
-rw-r--r--compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs29
-rw-r--r--compiler/rustc_borrowck/src/diagnostics/mod.rs2
-rw-r--r--compiler/rustc_borrowck/src/diagnostics/move_errors.rs50
-rw-r--r--compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs3
-rw-r--r--compiler/rustc_borrowck/src/diagnostics/opaque_types.rs (renamed from compiler/rustc_borrowck/src/diagnostics/opaque_suggestions.rs)19
-rw-r--r--compiler/rustc_borrowck/src/diagnostics/region_errors.rs3
-rw-r--r--compiler/rustc_borrowck/src/handle_placeholders.rs19
-rw-r--r--compiler/rustc_borrowck/src/lib.rs51
-rw-r--r--compiler/rustc_borrowck/src/nll.rs51
-rw-r--r--compiler/rustc_borrowck/src/polonius/constraints.rs4
-rw-r--r--compiler/rustc_borrowck/src/polonius/legacy/facts.rs16
-rw-r--r--compiler/rustc_borrowck/src/polonius/liveness_constraints.rs12
-rw-r--r--compiler/rustc_borrowck/src/polonius/loan_liveness.rs191
-rw-r--r--compiler/rustc_borrowck/src/polonius/mod.rs6
-rw-r--r--compiler/rustc_borrowck/src/polonius/typeck_constraints.rs19
-rw-r--r--compiler/rustc_borrowck/src/region_infer/graphviz.rs17
-rw-r--r--compiler/rustc_borrowck/src/region_infer/mod.rs24
-rw-r--r--compiler/rustc_borrowck/src/region_infer/opaque_types.rs78
-rw-r--r--compiler/rustc_borrowck/src/renumber.rs2
-rw-r--r--compiler/rustc_borrowck/src/type_check/mod.rs16
-rw-r--r--compiler/rustc_borrowck/src/type_check/relate_tys.rs16
-rw-r--r--compiler/rustc_borrowck/src/universal_regions.rs10
-rw-r--r--compiler/rustc_builtin_macros/messages.ftl11
-rw-r--r--compiler/rustc_builtin_macros/src/alloc_error_handler.rs3
-rw-r--r--compiler/rustc_builtin_macros/src/asm.rs13
-rw-r--r--compiler/rustc_builtin_macros/src/assert.rs42
-rw-r--r--compiler/rustc_builtin_macros/src/assert/context.rs32
-rw-r--r--compiler/rustc_builtin_macros/src/autodiff.rs472
-rw-r--r--compiler/rustc_builtin_macros/src/cfg_accessible.rs2
-rw-r--r--compiler/rustc_builtin_macros/src/cfg_eval.rs15
-rw-r--r--compiler/rustc_builtin_macros/src/concat_bytes.rs3
-rw-r--r--compiler/rustc_builtin_macros/src/derive.rs6
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs9
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/coerce_pointee.rs32
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/debug.rs2
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/default.rs2
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/from.rs132
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/generic/mod.rs100
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/generic/ty.rs18
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/mod.rs14
-rw-r--r--compiler/rustc_builtin_macros/src/edition_panic.rs5
-rw-r--r--compiler/rustc_builtin_macros/src/errors.rs26
-rw-r--r--compiler/rustc_builtin_macros/src/format.rs5
-rw-r--r--compiler/rustc_builtin_macros/src/format_foreign.rs12
-rw-r--r--compiler/rustc_builtin_macros/src/global_allocator.rs13
-rw-r--r--compiler/rustc_builtin_macros/src/iter.rs3
-rw-r--r--compiler/rustc_builtin_macros/src/lib.rs1
-rw-r--r--compiler/rustc_builtin_macros/src/pattern_type.rs16
-rw-r--r--compiler/rustc_builtin_macros/src/proc_macro_harness.rs10
-rw-r--r--compiler/rustc_builtin_macros/src/source_util.rs5
-rw-r--r--compiler/rustc_builtin_macros/src/test.rs66
-rw-r--r--compiler/rustc_builtin_macros/src/test_harness.rs7
-rw-r--r--compiler/rustc_builtin_macros/src/util.rs11
-rw-r--r--compiler/rustc_codegen_cranelift/src/constant.rs13
-rw-r--r--compiler/rustc_codegen_cranelift/src/driver/aot.rs5
-rw-r--r--compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs24
-rw-r--r--compiler/rustc_codegen_cranelift/src/linkage.rs3
-rw-r--r--compiler/rustc_codegen_gcc/src/base.rs2
-rw-r--r--compiler/rustc_codegen_gcc/src/builder.rs7
-rw-r--r--compiler/rustc_codegen_gcc/src/consts.rs7
-rw-r--r--compiler/rustc_codegen_gcc/src/debuginfo.rs3
-rw-r--r--compiler/rustc_codegen_gcc/src/lib.rs6
-rw-r--r--compiler/rustc_codegen_gcc/src/mono_item.rs3
-rw-r--r--compiler/rustc_codegen_llvm/src/abi.rs12
-rw-r--r--compiler/rustc_codegen_llvm/src/allocator.rs17
-rw-r--r--compiler/rustc_codegen_llvm/src/attributes.rs16
-rw-r--r--compiler/rustc_codegen_llvm/src/back/lto.rs28
-rw-r--r--compiler/rustc_codegen_llvm/src/back/write.rs11
-rw-r--r--compiler/rustc_codegen_llvm/src/base.rs15
-rw-r--r--compiler/rustc_codegen_llvm/src/builder.rs90
-rw-r--r--compiler/rustc_codegen_llvm/src/builder/autodiff.rs426
-rw-r--r--compiler/rustc_codegen_llvm/src/consts.rs9
-rw-r--r--compiler/rustc_codegen_llvm/src/context.rs21
-rw-r--r--compiler/rustc_codegen_llvm/src/coverageinfo/ffi.rs78
-rw-r--r--compiler/rustc_codegen_llvm/src/coverageinfo/llvm_cov.rs12
-rw-r--r--compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/covfun.rs16
-rw-r--r--compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs86
-rw-r--r--compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs57
-rw-r--r--compiler/rustc_codegen_llvm/src/debuginfo/mod.rs79
-rw-r--r--compiler/rustc_codegen_llvm/src/intrinsic.rs152
-rw-r--r--compiler/rustc_codegen_llvm/src/lib.rs6
-rw-r--r--compiler/rustc_codegen_llvm/src/llvm/ffi.rs5
-rw-r--r--compiler/rustc_codegen_llvm/src/llvm/mod.rs26
-rw-r--r--compiler/rustc_codegen_llvm/src/llvm_util.rs42
-rw-r--r--compiler/rustc_codegen_llvm/src/mono_item.rs3
-rw-r--r--compiler/rustc_codegen_ssa/Cargo.toml1
-rw-r--r--compiler/rustc_codegen_ssa/messages.ftl9
-rw-r--r--compiler/rustc_codegen_ssa/src/assert_module_sources.rs9
-rw-r--r--compiler/rustc_codegen_ssa/src/back/apple.rs28
-rw-r--r--compiler/rustc_codegen_ssa/src/back/link.rs99
-rw-r--r--compiler/rustc_codegen_ssa/src/back/linker.rs15
-rw-r--r--compiler/rustc_codegen_ssa/src/back/symbol_export.rs24
-rw-r--r--compiler/rustc_codegen_ssa/src/back/write.rs33
-rw-r--r--compiler/rustc_codegen_ssa/src/base.rs63
-rw-r--r--compiler/rustc_codegen_ssa/src/codegen_attrs.rs108
-rw-r--r--compiler/rustc_codegen_ssa/src/errors.rs20
-rw-r--r--compiler/rustc_codegen_ssa/src/mir/block.rs34
-rw-r--r--compiler/rustc_codegen_ssa/src/mir/intrinsic.rs82
-rw-r--r--compiler/rustc_codegen_ssa/src/mir/mod.rs4
-rw-r--r--compiler/rustc_codegen_ssa/src/mir/naked_asm.rs4
-rw-r--r--compiler/rustc_codegen_ssa/src/mir/operand.rs43
-rw-r--r--compiler/rustc_codegen_ssa/src/mono_item.rs3
-rw-r--r--compiler/rustc_codegen_ssa/src/target_features.rs15
-rw-r--r--compiler/rustc_codegen_ssa/src/traits/builder.rs3
-rw-r--r--compiler/rustc_codegen_ssa/src/traits/coverageinfo.rs5
-rw-r--r--compiler/rustc_codegen_ssa/src/traits/debuginfo.rs2
-rw-r--r--compiler/rustc_codegen_ssa/src/traits/declare.rs3
-rw-r--r--compiler/rustc_codegen_ssa/src/traits/write.rs2
-rw-r--r--compiler/rustc_const_eval/messages.ftl11
-rw-r--r--compiler/rustc_const_eval/src/check_consts/check.rs6
-rw-r--r--compiler/rustc_const_eval/src/check_consts/ops.rs2
-rw-r--r--compiler/rustc_const_eval/src/const_eval/eval_queries.rs7
-rw-r--r--compiler/rustc_const_eval/src/const_eval/machine.rs2
-rw-r--r--compiler/rustc_const_eval/src/errors.rs16
-rw-r--r--compiler/rustc_const_eval/src/interpret/call.rs31
-rw-r--r--compiler/rustc_const_eval/src/interpret/cast.rs34
-rw-r--r--compiler/rustc_const_eval/src/interpret/eval_context.rs9
-rw-r--r--compiler/rustc_const_eval/src/interpret/intern.rs97
-rw-r--r--compiler/rustc_const_eval/src/interpret/memory.rs44
-rw-r--r--compiler/rustc_const_eval/src/interpret/operand.rs4
-rw-r--r--compiler/rustc_const_eval/src/interpret/place.rs10
-rw-r--r--compiler/rustc_const_eval/src/interpret/step.rs10
-rw-r--r--compiler/rustc_const_eval/src/interpret/util.rs14
-rw-r--r--compiler/rustc_const_eval/src/interpret/validity.rs6
-rw-r--r--compiler/rustc_const_eval/src/lib.rs2
-rw-r--r--compiler/rustc_const_eval/src/util/type_name.rs48
-rw-r--r--compiler/rustc_error_codes/src/error_codes/E0518.md4
-rw-r--r--compiler/rustc_error_codes/src/error_codes/E0578.md4
-rw-r--r--compiler/rustc_error_codes/src/error_codes/E0701.md4
-rw-r--r--compiler/rustc_error_codes/src/error_codes/E0739.md4
-rw-r--r--compiler/rustc_error_codes/src/error_codes/E0755.md4
-rw-r--r--compiler/rustc_error_codes/src/error_codes/E0756.md4
-rw-r--r--compiler/rustc_error_codes/src/error_codes/E0788.md4
-rw-r--r--compiler/rustc_error_codes/src/error_codes/E0793.md34
-rw-r--r--compiler/rustc_errors/src/diagnostic.rs14
-rw-r--r--compiler/rustc_errors/src/emitter.rs4
-rw-r--r--compiler/rustc_expand/messages.ftl3
-rw-r--r--compiler/rustc_expand/src/base.rs148
-rw-r--r--compiler/rustc_expand/src/build.rs218
-rw-r--r--compiler/rustc_expand/src/errors.rs18
-rw-r--r--compiler/rustc_expand/src/expand.rs150
-rw-r--r--compiler/rustc_expand/src/mbe/diagnostics.rs43
-rw-r--r--compiler/rustc_expand/src/mbe/macro_check.rs24
-rw-r--r--compiler/rustc_expand/src/mbe/macro_rules.rs266
-rw-r--r--compiler/rustc_expand/src/module.rs3
-rw-r--r--compiler/rustc_expand/src/placeholders.rs68
-rw-r--r--compiler/rustc_expand/src/proc_macro.rs3
-rw-r--r--compiler/rustc_expand/src/stats.rs3
-rw-r--r--compiler/rustc_feature/src/accepted.rs4
-rw-r--r--compiler/rustc_feature/src/builtin_attrs.rs461
-rw-r--r--compiler/rustc_feature/src/removed.rs4
-rw-r--r--compiler/rustc_feature/src/unstable.rs13
-rw-r--r--compiler/rustc_hir/Cargo.toml1
-rw-r--r--compiler/rustc_hir/src/attrs/data_structures.rs27
-rw-r--r--compiler/rustc_hir/src/attrs/encode_cross_crate.rs3
-rw-r--r--compiler/rustc_hir/src/def.rs101
-rw-r--r--compiler/rustc_hir/src/hir.rs49
-rw-r--r--compiler/rustc_hir/src/intravisit.rs26
-rw-r--r--compiler/rustc_hir/src/lang_items.rs1
-rw-r--r--compiler/rustc_hir/src/lints.rs5
-rw-r--r--compiler/rustc_hir/src/target.rs152
-rw-r--r--compiler/rustc_hir_analysis/src/check/compare_impl_item.rs6
-rw-r--r--compiler/rustc_hir_analysis/src/check/intrinsic.rs14
-rw-r--r--compiler/rustc_hir_analysis/src/check/region.rs5
-rw-r--r--compiler/rustc_hir_analysis/src/check/wfcheck.rs96
-rw-r--r--compiler/rustc_hir_analysis/src/coherence/builtin.rs6
-rw-r--r--compiler/rustc_hir_analysis/src/coherence/orphan.rs4
-rw-r--r--compiler/rustc_hir_analysis/src/collect.rs36
-rw-r--r--compiler/rustc_hir_analysis/src/collect/predicates_of.rs7
-rw-r--r--compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs17
-rw-r--r--compiler/rustc_hir_analysis/src/collect/type_of.rs2
-rw-r--r--compiler/rustc_hir_analysis/src/errors/wrong_number_of_generic_args.rs6
-rw-r--r--compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs8
-rw-r--r--compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs2
-rw-r--r--compiler/rustc_hir_analysis/src/hir_ty_lowering/lint.rs6
-rw-r--r--compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs7
-rw-r--r--compiler/rustc_hir_analysis/src/hir_wf_check.rs5
-rw-r--r--compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs34
-rw-r--r--compiler/rustc_hir_pretty/src/lib.rs61
-rw-r--r--compiler/rustc_hir_typeck/messages.ftl4
-rw-r--r--compiler/rustc_hir_typeck/src/callee.rs1
-rw-r--r--compiler/rustc_hir_typeck/src/demand.rs2
-rw-r--r--compiler/rustc_hir_typeck/src/errors.rs8
-rw-r--r--compiler/rustc_hir_typeck/src/expr.rs99
-rw-r--r--compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs50
-rw-r--r--compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs11
-rw-r--r--compiler/rustc_hir_typeck/src/method/suggest.rs149
-rw-r--r--compiler/rustc_hir_typeck/src/pat.rs2
-rw-r--r--compiler/rustc_infer/src/infer/mod.rs12
-rw-r--r--compiler/rustc_interface/src/passes.rs4
-rw-r--r--compiler/rustc_interface/src/tests.rs3
-rw-r--r--compiler/rustc_lint/messages.ftl2
-rw-r--r--compiler/rustc_lint/src/builtin.rs25
-rw-r--r--compiler/rustc_lint/src/context.rs24
-rw-r--r--compiler/rustc_lint/src/default_could_be_derived.rs3
-rw-r--r--compiler/rustc_lint/src/deref_into_dyn_supertrait.rs4
-rw-r--r--compiler/rustc_lint/src/drop_forget_useless.rs2
-rw-r--r--compiler/rustc_lint/src/early.rs3
-rw-r--r--compiler/rustc_lint/src/early/diagnostics.rs14
-rw-r--r--compiler/rustc_lint/src/internal.rs12
-rw-r--r--compiler/rustc_lint/src/lifetime_syntax.rs9
-rw-r--r--compiler/rustc_lint/src/lints.rs69
-rw-r--r--compiler/rustc_lint/src/map_unit_fn.rs103
-rw-r--r--compiler/rustc_lint/src/non_local_def.rs8
-rw-r--r--compiler/rustc_lint/src/nonstandard_style.rs2
-rw-r--r--compiler/rustc_lint/src/pass_by_value.rs6
-rw-r--r--compiler/rustc_lint/src/types.rs5
-rw-r--r--compiler/rustc_lint_defs/src/builtin.rs48
-rw-r--r--compiler/rustc_lint_defs/src/lib.rs2
-rw-r--r--compiler/rustc_llvm/build.rs12
-rw-r--r--compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp65
-rw-r--r--compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp7
-rw-r--r--compiler/rustc_macros/src/diagnostics/utils.rs2
-rw-r--r--compiler/rustc_metadata/src/native_libs.rs2
-rw-r--r--compiler/rustc_metadata/src/rmeta/decoder.rs2
-rw-r--r--compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs19
-rw-r--r--compiler/rustc_metadata/src/rmeta/encoder.rs18
-rw-r--r--compiler/rustc_metadata/src/rmeta/mod.rs2
-rw-r--r--compiler/rustc_metadata/src/rmeta/parameterized.rs7
-rw-r--r--compiler/rustc_metadata/src/rmeta/table.rs89
-rw-r--r--compiler/rustc_middle/messages.ftl4
-rw-r--r--compiler/rustc_middle/src/error.rs11
-rw-r--r--compiler/rustc_middle/src/middle/codegen_fn_attrs.rs14
-rw-r--r--compiler/rustc_middle/src/middle/privacy.rs6
-rw-r--r--compiler/rustc_middle/src/middle/region.rs6
-rw-r--r--compiler/rustc_middle/src/mir/consts.rs5
-rw-r--r--compiler/rustc_middle/src/mir/coverage.rs85
-rw-r--r--compiler/rustc_middle/src/mir/interpret/allocation.rs84
-rw-r--r--compiler/rustc_middle/src/mir/interpret/allocation/provenance_map.rs142
-rw-r--r--compiler/rustc_middle/src/mir/interpret/error.rs3
-rw-r--r--compiler/rustc_middle/src/mir/interpret/pointer.rs12
-rw-r--r--compiler/rustc_middle/src/mir/mono.rs89
-rw-r--r--compiler/rustc_middle/src/mir/pretty.rs47
-rw-r--r--compiler/rustc_middle/src/query/mod.rs6
-rw-r--r--compiler/rustc_middle/src/thir.rs70
-rw-r--r--compiler/rustc_middle/src/ty/consts/valtree.rs15
-rw-r--r--compiler/rustc_middle/src/ty/context.rs7
-rw-r--r--compiler/rustc_middle/src/ty/diagnostics.rs13
-rw-r--r--compiler/rustc_middle/src/ty/error.rs38
-rw-r--r--compiler/rustc_middle/src/ty/generic_args.rs20
-rw-r--r--compiler/rustc_middle/src/ty/instance.rs74
-rw-r--r--compiler/rustc_middle/src/ty/mod.rs43
-rw-r--r--compiler/rustc_middle/src/ty/predicate.rs12
-rw-r--r--compiler/rustc_middle/src/ty/print/mod.rs151
-rw-r--r--compiler/rustc_middle/src/ty/print/pretty.rs125
-rw-r--r--compiler/rustc_middle/src/ty/rvalue_scopes.rs2
-rw-r--r--compiler/rustc_middle/src/ty/structural_impls.rs13
-rw-r--r--compiler/rustc_mir_build/messages.ftl2
-rw-r--r--compiler/rustc_mir_build/src/builder/block.rs12
-rw-r--r--compiler/rustc_mir_build/src/builder/coverageinfo.rs59
-rw-r--r--compiler/rustc_mir_build/src/builder/coverageinfo/mcdc.rs295
-rw-r--r--compiler/rustc_mir_build/src/builder/custom/parse/instruction.rs2
-rw-r--r--compiler/rustc_mir_build/src/builder/expr/into.rs2
-rw-r--r--compiler/rustc_mir_build/src/builder/matches/match_pair.rs20
-rw-r--r--compiler/rustc_mir_build/src/builder/matches/mod.rs293
-rw-r--r--compiler/rustc_mir_build/src/builder/matches/test.rs68
-rw-r--r--compiler/rustc_mir_build/src/builder/matches/util.rs8
-rw-r--r--compiler/rustc_mir_build/src/builder/scope.rs37
-rw-r--r--compiler/rustc_mir_build/src/check_tail_calls.rs11
-rw-r--r--compiler/rustc_mir_build/src/errors.rs9
-rw-r--r--compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs16
-rw-r--r--compiler/rustc_mir_build/src/thir/pattern/mod.rs8
-rw-r--r--compiler/rustc_mir_build/src/thir/print.rs2
-rw-r--r--compiler/rustc_mir_dataflow/src/framework/graphviz.rs1
-rw-r--r--compiler/rustc_mir_transform/messages.ftl2
-rw-r--r--compiler/rustc_mir_transform/src/check_call_recursion.rs4
-rw-r--r--compiler/rustc_mir_transform/src/check_inline.rs6
-rw-r--r--compiler/rustc_mir_transform/src/check_packed_ref.rs2
-rw-r--r--compiler/rustc_mir_transform/src/coverage/hir_info.rs128
-rw-r--r--compiler/rustc_mir_transform/src/coverage/mappings.rs294
-rw-r--r--compiler/rustc_mir_transform/src/coverage/mod.rs294
-rw-r--r--compiler/rustc_mir_transform/src/coverage/query.rs5
-rw-r--r--compiler/rustc_mir_transform/src/coverage/spans.rs13
-rw-r--r--compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs6
-rw-r--r--compiler/rustc_mir_transform/src/cross_crate_inline.rs2
-rw-r--r--compiler/rustc_mir_transform/src/errors.rs8
-rw-r--r--compiler/rustc_mir_transform/src/gvn.rs15
-rw-r--r--compiler/rustc_mir_transform/src/pass_manager.rs45
-rw-r--r--compiler/rustc_mir_transform/src/remove_unneeded_drops.rs31
-rw-r--r--compiler/rustc_mir_transform/src/shim.rs2
-rw-r--r--compiler/rustc_monomorphize/Cargo.toml2
-rw-r--r--compiler/rustc_monomorphize/messages.ftl9
-rw-r--r--compiler/rustc_monomorphize/src/collector.rs81
-rw-r--r--compiler/rustc_monomorphize/src/collector/autodiff.rs48
-rw-r--r--compiler/rustc_monomorphize/src/errors.rs23
-rw-r--r--compiler/rustc_monomorphize/src/partitioning.rs51
-rw-r--r--compiler/rustc_monomorphize/src/partitioning/autodiff.rs143
-rw-r--r--compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs99
-rw-r--r--compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs6
-rw-r--r--compiler/rustc_next_trait_solver/src/solve/eval_ctxt/probe.rs18
-rw-r--r--compiler/rustc_next_trait_solver/src/solve/inspect/build.rs16
-rw-r--r--compiler/rustc_next_trait_solver/src/solve/mod.rs26
-rw-r--r--compiler/rustc_next_trait_solver/src/solve/search_graph.rs4
-rw-r--r--compiler/rustc_next_trait_solver/src/solve/trait_goals.rs55
-rw-r--r--compiler/rustc_parse/messages.ftl11
-rw-r--r--compiler/rustc_parse/src/errors.rs42
-rw-r--r--compiler/rustc_parse/src/parser/asm.rs3
-rw-r--r--compiler/rustc_parse/src/parser/attr.rs3
-rw-r--r--compiler/rustc_parse/src/parser/cfg_select.rs30
-rw-r--r--compiler/rustc_parse/src/parser/diagnostics.rs112
-rw-r--r--compiler/rustc_parse/src/parser/expr.rs208
-rw-r--r--compiler/rustc_parse/src/parser/generics.rs6
-rw-r--r--compiler/rustc_parse/src/parser/item.rs163
-rw-r--r--compiler/rustc_parse/src/parser/mod.rs33
-rw-r--r--compiler/rustc_parse/src/parser/nonterminal.rs16
-rw-r--r--compiler/rustc_parse/src/parser/pat.rs57
-rw-r--r--compiler/rustc_parse/src/parser/path.rs21
-rw-r--r--compiler/rustc_parse/src/parser/stmt.rs33
-rw-r--r--compiler/rustc_parse/src/parser/tests.rs9
-rw-r--r--compiler/rustc_parse/src/parser/ty.rs65
-rw-r--r--compiler/rustc_parse/src/validate_attr.rs41
-rw-r--r--compiler/rustc_passes/messages.ftl155
-rw-r--r--compiler/rustc_passes/src/check_attr.rs957
-rw-r--r--compiler/rustc_passes/src/dead.rs10
-rw-r--r--compiler/rustc_passes/src/errors.rs304
-rw-r--r--compiler/rustc_passes/src/input_stats.rs4
-rw-r--r--compiler/rustc_passes/src/lang_items.rs2
-rw-r--r--compiler/rustc_passes/src/reachable.rs5
-rw-r--r--compiler/rustc_passes/src/stability.rs135
-rw-r--r--compiler/rustc_pattern_analysis/src/constructor.rs10
-rw-r--r--compiler/rustc_pattern_analysis/src/rustc.rs98
-rw-r--r--compiler/rustc_pattern_analysis/tests/exhaustiveness.rs3
-rw-r--r--compiler/rustc_privacy/src/lib.rs3
-rw-r--r--compiler/rustc_public/src/mir/body.rs32
-rw-r--r--compiler/rustc_public/src/mir/pretty.rs2
-rw-r--r--compiler/rustc_public/src/ty.rs34
-rw-r--r--compiler/rustc_resolve/messages.ftl5
-rw-r--r--compiler/rustc_resolve/src/build_reduced_graph.rs82
-rw-r--r--compiler/rustc_resolve/src/check_unused.rs4
-rw-r--r--compiler/rustc_resolve/src/def_collector.rs6
-rw-r--r--compiler/rustc_resolve/src/diagnostics.rs290
-rw-r--r--compiler/rustc_resolve/src/errors.rs6
-rw-r--r--compiler/rustc_resolve/src/ident.rs334
-rw-r--r--compiler/rustc_resolve/src/imports.rs89
-rw-r--r--compiler/rustc_resolve/src/late.rs166
-rw-r--r--compiler/rustc_resolve/src/late/diagnostics.rs111
-rw-r--r--compiler/rustc_resolve/src/lib.rs311
-rw-r--r--compiler/rustc_resolve/src/macros.rs126
-rw-r--r--compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/transform.rs4
-rw-r--r--compiler/rustc_session/src/config.rs59
-rw-r--r--compiler/rustc_session/src/options.rs5
-rw-r--r--compiler/rustc_session/src/session.rs5
-rw-r--r--compiler/rustc_span/src/lib.rs3
-rw-r--r--compiler/rustc_span/src/symbol.rs70
-rw-r--r--compiler/rustc_symbol_mangling/src/export.rs9
-rw-r--r--compiler/rustc_symbol_mangling/src/legacy.rs41
-rw-r--r--compiler/rustc_symbol_mangling/src/lib.rs55
-rw-r--r--compiler/rustc_symbol_mangling/src/v0.rs28
-rw-r--r--compiler/rustc_target/src/spec/abi_map.rs15
-rw-r--r--compiler/rustc_target/src/spec/base/apple/mod.rs67
-rw-r--r--compiler/rustc_target/src/spec/base/apple/tests.rs6
-rw-r--r--compiler/rustc_target/src/spec/json.rs6
-rw-r--r--compiler/rustc_target/src/spec/mod.rs8
-rw-r--r--compiler/rustc_target/src/spec/targets/aarch64_apple_darwin.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/aarch64_apple_ios.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/aarch64_apple_ios_macabi.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/aarch64_apple_ios_sim.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/aarch64_apple_tvos.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/aarch64_apple_tvos_sim.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/aarch64_apple_visionos.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/aarch64_apple_visionos_sim.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/aarch64_apple_watchos.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/aarch64_apple_watchos_sim.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/aarch64_be_unknown_none_softfloat.rs43
-rw-r--r--compiler/rustc_target/src/spec/targets/arm64_32_apple_watchos.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/arm64e_apple_darwin.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/arm64e_apple_ios.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/arm64e_apple_tvos.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/armv7a_vex_v5.rs44
-rw-r--r--compiler/rustc_target/src/spec/targets/armv7a_vex_v5_linker_script.ld144
-rw-r--r--compiler/rustc_target/src/spec/targets/armv7k_apple_watchos.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/armv7s_apple_ios.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/avr_none.rs2
-rw-r--r--compiler/rustc_target/src/spec/targets/i386_apple_ios.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/i686_apple_darwin.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/x86_64_apple_darwin.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/x86_64_apple_ios.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/x86_64_apple_ios_macabi.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/x86_64_apple_tvos.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/x86_64_apple_watchos_sim.rs4
-rw-r--r--compiler/rustc_target/src/spec/targets/x86_64h_apple_darwin.rs4
-rw-r--r--compiler/rustc_target/src/target_features.rs77
-rw-r--r--compiler/rustc_trait_selection/messages.ftl2
-rw-r--r--compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs106
-rw-r--r--compiler/rustc_trait_selection/src/error_reporting/infer/need_type_info.rs32
-rw-r--r--compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs5
-rw-r--r--compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs57
-rw-r--r--compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs145
-rw-r--r--compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs2
-rw-r--r--compiler/rustc_trait_selection/src/error_reporting/traits/on_unimplemented.rs4
-rw-r--r--compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs77
-rw-r--r--compiler/rustc_trait_selection/src/errors.rs11
-rw-r--r--compiler/rustc_trait_selection/src/traits/mod.rs2
-rw-r--r--compiler/rustc_trait_selection/src/traits/project.rs2
-rw-r--r--compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs74
-rw-r--r--compiler/rustc_trait_selection/src/traits/select/mod.rs17
-rw-r--r--compiler/rustc_ty_utils/src/abi.rs36
-rw-r--r--compiler/rustc_ty_utils/src/assoc.rs4
-rw-r--r--compiler/rustc_ty_utils/src/implied_bounds.rs8
-rw-r--r--compiler/rustc_ty_utils/src/instance.rs4
-rw-r--r--compiler/rustc_ty_utils/src/sig_types.rs2
-rw-r--r--compiler/rustc_ty_utils/src/ty.rs6
-rw-r--r--compiler/rustc_type_ir/src/binder.rs81
-rw-r--r--compiler/rustc_type_ir/src/canonical.rs25
-rw-r--r--compiler/rustc_type_ir/src/const_kind.rs8
-rw-r--r--compiler/rustc_type_ir/src/error.rs4
-rw-r--r--compiler/rustc_type_ir/src/generic_arg.rs8
-rw-r--r--compiler/rustc_type_ir/src/infer_ctxt.rs6
-rw-r--r--compiler/rustc_type_ir/src/opaque_ty.rs4
-rw-r--r--compiler/rustc_type_ir/src/pattern.rs4
-rw-r--r--compiler/rustc_type_ir/src/predicate.rs63
-rw-r--r--compiler/rustc_type_ir/src/predicate_kind.rs8
-rw-r--r--compiler/rustc_type_ir/src/region_kind.rs4
-rw-r--r--compiler/rustc_type_ir/src/relate.rs4
-rw-r--r--compiler/rustc_type_ir/src/search_graph/mod.rs505
-rw-r--r--compiler/rustc_type_ir/src/search_graph/stack.rs48
-rw-r--r--compiler/rustc_type_ir/src/solve/inspect.rs31
-rw-r--r--compiler/rustc_type_ir/src/solve/mod.rs37
-rw-r--r--compiler/rustc_type_ir/src/ty_kind.rs32
-rw-r--r--compiler/rustc_type_ir/src/ty_kind/closure.rs19
473 files changed, 9672 insertions, 9104 deletions
diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index fdff18ffd47..87c9c797ea5 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -35,7 +35,6 @@ use rustc_span::{ByteSymbol, DUMMY_SP, ErrorGuaranteed, Ident, Span, Symbol, kw,
 use thin_vec::{ThinVec, thin_vec};
 
 pub use crate::format::*;
-use crate::ptr::P;
 use crate::token::{self, CommentKind, Delimiter};
 use crate::tokenstream::{DelimSpan, LazyAttrTokenStream, TokenStream};
 use crate::util::parser::{ExprPrecedence, Fixity};
@@ -225,7 +224,7 @@ pub struct PathSegment {
     /// `Some` means that parameter list is supplied (`Path<X, Y>`)
     /// but it can be empty (`Path<>`).
     /// `P` is used as a size optimization for the common case with no parameters.
-    pub args: Option<P<GenericArgs>>,
+    pub args: Option<Box<GenericArgs>>,
 }
 
 // Succeeds if the path segment is arg-free and matches the given symbol.
@@ -286,7 +285,7 @@ pub enum GenericArg {
     /// `'a` in `Foo<'a>`.
     Lifetime(#[visitable(extra = LifetimeCtxt::GenericArg)] Lifetime),
     /// `Bar` in `Foo<Bar>`.
-    Type(P<Ty>),
+    Type(Box<Ty>),
     /// `1` in `Foo<1>`.
     Const(AnonConst),
 }
@@ -328,15 +327,15 @@ impl AngleBracketedArg {
     }
 }
 
-impl From<AngleBracketedArgs> for P<GenericArgs> {
+impl From<AngleBracketedArgs> for Box<GenericArgs> {
     fn from(val: AngleBracketedArgs) -> Self {
-        P(GenericArgs::AngleBracketed(val))
+        Box::new(GenericArgs::AngleBracketed(val))
     }
 }
 
-impl From<ParenthesizedArgs> for P<GenericArgs> {
+impl From<ParenthesizedArgs> for Box<GenericArgs> {
     fn from(val: ParenthesizedArgs) -> Self {
-        P(GenericArgs::Parenthesized(val))
+        Box::new(GenericArgs::Parenthesized(val))
     }
 }
 
@@ -350,7 +349,7 @@ pub struct ParenthesizedArgs {
     pub span: Span,
 
     /// `(A, B)`
-    pub inputs: ThinVec<P<Ty>>,
+    pub inputs: ThinVec<Box<Ty>>,
 
     /// ```text
     /// Foo(A, B) -> C
@@ -435,10 +434,10 @@ pub enum GenericParamKind {
     /// A lifetime definition (e.g., `'a: 'b + 'c + 'd`).
     Lifetime,
     Type {
-        default: Option<P<Ty>>,
+        default: Option<Box<Ty>>,
     },
     Const {
-        ty: P<Ty>,
+        ty: Box<Ty>,
         /// Span of the whole parameter definition, including default.
         span: Span,
         /// Optional default value for the const generic param.
@@ -526,7 +525,7 @@ pub struct WhereBoundPredicate {
     /// Any generics from a `for` binding.
     pub bound_generic_params: ThinVec<GenericParam>,
     /// The type being bounded.
-    pub bounded_ty: P<Ty>,
+    pub bounded_ty: Box<Ty>,
     /// Trait and lifetime bounds (`Clone + Send + 'static`).
     #[visitable(extra = BoundKind::Bound)]
     pub bounds: GenericBounds,
@@ -548,8 +547,8 @@ pub struct WhereRegionPredicate {
 /// E.g., `T = int`.
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct WhereEqPredicate {
-    pub lhs_ty: P<Ty>,
-    pub rhs_ty: P<Ty>,
+    pub lhs_ty: Box<Ty>,
+    pub rhs_ty: Box<Ty>,
 }
 
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
@@ -558,7 +557,7 @@ pub struct Crate {
     /// expansion placeholders or an unassigned value (`DUMMY_NODE_ID`) before that.
     pub id: NodeId,
     pub attrs: AttrVec,
-    pub items: ThinVec<P<Item>>,
+    pub items: ThinVec<Box<Item>>,
     pub spans: ModSpans,
     pub is_placeholder: bool,
 }
@@ -638,7 +637,7 @@ pub struct Pat {
 impl Pat {
     /// Attempt reparsing the pattern as a type.
     /// This is intended for use by diagnostics.
-    pub fn to_ty(&self) -> Option<P<Ty>> {
+    pub fn to_ty(&self) -> Option<Box<Ty>> {
         let kind = match &self.kind {
             PatKind::Missing => unreachable!(),
             // In a type expression `_` is an inference variable.
@@ -671,7 +670,7 @@ impl Pat {
             _ => return None,
         };
 
-        Some(P(Ty { kind, id: self.id, span: self.span, tokens: None }))
+        Some(Box::new(Ty { kind, id: self.id, span: self.span, tokens: None }))
     }
 
     /// Walk top-down and call `it` in each place where a pattern occurs
@@ -764,8 +763,8 @@ impl Pat {
     }
 }
 
-impl From<P<Pat>> for Pat {
-    fn from(value: P<Pat>) -> Self {
+impl From<Box<Pat>> for Pat {
+    fn from(value: Box<Pat>) -> Self {
         *value
     }
 }
@@ -780,7 +779,7 @@ pub struct PatField {
     /// The identifier for the field.
     pub ident: Ident,
     /// The pattern the field is destructured to.
-    pub pat: P<Pat>,
+    pub pat: Box<Pat>,
     pub is_shorthand: bool,
     pub attrs: AttrVec,
     pub id: NodeId,
@@ -865,44 +864,44 @@ pub enum PatKind {
     /// or a unit struct/variant pattern, or a const pattern (in the last two cases the third
     /// field must be `None`). Disambiguation cannot be done with parser alone, so it happens
     /// during name resolution.
-    Ident(BindingMode, Ident, Option<P<Pat>>),
+    Ident(BindingMode, Ident, Option<Box<Pat>>),
 
     /// A struct or struct variant pattern (e.g., `Variant {x, y, ..}`).
-    Struct(Option<P<QSelf>>, Path, ThinVec<PatField>, PatFieldsRest),
+    Struct(Option<Box<QSelf>>, Path, ThinVec<PatField>, PatFieldsRest),
 
     /// A tuple struct/variant pattern (`Variant(x, y, .., z)`).
-    TupleStruct(Option<P<QSelf>>, Path, ThinVec<P<Pat>>),
+    TupleStruct(Option<Box<QSelf>>, Path, ThinVec<Box<Pat>>),
 
     /// An or-pattern `A | B | C`.
     /// Invariant: `pats.len() >= 2`.
-    Or(ThinVec<P<Pat>>),
+    Or(ThinVec<Box<Pat>>),
 
     /// A possibly qualified path pattern.
     /// Unqualified path patterns `A::B::C` can legally refer to variants, structs, constants
     /// or associated constants. Qualified path patterns `<A>::B::C`/`<A as Trait>::B::C` can
     /// only legally refer to associated constants.
-    Path(Option<P<QSelf>>, Path),
+    Path(Option<Box<QSelf>>, Path),
 
     /// A tuple pattern (`(a, b)`).
-    Tuple(ThinVec<P<Pat>>),
+    Tuple(ThinVec<Box<Pat>>),
 
     /// A `box` pattern.
-    Box(P<Pat>),
+    Box(Box<Pat>),
 
     /// A `deref` pattern (currently `deref!()` macro-based syntax).
-    Deref(P<Pat>),
+    Deref(Box<Pat>),
 
     /// A reference pattern (e.g., `&mut (a, b)`).
-    Ref(P<Pat>, Mutability),
+    Ref(Box<Pat>, Mutability),
 
     /// A literal, const block or path.
-    Expr(P<Expr>),
+    Expr(Box<Expr>),
 
     /// A range pattern (e.g., `1...2`, `1..2`, `1..`, `..2`, `1..=2`, `..=2`).
-    Range(Option<P<Expr>>, Option<P<Expr>>, Spanned<RangeEnd>),
+    Range(Option<Box<Expr>>, Option<Box<Expr>>, Spanned<RangeEnd>),
 
     /// A slice pattern `[a, b, c]`.
-    Slice(ThinVec<P<Pat>>),
+    Slice(ThinVec<Box<Pat>>),
 
     /// A rest pattern `..`.
     ///
@@ -922,13 +921,13 @@ pub enum PatKind {
     Never,
 
     /// A guard pattern (e.g., `x if guard(x)`).
-    Guard(P<Pat>, P<Expr>),
+    Guard(Box<Pat>, Box<Expr>),
 
     /// Parentheses in patterns used for grouping (i.e., `(PAT)`).
-    Paren(P<Pat>),
+    Paren(Box<Pat>),
 
     /// A macro pattern; pre-expansion.
-    MacCall(P<MacCall>),
+    MacCall(Box<MacCall>),
 
     /// Placeholder for a pattern that wasn't syntactically well formed in some way.
     Err(ErrorGuaranteed),
@@ -1223,22 +1222,22 @@ impl Stmt {
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub enum StmtKind {
     /// A local (let) binding.
-    Let(P<Local>),
+    Let(Box<Local>),
     /// An item definition.
-    Item(P<Item>),
+    Item(Box<Item>),
     /// Expr without trailing semi-colon.
-    Expr(P<Expr>),
+    Expr(Box<Expr>),
     /// Expr with a trailing semi-colon.
-    Semi(P<Expr>),
+    Semi(Box<Expr>),
     /// Just a trailing semi-colon.
     Empty,
     /// Macro.
-    MacCall(P<MacCallStmt>),
+    MacCall(Box<MacCallStmt>),
 }
 
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct MacCallStmt {
-    pub mac: P<MacCall>,
+    pub mac: Box<MacCall>,
     pub style: MacStmtStyle,
     pub attrs: AttrVec,
     pub tokens: Option<LazyAttrTokenStream>,
@@ -1262,8 +1261,8 @@ pub enum MacStmtStyle {
 pub struct Local {
     pub id: NodeId,
     pub super_: Option<Span>,
-    pub pat: P<Pat>,
-    pub ty: Option<P<Ty>>,
+    pub pat: Box<Pat>,
+    pub ty: Option<Box<Ty>>,
     pub kind: LocalKind,
     pub span: Span,
     pub colon_sp: Option<Span>,
@@ -1278,10 +1277,10 @@ pub enum LocalKind {
     Decl,
     /// Local declaration with an initializer.
     /// Example: `let x = y;`
-    Init(P<Expr>),
+    Init(Box<Expr>),
     /// Local declaration with an initializer and an `else` clause.
     /// Example: `let Some(x) = y else { return };`
-    InitElse(P<Expr>, P<Block>),
+    InitElse(Box<Expr>, Box<Block>),
 }
 
 impl LocalKind {
@@ -1315,11 +1314,11 @@ impl LocalKind {
 pub struct Arm {
     pub attrs: AttrVec,
     /// Match arm pattern, e.g. `10` in `match foo { 10 => {}, _ => {} }`.
-    pub pat: P<Pat>,
+    pub pat: Box<Pat>,
     /// Match arm guard, e.g. `n > 10` in `match foo { n if n > 10 => {}, _ => {} }`.
-    pub guard: Option<P<Expr>>,
+    pub guard: Option<Box<Expr>>,
     /// Match arm body. Omitted if the pattern is a never pattern.
-    pub body: Option<P<Expr>>,
+    pub body: Option<Box<Expr>>,
     pub span: Span,
     pub id: NodeId,
     pub is_placeholder: bool,
@@ -1332,7 +1331,7 @@ pub struct ExprField {
     pub id: NodeId,
     pub span: Span,
     pub ident: Ident,
-    pub expr: P<Expr>,
+    pub expr: Box<Expr>,
     pub is_shorthand: bool,
     pub is_placeholder: bool,
 }
@@ -1357,7 +1356,7 @@ pub enum UnsafeSource {
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct AnonConst {
     pub id: NodeId,
-    pub value: P<Expr>,
+    pub value: Box<Expr>,
 }
 
 /// An expression.
@@ -1469,7 +1468,7 @@ impl Expr {
     }
 
     /// Attempts to reparse as `Ty` (for diagnostic purposes).
-    pub fn to_ty(&self) -> Option<P<Ty>> {
+    pub fn to_ty(&self) -> Option<Box<Ty>> {
         let kind = match &self.kind {
             // Trivial conversions.
             ExprKind::Path(qself, path) => TyKind::Path(qself.clone(), path.clone()),
@@ -1511,7 +1510,7 @@ impl Expr {
             _ => return None,
         };
 
-        Some(P(Ty { kind, id: self.id, span: self.span, tokens: None }))
+        Some(Box::new(Ty { kind, id: self.id, span: self.span, tokens: None }))
     }
 
     pub fn precedence(&self) -> ExprPrecedence {
@@ -1632,8 +1631,8 @@ impl Expr {
     }
 }
 
-impl From<P<Expr>> for Expr {
-    fn from(value: P<Expr>) -> Self {
+impl From<Box<Expr>> for Expr {
+    fn from(value: Box<Expr>) -> Self {
         *value
     }
 }
@@ -1645,8 +1644,8 @@ pub struct Closure {
     pub constness: Const,
     pub coroutine_kind: Option<CoroutineKind>,
     pub movability: Movability,
-    pub fn_decl: P<FnDecl>,
-    pub body: P<Expr>,
+    pub fn_decl: Box<FnDecl>,
+    pub body: Box<Expr>,
     /// The span of the declaration block: 'move |...| -> ...'
     pub fn_decl_span: Span,
     /// The span of the argument block `|...|`
@@ -1677,9 +1676,9 @@ pub struct MethodCall {
     /// The method name and its generic arguments, e.g. `foo::<Bar, Baz>`.
     pub seg: PathSegment,
     /// The receiver, e.g. `x`.
-    pub receiver: P<Expr>,
+    pub receiver: Box<Expr>,
     /// The arguments, e.g. `a, b, c`.
-    pub args: ThinVec<P<Expr>>,
+    pub args: ThinVec<Box<Expr>>,
     /// The span of the function, without the dot and receiver e.g. `foo::<Bar,
     /// Baz>(a, b, c)`.
     pub span: Span,
@@ -1688,7 +1687,7 @@ pub struct MethodCall {
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub enum StructRest {
     /// `..x`.
-    Base(P<Expr>),
+    Base(Box<Expr>),
     /// `..`.
     Rest(Span),
     /// No trailing `..` or expression.
@@ -1697,7 +1696,7 @@ pub enum StructRest {
 
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct StructExpr {
-    pub qself: Option<P<QSelf>>,
+    pub qself: Option<Box<QSelf>>,
     pub path: Path,
     pub fields: ThinVec<ExprField>,
     pub rest: StructRest,
@@ -1707,7 +1706,7 @@ pub struct StructExpr {
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub enum ExprKind {
     /// An array (e.g, `[a, b, c, d]`).
-    Array(ThinVec<P<Expr>>),
+    Array(ThinVec<Box<Expr>>),
     /// Allow anonymous constants from an inline `const` block.
     ConstBlock(AnonConst),
     /// A function call.
@@ -1716,90 +1715,90 @@ pub enum ExprKind {
     /// and the second field is the list of arguments.
     /// This also represents calling the constructor of
     /// tuple-like ADTs such as tuple structs and enum variants.
-    Call(P<Expr>, ThinVec<P<Expr>>),
+    Call(Box<Expr>, ThinVec<Box<Expr>>),
     /// A method call (e.g., `x.foo::<Bar, Baz>(a, b, c)`).
     MethodCall(Box<MethodCall>),
     /// A tuple (e.g., `(a, b, c, d)`).
-    Tup(ThinVec<P<Expr>>),
+    Tup(ThinVec<Box<Expr>>),
     /// A binary operation (e.g., `a + b`, `a * b`).
-    Binary(BinOp, P<Expr>, P<Expr>),
+    Binary(BinOp, Box<Expr>, Box<Expr>),
     /// A unary operation (e.g., `!x`, `*x`).
-    Unary(UnOp, P<Expr>),
+    Unary(UnOp, Box<Expr>),
     /// A literal (e.g., `1`, `"foo"`).
     Lit(token::Lit),
     /// A cast (e.g., `foo as f64`).
-    Cast(P<Expr>, P<Ty>),
+    Cast(Box<Expr>, Box<Ty>),
     /// A type ascription (e.g., `builtin # type_ascribe(42, usize)`).
     ///
     /// Usually not written directly in user code but
     /// indirectly via the macro `type_ascribe!(...)`.
-    Type(P<Expr>, P<Ty>),
+    Type(Box<Expr>, Box<Ty>),
     /// A `let pat = expr` expression that is only semantically allowed in the condition
     /// of `if` / `while` expressions. (e.g., `if let 0 = x { .. }`).
     ///
     /// `Span` represents the whole `let pat = expr` statement.
-    Let(P<Pat>, P<Expr>, Span, Recovered),
+    Let(Box<Pat>, Box<Expr>, Span, Recovered),
     /// An `if` block, with an optional `else` block.
     ///
     /// `if expr { block } else { expr }`
     ///
     /// If present, the "else" expr is always `ExprKind::Block` (for `else`) or
     /// `ExprKind::If` (for `else if`).
-    If(P<Expr>, P<Block>, Option<P<Expr>>),
+    If(Box<Expr>, Box<Block>, Option<Box<Expr>>),
     /// A while loop, with an optional label.
     ///
     /// `'label: while expr { block }`
-    While(P<Expr>, P<Block>, Option<Label>),
+    While(Box<Expr>, Box<Block>, Option<Label>),
     /// A `for` loop, with an optional label.
     ///
     /// `'label: for await? pat in iter { block }`
     ///
     /// This is desugared to a combination of `loop` and `match` expressions.
     ForLoop {
-        pat: P<Pat>,
-        iter: P<Expr>,
-        body: P<Block>,
+        pat: Box<Pat>,
+        iter: Box<Expr>,
+        body: Box<Block>,
         label: Option<Label>,
         kind: ForLoopKind,
     },
     /// Conditionless loop (can be exited with `break`, `continue`, or `return`).
     ///
     /// `'label: loop { block }`
-    Loop(P<Block>, Option<Label>, Span),
+    Loop(Box<Block>, Option<Label>, Span),
     /// A `match` block.
-    Match(P<Expr>, ThinVec<Arm>, MatchKind),
+    Match(Box<Expr>, ThinVec<Arm>, MatchKind),
     /// A closure (e.g., `move |a, b, c| a + b + c`).
     Closure(Box<Closure>),
     /// A block (`'label: { ... }`).
-    Block(P<Block>, Option<Label>),
+    Block(Box<Block>, Option<Label>),
     /// An `async` block (`async move { ... }`),
     /// or a `gen` block (`gen move { ... }`).
     ///
     /// The span is the "decl", which is the header before the body `{ }`
     /// including the `asyng`/`gen` keywords and possibly `move`.
-    Gen(CaptureBy, P<Block>, GenBlockKind, Span),
+    Gen(CaptureBy, Box<Block>, GenBlockKind, Span),
     /// An await expression (`my_future.await`). Span is of await keyword.
-    Await(P<Expr>, Span),
+    Await(Box<Expr>, Span),
     /// A use expression (`x.use`). Span is of use keyword.
-    Use(P<Expr>, Span),
+    Use(Box<Expr>, Span),
 
     /// A try block (`try { ... }`).
-    TryBlock(P<Block>),
+    TryBlock(Box<Block>),
 
     /// An assignment (`a = foo()`).
     /// The `Span` argument is the span of the `=` token.
-    Assign(P<Expr>, P<Expr>, Span),
+    Assign(Box<Expr>, Box<Expr>, Span),
     /// An assignment with an operator.
     ///
     /// E.g., `a += 1`.
-    AssignOp(AssignOp, P<Expr>, P<Expr>),
+    AssignOp(AssignOp, Box<Expr>, Box<Expr>),
     /// Access of a named (e.g., `obj.foo`) or unnamed (e.g., `obj.0`) struct field.
-    Field(P<Expr>, Ident),
+    Field(Box<Expr>, Ident),
     /// An indexing operation (e.g., `foo[2]`).
     /// The span represents the span of the `[2]`, including brackets.
-    Index(P<Expr>, P<Expr>, Span),
+    Index(Box<Expr>, Box<Expr>, Span),
     /// A range (e.g., `1..2`, `1..`, `..2`, `1..=2`, `..=2`; and `..` in destructuring assignment).
-    Range(Option<P<Expr>>, Option<P<Expr>>, RangeLimits),
+    Range(Option<Box<Expr>>, Option<Box<Expr>>, RangeLimits),
     /// An underscore, used in destructuring assignment to ignore a value.
     Underscore,
 
@@ -1807,57 +1806,57 @@ pub enum ExprKind {
     /// parameters (e.g., `foo::bar::<baz>`).
     ///
     /// Optionally "qualified" (e.g., `<Vec<T> as SomeTrait>::SomeType`).
-    Path(Option<P<QSelf>>, Path),
+    Path(Option<Box<QSelf>>, Path),
 
     /// A referencing operation (`&a`, `&mut a`, `&raw const a` or `&raw mut a`).
-    AddrOf(BorrowKind, Mutability, P<Expr>),
+    AddrOf(BorrowKind, Mutability, Box<Expr>),
     /// A `break`, with an optional label to break, and an optional expression.
-    Break(Option<Label>, Option<P<Expr>>),
+    Break(Option<Label>, Option<Box<Expr>>),
     /// A `continue`, with an optional label.
     Continue(Option<Label>),
     /// A `return`, with an optional value to be returned.
-    Ret(Option<P<Expr>>),
+    Ret(Option<Box<Expr>>),
 
     /// Output of the `asm!()` macro.
-    InlineAsm(P<InlineAsm>),
+    InlineAsm(Box<InlineAsm>),
 
     /// An `offset_of` expression (e.g., `builtin # offset_of(Struct, field)`).
     ///
     /// Usually not written directly in user code but
     /// indirectly via the macro `core::mem::offset_of!(...)`.
-    OffsetOf(P<Ty>, Vec<Ident>),
+    OffsetOf(Box<Ty>, Vec<Ident>),
 
     /// A macro invocation; pre-expansion.
-    MacCall(P<MacCall>),
+    MacCall(Box<MacCall>),
 
     /// A struct literal expression.
     ///
     /// E.g., `Foo {x: 1, y: 2}`, or `Foo {x: 1, .. rest}`.
-    Struct(P<StructExpr>),
+    Struct(Box<StructExpr>),
 
     /// An array literal constructed from one repeated element.
     ///
     /// E.g., `[1; 5]`. The expression is the element to be
     /// repeated; the constant is the number of times to repeat it.
-    Repeat(P<Expr>, AnonConst),
+    Repeat(Box<Expr>, AnonConst),
 
     /// No-op: used solely so we can pretty-print faithfully.
-    Paren(P<Expr>),
+    Paren(Box<Expr>),
 
     /// A try expression (`expr?`).
-    Try(P<Expr>),
+    Try(Box<Expr>),
 
     /// A `yield`, with an optional value to be yielded.
     Yield(YieldKind),
 
     /// A `do yeet` (aka `throw`/`fail`/`bail`/`raise`/whatever),
     /// with an optional value to be returned.
-    Yeet(Option<P<Expr>>),
+    Yeet(Option<Box<Expr>>),
 
     /// A tail call return, with the value to be returned.
     ///
     /// While `.0` must be a function call, we check this later, after parsing.
-    Become(P<Expr>),
+    Become(Box<Expr>),
 
     /// Bytes included via `include_bytes!`
     ///
@@ -1873,9 +1872,9 @@ pub enum ExprKind {
     IncludedBytes(ByteSymbol),
 
     /// A `format_args!()` expression.
-    FormatArgs(P<FormatArgs>),
+    FormatArgs(Box<FormatArgs>),
 
-    UnsafeBinderCast(UnsafeBinderCastKind, P<Expr>, Option<P<Ty>>),
+    UnsafeBinderCast(UnsafeBinderCastKind, Box<Expr>, Option<Box<Ty>>),
 
     /// Placeholder for an expression that wasn't syntactically well formed in some way.
     Err(ErrorGuaranteed),
@@ -1941,7 +1940,7 @@ pub enum UnsafeBinderCastKind {
 /// ```
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct QSelf {
-    pub ty: P<Ty>,
+    pub ty: Box<Ty>,
 
     /// The span of `a::b::Trait` in a path like `<Vec<T> as
     /// a::b::Trait>::AssociatedItem`; in the case where `position ==
@@ -2001,7 +2000,7 @@ pub enum ClosureBinder {
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct MacCall {
     pub path: Path,
-    pub args: P<DelimArgs>,
+    pub args: Box<DelimArgs>,
 }
 
 impl MacCall {
@@ -2021,7 +2020,7 @@ pub enum AttrArgs {
     Eq {
         /// Span of the `=` token.
         eq_span: Span,
-        expr: P<Expr>,
+        expr: Box<Expr>,
     },
 }
 
@@ -2064,7 +2063,7 @@ impl DelimArgs {
 /// Represents a macro definition.
 #[derive(Clone, Encodable, Decodable, Debug, HashStable_Generic, Walkable)]
 pub struct MacroDef {
-    pub body: P<DelimArgs>,
+    pub body: Box<DelimArgs>,
     /// `true` if macro was defined with `macro_rules`.
     pub macro_rules: bool,
 }
@@ -2093,16 +2092,16 @@ pub enum MatchKind {
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub enum YieldKind {
     /// yield expr { ... }
-    Prefix(Option<P<Expr>>),
+    Prefix(Option<Box<Expr>>),
     /// expr.yield { ... }
-    Postfix(P<Expr>),
+    Postfix(Box<Expr>),
 }
 
 impl YieldKind {
     /// Returns the expression inside the yield expression, if any.
     ///
     /// For postfix yields, this is guaranteed to be `Some`.
-    pub const fn expr(&self) -> Option<&P<Expr>> {
+    pub const fn expr(&self) -> Option<&Box<Expr>> {
         match self {
             YieldKind::Prefix(expr) => expr.as_ref(),
             YieldKind::Postfix(expr) => Some(expr),
@@ -2110,7 +2109,7 @@ impl YieldKind {
     }
 
     /// Returns a mutable reference to the expression being yielded, if any.
-    pub const fn expr_mut(&mut self) -> Option<&mut P<Expr>> {
+    pub const fn expr_mut(&mut self) -> Option<&mut Box<Expr>> {
         match self {
             YieldKind::Prefix(expr) => expr.as_mut(),
             YieldKind::Postfix(expr) => Some(expr),
@@ -2272,7 +2271,7 @@ impl LitKind {
 // type structure in `middle/ty.rs` as well.
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct MutTy {
-    pub ty: P<Ty>,
+    pub ty: Box<Ty>,
     pub mutbl: Mutability,
 }
 
@@ -2281,7 +2280,7 @@ pub struct MutTy {
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct FnSig {
     pub header: FnHeader,
-    pub decl: P<FnDecl>,
+    pub decl: Box<FnDecl>,
     pub span: Span,
 }
 
@@ -2306,12 +2305,12 @@ pub struct AssocItemConstraint {
 
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub enum Term {
-    Ty(P<Ty>),
+    Ty(Box<Ty>),
     Const(AnonConst),
 }
 
-impl From<P<Ty>> for Term {
-    fn from(v: P<Ty>) -> Self {
+impl From<Box<Ty>> for Term {
+    fn from(v: Box<Ty>) -> Self {
         Term::Ty(v)
     }
 }
@@ -2358,8 +2357,8 @@ impl Clone for Ty {
     }
 }
 
-impl From<P<Ty>> for Ty {
-    fn from(value: P<Ty>) -> Self {
+impl From<Box<Ty>> for Ty {
+    fn from(value: Box<Ty>) -> Self {
         *value
     }
 }
@@ -2388,7 +2387,7 @@ pub struct FnPtrTy {
     pub safety: Safety,
     pub ext: Extern,
     pub generic_params: ThinVec<GenericParam>,
-    pub decl: P<FnDecl>,
+    pub decl: Box<FnDecl>,
     /// Span of the `[unsafe] [extern] fn(...) -> ...` part, i.e. everything
     /// after the generic params (if there are any, e.g. `for<'a>`).
     pub decl_span: Span,
@@ -2397,7 +2396,7 @@ pub struct FnPtrTy {
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct UnsafeBinderTy {
     pub generic_params: ThinVec<GenericParam>,
-    pub inner_ty: P<Ty>,
+    pub inner_ty: Box<Ty>,
 }
 
 /// The various kinds of type recognized by the compiler.
@@ -2406,9 +2405,9 @@ pub struct UnsafeBinderTy {
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub enum TyKind {
     /// A variable-length slice (`[T]`).
-    Slice(P<Ty>),
+    Slice(Box<Ty>),
     /// A fixed length array (`[T; n]`).
-    Array(P<Ty>, AnonConst),
+    Array(Box<Ty>, AnonConst),
     /// A raw pointer (`*const T` or `*mut T`).
     Ptr(MutTy),
     /// A reference (`&'a T` or `&'a mut T`).
@@ -2418,18 +2417,18 @@ pub enum TyKind {
     /// Desugars into `Pin<&'a T>` or `Pin<&'a mut T>`.
     PinnedRef(#[visitable(extra = LifetimeCtxt::Ref)] Option<Lifetime>, MutTy),
     /// A function pointer type (e.g., `fn(usize) -> bool`).
-    FnPtr(P<FnPtrTy>),
+    FnPtr(Box<FnPtrTy>),
     /// An unsafe existential lifetime binder (e.g., `unsafe<'a> &'a ()`).
-    UnsafeBinder(P<UnsafeBinderTy>),
+    UnsafeBinder(Box<UnsafeBinderTy>),
     /// The never type (`!`).
     Never,
     /// A tuple (`(A, B, C, D,...)`).
-    Tup(ThinVec<P<Ty>>),
+    Tup(ThinVec<Box<Ty>>),
     /// A path (`module::module::...::Type`), optionally
     /// "qualified", e.g., `<Vec<T> as SomeTrait>::SomeType`.
     ///
     /// Type parameters are stored in the `Path` itself.
-    Path(Option<P<QSelf>>, Path),
+    Path(Option<Box<QSelf>>, Path),
     /// A trait object type `Bound1 + Bound2 + Bound3`
     /// where `Bound` is a trait or a lifetime.
     TraitObject(#[visitable(extra = BoundKind::TraitObject)] GenericBounds, TraitObjectSyntax),
@@ -2441,7 +2440,7 @@ pub enum TyKind {
     /// the generation of opaque `type Foo = impl Trait` items significantly.
     ImplTrait(NodeId, #[visitable(extra = BoundKind::Impl)] GenericBounds),
     /// No-op; kept solely so that we can pretty-print faithfully.
-    Paren(P<Ty>),
+    Paren(Box<Ty>),
     /// Unused for now.
     Typeof(AnonConst),
     /// This means the type should be inferred instead of it having been
@@ -2450,12 +2449,12 @@ pub enum TyKind {
     /// Inferred type of a `self` or `&self` argument in a method.
     ImplicitSelf,
     /// A macro in the type position.
-    MacCall(P<MacCall>),
+    MacCall(Box<MacCall>),
     /// Placeholder for a `va_list`.
     CVarArgs,
     /// Pattern types like `pattern_type!(u32 is 1..=)`, which is the same as `NonZero<u32>`,
     /// just as part of the type system.
-    Pat(P<Ty>, P<TyPat>),
+    Pat(Box<Ty>, Box<TyPat>),
     /// Sometimes we need a dummy value when no error has occurred.
     Dummy,
     /// Placeholder for a kind that has failed to be defined.
@@ -2531,9 +2530,9 @@ pub struct TyPat {
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub enum TyPatKind {
     /// A range pattern (e.g., `1...2`, `1..2`, `1..`, `..2`, `1..=2`, `..=2`).
-    Range(Option<P<AnonConst>>, Option<P<AnonConst>>, Spanned<RangeEnd>),
+    Range(Option<Box<AnonConst>>, Option<Box<AnonConst>>, Spanned<RangeEnd>),
 
-    Or(ThinVec<P<TyPat>>),
+    Or(ThinVec<Box<TyPat>>),
 
     /// Placeholder for a pattern that wasn't syntactically well formed in some way.
     Err(ErrorGuaranteed),
@@ -2698,7 +2697,7 @@ impl InlineAsmTemplatePiece {
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct InlineAsmSym {
     pub id: NodeId,
-    pub qself: Option<P<QSelf>>,
+    pub qself: Option<Box<QSelf>>,
     pub path: Path,
 }
 
@@ -2709,23 +2708,23 @@ pub struct InlineAsmSym {
 pub enum InlineAsmOperand {
     In {
         reg: InlineAsmRegOrRegClass,
-        expr: P<Expr>,
+        expr: Box<Expr>,
     },
     Out {
         reg: InlineAsmRegOrRegClass,
         late: bool,
-        expr: Option<P<Expr>>,
+        expr: Option<Box<Expr>>,
     },
     InOut {
         reg: InlineAsmRegOrRegClass,
         late: bool,
-        expr: P<Expr>,
+        expr: Box<Expr>,
     },
     SplitInOut {
         reg: InlineAsmRegOrRegClass,
         late: bool,
-        in_expr: P<Expr>,
-        out_expr: Option<P<Expr>>,
+        in_expr: Box<Expr>,
+        out_expr: Option<Box<Expr>>,
     },
     Const {
         anon_const: AnonConst,
@@ -2734,7 +2733,7 @@ pub enum InlineAsmOperand {
         sym: InlineAsmSym,
     },
     Label {
-        block: P<Block>,
+        block: Box<Block>,
     },
 }
 
@@ -2807,8 +2806,8 @@ pub struct InlineAsm {
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct Param {
     pub attrs: AttrVec,
-    pub ty: P<Ty>,
-    pub pat: P<Pat>,
+    pub ty: Box<Ty>,
+    pub pat: Box<Pat>,
     pub id: NodeId,
     pub span: Span,
     pub is_placeholder: bool,
@@ -2826,7 +2825,7 @@ pub enum SelfKind {
     /// `&'lt pin const self`, `&'lt pin mut self`
     Pinned(Option<Lifetime>, Mutability),
     /// `self: TYPE`, `mut self: TYPE`
-    Explicit(P<Ty>, Mutability),
+    Explicit(Box<Ty>, Mutability),
 }
 
 impl SelfKind {
@@ -2882,7 +2881,7 @@ impl Param {
     /// Builds a `Param` object from `ExplicitSelf`.
     pub fn from_self(attrs: AttrVec, eself: ExplicitSelf, eself_ident: Ident) -> Param {
         let span = eself.span.to(eself_ident.span);
-        let infer_ty = P(Ty {
+        let infer_ty = Box::new(Ty {
             id: DUMMY_NODE_ID,
             kind: TyKind::ImplicitSelf,
             span: eself_ident.span,
@@ -2893,7 +2892,7 @@ impl Param {
             SelfKind::Value(mutbl) => (mutbl, infer_ty),
             SelfKind::Region(lt, mutbl) => (
                 Mutability::Not,
-                P(Ty {
+                Box::new(Ty {
                     id: DUMMY_NODE_ID,
                     kind: TyKind::Ref(lt, MutTy { ty: infer_ty, mutbl }),
                     span,
@@ -2902,7 +2901,7 @@ impl Param {
             ),
             SelfKind::Pinned(lt, mutbl) => (
                 mutbl,
-                P(Ty {
+                Box::new(Ty {
                     id: DUMMY_NODE_ID,
                     kind: TyKind::PinnedRef(lt, MutTy { ty: infer_ty, mutbl }),
                     span,
@@ -2912,7 +2911,7 @@ impl Param {
         };
         Param {
             attrs,
-            pat: P(Pat {
+            pat: Box::new(Pat {
                 id: DUMMY_NODE_ID,
                 kind: PatKind::Ident(BindingMode(ByRef::No, mutbl), eself_ident, None),
                 span,
@@ -3123,7 +3122,7 @@ pub enum FnRetTy {
     /// Span points to where return type would be inserted.
     Default(Span),
     /// Everything else.
-    Ty(P<Ty>),
+    Ty(Box<Ty>),
 }
 
 impl FnRetTy {
@@ -3148,7 +3147,7 @@ pub enum ModKind {
     /// or with definition outlined to a separate file `mod foo;` and already loaded from it.
     /// The inner span is from the first token past `{` to the last token until `}`,
     /// or from the first to the last token in the loaded file.
-    Loaded(ThinVec<P<Item>>, Inline, ModSpans, Result<(), ErrorGuaranteed>),
+    Loaded(ThinVec<Box<Item>>, Inline, ModSpans, Result<(), ErrorGuaranteed>),
     /// Module with definition outlined to a separate file `mod foo;` but not yet loaded from it.
     Unloaded,
 }
@@ -3172,7 +3171,7 @@ pub struct ForeignMod {
     /// semantically by Rust.
     pub safety: Safety,
     pub abi: Option<StrLit>,
-    pub items: ThinVec<P<ForeignItem>>,
+    pub items: ThinVec<Box<ForeignItem>>,
 }
 
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
@@ -3267,7 +3266,7 @@ pub struct Attribute {
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub enum AttrKind {
     /// A normal attribute.
-    Normal(P<NormalAttr>),
+    Normal(Box<NormalAttr>),
 
     /// A doc comment (e.g. `/// ...`, `//! ...`, `/** ... */`, `/*! ... */`).
     /// Doc attributes (e.g. `#[doc="..."]`) are represented with the `Normal`
@@ -3381,7 +3380,7 @@ pub struct Visibility {
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub enum VisibilityKind {
     Public,
-    Restricted { path: P<Path>, id: NodeId, shorthand: bool },
+    Restricted { path: Box<Path>, id: NodeId, shorthand: bool },
     Inherited,
 }
 
@@ -3403,7 +3402,7 @@ pub struct FieldDef {
     pub safety: Safety,
     pub ident: Option<Ident>,
 
-    pub ty: P<Ty>,
+    pub ty: Box<Ty>,
     pub default: Option<AnonConst>,
     pub is_placeholder: bool,
 }
@@ -3609,7 +3608,7 @@ pub struct Trait {
     #[visitable(extra = BoundKind::SuperTraits)]
     pub bounds: GenericBounds,
     #[visitable(extra = AssocCtxt::Trait)]
-    pub items: ThinVec<P<AssocItem>>,
+    pub items: ThinVec<Box<AssocItem>>,
 }
 
 /// The location of a where clause on a `TyAlias` (`Span`) and whether there was
@@ -3657,26 +3656,30 @@ pub struct TyAlias {
     pub where_clauses: TyAliasWhereClauses,
     #[visitable(extra = BoundKind::Bound)]
     pub bounds: GenericBounds,
-    pub ty: Option<P<Ty>>,
+    pub ty: Option<Box<Ty>>,
 }
 
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct Impl {
+    pub generics: Generics,
+    pub of_trait: Option<Box<TraitImplHeader>>,
+    pub self_ty: Box<Ty>,
+    pub items: ThinVec<Box<AssocItem>>,
+}
+
+#[derive(Clone, Encodable, Decodable, Debug)]
+pub struct TraitImplHeader {
     pub defaultness: Defaultness,
     pub safety: Safety,
-    pub generics: Generics,
     pub constness: Const,
     pub polarity: ImplPolarity,
-    /// The trait being implemented, if any.
-    pub of_trait: Option<TraitRef>,
-    pub self_ty: P<Ty>,
-    pub items: ThinVec<P<AssocItem>>,
+    pub trait_ref: TraitRef,
 }
 
 #[derive(Clone, Encodable, Decodable, Debug, Default, Walkable)]
 pub struct FnContract {
-    pub requires: Option<P<Expr>>,
-    pub ensures: Option<P<Expr>>,
+    pub requires: Option<Box<Expr>>,
+    pub ensures: Option<Box<Expr>>,
 }
 
 #[derive(Clone, Encodable, Decodable, Debug)]
@@ -3685,40 +3688,40 @@ pub struct Fn {
     pub ident: Ident,
     pub generics: Generics,
     pub sig: FnSig,
-    pub contract: Option<P<FnContract>>,
+    pub contract: Option<Box<FnContract>>,
     pub define_opaque: Option<ThinVec<(NodeId, Path)>>,
-    pub body: Option<P<Block>>,
+    pub body: Option<Box<Block>>,
 }
 
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct Delegation {
     /// Path resolution id.
     pub id: NodeId,
-    pub qself: Option<P<QSelf>>,
+    pub qself: Option<Box<QSelf>>,
     pub path: Path,
     pub ident: Ident,
     pub rename: Option<Ident>,
-    pub body: Option<P<Block>>,
+    pub body: Option<Box<Block>>,
     /// The item was expanded from a glob delegation item.
     pub from_glob: bool,
 }
 
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct DelegationMac {
-    pub qself: Option<P<QSelf>>,
+    pub qself: Option<Box<QSelf>>,
     pub prefix: Path,
     // Some for list delegation, and None for glob delegation.
     pub suffixes: Option<ThinVec<(Ident, Option<Ident>)>>,
-    pub body: Option<P<Block>>,
+    pub body: Option<Box<Block>>,
 }
 
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct StaticItem {
     pub ident: Ident,
-    pub ty: P<Ty>,
+    pub ty: Box<Ty>,
     pub safety: Safety,
     pub mutability: Mutability,
-    pub expr: Option<P<Expr>>,
+    pub expr: Option<Box<Expr>>,
     pub define_opaque: Option<ThinVec<(NodeId, Path)>>,
 }
 
@@ -3727,8 +3730,8 @@ pub struct ConstItem {
     pub defaultness: Defaultness,
     pub ident: Ident,
     pub generics: Generics,
-    pub ty: P<Ty>,
-    pub expr: Option<P<Expr>>,
+    pub ty: Box<Ty>,
+    pub expr: Option<Box<Expr>>,
     pub define_opaque: Option<ThinVec<(NodeId, Path)>>,
 }
 
@@ -3794,11 +3797,11 @@ pub enum ItemKind {
     /// An implementation.
     ///
     /// E.g., `impl<A> Foo<A> { .. }` or `impl<A> Trait for Foo<A> { .. }`.
-    Impl(Box<Impl>),
+    Impl(Impl),
     /// A macro invocation.
     ///
     /// E.g., `foo!(..)`.
-    MacCall(P<MacCall>),
+    MacCall(Box<MacCall>),
     /// A macro definition.
     MacroDef(Ident, MacroDef),
     /// A single delegation item (`reuse`).
@@ -3881,7 +3884,7 @@ impl ItemKind {
             | Self::Union(_, generics, _)
             | Self::Trait(box Trait { generics, .. })
             | Self::TraitAlias(_, generics, _)
-            | Self::Impl(box Impl { generics, .. }) => Some(generics),
+            | Self::Impl(Impl { generics, .. }) => Some(generics),
             _ => None,
         }
     }
@@ -3908,7 +3911,7 @@ pub enum AssocItemKind {
     /// An associated type.
     Type(Box<TyAlias>),
     /// A macro expanding to associated items.
-    MacCall(P<MacCall>),
+    MacCall(Box<MacCall>),
     /// An associated delegation item.
     Delegation(Box<Delegation>),
     /// An associated list or glob delegation item.
@@ -3978,7 +3981,7 @@ pub enum ForeignItemKind {
     /// A foreign type.
     TyAlias(Box<TyAlias>),
     /// A macro expanding to foreign items.
-    MacCall(P<MacCall>),
+    MacCall(Box<MacCall>),
 }
 
 impl ForeignItemKind {
@@ -4041,7 +4044,7 @@ mod size_asserts {
     static_assert_size!(GenericArg, 24);
     static_assert_size!(GenericBound, 88);
     static_assert_size!(Generics, 40);
-    static_assert_size!(Impl, 136);
+    static_assert_size!(Impl, 64);
     static_assert_size!(Item, 144);
     static_assert_size!(ItemKind, 80);
     static_assert_size!(LitKind, 24);
@@ -4054,6 +4057,7 @@ mod size_asserts {
     static_assert_size!(PathSegment, 24);
     static_assert_size!(Stmt, 32);
     static_assert_size!(StmtKind, 16);
+    static_assert_size!(TraitImplHeader, 80);
     static_assert_size!(Ty, 64);
     static_assert_size!(TyKind, 40);
     // tidy-alphabetical-end
diff --git a/compiler/rustc_ast/src/ast_traits.rs b/compiler/rustc_ast/src/ast_traits.rs
index 9d91f41d6c7..3d2477e5f03 100644
--- a/compiler/rustc_ast/src/ast_traits.rs
+++ b/compiler/rustc_ast/src/ast_traits.rs
@@ -5,7 +5,6 @@
 use std::fmt;
 use std::marker::PhantomData;
 
-use crate::ptr::P;
 use crate::tokenstream::LazyAttrTokenStream;
 use crate::{
     Arm, AssocItem, AttrItem, AttrKind, AttrVec, Attribute, Block, Crate, Expr, ExprField,
@@ -53,7 +52,7 @@ impl_has_node_id!(
     WherePredicate,
 );
 
-impl<T: HasNodeId> HasNodeId for P<T> {
+impl<T: HasNodeId> HasNodeId for Box<T> {
     fn node_id(&self) -> NodeId {
         (**self).node_id()
     }
@@ -119,7 +118,7 @@ impl<T: HasTokens> HasTokens for Option<T> {
     }
 }
 
-impl<T: HasTokens> HasTokens for P<T> {
+impl<T: HasTokens> HasTokens for Box<T> {
     fn tokens(&self) -> Option<&LazyAttrTokenStream> {
         (**self).tokens()
     }
@@ -245,7 +244,7 @@ impl_has_attrs!(
 );
 impl_has_attrs_none!(Attribute, AttrItem, Block, Pat, Path, Ty, Visibility);
 
-impl<T: HasAttrs> HasAttrs for P<T> {
+impl<T: HasAttrs> HasAttrs for Box<T> {
     const SUPPORTS_CUSTOM_INNER_ATTRS: bool = T::SUPPORTS_CUSTOM_INNER_ATTRS;
     fn attrs(&self) -> &[Attribute] {
         (**self).attrs()
@@ -322,8 +321,8 @@ impl<Wrapped, Tag> AstNodeWrapper<Wrapped, Tag> {
 }
 
 // FIXME: remove after `stmt_expr_attributes` is stabilized.
-impl<T, Tag> From<AstNodeWrapper<P<T>, Tag>> for AstNodeWrapper<T, Tag> {
-    fn from(value: AstNodeWrapper<P<T>, Tag>) -> Self {
+impl<T, Tag> From<AstNodeWrapper<Box<T>, Tag>> for AstNodeWrapper<T, Tag> {
+    fn from(value: AstNodeWrapper<Box<T>, Tag>) -> Self {
         AstNodeWrapper { wrapped: *value.wrapped, tag: value.tag }
     }
 }
diff --git a/compiler/rustc_ast/src/attr/mod.rs b/compiler/rustc_ast/src/attr/mod.rs
index 4348a4bb120..6ada93b4c89 100644
--- a/compiler/rustc_ast/src/attr/mod.rs
+++ b/compiler/rustc_ast/src/attr/mod.rs
@@ -13,7 +13,6 @@ use crate::ast::{
     Expr, ExprKind, LitKind, MetaItem, MetaItemInner, MetaItemKind, MetaItemLit, NormalAttr, Path,
     PathSegment, Safety,
 };
-use crate::ptr::P;
 use crate::token::{self, CommentKind, Delimiter, InvisibleOrigin, MetaVarKind, Token};
 use crate::tokenstream::{
     DelimSpan, LazyAttrTokenStream, Spacing, TokenStream, TokenStreamIter, TokenTree,
@@ -660,7 +659,7 @@ pub fn mk_attr_from_item(
     span: Span,
 ) -> Attribute {
     Attribute {
-        kind: AttrKind::Normal(P(NormalAttr { item, tokens })),
+        kind: AttrKind::Normal(Box::new(NormalAttr { item, tokens })),
         id: g.mk_attr_id(),
         style,
         span,
@@ -710,7 +709,7 @@ pub fn mk_attr_name_value_str(
     span: Span,
 ) -> Attribute {
     let lit = token::Lit::new(token::Str, escape_string_symbol(val), None);
-    let expr = P(Expr {
+    let expr = Box::new(Expr {
         id: DUMMY_NODE_ID,
         kind: ExprKind::Lit(lit),
         span,
diff --git a/compiler/rustc_ast/src/expand/autodiff_attrs.rs b/compiler/rustc_ast/src/expand/autodiff_attrs.rs
index 2f918faaf75..33451f99748 100644
--- a/compiler/rustc_ast/src/expand/autodiff_attrs.rs
+++ b/compiler/rustc_ast/src/expand/autodiff_attrs.rs
@@ -7,7 +7,6 @@ use std::fmt::{self, Display, Formatter};
 use std::str::FromStr;
 
 use crate::expand::{Decodable, Encodable, HashStable_Generic};
-use crate::ptr::P;
 use crate::{Ty, TyKind};
 
 /// Forward and Reverse Mode are well known names for automatic differentiation implementations.
@@ -162,7 +161,7 @@ pub fn valid_ret_activity(mode: DiffMode, activity: DiffActivity) -> bool {
 /// since Duplicated expects a mutable ref/ptr and we would thus end up with a shadow value
 /// who is an indirect type, which doesn't match the primal scalar type. We can't prevent
 /// users here from marking scalars as Duplicated, due to type aliases.
-pub fn valid_ty_for_activity(ty: &P<Ty>, activity: DiffActivity) -> bool {
+pub fn valid_ty_for_activity(ty: &Box<Ty>, activity: DiffActivity) -> bool {
     use DiffActivity::*;
     // It's always allowed to mark something as Const, since we won't compute derivatives wrt. it.
     // Dual variants also support all types.
diff --git a/compiler/rustc_ast/src/format.rs b/compiler/rustc_ast/src/format.rs
index c2a1de60a98..cadebb2254d 100644
--- a/compiler/rustc_ast/src/format.rs
+++ b/compiler/rustc_ast/src/format.rs
@@ -3,7 +3,6 @@ use rustc_macros::{Decodable, Encodable, Walkable};
 use rustc_span::{Ident, Span, Symbol};
 
 use crate::Expr;
-use crate::ptr::P;
 use crate::token::LitKind;
 
 // Definitions:
@@ -147,7 +146,7 @@ impl FormatArguments {
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
 pub struct FormatArgument {
     pub kind: FormatArgumentKind,
-    pub expr: P<Expr>,
+    pub expr: Box<Expr>,
 }
 
 #[derive(Clone, Encodable, Decodable, Debug, Walkable)]
diff --git a/compiler/rustc_ast/src/lib.rs b/compiler/rustc_ast/src/lib.rs
index 896d1e1148a..f1951049b47 100644
--- a/compiler/rustc_ast/src/lib.rs
+++ b/compiler/rustc_ast/src/lib.rs
@@ -37,7 +37,6 @@ pub mod expand;
 pub mod format;
 pub mod mut_visit;
 pub mod node_id;
-pub mod ptr;
 pub mod token;
 pub mod tokenstream;
 pub mod visit;
diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
index 06708e2e703..be8e1d22c9d 100644
--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@@ -17,7 +17,6 @@ use smallvec::{SmallVec, smallvec};
 use thin_vec::ThinVec;
 
 use crate::ast::*;
-use crate::ptr::P;
 use crate::tokenstream::*;
 use crate::visit::{AssocCtxt, BoundKind, FnCtxt, LifetimeCtxt, VisitorResult, try_visit};
 
@@ -41,7 +40,7 @@ pub(crate) trait MutVisitable<V: MutVisitor> {
     fn visit_mut(&mut self, visitor: &mut V, extra: Self::Extra);
 }
 
-impl<V: MutVisitor, T: ?Sized> MutVisitable<V> for P<T>
+impl<V: MutVisitor, T: ?Sized> MutVisitable<V> for Box<T>
 where
     T: MutVisitable<V>,
 {
@@ -293,15 +292,15 @@ macro_rules! generate_flat_map_visitor_fns {
 }
 
 generate_flat_map_visitor_fns! {
-    visit_items, P<Item>, flat_map_item;
-    visit_foreign_items, P<ForeignItem>, flat_map_foreign_item;
+    visit_items, Box<Item>, flat_map_item;
+    visit_foreign_items, Box<ForeignItem>, flat_map_foreign_item;
     visit_generic_params, GenericParam, flat_map_generic_param;
     visit_stmts, Stmt, flat_map_stmt;
-    visit_exprs, P<Expr>, filter_map_expr;
+    visit_exprs, Box<Expr>, filter_map_expr;
     visit_expr_fields, ExprField, flat_map_expr_field;
     visit_pat_fields, PatField, flat_map_pat_field;
     visit_variants, Variant, flat_map_variant;
-    visit_assoc_items, P<AssocItem>, flat_map_assoc_item, ctxt: AssocCtxt;
+    visit_assoc_items, Box<AssocItem>, flat_map_assoc_item, ctxt: AssocCtxt;
     visit_where_predicates, WherePredicate, flat_map_where_predicate;
     visit_params, Param, flat_map_param;
     visit_field_defs, FieldDef, flat_map_field_def;
@@ -333,12 +332,12 @@ generate_walk_flat_map_fns! {
     walk_flat_map_where_predicate(WherePredicate) => visit_where_predicate;
     walk_flat_map_field_def(FieldDef) => visit_field_def;
     walk_flat_map_expr_field(ExprField) => visit_expr_field;
-    walk_flat_map_item(P<Item>) => visit_item;
-    walk_flat_map_foreign_item(P<ForeignItem>) => visit_foreign_item;
-    walk_flat_map_assoc_item(P<AssocItem>, ctxt: AssocCtxt) => visit_assoc_item;
+    walk_flat_map_item(Box<Item>) => visit_item;
+    walk_flat_map_foreign_item(Box<ForeignItem>) => visit_foreign_item;
+    walk_flat_map_assoc_item(Box<AssocItem>, ctxt: AssocCtxt) => visit_assoc_item;
 }
 
-pub fn walk_filter_map_expr<T: MutVisitor>(vis: &mut T, mut e: P<Expr>) -> Option<P<Expr>> {
+pub fn walk_filter_map_expr<T: MutVisitor>(vis: &mut T, mut e: Box<Expr>) -> Option<Box<Expr>> {
     vis.visit_expr(&mut e);
     Some(e)
 }
diff --git a/compiler/rustc_ast/src/ptr.rs b/compiler/rustc_ast/src/ptr.rs
deleted file mode 100644
index fffeab8bbca..00000000000
--- a/compiler/rustc_ast/src/ptr.rs
+++ /dev/null
@@ -1,11 +0,0 @@
-/// A pointer type that uniquely owns a heap allocation of type T.
-///
-/// This used to be its own type, but now it's just a typedef for `Box` and we are planning to
-/// remove it soon.
-pub type P<T> = Box<T>;
-
-/// Construct a `P<T>` from a `T` value.
-#[allow(non_snake_case)]
-pub fn P<T>(value: T) -> P<T> {
-    Box::new(value)
-}
diff --git a/compiler/rustc_ast/src/visit.rs b/compiler/rustc_ast/src/visit.rs
index ab15cb28fa1..68b3d2b0368 100644
--- a/compiler/rustc_ast/src/visit.rs
+++ b/compiler/rustc_ast/src/visit.rs
@@ -20,7 +20,6 @@ use rustc_span::{Ident, Span, Symbol};
 use thin_vec::ThinVec;
 
 use crate::ast::*;
-use crate::ptr::P;
 use crate::tokenstream::DelimSpan;
 
 #[derive(Copy, Clone, Debug, PartialEq)]
@@ -82,7 +81,7 @@ pub(crate) trait Visitable<'a, V: Visitor<'a>> {
     fn visit(&'a self, visitor: &mut V, extra: Self::Extra) -> V::Result;
 }
 
-impl<'a, V: Visitor<'a>, T: ?Sized> Visitable<'a, V> for P<T>
+impl<'a, V: Visitor<'a>, T: ?Sized> Visitable<'a, V> for Box<T>
 where
     T: Visitable<'a, V>,
 {
@@ -322,7 +321,7 @@ macro_rules! common_visitor_and_walkers {
             Fn(FnCtxt, &'a $($mut)? Visibility, &'a $($mut)? Fn),
 
             /// E.g., `|x, y| body`.
-            Closure(&'a $($mut)? ClosureBinder, &'a $($mut)? Option<CoroutineKind>, &'a $($mut)? P<FnDecl>, &'a $($mut)? P<Expr>),
+            Closure(&'a $($mut)? ClosureBinder, &'a $($mut)? Option<CoroutineKind>, &'a $($mut)? Box<FnDecl>, &'a $($mut)? Box<Expr>),
         }
 
         impl<'a> FnKind<'a> {
@@ -390,9 +389,9 @@ macro_rules! common_visitor_and_walkers {
             ThinVec<(NodeId, Path)>,
             ThinVec<PathSegment>,
             ThinVec<PreciseCapturingArg>,
-            ThinVec<P<Pat>>,
-            ThinVec<P<Ty>>,
-            ThinVec<P<TyPat>>,
+            ThinVec<Box<Pat>>,
+            ThinVec<Box<Ty>>,
+            ThinVec<Box<TyPat>>,
         );
 
         // This macro generates `impl Visitable` and `impl MutVisitable` that forward to `Walkable`
@@ -676,11 +675,11 @@ macro_rules! common_visitor_and_walkers {
                     // Do nothing.
                 }
 
-                fn flat_map_foreign_item(&mut self, ni: P<ForeignItem>) -> SmallVec<[P<ForeignItem>; 1]> {
+                fn flat_map_foreign_item(&mut self, ni: Box<ForeignItem>) -> SmallVec<[Box<ForeignItem>; 1]> {
                     walk_flat_map_foreign_item(self, ni)
                 }
 
-                fn flat_map_item(&mut self, i: P<Item>) -> SmallVec<[P<Item>; 1]> {
+                fn flat_map_item(&mut self, i: Box<Item>) -> SmallVec<[Box<Item>; 1]> {
                     walk_flat_map_item(self, i)
                 }
 
@@ -690,9 +689,9 @@ macro_rules! common_visitor_and_walkers {
 
                 fn flat_map_assoc_item(
                     &mut self,
-                    i: P<AssocItem>,
+                    i: Box<AssocItem>,
                     ctxt: AssocCtxt,
-                ) -> SmallVec<[P<AssocItem>; 1]> {
+                ) -> SmallVec<[Box<AssocItem>; 1]> {
                     walk_flat_map_assoc_item(self, i, ctxt)
                 }
 
@@ -704,7 +703,7 @@ macro_rules! common_visitor_and_walkers {
                     walk_flat_map_arm(self, arm)
                 }
 
-                fn filter_map_expr(&mut self, e: P<Expr>) -> Option<P<Expr>> {
+                fn filter_map_expr(&mut self, e: Box<Expr>) -> Option<Box<Expr>> {
                     walk_filter_map_expr(self, e)
                 }
 
@@ -930,8 +929,13 @@ macro_rules! common_visitor_and_walkers {
         }
 
         impl_walkable!(|&$($mut)? $($lt)? self: Impl, vis: &mut V| {
-            let Impl { defaultness, safety, generics, constness, polarity, of_trait, self_ty, items } = self;
-            visit_visitable!($($mut)? vis, defaultness, safety, generics, constness, polarity, of_trait, self_ty);
+            let Impl { generics, of_trait, self_ty, items } = self;
+            try_visit!(vis.visit_generics(generics));
+            if let Some(box of_trait) = of_trait {
+                let TraitImplHeader { defaultness, safety, constness, polarity, trait_ref } = of_trait;
+                visit_visitable!($($mut)? vis, defaultness, safety, constness, polarity, trait_ref);
+            }
+            try_visit!(vis.visit_ty(self_ty));
             visit_visitable_with!($($mut)? vis, items, AssocCtxt::Impl { of_trait: of_trait.is_some() });
             V::Result::output()
         });
@@ -1144,15 +1148,15 @@ macro_rules! generate_list_visit_fns {
 }
 
 generate_list_visit_fns! {
-    visit_items, P<Item>, visit_item;
-    visit_foreign_items, P<ForeignItem>, visit_foreign_item;
+    visit_items, Box<Item>, visit_item;
+    visit_foreign_items, Box<ForeignItem>, visit_foreign_item;
     visit_generic_params, GenericParam, visit_generic_param;
     visit_stmts, Stmt, visit_stmt;
-    visit_exprs, P<Expr>, visit_expr;
+    visit_exprs, Box<Expr>, visit_expr;
     visit_expr_fields, ExprField, visit_expr_field;
     visit_pat_fields, PatField, visit_pat_field;
     visit_variants, Variant, visit_variant;
-    visit_assoc_items, P<AssocItem>, visit_assoc_item, ctxt: AssocCtxt;
+    visit_assoc_items, Box<AssocItem>, visit_assoc_item, ctxt: AssocCtxt;
     visit_where_predicates, WherePredicate, visit_where_predicate;
     visit_params, Param, visit_param;
     visit_field_defs, FieldDef, visit_field_def;
diff --git a/compiler/rustc_ast_lowering/src/asm.rs b/compiler/rustc_ast_lowering/src/asm.rs
index af279e07acc..d44faad017e 100644
--- a/compiler/rustc_ast_lowering/src/asm.rs
+++ b/compiler/rustc_ast_lowering/src/asm.rs
@@ -48,6 +48,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     | asm::InlineAsmArch::Arm64EC
                     | asm::InlineAsmArch::RiscV32
                     | asm::InlineAsmArch::RiscV64
+                    | asm::InlineAsmArch::LoongArch32
                     | asm::InlineAsmArch::LoongArch64
                     | asm::InlineAsmArch::S390x
             );
diff --git a/compiler/rustc_ast_lowering/src/block.rs b/compiler/rustc_ast_lowering/src/block.rs
index 2cc07694afb..f1e810a8b9e 100644
--- a/compiler/rustc_ast_lowering/src/block.rs
+++ b/compiler/rustc_ast_lowering/src/block.rs
@@ -1,5 +1,6 @@
 use rustc_ast::{Block, BlockCheckMode, Local, LocalKind, Stmt, StmtKind};
 use rustc_hir as hir;
+use rustc_hir::Target;
 use rustc_span::sym;
 use smallvec::SmallVec;
 
@@ -109,7 +110,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         };
         let span = self.lower_span(l.span);
         let source = hir::LocalSource::Normal;
-        self.lower_attrs(hir_id, &l.attrs, l.span);
+        self.lower_attrs(hir_id, &l.attrs, l.span, Target::Statement);
         self.arena.alloc(hir::LetStmt { hir_id, super_, ty, pat, init, els, span, source })
     }
 
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index fb42cfea30b..cbd17d66b75 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -1,14 +1,13 @@
 use std::ops::ControlFlow;
 use std::sync::Arc;
 
-use rustc_ast::ptr::P as AstP;
 use rustc_ast::*;
 use rustc_ast_pretty::pprust::expr_to_string;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_hir as hir;
 use rustc_hir::attrs::AttributeKind;
 use rustc_hir::def::{DefKind, Res};
-use rustc_hir::{HirId, find_attr};
+use rustc_hir::{HirId, Target, find_attr};
 use rustc_middle::span_bug;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::errors::report_lit_error;
@@ -53,7 +52,7 @@ impl<'v> rustc_ast::visit::Visitor<'v> for WillCreateDefIdsVisitor {
 }
 
 impl<'hir> LoweringContext<'_, 'hir> {
-    fn lower_exprs(&mut self, exprs: &[AstP<Expr>]) -> &'hir [hir::Expr<'hir>] {
+    fn lower_exprs(&mut self, exprs: &[Box<Expr>]) -> &'hir [hir::Expr<'hir>] {
         self.arena.alloc_from_iter(exprs.iter().map(|x| self.lower_expr_mut(x)))
     }
 
@@ -75,7 +74,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     if !e.attrs.is_empty() {
                         let old_attrs = self.attrs.get(&ex.hir_id.local_id).copied().unwrap_or(&[]);
                         let new_attrs = self
-                            .lower_attrs_vec(&e.attrs, e.span, ex.hir_id)
+                            .lower_attrs_vec(&e.attrs, e.span, ex.hir_id, Target::from_expr(e))
                             .into_iter()
                             .chain(old_attrs.iter().cloned());
                         let new_attrs = &*self.arena.alloc_from_iter(new_attrs);
@@ -98,7 +97,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             }
 
             let expr_hir_id = self.lower_node_id(e.id);
-            let attrs = self.lower_attrs(expr_hir_id, &e.attrs, e.span);
+            let attrs = self.lower_attrs(expr_hir_id, &e.attrs, e.span, Target::from_expr(e));
 
             let kind = match &e.kind {
                 ExprKind::Array(exprs) => hir::ExprKind::Array(self.lower_exprs(exprs)),
@@ -455,7 +454,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     fn lower_legacy_const_generics(
         &mut self,
         mut f: Expr,
-        args: ThinVec<AstP<Expr>>,
+        args: ThinVec<Box<Expr>>,
         legacy_args_idx: &[usize],
     ) -> hir::ExprKind<'hir> {
         let ExprKind::Path(None, path) = &mut f.kind else {
@@ -495,7 +494,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 self.create_def(node_id, None, DefKind::AnonConst, f.span);
                 let mut visitor = WillCreateDefIdsVisitor {};
                 let const_value = if let ControlFlow::Break(span) = visitor.visit_expr(&arg) {
-                    AstP(Expr {
+                    Box::new(Expr {
                         id: self.next_node_id(),
                         kind: ExprKind::Err(invalid_expr_error(self.tcx, span)),
                         span: f.span,
@@ -516,7 +515,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // Add generic args to the last element of the path.
         let last_segment = path.segments.last_mut().unwrap();
         assert!(last_segment.args.is_none());
-        last_segment.args = Some(AstP(GenericArgs::AngleBracketed(AngleBracketedArgs {
+        last_segment.args = Some(Box::new(GenericArgs::AngleBracketed(AngleBracketedArgs {
             span: DUMMY_SP,
             args: generic_args,
         })));
@@ -640,7 +639,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let guard = arm.guard.as_ref().map(|cond| self.lower_expr(cond));
         let hir_id = self.next_id();
         let span = self.lower_span(arm.span);
-        self.lower_attrs(hir_id, &arm.attrs, arm.span);
+        self.lower_attrs(hir_id, &arm.attrs, arm.span, Target::Arm);
         let is_never_pattern = pat.is_never_pattern();
         // We need to lower the body even if it's unneeded for never pattern in match,
         // ensure that we can get HirId for DefId if need (issue #137708).
@@ -812,7 +811,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             self.lower_attrs(
                 inner_hir_id,
                 &[Attribute {
-                    kind: AttrKind::Normal(ptr::P(NormalAttr::from_ident(Ident::new(
+                    kind: AttrKind::Normal(Box::new(NormalAttr::from_ident(Ident::new(
                         sym::track_caller,
                         span,
                     )))),
@@ -821,6 +820,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     span: unstable_span,
                 }],
                 span,
+                Target::Fn,
             );
         }
     }
@@ -1285,7 +1285,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     fn extract_tuple_struct_path<'a>(
         &mut self,
         expr: &'a Expr,
-    ) -> Option<(&'a Option<AstP<QSelf>>, &'a Path)> {
+    ) -> Option<(&'a Option<Box<QSelf>>, &'a Path)> {
         if let ExprKind::Path(qself, path) = &expr.kind {
             // Does the path resolve to something disallowed in a tuple struct/variant pattern?
             if let Some(partial_res) = self.resolver.get_partial_res(expr.id) {
@@ -1307,7 +1307,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     fn extract_unit_struct_path<'a>(
         &mut self,
         expr: &'a Expr,
-    ) -> Option<(&'a Option<AstP<QSelf>>, &'a Path)> {
+    ) -> Option<(&'a Option<Box<QSelf>>, &'a Path)> {
         if let ExprKind::Path(qself, path) = &expr.kind {
             // Does the path resolve to something disallowed in a unit struct/variant pattern?
             if let Some(partial_res) = self.resolver.get_partial_res(expr.id) {
@@ -1478,7 +1478,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     /// Each sub-assignment is recorded in `assignments`.
     fn destructure_sequence(
         &mut self,
-        elements: &[AstP<Expr>],
+        elements: &[Box<Expr>],
         ctx: &str,
         eq_sign_span: Span,
         assignments: &mut Vec<hir::Stmt<'hir>>,
@@ -1655,7 +1655,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
     fn lower_expr_field(&mut self, f: &ExprField) -> hir::ExprField<'hir> {
         let hir_id = self.lower_node_id(f.id);
-        self.lower_attrs(hir_id, &f.attrs, f.span);
+        self.lower_attrs(hir_id, &f.attrs, f.span, Target::ExprField);
         hir::ExprField {
             hir_id,
             ident: self.lower_ident(f.ident),
@@ -1911,7 +1911,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         //
         // Also, add the attributes to the outer returned expr node.
         let expr = self.expr_drop_temps_mut(for_span, match_expr);
-        self.lower_attrs(expr.hir_id, &e.attrs, e.span);
+        self.lower_attrs(expr.hir_id, &e.attrs, e.span, Target::from_expr(e));
         expr
     }
 
@@ -1968,7 +1968,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             let val_ident = Ident::with_dummy_span(sym::val);
             let (val_pat, val_pat_nid) = self.pat_ident(span, val_ident);
             let val_expr = self.expr_ident(span, val_ident, val_pat_nid);
-            self.lower_attrs(val_expr.hir_id, &attrs, span);
+            self.lower_attrs(val_expr.hir_id, &attrs, span, Target::Expression);
             let continue_pat = self.pat_cf_continue(unstable_span, val_pat);
             self.arm(continue_pat, val_expr)
         };
@@ -1999,7 +1999,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 let ret_expr = self.checked_return(Some(from_residual_expr));
                 self.arena.alloc(self.expr(try_span, ret_expr))
             };
-            self.lower_attrs(ret_expr.hir_id, &attrs, span);
+            self.lower_attrs(ret_expr.hir_id, &attrs, span, Target::Expression);
 
             let break_pat = self.pat_cf_break(try_span, residual_local);
             self.arm(break_pat, ret_expr)
diff --git a/compiler/rustc_ast_lowering/src/item.rs b/compiler/rustc_ast_lowering/src/item.rs
index 9f54af57528..72817a0a9a0 100644
--- a/compiler/rustc_ast_lowering/src/item.rs
+++ b/compiler/rustc_ast_lowering/src/item.rs
@@ -1,12 +1,11 @@
 use rustc_abi::ExternAbi;
-use rustc_ast::ptr::P;
 use rustc_ast::visit::AssocCtxt;
 use rustc_ast::*;
 use rustc_errors::{E0570, ErrorGuaranteed, struct_span_code_err};
 use rustc_hir::attrs::AttributeKind;
 use rustc_hir::def::{DefKind, PerNS, Res};
 use rustc_hir::def_id::{CRATE_DEF_ID, LocalDefId};
-use rustc_hir::{self as hir, HirId, LifetimeSource, PredicateOrigin, find_attr};
+use rustc_hir::{self as hir, HirId, LifetimeSource, PredicateOrigin, Target, find_attr};
 use rustc_index::{IndexSlice, IndexVec};
 use rustc_middle::span_bug;
 use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
@@ -81,7 +80,7 @@ impl<'a, 'hir> ItemLowerer<'a, 'hir> {
                     self.with_lctx(CRATE_NODE_ID, |lctx| {
                         let module = lctx.lower_mod(&c.items, &c.spans);
                         // FIXME(jdonszelman): is dummy span ever a problem here?
-                        lctx.lower_attrs(hir::CRATE_HIR_ID, &c.attrs, DUMMY_SP);
+                        lctx.lower_attrs(hir::CRATE_HIR_ID, &c.attrs, DUMMY_SP, Target::Crate);
                         hir::OwnerNode::Crate(module)
                     })
                 }
@@ -102,7 +101,7 @@ impl<'a, 'hir> ItemLowerer<'a, 'hir> {
 impl<'hir> LoweringContext<'_, 'hir> {
     pub(super) fn lower_mod(
         &mut self,
-        items: &[P<Item>],
+        items: &[Box<Item>],
         spans: &ModSpans,
     ) -> &'hir hir::Mod<'hir> {
         self.arena.alloc(hir::Mod {
@@ -137,7 +136,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     fn lower_item(&mut self, i: &Item) -> &'hir hir::Item<'hir> {
         let vis_span = self.lower_span(i.vis.span);
         let hir_id = hir::HirId::make_owner(self.current_hir_id_owner.def_id);
-        let attrs = self.lower_attrs(hir_id, &i.attrs, i.span);
+        let attrs = self.lower_attrs(hir_id, &i.attrs, i.span, Target::from_ast_item(i));
         let kind = self.lower_item_kind(i.span, i.id, hir_id, attrs, vis_span, &i.kind);
         let item = hir::Item {
             owner_id: hir_id.expect_owner(),
@@ -341,13 +340,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 );
                 hir::ItemKind::Union(ident, generics, vdata)
             }
-            ItemKind::Impl(box Impl {
-                safety,
-                polarity,
-                defaultness,
-                constness,
+            ItemKind::Impl(Impl {
                 generics: ast_generics,
-                of_trait: trait_ref,
+                of_trait,
                 self_ty: ty,
                 items: impl_items,
             }) => {
@@ -365,54 +360,30 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 // lifetime to be added, but rather a reference to a
                 // parent lifetime.
                 let itctx = ImplTraitContext::Universal;
-                let (generics, (trait_ref, lowered_ty)) =
+                let (generics, (of_trait, lowered_ty)) =
                     self.lower_generics(ast_generics, id, itctx, |this| {
-                        let modifiers = TraitBoundModifiers {
-                            constness: BoundConstness::Never,
-                            asyncness: BoundAsyncness::Normal,
-                            // we don't use this in bound lowering
-                            polarity: BoundPolarity::Positive,
-                        };
-
-                        let trait_ref = trait_ref.as_ref().map(|trait_ref| {
-                            this.lower_trait_ref(
-                                modifiers,
-                                trait_ref,
-                                ImplTraitContext::Disallowed(ImplTraitPosition::Trait),
-                            )
-                        });
+                        let of_trait = of_trait
+                            .as_deref()
+                            .map(|of_trait| this.lower_trait_impl_header(of_trait));
 
                         let lowered_ty = this.lower_ty(
                             ty,
                             ImplTraitContext::Disallowed(ImplTraitPosition::ImplSelf),
                         );
 
-                        (trait_ref, lowered_ty)
+                        (of_trait, lowered_ty)
                     });
 
                 let new_impl_items = self
                     .arena
                     .alloc_from_iter(impl_items.iter().map(|item| self.lower_impl_item_ref(item)));
 
-                // `defaultness.has_value()` is never called for an `impl`, always `true` in order
-                // to not cause an assertion failure inside the `lower_defaultness` function.
-                let has_val = true;
-                let (defaultness, defaultness_span) = self.lower_defaultness(*defaultness, has_val);
-                let polarity = match polarity {
-                    ImplPolarity::Positive => ImplPolarity::Positive,
-                    ImplPolarity::Negative(s) => ImplPolarity::Negative(self.lower_span(*s)),
-                };
-                hir::ItemKind::Impl(self.arena.alloc(hir::Impl {
-                    constness: self.lower_constness(*constness),
-                    safety: self.lower_safety(*safety, hir::Safety::Safe),
-                    polarity,
-                    defaultness,
-                    defaultness_span,
+                hir::ItemKind::Impl(hir::Impl {
                     generics,
-                    of_trait: trait_ref,
+                    of_trait,
                     self_ty: lowered_ty,
                     items: new_impl_items,
-                }))
+                })
             }
             ItemKind::Trait(box Trait {
                 constness,
@@ -462,17 +433,17 @@ impl<'hir> LoweringContext<'_, 'hir> {
             }
             ItemKind::MacroDef(ident, MacroDef { body, macro_rules }) => {
                 let ident = self.lower_ident(*ident);
-                let body = P(self.lower_delim_args(body));
+                let body = Box::new(self.lower_delim_args(body));
                 let def_id = self.local_def_id(id);
                 let def_kind = self.tcx.def_kind(def_id);
-                let DefKind::Macro(macro_kind) = def_kind else {
+                let DefKind::Macro(macro_kinds) = def_kind else {
                     unreachable!(
                         "expected DefKind::Macro for macro item, found {}",
                         def_kind.descr(def_id.to_def_id())
                     );
                 };
                 let macro_def = self.arena.alloc(ast::MacroDef { body, macro_rules: *macro_rules });
-                hir::ItemKind::Macro(ident, macro_def, macro_kind)
+                hir::ItemKind::Macro(ident, macro_def, macro_kinds)
             }
             ItemKind::Delegation(box delegation) => {
                 let delegation_results = self.lower_delegation(delegation, id, false);
@@ -650,7 +621,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
     fn lower_foreign_item(&mut self, i: &ForeignItem) -> &'hir hir::ForeignItem<'hir> {
         let hir_id = hir::HirId::make_owner(self.current_hir_id_owner.def_id);
         let owner_id = hir_id.expect_owner();
-        let attrs = self.lower_attrs(hir_id, &i.attrs, i.span);
+        let attrs =
+            self.lower_attrs(hir_id, &i.attrs, i.span, Target::from_foreign_item_kind(&i.kind));
         let (ident, kind) = match &i.kind {
             ForeignItemKind::Fn(box Fn { sig, ident, generics, define_opaque, .. }) => {
                 let fdec = &sig.decl;
@@ -719,7 +691,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
     fn lower_variant(&mut self, item_kind: &ItemKind, v: &Variant) -> hir::Variant<'hir> {
         let hir_id = self.lower_node_id(v.id);
-        self.lower_attrs(hir_id, &v.attrs, v.span);
+        self.lower_attrs(hir_id, &v.attrs, v.span, Target::Variant);
         hir::Variant {
             hir_id,
             def_id: self.local_def_id(v.id),
@@ -802,7 +774,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     ) -> hir::FieldDef<'hir> {
         let ty = self.lower_ty(&f.ty, ImplTraitContext::Disallowed(ImplTraitPosition::FieldTy));
         let hir_id = self.lower_node_id(f.id);
-        self.lower_attrs(hir_id, &f.attrs, f.span);
+        self.lower_attrs(hir_id, &f.attrs, f.span, Target::Field);
         hir::FieldDef {
             span: self.lower_span(f.span),
             hir_id,
@@ -821,7 +793,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
     fn lower_trait_item(&mut self, i: &AssocItem) -> &'hir hir::TraitItem<'hir> {
         let hir_id = hir::HirId::make_owner(self.current_hir_id_owner.def_id);
-        let attrs = self.lower_attrs(hir_id, &i.attrs, i.span);
+        let attrs = self.lower_attrs(
+            hir_id,
+            &i.attrs,
+            i.span,
+            Target::from_assoc_item_kind(&i.kind, AssocCtxt::Trait),
+        );
         let trait_item_def_id = hir_id.expect_owner();
 
         let (ident, generics, kind, has_default) = match &i.kind {
@@ -983,6 +960,44 @@ impl<'hir> LoweringContext<'_, 'hir> {
         self.expr(span, hir::ExprKind::Err(guar))
     }
 
+    fn lower_trait_impl_header(
+        &mut self,
+        trait_impl_header: &TraitImplHeader,
+    ) -> &'hir hir::TraitImplHeader<'hir> {
+        let TraitImplHeader { constness, safety, polarity, defaultness, ref trait_ref } =
+            *trait_impl_header;
+        let constness = self.lower_constness(constness);
+        let safety = self.lower_safety(safety, hir::Safety::Safe);
+        let polarity = match polarity {
+            ImplPolarity::Positive => ImplPolarity::Positive,
+            ImplPolarity::Negative(s) => ImplPolarity::Negative(self.lower_span(s)),
+        };
+        // `defaultness.has_value()` is never called for an `impl`, always `true` in order
+        // to not cause an assertion failure inside the `lower_defaultness` function.
+        let has_val = true;
+        let (defaultness, defaultness_span) = self.lower_defaultness(defaultness, has_val);
+        let modifiers = TraitBoundModifiers {
+            constness: BoundConstness::Never,
+            asyncness: BoundAsyncness::Normal,
+            // we don't use this in bound lowering
+            polarity: BoundPolarity::Positive,
+        };
+        let trait_ref = self.lower_trait_ref(
+            modifiers,
+            trait_ref,
+            ImplTraitContext::Disallowed(ImplTraitPosition::Trait),
+        );
+
+        self.arena.alloc(hir::TraitImplHeader {
+            constness,
+            safety,
+            polarity,
+            defaultness,
+            defaultness_span,
+            trait_ref,
+        })
+    }
+
     fn lower_impl_item(
         &mut self,
         i: &AssocItem,
@@ -992,7 +1007,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let has_value = true;
         let (defaultness, _) = self.lower_defaultness(i.kind.defaultness(), has_value);
         let hir_id = hir::HirId::make_owner(self.current_hir_id_owner.def_id);
-        let attrs = self.lower_attrs(hir_id, &i.attrs, i.span);
+        let attrs = self.lower_attrs(
+            hir_id,
+            &i.attrs,
+            i.span,
+            Target::from_assoc_item_kind(&i.kind, AssocCtxt::Impl { of_trait: is_in_trait_impl }),
+        );
 
         let (ident, (generics, kind)) = match &i.kind {
             AssocItemKind::Const(box ConstItem {
@@ -1162,7 +1182,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
 
     fn lower_param(&mut self, param: &Param) -> hir::Param<'hir> {
         let hir_id = self.lower_node_id(param.id);
-        self.lower_attrs(hir_id, &param.attrs, param.span);
+        self.lower_attrs(hir_id, &param.attrs, param.span, Target::Param);
         hir::Param {
             hir_id,
             pat: self.lower_pat(&param.pat),
@@ -1842,7 +1862,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     ) -> hir::WherePredicate<'hir> {
         let hir_id = self.lower_node_id(pred.id);
         let span = self.lower_span(pred.span);
-        self.lower_attrs(hir_id, &pred.attrs, span);
+        self.lower_attrs(hir_id, &pred.attrs, span, Target::WherePredicate);
         let kind = self.arena.alloc(match &pred.kind {
             WherePredicateKind::BoundPredicate(WhereBoundPredicate {
                 bound_generic_params,
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index d097e3cbaa8..70595391b85 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -54,7 +54,7 @@ use rustc_hir::def_id::{CRATE_DEF_ID, LOCAL_CRATE, LocalDefId};
 use rustc_hir::lints::DelayedLint;
 use rustc_hir::{
     self as hir, AngleBrackets, ConstArg, GenericArg, HirId, ItemLocalMap, LifetimeSource,
-    LifetimeSyntax, ParamName, TraitCandidate,
+    LifetimeSyntax, ParamName, Target, TraitCandidate,
 };
 use rustc_index::{Idx, IndexSlice, IndexVec};
 use rustc_macros::extension;
@@ -296,6 +296,7 @@ enum RelaxedBoundPolicy<'a> {
 enum RelaxedBoundForbiddenReason {
     TraitObjectTy,
     SuperTrait,
+    AssocTyBounds,
     LateBoundVarsInScope,
 }
 
@@ -942,11 +943,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         id: HirId,
         attrs: &[Attribute],
         target_span: Span,
+        target: Target,
     ) -> &'hir [hir::Attribute] {
         if attrs.is_empty() {
             &[]
         } else {
-            let lowered_attrs = self.lower_attrs_vec(attrs, self.lower_span(target_span), id);
+            let lowered_attrs =
+                self.lower_attrs_vec(attrs, self.lower_span(target_span), id, target);
 
             assert_eq!(id.owner, self.current_hir_id_owner);
             let ret = self.arena.alloc_from_iter(lowered_attrs);
@@ -971,12 +974,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         attrs: &[Attribute],
         target_span: Span,
         target_hir_id: HirId,
+        target: Target,
     ) -> Vec<hir::Attribute> {
         let l = self.span_lowerer();
         self.attribute_parser.parse_attribute_list(
             attrs,
             target_span,
             target_hir_id,
+            target,
             OmitDoc::Lower,
             |s| l.lower(s),
             |l| {
@@ -1109,9 +1114,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         &*self.arena.alloc(self.ty(constraint.span, hir::TyKind::Err(guar)));
                     hir::AssocItemConstraintKind::Equality { term: err_ty.into() }
                 } else {
-                    // FIXME(#135229): These should be forbidden!
-                    let bounds =
-                        self.lower_param_bounds(bounds, RelaxedBoundPolicy::Allowed, itctx);
+                    let bounds = self.lower_param_bounds(
+                        bounds,
+                        RelaxedBoundPolicy::Forbidden(RelaxedBoundForbiddenReason::AssocTyBounds),
+                        itctx,
+                    );
                     hir::AssocItemConstraintKind::Bound { bounds }
                 }
             }
@@ -1217,7 +1224,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     fn lower_path_ty(
         &mut self,
         t: &Ty,
-        qself: &Option<ptr::P<QSelf>>,
+        qself: &Option<Box<QSelf>>,
         path: &Path,
         param_mode: ParamMode,
         itctx: ImplTraitContext,
@@ -1939,7 +1946,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         let (name, kind) = self.lower_generic_param_kind(param, source);
 
         let hir_id = self.lower_node_id(param.id);
-        self.lower_attrs(hir_id, &param.attrs, param.span());
+        self.lower_attrs(hir_id, &param.attrs, param.span(), Target::Param);
         hir::GenericParam {
             hir_id,
             def_id: self.local_def_id(param.id),
@@ -2124,7 +2131,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         diag.emit();
                         return;
                     }
-                    RelaxedBoundForbiddenReason::LateBoundVarsInScope => {}
+                    RelaxedBoundForbiddenReason::AssocTyBounds
+                    | RelaxedBoundForbiddenReason::LateBoundVarsInScope => {}
                 };
             }
         }
diff --git a/compiler/rustc_ast_lowering/src/pat.rs b/compiler/rustc_ast_lowering/src/pat.rs
index e4440621048..b8f86247875 100644
--- a/compiler/rustc_ast_lowering/src/pat.rs
+++ b/compiler/rustc_ast_lowering/src/pat.rs
@@ -1,10 +1,9 @@
 use std::sync::Arc;
 
-use rustc_ast::ptr::P;
 use rustc_ast::*;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_hir::def::{DefKind, Res};
-use rustc_hir::{self as hir, LangItem};
+use rustc_hir::{self as hir, LangItem, Target};
 use rustc_middle::span_bug;
 use rustc_span::source_map::{Spanned, respan};
 use rustc_span::{DesugaringKind, Ident, Span};
@@ -94,7 +93,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
                         let fs = self.arena.alloc_from_iter(fields.iter().map(|f| {
                             let hir_id = self.lower_node_id(f.id);
-                            self.lower_attrs(hir_id, &f.attrs, f.span);
+                            self.lower_attrs(hir_id, &f.attrs, f.span, Target::PatField);
 
                             hir::PatField {
                                 hir_id,
@@ -154,7 +153,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
     fn lower_pat_tuple(
         &mut self,
-        pats: &[P<Pat>],
+        pats: &[Box<Pat>],
         ctx: &str,
     ) -> (&'hir [hir::Pat<'hir>], hir::DotDotPos) {
         let mut elems = Vec::with_capacity(pats.len());
@@ -209,7 +208,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     /// When encountering `($binding_mode $ident @)? ..` (`slice`),
     /// this is interpreted as a sub-slice pattern semantically.
     /// Patterns that follow, which are not like `slice` -- or an error occurs, are in `after`.
-    fn lower_pat_slice(&mut self, pats: &[P<Pat>]) -> hir::PatKind<'hir> {
+    fn lower_pat_slice(&mut self, pats: &[Box<Pat>]) -> hir::PatKind<'hir> {
         let mut before = Vec::new();
         let mut after = Vec::new();
         let mut slice = None;
diff --git a/compiler/rustc_ast_lowering/src/path.rs b/compiler/rustc_ast_lowering/src/path.rs
index c80ef275c80..3322e0fb66b 100644
--- a/compiler/rustc_ast_lowering/src/path.rs
+++ b/compiler/rustc_ast_lowering/src/path.rs
@@ -24,7 +24,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     pub(crate) fn lower_qpath(
         &mut self,
         id: NodeId,
-        qself: &Option<ptr::P<QSelf>>,
+        qself: &Option<Box<QSelf>>,
         p: &Path,
         param_mode: ParamMode,
         allow_return_type_notation: AllowReturnTypeNotation,
diff --git a/compiler/rustc_ast_passes/messages.ftl b/compiler/rustc_ast_passes/messages.ftl
index 42f3569f0f1..73cbcdd30ce 100644
--- a/compiler/rustc_ast_passes/messages.ftl
+++ b/compiler/rustc_ast_passes/messages.ftl
@@ -17,7 +17,7 @@ ast_passes_abi_must_not_have_parameters_or_return_type=
 
 ast_passes_abi_must_not_have_return_type=
     invalid signature for `extern {$abi}` function
-    .note = functions with the "custom" ABI cannot have a return type
+    .note = functions with the {$abi} ABI cannot have a return type
     .help = remove the return type
 
 ast_passes_assoc_const_without_body =
@@ -32,6 +32,13 @@ ast_passes_assoc_type_without_body =
     associated type in `impl` without body
     .suggestion = provide a definition for the type
 
+ast_passes_async_fn_in_const_trait_or_trait_impl =
+    async functions are not allowed in `const` {$in_impl ->
+        [true] trait impls
+        *[false] traits
+    }
+    .label = associated functions of `const` cannot be declared `async`
+
 ast_passes_at_least_one_trait = at least one trait must be specified
 
 ast_passes_auto_generic = auto traits cannot have generic parameters
@@ -40,7 +47,7 @@ ast_passes_auto_generic = auto traits cannot have generic parameters
 
 ast_passes_auto_items = auto traits cannot have associated items
     .label = {ast_passes_auto_items}
-    .suggestion = remove these associated items
+    .suggestion = remove the associated items
 
 ast_passes_auto_super_lifetime = auto traits cannot have super traits or lifetime bounds
     .label = {ast_passes_auto_super_lifetime}
@@ -175,11 +182,6 @@ ast_passes_generic_default_trailing = generic parameters with a default must be
 ast_passes_incompatible_features = `{$f1}` and `{$f2}` are incompatible, using them at the same time is not allowed
     .help = remove one of these features
 
-ast_passes_inherent_cannot_be = inherent impls cannot be {$annotation}
-    .because = {$annotation} because of this
-    .type = inherent impl for this type
-    .only_trait = only trait implementations may be annotated with {$annotation}
-
 ast_passes_item_invalid_safety = items outside of `unsafe extern {"{ }"}` cannot be declared with `safe` safety qualifier
     .suggestion = remove safe from this item
 
diff --git a/compiler/rustc_ast_passes/src/ast_validation.rs b/compiler/rustc_ast_passes/src/ast_validation.rs
index ae482ceb9b7..0c72f319007 100644
--- a/compiler/rustc_ast_passes/src/ast_validation.rs
+++ b/compiler/rustc_ast_passes/src/ast_validation.rs
@@ -22,7 +22,6 @@ use std::str::FromStr;
 
 use itertools::{Either, Itertools};
 use rustc_abi::{CanonAbi, ExternAbi, InterruptKind};
-use rustc_ast::ptr::P;
 use rustc_ast::visit::{AssocCtxt, BoundKind, FnCtxt, FnKind, Visitor, walk_list};
 use rustc_ast::*;
 use rustc_ast_pretty::pprust::{self, State};
@@ -294,6 +293,21 @@ impl<'a> AstValidator<'a> {
         });
     }
 
+    fn check_async_fn_in_const_trait_or_impl(&self, sig: &FnSig, parent: &TraitOrTraitImpl) {
+        let Some(const_keyword) = parent.constness() else { return };
+
+        let Some(CoroutineKind::Async { span: async_keyword, .. }) = sig.header.coroutine_kind
+        else {
+            return;
+        };
+
+        self.dcx().emit_err(errors::AsyncFnInConstTraitOrTraitImpl {
+            async_keyword,
+            in_impl: matches!(parent, TraitOrTraitImpl::TraitImpl { .. }),
+            const_keyword,
+        });
+    }
+
     fn check_fn_decl(&self, fn_decl: &FnDecl, self_semantic: SelfSemantic) {
         self.check_decl_num_args(fn_decl);
         self.check_decl_cvariadic_pos(fn_decl);
@@ -391,7 +405,13 @@ impl<'a> AstValidator<'a> {
                         if let InterruptKind::X86 = interrupt_kind {
                             // "x86-interrupt" is special because it does have arguments.
                             // FIXME(workingjubilee): properly lint on acceptable input types.
-                            if let FnRetTy::Ty(ref ret_ty) = sig.decl.output {
+                            if let FnRetTy::Ty(ref ret_ty) = sig.decl.output
+                                && match &ret_ty.kind {
+                                    TyKind::Never => false,
+                                    TyKind::Tup(tup) if tup.is_empty() => false,
+                                    _ => true,
+                                }
+                            {
                                 self.dcx().emit_err(errors::AbiMustNotHaveReturnType {
                                     span: ret_ty.span,
                                     abi,
@@ -450,7 +470,13 @@ impl<'a> AstValidator<'a> {
 
     fn reject_params_or_return(&self, abi: ExternAbi, ident: &Ident, sig: &FnSig) {
         let mut spans: Vec<_> = sig.decl.inputs.iter().map(|p| p.span).collect();
-        if let FnRetTy::Ty(ref ret_ty) = sig.decl.output {
+        if let FnRetTy::Ty(ref ret_ty) = sig.decl.output
+            && match &ret_ty.kind {
+                TyKind::Never => false,
+                TyKind::Tup(tup) if tup.is_empty() => false,
+                _ => true,
+            }
+        {
             spans.push(ret_ty.span);
         }
 
@@ -699,23 +725,27 @@ impl<'a> AstValidator<'a> {
         }
     }
 
-    fn deny_super_traits(&self, bounds: &GenericBounds, ident_span: Span) {
+    fn deny_super_traits(&self, bounds: &GenericBounds, ident: Span) {
         if let [.., last] = &bounds[..] {
-            let span = ident_span.shrink_to_hi().to(last.span());
-            self.dcx().emit_err(errors::AutoTraitBounds { span, ident: ident_span });
+            let span = bounds.iter().map(|b| b.span()).collect();
+            let removal = ident.shrink_to_hi().to(last.span());
+            self.dcx().emit_err(errors::AutoTraitBounds { span, removal, ident });
         }
     }
 
-    fn deny_where_clause(&self, where_clause: &WhereClause, ident_span: Span) {
+    fn deny_where_clause(&self, where_clause: &WhereClause, ident: Span) {
         if !where_clause.predicates.is_empty() {
             // FIXME: The current diagnostic is misleading since it only talks about
             // super trait and lifetime bounds while we should just say “bounds”.
-            self.dcx()
-                .emit_err(errors::AutoTraitBounds { span: where_clause.span, ident: ident_span });
+            self.dcx().emit_err(errors::AutoTraitBounds {
+                span: vec![where_clause.span],
+                removal: where_clause.span,
+                ident,
+            });
         }
     }
 
-    fn deny_items(&self, trait_items: &[P<AssocItem>], ident_span: Span) {
+    fn deny_items(&self, trait_items: &[Box<AssocItem>], ident_span: Span) {
         if !trait_items.is_empty() {
             let spans: Vec<_> = trait_items.iter().map(|i| i.kind.ident().unwrap().span).collect();
             let total = trait_items.first().unwrap().span.to(trait_items.last().unwrap().span);
@@ -951,13 +981,16 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
         }
 
         match &item.kind {
-            ItemKind::Impl(box Impl {
-                safety,
-                polarity,
-                defaultness: _,
-                constness,
+            ItemKind::Impl(Impl {
                 generics,
-                of_trait: Some(t),
+                of_trait:
+                    Some(box TraitImplHeader {
+                        safety,
+                        polarity,
+                        defaultness: _,
+                        constness,
+                        trait_ref: t,
+                    }),
                 self_ty,
                 items,
             }) => {
@@ -989,46 +1022,12 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     walk_list!(this, visit_assoc_item, items, AssocCtxt::Impl { of_trait: true });
                 });
             }
-            ItemKind::Impl(box Impl {
-                safety,
-                polarity,
-                defaultness,
-                constness,
-                generics,
-                of_trait: None,
-                self_ty,
-                items,
-            }) => {
-                let error = |annotation_span, annotation, only_trait| errors::InherentImplCannot {
-                    span: self_ty.span,
-                    annotation_span,
-                    annotation,
-                    self_ty: self_ty.span,
-                    only_trait,
-                };
-
+            ItemKind::Impl(Impl { generics, of_trait: None, self_ty, items }) => {
                 self.visit_attrs_vis(&item.attrs, &item.vis);
                 self.visibility_not_permitted(
                     &item.vis,
                     errors::VisibilityNotPermittedNote::IndividualImplItems,
                 );
-                if let &Safety::Unsafe(span) = safety {
-                    self.dcx().emit_err(errors::InherentImplCannotUnsafe {
-                        span: self_ty.span,
-                        annotation_span: span,
-                        annotation: "unsafe",
-                        self_ty: self_ty.span,
-                    });
-                }
-                if let &ImplPolarity::Negative(span) = polarity {
-                    self.dcx().emit_err(error(span, "negative", false));
-                }
-                if let &Defaultness::Default(def_span) = defaultness {
-                    self.dcx().emit_err(error(def_span, "`default`", true));
-                }
-                if let &Const::Yes(span) = constness {
-                    self.dcx().emit_err(error(span, "`const`", true));
-                }
 
                 self.with_tilde_const(Some(TildeConstReason::Impl { span: item.span }), |this| {
                     this.visit_generics(generics)
@@ -1594,6 +1593,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             self.visibility_not_permitted(&item.vis, errors::VisibilityNotPermittedNote::TraitImpl);
             if let AssocItemKind::Fn(box Fn { sig, .. }) = &item.kind {
                 self.check_trait_fn_not_const(sig.header.constness, parent);
+                self.check_async_fn_in_const_trait_or_impl(sig, parent);
             }
         }
 
@@ -1769,7 +1769,7 @@ fn deny_equality_constraints(
                         .map(|segment| segment.ident.name)
                         .zip(poly.trait_ref.path.segments.iter().map(|segment| segment.ident.name))
                         .all(|(a, b)| a == b)
-                        && let Some(potential_assoc) = full_path.segments.iter().last()
+                        && let Some(potential_assoc) = full_path.segments.last()
                     {
                         suggest(poly, potential_assoc, predicate);
                     }
diff --git a/compiler/rustc_ast_passes/src/errors.rs b/compiler/rustc_ast_passes/src/errors.rs
index 8b5873a3ef3..5ecc0d21411 100644
--- a/compiler/rustc_ast_passes/src/errors.rs
+++ b/compiler/rustc_ast_passes/src/errors.rs
@@ -63,6 +63,16 @@ pub(crate) struct TraitFnConst {
 }
 
 #[derive(Diagnostic)]
+#[diag(ast_passes_async_fn_in_const_trait_or_trait_impl)]
+pub(crate) struct AsyncFnInConstTraitOrTraitImpl {
+    #[primary_span]
+    pub async_keyword: Span,
+    pub in_impl: bool,
+    #[label]
+    pub const_keyword: Span,
+}
+
+#[derive(Diagnostic)]
 #[diag(ast_passes_forbidden_bound)]
 pub(crate) struct ForbiddenBound {
     #[primary_span]
@@ -344,7 +354,7 @@ pub(crate) struct ModuleNonAscii {
 #[diag(ast_passes_auto_generic, code = E0567)]
 pub(crate) struct AutoTraitGeneric {
     #[primary_span]
-    #[suggestion(code = "", applicability = "machine-applicable")]
+    #[suggestion(code = "", applicability = "machine-applicable", style = "tool-only")]
     pub span: Span,
     #[label]
     pub ident: Span,
@@ -354,8 +364,9 @@ pub(crate) struct AutoTraitGeneric {
 #[diag(ast_passes_auto_super_lifetime, code = E0568)]
 pub(crate) struct AutoTraitBounds {
     #[primary_span]
-    #[suggestion(code = "", applicability = "machine-applicable")]
-    pub span: Span,
+    pub span: Vec<Span>,
+    #[suggestion(code = "", applicability = "machine-applicable", style = "tool-only")]
+    pub removal: Span,
     #[label]
     pub ident: Span,
 }
@@ -365,7 +376,7 @@ pub(crate) struct AutoTraitBounds {
 pub(crate) struct AutoTraitItems {
     #[primary_span]
     pub spans: Vec<Span>,
-    #[suggestion(code = "", applicability = "machine-applicable")]
+    #[suggestion(code = "", applicability = "machine-applicable", style = "tool-only")]
     pub total: Span,
     #[label]
     pub ident: Span,
@@ -464,32 +475,6 @@ pub(crate) struct UnsafeNegativeImpl {
 }
 
 #[derive(Diagnostic)]
-#[diag(ast_passes_inherent_cannot_be)]
-pub(crate) struct InherentImplCannot<'a> {
-    #[primary_span]
-    pub span: Span,
-    #[label(ast_passes_because)]
-    pub annotation_span: Span,
-    pub annotation: &'a str,
-    #[label(ast_passes_type)]
-    pub self_ty: Span,
-    #[note(ast_passes_only_trait)]
-    pub only_trait: bool,
-}
-
-#[derive(Diagnostic)]
-#[diag(ast_passes_inherent_cannot_be, code = E0197)]
-pub(crate) struct InherentImplCannotUnsafe<'a> {
-    #[primary_span]
-    pub span: Span,
-    #[label(ast_passes_because)]
-    pub annotation_span: Span,
-    pub annotation: &'a str,
-    #[label(ast_passes_type)]
-    pub self_ty: Span,
-}
-
-#[derive(Diagnostic)]
 #[diag(ast_passes_unsafe_item)]
 pub(crate) struct UnsafeItem {
     #[primary_span]
diff --git a/compiler/rustc_ast_passes/src/feature_gate.rs b/compiler/rustc_ast_passes/src/feature_gate.rs
index 662357ce884..c9344a76a7b 100644
--- a/compiler/rustc_ast_passes/src/feature_gate.rs
+++ b/compiler/rustc_ast_passes/src/feature_gate.rs
@@ -217,18 +217,18 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 }
             }
 
-            ast::ItemKind::Impl(box ast::Impl { polarity, defaultness, of_trait, .. }) => {
-                if let &ast::ImplPolarity::Negative(span) = polarity {
+            ast::ItemKind::Impl(ast::Impl { of_trait: Some(of_trait), .. }) => {
+                if let ast::ImplPolarity::Negative(span) = of_trait.polarity {
                     gate!(
                         &self,
                         negative_impls,
-                        span.to(of_trait.as_ref().map_or(span, |t| t.path.span)),
+                        span.to(of_trait.trait_ref.path.span),
                         "negative trait bounds are not fully implemented; \
                          use marker types for now"
                     );
                 }
 
-                if let ast::Defaultness::Default(_) = defaultness {
+                if let ast::Defaultness::Default(_) = of_trait.defaultness {
                     gate!(&self, specialization, i.span, "specialization is unstable");
                 }
             }
diff --git a/compiler/rustc_ast_pretty/src/pprust/state.rs b/compiler/rustc_ast_pretty/src/pprust/state.rs
index f0cf0c1487f..85f76036df7 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state.rs
@@ -10,7 +10,6 @@ use std::borrow::Cow;
 use std::sync::Arc;
 
 use rustc_ast::attr::AttrIdGenerator;
-use rustc_ast::ptr::P;
 use rustc_ast::token::{self, CommentKind, Delimiter, IdentIsRaw, Token, TokenKind};
 use rustc_ast::tokenstream::{Spacing, TokenStream, TokenTree};
 use rustc_ast::util::classify;
@@ -1178,7 +1177,7 @@ impl<'a> State<'a> {
         self.end(rb);
     }
 
-    fn commasep_exprs(&mut self, b: Breaks, exprs: &[P<ast::Expr>]) {
+    fn commasep_exprs(&mut self, b: Breaks, exprs: &[Box<ast::Expr>]) {
         self.commasep_cmnt(b, exprs, |s, e| s.print_expr(e, FixupContext::default()), |e| e.span)
     }
 
diff --git a/compiler/rustc_ast_pretty/src/pprust/state/expr.rs b/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
index 8a2cb64b2a0..bdf73ac32f0 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state/expr.rs
@@ -2,7 +2,6 @@ use std::fmt::Write;
 
 use ast::{ForLoopKind, MatchKind};
 use itertools::{Itertools, Position};
-use rustc_ast::ptr::P;
 use rustc_ast::util::classify;
 use rustc_ast::util::literal::escape_byte_str_symbol;
 use rustc_ast::util::parser::{self, ExprPrecedence, Fixity};
@@ -54,7 +53,7 @@ impl<'a> State<'a> {
         self.print_else(elseopt)
     }
 
-    fn print_call_post(&mut self, args: &[P<ast::Expr>]) {
+    fn print_call_post(&mut self, args: &[Box<ast::Expr>]) {
         self.popen();
         self.commasep_exprs(Inconsistent, args);
         self.pclose()
@@ -111,7 +110,7 @@ impl<'a> State<'a> {
         }
     }
 
-    fn print_expr_vec(&mut self, exprs: &[P<ast::Expr>]) {
+    fn print_expr_vec(&mut self, exprs: &[Box<ast::Expr>]) {
         let ib = self.ibox(INDENT_UNIT);
         self.word("[");
         self.commasep_exprs(Inconsistent, exprs);
@@ -149,7 +148,7 @@ impl<'a> State<'a> {
 
     fn print_expr_struct(
         &mut self,
-        qself: &Option<P<ast::QSelf>>,
+        qself: &Option<Box<ast::QSelf>>,
         path: &ast::Path,
         fields: &[ast::ExprField],
         rest: &ast::StructRest,
@@ -204,7 +203,7 @@ impl<'a> State<'a> {
         self.word("}");
     }
 
-    fn print_expr_tup(&mut self, exprs: &[P<ast::Expr>]) {
+    fn print_expr_tup(&mut self, exprs: &[Box<ast::Expr>]) {
         self.popen();
         self.commasep_exprs(Inconsistent, exprs);
         if exprs.len() == 1 {
@@ -213,7 +212,7 @@ impl<'a> State<'a> {
         self.pclose()
     }
 
-    fn print_expr_call(&mut self, func: &ast::Expr, args: &[P<ast::Expr>], fixup: FixupContext) {
+    fn print_expr_call(&mut self, func: &ast::Expr, args: &[Box<ast::Expr>], fixup: FixupContext) {
         // Independent of parenthesization related to precedence, we must
         // parenthesize `func` if this is a statement context in which without
         // parentheses, a statement boundary would occur inside `func` or
@@ -247,7 +246,7 @@ impl<'a> State<'a> {
         &mut self,
         segment: &ast::PathSegment,
         receiver: &ast::Expr,
-        base_args: &[P<ast::Expr>],
+        base_args: &[Box<ast::Expr>],
         fixup: FixupContext,
     ) {
         // The fixup here is different than in `print_expr_call` because
diff --git a/compiler/rustc_ast_pretty/src/pprust/state/item.rs b/compiler/rustc_ast_pretty/src/pprust/state/item.rs
index 11c97a552c6..ab402cbb8dc 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state/item.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state/item.rs
@@ -2,7 +2,6 @@ use ast::StaticItem;
 use itertools::{Itertools, Position};
 use rustc_ast as ast;
 use rustc_ast::ModKind;
-use rustc_ast::ptr::P;
 use rustc_span::Ident;
 
 use crate::pp::BoxMarker;
@@ -309,39 +308,41 @@ impl<'a> State<'a> {
                 let (cb, ib) = self.head(visibility_qualified(&item.vis, "union"));
                 self.print_struct(struct_def, generics, *ident, item.span, true, cb, ib);
             }
-            ast::ItemKind::Impl(box ast::Impl {
-                safety,
-                polarity,
-                defaultness,
-                constness,
-                generics,
-                of_trait,
-                self_ty,
-                items,
-            }) => {
+            ast::ItemKind::Impl(ast::Impl { generics, of_trait, self_ty, items }) => {
                 let (cb, ib) = self.head("");
                 self.print_visibility(&item.vis);
-                self.print_defaultness(*defaultness);
-                self.print_safety(*safety);
-                self.word("impl");
-
-                if generics.params.is_empty() {
-                    self.nbsp();
-                } else {
-                    self.print_generic_params(&generics.params);
-                    self.space();
-                }
 
-                self.print_constness(*constness);
+                let impl_generics = |this: &mut Self| {
+                    this.word("impl");
 
-                if let ast::ImplPolarity::Negative(_) = polarity {
-                    self.word("!");
-                }
-
-                if let Some(t) = of_trait {
-                    self.print_trait_ref(t);
+                    if generics.params.is_empty() {
+                        this.nbsp();
+                    } else {
+                        this.print_generic_params(&generics.params);
+                        this.space();
+                    }
+                };
+
+                if let Some(box of_trait) = of_trait {
+                    let ast::TraitImplHeader {
+                        defaultness,
+                        safety,
+                        constness,
+                        polarity,
+                        ref trait_ref,
+                    } = *of_trait;
+                    self.print_defaultness(defaultness);
+                    self.print_safety(safety);
+                    impl_generics(self);
+                    self.print_constness(constness);
+                    if let ast::ImplPolarity::Negative(_) = polarity {
+                        self.word("!");
+                    }
+                    self.print_trait_ref(trait_ref);
                     self.space();
                     self.word_space("for");
+                } else {
+                    impl_generics(self);
                 }
 
                 self.print_type(self_ty);
@@ -628,10 +629,10 @@ impl<'a> State<'a> {
         &mut self,
         attrs: &[ast::Attribute],
         vis: &ast::Visibility,
-        qself: &Option<P<ast::QSelf>>,
+        qself: &Option<Box<ast::QSelf>>,
         path: &ast::Path,
         kind: DelegationKind<'_>,
-        body: &Option<P<ast::Block>>,
+        body: &Option<Box<ast::Block>>,
     ) {
         let body_cb_ib = body.as_ref().map(|body| (body, self.head("")));
         self.print_visibility(vis);
diff --git a/compiler/rustc_attr_parsing/Cargo.toml b/compiler/rustc_attr_parsing/Cargo.toml
index cec9d62e656..bac89373b67 100644
--- a/compiler/rustc_attr_parsing/Cargo.toml
+++ b/compiler/rustc_attr_parsing/Cargo.toml
@@ -5,6 +5,7 @@ edition = "2024"
 
 [dependencies]
 # tidy-alphabetical-start
+itertools = "0.12"
 rustc_abi = { path = "../rustc_abi" }
 rustc_ast = { path = "../rustc_ast" }
 rustc_ast_pretty = { path = "../rustc_ast_pretty" }
diff --git a/compiler/rustc_attr_parsing/messages.ftl b/compiler/rustc_attr_parsing/messages.ftl
index 35ff48cb5f2..4fb66a81652 100644
--- a/compiler/rustc_attr_parsing/messages.ftl
+++ b/compiler/rustc_attr_parsing/messages.ftl
@@ -10,6 +10,12 @@ attr_parsing_empty_attribute =
     unused attribute
     .suggestion = remove this attribute
 
+attr_parsing_invalid_target = `#[{$name}]` attribute cannot be used on {$target}
+    .help = `#[{$name}]` can {$only}be applied to {$applied}
+attr_parsing_invalid_target_lint = `#[{$name}]` attribute cannot be used on {$target}
+    .warn = {-attr_parsing_previously_accepted}
+    .help = `#[{$name}]` can {$only}be applied to {$applied}
+
 attr_parsing_empty_confusables =
     expected at least one confusable name
 attr_parsing_expected_one_cfg_pattern =
@@ -132,6 +138,7 @@ attr_parsing_unknown_version_literal =
 attr_parsing_unrecognized_repr_hint =
     unrecognized representation hint
     .help = valid reprs are `Rust` (default), `C`, `align`, `packed`, `transparent`, `simd`, `i8`, `u8`, `i16`, `u16`, `i32`, `u32`, `i64`, `u64`, `i128`, `u128`, `isize`, `usize`
+    .note = for more information, visit <https://doc.rust-lang.org/reference/type-layout.html?highlight=repr#representations>
 
 attr_parsing_unstable_cfg_target_compact =
     compact `cfg(target(..))` is experimental and subject to change
diff --git a/compiler/rustc_attr_parsing/src/attributes/allow_unstable.rs b/compiler/rustc_attr_parsing/src/attributes/allow_unstable.rs
index 95104b896ac..4d995027814 100644
--- a/compiler/rustc_attr_parsing/src/attributes/allow_unstable.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/allow_unstable.rs
@@ -2,10 +2,12 @@ use std::iter;
 
 use rustc_feature::{AttributeTemplate, template};
 use rustc_hir::attrs::AttributeKind;
+use rustc_hir::{MethodKind, Target};
 use rustc_span::{Span, Symbol, sym};
 
 use super::{CombineAttributeParser, ConvertFn};
-use crate::context::{AcceptContext, Stage};
+use crate::context::MaybeWarn::{Allow, Warn};
+use crate::context::{AcceptContext, AllowedTargets, Stage};
 use crate::parser::ArgParser;
 use crate::session_diagnostics;
 
@@ -15,7 +17,13 @@ impl<S: Stage> CombineAttributeParser<S> for AllowInternalUnstableParser {
     type Item = (Symbol, Span);
     const CONVERT: ConvertFn<Self::Item> =
         |items, span| AttributeKind::AllowInternalUnstable(items, span);
-    const TEMPLATE: AttributeTemplate = template!(Word, List: "feat1, feat2, ...");
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::MacroDef),
+        Allow(Target::Fn),
+        Warn(Target::Field),
+        Warn(Target::Arm),
+    ]);
+    const TEMPLATE: AttributeTemplate = template!(Word, List: &["feat1, feat2, ..."]);
 
     fn extend<'c>(
         cx: &'c mut AcceptContext<'_, '_, S>,
@@ -32,7 +40,12 @@ impl<S: Stage> CombineAttributeParser<S> for UnstableFeatureBoundParser {
     const PATH: &'static [rustc_span::Symbol] = &[sym::unstable_feature_bound];
     type Item = (Symbol, Span);
     const CONVERT: ConvertFn<Self::Item> = |items, _| AttributeKind::UnstableFeatureBound(items);
-    const TEMPLATE: AttributeTemplate = template!(Word, List: "feat1, feat2, ...");
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Fn),
+        Allow(Target::Impl { of_trait: true }),
+        Allow(Target::Trait),
+    ]);
+    const TEMPLATE: AttributeTemplate = template!(Word, List: &["feat1, feat2, ..."]);
 
     fn extend<'c>(
         cx: &'c mut AcceptContext<'_, '_, S>,
@@ -53,7 +66,14 @@ impl<S: Stage> CombineAttributeParser<S> for AllowConstFnUnstableParser {
     type Item = Symbol;
     const CONVERT: ConvertFn<Self::Item> =
         |items, first_span| AttributeKind::AllowConstFnUnstable(items, first_span);
-    const TEMPLATE: AttributeTemplate = template!(Word, List: "feat1, feat2, ...");
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Fn),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::Method(MethodKind::Trait { body: false })),
+        Allow(Target::Method(MethodKind::Trait { body: true })),
+        Allow(Target::Method(MethodKind::TraitImpl)),
+    ]);
+    const TEMPLATE: AttributeTemplate = template!(Word, List: &["feat1, feat2, ..."]);
 
     fn extend<'c>(
         cx: &'c mut AcceptContext<'_, '_, S>,
diff --git a/compiler/rustc_attr_parsing/src/attributes/body.rs b/compiler/rustc_attr_parsing/src/attributes/body.rs
index ab9330216f6..88540384621 100644
--- a/compiler/rustc_attr_parsing/src/attributes/body.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/body.rs
@@ -1,15 +1,18 @@
 //! Attributes that can be found in function body.
 
+use rustc_hir::Target;
 use rustc_hir::attrs::AttributeKind;
 use rustc_span::{Symbol, sym};
 
 use super::{NoArgsAttributeParser, OnDuplicate};
-use crate::context::Stage;
+use crate::context::MaybeWarn::Allow;
+use crate::context::{AllowedTargets, Stage};
 
 pub(crate) struct CoroutineParser;
 
 impl<S: Stage> NoArgsAttributeParser<S> for CoroutineParser {
     const PATH: &[Symbol] = &[sym::coroutine];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Closure)]);
     const CREATE: fn(rustc_span::Span) -> AttributeKind = |span| AttributeKind::Coroutine(span);
 }
diff --git a/compiler/rustc_attr_parsing/src/attributes/cfg.rs b/compiler/rustc_attr_parsing/src/attributes/cfg.rs
index 947be28bc95..695ee666476 100644
--- a/compiler/rustc_attr_parsing/src/attributes/cfg.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/cfg.rs
@@ -16,7 +16,10 @@ use crate::{
     CfgMatchesLintEmitter, fluent_generated, parse_version, session_diagnostics, try_gate_cfg,
 };
 
-pub const CFG_TEMPLATE: AttributeTemplate = template!(List: "predicate");
+pub const CFG_TEMPLATE: AttributeTemplate = template!(
+    List: &["predicate"],
+    "https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg-attribute"
+);
 
 pub fn parse_cfg_attr<'c, S: Stage>(
     cx: &'c mut AcceptContext<'_, '_, S>,
diff --git a/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs b/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
index c5fb11dbf6a..6ea073896c2 100644
--- a/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
@@ -1,5 +1,6 @@
 use rustc_feature::{AttributeTemplate, template};
 use rustc_hir::attrs::{AttributeKind, CoverageAttrKind, OptimizeAttr, UsedBy};
+use rustc_hir::{MethodKind, Target};
 use rustc_session::parse::feature_err;
 use rustc_span::{Span, Symbol, sym};
 
@@ -7,7 +8,8 @@ use super::{
     AcceptMapping, AttributeOrder, AttributeParser, CombineAttributeParser, ConvertFn,
     NoArgsAttributeParser, OnDuplicate, SingleAttributeParser,
 };
-use crate::context::{AcceptContext, FinalizeContext, Stage};
+use crate::context::MaybeWarn::{Allow, Warn};
+use crate::context::{AcceptContext, AllowedTargets, FinalizeContext, Stage};
 use crate::parser::ArgParser;
 use crate::session_diagnostics::{NakedFunctionIncompatibleAttribute, NullOnExport};
 
@@ -17,7 +19,14 @@ impl<S: Stage> SingleAttributeParser<S> for OptimizeParser {
     const PATH: &[Symbol] = &[sym::optimize];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepOutermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::WarnButFutureError;
-    const TEMPLATE: AttributeTemplate = template!(List: "size|speed|none");
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Fn),
+        Allow(Target::Closure),
+        Allow(Target::Method(MethodKind::Trait { body: true })),
+        Allow(Target::Method(MethodKind::TraitImpl)),
+        Allow(Target::Method(MethodKind::Inherent)),
+    ]);
+    const TEMPLATE: AttributeTemplate = template!(List: &["size", "speed", "none"]);
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         let Some(list) = args.list() else {
@@ -49,6 +58,15 @@ pub(crate) struct ColdParser;
 impl<S: Stage> NoArgsAttributeParser<S> for ColdParser {
     const PATH: &[Symbol] = &[sym::cold];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowListWarnRest(&[
+        Allow(Target::Fn),
+        Allow(Target::Method(MethodKind::Trait { body: true })),
+        Allow(Target::Method(MethodKind::TraitImpl)),
+        Allow(Target::Method(MethodKind::Trait { body: false })),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::ForeignFn),
+        Allow(Target::Closure),
+    ]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::Cold;
 }
 
@@ -58,6 +76,17 @@ impl<S: Stage> SingleAttributeParser<S> for CoverageParser {
     const PATH: &[Symbol] = &[sym::coverage];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepOutermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Fn),
+        Allow(Target::Closure),
+        Allow(Target::Method(MethodKind::Trait { body: true })),
+        Allow(Target::Method(MethodKind::TraitImpl)),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::Impl { of_trait: true }),
+        Allow(Target::Impl { of_trait: false }),
+        Allow(Target::Mod),
+        Allow(Target::Crate),
+    ]);
     const TEMPLATE: AttributeTemplate = template!(OneOf: &[sym::off, sym::on]);
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
@@ -97,6 +126,16 @@ impl<S: Stage> SingleAttributeParser<S> for ExportNameParser {
     const PATH: &[rustc_span::Symbol] = &[sym::export_name];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepInnermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::WarnButFutureError;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Static),
+        Allow(Target::Fn),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::Method(MethodKind::Trait { body: true })),
+        Allow(Target::Method(MethodKind::TraitImpl)),
+        Warn(Target::Field),
+        Warn(Target::Arm),
+        Warn(Target::MacroDef),
+    ]);
     const TEMPLATE: AttributeTemplate = template!(NameValueStr: "name");
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
@@ -138,6 +177,12 @@ impl<S: Stage> AttributeParser<S> for NakedParser {
                 this.span = Some(cx.attr_span);
             }
         })];
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Fn),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::Method(MethodKind::Trait { body: true })),
+        Allow(Target::Method(MethodKind::TraitImpl)),
+    ]);
 
     fn finalize(self, cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {
         // FIXME(jdonszelmann): upgrade this list to *parsed* attributes
@@ -230,6 +275,18 @@ pub(crate) struct TrackCallerParser;
 impl<S: Stage> NoArgsAttributeParser<S> for TrackCallerParser {
     const PATH: &[Symbol] = &[sym::track_caller];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Fn),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::Method(MethodKind::Trait { body: true })),
+        Allow(Target::Method(MethodKind::TraitImpl)),
+        Allow(Target::Method(MethodKind::Trait { body: false })),
+        Allow(Target::ForeignFn),
+        Allow(Target::Closure),
+        Warn(Target::MacroDef),
+        Warn(Target::Arm),
+        Warn(Target::Field),
+    ]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::TrackCaller;
 }
 
@@ -237,6 +294,12 @@ pub(crate) struct NoMangleParser;
 impl<S: Stage> NoArgsAttributeParser<S> for NoMangleParser {
     const PATH: &[Symbol] = &[sym::no_mangle];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowListWarnRest(&[
+        Allow(Target::Fn),
+        Allow(Target::Static),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::Method(MethodKind::TraitImpl)),
+    ]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::NoMangle;
 }
 
@@ -253,7 +316,7 @@ pub(crate) struct UsedParser {
 impl<S: Stage> AttributeParser<S> for UsedParser {
     const ATTRIBUTES: AcceptMapping<Self, S> = &[(
         &[sym::used],
-        template!(Word, List: "compiler|linker"),
+        template!(Word, List: &["compiler", "linker"]),
         |group: &mut Self, cx, args| {
             let used_by = match args {
                 ArgParser::NoArgs => UsedBy::Linker,
@@ -310,6 +373,7 @@ impl<S: Stage> AttributeParser<S> for UsedParser {
             }
         },
     )];
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Static)]);
 
     fn finalize(self, _cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {
         // Ratcheting behaviour, if both `linker` and `compiler` are specified, use `linker`
@@ -327,7 +391,7 @@ impl<S: Stage> CombineAttributeParser<S> for TargetFeatureParser {
     type Item = (Symbol, Span);
     const PATH: &[Symbol] = &[sym::target_feature];
     const CONVERT: ConvertFn<Self::Item> = |items, span| AttributeKind::TargetFeature(items, span);
-    const TEMPLATE: AttributeTemplate = template!(List: "enable = \"feat1, feat2\"");
+    const TEMPLATE: AttributeTemplate = template!(List: &["enable = \"feat1, feat2\""]);
 
     fn extend<'c>(
         cx: &'c mut AcceptContext<'_, '_, S>,
@@ -373,4 +437,15 @@ impl<S: Stage> CombineAttributeParser<S> for TargetFeatureParser {
         }
         features
     }
+
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Fn),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::Method(MethodKind::Trait { body: true })),
+        Allow(Target::Method(MethodKind::TraitImpl)),
+        Warn(Target::Statement),
+        Warn(Target::Field),
+        Warn(Target::Arm),
+        Warn(Target::MacroDef),
+    ]);
 }
diff --git a/compiler/rustc_attr_parsing/src/attributes/confusables.rs b/compiler/rustc_attr_parsing/src/attributes/confusables.rs
index 7d24c89a6e8..00f949c82c5 100644
--- a/compiler/rustc_attr_parsing/src/attributes/confusables.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/confusables.rs
@@ -1,12 +1,13 @@
 use rustc_feature::template;
 use rustc_hir::attrs::AttributeKind;
+use rustc_hir::{MethodKind, Target};
 use rustc_span::{Span, Symbol, sym};
 use thin_vec::ThinVec;
 
 use super::{AcceptMapping, AttributeParser};
-use crate::context::{FinalizeContext, Stage};
+use crate::context::MaybeWarn::Allow;
+use crate::context::{AllowedTargets, FinalizeContext, Stage};
 use crate::session_diagnostics;
-
 #[derive(Default)]
 pub(crate) struct ConfusablesParser {
     confusables: ThinVec<Symbol>,
@@ -16,7 +17,7 @@ pub(crate) struct ConfusablesParser {
 impl<S: Stage> AttributeParser<S> for ConfusablesParser {
     const ATTRIBUTES: AcceptMapping<Self, S> = &[(
         &[sym::rustc_confusables],
-        template!(List: r#""name1", "name2", ..."#),
+        template!(List: &[r#""name1", "name2", ..."#]),
         |this, cx, args| {
             let Some(list) = args.list() else {
                 cx.expected_list(cx.attr_span);
@@ -41,6 +42,8 @@ impl<S: Stage> AttributeParser<S> for ConfusablesParser {
             this.first_span.get_or_insert(cx.attr_span);
         },
     )];
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowList(&[Allow(Target::Method(MethodKind::Inherent))]);
 
     fn finalize(self, _cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {
         if self.confusables.is_empty() {
diff --git a/compiler/rustc_attr_parsing/src/attributes/deprecation.rs b/compiler/rustc_attr_parsing/src/attributes/deprecation.rs
index 38ec4bd5645..8101c91460f 100644
--- a/compiler/rustc_attr_parsing/src/attributes/deprecation.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/deprecation.rs
@@ -1,13 +1,14 @@
 use rustc_feature::{AttributeTemplate, template};
 use rustc_hir::attrs::{AttributeKind, DeprecatedSince, Deprecation};
+use rustc_hir::{MethodKind, Target};
 use rustc_span::{Span, Symbol, sym};
 
 use super::util::parse_version;
 use super::{AttributeOrder, OnDuplicate, SingleAttributeParser};
-use crate::context::{AcceptContext, Stage};
+use crate::context::MaybeWarn::{Allow, Error};
+use crate::context::{AcceptContext, AllowedTargets, Stage};
 use crate::parser::ArgParser;
 use crate::session_diagnostics;
-
 pub(crate) struct DeprecationParser;
 
 fn get<S: Stage>(
@@ -38,9 +39,33 @@ impl<S: Stage> SingleAttributeParser<S> for DeprecationParser {
     const PATH: &[Symbol] = &[sym::deprecated];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepInnermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowListWarnRest(&[
+        Allow(Target::Fn),
+        Allow(Target::Mod),
+        Allow(Target::Struct),
+        Allow(Target::Enum),
+        Allow(Target::Union),
+        Allow(Target::Const),
+        Allow(Target::Static),
+        Allow(Target::MacroDef),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::Method(MethodKind::Trait { body: false })),
+        Allow(Target::Method(MethodKind::Trait { body: true })),
+        Allow(Target::TyAlias),
+        Allow(Target::Use),
+        Allow(Target::ForeignFn),
+        Allow(Target::Field),
+        Allow(Target::Trait),
+        Allow(Target::AssocTy),
+        Allow(Target::AssocConst),
+        Allow(Target::Variant),
+        Allow(Target::Impl { of_trait: false }), //FIXME This does not make sense
+        Allow(Target::Crate),
+        Error(Target::WherePredicate),
+    ]);
     const TEMPLATE: AttributeTemplate = template!(
         Word,
-        List: r#"/*opt*/ since = "version", /*opt*/ note = "reason""#,
+        List: &[r#"since = "version""#, r#"note = "reason""#, r#"since = "version", note = "reason""#],
         NameValueStr: "reason"
     );
 
diff --git a/compiler/rustc_attr_parsing/src/attributes/dummy.rs b/compiler/rustc_attr_parsing/src/attributes/dummy.rs
index bbcd9ab530c..85842b1b5c5 100644
--- a/compiler/rustc_attr_parsing/src/attributes/dummy.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/dummy.rs
@@ -3,14 +3,14 @@ use rustc_hir::attrs::AttributeKind;
 use rustc_span::{Symbol, sym};
 
 use crate::attributes::{AttributeOrder, OnDuplicate, SingleAttributeParser};
-use crate::context::{AcceptContext, Stage};
+use crate::context::{ALL_TARGETS, AcceptContext, AllowedTargets, Stage};
 use crate::parser::ArgParser;
-
 pub(crate) struct DummyParser;
 impl<S: Stage> SingleAttributeParser<S> for DummyParser {
     const PATH: &[Symbol] = &[sym::rustc_dummy];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepInnermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Ignore;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(ALL_TARGETS);
     const TEMPLATE: AttributeTemplate = template!(Word); // Anything, really
 
     fn convert(_: &mut AcceptContext<'_, '_, S>, _: &ArgParser<'_>) -> Option<AttributeKind> {
diff --git a/compiler/rustc_attr_parsing/src/attributes/inline.rs b/compiler/rustc_attr_parsing/src/attributes/inline.rs
index 8437713206e..6a659a95b85 100644
--- a/compiler/rustc_attr_parsing/src/attributes/inline.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/inline.rs
@@ -5,20 +5,39 @@
 use rustc_feature::{AttributeTemplate, template};
 use rustc_hir::attrs::{AttributeKind, InlineAttr};
 use rustc_hir::lints::AttributeLintKind;
+use rustc_hir::{MethodKind, Target};
 use rustc_span::{Symbol, sym};
 
 use super::{AcceptContext, AttributeOrder, OnDuplicate};
 use crate::attributes::SingleAttributeParser;
-use crate::context::Stage;
+use crate::context::MaybeWarn::{Allow, Warn};
+use crate::context::{AllowedTargets, Stage};
 use crate::parser::ArgParser;
-
 pub(crate) struct InlineParser;
 
 impl<S: Stage> SingleAttributeParser<S> for InlineParser {
     const PATH: &'static [Symbol] = &[sym::inline];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepOutermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::WarnButFutureError;
-    const TEMPLATE: AttributeTemplate = template!(Word, List: "always|never");
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Fn),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::Method(MethodKind::Trait { body: true })),
+        Allow(Target::Method(MethodKind::TraitImpl)),
+        Allow(Target::Closure),
+        Allow(Target::Delegation { mac: false }),
+        Warn(Target::Method(MethodKind::Trait { body: false })),
+        Warn(Target::ForeignFn),
+        Warn(Target::Field),
+        Warn(Target::MacroDef),
+        Warn(Target::Arm),
+        Warn(Target::AssocConst),
+    ]);
+    const TEMPLATE: AttributeTemplate = template!(
+        Word,
+        List: &["always", "never"],
+        "https://doc.rust-lang.org/reference/attributes/codegen.html#the-inline-attribute"
+    );
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         match args {
@@ -59,7 +78,8 @@ impl<S: Stage> SingleAttributeParser<S> for RustcForceInlineParser {
     const PATH: &'static [Symbol] = &[sym::rustc_force_inline];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepOutermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::WarnButFutureError;
-    const TEMPLATE: AttributeTemplate = template!(Word, List: "reason", NameValueStr: "reason");
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
+    const TEMPLATE: AttributeTemplate = template!(Word, List: &["reason"], NameValueStr: "reason");
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         let reason = match args {
diff --git a/compiler/rustc_attr_parsing/src/attributes/link_attrs.rs b/compiler/rustc_attr_parsing/src/attributes/link_attrs.rs
index 7eab3090870..552b9dfabc2 100644
--- a/compiler/rustc_attr_parsing/src/attributes/link_attrs.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/link_attrs.rs
@@ -1,22 +1,30 @@
 use rustc_feature::{AttributeTemplate, template};
-use rustc_hir::attrs::AttributeKind;
 use rustc_hir::attrs::AttributeKind::{LinkName, LinkOrdinal, LinkSection};
+use rustc_hir::attrs::{AttributeKind, Linkage};
+use rustc_hir::{MethodKind, Target};
 use rustc_span::{Span, Symbol, sym};
 
 use crate::attributes::{
     AttributeOrder, NoArgsAttributeParser, OnDuplicate, SingleAttributeParser,
 };
-use crate::context::{AcceptContext, Stage, parse_single_integer};
+use crate::context::MaybeWarn::Allow;
+use crate::context::{ALL_TARGETS, AcceptContext, AllowedTargets, Stage, parse_single_integer};
 use crate::parser::ArgParser;
 use crate::session_diagnostics::{LinkOrdinalOutOfRange, NullOnLinkSection};
-
 pub(crate) struct LinkNameParser;
 
 impl<S: Stage> SingleAttributeParser<S> for LinkNameParser {
     const PATH: &[Symbol] = &[sym::link_name];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepInnermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::WarnButFutureError;
-    const TEMPLATE: AttributeTemplate = template!(NameValueStr: "name");
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowListWarnRest(&[
+        Allow(Target::ForeignFn),
+        Allow(Target::ForeignStatic),
+    ]);
+    const TEMPLATE: AttributeTemplate = template!(
+        NameValueStr: "name",
+        "https://doc.rust-lang.org/reference/items/external-blocks.html#the-link_name-attribute"
+    );
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         let Some(nv) = args.name_value() else {
@@ -38,7 +46,12 @@ impl<S: Stage> SingleAttributeParser<S> for LinkSectionParser {
     const PATH: &[Symbol] = &[sym::link_section];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepInnermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::WarnButFutureError;
-    const TEMPLATE: AttributeTemplate = template!(NameValueStr: "name");
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowListWarnRest(&[Allow(Target::Static), Allow(Target::Fn)]);
+    const TEMPLATE: AttributeTemplate = template!(
+        NameValueStr: "name",
+        "https://doc.rust-lang.org/reference/abi.html#the-link_section-attribute"
+    );
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         let Some(nv) = args.name_value() else {
@@ -64,6 +77,7 @@ pub(crate) struct ExportStableParser;
 impl<S: Stage> NoArgsAttributeParser<S> for ExportStableParser {
     const PATH: &[Symbol] = &[sym::export_stable];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(ALL_TARGETS); //FIXME Still checked fully in `check_attr.rs`
     const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::ExportStable;
 }
 
@@ -71,6 +85,7 @@ pub(crate) struct FfiConstParser;
 impl<S: Stage> NoArgsAttributeParser<S> for FfiConstParser {
     const PATH: &[Symbol] = &[sym::ffi_const];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::ForeignFn)]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::FfiConst;
 }
 
@@ -78,6 +93,7 @@ pub(crate) struct FfiPureParser;
 impl<S: Stage> NoArgsAttributeParser<S> for FfiPureParser {
     const PATH: &[Symbol] = &[sym::ffi_pure];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::ForeignFn)]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::FfiPure;
 }
 
@@ -85,6 +101,12 @@ pub(crate) struct StdInternalSymbolParser;
 impl<S: Stage> NoArgsAttributeParser<S> for StdInternalSymbolParser {
     const PATH: &[Symbol] = &[sym::rustc_std_internal_symbol];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Fn),
+        Allow(Target::ForeignFn),
+        Allow(Target::Static),
+        Allow(Target::ForeignStatic),
+    ]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::StdInternalSymbol;
 }
 
@@ -94,7 +116,12 @@ impl<S: Stage> SingleAttributeParser<S> for LinkOrdinalParser {
     const PATH: &[Symbol] = &[sym::link_ordinal];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepOutermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
-    const TEMPLATE: AttributeTemplate = template!(List: "ordinal");
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowList(&[Allow(Target::ForeignFn), Allow(Target::ForeignStatic)]);
+    const TEMPLATE: AttributeTemplate = template!(
+        List: &["ordinal"],
+        "https://doc.rust-lang.org/reference/items/external-blocks.html#the-link_ordinal-attribute"
+    );
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         let ordinal = parse_single_integer(cx, args)?;
@@ -120,3 +147,87 @@ impl<S: Stage> SingleAttributeParser<S> for LinkOrdinalParser {
         Some(LinkOrdinal { ordinal, span: cx.attr_span })
     }
 }
+
+pub(crate) struct LinkageParser;
+
+impl<S: Stage> SingleAttributeParser<S> for LinkageParser {
+    const PATH: &[Symbol] = &[sym::linkage];
+
+    const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepOutermost;
+
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Fn),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::Method(MethodKind::Trait { body: false })),
+        Allow(Target::Method(MethodKind::Trait { body: true })),
+        Allow(Target::Method(MethodKind::TraitImpl)),
+        Allow(Target::Static),
+        Allow(Target::ForeignStatic),
+        Allow(Target::ForeignFn),
+    ]);
+
+    const TEMPLATE: AttributeTemplate = template!(NameValueStr: [
+        "available_externally",
+        "common",
+        "extern_weak",
+        "external",
+        "internal",
+        "linkonce",
+        "linkonce_odr",
+        "weak",
+        "weak_odr",
+    ]);
+
+    fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
+        let Some(name_value) = args.name_value() else {
+            cx.expected_name_value(cx.attr_span, Some(sym::linkage));
+            return None;
+        };
+
+        let Some(value) = name_value.value_as_str() else {
+            cx.expected_string_literal(name_value.value_span, Some(name_value.value_as_lit()));
+            return None;
+        };
+
+        // Use the names from src/llvm/docs/LangRef.rst here. Most types are only
+        // applicable to variable declarations and may not really make sense for
+        // Rust code in the first place but allow them anyway and trust that the
+        // user knows what they're doing. Who knows, unanticipated use cases may pop
+        // up in the future.
+        //
+        // ghost, dllimport, dllexport and linkonce_odr_autohide are not supported
+        // and don't have to be, LLVM treats them as no-ops.
+        let linkage = match value {
+            sym::available_externally => Linkage::AvailableExternally,
+            sym::common => Linkage::Common,
+            sym::extern_weak => Linkage::ExternalWeak,
+            sym::external => Linkage::External,
+            sym::internal => Linkage::Internal,
+            sym::linkonce => Linkage::LinkOnceAny,
+            sym::linkonce_odr => Linkage::LinkOnceODR,
+            sym::weak => Linkage::WeakAny,
+            sym::weak_odr => Linkage::WeakODR,
+
+            _ => {
+                cx.expected_specific_argument(
+                    name_value.value_span,
+                    vec![
+                        "available_externally",
+                        "common",
+                        "extern_weak",
+                        "external",
+                        "internal",
+                        "linkonce",
+                        "linkonce_odr",
+                        "weak",
+                        "weak_odr",
+                    ],
+                );
+                return None;
+            }
+        };
+
+        Some(AttributeKind::Linkage(linkage, cx.attr_span))
+    }
+}
diff --git a/compiler/rustc_attr_parsing/src/attributes/lint_helpers.rs b/compiler/rustc_attr_parsing/src/attributes/lint_helpers.rs
index 9530fec07d6..2b586d4003c 100644
--- a/compiler/rustc_attr_parsing/src/attributes/lint_helpers.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/lint_helpers.rs
@@ -1,13 +1,21 @@
 use rustc_hir::attrs::AttributeKind;
+use rustc_hir::{MethodKind, Target};
 use rustc_span::{Span, Symbol, sym};
 
 use crate::attributes::{NoArgsAttributeParser, OnDuplicate};
-use crate::context::Stage;
-
+use crate::context::MaybeWarn::{Allow, Error};
+use crate::context::{AllowedTargets, Stage};
 pub(crate) struct AsPtrParser;
 impl<S: Stage> NoArgsAttributeParser<S> for AsPtrParser {
     const PATH: &[Symbol] = &[sym::rustc_as_ptr];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Fn),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::Method(MethodKind::Trait { body: false })),
+        Allow(Target::Method(MethodKind::Trait { body: true })),
+        Allow(Target::Method(MethodKind::TraitImpl)),
+    ]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::AsPtr;
 }
 
@@ -15,6 +23,11 @@ pub(crate) struct PubTransparentParser;
 impl<S: Stage> NoArgsAttributeParser<S> for PubTransparentParser {
     const PATH: &[Symbol] = &[sym::rustc_pub_transparent];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Struct),
+        Allow(Target::Enum),
+        Allow(Target::Union),
+    ]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::PubTransparent;
 }
 
@@ -22,6 +35,11 @@ pub(crate) struct PassByValueParser;
 impl<S: Stage> NoArgsAttributeParser<S> for PassByValueParser {
     const PATH: &[Symbol] = &[sym::rustc_pass_by_value];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Struct),
+        Allow(Target::Enum),
+        Allow(Target::TyAlias),
+    ]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::PassByValue;
 }
 
@@ -29,5 +47,10 @@ pub(crate) struct AutomaticallyDerivedParser;
 impl<S: Stage> NoArgsAttributeParser<S> for AutomaticallyDerivedParser {
     const PATH: &[Symbol] = &[sym::automatically_derived];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowListWarnRest(&[
+        Allow(Target::Impl { of_trait: true }),
+        Error(Target::Crate),
+        Error(Target::WherePredicate),
+    ]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::AutomaticallyDerived;
 }
diff --git a/compiler/rustc_attr_parsing/src/attributes/loop_match.rs b/compiler/rustc_attr_parsing/src/attributes/loop_match.rs
index 868c113a6d1..242e2f2c1bc 100644
--- a/compiler/rustc_attr_parsing/src/attributes/loop_match.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/loop_match.rs
@@ -1,13 +1,15 @@
+use rustc_hir::Target;
 use rustc_hir::attrs::AttributeKind;
 use rustc_span::{Span, Symbol, sym};
 
 use crate::attributes::{NoArgsAttributeParser, OnDuplicate};
-use crate::context::Stage;
-
+use crate::context::MaybeWarn::Allow;
+use crate::context::{AllowedTargets, Stage};
 pub(crate) struct LoopMatchParser;
 impl<S: Stage> NoArgsAttributeParser<S> for LoopMatchParser {
     const PATH: &[Symbol] = &[sym::loop_match];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Expression)]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::LoopMatch;
 }
 
@@ -15,5 +17,6 @@ pub(crate) struct ConstContinueParser;
 impl<S: Stage> NoArgsAttributeParser<S> for ConstContinueParser {
     const PATH: &[Symbol] = &[sym::const_continue];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Expression)]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::ConstContinue;
 }
diff --git a/compiler/rustc_attr_parsing/src/attributes/macro_attrs.rs b/compiler/rustc_attr_parsing/src/attributes/macro_attrs.rs
index 886f7a889d3..c9b5dd35fa1 100644
--- a/compiler/rustc_attr_parsing/src/attributes/macro_attrs.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/macro_attrs.rs
@@ -1,18 +1,20 @@
 use rustc_errors::DiagArgValue;
 use rustc_feature::{AttributeTemplate, template};
+use rustc_hir::Target;
 use rustc_hir::attrs::{AttributeKind, MacroUseArgs};
 use rustc_span::{Span, Symbol, sym};
 use thin_vec::ThinVec;
 
 use crate::attributes::{AcceptMapping, AttributeParser, NoArgsAttributeParser, OnDuplicate};
-use crate::context::{AcceptContext, FinalizeContext, Stage};
+use crate::context::MaybeWarn::{Allow, Error, Warn};
+use crate::context::{AcceptContext, AllowedTargets, FinalizeContext, Stage};
 use crate::parser::ArgParser;
 use crate::session_diagnostics;
-
 pub(crate) struct MacroEscapeParser;
 impl<S: Stage> NoArgsAttributeParser<S> for MacroEscapeParser {
     const PATH: &[Symbol] = &[sym::macro_escape];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets = MACRO_USE_ALLOWED_TARGETS;
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::MacroEscape;
 }
 
@@ -31,7 +33,16 @@ pub(crate) struct MacroUseParser {
     first_span: Option<Span>,
 }
 
-const MACRO_USE_TEMPLATE: AttributeTemplate = template!(Word, List: "name1, name2, ...");
+const MACRO_USE_TEMPLATE: AttributeTemplate = template!(
+    Word, List: &["name1, name2, ..."],
+    "https://doc.rust-lang.org/reference/macros-by-example.html#the-macro_use-attribute"
+);
+const MACRO_USE_ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowListWarnRest(&[
+    Allow(Target::Mod),
+    Allow(Target::ExternCrate),
+    Allow(Target::Crate),
+    Error(Target::WherePredicate),
+]);
 
 impl<S: Stage> AttributeParser<S> for MacroUseParser {
     const ATTRIBUTES: AcceptMapping<Self, S> = &[(
@@ -108,8 +119,23 @@ impl<S: Stage> AttributeParser<S> for MacroUseParser {
             }
         },
     )];
+    const ALLOWED_TARGETS: AllowedTargets = MACRO_USE_ALLOWED_TARGETS;
 
     fn finalize(self, _cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {
         Some(AttributeKind::MacroUse { span: self.first_span?, arguments: self.state })
     }
 }
+
+pub(crate) struct AllowInternalUnsafeParser;
+
+impl<S: Stage> NoArgsAttributeParser<S> for AllowInternalUnsafeParser {
+    const PATH: &[Symbol] = &[sym::allow_internal_unsafe];
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Ignore;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Fn),
+        Allow(Target::MacroDef),
+        Warn(Target::Field),
+        Warn(Target::Arm),
+    ]);
+    const CREATE: fn(Span) -> AttributeKind = |span| AttributeKind::AllowInternalUnsafe(span);
+}
diff --git a/compiler/rustc_attr_parsing/src/attributes/mod.rs b/compiler/rustc_attr_parsing/src/attributes/mod.rs
index f7946ade6d2..ed5d1d92b8c 100644
--- a/compiler/rustc_attr_parsing/src/attributes/mod.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/mod.rs
@@ -21,7 +21,7 @@ use rustc_hir::attrs::AttributeKind;
 use rustc_span::{Span, Symbol};
 use thin_vec::ThinVec;
 
-use crate::context::{AcceptContext, FinalizeContext, Stage};
+use crate::context::{AcceptContext, AllowedTargets, FinalizeContext, Stage};
 use crate::parser::ArgParser;
 use crate::session_diagnostics::UnusedMultiple;
 
@@ -80,6 +80,8 @@ pub(crate) trait AttributeParser<S: Stage>: Default + 'static {
     /// If an attribute has this symbol, the `accept` function will be called on it.
     const ATTRIBUTES: AcceptMapping<Self, S>;
 
+    const ALLOWED_TARGETS: AllowedTargets;
+
     /// The parser has gotten a chance to accept the attributes on an item,
     /// here it can produce an attribute.
     ///
@@ -116,6 +118,8 @@ pub(crate) trait SingleAttributeParser<S: Stage>: 'static {
     /// and this specified whether to, for example, warn or error on the other one.
     const ON_DUPLICATE: OnDuplicate<S>;
 
+    const ALLOWED_TARGETS: AllowedTargets;
+
     /// The template this attribute parser should implement. Used for diagnostics.
     const TEMPLATE: AttributeTemplate;
 
@@ -163,6 +167,7 @@ impl<T: SingleAttributeParser<S>, S: Stage> AttributeParser<S> for Single<T, S>
             }
         },
     )];
+    const ALLOWED_TARGETS: AllowedTargets = T::ALLOWED_TARGETS;
 
     fn finalize(self, _cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {
         Some(self.1?.0)
@@ -247,6 +252,7 @@ pub(crate) enum AttributeOrder {
 pub(crate) trait NoArgsAttributeParser<S: Stage>: 'static {
     const PATH: &[Symbol];
     const ON_DUPLICATE: OnDuplicate<S>;
+    const ALLOWED_TARGETS: AllowedTargets;
 
     /// Create the [`AttributeKind`] given attribute's [`Span`].
     const CREATE: fn(Span) -> AttributeKind;
@@ -264,6 +270,7 @@ impl<T: NoArgsAttributeParser<S>, S: Stage> SingleAttributeParser<S> for Without
     const PATH: &[Symbol] = T::PATH;
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepOutermost;
     const ON_DUPLICATE: OnDuplicate<S> = T::ON_DUPLICATE;
+    const ALLOWED_TARGETS: AllowedTargets = T::ALLOWED_TARGETS;
     const TEMPLATE: AttributeTemplate = template!(Word);
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
@@ -293,6 +300,8 @@ pub(crate) trait CombineAttributeParser<S: Stage>: 'static {
     ///  where `x` is a vec of these individual reprs.
     const CONVERT: ConvertFn<Self::Item>;
 
+    const ALLOWED_TARGETS: AllowedTargets;
+
     /// The template this attribute parser should implement. Used for diagnostics.
     const TEMPLATE: AttributeTemplate;
 
@@ -324,15 +333,13 @@ impl<T: CombineAttributeParser<S>, S: Stage> Default for Combine<T, S> {
 }
 
 impl<T: CombineAttributeParser<S>, S: Stage> AttributeParser<S> for Combine<T, S> {
-    const ATTRIBUTES: AcceptMapping<Self, S> = &[(
-        T::PATH,
-        <T as CombineAttributeParser<S>>::TEMPLATE,
-        |group: &mut Combine<T, S>, cx, args| {
+    const ATTRIBUTES: AcceptMapping<Self, S> =
+        &[(T::PATH, T::TEMPLATE, |group: &mut Combine<T, S>, cx, args| {
             // Keep track of the span of the first attribute, for diagnostics
             group.first_span.get_or_insert(cx.attr_span);
             group.items.extend(T::extend(cx, args))
-        },
-    )];
+        })];
+    const ALLOWED_TARGETS: AllowedTargets = T::ALLOWED_TARGETS;
 
     fn finalize(self, _cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {
         if let Some(first_span) = self.first_span {
diff --git a/compiler/rustc_attr_parsing/src/attributes/must_use.rs b/compiler/rustc_attr_parsing/src/attributes/must_use.rs
index d767abbc250..b6cfc780590 100644
--- a/compiler/rustc_attr_parsing/src/attributes/must_use.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/must_use.rs
@@ -4,17 +4,20 @@ use rustc_hir::attrs::AttributeKind;
 use rustc_span::{Symbol, sym};
 
 use crate::attributes::{AttributeOrder, OnDuplicate, SingleAttributeParser};
-use crate::context::{AcceptContext, Stage};
+use crate::context::{ALL_TARGETS, AcceptContext, AllowedTargets, Stage};
 use crate::parser::ArgParser;
 use crate::session_diagnostics;
-
 pub(crate) struct MustUseParser;
 
 impl<S: Stage> SingleAttributeParser<S> for MustUseParser {
     const PATH: &[Symbol] = &[sym::must_use];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepOutermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::WarnButFutureError;
-    const TEMPLATE: AttributeTemplate = template!(Word, NameValueStr: "reason");
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(ALL_TARGETS); //FIXME Still checked fully in `check_attr.rs`
+    const TEMPLATE: AttributeTemplate = template!(
+        Word, NameValueStr: "reason",
+        "https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute"
+    );
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         Some(AttributeKind::MustUse {
diff --git a/compiler/rustc_attr_parsing/src/attributes/no_implicit_prelude.rs b/compiler/rustc_attr_parsing/src/attributes/no_implicit_prelude.rs
index 40f8d00685e..589faf38f73 100644
--- a/compiler/rustc_attr_parsing/src/attributes/no_implicit_prelude.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/no_implicit_prelude.rs
@@ -1,13 +1,16 @@
+use rustc_hir::Target;
 use rustc_hir::attrs::AttributeKind;
 use rustc_span::{Span, sym};
 
 use crate::attributes::{NoArgsAttributeParser, OnDuplicate};
-use crate::context::Stage;
-
+use crate::context::MaybeWarn::Allow;
+use crate::context::{AllowedTargets, Stage};
 pub(crate) struct NoImplicitPreludeParser;
 
 impl<S: Stage> NoArgsAttributeParser<S> for NoImplicitPreludeParser {
     const PATH: &[rustc_span::Symbol] = &[sym::no_implicit_prelude];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowListWarnRest(&[Allow(Target::Mod), Allow(Target::Crate)]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::NoImplicitPrelude;
 }
diff --git a/compiler/rustc_attr_parsing/src/attributes/non_exhaustive.rs b/compiler/rustc_attr_parsing/src/attributes/non_exhaustive.rs
index 361ac8e959d..41e9ca4de41 100644
--- a/compiler/rustc_attr_parsing/src/attributes/non_exhaustive.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/non_exhaustive.rs
@@ -1,13 +1,22 @@
+use rustc_hir::Target;
 use rustc_hir::attrs::AttributeKind;
 use rustc_span::{Span, Symbol, sym};
 
 use crate::attributes::{NoArgsAttributeParser, OnDuplicate};
-use crate::context::Stage;
-
+use crate::context::MaybeWarn::{Allow, Warn};
+use crate::context::{AllowedTargets, Stage};
 pub(crate) struct NonExhaustiveParser;
 
 impl<S: Stage> NoArgsAttributeParser<S> for NonExhaustiveParser {
     const PATH: &[Symbol] = &[sym::non_exhaustive];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Enum),
+        Allow(Target::Struct),
+        Allow(Target::Variant),
+        Warn(Target::Field),
+        Warn(Target::Arm),
+        Warn(Target::MacroDef),
+    ]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::NonExhaustive;
 }
diff --git a/compiler/rustc_attr_parsing/src/attributes/path.rs b/compiler/rustc_attr_parsing/src/attributes/path.rs
index 5700d780d71..f9191d1abed 100644
--- a/compiler/rustc_attr_parsing/src/attributes/path.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/path.rs
@@ -1,18 +1,24 @@
 use rustc_feature::{AttributeTemplate, template};
+use rustc_hir::Target;
 use rustc_hir::attrs::AttributeKind;
 use rustc_span::{Symbol, sym};
 
 use crate::attributes::{AttributeOrder, OnDuplicate, SingleAttributeParser};
-use crate::context::{AcceptContext, Stage};
+use crate::context::MaybeWarn::{Allow, Error};
+use crate::context::{AcceptContext, AllowedTargets, Stage};
 use crate::parser::ArgParser;
-
 pub(crate) struct PathParser;
 
 impl<S: Stage> SingleAttributeParser<S> for PathParser {
     const PATH: &[Symbol] = &[sym::path];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepOutermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::WarnButFutureError;
-    const TEMPLATE: AttributeTemplate = template!(NameValueStr: "file");
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowListWarnRest(&[Allow(Target::Mod), Error(Target::Crate)]);
+    const TEMPLATE: AttributeTemplate = template!(
+        NameValueStr: "file",
+        "https://doc.rust-lang.org/reference/items/modules.html#the-path-attribute"
+    );
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         let Some(nv) = args.name_value() else {
diff --git a/compiler/rustc_attr_parsing/src/attributes/proc_macro_attrs.rs b/compiler/rustc_attr_parsing/src/attributes/proc_macro_attrs.rs
index b156a7c5845..4624fa36287 100644
--- a/compiler/rustc_attr_parsing/src/attributes/proc_macro_attrs.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/proc_macro_attrs.rs
@@ -1,4 +1,5 @@
 use rustc_feature::{AttributeTemplate, template};
+use rustc_hir::Target;
 use rustc_hir::attrs::AttributeKind;
 use rustc_span::{Span, Symbol, sym};
 use thin_vec::ThinVec;
@@ -6,13 +7,15 @@ use thin_vec::ThinVec;
 use crate::attributes::{
     AttributeOrder, NoArgsAttributeParser, OnDuplicate, SingleAttributeParser,
 };
-use crate::context::{AcceptContext, Stage};
+use crate::context::MaybeWarn::{Allow, Warn};
+use crate::context::{AcceptContext, AllowedTargets, Stage};
 use crate::parser::ArgParser;
-
 pub(crate) struct ProcMacroParser;
 impl<S: Stage> NoArgsAttributeParser<S> for ProcMacroParser {
     const PATH: &[Symbol] = &[sym::proc_macro];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowList(&[Allow(Target::Fn), Warn(Target::Crate)]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::ProcMacro;
 }
 
@@ -20,6 +23,8 @@ pub(crate) struct ProcMacroAttributeParser;
 impl<S: Stage> NoArgsAttributeParser<S> for ProcMacroAttributeParser {
     const PATH: &[Symbol] = &[sym::proc_macro_attribute];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowList(&[Allow(Target::Fn), Warn(Target::Crate)]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::ProcMacroAttribute;
 }
 
@@ -28,8 +33,12 @@ impl<S: Stage> SingleAttributeParser<S> for ProcMacroDeriveParser {
     const PATH: &[Symbol] = &[sym::proc_macro_derive];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepOutermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
-    const TEMPLATE: AttributeTemplate =
-        template!(List: "TraitName, /*opt*/ attributes(name1, name2, ...)");
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowList(&[Allow(Target::Fn), Warn(Target::Crate)]);
+    const TEMPLATE: AttributeTemplate = template!(
+        List: &["TraitName", "TraitName, attributes(name1, name2, ...)"],
+        "https://doc.rust-lang.org/reference/procedural-macros.html#derive-macros"
+    );
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         let (trait_name, helper_attrs) = parse_derive_like(cx, args, true)?;
@@ -46,8 +55,9 @@ impl<S: Stage> SingleAttributeParser<S> for RustcBuiltinMacroParser {
     const PATH: &[Symbol] = &[sym::rustc_builtin_macro];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepOutermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::MacroDef)]);
     const TEMPLATE: AttributeTemplate =
-        template!(List: "TraitName, /*opt*/ attributes(name1, name2, ...)");
+        template!(List: &["TraitName", "TraitName, attributes(name1, name2, ...)"]);
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         let (builtin_name, helper_attrs) = parse_derive_like(cx, args, false)?;
diff --git a/compiler/rustc_attr_parsing/src/attributes/repr.rs b/compiler/rustc_attr_parsing/src/attributes/repr.rs
index 6087afe6ded..7ab58ed9347 100644
--- a/compiler/rustc_attr_parsing/src/attributes/repr.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/repr.rs
@@ -2,14 +2,15 @@ use rustc_abi::Align;
 use rustc_ast::{IntTy, LitIntType, LitKind, UintTy};
 use rustc_feature::{AttributeTemplate, template};
 use rustc_hir::attrs::{AttributeKind, IntType, ReprAttr};
+use rustc_hir::{MethodKind, Target};
 use rustc_span::{DUMMY_SP, Span, Symbol, sym};
 
 use super::{AcceptMapping, AttributeParser, CombineAttributeParser, ConvertFn, FinalizeContext};
-use crate::context::{AcceptContext, Stage};
+use crate::context::MaybeWarn::Allow;
+use crate::context::{ALL_TARGETS, AcceptContext, AllowedTargets, Stage};
 use crate::parser::{ArgParser, MetaItemListParser, MetaItemParser};
 use crate::session_diagnostics;
 use crate::session_diagnostics::IncorrectReprFormatGenericCause;
-
 /// Parse #[repr(...)] forms.
 ///
 /// Valid repr contents: any of the primitive integral type names (see
@@ -26,8 +27,10 @@ impl<S: Stage> CombineAttributeParser<S> for ReprParser {
     const CONVERT: ConvertFn<Self::Item> =
         |items, first_span| AttributeKind::Repr { reprs: items, first_span };
     // FIXME(jdonszelmann): never used
-    const TEMPLATE: AttributeTemplate =
-        template!(List: "C | Rust | align(...) | packed(...) | <integer type> | transparent");
+    const TEMPLATE: AttributeTemplate = template!(
+        List: &["C", "Rust", "transparent", "align(...)", "packed(...)", "<integer type>"],
+        "https://doc.rust-lang.org/reference/type-layout.html#representations"
+    );
 
     fn extend<'c>(
         cx: &'c mut AcceptContext<'_, '_, S>,
@@ -58,6 +61,10 @@ impl<S: Stage> CombineAttributeParser<S> for ReprParser {
 
         reprs
     }
+
+    //FIXME Still checked fully in `check_attr.rs`
+    //This one is slightly more complicated because the allowed targets depend on the arguments
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(ALL_TARGETS);
 }
 
 macro_rules! int_pat {
@@ -275,7 +282,7 @@ pub(crate) struct AlignParser(Option<(Align, Span)>);
 
 impl AlignParser {
     const PATH: &'static [Symbol] = &[sym::rustc_align];
-    const TEMPLATE: AttributeTemplate = template!(List: "<alignment in bytes>");
+    const TEMPLATE: AttributeTemplate = template!(List: &["<alignment in bytes>"]);
 
     fn parse<'c, S: Stage>(
         &mut self,
@@ -316,6 +323,14 @@ impl AlignParser {
 
 impl<S: Stage> AttributeParser<S> for AlignParser {
     const ATTRIBUTES: AcceptMapping<Self, S> = &[(Self::PATH, Self::TEMPLATE, Self::parse)];
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Fn),
+        Allow(Target::Method(MethodKind::Inherent)),
+        Allow(Target::Method(MethodKind::Trait { body: true })),
+        Allow(Target::Method(MethodKind::TraitImpl)),
+        Allow(Target::Method(MethodKind::Trait { body: false })),
+        Allow(Target::ForeignFn),
+    ]);
 
     fn finalize(self, _cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {
         let (align, span) = self.0?;
diff --git a/compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs b/compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs
index b465d2e62ff..efd7b650e44 100644
--- a/compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs
@@ -1,18 +1,20 @@
 use rustc_feature::{AttributeTemplate, template};
+use rustc_hir::Target;
 use rustc_hir::attrs::AttributeKind;
 use rustc_span::{Symbol, sym};
 
 use crate::attributes::{AttributeOrder, OnDuplicate, SingleAttributeParser};
-use crate::context::{AcceptContext, Stage, parse_single_integer};
+use crate::context::MaybeWarn::Allow;
+use crate::context::{AcceptContext, AllowedTargets, Stage, parse_single_integer};
 use crate::parser::ArgParser;
-
 pub(crate) struct RustcLayoutScalarValidRangeStart;
 
 impl<S: Stage> SingleAttributeParser<S> for RustcLayoutScalarValidRangeStart {
     const PATH: &'static [Symbol] = &[sym::rustc_layout_scalar_valid_range_start];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepInnermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
-    const TEMPLATE: AttributeTemplate = template!(List: "start");
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Struct)]);
+    const TEMPLATE: AttributeTemplate = template!(List: &["start"]);
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         parse_single_integer(cx, args)
@@ -26,7 +28,8 @@ impl<S: Stage> SingleAttributeParser<S> for RustcLayoutScalarValidRangeEnd {
     const PATH: &'static [Symbol] = &[sym::rustc_layout_scalar_valid_range_end];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepInnermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
-    const TEMPLATE: AttributeTemplate = template!(List: "end");
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Struct)]);
+    const TEMPLATE: AttributeTemplate = template!(List: &["end"]);
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         parse_single_integer(cx, args)
@@ -40,6 +43,7 @@ impl<S: Stage> SingleAttributeParser<S> for RustcObjectLifetimeDefaultParser {
     const PATH: &[rustc_span::Symbol] = &[sym::rustc_object_lifetime_default];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepInnermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Struct)]);
     const TEMPLATE: AttributeTemplate = template!(Word);
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
diff --git a/compiler/rustc_attr_parsing/src/attributes/semantics.rs b/compiler/rustc_attr_parsing/src/attributes/semantics.rs
index 70a8a002099..d4ad861a3a2 100644
--- a/compiler/rustc_attr_parsing/src/attributes/semantics.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/semantics.rs
@@ -2,11 +2,11 @@ use rustc_hir::attrs::AttributeKind;
 use rustc_span::{Span, Symbol, sym};
 
 use crate::attributes::{NoArgsAttributeParser, OnDuplicate};
-use crate::context::Stage;
-
+use crate::context::{ALL_TARGETS, AllowedTargets, Stage};
 pub(crate) struct MayDangleParser;
 impl<S: Stage> NoArgsAttributeParser<S> for MayDangleParser {
     const PATH: &[Symbol] = &[sym::may_dangle];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(ALL_TARGETS); //FIXME Still checked fully in `check_attr.rs`
     const CREATE: fn(span: Span) -> AttributeKind = AttributeKind::MayDangle;
 }
diff --git a/compiler/rustc_attr_parsing/src/attributes/stability.rs b/compiler/rustc_attr_parsing/src/attributes/stability.rs
index 3c4ec133d51..5a26178f84b 100644
--- a/compiler/rustc_attr_parsing/src/attributes/stability.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/stability.rs
@@ -4,15 +4,16 @@ use rustc_errors::ErrorGuaranteed;
 use rustc_feature::template;
 use rustc_hir::attrs::AttributeKind;
 use rustc_hir::{
-    DefaultBodyStability, PartialConstStability, Stability, StabilityLevel, StableSince,
-    UnstableReason, VERSION_PLACEHOLDER,
+    DefaultBodyStability, MethodKind, PartialConstStability, Stability, StabilityLevel,
+    StableSince, Target, UnstableReason, VERSION_PLACEHOLDER,
 };
 use rustc_span::{Ident, Span, Symbol, sym};
 
 use super::util::parse_version;
 use super::{AcceptMapping, AttributeParser, OnDuplicate};
 use crate::attributes::NoArgsAttributeParser;
-use crate::context::{AcceptContext, FinalizeContext, Stage};
+use crate::context::MaybeWarn::Allow;
+use crate::context::{AcceptContext, AllowedTargets, FinalizeContext, Stage};
 use crate::parser::{ArgParser, MetaItemParser};
 use crate::session_diagnostics::{self, UnsupportedLiteralReason};
 
@@ -26,6 +27,35 @@ macro_rules! reject_outside_std {
     };
 }
 
+const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+    Allow(Target::Fn),
+    Allow(Target::Struct),
+    Allow(Target::Enum),
+    Allow(Target::Union),
+    Allow(Target::Method(MethodKind::Inherent)),
+    Allow(Target::Method(MethodKind::Trait { body: false })),
+    Allow(Target::Method(MethodKind::Trait { body: true })),
+    Allow(Target::Method(MethodKind::TraitImpl)),
+    Allow(Target::Impl { of_trait: false }),
+    Allow(Target::Impl { of_trait: true }),
+    Allow(Target::MacroDef),
+    Allow(Target::Crate),
+    Allow(Target::Mod),
+    Allow(Target::Use), // FIXME I don't think this does anything?
+    Allow(Target::Const),
+    Allow(Target::AssocConst),
+    Allow(Target::AssocTy),
+    Allow(Target::Trait),
+    Allow(Target::TraitAlias),
+    Allow(Target::TyAlias),
+    Allow(Target::Variant),
+    Allow(Target::Field),
+    Allow(Target::Param),
+    Allow(Target::Static),
+    Allow(Target::ForeignFn),
+    Allow(Target::ForeignStatic),
+]);
+
 #[derive(Default)]
 pub(crate) struct StabilityParser {
     allowed_through_unstable_modules: Option<Symbol>,
@@ -48,7 +78,7 @@ impl<S: Stage> AttributeParser<S> for StabilityParser {
     const ATTRIBUTES: AcceptMapping<Self, S> = &[
         (
             &[sym::stable],
-            template!(List: r#"feature = "name", since = "version""#),
+            template!(List: &[r#"feature = "name", since = "version""#]),
             |this, cx, args| {
                 reject_outside_std!(cx);
                 if !this.check_duplicate(cx)
@@ -60,7 +90,7 @@ impl<S: Stage> AttributeParser<S> for StabilityParser {
         ),
         (
             &[sym::unstable],
-            template!(List: r#"feature = "name", reason = "...", issue = "N""#),
+            template!(List: &[r#"feature = "name", reason = "...", issue = "N""#]),
             |this, cx, args| {
                 reject_outside_std!(cx);
                 if !this.check_duplicate(cx)
@@ -87,6 +117,7 @@ impl<S: Stage> AttributeParser<S> for StabilityParser {
             },
         ),
     ];
+    const ALLOWED_TARGETS: AllowedTargets = ALLOWED_TARGETS;
 
     fn finalize(mut self, cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {
         if let Some(atum) = self.allowed_through_unstable_modules {
@@ -131,7 +162,7 @@ pub(crate) struct BodyStabilityParser {
 impl<S: Stage> AttributeParser<S> for BodyStabilityParser {
     const ATTRIBUTES: AcceptMapping<Self, S> = &[(
         &[sym::rustc_default_body_unstable],
-        template!(List: r#"feature = "name", reason = "...", issue = "N""#),
+        template!(List: &[r#"feature = "name", reason = "...", issue = "N""#]),
         |this, cx, args| {
             reject_outside_std!(cx);
             if this.stability.is_some() {
@@ -142,6 +173,7 @@ impl<S: Stage> AttributeParser<S> for BodyStabilityParser {
             }
         },
     )];
+    const ALLOWED_TARGETS: AllowedTargets = ALLOWED_TARGETS;
 
     fn finalize(self, _cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {
         let (stability, span) = self.stability?;
@@ -154,6 +186,10 @@ pub(crate) struct ConstStabilityIndirectParser;
 impl<S: Stage> NoArgsAttributeParser<S> for ConstStabilityIndirectParser {
     const PATH: &[Symbol] = &[sym::rustc_const_stable_indirect];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Ignore;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Fn),
+        Allow(Target::Method(MethodKind::Inherent)),
+    ]);
     const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::ConstStabilityIndirect;
 }
 
@@ -177,34 +213,43 @@ impl ConstStabilityParser {
 
 impl<S: Stage> AttributeParser<S> for ConstStabilityParser {
     const ATTRIBUTES: AcceptMapping<Self, S> = &[
-        (&[sym::rustc_const_stable], template!(List: r#"feature = "name""#), |this, cx, args| {
-            reject_outside_std!(cx);
+        (
+            &[sym::rustc_const_stable],
+            template!(List: &[r#"feature = "name""#]),
+            |this, cx, args| {
+                reject_outside_std!(cx);
 
-            if !this.check_duplicate(cx)
-                && let Some((feature, level)) = parse_stability(cx, args)
-            {
-                this.stability = Some((
-                    PartialConstStability { level, feature, promotable: false },
-                    cx.attr_span,
-                ));
-            }
-        }),
-        (&[sym::rustc_const_unstable], template!(List: r#"feature = "name""#), |this, cx, args| {
-            reject_outside_std!(cx);
-            if !this.check_duplicate(cx)
-                && let Some((feature, level)) = parse_unstability(cx, args)
-            {
-                this.stability = Some((
-                    PartialConstStability { level, feature, promotable: false },
-                    cx.attr_span,
-                ));
-            }
-        }),
+                if !this.check_duplicate(cx)
+                    && let Some((feature, level)) = parse_stability(cx, args)
+                {
+                    this.stability = Some((
+                        PartialConstStability { level, feature, promotable: false },
+                        cx.attr_span,
+                    ));
+                }
+            },
+        ),
+        (
+            &[sym::rustc_const_unstable],
+            template!(List: &[r#"feature = "name""#]),
+            |this, cx, args| {
+                reject_outside_std!(cx);
+                if !this.check_duplicate(cx)
+                    && let Some((feature, level)) = parse_unstability(cx, args)
+                {
+                    this.stability = Some((
+                        PartialConstStability { level, feature, promotable: false },
+                        cx.attr_span,
+                    ));
+                }
+            },
+        ),
         (&[sym::rustc_promotable], template!(Word), |this, cx, _| {
             reject_outside_std!(cx);
             this.promotable = true;
         }),
     ];
+    const ALLOWED_TARGETS: AllowedTargets = ALLOWED_TARGETS;
 
     fn finalize(mut self, cx: &FinalizeContext<'_, '_, S>) -> Option<AttributeKind> {
         if self.promotable {
diff --git a/compiler/rustc_attr_parsing/src/attributes/test_attrs.rs b/compiler/rustc_attr_parsing/src/attributes/test_attrs.rs
index a90ed830cd1..8b666c3868b 100644
--- a/compiler/rustc_attr_parsing/src/attributes/test_attrs.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/test_attrs.rs
@@ -1,19 +1,25 @@
 use rustc_feature::{AttributeTemplate, template};
+use rustc_hir::Target;
 use rustc_hir::attrs::AttributeKind;
 use rustc_hir::lints::AttributeLintKind;
 use rustc_span::{Symbol, sym};
 
 use crate::attributes::{AttributeOrder, OnDuplicate, SingleAttributeParser};
-use crate::context::{AcceptContext, Stage};
+use crate::context::MaybeWarn::{Allow, Error};
+use crate::context::{AcceptContext, AllowedTargets, Stage};
 use crate::parser::ArgParser;
-
 pub(crate) struct IgnoreParser;
 
 impl<S: Stage> SingleAttributeParser<S> for IgnoreParser {
     const PATH: &[Symbol] = &[sym::ignore];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepOutermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
-    const TEMPLATE: AttributeTemplate = template!(Word, NameValueStr: "reason");
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowListWarnRest(&[Allow(Target::Fn), Error(Target::WherePredicate)]);
+    const TEMPLATE: AttributeTemplate = template!(
+        Word, NameValueStr: "reason",
+        "https://doc.rust-lang.org/reference/attributes/testing.html#the-ignore-attribute"
+    );
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         Some(AttributeKind::Ignore {
@@ -44,3 +50,59 @@ impl<S: Stage> SingleAttributeParser<S> for IgnoreParser {
         })
     }
 }
+
+pub(crate) struct ShouldPanicParser;
+
+impl<S: Stage> SingleAttributeParser<S> for ShouldPanicParser {
+    const PATH: &[Symbol] = &[sym::should_panic];
+    const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepOutermost;
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::WarnButFutureError;
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowListWarnRest(&[Allow(Target::Fn), Error(Target::WherePredicate)]);
+    const TEMPLATE: AttributeTemplate = template!(
+        Word, List: &[r#"expected = "reason""#], NameValueStr: "reason",
+        "https://doc.rust-lang.org/reference/attributes/testing.html#the-should_panic-attribute"
+    );
+
+    fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
+        Some(AttributeKind::ShouldPanic {
+            span: cx.attr_span,
+            reason: match args {
+                ArgParser::NoArgs => None,
+                ArgParser::NameValue(name_value) => {
+                    let Some(str_value) = name_value.value_as_str() else {
+                        cx.expected_string_literal(
+                            name_value.value_span,
+                            Some(name_value.value_as_lit()),
+                        );
+                        return None;
+                    };
+                    Some(str_value)
+                }
+                ArgParser::List(list) => {
+                    let Some(single) = list.single() else {
+                        cx.expected_single_argument(list.span);
+                        return None;
+                    };
+                    let Some(single) = single.meta_item() else {
+                        cx.expected_name_value(single.span(), Some(sym::expected));
+                        return None;
+                    };
+                    if !single.path().word_is(sym::expected) {
+                        cx.expected_specific_argument_strings(list.span, vec!["expected"]);
+                        return None;
+                    }
+                    let Some(nv) = single.args().name_value() else {
+                        cx.expected_name_value(single.span(), Some(sym::expected));
+                        return None;
+                    };
+                    let Some(expected) = nv.value_as_str() else {
+                        cx.expected_string_literal(nv.value_span, Some(nv.value_as_lit()));
+                        return None;
+                    };
+                    Some(expected)
+                }
+            },
+        })
+    }
+}
diff --git a/compiler/rustc_attr_parsing/src/attributes/traits.rs b/compiler/rustc_attr_parsing/src/attributes/traits.rs
index a954617ca57..ee9d7ba99cd 100644
--- a/compiler/rustc_attr_parsing/src/attributes/traits.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/traits.rs
@@ -2,21 +2,23 @@ use core::mem;
 
 use rustc_feature::{AttributeTemplate, template};
 use rustc_hir::attrs::AttributeKind;
+use rustc_hir::{MethodKind, Target};
 use rustc_span::{Span, Symbol, sym};
 
 use crate::attributes::{
     AttributeOrder, NoArgsAttributeParser, OnDuplicate, SingleAttributeParser,
 };
-use crate::context::{AcceptContext, Stage};
+use crate::context::MaybeWarn::{Allow, Warn};
+use crate::context::{ALL_TARGETS, AcceptContext, AllowedTargets, Stage};
 use crate::parser::ArgParser;
-
 pub(crate) struct SkipDuringMethodDispatchParser;
 impl<S: Stage> SingleAttributeParser<S> for SkipDuringMethodDispatchParser {
     const PATH: &[Symbol] = &[sym::rustc_skip_during_method_dispatch];
     const ATTRIBUTE_ORDER: AttributeOrder = AttributeOrder::KeepInnermost;
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Trait)]);
 
-    const TEMPLATE: AttributeTemplate = template!(List: "array, boxed_slice");
+    const TEMPLATE: AttributeTemplate = template!(List: &["array, boxed_slice"]);
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         let mut array = false;
@@ -58,6 +60,7 @@ pub(crate) struct ParenSugarParser;
 impl<S: Stage> NoArgsAttributeParser<S> for ParenSugarParser {
     const PATH: &[Symbol] = &[sym::rustc_paren_sugar];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Trait)]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::ParenSugar;
 }
 
@@ -65,6 +68,7 @@ pub(crate) struct TypeConstParser;
 impl<S: Stage> NoArgsAttributeParser<S> for TypeConstParser {
     const PATH: &[Symbol] = &[sym::type_const];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::AssocConst)]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::TypeConst;
 }
 
@@ -74,6 +78,12 @@ pub(crate) struct MarkerParser;
 impl<S: Stage> NoArgsAttributeParser<S> for MarkerParser {
     const PATH: &[Symbol] = &[sym::marker];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[
+        Allow(Target::Trait),
+        Warn(Target::Field),
+        Warn(Target::Arm),
+        Warn(Target::MacroDef),
+    ]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::Marker;
 }
 
@@ -81,6 +91,7 @@ pub(crate) struct DenyExplicitImplParser;
 impl<S: Stage> NoArgsAttributeParser<S> for DenyExplicitImplParser {
     const PATH: &[Symbol] = &[sym::rustc_deny_explicit_impl];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Trait)]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::DenyExplicitImpl;
 }
 
@@ -88,6 +99,7 @@ pub(crate) struct DoNotImplementViaObjectParser;
 impl<S: Stage> NoArgsAttributeParser<S> for DoNotImplementViaObjectParser {
     const PATH: &[Symbol] = &[sym::rustc_do_not_implement_via_object];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Trait)]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::DoNotImplementViaObject;
 }
 
@@ -98,6 +110,7 @@ pub(crate) struct ConstTraitParser;
 impl<S: Stage> NoArgsAttributeParser<S> for ConstTraitParser {
     const PATH: &[Symbol] = &[sym::const_trait];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Trait)]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::ConstTrait;
 }
 
@@ -107,6 +120,7 @@ pub(crate) struct SpecializationTraitParser;
 impl<S: Stage> NoArgsAttributeParser<S> for SpecializationTraitParser {
     const PATH: &[Symbol] = &[sym::rustc_specialization_trait];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Trait)]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::SpecializationTrait;
 }
 
@@ -114,6 +128,7 @@ pub(crate) struct UnsafeSpecializationMarkerParser;
 impl<S: Stage> NoArgsAttributeParser<S> for UnsafeSpecializationMarkerParser {
     const PATH: &[Symbol] = &[sym::rustc_unsafe_specialization_marker];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Trait)]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::UnsafeSpecializationMarker;
 }
 
@@ -123,6 +138,7 @@ pub(crate) struct CoinductiveParser;
 impl<S: Stage> NoArgsAttributeParser<S> for CoinductiveParser {
     const PATH: &[Symbol] = &[sym::rustc_coinductive];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Trait)]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::Coinductive;
 }
 
@@ -130,6 +146,8 @@ pub(crate) struct AllowIncoherentImplParser;
 impl<S: Stage> NoArgsAttributeParser<S> for AllowIncoherentImplParser {
     const PATH: &[Symbol] = &[sym::rustc_allow_incoherent_impl];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowList(&[Allow(Target::Method(MethodKind::Inherent))]);
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::AllowIncoherentImpl;
 }
 
@@ -137,6 +155,7 @@ pub(crate) struct CoherenceIsCoreParser;
 impl<S: Stage> NoArgsAttributeParser<S> for CoherenceIsCoreParser {
     const PATH: &[Symbol] = &[sym::rustc_coherence_is_core];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Crate)]);
     const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::CoherenceIsCore;
 }
 
@@ -144,6 +163,8 @@ pub(crate) struct FundamentalParser;
 impl<S: Stage> NoArgsAttributeParser<S> for FundamentalParser {
     const PATH: &[Symbol] = &[sym::fundamental];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets =
+        AllowedTargets::AllowList(&[Allow(Target::Struct), Allow(Target::Trait)]);
     const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::Fundamental;
 }
 
@@ -151,5 +172,6 @@ pub(crate) struct PointeeParser;
 impl<S: Stage> NoArgsAttributeParser<S> for PointeeParser {
     const PATH: &[Symbol] = &[sym::pointee];
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(ALL_TARGETS); //FIXME Still checked fully in `check_attr.rs`
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::Pointee;
 }
diff --git a/compiler/rustc_attr_parsing/src/attributes/transparency.rs b/compiler/rustc_attr_parsing/src/attributes/transparency.rs
index 1c57dc1ebe2..0ffcf434b52 100644
--- a/compiler/rustc_attr_parsing/src/attributes/transparency.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/transparency.rs
@@ -1,12 +1,13 @@
 use rustc_feature::{AttributeTemplate, template};
+use rustc_hir::Target;
 use rustc_hir::attrs::AttributeKind;
 use rustc_span::hygiene::Transparency;
 use rustc_span::{Symbol, sym};
 
 use super::{AttributeOrder, OnDuplicate, SingleAttributeParser};
-use crate::context::{AcceptContext, Stage};
+use crate::context::MaybeWarn::Allow;
+use crate::context::{AcceptContext, AllowedTargets, Stage};
 use crate::parser::ArgParser;
-
 pub(crate) struct TransparencyParser;
 
 // FIXME(jdonszelmann): make these proper diagnostics
@@ -18,8 +19,9 @@ impl<S: Stage> SingleAttributeParser<S> for TransparencyParser {
     const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Custom(|cx, used, unused| {
         cx.dcx().span_err(vec![used, unused], "multiple macro transparency attributes");
     });
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::MacroDef)]);
     const TEMPLATE: AttributeTemplate =
-        template!(NameValueStr: "transparent|semitransparent|opaque");
+        template!(NameValueStr: ["transparent", "semitransparent", "opaque"]);
 
     fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
         let Some(nv) = args.name_value() else {
diff --git a/compiler/rustc_attr_parsing/src/context.rs b/compiler/rustc_attr_parsing/src/context.rs
index 911d2e13310..bebe3350c4e 100644
--- a/compiler/rustc_attr_parsing/src/context.rs
+++ b/compiler/rustc_attr_parsing/src/context.rs
@@ -3,13 +3,16 @@ use std::collections::BTreeMap;
 use std::ops::{Deref, DerefMut};
 use std::sync::LazyLock;
 
+use itertools::Itertools;
 use private::Sealed;
 use rustc_ast::{self as ast, LitKind, MetaItemLit, NodeId};
 use rustc_errors::{DiagCtxtHandle, Diagnostic};
 use rustc_feature::{AttributeTemplate, Features};
 use rustc_hir::attrs::AttributeKind;
 use rustc_hir::lints::{AttributeLint, AttributeLintKind};
-use rustc_hir::{AttrArgs, AttrItem, AttrPath, Attribute, HashIgnoredAttrId, HirId};
+use rustc_hir::{
+    AttrArgs, AttrItem, AttrPath, Attribute, HashIgnoredAttrId, HirId, MethodKind, Target,
+};
 use rustc_session::Session;
 use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span, Symbol, sym};
 
@@ -27,13 +30,15 @@ use crate::attributes::dummy::DummyParser;
 use crate::attributes::inline::{InlineParser, RustcForceInlineParser};
 use crate::attributes::link_attrs::{
     ExportStableParser, FfiConstParser, FfiPureParser, LinkNameParser, LinkOrdinalParser,
-    LinkSectionParser, StdInternalSymbolParser,
+    LinkSectionParser, LinkageParser, StdInternalSymbolParser,
 };
 use crate::attributes::lint_helpers::{
     AsPtrParser, AutomaticallyDerivedParser, PassByValueParser, PubTransparentParser,
 };
 use crate::attributes::loop_match::{ConstContinueParser, LoopMatchParser};
-use crate::attributes::macro_attrs::{MacroEscapeParser, MacroUseParser};
+use crate::attributes::macro_attrs::{
+    AllowInternalUnsafeParser, MacroEscapeParser, MacroUseParser,
+};
 use crate::attributes::must_use::MustUseParser;
 use crate::attributes::no_implicit_prelude::NoImplicitPreludeParser;
 use crate::attributes::non_exhaustive::NonExhaustiveParser;
@@ -50,7 +55,7 @@ use crate::attributes::semantics::MayDangleParser;
 use crate::attributes::stability::{
     BodyStabilityParser, ConstStabilityIndirectParser, ConstStabilityParser, StabilityParser,
 };
-use crate::attributes::test_attrs::IgnoreParser;
+use crate::attributes::test_attrs::{IgnoreParser, ShouldPanicParser};
 use crate::attributes::traits::{
     AllowIncoherentImplParser, CoherenceIsCoreParser, CoinductiveParser, ConstTraitParser,
     DenyExplicitImplParser, DoNotImplementViaObjectParser, FundamentalParser, MarkerParser,
@@ -59,8 +64,11 @@ use crate::attributes::traits::{
 };
 use crate::attributes::transparency::TransparencyParser;
 use crate::attributes::{AttributeParser as _, Combine, Single, WithoutArgs};
+use crate::context::MaybeWarn::{Allow, Error, Warn};
 use crate::parser::{ArgParser, MetaItemParser, PathParser};
-use crate::session_diagnostics::{AttributeParseError, AttributeParseErrorReason, UnknownMetaItem};
+use crate::session_diagnostics::{
+    AttributeParseError, AttributeParseErrorReason, InvalidTarget, UnknownMetaItem,
+};
 
 type GroupType<S> = LazyLock<GroupTypeInner<S>>;
 
@@ -72,6 +80,7 @@ struct GroupTypeInner<S: Stage> {
 struct GroupTypeInnerAccept<S: Stage> {
     template: AttributeTemplate,
     accept_fn: AcceptFn<S>,
+    allowed_targets: AllowedTargets,
 }
 
 type AcceptFn<S> =
@@ -119,7 +128,8 @@ macro_rules! attribute_parsers {
                                 STATE_OBJECT.with_borrow_mut(|s| {
                                     accept_fn(s, cx, args)
                                 })
-                            })
+                            }),
+                            allowed_targets: <$names as crate::attributes::AttributeParser<$stage>>::ALLOWED_TARGETS,
                         });
                     }
 
@@ -165,6 +175,7 @@ attribute_parsers!(
         Single<LinkNameParser>,
         Single<LinkOrdinalParser>,
         Single<LinkSectionParser>,
+        Single<LinkageParser>,
         Single<MustUseParser>,
         Single<OptimizeParser>,
         Single<PathAttributeParser>,
@@ -174,9 +185,11 @@ attribute_parsers!(
         Single<RustcLayoutScalarValidRangeEnd>,
         Single<RustcLayoutScalarValidRangeStart>,
         Single<RustcObjectLifetimeDefaultParser>,
+        Single<ShouldPanicParser>,
         Single<SkipDuringMethodDispatchParser>,
         Single<TransparencyParser>,
         Single<WithoutArgs<AllowIncoherentImplParser>>,
+        Single<WithoutArgs<AllowInternalUnsafeParser>>,
         Single<WithoutArgs<AsPtrParser>>,
         Single<WithoutArgs<AutomaticallyDerivedParser>>,
         Single<WithoutArgs<CoherenceIsCoreParser>>,
@@ -638,6 +651,64 @@ impl ShouldEmit {
     }
 }
 
+#[derive(Debug)]
+pub(crate) enum AllowedTargets {
+    AllowList(&'static [MaybeWarn]),
+    AllowListWarnRest(&'static [MaybeWarn]),
+}
+
+pub(crate) enum AllowedResult {
+    Allowed,
+    Warn,
+    Error,
+}
+
+impl AllowedTargets {
+    pub(crate) fn is_allowed(&self, target: Target) -> AllowedResult {
+        match self {
+            AllowedTargets::AllowList(list) => {
+                if list.contains(&Allow(target)) {
+                    AllowedResult::Allowed
+                } else if list.contains(&Warn(target)) {
+                    AllowedResult::Warn
+                } else {
+                    AllowedResult::Error
+                }
+            }
+            AllowedTargets::AllowListWarnRest(list) => {
+                if list.contains(&Allow(target)) {
+                    AllowedResult::Allowed
+                } else if list.contains(&Error(target)) {
+                    AllowedResult::Error
+                } else {
+                    AllowedResult::Warn
+                }
+            }
+        }
+    }
+
+    pub(crate) fn allowed_targets(&self) -> Vec<Target> {
+        match self {
+            AllowedTargets::AllowList(list) => list,
+            AllowedTargets::AllowListWarnRest(list) => list,
+        }
+        .iter()
+        .filter_map(|target| match target {
+            Allow(target) => Some(*target),
+            Warn(_) => None,
+            Error(_) => None,
+        })
+        .collect()
+    }
+}
+
+#[derive(Debug, Eq, PartialEq)]
+pub(crate) enum MaybeWarn {
+    Allow(Target),
+    Warn(Target),
+    Error(Target),
+}
+
 /// Context created once, for example as part of the ast lowering
 /// context, through which all attributes can be lowered.
 pub struct AttributeParser<'sess, S: Stage = Late> {
@@ -686,6 +757,7 @@ impl<'sess> AttributeParser<'sess, Early> {
             attrs,
             target_span,
             target_node_id,
+            Target::Crate, // Does not matter, we're not going to emit errors anyways
             OmitDoc::Skip,
             std::convert::identity,
             |_lint| {
@@ -772,6 +844,7 @@ impl<'sess, S: Stage> AttributeParser<'sess, S> {
         attrs: &[ast::Attribute],
         target_span: Span,
         target_id: S::Id,
+        target: Target,
         omit_doc: OmitDoc,
 
         lower_span: impl Copy + Fn(Span) -> Span,
@@ -843,7 +916,48 @@ impl<'sess, S: Stage> AttributeParser<'sess, S> {
                                 attr_path: path.get_attribute_path(),
                             };
 
-                            (accept.accept_fn)(&mut cx, args)
+                            (accept.accept_fn)(&mut cx, args);
+
+                            if self.stage.should_emit().should_emit() {
+                                match accept.allowed_targets.is_allowed(target) {
+                                    AllowedResult::Allowed => {}
+                                    AllowedResult::Warn => {
+                                        let allowed_targets =
+                                            accept.allowed_targets.allowed_targets();
+                                        let (applied, only) = allowed_targets_applied(
+                                            allowed_targets,
+                                            target,
+                                            self.features,
+                                        );
+                                        emit_lint(AttributeLint {
+                                            id: target_id,
+                                            span: attr.span,
+                                            kind: AttributeLintKind::InvalidTarget {
+                                                name: parts[0],
+                                                target,
+                                                only: if only { "only " } else { "" },
+                                                applied,
+                                            },
+                                        });
+                                    }
+                                    AllowedResult::Error => {
+                                        let allowed_targets =
+                                            accept.allowed_targets.allowed_targets();
+                                        let (applied, only) = allowed_targets_applied(
+                                            allowed_targets,
+                                            target,
+                                            self.features,
+                                        );
+                                        self.dcx().emit_err(InvalidTarget {
+                                            span: attr.span,
+                                            name: parts[0],
+                                            target: target.plural_name(),
+                                            only: if only { "only " } else { "" },
+                                            applied,
+                                        });
+                                    }
+                                }
+                            }
                         }
                     } else {
                         // If we're here, we must be compiling a tool attribute... Or someone
@@ -931,6 +1045,132 @@ impl<'sess, S: Stage> AttributeParser<'sess, S> {
     }
 }
 
+/// Takes a list of `allowed_targets` for an attribute, and the `target` the attribute was applied to.
+/// Does some heuristic-based filtering to remove uninteresting targets, and formats the targets into a string
+pub(crate) fn allowed_targets_applied(
+    mut allowed_targets: Vec<Target>,
+    target: Target,
+    features: Option<&Features>,
+) -> (String, bool) {
+    // Remove unstable targets from `allowed_targets` if their features are not enabled
+    if let Some(features) = features {
+        if !features.fn_delegation() {
+            allowed_targets.retain(|t| !matches!(t, Target::Delegation { .. }));
+        }
+        if !features.stmt_expr_attributes() {
+            allowed_targets.retain(|t| !matches!(t, Target::Expression | Target::Statement));
+        }
+    }
+
+    // We define groups of "similar" targets.
+    // If at least two of the targets are allowed, and the `target` is not in the group,
+    // we collapse the entire group to a single entry to simplify the target list
+    const FUNCTION_LIKE: &[Target] = &[
+        Target::Fn,
+        Target::Closure,
+        Target::ForeignFn,
+        Target::Method(MethodKind::Inherent),
+        Target::Method(MethodKind::Trait { body: false }),
+        Target::Method(MethodKind::Trait { body: true }),
+        Target::Method(MethodKind::TraitImpl),
+    ];
+    const METHOD_LIKE: &[Target] = &[
+        Target::Method(MethodKind::Inherent),
+        Target::Method(MethodKind::Trait { body: false }),
+        Target::Method(MethodKind::Trait { body: true }),
+        Target::Method(MethodKind::TraitImpl),
+    ];
+    const IMPL_LIKE: &[Target] =
+        &[Target::Impl { of_trait: false }, Target::Impl { of_trait: true }];
+    const ADT_LIKE: &[Target] = &[Target::Struct, Target::Enum];
+
+    let mut added_fake_targets = Vec::new();
+    filter_targets(
+        &mut allowed_targets,
+        FUNCTION_LIKE,
+        "functions",
+        target,
+        &mut added_fake_targets,
+    );
+    filter_targets(&mut allowed_targets, METHOD_LIKE, "methods", target, &mut added_fake_targets);
+    filter_targets(&mut allowed_targets, IMPL_LIKE, "impl blocks", target, &mut added_fake_targets);
+    filter_targets(&mut allowed_targets, ADT_LIKE, "data types", target, &mut added_fake_targets);
+
+    // If there is now only 1 target left, show that as the only possible target
+    (
+        added_fake_targets
+            .iter()
+            .copied()
+            .chain(allowed_targets.iter().map(|t| t.plural_name()))
+            .join(", "),
+        allowed_targets.len() + added_fake_targets.len() == 1,
+    )
+}
+
+fn filter_targets(
+    allowed_targets: &mut Vec<Target>,
+    target_group: &'static [Target],
+    target_group_name: &'static str,
+    target: Target,
+    added_fake_targets: &mut Vec<&'static str>,
+) {
+    if target_group.contains(&target) {
+        return;
+    }
+    if allowed_targets.iter().filter(|at| target_group.contains(at)).count() < 2 {
+        return;
+    }
+    allowed_targets.retain(|t| !target_group.contains(t));
+    added_fake_targets.push(target_group_name);
+}
+
+/// This is the list of all targets to which a attribute can be applied
+/// This is used for:
+/// - `rustc_dummy`, which can be applied to all targets
+/// - Attributes that are not parted to the new target system yet can use this list as a placeholder
+pub(crate) const ALL_TARGETS: &'static [MaybeWarn] = &[
+    Allow(Target::ExternCrate),
+    Allow(Target::Use),
+    Allow(Target::Static),
+    Allow(Target::Const),
+    Allow(Target::Fn),
+    Allow(Target::Closure),
+    Allow(Target::Mod),
+    Allow(Target::ForeignMod),
+    Allow(Target::GlobalAsm),
+    Allow(Target::TyAlias),
+    Allow(Target::Enum),
+    Allow(Target::Variant),
+    Allow(Target::Struct),
+    Allow(Target::Field),
+    Allow(Target::Union),
+    Allow(Target::Trait),
+    Allow(Target::TraitAlias),
+    Allow(Target::Impl { of_trait: false }),
+    Allow(Target::Impl { of_trait: true }),
+    Allow(Target::Expression),
+    Allow(Target::Statement),
+    Allow(Target::Arm),
+    Allow(Target::AssocConst),
+    Allow(Target::Method(MethodKind::Inherent)),
+    Allow(Target::Method(MethodKind::Trait { body: false })),
+    Allow(Target::Method(MethodKind::Trait { body: true })),
+    Allow(Target::Method(MethodKind::TraitImpl)),
+    Allow(Target::AssocTy),
+    Allow(Target::ForeignFn),
+    Allow(Target::ForeignStatic),
+    Allow(Target::ForeignTy),
+    Allow(Target::MacroDef),
+    Allow(Target::Param),
+    Allow(Target::PatField),
+    Allow(Target::ExprField),
+    Allow(Target::WherePredicate),
+    Allow(Target::MacroCall),
+    Allow(Target::Crate),
+    Allow(Target::Delegation { mac: false }),
+    Allow(Target::Delegation { mac: true }),
+];
+
 /// Parse a single integer.
 ///
 /// Used by attributes that take a single integer as argument, such as
diff --git a/compiler/rustc_attr_parsing/src/lints.rs b/compiler/rustc_attr_parsing/src/lints.rs
index 22f5531bc80..733225bab59 100644
--- a/compiler/rustc_attr_parsing/src/lints.rs
+++ b/compiler/rustc_attr_parsing/src/lints.rs
@@ -1,6 +1,7 @@
 use rustc_errors::{DiagArgValue, LintEmitter};
-use rustc_hir::HirId;
 use rustc_hir::lints::{AttributeLint, AttributeLintKind};
+use rustc_hir::{HirId, Target};
+use rustc_span::sym;
 
 use crate::session_diagnostics;
 
@@ -34,5 +35,25 @@ pub fn emit_attribute_lint<L: LintEmitter>(lint: &AttributeLint<HirId>, lint_emi
             *first_span,
             session_diagnostics::EmptyAttributeList { attr_span: *first_span },
         ),
+        &AttributeLintKind::InvalidTarget { name, target, ref applied, only } => lint_emitter
+            .emit_node_span_lint(
+                // This check is here because `deprecated` had its own lint group and removing this would be a breaking change
+                if name == sym::deprecated
+                    && ![Target::Closure, Target::Expression, Target::Statement, Target::Arm]
+                        .contains(&target)
+                {
+                    rustc_session::lint::builtin::USELESS_DEPRECATED
+                } else {
+                    rustc_session::lint::builtin::UNUSED_ATTRIBUTES
+                },
+                *id,
+                *span,
+                session_diagnostics::InvalidTargetLint {
+                    name,
+                    target: target.plural_name(),
+                    applied: applied.clone(),
+                    only,
+                },
+            ),
     }
 }
diff --git a/compiler/rustc_attr_parsing/src/session_diagnostics.rs b/compiler/rustc_attr_parsing/src/session_diagnostics.rs
index 1de25ca252b..95e85667cd6 100644
--- a/compiler/rustc_attr_parsing/src/session_diagnostics.rs
+++ b/compiler/rustc_attr_parsing/src/session_diagnostics.rs
@@ -480,6 +480,29 @@ pub(crate) struct EmptyAttributeList {
     pub attr_span: Span,
 }
 
+#[derive(LintDiagnostic)]
+#[diag(attr_parsing_invalid_target_lint)]
+#[warning]
+#[help]
+pub(crate) struct InvalidTargetLint {
+    pub name: Symbol,
+    pub target: &'static str,
+    pub applied: String,
+    pub only: &'static str,
+}
+
+#[derive(Diagnostic)]
+#[help]
+#[diag(attr_parsing_invalid_target)]
+pub(crate) struct InvalidTarget {
+    #[primary_span]
+    pub span: Span,
+    pub name: Symbol,
+    pub target: &'static str,
+    pub applied: String,
+    pub only: &'static str,
+}
+
 #[derive(Diagnostic)]
 #[diag(attr_parsing_invalid_alignment_value, code = E0589)]
 pub(crate) struct InvalidAlignmentValue {
@@ -498,6 +521,7 @@ pub(crate) struct ReprIdent {
 #[derive(Diagnostic)]
 #[diag(attr_parsing_unrecognized_repr_hint, code = E0552)]
 #[help]
+#[note]
 pub(crate) struct UnrecognizedReprHint {
     #[primary_span]
     pub span: Span,
@@ -690,6 +714,9 @@ impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for AttributeParseError {
             }
         }
 
+        if let Some(link) = self.template.docs {
+            diag.note(format!("for more information, visit <{link}>"));
+        }
         let suggestions = self.template.suggestions(false, &name);
         diag.span_suggestions(
             self.attr_span,
diff --git a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
index be8b3f0bc1e..7e20a5133e0 100644
--- a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
@@ -410,18 +410,18 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                 }
                 let typeck = self.infcx.tcx.typeck(self.mir_def_id());
                 let parent = self.infcx.tcx.parent_hir_node(expr.hir_id);
-                let (def_id, call_id, args, offset) = if let hir::Node::Expr(parent_expr) = parent
+                let (def_id, args, offset) = if let hir::Node::Expr(parent_expr) = parent
                     && let hir::ExprKind::MethodCall(_, _, args, _) = parent_expr.kind
                 {
                     let def_id = typeck.type_dependent_def_id(parent_expr.hir_id);
-                    (def_id, Some(parent_expr.hir_id), args, 1)
+                    (def_id, args, 1)
                 } else if let hir::Node::Expr(parent_expr) = parent
                     && let hir::ExprKind::Call(call, args) = parent_expr.kind
                     && let ty::FnDef(def_id, _) = typeck.node_type(call.hir_id).kind()
                 {
-                    (Some(*def_id), Some(call.hir_id), args, 0)
+                    (Some(*def_id), args, 0)
                 } else {
-                    (None, None, &[][..], 0)
+                    (None, &[][..], 0)
                 };
                 let ty = place.ty(self.body, self.infcx.tcx).ty;
 
@@ -459,11 +459,12 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                     // If the moved place is used generically by the callee and a reference to it
                     // would still satisfy any bounds on its type, suggest borrowing.
                     if let Some(&param) = arg_param
-                        && let Some(generic_args) = call_id.and_then(|id| typeck.node_args_opt(id))
+                        && let hir::Node::Expr(call_expr) = parent
                         && let Some(ref_mutability) = self.suggest_borrow_generic_arg(
                             err,
+                            typeck,
+                            call_expr,
                             def_id,
-                            generic_args,
                             param,
                             moved_place,
                             pos + offset,
@@ -627,8 +628,9 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
     fn suggest_borrow_generic_arg(
         &self,
         err: &mut Diag<'_>,
+        typeck: &ty::TypeckResults<'tcx>,
+        call_expr: &hir::Expr<'tcx>,
         callee_did: DefId,
-        generic_args: ty::GenericArgsRef<'tcx>,
         param: ty::ParamTy,
         moved_place: PlaceRef<'tcx>,
         moved_arg_pos: usize,
@@ -639,6 +641,19 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         let sig = tcx.fn_sig(callee_did).instantiate_identity().skip_binder();
         let clauses = tcx.predicates_of(callee_did);
 
+        let generic_args = match call_expr.kind {
+            // For method calls, generic arguments are attached to the call node.
+            hir::ExprKind::MethodCall(..) => typeck.node_args_opt(call_expr.hir_id)?,
+            // For normal calls, generic arguments are in the callee's type.
+            // This diagnostic is only run for `FnDef` callees.
+            hir::ExprKind::Call(callee, _)
+                if let &ty::FnDef(_, args) = typeck.node_type(callee.hir_id).kind() =>
+            {
+                args
+            }
+            _ => return None,
+        };
+
         // First, is there at least one method on one of `param`'s trait bounds?
         // This keeps us from suggesting borrowing the argument to `mem::drop`, e.g.
         if !clauses.instantiate_identity(tcx).predicates.iter().any(|clause| {
diff --git a/compiler/rustc_borrowck/src/diagnostics/mod.rs b/compiler/rustc_borrowck/src/diagnostics/mod.rs
index 34bed375cb9..b67dba3af96 100644
--- a/compiler/rustc_borrowck/src/diagnostics/mod.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/mod.rs
@@ -51,7 +51,7 @@ mod conflict_errors;
 mod explain_borrow;
 mod move_errors;
 mod mutability_errors;
-mod opaque_suggestions;
+mod opaque_types;
 mod region_errors;
 
 pub(crate) use bound_region_errors::{ToUniverseInfo, UniverseInfo};
diff --git a/compiler/rustc_borrowck/src/diagnostics/move_errors.rs b/compiler/rustc_borrowck/src/diagnostics/move_errors.rs
index 1067f1e40ef..0b3151fd8b8 100644
--- a/compiler/rustc_borrowck/src/diagnostics/move_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/move_errors.rs
@@ -9,7 +9,8 @@ use rustc_middle::bug;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_mir_dataflow::move_paths::{LookupResult, MovePathIndex};
-use rustc_span::{BytePos, ExpnKind, MacroKind, Span};
+use rustc_span::def_id::DefId;
+use rustc_span::{BytePos, DUMMY_SP, ExpnKind, MacroKind, Span};
 use rustc_trait_selection::error_reporting::traits::FindExprBySpan;
 use rustc_trait_selection::infer::InferCtxtExt;
 use tracing::debug;
@@ -507,12 +508,18 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                 );
 
                 let closure_span = tcx.def_span(def_id);
+
                 self.cannot_move_out_of(span, &place_description)
                     .with_span_label(upvar_span, "captured outer variable")
                     .with_span_label(
                         closure_span,
                         format!("captured by this `{closure_kind}` closure"),
                     )
+                    .with_span_help(
+                        self.get_closure_bound_clause_span(*def_id),
+                        "`Fn` and `FnMut` closures require captured values to be able to be \
+                         consumed multiple times, but `FnOnce` closures may consume them only once",
+                    )
             }
             _ => {
                 let source = self.borrowed_content_source(deref_base);
@@ -561,6 +568,47 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         err
     }
 
+    fn get_closure_bound_clause_span(&self, def_id: DefId) -> Span {
+        let tcx = self.infcx.tcx;
+        let typeck_result = tcx.typeck(self.mir_def_id());
+        // Check whether the closure is an argument to a call, if so,
+        // get the instantiated where-bounds of that call.
+        let closure_hir_id = tcx.local_def_id_to_hir_id(def_id.expect_local());
+        let hir::Node::Expr(parent) = tcx.parent_hir_node(closure_hir_id) else { return DUMMY_SP };
+
+        let predicates = match parent.kind {
+            hir::ExprKind::Call(callee, _) => {
+                let Some(ty) = typeck_result.node_type_opt(callee.hir_id) else { return DUMMY_SP };
+                let ty::FnDef(fn_def_id, args) = ty.kind() else { return DUMMY_SP };
+                tcx.predicates_of(fn_def_id).instantiate(tcx, args)
+            }
+            hir::ExprKind::MethodCall(..) => {
+                let Some((_, method)) = typeck_result.type_dependent_def(parent.hir_id) else {
+                    return DUMMY_SP;
+                };
+                let args = typeck_result.node_args(parent.hir_id);
+                tcx.predicates_of(method).instantiate(tcx, args)
+            }
+            _ => return DUMMY_SP,
+        };
+
+        // Check whether one of the where-bounds requires the closure to impl `Fn[Mut]`.
+        for (pred, span) in predicates.predicates.iter().zip(predicates.spans.iter()) {
+            if let Some(clause) = pred.as_trait_clause()
+                && let ty::Closure(clause_closure_def_id, _) = clause.self_ty().skip_binder().kind()
+                && *clause_closure_def_id == def_id
+                && (tcx.lang_items().fn_mut_trait() == Some(clause.def_id())
+                    || tcx.lang_items().fn_trait() == Some(clause.def_id()))
+            {
+                // Found `<TyOfCapturingClosure as FnMut>`
+                // We point at the `Fn()` or `FnMut()` bound that coerced the closure, which
+                // could be changed to `FnOnce()` to avoid the move error.
+                return *span;
+            }
+        }
+        DUMMY_SP
+    }
+
     fn add_move_hints(&self, error: GroupedMoveError<'tcx>, err: &mut Diag<'_>, span: Span) {
         match error {
             GroupedMoveError::MovesFromPlace { mut binds_to, move_from, .. } => {
diff --git a/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs b/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
index 5d9416b59fc..c0ca35f9ff8 100644
--- a/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
@@ -677,12 +677,13 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
     ///  - is the trait from the local crate? If not, we can't suggest changing signatures
     ///  - `Span` of the argument in the trait definition
     fn is_error_in_trait(&self, local: Local) -> (bool, bool, Option<Span>) {
+        let tcx = self.infcx.tcx;
         if self.body.local_kind(local) != LocalKind::Arg {
             return (false, false, None);
         }
         let my_def = self.body.source.def_id();
         let Some(td) =
-            self.infcx.tcx.impl_of_assoc(my_def).and_then(|x| self.infcx.tcx.trait_id_of_impl(x))
+            tcx.trait_impl_of_assoc(my_def).and_then(|id| self.infcx.tcx.trait_id_of_impl(id))
         else {
             return (false, false, None);
         };
diff --git a/compiler/rustc_borrowck/src/diagnostics/opaque_suggestions.rs b/compiler/rustc_borrowck/src/diagnostics/opaque_types.rs
index 7192a889adc..83fe4a9f98f 100644
--- a/compiler/rustc_borrowck/src/diagnostics/opaque_suggestions.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/opaque_types.rs
@@ -18,9 +18,28 @@ use rustc_trait_selection::errors::impl_trait_overcapture_suggestion;
 use crate::MirBorrowckCtxt;
 use crate::borrow_set::BorrowData;
 use crate::consumers::RegionInferenceContext;
+use crate::region_infer::opaque_types::DeferredOpaqueTypeError;
 use crate::type_check::Locations;
 
 impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
+    pub(crate) fn report_opaque_type_errors(&mut self, errors: Vec<DeferredOpaqueTypeError<'tcx>>) {
+        if errors.is_empty() {
+            return;
+        }
+        let mut guar = None;
+        for error in errors {
+            guar = Some(match error {
+                DeferredOpaqueTypeError::InvalidOpaqueTypeArgs(err) => err.report(self.infcx),
+                DeferredOpaqueTypeError::LifetimeMismatchOpaqueParam(err) => {
+                    self.infcx.dcx().emit_err(err)
+                }
+            });
+        }
+        let guar = guar.unwrap();
+        self.root_cx.set_tainted_by_errors(guar);
+        self.infcx.set_tainted_by_errors(guar);
+    }
+
     /// Try to note when an opaque is involved in a borrowck error and that
     /// opaque captures lifetimes due to edition 2024.
     // FIXME: This code is otherwise somewhat general, and could easily be adapted
diff --git a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
index b130cf8ed27..2b74f1a48f7 100644
--- a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
@@ -92,9 +92,6 @@ impl<'tcx> RegionErrors<'tcx> {
     ) -> impl Iterator<Item = (RegionErrorKind<'tcx>, ErrorGuaranteed)> {
         self.0.into_iter()
     }
-    pub(crate) fn has_errors(&self) -> Option<ErrorGuaranteed> {
-        self.0.get(0).map(|x| x.1)
-    }
 }
 
 impl std::fmt::Debug for RegionErrors<'_> {
diff --git a/compiler/rustc_borrowck/src/handle_placeholders.rs b/compiler/rustc_borrowck/src/handle_placeholders.rs
index aaaf2f45c86..1614c112ab5 100644
--- a/compiler/rustc_borrowck/src/handle_placeholders.rs
+++ b/compiler/rustc_borrowck/src/handle_placeholders.rs
@@ -103,6 +103,10 @@ impl RegionTracker {
         self.max_nameable_universe
     }
 
+    pub(crate) fn max_placeholder_universe_reached(self) -> UniverseIndex {
+        self.max_placeholder_universe_reached
+    }
+
     fn merge_min_max_seen(&mut self, other: &Self) {
         self.max_placeholder_universe_reached = std::cmp::max(
             self.max_placeholder_universe_reached,
@@ -157,7 +161,7 @@ fn region_definitions<'tcx>(
     for info in var_infos.iter() {
         let origin = match info.origin {
             RegionVariableOrigin::Nll(origin) => origin,
-            _ => NllRegionVariableOrigin::Existential { from_forall: false },
+            _ => NllRegionVariableOrigin::Existential { name: None },
         };
 
         let definition = RegionDefinition { origin, universe: info.universe, external_name: None };
@@ -216,22 +220,11 @@ pub(crate) fn compute_sccs_applying_placeholder_outlives_constraints<'tcx>(
         placeholder_index_to_region: _,
         liveness_constraints,
         mut outlives_constraints,
-        mut member_constraints,
+        member_constraints,
         universe_causes,
         type_tests,
     } = constraints;
 
-    if let Some(guar) = universal_regions.tainted_by_errors() {
-        debug!("Universal regions tainted by errors; removing constraints!");
-        // Suppress unhelpful extra errors in `infer_opaque_types` by clearing out all
-        // outlives bounds that we may end up checking.
-        outlives_constraints = Default::default();
-        member_constraints = Default::default();
-
-        // Also taint the entire scope.
-        infcx.set_tainted_by_errors(guar);
-    }
-
     let fr_static = universal_regions.fr_static;
     let compute_sccs =
         |constraints: &OutlivesConstraintSet<'tcx>,
diff --git a/compiler/rustc_borrowck/src/lib.rs b/compiler/rustc_borrowck/src/lib.rs
index 321b18c9b78..d76d6a04e6e 100644
--- a/compiler/rustc_borrowck/src/lib.rs
+++ b/compiler/rustc_borrowck/src/lib.rs
@@ -19,6 +19,7 @@ use std::borrow::Cow;
 use std::cell::{OnceCell, RefCell};
 use std::marker::PhantomData;
 use std::ops::{ControlFlow, Deref};
+use std::rc::Rc;
 
 use borrow_set::LocalsStateAtExit;
 use root_cx::BorrowCheckRootCtxt;
@@ -44,6 +45,7 @@ use rustc_mir_dataflow::impls::{EverInitializedPlaces, MaybeUninitializedPlaces}
 use rustc_mir_dataflow::move_paths::{
     InitIndex, InitLocation, LookupResult, MoveData, MovePathIndex,
 };
+use rustc_mir_dataflow::points::DenseLocationMap;
 use rustc_mir_dataflow::{Analysis, Results, ResultsVisitor, visit_results};
 use rustc_session::lint::builtin::{TAIL_EXPR_DROP_ORDER, UNUSED_MUT};
 use rustc_span::{ErrorGuaranteed, Span, Symbol};
@@ -60,11 +62,14 @@ use crate::path_utils::*;
 use crate::place_ext::PlaceExt;
 use crate::places_conflict::{PlaceConflictBias, places_conflict};
 use crate::polonius::PoloniusDiagnosticsContext;
-use crate::polonius::legacy::{PoloniusLocationTable, PoloniusOutput};
+use crate::polonius::legacy::{
+    PoloniusFacts, PoloniusFactsExt, PoloniusLocationTable, PoloniusOutput,
+};
 use crate::prefixes::PrefixSet;
 use crate::region_infer::RegionInferenceContext;
 use crate::renumber::RegionCtxt;
 use crate::session_diagnostics::VarNeedNotMut;
+use crate::type_check::MirTypeckResults;
 
 mod borrow_set;
 mod borrowck_errors;
@@ -321,7 +326,34 @@ fn do_mir_borrowck<'tcx>(
     let locals_are_invalidated_at_exit = tcx.hir_body_owner_kind(def).is_fn_or_closure();
     let borrow_set = BorrowSet::build(tcx, body, locals_are_invalidated_at_exit, &move_data);
 
-    // Compute non-lexical lifetimes.
+    let location_map = Rc::new(DenseLocationMap::new(body));
+
+    let polonius_input = root_cx.consumer.as_ref().map_or(false, |c| c.polonius_input())
+        || infcx.tcx.sess.opts.unstable_opts.polonius.is_legacy_enabled();
+    let mut polonius_facts =
+        (polonius_input || PoloniusFacts::enabled(infcx.tcx)).then_some(PoloniusFacts::default());
+
+    // Run the MIR type-checker.
+    let MirTypeckResults {
+        constraints,
+        universal_region_relations,
+        opaque_type_values,
+        polonius_context,
+    } = type_check::type_check(
+        root_cx,
+        &infcx,
+        body,
+        &promoted,
+        universal_regions,
+        &location_table,
+        &borrow_set,
+        &mut polonius_facts,
+        &move_data,
+        Rc::clone(&location_map),
+    );
+
+    // Compute non-lexical lifetimes using the constraints computed
+    // by typechecking the MIR body.
     let nll::NllOutput {
         regioncx,
         polonius_input,
@@ -332,14 +364,19 @@ fn do_mir_borrowck<'tcx>(
     } = nll::compute_regions(
         root_cx,
         &infcx,
-        universal_regions,
         body,
-        &promoted,
         &location_table,
         &move_data,
         &borrow_set,
+        location_map,
+        universal_region_relations,
+        constraints,
+        polonius_facts,
+        polonius_context,
     );
 
+    let opaque_type_errors = regioncx.infer_opaque_types(root_cx, &infcx, opaque_type_values);
+
     // Dump MIR results into a file, if that is enabled. This lets us
     // write unit-tests, as well as helping with debugging.
     nll::dump_nll_mir(&infcx, body, &regioncx, &opt_closure_req, &borrow_set);
@@ -434,7 +471,11 @@ fn do_mir_borrowck<'tcx>(
     };
 
     // Compute and report region errors, if any.
-    mbcx.report_region_errors(nll_errors);
+    if nll_errors.is_empty() {
+        mbcx.report_opaque_type_errors(opaque_type_errors);
+    } else {
+        mbcx.report_region_errors(nll_errors);
+    }
 
     let (mut flow_analysis, flow_entry_states) =
         get_flow_results(tcx, body, &move_data, &borrow_set, &regioncx);
diff --git a/compiler/rustc_borrowck/src/nll.rs b/compiler/rustc_borrowck/src/nll.rs
index 41f67e78930..8608a8a3a66 100644
--- a/compiler/rustc_borrowck/src/nll.rs
+++ b/compiler/rustc_borrowck/src/nll.rs
@@ -5,7 +5,8 @@ use std::path::PathBuf;
 use std::rc::Rc;
 use std::str::FromStr;
 
-use polonius_engine::{Algorithm, Output};
+use polonius_engine::{Algorithm, AllFacts, Output};
+use rustc_data_structures::frozen::Frozen;
 use rustc_index::IndexSlice;
 use rustc_middle::mir::pretty::{PrettyPrintMirOptions, dump_mir_with_options};
 use rustc_middle::mir::{Body, PassWhere, Promoted, create_dump_file, dump_enabled, dump_mir};
@@ -18,14 +19,16 @@ use rustc_span::sym;
 use tracing::{debug, instrument};
 
 use crate::borrow_set::BorrowSet;
+use crate::consumers::RustcFacts;
 use crate::diagnostics::RegionErrors;
 use crate::handle_placeholders::compute_sccs_applying_placeholder_outlives_constraints;
-use crate::polonius::PoloniusDiagnosticsContext;
 use crate::polonius::legacy::{
     PoloniusFacts, PoloniusFactsExt, PoloniusLocationTable, PoloniusOutput,
 };
+use crate::polonius::{PoloniusContext, PoloniusDiagnosticsContext};
 use crate::region_infer::RegionInferenceContext;
-use crate::type_check::{self, MirTypeckResults};
+use crate::type_check::MirTypeckRegionConstraints;
+use crate::type_check::free_region_relations::UniversalRegionRelations;
 use crate::universal_regions::UniversalRegions;
 use crate::{
     BorrowCheckRootCtxt, BorrowckInferCtxt, ClosureOutlivesSubject, ClosureRegionRequirements,
@@ -76,41 +79,18 @@ pub(crate) fn replace_regions_in_mir<'tcx>(
 pub(crate) fn compute_regions<'tcx>(
     root_cx: &mut BorrowCheckRootCtxt<'tcx>,
     infcx: &BorrowckInferCtxt<'tcx>,
-    universal_regions: UniversalRegions<'tcx>,
     body: &Body<'tcx>,
-    promoted: &IndexSlice<Promoted, Body<'tcx>>,
     location_table: &PoloniusLocationTable,
     move_data: &MoveData<'tcx>,
     borrow_set: &BorrowSet<'tcx>,
+    location_map: Rc<DenseLocationMap>,
+    universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
+    constraints: MirTypeckRegionConstraints<'tcx>,
+    mut polonius_facts: Option<AllFacts<RustcFacts>>,
+    polonius_context: Option<PoloniusContext>,
 ) -> NllOutput<'tcx> {
-    let is_polonius_legacy_enabled = infcx.tcx.sess.opts.unstable_opts.polonius.is_legacy_enabled();
-    let polonius_input = root_cx.consumer.as_ref().map_or(false, |c| c.polonius_input())
-        || is_polonius_legacy_enabled;
     let polonius_output = root_cx.consumer.as_ref().map_or(false, |c| c.polonius_output())
-        || is_polonius_legacy_enabled;
-    let mut polonius_facts =
-        (polonius_input || PoloniusFacts::enabled(infcx.tcx)).then_some(PoloniusFacts::default());
-
-    let location_map = Rc::new(DenseLocationMap::new(body));
-
-    // Run the MIR type-checker.
-    let MirTypeckResults {
-        constraints,
-        universal_region_relations,
-        opaque_type_values,
-        polonius_context,
-    } = type_check::type_check(
-        root_cx,
-        infcx,
-        body,
-        promoted,
-        universal_regions,
-        location_table,
-        borrow_set,
-        &mut polonius_facts,
-        move_data,
-        Rc::clone(&location_map),
-    );
+        || infcx.tcx.sess.opts.unstable_opts.polonius.is_legacy_enabled();
 
     let lowered_constraints = compute_sccs_applying_placeholder_outlives_constraints(
         constraints,
@@ -168,13 +148,6 @@ pub(crate) fn compute_regions<'tcx>(
     let (closure_region_requirements, nll_errors) =
         regioncx.solve(infcx, body, polonius_output.clone());
 
-    if let Some(guar) = nll_errors.has_errors() {
-        // Suppress unhelpful extra errors in `infer_opaque_types`.
-        infcx.set_tainted_by_errors(guar);
-    }
-
-    regioncx.infer_opaque_types(root_cx, infcx, opaque_type_values);
-
     NllOutput {
         regioncx,
         polonius_input: polonius_facts.map(Box::new),
diff --git a/compiler/rustc_borrowck/src/polonius/constraints.rs b/compiler/rustc_borrowck/src/polonius/constraints.rs
index 50f59dd0dee..52595757859 100644
--- a/compiler/rustc_borrowck/src/polonius/constraints.rs
+++ b/compiler/rustc_borrowck/src/polonius/constraints.rs
@@ -7,9 +7,7 @@ use rustc_mir_dataflow::points::PointIndex;
 ///
 /// This models two sources of constraints:
 /// - constraints that traverse the subsets between regions at a given point, `a@p: b@p`. These
-///   depend on typeck constraints generated via assignments, calls, etc. (In practice there are
-///   subtleties where a statement's effect only starts being visible at the successor point, via
-///   the "result" of that statement).
+///   depend on typeck constraints generated via assignments, calls, etc.
 /// - constraints that traverse the CFG via the same region, `a@p: a@q`, where `p` is a predecessor
 ///   of `q`. These depend on the liveness of the regions at these points, as well as their
 ///   variance.
diff --git a/compiler/rustc_borrowck/src/polonius/legacy/facts.rs b/compiler/rustc_borrowck/src/polonius/legacy/facts.rs
index 64389b11a65..1f8177477e6 100644
--- a/compiler/rustc_borrowck/src/polonius/legacy/facts.rs
+++ b/compiler/rustc_borrowck/src/polonius/legacy/facts.rs
@@ -184,22 +184,6 @@ where
     }
 }
 
-impl<A, B, C, D> FactRow for (A, B, C, D)
-where
-    A: FactCell,
-    B: FactCell,
-    C: FactCell,
-    D: FactCell,
-{
-    fn write(
-        &self,
-        out: &mut dyn Write,
-        location_table: &PoloniusLocationTable,
-    ) -> Result<(), Box<dyn Error>> {
-        write_row(out, location_table, &[&self.0, &self.1, &self.2, &self.3])
-    }
-}
-
 fn write_row(
     out: &mut dyn Write,
     location_table: &PoloniusLocationTable,
diff --git a/compiler/rustc_borrowck/src/polonius/liveness_constraints.rs b/compiler/rustc_borrowck/src/polonius/liveness_constraints.rs
index 6ab09f731c0..2ba72180d66 100644
--- a/compiler/rustc_borrowck/src/polonius/liveness_constraints.rs
+++ b/compiler/rustc_borrowck/src/polonius/liveness_constraints.rs
@@ -105,22 +105,14 @@ fn propagate_loans_between_points(
         });
     }
 
-    let Some(current_live_regions) = live_regions.row(current_point) else {
-        // There are no constraints to add: there are no live regions at the current point.
-        return;
-    };
     let Some(next_live_regions) = live_regions.row(next_point) else {
         // There are no constraints to add: there are no live regions at the next point.
         return;
     };
 
     for region in next_live_regions.iter() {
-        if !current_live_regions.contains(region) {
-            continue;
-        }
-
-        // `region` is indeed live at both points, add a constraint between them, according to
-        // variance.
+        // `region` could be live at the current point, and is live at the next point: add a
+        // constraint between them, according to variance.
         if let Some(&direction) = live_region_variances.get(&region) {
             add_liveness_constraint(
                 region,
diff --git a/compiler/rustc_borrowck/src/polonius/loan_liveness.rs b/compiler/rustc_borrowck/src/polonius/loan_liveness.rs
index 5cd265e0db9..bdc3047e5ba 100644
--- a/compiler/rustc_borrowck/src/polonius/loan_liveness.rs
+++ b/compiler/rustc_borrowck/src/polonius/loan_liveness.rs
@@ -1,27 +1,18 @@
-use std::collections::{BTreeMap, BTreeSet};
-
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
-use rustc_middle::mir::visit::Visitor;
-use rustc_middle::mir::{
-    Body, Local, Location, Place, Rvalue, Statement, StatementKind, Terminator, TerminatorKind,
-};
-use rustc_middle::ty::{RegionVid, TyCtxt};
+use rustc_middle::ty::RegionVid;
 use rustc_mir_dataflow::points::PointIndex;
 
 use super::{LiveLoans, LocalizedOutlivesConstraintSet};
+use crate::BorrowSet;
 use crate::constraints::OutlivesConstraint;
-use crate::dataflow::BorrowIndex;
 use crate::region_infer::values::LivenessValues;
 use crate::type_check::Locations;
-use crate::{BorrowSet, PlaceConflictBias, places_conflict};
 
-/// Compute loan reachability, stop at kills, and trace loan liveness throughout the CFG, by
+/// Compute loan reachability to approximately trace loan liveness throughout the CFG, by
 /// traversing the full graph of constraints that combines:
 /// - the localized constraints (the physical edges),
 /// - with the constraints that hold at all points (the logical edges).
 pub(super) fn compute_loan_liveness<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    body: &Body<'tcx>,
     liveness: &LivenessValues,
     outlives_constraints: impl Iterator<Item = OutlivesConstraint<'tcx>>,
     borrow_set: &BorrowSet<'tcx>,
@@ -29,11 +20,6 @@ pub(super) fn compute_loan_liveness<'tcx>(
 ) -> LiveLoans {
     let mut live_loans = LiveLoans::new(borrow_set.len());
 
-    // FIXME: it may be preferable for kills to be encoded in the edges themselves, to simplify and
-    // likely make traversal (and constraint generation) more efficient. We also display kills on
-    // edges when visualizing the constraint graph anyways.
-    let kills = collect_kills(body, tcx, borrow_set);
-
     // Create the full graph with the physical edges we've localized earlier, and the logical edges
     // of constraints that hold at all points.
     let logical_constraints =
@@ -59,15 +45,15 @@ pub(super) fn compute_loan_liveness<'tcx>(
                 continue;
             }
 
-            // Record the loan as being live on entry to this point.
-            live_loans.insert(node.point, loan_idx);
-
-            // Here, we have a conundrum. There's currently a weakness in our theory, in that
-            // we're using a single notion of reachability to represent what used to be _two_
-            // different transitive closures. It didn't seem impactful when coming up with the
-            // single-graph and reachability through space (regions) + time (CFG) concepts, but in
-            // practice the combination of time-traveling with kills is more impactful than
-            // initially anticipated.
+            // Record the loan as being live on entry to this point if it reaches a live region
+            // there.
+            //
+            // This is an approximation of liveness (which is the thing we want), in that we're
+            // using a single notion of reachability to represent what used to be _two_ different
+            // transitive closures. It didn't seem impactful when coming up with the single-graph
+            // and reachability through space (regions) + time (CFG) concepts, but in practice the
+            // combination of time-traveling with kills is more impactful than initially
+            // anticipated.
             //
             // Kills should prevent a loan from reaching its successor points in the CFG, but not
             // while time-traveling: we're not actually at that CFG point, but looking for
@@ -92,40 +78,20 @@ pub(super) fn compute_loan_liveness<'tcx>(
             //   two-step traversal described above: only kills encountered on exit via a backward
             //   edge are ignored.
             //
-            // In our test suite, there are a couple of cases where kills are encountered while
-            // time-traveling, however as far as we can tell, always in cases where they would be
-            // unreachable. We have reason to believe that this is a property of the single-graph
-            // approach (but haven't proved it yet):
-            // - reachable kills while time-traveling would also be encountered via regular
-            //   traversal
-            // - it makes _some_ sense to ignore unreachable kills, but subtleties around dead code
-            //   in general need to be better thought through (like they were for NLLs).
-            // - ignoring kills is a conservative approximation: the loan is still live and could
-            //   cause false positive errors at another place access. Soundness issues in this
-            //   domain should look more like the absence of reachability instead.
-            //
-            // This is enough in practice to pass tests, and therefore is what we have implemented
-            // for now.
+            // This version of the analysis, however, is enough in practice to pass the tests that
+            // we care about and NLLs reject, without regressions on crater, and is an actionable
+            // subset of the full analysis. It also naturally points to areas of improvement that we
+            // wish to explore later, namely handling kills appropriately during traversal, instead
+            // of continuing traversal to all the reachable nodes.
             //
-            // FIXME: all of the above. Analyze potential unsoundness, possibly in concert with a
-            // borrowck implementation in a-mir-formality, fuzzing, or manually crafting
-            // counter-examples.
+            // FIXME: analyze potential unsoundness, possibly in concert with a borrowck
+            // implementation in a-mir-formality, fuzzing, or manually crafting counter-examples.
 
-            // Continuing traversal will depend on whether the loan is killed at this point, and
-            // whether we're time-traveling.
-            let current_location = liveness.location_from_point(node.point);
-            let is_loan_killed =
-                kills.get(&current_location).is_some_and(|kills| kills.contains(&loan_idx));
+            if liveness.is_live_at(node.region, liveness.location_from_point(node.point)) {
+                live_loans.insert(node.point, loan_idx);
+            }
 
             for succ in graph.outgoing_edges(node) {
-                // If the loan is killed at this point, it is killed _on exit_. But only during
-                // forward traversal.
-                if is_loan_killed {
-                    let destination = liveness.location_from_point(succ.point);
-                    if current_location.is_predecessor_of(destination, body) {
-                        continue;
-                    }
-                }
                 stack.push(succ);
             }
         }
@@ -192,116 +158,3 @@ impl LocalizedConstraintGraph {
         physical_edges.chain(materialized_edges)
     }
 }
-
-/// Traverses the MIR and collects kills.
-fn collect_kills<'tcx>(
-    body: &Body<'tcx>,
-    tcx: TyCtxt<'tcx>,
-    borrow_set: &BorrowSet<'tcx>,
-) -> BTreeMap<Location, BTreeSet<BorrowIndex>> {
-    let mut collector = KillsCollector { borrow_set, tcx, body, kills: BTreeMap::default() };
-    for (block, data) in body.basic_blocks.iter_enumerated() {
-        collector.visit_basic_block_data(block, data);
-    }
-    collector.kills
-}
-
-struct KillsCollector<'a, 'tcx> {
-    body: &'a Body<'tcx>,
-    tcx: TyCtxt<'tcx>,
-    borrow_set: &'a BorrowSet<'tcx>,
-
-    /// The set of loans killed at each location.
-    kills: BTreeMap<Location, BTreeSet<BorrowIndex>>,
-}
-
-// This visitor has a similar structure to the `Borrows` dataflow computation with respect to kills,
-// and the datalog polonius fact generation for the `loan_killed_at` relation.
-impl<'tcx> KillsCollector<'_, 'tcx> {
-    /// Records the borrows on the specified place as `killed`. For example, when assigning to a
-    /// local, or on a call's return destination.
-    fn record_killed_borrows_for_place(&mut self, place: Place<'tcx>, location: Location) {
-        // For the reasons described in graph traversal, we also filter out kills
-        // unreachable from the loan's introduction point, as they would stop traversal when
-        // e.g. checking for reachability in the subset graph through invariance constraints
-        // higher up.
-        let filter_unreachable_kills = |loan| {
-            let introduction = self.borrow_set[loan].reserve_location;
-            let reachable = introduction.is_predecessor_of(location, self.body);
-            reachable
-        };
-
-        let other_borrows_of_local = self
-            .borrow_set
-            .local_map
-            .get(&place.local)
-            .into_iter()
-            .flat_map(|bs| bs.iter())
-            .copied();
-
-        // If the borrowed place is a local with no projections, all other borrows of this
-        // local must conflict. This is purely an optimization so we don't have to call
-        // `places_conflict` for every borrow.
-        if place.projection.is_empty() {
-            if !self.body.local_decls[place.local].is_ref_to_static() {
-                self.kills
-                    .entry(location)
-                    .or_default()
-                    .extend(other_borrows_of_local.filter(|&loan| filter_unreachable_kills(loan)));
-            }
-            return;
-        }
-
-        // By passing `PlaceConflictBias::NoOverlap`, we conservatively assume that any given
-        // pair of array indices are not equal, so that when `places_conflict` returns true, we
-        // will be assured that two places being compared definitely denotes the same sets of
-        // locations.
-        let definitely_conflicting_borrows = other_borrows_of_local
-            .filter(|&i| {
-                places_conflict(
-                    self.tcx,
-                    self.body,
-                    self.borrow_set[i].borrowed_place,
-                    place,
-                    PlaceConflictBias::NoOverlap,
-                )
-            })
-            .filter(|&loan| filter_unreachable_kills(loan));
-
-        self.kills.entry(location).or_default().extend(definitely_conflicting_borrows);
-    }
-
-    /// Records the borrows on the specified local as `killed`.
-    fn record_killed_borrows_for_local(&mut self, local: Local, location: Location) {
-        if let Some(borrow_indices) = self.borrow_set.local_map.get(&local) {
-            self.kills.entry(location).or_default().extend(borrow_indices.iter());
-        }
-    }
-}
-
-impl<'tcx> Visitor<'tcx> for KillsCollector<'_, 'tcx> {
-    fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
-        // Make sure there are no remaining borrows for locals that have gone out of scope.
-        if let StatementKind::StorageDead(local) = statement.kind {
-            self.record_killed_borrows_for_local(local, location);
-        }
-
-        self.super_statement(statement, location);
-    }
-
-    fn visit_assign(&mut self, place: &Place<'tcx>, rvalue: &Rvalue<'tcx>, location: Location) {
-        // When we see `X = ...`, then kill borrows of `(*X).foo` and so forth.
-        self.record_killed_borrows_for_place(*place, location);
-        self.super_assign(place, rvalue, location);
-    }
-
-    fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
-        // A `Call` terminator's return value can be a local which has borrows, so we need to record
-        // those as killed as well.
-        if let TerminatorKind::Call { destination, .. } = terminator.kind {
-            self.record_killed_borrows_for_place(destination, location);
-        }
-
-        self.super_terminator(terminator, location);
-    }
-}
diff --git a/compiler/rustc_borrowck/src/polonius/mod.rs b/compiler/rustc_borrowck/src/polonius/mod.rs
index 142ef8ba28e..a9092b1981e 100644
--- a/compiler/rustc_borrowck/src/polonius/mod.rs
+++ b/compiler/rustc_borrowck/src/polonius/mod.rs
@@ -146,8 +146,8 @@ impl PoloniusContext {
     /// - converting NLL typeck constraints to be localized
     /// - encoding liveness constraints
     ///
-    /// Then, this graph is traversed, and combined with kills, reachability is recorded as loan
-    /// liveness, to be used by the loan scope and active loans computations.
+    /// Then, this graph is traversed, reachability is recorded as loan liveness, to be used by the
+    /// loan scope and active loans computations.
     ///
     /// The constraint data will be used to compute errors and diagnostics.
     pub(crate) fn compute_loan_liveness<'tcx>(
@@ -182,8 +182,6 @@ impl PoloniusContext {
         // Now that we have a complete graph, we can compute reachability to trace the liveness of
         // loans for the next step in the chain, the NLL loan scope and active loans computations.
         let live_loans = compute_loan_liveness(
-            tcx,
-            body,
             regioncx.liveness_constraints(),
             regioncx.outlives_constraints(),
             borrow_set,
diff --git a/compiler/rustc_borrowck/src/polonius/typeck_constraints.rs b/compiler/rustc_borrowck/src/polonius/typeck_constraints.rs
index 1289b1899eb..e4e52962bf7 100644
--- a/compiler/rustc_borrowck/src/polonius/typeck_constraints.rs
+++ b/compiler/rustc_borrowck/src/polonius/typeck_constraints.rs
@@ -47,9 +47,7 @@ pub(super) fn convert_typeck_constraints<'tcx>(
                         tcx,
                         body,
                         stmt,
-                        liveness,
                         &outlives_constraint,
-                        location,
                         point,
                         universal_regions,
                     )
@@ -78,9 +76,7 @@ fn localize_statement_constraint<'tcx>(
     tcx: TyCtxt<'tcx>,
     body: &Body<'tcx>,
     stmt: &Statement<'tcx>,
-    liveness: &LivenessValues,
     outlives_constraint: &OutlivesConstraint<'tcx>,
-    current_location: Location,
     current_point: PointIndex,
     universal_regions: &UniversalRegions<'tcx>,
 ) -> LocalizedOutlivesConstraint {
@@ -98,8 +94,8 @@ fn localize_statement_constraint<'tcx>(
             // - and that should be impossible in MIR
             //
             // When we have a more complete implementation in the future, tested with crater, etc,
-            // we can relax this to a debug assert instead, or remove it.
-            assert!(
+            // we can remove this assertion. It's a debug assert because it can be expensive.
+            debug_assert!(
                 {
                     let mut lhs_regions = FxHashSet::default();
                     tcx.for_each_free_region(lhs, |region| {
@@ -119,16 +115,8 @@ fn localize_statement_constraint<'tcx>(
                 "there should be no common regions between the LHS and RHS of an assignment"
             );
 
-            // As mentioned earlier, we should be tracking these better upstream but: we want to
-            // relate the types on entry to the type of the place on exit. That is, outlives
-            // constraints on the RHS are on entry, and outlives constraints to/from the LHS are on
-            // exit (i.e. on entry to the successor location).
             let lhs_ty = body.local_decls[lhs.local].ty;
-            let successor_location = Location {
-                block: current_location.block,
-                statement_index: current_location.statement_index + 1,
-            };
-            let successor_point = liveness.point_from_location(successor_location);
+            let successor_point = current_point;
             compute_constraint_direction(
                 tcx,
                 outlives_constraint,
@@ -195,6 +183,7 @@ fn localize_terminator_constraint<'tcx>(
         }
     }
 }
+
 /// For a given outlives constraint and CFG edge, returns the localized constraint with the
 /// appropriate `from`-`to` direction. This is computed according to whether the constraint flows to
 /// or from a free region in the given `value`, some kind of result for an effectful operation, like
diff --git a/compiler/rustc_borrowck/src/region_infer/graphviz.rs b/compiler/rustc_borrowck/src/region_infer/graphviz.rs
index a3e29982e90..b2f67c43125 100644
--- a/compiler/rustc_borrowck/src/region_infer/graphviz.rs
+++ b/compiler/rustc_borrowck/src/region_infer/graphviz.rs
@@ -41,7 +41,22 @@ fn render_region_vid<'tcx>(
         "".to_string()
     };
 
-    format!("{:?}{universe_str}{external_name_str}", rvid)
+    let extra_info = match regioncx.region_definition(rvid).origin {
+        NllRegionVariableOrigin::FreeRegion => "".to_string(),
+        NllRegionVariableOrigin::Placeholder(p) => match p.bound.kind {
+            ty::BoundRegionKind::Named(def_id) => {
+                format!(" (for<{}>)", tcx.item_name(def_id))
+            }
+            ty::BoundRegionKind::ClosureEnv | ty::BoundRegionKind::Anon => " (for<'_>)".to_string(),
+            ty::BoundRegionKind::NamedAnon(_) => {
+                bug!("only used for pretty printing")
+            }
+        },
+        NllRegionVariableOrigin::Existential { name: Some(name), .. } => format!(" (ex<{name}>)"),
+        NllRegionVariableOrigin::Existential { .. } => format!(" (ex<'_>)"),
+    };
+
+    format!("{:?}{universe_str}{external_name_str}{extra_info}", rvid)
 }
 
 impl<'tcx> RegionInferenceContext<'tcx> {
diff --git a/compiler/rustc_borrowck/src/region_infer/mod.rs b/compiler/rustc_borrowck/src/region_infer/mod.rs
index f1320048533..c76c5c17431 100644
--- a/compiler/rustc_borrowck/src/region_infer/mod.rs
+++ b/compiler/rustc_borrowck/src/region_infer/mod.rs
@@ -44,7 +44,7 @@ use crate::{
 
 mod dump_mir;
 mod graphviz;
-mod opaque_types;
+pub(crate) mod opaque_types;
 mod reverse_sccs;
 
 pub(crate) mod values;
@@ -713,7 +713,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
 
         // If the member region lives in a higher universe, we currently choose
         // the most conservative option by leaving it unchanged.
-        if !self.max_nameable_universe(scc).is_root() {
+        if !self.max_placeholder_universe_reached(scc).is_root() {
             return;
         }
 
@@ -1376,6 +1376,13 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         self.scc_annotations[scc].max_nameable_universe()
     }
 
+    pub(crate) fn max_placeholder_universe_reached(
+        &self,
+        scc: ConstraintSccIndex,
+    ) -> UniverseIndex {
+        self.scc_annotations[scc].max_placeholder_universe_reached()
+    }
+
     /// Checks the final value for the free region `fr` to see if it
     /// grew too large. In particular, examine what `end(X)` points
     /// wound up in `fr`'s final value; for each `end(X)` where `X !=
@@ -1939,10 +1946,15 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         //
         // and here we prefer to blame the source (the y = x statement).
         let blame_source = match from_region_origin {
-            NllRegionVariableOrigin::FreeRegion
-            | NllRegionVariableOrigin::Existential { from_forall: false } => true,
-            NllRegionVariableOrigin::Placeholder(_)
-            | NllRegionVariableOrigin::Existential { from_forall: true } => false,
+            NllRegionVariableOrigin::FreeRegion => true,
+            NllRegionVariableOrigin::Placeholder(_) => false,
+            // `'existential: 'whatever` never results in a region error by itself.
+            // We may always infer it to `'static` afterall. This means while an error
+            // path may go through an existential, these existentials are never the
+            // `from_region`.
+            NllRegionVariableOrigin::Existential { name: _ } => {
+                unreachable!("existentials can outlive everything")
+            }
         };
 
         // To pick a constraint to blame, we organize constraints by how interesting we expect them
diff --git a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
index 6270e6d9a60..23c4554aa15 100644
--- a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
+++ b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
@@ -6,7 +6,9 @@ use rustc_middle::ty::{
     TypeVisitableExt, fold_regions,
 };
 use rustc_span::Span;
-use rustc_trait_selection::opaque_types::check_opaque_type_parameter_valid;
+use rustc_trait_selection::opaque_types::{
+    InvalidOpaqueTypeArgs, check_opaque_type_parameter_valid,
+};
 use tracing::{debug, instrument};
 
 use super::RegionInferenceContext;
@@ -14,6 +16,11 @@ use crate::BorrowCheckRootCtxt;
 use crate::session_diagnostics::LifetimeMismatchOpaqueParam;
 use crate::universal_regions::RegionClassification;
 
+pub(crate) enum DeferredOpaqueTypeError<'tcx> {
+    InvalidOpaqueTypeArgs(InvalidOpaqueTypeArgs<'tcx>),
+    LifetimeMismatchOpaqueParam(LifetimeMismatchOpaqueParam<'tcx>),
+}
+
 impl<'tcx> RegionInferenceContext<'tcx> {
     /// Resolve any opaque types that were encountered while borrow checking
     /// this item. This is then used to get the type in the `type_of` query.
@@ -58,13 +65,14 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     ///
     /// [rustc-dev-guide chapter]:
     /// https://rustc-dev-guide.rust-lang.org/opaque-types-region-infer-restrictions.html
-    #[instrument(level = "debug", skip(self, root_cx, infcx), ret)]
+    #[instrument(level = "debug", skip(self, root_cx, infcx))]
     pub(crate) fn infer_opaque_types(
         &self,
         root_cx: &mut BorrowCheckRootCtxt<'tcx>,
         infcx: &InferCtxt<'tcx>,
         opaque_ty_decls: FxIndexMap<OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>>,
-    ) {
+    ) -> Vec<DeferredOpaqueTypeError<'tcx>> {
+        let mut errors = Vec::new();
         let mut decls_modulo_regions: FxIndexMap<OpaqueTypeKey<'tcx>, (OpaqueTypeKey<'tcx>, Span)> =
             FxIndexMap::default();
 
@@ -124,8 +132,15 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             });
             debug!(?concrete_type);
 
-            let ty =
-                infcx.infer_opaque_definition_from_instantiation(opaque_type_key, concrete_type);
+            let ty = match infcx
+                .infer_opaque_definition_from_instantiation(opaque_type_key, concrete_type)
+            {
+                Ok(ty) => ty,
+                Err(err) => {
+                    errors.push(DeferredOpaqueTypeError::InvalidOpaqueTypeArgs(err));
+                    continue;
+                }
+            };
 
             // Sometimes, when the hidden type is an inference variable, it can happen that
             // the hidden type becomes the opaque type itself. In this case, this was an opaque
@@ -149,25 +164,27 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             // non-region parameters. This is necessary because within the new solver we perform
             // various query operations modulo regions, and thus could unsoundly select some impls
             // that don't hold.
-            if !ty.references_error()
-                && let Some((prev_decl_key, prev_span)) = decls_modulo_regions.insert(
-                    infcx.tcx.erase_regions(opaque_type_key),
-                    (opaque_type_key, concrete_type.span),
-                )
-                && let Some((arg1, arg2)) = std::iter::zip(
-                    prev_decl_key.iter_captured_args(infcx.tcx).map(|(_, arg)| arg),
-                    opaque_type_key.iter_captured_args(infcx.tcx).map(|(_, arg)| arg),
-                )
-                .find(|(arg1, arg2)| arg1 != arg2)
+            if let Some((prev_decl_key, prev_span)) = decls_modulo_regions.insert(
+                infcx.tcx.erase_regions(opaque_type_key),
+                (opaque_type_key, concrete_type.span),
+            ) && let Some((arg1, arg2)) = std::iter::zip(
+                prev_decl_key.iter_captured_args(infcx.tcx).map(|(_, arg)| arg),
+                opaque_type_key.iter_captured_args(infcx.tcx).map(|(_, arg)| arg),
+            )
+            .find(|(arg1, arg2)| arg1 != arg2)
             {
-                infcx.dcx().emit_err(LifetimeMismatchOpaqueParam {
-                    arg: arg1,
-                    prev: arg2,
-                    span: prev_span,
-                    prev_span: concrete_type.span,
-                });
+                errors.push(DeferredOpaqueTypeError::LifetimeMismatchOpaqueParam(
+                    LifetimeMismatchOpaqueParam {
+                        arg: arg1,
+                        prev: arg2,
+                        span: prev_span,
+                        prev_span: concrete_type.span,
+                    },
+                ));
             }
         }
+
+        errors
     }
 
     /// Map the regions in the type to named regions. This is similar to what
@@ -260,19 +277,13 @@ impl<'tcx> InferCtxt<'tcx> {
         &self,
         opaque_type_key: OpaqueTypeKey<'tcx>,
         instantiated_ty: OpaqueHiddenType<'tcx>,
-    ) -> Ty<'tcx> {
-        if let Some(e) = self.tainted_by_errors() {
-            return Ty::new_error(self.tcx, e);
-        }
-
-        if let Err(err) = check_opaque_type_parameter_valid(
+    ) -> Result<Ty<'tcx>, InvalidOpaqueTypeArgs<'tcx>> {
+        check_opaque_type_parameter_valid(
             self,
             opaque_type_key,
             instantiated_ty.span,
             DefiningScopeKind::MirBorrowck,
-        ) {
-            return Ty::new_error(self.tcx, err.report(self));
-        }
+        )?;
 
         let definition_ty = instantiated_ty
             .remap_generic_params_to_declaration_params(
@@ -282,10 +293,7 @@ impl<'tcx> InferCtxt<'tcx> {
             )
             .ty;
 
-        if let Err(e) = definition_ty.error_reported() {
-            return Ty::new_error(self.tcx, e);
-        }
-
-        definition_ty
+        definition_ty.error_reported()?;
+        Ok(definition_ty)
     }
 }
diff --git a/compiler/rustc_borrowck/src/renumber.rs b/compiler/rustc_borrowck/src/renumber.rs
index ff92b4168a8..fa3064afee8 100644
--- a/compiler/rustc_borrowck/src/renumber.rs
+++ b/compiler/rustc_borrowck/src/renumber.rs
@@ -66,7 +66,7 @@ impl<'a, 'tcx> RegionRenumberer<'a, 'tcx> {
         T: TypeFoldable<TyCtxt<'tcx>>,
         F: Fn() -> RegionCtxt,
     {
-        let origin = NllRegionVariableOrigin::Existential { from_forall: false };
+        let origin = NllRegionVariableOrigin::Existential { name: None };
         fold_regions(self.infcx.tcx, value, |_region, _depth| {
             self.infcx.next_nll_region_var(origin, || region_ctxt_fn())
         })
diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index 148d0de3bab..a960b96b91c 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -182,6 +182,17 @@ pub(crate) fn type_check<'tcx>(
         )
     });
 
+    // In case type check encountered an error region, we suppress unhelpful extra
+    // errors in by clearing out all outlives bounds that we may end up checking.
+    if let Some(guar) = universal_region_relations.universal_regions.encountered_re_error() {
+        debug!("encountered an error region; removing constraints!");
+        constraints.outlives_constraints = Default::default();
+        constraints.member_constraints = Default::default();
+        constraints.type_tests = Default::default();
+        root_cx.set_tainted_by_errors(guar);
+        infcx.set_tainted_by_errors(guar);
+    }
+
     MirTypeckResults {
         constraints,
         universal_region_relations,
@@ -1762,10 +1773,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                     locations,
                 );
 
-                assert!(!matches!(
-                    tcx.impl_of_assoc(def_id).map(|imp| tcx.def_kind(imp)),
-                    Some(DefKind::Impl { of_trait: true })
-                ));
+                assert_eq!(tcx.trait_impl_of_assoc(def_id), None);
                 self.prove_predicates(
                     args.types().map(|ty| ty::ClauseKind::WellFormed(ty.into())),
                     locations,
diff --git a/compiler/rustc_borrowck/src/type_check/relate_tys.rs b/compiler/rustc_borrowck/src/type_check/relate_tys.rs
index bb72d1d52f3..84ca9bad2c1 100644
--- a/compiler/rustc_borrowck/src/type_check/relate_tys.rs
+++ b/compiler/rustc_borrowck/src/type_check/relate_tys.rs
@@ -216,7 +216,7 @@ impl<'a, 'b, 'tcx> NllTypeRelating<'a, 'b, 'tcx> {
                     *ex_reg_var
                 } else {
                     let ex_reg_var =
-                        self.next_existential_region_var(true, br.kind.get_name(infcx.infcx.tcx));
+                        self.next_existential_region_var(br.kind.get_name(infcx.infcx.tcx));
                     debug!(?ex_reg_var);
                     reg_map.insert(br, ex_reg_var);
 
@@ -244,17 +244,9 @@ impl<'a, 'b, 'tcx> NllTypeRelating<'a, 'b, 'tcx> {
     }
 
     #[instrument(skip(self), level = "debug")]
-    fn next_existential_region_var(
-        &mut self,
-        from_forall: bool,
-        name: Option<Symbol>,
-    ) -> ty::Region<'tcx> {
-        let origin = NllRegionVariableOrigin::Existential { from_forall };
-
-        let reg_var =
-            self.type_checker.infcx.next_nll_region_var(origin, || RegionCtxt::Existential(name));
-
-        reg_var
+    fn next_existential_region_var(&mut self, name: Option<Symbol>) -> ty::Region<'tcx> {
+        let origin = NllRegionVariableOrigin::Existential { name };
+        self.type_checker.infcx.next_nll_region_var(origin, || RegionCtxt::Existential(name))
     }
 
     #[instrument(skip(self), level = "debug")]
diff --git a/compiler/rustc_borrowck/src/universal_regions.rs b/compiler/rustc_borrowck/src/universal_regions.rs
index 240c9a5223b..296a2735533 100644
--- a/compiler/rustc_borrowck/src/universal_regions.rs
+++ b/compiler/rustc_borrowck/src/universal_regions.rs
@@ -217,7 +217,7 @@ struct UniversalRegionIndices<'tcx> {
 
     /// Whether we've encountered an error region. If we have, cancel all
     /// outlives errors, as they are likely bogus.
-    pub tainted_by_errors: Cell<Option<ErrorGuaranteed>>,
+    pub encountered_re_error: Cell<Option<ErrorGuaranteed>>,
 }
 
 #[derive(Debug, PartialEq)]
@@ -442,8 +442,8 @@ impl<'tcx> UniversalRegions<'tcx> {
         self.fr_fn_body
     }
 
-    pub(crate) fn tainted_by_errors(&self) -> Option<ErrorGuaranteed> {
-        self.indices.tainted_by_errors.get()
+    pub(crate) fn encountered_re_error(&self) -> Option<ErrorGuaranteed> {
+        self.indices.encountered_re_error.get()
     }
 }
 
@@ -706,7 +706,7 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
         UniversalRegionIndices {
             indices: global_mapping.chain(arg_mapping).collect(),
             fr_static,
-            tainted_by_errors: Cell::new(None),
+            encountered_re_error: Cell::new(None),
         }
     }
 
@@ -916,7 +916,7 @@ impl<'tcx> UniversalRegionIndices<'tcx> {
         match r.kind() {
             ty::ReVar(..) => r.as_var(),
             ty::ReError(guar) => {
-                self.tainted_by_errors.set(Some(guar));
+                self.encountered_re_error.set(Some(guar));
                 // We use the `'static` `RegionVid` because `ReError` doesn't actually exist in the
                 // `UniversalRegionIndices`. This is fine because 1) it is a fallback only used if
                 // errors are being emitted and 2) it leaves the happy path unaffected.
diff --git a/compiler/rustc_builtin_macros/messages.ftl b/compiler/rustc_builtin_macros/messages.ftl
index ae186d744c4..358c0d3db46 100644
--- a/compiler/rustc_builtin_macros/messages.ftl
+++ b/compiler/rustc_builtin_macros/messages.ftl
@@ -222,6 +222,15 @@ builtin_macros_format_unused_args = multiple unused formatting arguments
 
 builtin_macros_format_use_positional = consider using a positional formatting argument instead
 
+builtin_macros_derive_from_wrong_target = `#[derive(From)]` used on {$kind}
+
+builtin_macros_derive_from_wrong_field_count = `#[derive(From)]` used on a struct with {$multiple_fields ->
+    [true] multiple fields
+    *[false] no fields
+}
+
+builtin_macros_derive_from_usage_note = `#[derive(From)]` can only be used on structs with exactly one field
+
 builtin_macros_multiple_default_attrs = multiple `#[default]` attributes
     .note = only one `#[default]` attribute is needed
     .label = `#[default]` used here
@@ -259,8 +268,6 @@ builtin_macros_only_one_argument = {$name} takes 1 argument
 
 builtin_macros_proc_macro = `proc-macro` crate types currently cannot export any items other than functions tagged with `#[proc_macro]`, `#[proc_macro_derive]`, or `#[proc_macro_attribute]`
 
-builtin_macros_proc_macro_attribute_only_be_used_on_bare_functions = the `#[{$path}]` attribute may only be used on bare functions
-
 builtin_macros_proc_macro_attribute_only_usable_with_crate_type = the `#[{$path}]` attribute is only usable with crates of the `proc-macro` crate type
 
 builtin_macros_requires_cfg_pattern =
diff --git a/compiler/rustc_builtin_macros/src/alloc_error_handler.rs b/compiler/rustc_builtin_macros/src/alloc_error_handler.rs
index e75bc944d7e..35ef6be095e 100644
--- a/compiler/rustc_builtin_macros/src/alloc_error_handler.rs
+++ b/compiler/rustc_builtin_macros/src/alloc_error_handler.rs
@@ -1,4 +1,3 @@
-use rustc_ast::ptr::P;
 use rustc_ast::{
     self as ast, Fn, FnHeader, FnSig, Generics, ItemKind, Safety, Stmt, StmtKind, TyKind,
 };
@@ -46,7 +45,7 @@ pub(crate) fn expand(
     let const_body = ecx.expr_block(ecx.block(span, stmts));
     let const_item = ecx.item_const(span, Ident::new(kw::Underscore, span), const_ty, const_body);
     let const_item = if is_stmt {
-        Annotatable::Stmt(P(ecx.stmt_item(span, const_item)))
+        Annotatable::Stmt(Box::new(ecx.stmt_item(span, const_item)))
     } else {
         Annotatable::Item(const_item)
     };
diff --git a/compiler/rustc_builtin_macros/src/asm.rs b/compiler/rustc_builtin_macros/src/asm.rs
index 1fb99817222..86b8e1ff8db 100644
--- a/compiler/rustc_builtin_macros/src/asm.rs
+++ b/compiler/rustc_builtin_macros/src/asm.rs
@@ -1,5 +1,4 @@
 use lint::BuiltinLintDiag;
-use rustc_ast::ptr::P;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::{AsmMacro, token};
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
@@ -19,7 +18,7 @@ use crate::{errors, fluent_generated as fluent};
 
 /// Validated assembly arguments, ready for macro expansion.
 struct ValidatedAsmArgs {
-    pub templates: Vec<P<ast::Expr>>,
+    pub templates: Vec<Box<ast::Expr>>,
     pub operands: Vec<(ast::InlineAsmOperand, Span)>,
     named_args: FxIndexMap<Symbol, usize>,
     reg_args: GrowableBitSet<usize>,
@@ -600,9 +599,9 @@ pub(super) fn expand_asm<'cx>(
                 return ExpandResult::Retry(());
             };
             let expr = match mac {
-                Ok(inline_asm) => P(ast::Expr {
+                Ok(inline_asm) => Box::new(ast::Expr {
                     id: ast::DUMMY_NODE_ID,
-                    kind: ast::ExprKind::InlineAsm(P(inline_asm)),
+                    kind: ast::ExprKind::InlineAsm(Box::new(inline_asm)),
                     span: sp,
                     attrs: ast::AttrVec::new(),
                     tokens: None,
@@ -630,9 +629,9 @@ pub(super) fn expand_naked_asm<'cx>(
                 return ExpandResult::Retry(());
             };
             let expr = match mac {
-                Ok(inline_asm) => P(ast::Expr {
+                Ok(inline_asm) => Box::new(ast::Expr {
                     id: ast::DUMMY_NODE_ID,
-                    kind: ast::ExprKind::InlineAsm(P(inline_asm)),
+                    kind: ast::ExprKind::InlineAsm(Box::new(inline_asm)),
                     span: sp,
                     attrs: ast::AttrVec::new(),
                     tokens: None,
@@ -660,7 +659,7 @@ pub(super) fn expand_global_asm<'cx>(
                 return ExpandResult::Retry(());
             };
             match mac {
-                Ok(inline_asm) => MacEager::items(smallvec![P(ast::Item {
+                Ok(inline_asm) => MacEager::items(smallvec![Box::new(ast::Item {
                     attrs: ast::AttrVec::new(),
                     id: ast::DUMMY_NODE_ID,
                     kind: ast::ItemKind::GlobalAsm(Box::new(inline_asm)),
diff --git a/compiler/rustc_builtin_macros/src/assert.rs b/compiler/rustc_builtin_macros/src/assert.rs
index c659b1cff59..013258a1b4e 100644
--- a/compiler/rustc_builtin_macros/src/assert.rs
+++ b/compiler/rustc_builtin_macros/src/assert.rs
@@ -1,9 +1,8 @@
 mod context;
 
-use rustc_ast::ptr::P;
-use rustc_ast::token::Delimiter;
+use rustc_ast::token::{self, Delimiter};
 use rustc_ast::tokenstream::{DelimSpan, TokenStream};
-use rustc_ast::{DelimArgs, Expr, ExprKind, MacCall, Path, PathSegment, UnOp, token};
+use rustc_ast::{DelimArgs, Expr, ExprKind, MacCall, Path, PathSegment};
 use rustc_ast_pretty::pprust;
 use rustc_errors::PResult;
 use rustc_expand::base::{DummyResult, ExpandResult, ExtCtxt, MacEager, MacroExpanderResult};
@@ -30,7 +29,7 @@ pub(crate) fn expand_assert<'cx>(
 
     // `core::panic` and `std::panic` are different macros, so we use call-site
     // context to pick up whichever is currently in scope.
-    let call_site_span = cx.with_call_site_ctxt(span);
+    let call_site_span = cx.with_call_site_ctxt(cond_expr.span);
 
     let panic_path = || {
         if use_panic_2021(span) {
@@ -55,16 +54,16 @@ pub(crate) fn expand_assert<'cx>(
     let expr = if let Some(tokens) = custom_message {
         let then = cx.expr(
             call_site_span,
-            ExprKind::MacCall(P(MacCall {
+            ExprKind::MacCall(Box::new(MacCall {
                 path: panic_path(),
-                args: P(DelimArgs {
+                args: Box::new(DelimArgs {
                     dspan: DelimSpan::from_single(call_site_span),
                     delim: Delimiter::Parenthesis,
                     tokens,
                 }),
             })),
         );
-        expr_if_not(cx, call_site_span, cond_expr, then, None)
+        assert_cond_check(cx, call_site_span, cond_expr, then)
     }
     // If `generic_assert` is enabled, generates rich captured outputs
     //
@@ -89,26 +88,33 @@ pub(crate) fn expand_assert<'cx>(
                 )),
             )],
         );
-        expr_if_not(cx, call_site_span, cond_expr, then, None)
+        assert_cond_check(cx, call_site_span, cond_expr, then)
     };
 
     ExpandResult::Ready(MacEager::expr(expr))
 }
 
+/// `assert!($cond_expr, $custom_message)`
 struct Assert {
-    cond_expr: P<Expr>,
+    cond_expr: Box<Expr>,
     custom_message: Option<TokenStream>,
 }
 
-// if !{ ... } { ... } else { ... }
-fn expr_if_not(
-    cx: &ExtCtxt<'_>,
-    span: Span,
-    cond: P<Expr>,
-    then: P<Expr>,
-    els: Option<P<Expr>>,
-) -> P<Expr> {
-    cx.expr_if(span, cx.expr(span, ExprKind::Unary(UnOp::Not, cond)), then, els)
+/// `match <cond> { true => {} _ => <then> }`
+fn assert_cond_check(cx: &ExtCtxt<'_>, span: Span, cond: Box<Expr>, then: Box<Expr>) -> Box<Expr> {
+    // Instead of expanding to `if !<cond> { <then> }`, we expand to
+    // `match <cond> { true => {} _ => <then> }`.
+    // This allows us to always complain about mismatched types instead of "cannot apply unary
+    // operator `!` to type `X`" when passing an invalid `<cond>`, while also allowing `<cond>` to
+    // be `&true`.
+    let els = cx.expr_block(cx.block(span, thin_vec![]));
+    let mut arms = thin_vec![];
+    arms.push(cx.arm(span, cx.pat_lit(span, cx.expr_bool(span, true)), els));
+    arms.push(cx.arm(span, cx.pat_wild(span), then));
+
+    // We wrap the `match` in a statement to limit the length of any borrows introduced in the
+    // condition.
+    cx.expr_block(cx.block(span, [cx.stmt_expr(cx.expr_match(span, cond, arms))].into()))
 }
 
 fn parse_assert<'a>(cx: &ExtCtxt<'a>, sp: Span, stream: TokenStream) -> PResult<'a, Assert> {
diff --git a/compiler/rustc_builtin_macros/src/assert/context.rs b/compiler/rustc_builtin_macros/src/assert/context.rs
index ea7248ca539..31855cbd4e6 100644
--- a/compiler/rustc_builtin_macros/src/assert/context.rs
+++ b/compiler/rustc_builtin_macros/src/assert/context.rs
@@ -1,4 +1,3 @@
-use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Delimiter, IdentIsRaw};
 use rustc_ast::tokenstream::{DelimSpan, TokenStream, TokenTree};
 use rustc_ast::{
@@ -70,7 +69,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
     ///   }
     /// }
     /// ```
-    pub(super) fn build(mut self, mut cond_expr: P<Expr>, panic_path: Path) -> P<Expr> {
+    pub(super) fn build(mut self, mut cond_expr: Box<Expr>, panic_path: Path) -> Box<Expr> {
         let expr_str = pprust::expr_to_string(&cond_expr);
         self.manage_cond_expr(&mut cond_expr);
         let initial_imports = self.build_initial_imports();
@@ -129,7 +128,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
     }
 
     /// Takes the conditional expression of `assert!` and then wraps it inside `unlikely`
-    fn build_unlikely(&self, cond_expr: P<Expr>) -> P<Expr> {
+    fn build_unlikely(&self, cond_expr: Box<Expr>) -> Box<Expr> {
         let unlikely_path = self.cx.std_path(&[sym::intrinsics, sym::unlikely]);
         self.cx.expr_call(
             self.span,
@@ -145,7 +144,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
     ///     __capture0,
     ///     ...
     /// );
-    fn build_panic(&self, expr_str: &str, panic_path: Path) -> P<Expr> {
+    fn build_panic(&self, expr_str: &str, panic_path: Path) -> Box<Expr> {
         let escaped_expr_str = escape_to_fmt(expr_str);
         let initial = [
             TokenTree::token_joint(
@@ -176,9 +175,9 @@ impl<'cx, 'a> Context<'cx, 'a> {
         });
         self.cx.expr(
             self.span,
-            ExprKind::MacCall(P(MacCall {
+            ExprKind::MacCall(Box::new(MacCall {
                 path: panic_path,
-                args: P(DelimArgs {
+                args: Box::new(DelimArgs {
                     dspan: DelimSpan::from_single(self.span),
                     delim: Delimiter::Parenthesis,
                     tokens: initial.into_iter().chain(captures).collect::<TokenStream>(),
@@ -190,7 +189,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
     /// Recursive function called until `cond_expr` and `fmt_str` are fully modified.
     ///
     /// See [Self::manage_initial_capture] and [Self::manage_try_capture]
-    fn manage_cond_expr(&mut self, expr: &mut P<Expr>) {
+    fn manage_cond_expr(&mut self, expr: &mut Box<Expr>) {
         match &mut expr.kind {
             ExprKind::AddrOf(_, mutability, local_expr) => {
                 self.with_is_consumed_management(matches!(mutability, Mutability::Mut), |this| {
@@ -331,7 +330,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
     ///
     /// `fmt_str`, the formatting string used for debugging, is constructed to show possible
     /// captured variables.
-    fn manage_initial_capture(&mut self, expr: &mut P<Expr>, path_ident: Ident) {
+    fn manage_initial_capture(&mut self, expr: &mut Box<Expr>, path_ident: Ident) {
         if self.paths.contains(&path_ident) {
             return;
         } else {
@@ -360,7 +359,12 @@ impl<'cx, 'a> Context<'cx, 'a> {
     ///    (&Wrapper(__local_bindN)).try_capture(&mut __captureN);
     ///    __local_bindN
     /// }
-    fn manage_try_capture(&mut self, capture: Ident, curr_capture_idx: usize, expr: &mut P<Expr>) {
+    fn manage_try_capture(
+        &mut self,
+        capture: Ident,
+        curr_capture_idx: usize,
+        expr: &mut Box<Expr>,
+    ) {
         let local_bind_string = format!("__local_bind{curr_capture_idx}");
         let local_bind = Ident::new(Symbol::intern(&local_bind_string), self.span);
         self.local_bind_decls.push(self.cx.stmt_let(
@@ -441,20 +445,20 @@ fn escape_to_fmt(s: &str) -> String {
     rslt
 }
 
-fn expr_addr_of_mut(cx: &ExtCtxt<'_>, sp: Span, e: P<Expr>) -> P<Expr> {
+fn expr_addr_of_mut(cx: &ExtCtxt<'_>, sp: Span, e: Box<Expr>) -> Box<Expr> {
     cx.expr(sp, ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mut, e))
 }
 
 fn expr_method_call(
     cx: &ExtCtxt<'_>,
     seg: PathSegment,
-    receiver: P<Expr>,
-    args: ThinVec<P<Expr>>,
+    receiver: Box<Expr>,
+    args: ThinVec<Box<Expr>>,
     span: Span,
-) -> P<Expr> {
+) -> Box<Expr> {
     cx.expr(span, ExprKind::MethodCall(Box::new(MethodCall { seg, receiver, args, span })))
 }
 
-fn expr_paren(cx: &ExtCtxt<'_>, sp: Span, e: P<Expr>) -> P<Expr> {
+fn expr_paren(cx: &ExtCtxt<'_>, sp: Span, e: Box<Expr>) -> Box<Expr> {
     cx.expr(sp, ExprKind::Paren(e))
 }
diff --git a/compiler/rustc_builtin_macros/src/autodiff.rs b/compiler/rustc_builtin_macros/src/autodiff.rs
index c7844778332..48d0795af5e 100644
--- a/compiler/rustc_builtin_macros/src/autodiff.rs
+++ b/compiler/rustc_builtin_macros/src/autodiff.rs
@@ -11,23 +11,23 @@ mod llvm_enzyme {
         AutoDiffAttrs, DiffActivity, DiffMode, valid_input_activity, valid_ret_activity,
         valid_ty_for_activity,
     };
-    use rustc_ast::ptr::P;
     use rustc_ast::token::{Lit, LitKind, Token, TokenKind};
     use rustc_ast::tokenstream::*;
     use rustc_ast::visit::AssocCtxt::*;
     use rustc_ast::{
-        self as ast, AssocItemKind, BindingMode, ExprKind, FnRetTy, FnSig, Generics, ItemKind,
-        MetaItemInner, PatKind, QSelf, TyKind, Visibility,
+        self as ast, AngleBracketedArg, AngleBracketedArgs, AnonConst, AssocItemKind, BindingMode,
+        FnRetTy, FnSig, GenericArg, GenericArgs, GenericParamKind, Generics, ItemKind,
+        MetaItemInner, PatKind, Path, PathSegment, TyKind, Visibility,
     };
     use rustc_expand::base::{Annotatable, ExtCtxt};
-    use rustc_span::{Ident, Span, Symbol, kw, sym};
+    use rustc_span::{Ident, Span, Symbol, sym};
     use thin_vec::{ThinVec, thin_vec};
     use tracing::{debug, trace};
 
     use crate::errors;
 
     pub(crate) fn outer_normal_attr(
-        kind: &P<rustc_ast::NormalAttr>,
+        kind: &Box<rustc_ast::NormalAttr>,
         id: rustc_ast::AttrId,
         span: Span,
     ) -> rustc_ast::Attribute {
@@ -73,7 +73,7 @@ mod llvm_enzyme {
     }
 
     // Get information about the function the macro is applied to
-    fn extract_item_info(iitem: &P<ast::Item>) -> Option<(Visibility, FnSig, Ident, Generics)> {
+    fn extract_item_info(iitem: &Box<ast::Item>) -> Option<(Visibility, FnSig, Ident, Generics)> {
         match &iitem.kind {
             ItemKind::Fn(box ast::Fn { sig, ident, generics, .. }) => {
                 Some((iitem.vis.clone(), sig.clone(), ident.clone(), generics.clone()))
@@ -180,11 +180,8 @@ mod llvm_enzyme {
     }
 
     /// We expand the autodiff macro to generate a new placeholder function which passes
-    /// type-checking and can be called by users. The function body of the placeholder function will
-    /// later be replaced on LLVM-IR level, so the design of the body is less important and for now
-    /// should just prevent early inlining and optimizations which alter the function signature.
-    /// The exact signature of the generated function depends on the configuration provided by the
-    /// user, but here is an example:
+    /// type-checking and can be called by users. The exact signature of the generated function
+    /// depends on the configuration provided by the user, but here is an example:
     ///
     /// ```
     /// #[autodiff(cos_box, Reverse, Duplicated, Active)]
@@ -195,19 +192,12 @@ mod llvm_enzyme {
     /// which becomes expanded to:
     /// ```
     /// #[rustc_autodiff]
-    /// #[inline(never)]
     /// fn sin(x: &Box<f32>) -> f32 {
     ///     f32::sin(**x)
     /// }
     /// #[rustc_autodiff(Reverse, Duplicated, Active)]
-    /// #[inline(never)]
     /// fn cos_box(x: &Box<f32>, dx: &mut Box<f32>, dret: f32) -> f32 {
-    ///     unsafe {
-    ///         asm!("NOP");
-    ///     };
-    ///     ::core::hint::black_box(sin(x));
-    ///     ::core::hint::black_box((dx, dret));
-    ///     ::core::hint::black_box(sin(x))
+    ///     std::intrinsics::autodiff(sin::<>, cos_box::<>, (x, dx, dret))
     /// }
     /// ```
     /// FIXME(ZuseZ4): Once autodiff is enabled by default, make this a doc comment which is checked
@@ -228,16 +218,24 @@ mod llvm_enzyme {
         // first get information about the annotable item: visibility, signature, name and generic
         // parameters.
         // these will be used to generate the differentiated version of the function
-        let Some((vis, sig, primal, generics)) = (match &item {
-            Annotatable::Item(iitem) => extract_item_info(iitem),
+        let Some((vis, sig, primal, generics, impl_of_trait)) = (match &item {
+            Annotatable::Item(iitem) => {
+                extract_item_info(iitem).map(|(v, s, p, g)| (v, s, p, g, false))
+            }
             Annotatable::Stmt(stmt) => match &stmt.kind {
-                ast::StmtKind::Item(iitem) => extract_item_info(iitem),
+                ast::StmtKind::Item(iitem) => {
+                    extract_item_info(iitem).map(|(v, s, p, g)| (v, s, p, g, false))
+                }
                 _ => None,
             },
-            Annotatable::AssocItem(assoc_item, Impl { .. }) => match &assoc_item.kind {
-                ast::AssocItemKind::Fn(box ast::Fn { sig, ident, generics, .. }) => {
-                    Some((assoc_item.vis.clone(), sig.clone(), ident.clone(), generics.clone()))
-                }
+            Annotatable::AssocItem(assoc_item, Impl { of_trait }) => match &assoc_item.kind {
+                ast::AssocItemKind::Fn(box ast::Fn { sig, ident, generics, .. }) => Some((
+                    assoc_item.vis.clone(),
+                    sig.clone(),
+                    ident.clone(),
+                    generics.clone(),
+                    *of_trait,
+                )),
                 _ => None,
             },
             _ => None,
@@ -255,7 +253,6 @@ mod llvm_enzyme {
         };
 
         let has_ret = has_ret(&sig.decl.output);
-        let sig_span = ecx.with_call_site_ctxt(sig.span);
 
         // create TokenStream from vec elemtents:
         // meta_item doesn't have a .tokens field
@@ -324,19 +321,23 @@ mod llvm_enzyme {
         }
         let span = ecx.with_def_site_ctxt(expand_span);
 
-        let n_active: u32 = x
-            .input_activity
-            .iter()
-            .filter(|a| **a == DiffActivity::Active || **a == DiffActivity::ActiveOnly)
-            .count() as u32;
-        let (d_sig, new_args, idents, errored) = gen_enzyme_decl(ecx, &sig, &x, span);
-        let d_body = gen_enzyme_body(
-            ecx, &x, n_active, &sig, &d_sig, primal, &new_args, span, sig_span, idents, errored,
-            &generics,
+        let d_sig = gen_enzyme_decl(ecx, &sig, &x, span);
+
+        let d_body = ecx.block(
+            span,
+            thin_vec![call_autodiff(
+                ecx,
+                primal,
+                first_ident(&meta_item_vec[0]),
+                span,
+                &d_sig,
+                &generics,
+                impl_of_trait,
+            )],
         );
 
         // The first element of it is the name of the function to be generated
-        let asdf = Box::new(ast::Fn {
+        let d_fn = Box::new(ast::Fn {
             defaultness: ast::Defaultness::Final,
             sig: d_sig,
             ident: first_ident(&meta_item_vec[0]),
@@ -346,7 +347,7 @@ mod llvm_enzyme {
             define_opaque: None,
         });
         let mut rustc_ad_attr =
-            P(ast::NormalAttr::from_ident(Ident::with_dummy_span(sym::rustc_autodiff)));
+            Box::new(ast::NormalAttr::from_ident(Ident::with_dummy_span(sym::rustc_autodiff)));
 
         let ts2: Vec<TokenTree> = vec![TokenTree::Token(
             Token::new(TokenKind::Ident(sym::never, false.into()), span),
@@ -363,13 +364,13 @@ mod llvm_enzyme {
             args: ast::AttrArgs::Delimited(never_arg),
             tokens: None,
         };
-        let inline_never_attr = P(ast::NormalAttr { item: inline_item, tokens: None });
+        let inline_never_attr = Box::new(ast::NormalAttr { item: inline_item, tokens: None });
         let new_id = ecx.sess.psess.attr_id_generator.mk_attr_id();
         let attr = outer_normal_attr(&rustc_ad_attr, new_id, span);
         let new_id = ecx.sess.psess.attr_id_generator.mk_attr_id();
         let inline_never = outer_normal_attr(&inline_never_attr, new_id, span);
 
-        // We're avoid duplicating the attributes `#[rustc_autodiff]` and `#[inline(never)]`.
+        // We're avoid duplicating the attribute `#[rustc_autodiff]`.
         fn same_attribute(attr: &ast::AttrKind, item: &ast::AttrKind) -> bool {
             match (attr, item) {
                 (ast::AttrKind::Normal(a), ast::AttrKind::Normal(b)) => {
@@ -382,14 +383,16 @@ mod llvm_enzyme {
             }
         }
 
+        let mut has_inline_never = false;
+
         // Don't add it multiple times:
         let orig_annotatable: Annotatable = match item {
             Annotatable::Item(ref mut iitem) => {
                 if !iitem.attrs.iter().any(|a| same_attribute(&a.kind, &attr.kind)) {
                     iitem.attrs.push(attr);
                 }
-                if !iitem.attrs.iter().any(|a| same_attribute(&a.kind, &inline_never.kind)) {
-                    iitem.attrs.push(inline_never.clone());
+                if iitem.attrs.iter().any(|a| same_attribute(&a.kind, &inline_never.kind)) {
+                    has_inline_never = true;
                 }
                 Annotatable::Item(iitem.clone())
             }
@@ -397,8 +400,8 @@ mod llvm_enzyme {
                 if !assoc_item.attrs.iter().any(|a| same_attribute(&a.kind, &attr.kind)) {
                     assoc_item.attrs.push(attr);
                 }
-                if !assoc_item.attrs.iter().any(|a| same_attribute(&a.kind, &inline_never.kind)) {
-                    assoc_item.attrs.push(inline_never.clone());
+                if assoc_item.attrs.iter().any(|a| same_attribute(&a.kind, &inline_never.kind)) {
+                    has_inline_never = true;
                 }
                 Annotatable::AssocItem(assoc_item.clone(), i)
             }
@@ -408,9 +411,8 @@ mod llvm_enzyme {
                         if !iitem.attrs.iter().any(|a| same_attribute(&a.kind, &attr.kind)) {
                             iitem.attrs.push(attr);
                         }
-                        if !iitem.attrs.iter().any(|a| same_attribute(&a.kind, &inline_never.kind))
-                        {
-                            iitem.attrs.push(inline_never.clone());
+                        if iitem.attrs.iter().any(|a| same_attribute(&a.kind, &inline_never.kind)) {
+                            has_inline_never = true;
                         }
                     }
                     _ => unreachable!("stmt kind checked previously"),
@@ -429,12 +431,21 @@ mod llvm_enzyme {
             tokens: ts,
         });
 
+        let new_id = ecx.sess.psess.attr_id_generator.mk_attr_id();
         let d_attr = outer_normal_attr(&rustc_ad_attr, new_id, span);
+
+        // If the source function has the `#[inline(never)]` attribute, we'll also add it to the diff function
+        let mut d_attrs = thin_vec![d_attr];
+
+        if has_inline_never {
+            d_attrs.push(inline_never);
+        }
+
         let d_annotatable = match &item {
             Annotatable::AssocItem(_, _) => {
-                let assoc_item: AssocItemKind = ast::AssocItemKind::Fn(asdf);
-                let d_fn = P(ast::AssocItem {
-                    attrs: thin_vec![d_attr, inline_never],
+                let assoc_item: AssocItemKind = ast::AssocItemKind::Fn(d_fn);
+                let d_fn = Box::new(ast::AssocItem {
+                    attrs: d_attrs,
                     id: ast::DUMMY_NODE_ID,
                     span,
                     vis,
@@ -444,16 +455,16 @@ mod llvm_enzyme {
                 Annotatable::AssocItem(d_fn, Impl { of_trait: false })
             }
             Annotatable::Item(_) => {
-                let mut d_fn = ecx.item(span, thin_vec![d_attr, inline_never], ItemKind::Fn(asdf));
+                let mut d_fn = ecx.item(span, d_attrs, ItemKind::Fn(d_fn));
                 d_fn.vis = vis;
 
                 Annotatable::Item(d_fn)
             }
             Annotatable::Stmt(_) => {
-                let mut d_fn = ecx.item(span, thin_vec![d_attr, inline_never], ItemKind::Fn(asdf));
+                let mut d_fn = ecx.item(span, d_attrs, ItemKind::Fn(d_fn));
                 d_fn.vis = vis;
 
-                Annotatable::Stmt(P(ast::Stmt {
+                Annotatable::Stmt(Box::new(ast::Stmt {
                     id: ast::DUMMY_NODE_ID,
                     kind: ast::StmtKind::Item(d_fn),
                     span,
@@ -485,282 +496,95 @@ mod llvm_enzyme {
         ty
     }
 
-    // Will generate a body of the type:
+    // Generate `autodiff` intrinsic call
     // ```
-    // {
-    //   unsafe {
-    //   asm!("NOP");
-    //   }
-    //   ::core::hint::black_box(primal(args));
-    //   ::core::hint::black_box((args, ret));
-    //   <This part remains to be done by following function>
-    // }
+    // std::intrinsics::autodiff(source, diff, (args))
     // ```
-    fn init_body_helper(
+    fn call_autodiff(
         ecx: &ExtCtxt<'_>,
-        span: Span,
         primal: Ident,
-        new_names: &[String],
-        sig_span: Span,
-        new_decl_span: Span,
-        idents: &[Ident],
-        errored: bool,
+        diff: Ident,
+        span: Span,
+        d_sig: &FnSig,
         generics: &Generics,
-    ) -> (P<ast::Block>, P<ast::Expr>, P<ast::Expr>, P<ast::Expr>) {
-        let blackbox_path = ecx.std_path(&[sym::hint, sym::black_box]);
-        let noop = ast::InlineAsm {
-            asm_macro: ast::AsmMacro::Asm,
-            template: vec![ast::InlineAsmTemplatePiece::String("NOP".into())],
-            template_strs: Box::new([]),
-            operands: vec![],
-            clobber_abis: vec![],
-            options: ast::InlineAsmOptions::PURE | ast::InlineAsmOptions::NOMEM,
-            line_spans: vec![],
-        };
-        let noop_expr = ecx.expr_asm(span, P(noop));
-        let unsf = ast::BlockCheckMode::Unsafe(ast::UnsafeSource::CompilerGenerated);
-        let unsf_block = ast::Block {
-            stmts: thin_vec![ecx.stmt_semi(noop_expr)],
-            id: ast::DUMMY_NODE_ID,
-            tokens: None,
-            rules: unsf,
+        is_impl: bool,
+    ) -> rustc_ast::Stmt {
+        let primal_path_expr = gen_turbofish_expr(ecx, primal, generics, span, is_impl);
+        let diff_path_expr = gen_turbofish_expr(ecx, diff, generics, span, is_impl);
+
+        let tuple_expr = ecx.expr_tuple(
             span,
-        };
-        let unsf_expr = ecx.expr_block(P(unsf_block));
-        let blackbox_call_expr = ecx.expr_path(ecx.path(span, blackbox_path));
-        let primal_call = gen_primal_call(ecx, span, primal, idents, generics);
-        let black_box_primal_call = ecx.expr_call(
-            new_decl_span,
-            blackbox_call_expr.clone(),
-            thin_vec![primal_call.clone()],
+            d_sig
+                .decl
+                .inputs
+                .iter()
+                .map(|arg| match arg.pat.kind {
+                    PatKind::Ident(_, ident, _) => ecx.expr_path(ecx.path_ident(span, ident)),
+                    _ => todo!(),
+                })
+                .collect::<ThinVec<_>>()
+                .into(),
         );
-        let tup_args = new_names
-            .iter()
-            .map(|arg| ecx.expr_path(ecx.path_ident(span, Ident::from_str(arg))))
-            .collect();
 
-        let black_box_remaining_args = ecx.expr_call(
-            sig_span,
-            blackbox_call_expr.clone(),
-            thin_vec![ecx.expr_tuple(sig_span, tup_args)],
+        let enzyme_path_idents = ecx.std_path(&[sym::intrinsics, sym::autodiff]);
+        let enzyme_path = ecx.path(span, enzyme_path_idents);
+        let call_expr = ecx.expr_call(
+            span,
+            ecx.expr_path(enzyme_path),
+            vec![primal_path_expr, diff_path_expr, tuple_expr].into(),
         );
 
-        let mut body = ecx.block(span, ThinVec::new());
-        body.stmts.push(ecx.stmt_semi(unsf_expr));
-
-        // This uses primal args which won't be available if we errored before
-        if !errored {
-            body.stmts.push(ecx.stmt_semi(black_box_primal_call.clone()));
-        }
-        body.stmts.push(ecx.stmt_semi(black_box_remaining_args));
-
-        (body, primal_call, black_box_primal_call, blackbox_call_expr)
+        ecx.stmt_expr(call_expr)
     }
 
-    /// We only want this function to type-check, since we will replace the body
-    /// later on llvm level. Using `loop {}` does not cover all return types anymore,
-    /// so instead we manually build something that should pass the type checker.
-    /// We also add a inline_asm line, as one more barrier for rustc to prevent inlining
-    /// or const propagation. inline_asm will also triggers an Enzyme crash if due to another
-    /// bug would ever try to accidentally differentiate this placeholder function body.
-    /// Finally, we also add back_box usages of all input arguments, to prevent rustc
-    /// from optimizing any arguments away.
-    fn gen_enzyme_body(
+    // Generate turbofish expression from fn name and generics
+    // Given `foo` and `<A, B, C>` params, gen `foo::<A, B, C>`
+    // We use this expression when passing primal and diff function to the autodiff intrinsic
+    fn gen_turbofish_expr(
         ecx: &ExtCtxt<'_>,
-        x: &AutoDiffAttrs,
-        n_active: u32,
-        sig: &ast::FnSig,
-        d_sig: &ast::FnSig,
-        primal: Ident,
-        new_names: &[String],
-        span: Span,
-        sig_span: Span,
-        idents: Vec<Ident>,
-        errored: bool,
+        ident: Ident,
         generics: &Generics,
-    ) -> P<ast::Block> {
-        let new_decl_span = d_sig.span;
-
-        // Just adding some default inline-asm and black_box usages to prevent early inlining
-        // and optimizations which alter the function signature.
-        //
-        // The bb_primal_call is the black_box call of the primal function. We keep it around,
-        // since it has the convenient property of returning the type of the primal function,
-        // Remember, we only care to match types here.
-        // No matter which return we pick, we always wrap it into a std::hint::black_box call,
-        // to prevent rustc from propagating it into the caller.
-        let (mut body, primal_call, bb_primal_call, bb_call_expr) = init_body_helper(
-            ecx,
-            span,
-            primal,
-            new_names,
-            sig_span,
-            new_decl_span,
-            &idents,
-            errored,
-            generics,
-        );
-
-        if !has_ret(&d_sig.decl.output) {
-            // there is no return type that we have to match, () works fine.
-            return body;
-        }
-
-        // Everything from here onwards just tries to fulfil the return type. Fun!
-
-        // having an active-only return means we'll drop the original return type.
-        // So that can be treated identical to not having one in the first place.
-        let primal_ret = has_ret(&sig.decl.output) && !x.has_active_only_ret();
-
-        if primal_ret && n_active == 0 && x.mode.is_rev() {
-            // We only have the primal ret.
-            body.stmts.push(ecx.stmt_expr(bb_primal_call));
-            return body;
-        }
-
-        if !primal_ret && n_active == 1 {
-            // Again no tuple return, so return default float val.
-            let ty = match d_sig.decl.output {
-                FnRetTy::Ty(ref ty) => ty.clone(),
-                FnRetTy::Default(span) => {
-                    panic!("Did not expect Default ret ty: {:?}", span);
+        span: Span,
+        is_impl: bool,
+    ) -> Box<ast::Expr> {
+        let generic_args = generics
+            .params
+            .iter()
+            .filter_map(|p| match &p.kind {
+                GenericParamKind::Type { .. } => {
+                    let path = ast::Path::from_ident(p.ident);
+                    let ty = ecx.ty_path(path);
+                    Some(AngleBracketedArg::Arg(GenericArg::Type(ty)))
                 }
-            };
-            let arg = ty.kind.is_simple_path().unwrap();
-            let tmp = ecx.def_site_path(&[arg, kw::Default]);
-            let default_call_expr = ecx.expr_path(ecx.path(span, tmp));
-            let default_call_expr = ecx.expr_call(new_decl_span, default_call_expr, thin_vec![]);
-            body.stmts.push(ecx.stmt_expr(default_call_expr));
-            return body;
-        }
-
-        let mut exprs: P<ast::Expr> = primal_call;
-        let d_ret_ty = match d_sig.decl.output {
-            FnRetTy::Ty(ref ty) => ty.clone(),
-            FnRetTy::Default(span) => {
-                panic!("Did not expect Default ret ty: {:?}", span);
-            }
-        };
-        if x.mode.is_fwd() {
-            // Fwd mode is easy. If the return activity is Const, we support arbitrary types.
-            // Otherwise, we only support a scalar, a pair of scalars, or an array of scalars.
-            // We checked that (on a best-effort base) in the preceding gen_enzyme_decl function.
-            // In all three cases, we can return `std::hint::black_box(<T>::default())`.
-            if x.ret_activity == DiffActivity::Const {
-                // Here we call the primal function, since our dummy function has the same return
-                // type due to the Const return activity.
-                exprs = ecx.expr_call(new_decl_span, bb_call_expr, thin_vec![exprs]);
-            } else {
-                let q = QSelf { ty: d_ret_ty, path_span: span, position: 0 };
-                let y = ExprKind::Path(
-                    Some(P(q)),
-                    ecx.path_ident(span, Ident::with_dummy_span(kw::Default)),
-                );
-                let default_call_expr = ecx.expr(span, y);
-                let default_call_expr =
-                    ecx.expr_call(new_decl_span, default_call_expr, thin_vec![]);
-                exprs = ecx.expr_call(new_decl_span, bb_call_expr, thin_vec![default_call_expr]);
-            }
-        } else if x.mode.is_rev() {
-            if x.width == 1 {
-                // We either have `-> ArbitraryType` or `-> (ArbitraryType, repeated_float_scalars)`.
-                match d_ret_ty.kind {
-                    TyKind::Tup(ref args) => {
-                        // We have a tuple return type. We need to create a tuple of the same size
-                        // and fill it with default values.
-                        let mut exprs2 = thin_vec![exprs];
-                        for arg in args.iter().skip(1) {
-                            let arg = arg.kind.is_simple_path().unwrap();
-                            let tmp = ecx.def_site_path(&[arg, kw::Default]);
-                            let default_call_expr = ecx.expr_path(ecx.path(span, tmp));
-                            let default_call_expr =
-                                ecx.expr_call(new_decl_span, default_call_expr, thin_vec![]);
-                            exprs2.push(default_call_expr);
-                        }
-                        exprs = ecx.expr_tuple(new_decl_span, exprs2);
-                    }
-                    _ => {
-                        // Interestingly, even the `-> ArbitraryType` case
-                        // ends up getting matched and handled correctly above,
-                        // so we don't have to handle any other case for now.
-                        panic!("Unsupported return type: {:?}", d_ret_ty);
-                    }
+                GenericParamKind::Const { .. } => {
+                    let expr = ecx.expr_path(ast::Path::from_ident(p.ident));
+                    let anon_const = AnonConst { id: ast::DUMMY_NODE_ID, value: expr };
+                    Some(AngleBracketedArg::Arg(GenericArg::Const(anon_const)))
                 }
-            }
-            exprs = ecx.expr_call(new_decl_span, bb_call_expr, thin_vec![exprs]);
-        } else {
-            unreachable!("Unsupported mode: {:?}", x.mode);
-        }
+                GenericParamKind::Lifetime { .. } => None,
+            })
+            .collect::<ThinVec<_>>();
 
-        body.stmts.push(ecx.stmt_expr(exprs));
+        let args: AngleBracketedArgs = AngleBracketedArgs { span, args: generic_args };
 
-        body
-    }
+        let segment = PathSegment {
+            ident,
+            id: ast::DUMMY_NODE_ID,
+            args: Some(Box::new(GenericArgs::AngleBracketed(args))),
+        };
 
-    fn gen_primal_call(
-        ecx: &ExtCtxt<'_>,
-        span: Span,
-        primal: Ident,
-        idents: &[Ident],
-        generics: &Generics,
-    ) -> P<ast::Expr> {
-        let has_self = idents.len() > 0 && idents[0].name == kw::SelfLower;
-
-        if has_self {
-            let args: ThinVec<_> =
-                idents[1..].iter().map(|arg| ecx.expr_path(ecx.path_ident(span, *arg))).collect();
-            let self_expr = ecx.expr_self(span);
-            ecx.expr_method_call(span, self_expr, primal, args)
+        let segments = if is_impl {
+            thin_vec![
+                PathSegment { ident: Ident::from_str("Self"), id: ast::DUMMY_NODE_ID, args: None },
+                segment,
+            ]
         } else {
-            let args: ThinVec<_> =
-                idents.iter().map(|arg| ecx.expr_path(ecx.path_ident(span, *arg))).collect();
-            let mut primal_path = ecx.path_ident(span, primal);
-
-            let is_generic = !generics.params.is_empty();
-
-            match (is_generic, primal_path.segments.last_mut()) {
-                (true, Some(function_path)) => {
-                    let primal_generic_types = generics
-                        .params
-                        .iter()
-                        .filter(|param| matches!(param.kind, ast::GenericParamKind::Type { .. }));
-
-                    let generated_generic_types = primal_generic_types
-                        .map(|type_param| {
-                            let generic_param = TyKind::Path(
-                                None,
-                                ast::Path {
-                                    span,
-                                    segments: thin_vec![ast::PathSegment {
-                                        ident: type_param.ident,
-                                        args: None,
-                                        id: ast::DUMMY_NODE_ID,
-                                    }],
-                                    tokens: None,
-                                },
-                            );
-
-                            ast::AngleBracketedArg::Arg(ast::GenericArg::Type(P(ast::Ty {
-                                id: type_param.id,
-                                span,
-                                kind: generic_param,
-                                tokens: None,
-                            })))
-                        })
-                        .collect();
-
-                    function_path.args =
-                        Some(P(ast::GenericArgs::AngleBracketed(ast::AngleBracketedArgs {
-                            span,
-                            args: generated_generic_types,
-                        })));
-                }
-                _ => {}
-            }
+            thin_vec![segment]
+        };
 
-            let primal_call_expr = ecx.expr_path(primal_path);
-            ecx.expr_call(span, primal_call_expr, args)
-        }
+        let path = Path { span, segments, tokens: None };
+
+        ecx.expr_path(path)
     }
 
     // Generate the new function declaration. Const arguments are kept as is. Duplicated arguments must
@@ -779,7 +603,7 @@ mod llvm_enzyme {
         sig: &ast::FnSig,
         x: &AutoDiffAttrs,
         span: Span,
-    ) -> (ast::FnSig, Vec<String>, Vec<Ident>, bool) {
+    ) -> ast::FnSig {
         let dcx = ecx.sess.dcx();
         let has_ret = has_ret(&sig.decl.output);
         let sig_args = sig.decl.inputs.len() + if has_ret { 1 } else { 0 };
@@ -791,7 +615,7 @@ mod llvm_enzyme {
                 found: num_activities,
             });
             // This is not the right signature, but we can continue parsing.
-            return (sig.clone(), vec![], vec![], true);
+            return sig.clone();
         }
         assert!(sig.decl.inputs.len() == x.input_activity.len());
         assert!(has_ret == x.has_ret_activity());
@@ -834,7 +658,7 @@ mod llvm_enzyme {
 
         if errors {
             // This is not the right signature, but we can continue parsing.
-            return (sig.clone(), new_inputs, idents, true);
+            return sig.clone();
         }
 
         let unsafe_activities = x
@@ -856,7 +680,7 @@ mod llvm_enzyme {
                     for i in 0..x.width {
                         let mut shadow_arg = arg.clone();
                         // We += into the shadow in reverse mode.
-                        shadow_arg.ty = P(assure_mut_ref(&arg.ty));
+                        shadow_arg.ty = Box::new(assure_mut_ref(&arg.ty));
                         let old_name = if let PatKind::Ident(_, ident, _) = arg.pat.kind {
                             ident.name
                         } else {
@@ -866,7 +690,7 @@ mod llvm_enzyme {
                         let name: String = format!("d{}_{}", old_name, i);
                         new_inputs.push(name.clone());
                         let ident = Ident::from_str_and_span(&name, shadow_arg.pat.span);
-                        shadow_arg.pat = P(ast::Pat {
+                        shadow_arg.pat = Box::new(ast::Pat {
                             id: ast::DUMMY_NODE_ID,
                             kind: PatKind::Ident(BindingMode::NONE, ident, None),
                             span: shadow_arg.pat.span,
@@ -898,7 +722,7 @@ mod llvm_enzyme {
                         let name: String = format!("b{}_{}", old_name, i);
                         new_inputs.push(name.clone());
                         let ident = Ident::from_str_and_span(&name, shadow_arg.pat.span);
-                        shadow_arg.pat = P(ast::Pat {
+                        shadow_arg.pat = Box::new(ast::Pat {
                             id: ast::DUMMY_NODE_ID,
                             kind: PatKind::Ident(BindingMode::NONE, ident, None),
                             span: shadow_arg.pat.span,
@@ -942,7 +766,7 @@ mod llvm_enzyme {
                     let shadow_arg = ast::Param {
                         attrs: ThinVec::new(),
                         ty: ty.clone(),
-                        pat: P(ast::Pat {
+                        pat: Box::new(ast::Pat {
                             id: ast::DUMMY_NODE_ID,
                             kind: PatKind::Ident(BindingMode::NONE, ident, None),
                             span: ty.span,
@@ -966,7 +790,12 @@ mod llvm_enzyme {
                 FnRetTy::Default(span) => {
                     // We want to return std::hint::black_box(()).
                     let kind = TyKind::Tup(ThinVec::new());
-                    let ty = P(rustc_ast::Ty { kind, id: ast::DUMMY_NODE_ID, span, tokens: None });
+                    let ty = Box::new(rustc_ast::Ty {
+                        kind,
+                        id: ast::DUMMY_NODE_ID,
+                        span,
+                        tokens: None,
+                    });
                     d_decl.output = FnRetTy::Ty(ty.clone());
                     assert!(matches!(x.ret_activity, DiffActivity::None));
                     // this won't be used below, so any type would be fine.
@@ -987,7 +816,7 @@ mod llvm_enzyme {
                     };
                     TyKind::Array(ty.clone(), anon_const)
                 };
-                let ty = P(rustc_ast::Ty { kind, id: ty.id, span: ty.span, tokens: None });
+                let ty = Box::new(rustc_ast::Ty { kind, id: ty.id, span: ty.span, tokens: None });
                 d_decl.output = FnRetTy::Ty(ty);
             }
             if matches!(x.ret_activity, DiffActivity::DualOnly | DiffActivity::DualvOnly) {
@@ -1000,7 +829,8 @@ mod llvm_enzyme {
                         value: ecx.expr_usize(span, x.width as usize),
                     };
                     let kind = TyKind::Array(ty.clone(), anon_const);
-                    let ty = P(rustc_ast::Ty { kind, id: ty.id, span: ty.span, tokens: None });
+                    let ty =
+                        Box::new(rustc_ast::Ty { kind, id: ty.id, span: ty.span, tokens: None });
                     d_decl.output = FnRetTy::Ty(ty);
                 }
             }
@@ -1022,14 +852,14 @@ mod llvm_enzyme {
                         act_ret.insert(0, ty.clone());
                     }
                     let kind = TyKind::Tup(act_ret);
-                    P(rustc_ast::Ty { kind, id: ty.id, span: ty.span, tokens: None })
+                    Box::new(rustc_ast::Ty { kind, id: ty.id, span: ty.span, tokens: None })
                 }
                 FnRetTy::Default(span) => {
                     if act_ret.len() == 1 {
                         act_ret[0].clone()
                     } else {
                         let kind = TyKind::Tup(act_ret.iter().map(|arg| arg.clone()).collect());
-                        P(rustc_ast::Ty { kind, id: ast::DUMMY_NODE_ID, span, tokens: None })
+                        Box::new(rustc_ast::Ty { kind, id: ast::DUMMY_NODE_ID, span, tokens: None })
                     }
                 }
             };
@@ -1042,7 +872,7 @@ mod llvm_enzyme {
         }
         let d_sig = FnSig { header: d_header, decl: d_decl, span };
         trace!("Generated signature: {:?}", d_sig);
-        (d_sig, new_inputs, idents, false)
+        d_sig
     }
 }
 
diff --git a/compiler/rustc_builtin_macros/src/cfg_accessible.rs b/compiler/rustc_builtin_macros/src/cfg_accessible.rs
index 5f203dd5d11..f7d8f4aa783 100644
--- a/compiler/rustc_builtin_macros/src/cfg_accessible.rs
+++ b/compiler/rustc_builtin_macros/src/cfg_accessible.rs
@@ -44,7 +44,7 @@ impl MultiItemModifier for Expander {
         item: Annotatable,
         _is_derive_const: bool,
     ) -> ExpandResult<Vec<Annotatable>, Annotatable> {
-        let template = AttributeTemplate { list: Some("path"), ..Default::default() };
+        let template = AttributeTemplate { list: Some(&["path"]), ..Default::default() };
         validate_attr::check_builtin_meta_item(
             &ecx.sess.psess,
             meta_item,
diff --git a/compiler/rustc_builtin_macros/src/cfg_eval.rs b/compiler/rustc_builtin_macros/src/cfg_eval.rs
index ec3b87467a9..dd770fe5f1a 100644
--- a/compiler/rustc_builtin_macros/src/cfg_eval.rs
+++ b/compiler/rustc_builtin_macros/src/cfg_eval.rs
@@ -2,7 +2,6 @@ use core::ops::ControlFlow;
 
 use rustc_ast as ast;
 use rustc_ast::mut_visit::MutVisitor;
-use rustc_ast::ptr::P;
 use rustc_ast::visit::{AssocCtxt, Visitor};
 use rustc_ast::{Attribute, HasAttrs, HasTokens, NodeId, mut_visit, visit};
 use rustc_errors::PResult;
@@ -132,7 +131,7 @@ impl CfgEval<'_> {
                     let stmt = parser
                         .parse_stmt_without_recovery(false, ForceCollect::Yes, false)?
                         .unwrap();
-                    Annotatable::Stmt(P(self.flat_map_stmt(stmt).pop().unwrap()))
+                    Annotatable::Stmt(Box::new(self.flat_map_stmt(stmt).pop().unwrap()))
                 }
                 Annotatable::Expr(_) => {
                     let mut expr = parser.parse_expr_force_collect()?;
@@ -166,7 +165,7 @@ impl MutVisitor for CfgEval<'_> {
         mut_visit::walk_expr(self, expr);
     }
 
-    fn filter_map_expr(&mut self, expr: P<ast::Expr>) -> Option<P<ast::Expr>> {
+    fn filter_map_expr(&mut self, expr: Box<ast::Expr>) -> Option<Box<ast::Expr>> {
         let mut expr = configure!(self, expr);
         mut_visit::walk_expr(self, &mut expr);
         Some(expr)
@@ -185,24 +184,24 @@ impl MutVisitor for CfgEval<'_> {
         mut_visit::walk_flat_map_stmt(self, stmt)
     }
 
-    fn flat_map_item(&mut self, item: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
+    fn flat_map_item(&mut self, item: Box<ast::Item>) -> SmallVec<[Box<ast::Item>; 1]> {
         let item = configure!(self, item);
         mut_visit::walk_flat_map_item(self, item)
     }
 
     fn flat_map_assoc_item(
         &mut self,
-        item: P<ast::AssocItem>,
+        item: Box<ast::AssocItem>,
         ctxt: AssocCtxt,
-    ) -> SmallVec<[P<ast::AssocItem>; 1]> {
+    ) -> SmallVec<[Box<ast::AssocItem>; 1]> {
         let item = configure!(self, item);
         mut_visit::walk_flat_map_assoc_item(self, item, ctxt)
     }
 
     fn flat_map_foreign_item(
         &mut self,
-        foreign_item: P<ast::ForeignItem>,
-    ) -> SmallVec<[P<ast::ForeignItem>; 1]> {
+        foreign_item: Box<ast::ForeignItem>,
+    ) -> SmallVec<[Box<ast::ForeignItem>; 1]> {
         let foreign_item = configure!(self, foreign_item);
         mut_visit::walk_flat_map_foreign_item(self, foreign_item)
     }
diff --git a/compiler/rustc_builtin_macros/src/concat_bytes.rs b/compiler/rustc_builtin_macros/src/concat_bytes.rs
index fd2d740c020..8885017b930 100644
--- a/compiler/rustc_builtin_macros/src/concat_bytes.rs
+++ b/compiler/rustc_builtin_macros/src/concat_bytes.rs
@@ -1,4 +1,3 @@
-use rustc_ast::ptr::P;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::{ExprKind, LitIntType, LitKind, StrStyle, UintTy, token};
 use rustc_expand::base::{DummyResult, ExpandResult, ExtCtxt, MacEager, MacroExpanderResult};
@@ -90,7 +89,7 @@ fn handle_array_element(
     cx: &ExtCtxt<'_>,
     guar: &mut Option<ErrorGuaranteed>,
     missing_literals: &mut Vec<rustc_span::Span>,
-    expr: &P<rustc_ast::Expr>,
+    expr: &Box<rustc_ast::Expr>,
 ) -> Option<u8> {
     let dcx = cx.dcx();
 
diff --git a/compiler/rustc_builtin_macros/src/derive.rs b/compiler/rustc_builtin_macros/src/derive.rs
index e259f5b3955..a33eca43de5 100644
--- a/compiler/rustc_builtin_macros/src/derive.rs
+++ b/compiler/rustc_builtin_macros/src/derive.rs
@@ -34,8 +34,10 @@ impl MultiItemModifier for Expander {
         let (sess, features) = (ecx.sess, ecx.ecfg.features);
         let result =
             ecx.resolver.resolve_derives(ecx.current_expansion.id, ecx.force_mode, &|| {
-                let template =
-                    AttributeTemplate { list: Some("Trait1, Trait2, ..."), ..Default::default() };
+                let template = AttributeTemplate {
+                    list: Some(&["Trait1, Trait2, ..."]),
+                    ..Default::default()
+                };
                 validate_attr::check_builtin_meta_item(
                     &sess.psess,
                     meta_item,
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
index 990835fa277..a0f71a1868b 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
@@ -1,4 +1,3 @@
-use rustc_ast::ptr::P;
 use rustc_ast::{BinOpKind, BorrowKind, Expr, ExprKind, MetaItem, Mutability};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::{Span, sym};
@@ -119,7 +118,7 @@ fn get_substructure_equality_expr(
     cx: &ExtCtxt<'_>,
     span: Span,
     substructure: &Substructure<'_>,
-) -> P<Expr> {
+) -> Box<Expr> {
     use SubstructureFields::*;
 
     match substructure.fields {
@@ -180,7 +179,7 @@ fn get_substructure_equality_expr(
 ///
 /// Panics if there are not exactly two arguments to compare (should be `self`
 /// and `other`).
-fn get_field_equality_expr(cx: &ExtCtxt<'_>, field: &FieldInfo) -> P<Expr> {
+fn get_field_equality_expr(cx: &ExtCtxt<'_>, field: &FieldInfo) -> Box<Expr> {
     let [rhs] = &field.other_selflike_exprs[..] else {
         cx.dcx().span_bug(field.span, "not exactly 2 arguments in `derive(PartialEq)`");
     };
@@ -198,7 +197,7 @@ fn get_field_equality_expr(cx: &ExtCtxt<'_>, field: &FieldInfo) -> P<Expr> {
 /// This is used to strip away any number of leading `&` from an expression
 /// (e.g., `&&&T` becomes `T`). Only removes immutable references; mutable
 /// references are preserved.
-fn peel_refs(mut expr: &P<Expr>) -> P<Expr> {
+fn peel_refs(mut expr: &Box<Expr>) -> Box<Expr> {
     while let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, inner) = &expr.kind {
         expr = &inner;
     }
@@ -210,7 +209,7 @@ fn peel_refs(mut expr: &P<Expr>) -> P<Expr> {
 ///
 /// If the given expression is a block, it is wrapped in parentheses; otherwise,
 /// it is returned unchanged.
-fn wrap_block_expr(cx: &ExtCtxt<'_>, expr: P<Expr>) -> P<Expr> {
+fn wrap_block_expr(cx: &ExtCtxt<'_>, expr: Box<Expr>) -> Box<Expr> {
     if matches!(&expr.kind, ExprKind::Block(..)) {
         return cx.expr_paren(expr.span, expr);
     }
diff --git a/compiler/rustc_builtin_macros/src/deriving/coerce_pointee.rs b/compiler/rustc_builtin_macros/src/deriving/coerce_pointee.rs
index 6082e376435..75db5d77783 100644
--- a/compiler/rustc_builtin_macros/src/deriving/coerce_pointee.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/coerce_pointee.rs
@@ -108,11 +108,7 @@ pub(crate) fn expand_deriving_coerce_pointee(
             cx.item(
                 span,
                 attrs.clone(),
-                ast::ItemKind::Impl(Box::new(ast::Impl {
-                    safety: ast::Safety::Default,
-                    polarity: ast::ImplPolarity::Positive,
-                    defaultness: ast::Defaultness::Final,
-                    constness: ast::Const::No,
+                ast::ItemKind::Impl(ast::Impl {
                     generics: Generics {
                         params: generics
                             .params
@@ -137,10 +133,16 @@ pub(crate) fn expand_deriving_coerce_pointee(
                         where_clause: generics.where_clause.clone(),
                         span: generics.span,
                     },
-                    of_trait: Some(trait_ref),
+                    of_trait: Some(Box::new(ast::TraitImplHeader {
+                        safety: ast::Safety::Default,
+                        polarity: ast::ImplPolarity::Positive,
+                        defaultness: ast::Defaultness::Final,
+                        constness: ast::Const::No,
+                        trait_ref,
+                    })),
                     self_ty: self_type.clone(),
                     items: ThinVec::new(),
-                })),
+                }),
             ),
         ));
     }
@@ -152,16 +154,18 @@ pub(crate) fn expand_deriving_coerce_pointee(
         let item = cx.item(
             span,
             attrs.clone(),
-            ast::ItemKind::Impl(Box::new(ast::Impl {
-                safety: ast::Safety::Default,
-                polarity: ast::ImplPolarity::Positive,
-                defaultness: ast::Defaultness::Final,
-                constness: ast::Const::No,
+            ast::ItemKind::Impl(ast::Impl {
                 generics,
-                of_trait: Some(trait_ref),
+                of_trait: Some(Box::new(ast::TraitImplHeader {
+                    safety: ast::Safety::Default,
+                    polarity: ast::ImplPolarity::Positive,
+                    defaultness: ast::Defaultness::Final,
+                    constness: ast::Const::No,
+                    trait_ref,
+                })),
                 self_ty: self_type.clone(),
                 items: ThinVec::new(),
-            })),
+            }),
         );
         push(Annotatable::Item(item));
     };
diff --git a/compiler/rustc_builtin_macros/src/deriving/debug.rs b/compiler/rustc_builtin_macros/src/deriving/debug.rs
index 1d63ce7d5fd..597af0e09c0 100644
--- a/compiler/rustc_builtin_macros/src/deriving/debug.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/debug.rs
@@ -94,7 +94,7 @@ fn show_substructure(cx: &ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) ->
         field: &FieldInfo,
         index: usize,
         len: usize,
-    ) -> ast::ptr::P<ast::Expr> {
+    ) -> Box<ast::Expr> {
         if index < len - 1 {
             field.self_expr.clone()
         } else {
diff --git a/compiler/rustc_builtin_macros/src/deriving/default.rs b/compiler/rustc_builtin_macros/src/deriving/default.rs
index b4e2d27fed3..2462114ec24 100644
--- a/compiler/rustc_builtin_macros/src/deriving/default.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/default.rs
@@ -56,7 +56,7 @@ pub(crate) fn expand_deriving_default(
     trait_def.expand(cx, mitem, item, push)
 }
 
-fn default_call(cx: &ExtCtxt<'_>, span: Span) -> ast::ptr::P<ast::Expr> {
+fn default_call(cx: &ExtCtxt<'_>, span: Span) -> Box<ast::Expr> {
     // Note that `kw::Default` is "default" and `sym::Default` is "Default"!
     let default_ident = cx.std_path(&[kw::Default, sym::Default, kw::Default]);
     cx.expr_call_global(span, default_ident, ThinVec::new())
diff --git a/compiler/rustc_builtin_macros/src/deriving/from.rs b/compiler/rustc_builtin_macros/src/deriving/from.rs
new file mode 100644
index 00000000000..ef0e6ca324a
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/deriving/from.rs
@@ -0,0 +1,132 @@
+use rustc_ast as ast;
+use rustc_ast::{ItemKind, VariantData};
+use rustc_errors::MultiSpan;
+use rustc_expand::base::{Annotatable, DummyResult, ExtCtxt};
+use rustc_span::{Ident, Span, kw, sym};
+use thin_vec::thin_vec;
+
+use crate::deriving::generic::ty::{Bounds, Path, PathKind, Ty};
+use crate::deriving::generic::{
+    BlockOrExpr, FieldlessVariantsStrategy, MethodDef, SubstructureFields, TraitDef,
+    combine_substructure,
+};
+use crate::deriving::pathvec_std;
+use crate::errors;
+
+/// Generate an implementation of the `From` trait, provided that `item`
+/// is a struct or a tuple struct with exactly one field.
+pub(crate) fn expand_deriving_from(
+    cx: &ExtCtxt<'_>,
+    span: Span,
+    mitem: &ast::MetaItem,
+    annotatable: &Annotatable,
+    push: &mut dyn FnMut(Annotatable),
+    is_const: bool,
+) {
+    let Annotatable::Item(item) = &annotatable else {
+        cx.dcx().bug("derive(From) used on something else than an item");
+    };
+
+    // #[derive(From)] is currently usable only on structs with exactly one field.
+    let field = if let ItemKind::Struct(_, _, data) = &item.kind
+        && let [field] = data.fields()
+    {
+        Some(field.clone())
+    } else {
+        None
+    };
+
+    let from_type = match &field {
+        Some(field) => Ty::AstTy(field.ty.clone()),
+        // We don't have a type to put into From<...> if we don't have a single field, so just put
+        // unit there.
+        None => Ty::Unit,
+    };
+    let path =
+        Path::new_(pathvec_std!(convert::From), vec![Box::new(from_type.clone())], PathKind::Std);
+
+    // Generate code like this:
+    //
+    // struct S(u32);
+    // #[automatically_derived]
+    // impl ::core::convert::From<u32> for S {
+    //     #[inline]
+    //     fn from(value: u32) -> S {
+    //         Self(value)
+    //     }
+    // }
+    let from_trait_def = TraitDef {
+        span,
+        path,
+        skip_path_as_bound: true,
+        needs_copy_as_bound_if_packed: false,
+        additional_bounds: Vec::new(),
+        supports_unions: false,
+        methods: vec![MethodDef {
+            name: sym::from,
+            generics: Bounds { bounds: vec![] },
+            explicit_self: false,
+            nonself_args: vec![(from_type, sym::value)],
+            ret_ty: Ty::Self_,
+            attributes: thin_vec![cx.attr_word(sym::inline, span)],
+            fieldless_variants_strategy: FieldlessVariantsStrategy::Default,
+            combine_substructure: combine_substructure(Box::new(|cx, span, substructure| {
+                let Some(field) = &field else {
+                    let item_span = item.kind.ident().map(|ident| ident.span).unwrap_or(item.span);
+                    let err_span = MultiSpan::from_spans(vec![span, item_span]);
+                    let error = match &item.kind {
+                        ItemKind::Struct(_, _, data) => {
+                            cx.dcx().emit_err(errors::DeriveFromWrongFieldCount {
+                                span: err_span,
+                                multiple_fields: data.fields().len() > 1,
+                            })
+                        }
+                        ItemKind::Enum(_, _, _) | ItemKind::Union(_, _, _) => {
+                            cx.dcx().emit_err(errors::DeriveFromWrongTarget {
+                                span: err_span,
+                                kind: &format!("{} {}", item.kind.article(), item.kind.descr()),
+                            })
+                        }
+                        _ => cx.dcx().bug("Invalid derive(From) ADT input"),
+                    };
+
+                    return BlockOrExpr::new_expr(DummyResult::raw_expr(span, Some(error)));
+                };
+
+                let self_kw = Ident::new(kw::SelfUpper, span);
+                let expr: Box<ast::Expr> = match substructure.fields {
+                    SubstructureFields::StaticStruct(variant, _) => match variant {
+                        // Self {
+                        //     field: value
+                        // }
+                        VariantData::Struct { .. } => cx.expr_struct_ident(
+                            span,
+                            self_kw,
+                            thin_vec![cx.field_imm(
+                                span,
+                                field.ident.unwrap(),
+                                cx.expr_ident(span, Ident::new(sym::value, span))
+                            )],
+                        ),
+                        // Self(value)
+                        VariantData::Tuple(_, _) => cx.expr_call_ident(
+                            span,
+                            self_kw,
+                            thin_vec![cx.expr_ident(span, Ident::new(sym::value, span))],
+                        ),
+                        variant => {
+                            cx.dcx().bug(format!("Invalid derive(From) ADT variant: {variant:?}"));
+                        }
+                    },
+                    _ => cx.dcx().bug("Invalid derive(From) ADT input"),
+                };
+                BlockOrExpr::new_expr(expr)
+            })),
+        }],
+        associated_types: Vec::new(),
+        is_const,
+        is_staged_api_crate: cx.ecfg.features.staged_api(),
+    };
+
+    from_trait_def.expand(cx, mitem, annotatable, push);
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
index fc9eed24ee0..3fcf9da9450 100644
--- a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@@ -180,7 +180,6 @@ use std::{iter, vec};
 
 pub(crate) use StaticFields::*;
 pub(crate) use SubstructureFields::*;
-use rustc_ast::ptr::P;
 use rustc_ast::token::{IdentIsRaw, LitKind, Token, TokenKind};
 use rustc_ast::tokenstream::{DelimSpan, Spacing, TokenTree};
 use rustc_ast::{
@@ -272,7 +271,7 @@ pub(crate) struct Substructure<'a> {
     pub type_ident: Ident,
     /// Verbatim access to any non-selflike arguments, i.e. arguments that
     /// don't have type `&Self`.
-    pub nonselflike_args: &'a [P<Expr>],
+    pub nonselflike_args: &'a [Box<Expr>],
     pub fields: &'a SubstructureFields<'a>,
 }
 
@@ -284,10 +283,10 @@ pub(crate) struct FieldInfo {
     pub name: Option<Ident>,
     /// The expression corresponding to this field of `self`
     /// (specifically, a reference to it).
-    pub self_expr: P<Expr>,
+    pub self_expr: Box<Expr>,
     /// The expressions corresponding to references to this field in
     /// the other selflike arguments.
-    pub other_selflike_exprs: Vec<P<Expr>>,
+    pub other_selflike_exprs: Vec<Box<Expr>>,
     pub maybe_scalar: bool,
 }
 
@@ -323,7 +322,7 @@ pub(crate) enum SubstructureFields<'a> {
     /// The discriminant of an enum. The first field is a `FieldInfo` for the discriminants, as
     /// if they were fields. The second field is the expression to combine the
     /// discriminant expression with; it will be `None` if no match is necessary.
-    EnumDiscr(FieldInfo, Option<P<Expr>>),
+    EnumDiscr(FieldInfo, Option<Box<Expr>>),
 
     /// A static method where `Self` is a struct.
     StaticStruct(&'a ast::VariantData, StaticFields),
@@ -345,7 +344,7 @@ pub(crate) fn combine_substructure(
 
 struct TypeParameter {
     bound_generic_params: ThinVec<ast::GenericParam>,
-    ty: P<ast::Ty>,
+    ty: Box<ast::Ty>,
 }
 
 /// The code snippets built up for derived code are sometimes used as blocks
@@ -354,23 +353,23 @@ struct TypeParameter {
 /// avoiding the insertion of any unnecessary blocks.
 ///
 /// The statements come before the expression.
-pub(crate) struct BlockOrExpr(ThinVec<ast::Stmt>, Option<P<Expr>>);
+pub(crate) struct BlockOrExpr(ThinVec<ast::Stmt>, Option<Box<Expr>>);
 
 impl BlockOrExpr {
     pub(crate) fn new_stmts(stmts: ThinVec<ast::Stmt>) -> BlockOrExpr {
         BlockOrExpr(stmts, None)
     }
 
-    pub(crate) fn new_expr(expr: P<Expr>) -> BlockOrExpr {
+    pub(crate) fn new_expr(expr: Box<Expr>) -> BlockOrExpr {
         BlockOrExpr(ThinVec::new(), Some(expr))
     }
 
-    pub(crate) fn new_mixed(stmts: ThinVec<ast::Stmt>, expr: Option<P<Expr>>) -> BlockOrExpr {
+    pub(crate) fn new_mixed(stmts: ThinVec<ast::Stmt>, expr: Option<Box<Expr>>) -> BlockOrExpr {
         BlockOrExpr(stmts, expr)
     }
 
     // Converts it into a block.
-    fn into_block(mut self, cx: &ExtCtxt<'_>, span: Span) -> P<ast::Block> {
+    fn into_block(mut self, cx: &ExtCtxt<'_>, span: Span) -> Box<ast::Block> {
         if let Some(expr) = self.1 {
             self.0.push(cx.stmt_expr(expr));
         }
@@ -378,7 +377,7 @@ impl BlockOrExpr {
     }
 
     // Converts it into an expression.
-    fn into_expr(self, cx: &ExtCtxt<'_>, span: Span) -> P<Expr> {
+    fn into_expr(self, cx: &ExtCtxt<'_>, span: Span) -> Box<Expr> {
         if self.0.is_empty() {
             match self.1 {
                 None => cx.expr_block(cx.block(span, ThinVec::new())),
@@ -432,7 +431,7 @@ fn find_type_parameters(
             {
                 self.type_params.push(TypeParameter {
                     bound_generic_params: self.bound_generic_params_stack.clone(),
-                    ty: P(ty.clone()),
+                    ty: Box::new(ty.clone()),
                 });
             }
 
@@ -544,7 +543,7 @@ impl<'a> TraitDef<'a> {
                         })
                         .cloned(),
                 );
-                push(Annotatable::Item(P(ast::Item { attrs, ..(*newitem).clone() })))
+                push(Annotatable::Item(Box::new(ast::Item { attrs, ..(*newitem).clone() })))
             }
             _ => unreachable!(),
         }
@@ -590,15 +589,15 @@ impl<'a> TraitDef<'a> {
         cx: &ExtCtxt<'_>,
         type_ident: Ident,
         generics: &Generics,
-        field_tys: Vec<P<ast::Ty>>,
-        methods: Vec<P<ast::AssocItem>>,
+        field_tys: Vec<Box<ast::Ty>>,
+        methods: Vec<Box<ast::AssocItem>>,
         is_packed: bool,
-    ) -> P<ast::Item> {
+    ) -> Box<ast::Item> {
         let trait_path = self.path.to_path(cx, self.span, type_ident, generics);
 
         // Transform associated types from `deriving::ty::Ty` into `ast::AssocItem`
         let associated_types = self.associated_types.iter().map(|&(ident, ref type_def)| {
-            P(ast::AssocItem {
+            Box::new(ast::AssocItem {
                 id: ast::DUMMY_NODE_ID,
                 span: self.span,
                 vis: ast::Visibility {
@@ -827,21 +826,25 @@ impl<'a> TraitDef<'a> {
             )
         }
 
-        let opt_trait_ref = Some(trait_ref);
-
         cx.item(
             self.span,
             attrs,
-            ast::ItemKind::Impl(Box::new(ast::Impl {
-                safety: ast::Safety::Default,
-                polarity: ast::ImplPolarity::Positive,
-                defaultness: ast::Defaultness::Final,
-                constness: if self.is_const { ast::Const::Yes(DUMMY_SP) } else { ast::Const::No },
+            ast::ItemKind::Impl(ast::Impl {
                 generics: trait_generics,
-                of_trait: opt_trait_ref,
+                of_trait: Some(Box::new(ast::TraitImplHeader {
+                    safety: ast::Safety::Default,
+                    polarity: ast::ImplPolarity::Positive,
+                    defaultness: ast::Defaultness::Final,
+                    constness: if self.is_const {
+                        ast::Const::Yes(DUMMY_SP)
+                    } else {
+                        ast::Const::No
+                    },
+                    trait_ref,
+                })),
                 self_ty: self_type,
                 items: methods.into_iter().chain(associated_types).collect(),
-            })),
+            }),
         )
     }
 
@@ -853,8 +856,8 @@ impl<'a> TraitDef<'a> {
         generics: &Generics,
         from_scratch: bool,
         is_packed: bool,
-    ) -> P<ast::Item> {
-        let field_tys: Vec<P<ast::Ty>> =
+    ) -> Box<ast::Item> {
+        let field_tys: Vec<Box<ast::Ty>> =
             struct_def.fields().iter().map(|field| field.ty.clone()).collect();
 
         let methods = self
@@ -906,7 +909,7 @@ impl<'a> TraitDef<'a> {
         type_ident: Ident,
         generics: &Generics,
         from_scratch: bool,
-    ) -> P<ast::Item> {
+    ) -> Box<ast::Item> {
         let mut field_tys = Vec::new();
 
         for variant in &enum_def.variants {
@@ -962,7 +965,7 @@ impl<'a> MethodDef<'a> {
         cx: &ExtCtxt<'_>,
         trait_: &TraitDef<'_>,
         type_ident: Ident,
-        nonselflike_args: &[P<Expr>],
+        nonselflike_args: &[Box<Expr>],
         fields: &SubstructureFields<'_>,
     ) -> BlockOrExpr {
         let span = trait_.span;
@@ -978,7 +981,7 @@ impl<'a> MethodDef<'a> {
         trait_: &TraitDef<'_>,
         generics: &Generics,
         type_ident: Ident,
-    ) -> P<ast::Ty> {
+    ) -> Box<ast::Ty> {
         self.ret_ty.to_ty(cx, trait_.span, type_ident, generics)
     }
 
@@ -999,7 +1002,8 @@ impl<'a> MethodDef<'a> {
         trait_: &TraitDef<'_>,
         type_ident: Ident,
         generics: &Generics,
-    ) -> (Option<ast::ExplicitSelf>, ThinVec<P<Expr>>, Vec<P<Expr>>, Vec<(Ident, P<ast::Ty>)>) {
+    ) -> (Option<ast::ExplicitSelf>, ThinVec<Box<Expr>>, Vec<Box<Expr>>, Vec<(Ident, Box<ast::Ty>)>)
+    {
         let mut selflike_args = ThinVec::new();
         let mut nonselflike_args = Vec::new();
         let mut nonself_arg_tys = Vec::new();
@@ -1036,9 +1040,9 @@ impl<'a> MethodDef<'a> {
         type_ident: Ident,
         generics: &Generics,
         explicit_self: Option<ast::ExplicitSelf>,
-        nonself_arg_tys: Vec<(Ident, P<ast::Ty>)>,
+        nonself_arg_tys: Vec<(Ident, Box<ast::Ty>)>,
         body: BlockOrExpr,
-    ) -> P<ast::AssocItem> {
+    ) -> Box<ast::AssocItem> {
         let span = trait_.span;
         // Create the generics that aren't for `Self`.
         let fn_generics = self.generics.to_generics(cx, span, type_ident, generics);
@@ -1065,7 +1069,7 @@ impl<'a> MethodDef<'a> {
         let defaultness = ast::Defaultness::Final;
 
         // Create the method.
-        P(ast::AssocItem {
+        Box::new(ast::AssocItem {
             id: ast::DUMMY_NODE_ID,
             attrs: self.attributes.clone(),
             span,
@@ -1128,8 +1132,8 @@ impl<'a> MethodDef<'a> {
         trait_: &TraitDef<'b>,
         struct_def: &'b VariantData,
         type_ident: Ident,
-        selflike_args: &[P<Expr>],
-        nonselflike_args: &[P<Expr>],
+        selflike_args: &[Box<Expr>],
+        nonselflike_args: &[Box<Expr>],
         is_packed: bool,
     ) -> BlockOrExpr {
         assert!(selflike_args.len() == 1 || selflike_args.len() == 2);
@@ -1151,7 +1155,7 @@ impl<'a> MethodDef<'a> {
         trait_: &TraitDef<'_>,
         struct_def: &VariantData,
         type_ident: Ident,
-        nonselflike_args: &[P<Expr>],
+        nonselflike_args: &[Box<Expr>],
     ) -> BlockOrExpr {
         let summary = trait_.summarise_struct(cx, struct_def);
 
@@ -1205,8 +1209,8 @@ impl<'a> MethodDef<'a> {
         trait_: &TraitDef<'b>,
         enum_def: &'b EnumDef,
         type_ident: Ident,
-        mut selflike_args: ThinVec<P<Expr>>,
-        nonselflike_args: &[P<Expr>],
+        mut selflike_args: ThinVec<Box<Expr>>,
+        nonselflike_args: &[Box<Expr>],
     ) -> BlockOrExpr {
         assert!(
             !selflike_args.is_empty(),
@@ -1418,7 +1422,7 @@ impl<'a> MethodDef<'a> {
         //          ...
         //          _ => ::core::intrinsics::unreachable(),
         //      }
-        let get_match_expr = |mut selflike_args: ThinVec<P<Expr>>| {
+        let get_match_expr = |mut selflike_args: ThinVec<Box<Expr>>| {
             let match_arg = if selflike_args.len() == 1 {
                 selflike_args.pop().unwrap()
             } else {
@@ -1454,7 +1458,7 @@ impl<'a> MethodDef<'a> {
         trait_: &TraitDef<'_>,
         enum_def: &EnumDef,
         type_ident: Ident,
-        nonselflike_args: &[P<Expr>],
+        nonselflike_args: &[Box<Expr>],
     ) -> BlockOrExpr {
         self.call_substructure_method(
             cx,
@@ -1503,7 +1507,7 @@ impl<'a> TraitDef<'a> {
         struct_def: &'a VariantData,
         prefixes: &[String],
         by_ref: ByRef,
-    ) -> ThinVec<P<ast::Pat>> {
+    ) -> ThinVec<Box<ast::Pat>> {
         prefixes
             .iter()
             .map(|prefix| {
@@ -1558,7 +1562,7 @@ impl<'a> TraitDef<'a> {
 
     fn create_fields<F>(&self, struct_def: &'a VariantData, mk_exprs: F) -> Vec<FieldInfo>
     where
-        F: Fn(usize, &ast::FieldDef, Span) -> Vec<P<ast::Expr>>,
+        F: Fn(usize, &ast::FieldDef, Span) -> Vec<Box<ast::Expr>>,
     {
         struct_def
             .fields()
@@ -1606,7 +1610,7 @@ impl<'a> TraitDef<'a> {
     fn create_struct_field_access_fields(
         &self,
         cx: &ExtCtxt<'_>,
-        selflike_args: &[P<Expr>],
+        selflike_args: &[Box<Expr>],
         struct_def: &'a VariantData,
         is_packed: bool,
     ) -> Vec<FieldInfo> {
@@ -1651,7 +1655,7 @@ pub(crate) enum CsFold<'a> {
 
     /// The combination of two field expressions. E.g. for `PartialEq::eq` this
     /// is something like `<field1 equality> && <field2 equality>`.
-    Combine(Span, P<Expr>, P<Expr>),
+    Combine(Span, Box<Expr>, Box<Expr>),
 
     // The fallback case for a struct or enum variant with no fields.
     Fieldless,
@@ -1665,9 +1669,9 @@ pub(crate) fn cs_fold<F>(
     trait_span: Span,
     substructure: &Substructure<'_>,
     mut f: F,
-) -> P<Expr>
+) -> Box<Expr>
 where
-    F: FnMut(&ExtCtxt<'_>, CsFold<'_>) -> P<Expr>,
+    F: FnMut(&ExtCtxt<'_>, CsFold<'_>) -> Box<Expr>,
 {
     match substructure.fields {
         EnumMatching(.., all_fields) | Struct(_, all_fields) => {
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs b/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
index f34a6ae1d98..1458553d492 100644
--- a/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
@@ -2,8 +2,7 @@
 //! when specifying impls to be derived.
 
 pub(crate) use Ty::*;
-use rustc_ast::ptr::P;
-use rustc_ast::{self as ast, Expr, GenericArg, GenericParamKind, Generics, SelfKind};
+use rustc_ast::{self as ast, Expr, GenericArg, GenericParamKind, Generics, SelfKind, TyKind};
 use rustc_expand::base::ExtCtxt;
 use rustc_span::source_map::respan;
 use rustc_span::{DUMMY_SP, Ident, Span, Symbol, kw};
@@ -41,7 +40,7 @@ impl Path {
         span: Span,
         self_ty: Ident,
         self_generics: &Generics,
-    ) -> P<ast::Ty> {
+    ) -> Box<ast::Ty> {
         cx.ty_path(self.to_path(cx, span, self_ty, self_generics))
     }
     pub(crate) fn to_path(
@@ -66,7 +65,7 @@ impl Path {
     }
 }
 
-/// A type. Supports pointers, Self, and literals.
+/// A type. Supports pointers, Self, literals, unit or an arbitrary AST path.
 #[derive(Clone)]
 pub(crate) enum Ty {
     Self_,
@@ -77,6 +76,8 @@ pub(crate) enum Ty {
     Path(Path),
     /// For () return types.
     Unit,
+    /// An arbitrary type.
+    AstTy(Box<ast::Ty>),
 }
 
 pub(crate) fn self_ref() -> Ty {
@@ -90,7 +91,7 @@ impl Ty {
         span: Span,
         self_ty: Ident,
         self_generics: &Generics,
-    ) -> P<ast::Ty> {
+    ) -> Box<ast::Ty> {
         match self {
             Ref(ty, mutbl) => {
                 let raw_ty = ty.to_ty(cx, span, self_ty, self_generics);
@@ -102,6 +103,7 @@ impl Ty {
                 let ty = ast::TyKind::Tup(ThinVec::new());
                 cx.ty(span, ty)
             }
+            AstTy(ty) => ty.clone(),
         }
     }
 
@@ -133,6 +135,10 @@ impl Ty {
                 cx.path_all(span, false, vec![self_ty], params)
             }
             Path(p) => p.to_path(cx, span, self_ty, generics),
+            AstTy(ty) => match &ty.kind {
+                TyKind::Path(_, path) => path.clone(),
+                _ => cx.dcx().span_bug(span, "non-path in a path in generic `derive`"),
+            },
             Ref(..) => cx.dcx().span_bug(span, "ref in a path in generic `derive`"),
             Unit => cx.dcx().span_bug(span, "unit in a path in generic `derive`"),
         }
@@ -192,7 +198,7 @@ impl Bounds {
     }
 }
 
-pub(crate) fn get_explicit_self(cx: &ExtCtxt<'_>, span: Span) -> (P<Expr>, ast::ExplicitSelf) {
+pub(crate) fn get_explicit_self(cx: &ExtCtxt<'_>, span: Span) -> (Box<Expr>, ast::ExplicitSelf) {
     // This constructs a fresh `self` path.
     let self_path = cx.expr_self(span);
     let self_ty = respan(span, SelfKind::Region(None, ast::Mutability::Not));
diff --git a/compiler/rustc_builtin_macros/src/deriving/mod.rs b/compiler/rustc_builtin_macros/src/deriving/mod.rs
index e45d09b5796..cee6952fa34 100644
--- a/compiler/rustc_builtin_macros/src/deriving/mod.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/mod.rs
@@ -1,7 +1,6 @@
 //! The compiler code necessary to implement the `#[derive]` extensions.
 
 use rustc_ast as ast;
-use rustc_ast::ptr::P;
 use rustc_ast::{GenericArg, MetaItem};
 use rustc_expand::base::{Annotatable, ExpandResult, ExtCtxt, MultiItemModifier};
 use rustc_span::{Span, Symbol, sym};
@@ -24,6 +23,7 @@ pub(crate) mod clone;
 pub(crate) mod coerce_pointee;
 pub(crate) mod debug;
 pub(crate) mod default;
+pub(crate) mod from;
 pub(crate) mod hash;
 
 #[path = "cmp/eq.rs"]
@@ -66,7 +66,7 @@ impl MultiItemModifier for BuiltinDerive {
                         &mut |a| {
                             // Cannot use 'ecx.stmt_item' here, because we need to pass 'ecx'
                             // to the function
-                            items.push(Annotatable::Stmt(P(ast::Stmt {
+                            items.push(Annotatable::Stmt(Box::new(ast::Stmt {
                                 id: ast::DUMMY_NODE_ID,
                                 kind: ast::StmtKind::Item(a.expect_item()),
                                 span,
@@ -91,20 +91,20 @@ fn call_intrinsic(
     cx: &ExtCtxt<'_>,
     span: Span,
     intrinsic: Symbol,
-    args: ThinVec<P<ast::Expr>>,
-) -> P<ast::Expr> {
+    args: ThinVec<Box<ast::Expr>>,
+) -> Box<ast::Expr> {
     let span = cx.with_def_site_ctxt(span);
     let path = cx.std_path(&[sym::intrinsics, intrinsic]);
     cx.expr_call_global(span, path, args)
 }
 
 /// Constructs an expression that calls the `unreachable` intrinsic.
-fn call_unreachable(cx: &ExtCtxt<'_>, span: Span) -> P<ast::Expr> {
+fn call_unreachable(cx: &ExtCtxt<'_>, span: Span) -> Box<ast::Expr> {
     let span = cx.with_def_site_ctxt(span);
     let path = cx.std_path(&[sym::intrinsics, sym::unreachable]);
     let call = cx.expr_call_global(span, path, ThinVec::new());
 
-    cx.expr_block(P(ast::Block {
+    cx.expr_block(Box::new(ast::Block {
         stmts: thin_vec![cx.stmt_expr(call)],
         id: ast::DUMMY_NODE_ID,
         rules: ast::BlockCheckMode::Unsafe(ast::CompilerGenerated),
@@ -116,7 +116,7 @@ fn call_unreachable(cx: &ExtCtxt<'_>, span: Span) -> P<ast::Expr> {
 fn assert_ty_bounds(
     cx: &ExtCtxt<'_>,
     stmts: &mut ThinVec<ast::Stmt>,
-    ty: P<ast::Ty>,
+    ty: Box<ast::Ty>,
     span: Span,
     assert_path: &[Symbol],
 ) {
diff --git a/compiler/rustc_builtin_macros/src/edition_panic.rs b/compiler/rustc_builtin_macros/src/edition_panic.rs
index ccfcc3079eb..08f555b9e52 100644
--- a/compiler/rustc_builtin_macros/src/edition_panic.rs
+++ b/compiler/rustc_builtin_macros/src/edition_panic.rs
@@ -1,4 +1,3 @@
-use rustc_ast::ptr::P;
 use rustc_ast::token::Delimiter;
 use rustc_ast::tokenstream::{DelimSpan, TokenStream};
 use rustc_ast::*;
@@ -48,7 +47,7 @@ fn expand<'cx>(
     ExpandResult::Ready(MacEager::expr(
         cx.expr(
             sp,
-            ExprKind::MacCall(P(MacCall {
+            ExprKind::MacCall(Box::new(MacCall {
                 path: Path {
                     span: sp,
                     segments: cx
@@ -58,7 +57,7 @@ fn expand<'cx>(
                         .collect(),
                     tokens: None,
                 },
-                args: P(DelimArgs {
+                args: Box::new(DelimArgs {
                     dspan: DelimSpan::from_single(sp),
                     delim: Delimiter::Parenthesis,
                     tokens: tts,
diff --git a/compiler/rustc_builtin_macros/src/errors.rs b/compiler/rustc_builtin_macros/src/errors.rs
index 6bcf4d3e0a2..54e8f750337 100644
--- a/compiler/rustc_builtin_macros/src/errors.rs
+++ b/compiler/rustc_builtin_macros/src/errors.rs
@@ -447,6 +447,24 @@ pub(crate) struct DefaultHasArg {
 }
 
 #[derive(Diagnostic)]
+#[diag(builtin_macros_derive_from_wrong_target)]
+#[note(builtin_macros_derive_from_usage_note)]
+pub(crate) struct DeriveFromWrongTarget<'a> {
+    #[primary_span]
+    pub(crate) span: MultiSpan,
+    pub(crate) kind: &'a str,
+}
+
+#[derive(Diagnostic)]
+#[diag(builtin_macros_derive_from_wrong_field_count)]
+#[note(builtin_macros_derive_from_usage_note)]
+pub(crate) struct DeriveFromWrongFieldCount {
+    #[primary_span]
+    pub(crate) span: MultiSpan,
+    pub(crate) multiple_fields: bool,
+}
+
+#[derive(Diagnostic)]
 #[diag(builtin_macros_derive_macro_call)]
 pub(crate) struct DeriveMacroCall {
     #[primary_span]
@@ -906,14 +924,6 @@ pub(crate) struct TakesNoArguments<'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(builtin_macros_proc_macro_attribute_only_be_used_on_bare_functions)]
-pub(crate) struct AttributeOnlyBeUsedOnBareFunctions<'a> {
-    #[primary_span]
-    pub span: Span,
-    pub path: &'a str,
-}
-
-#[derive(Diagnostic)]
 #[diag(builtin_macros_proc_macro_attribute_only_usable_with_crate_type)]
 pub(crate) struct AttributeOnlyUsableWithCrateType<'a> {
     #[primary_span]
diff --git a/compiler/rustc_builtin_macros/src/format.rs b/compiler/rustc_builtin_macros/src/format.rs
index 6785cb6aef5..ec613b7b710 100644
--- a/compiler/rustc_builtin_macros/src/format.rs
+++ b/compiler/rustc_builtin_macros/src/format.rs
@@ -1,7 +1,6 @@
 use std::ops::Range;
 
 use parse::Position::ArgumentNamed;
-use rustc_ast::ptr::P;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::{
     Expr, ExprKind, FormatAlignment, FormatArgPosition, FormatArgPositionKind, FormatArgs,
@@ -45,7 +44,7 @@ use PositionUsedAs::*;
 
 #[derive(Debug)]
 struct MacroInput {
-    fmtstr: P<Expr>,
+    fmtstr: Box<Expr>,
     args: FormatArguments,
     /// Whether the first argument was a string literal or a result from eager macro expansion.
     /// If it's not a string literal, we disallow implicit argument capturing.
@@ -1018,7 +1017,7 @@ fn expand_format_args_impl<'cx>(
             };
             match mac {
                 Ok(format_args) => {
-                    MacEager::expr(ecx.expr(sp, ExprKind::FormatArgs(P(format_args))))
+                    MacEager::expr(ecx.expr(sp, ExprKind::FormatArgs(Box::new(format_args))))
                 }
                 Err(guar) => MacEager::expr(DummyResult::raw_expr(sp, Some(guar))),
             }
diff --git a/compiler/rustc_builtin_macros/src/format_foreign.rs b/compiler/rustc_builtin_macros/src/format_foreign.rs
index 13d5b42942a..3e5a26c0556 100644
--- a/compiler/rustc_builtin_macros/src/format_foreign.rs
+++ b/compiler/rustc_builtin_macros/src/format_foreign.rs
@@ -346,18 +346,18 @@ pub(crate) mod printf {
         // ```regex
         // (?x)
         // ^ %
-        // (?: (?P<parameter> \d+) \$ )?
-        // (?P<flags> [-+ 0\#']* )
-        // (?P<width> \d+ | \* (?: (?P<widtha> \d+) \$ )? )?
-        // (?: \. (?P<precision> \d+ | \* (?: (?P<precisiona> \d+) \$ )? ) )?
-        // (?P<length>
+        // (?: (?Box<parameter> \d+) \$ )?
+        // (?Box<flags> [-+ 0\#']* )
+        // (?Box<width> \d+ | \* (?: (?Box<widtha> \d+) \$ )? )?
+        // (?: \. (?Box<precision> \d+ | \* (?: (?Box<precisiona> \d+) \$ )? ) )?
+        // (?Box<length>
         //     # Standard
         //     hh | h | ll | l | L | z | j | t
         //
         //     # Other
         //     | I32 | I64 | I | q
         // )?
-        // (?P<type> . )
+        // (?Box<type> . )
         // ```
 
         // Used to establish the full span at the end.
diff --git a/compiler/rustc_builtin_macros/src/global_allocator.rs b/compiler/rustc_builtin_macros/src/global_allocator.rs
index 4b1958bce32..f14b1920722 100644
--- a/compiler/rustc_builtin_macros/src/global_allocator.rs
+++ b/compiler/rustc_builtin_macros/src/global_allocator.rs
@@ -1,7 +1,6 @@
 use rustc_ast::expand::allocator::{
     ALLOCATOR_METHODS, AllocatorMethod, AllocatorMethodInput, AllocatorTy, global_fn_name,
 };
-use rustc_ast::ptr::P;
 use rustc_ast::{
     self as ast, AttrVec, Expr, Fn, FnHeader, FnSig, Generics, ItemKind, Mutability, Param, Safety,
     Stmt, StmtKind, Ty, TyKind,
@@ -51,7 +50,7 @@ pub(crate) fn expand(
     let const_body = ecx.expr_block(ecx.block(span, stmts));
     let const_item = ecx.item_const(span, Ident::new(kw::Underscore, span), const_ty, const_body);
     let const_item = if is_stmt {
-        Annotatable::Stmt(P(ecx.stmt_item(span, const_item)))
+        Annotatable::Stmt(Box::new(ecx.stmt_item(span, const_item)))
     } else {
         Annotatable::Item(const_item)
     };
@@ -90,7 +89,7 @@ impl AllocFnFactory<'_, '_> {
         self.cx.stmt_item(self.ty_span, item)
     }
 
-    fn call_allocator(&self, method: Symbol, mut args: ThinVec<P<Expr>>) -> P<Expr> {
+    fn call_allocator(&self, method: Symbol, mut args: ThinVec<Box<Expr>>) -> Box<Expr> {
         let method = self.cx.std_path(&[sym::alloc, sym::GlobalAlloc, method]);
         let method = self.cx.expr_path(self.cx.path(self.ty_span, method));
         let allocator = self.cx.path_ident(self.ty_span, self.global);
@@ -105,7 +104,7 @@ impl AllocFnFactory<'_, '_> {
         thin_vec![self.cx.attr_word(sym::rustc_std_internal_symbol, self.span)]
     }
 
-    fn arg_ty(&self, input: &AllocatorMethodInput, args: &mut ThinVec<Param>) -> P<Expr> {
+    fn arg_ty(&self, input: &AllocatorMethodInput, args: &mut ThinVec<Param>) -> Box<Expr> {
         match input.ty {
             AllocatorTy::Layout => {
                 // If an allocator method is ever introduced having multiple
@@ -148,7 +147,7 @@ impl AllocFnFactory<'_, '_> {
         }
     }
 
-    fn ret_ty(&self, ty: &AllocatorTy) -> P<Ty> {
+    fn ret_ty(&self, ty: &AllocatorTy) -> Box<Ty> {
         match *ty {
             AllocatorTy::ResultPtr => self.ptr_u8(),
 
@@ -160,12 +159,12 @@ impl AllocFnFactory<'_, '_> {
         }
     }
 
-    fn usize(&self) -> P<Ty> {
+    fn usize(&self) -> Box<Ty> {
         let usize = self.cx.path_ident(self.span, Ident::new(sym::usize, self.span));
         self.cx.ty_path(usize)
     }
 
-    fn ptr_u8(&self) -> P<Ty> {
+    fn ptr_u8(&self) -> Box<Ty> {
         let u8 = self.cx.path_ident(self.span, Ident::new(sym::u8, self.span));
         let ty_u8 = self.cx.ty_path(u8);
         self.cx.ty_ptr(self.span, ty_u8, Mutability::Mut)
diff --git a/compiler/rustc_builtin_macros/src/iter.rs b/compiler/rustc_builtin_macros/src/iter.rs
index 7ad83903a1b..e9f340ef119 100644
--- a/compiler/rustc_builtin_macros/src/iter.rs
+++ b/compiler/rustc_builtin_macros/src/iter.rs
@@ -1,4 +1,3 @@
-use rustc_ast::ptr::P;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::{CoroutineKind, DUMMY_NODE_ID, Expr, ast, token};
 use rustc_errors::PResult;
@@ -24,7 +23,7 @@ fn parse_closure<'a>(
     cx: &mut ExtCtxt<'a>,
     span: Span,
     stream: TokenStream,
-) -> PResult<'a, P<Expr>> {
+) -> PResult<'a, Box<Expr>> {
     let mut closure_parser = cx.new_parser_from_tts(stream);
 
     let coroutine_kind = Some(CoroutineKind::Gen {
diff --git a/compiler/rustc_builtin_macros/src/lib.rs b/compiler/rustc_builtin_macros/src/lib.rs
index 7bc448a9acb..86a4927f390 100644
--- a/compiler/rustc_builtin_macros/src/lib.rs
+++ b/compiler/rustc_builtin_macros/src/lib.rs
@@ -139,6 +139,7 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
         PartialEq: partial_eq::expand_deriving_partial_eq,
         PartialOrd: partial_ord::expand_deriving_partial_ord,
         CoercePointee: coerce_pointee::expand_deriving_coerce_pointee,
+        From: from::expand_deriving_from,
     }
 
     let client = rustc_proc_macro::bridge::client::Client::expand1(rustc_proc_macro::quote);
diff --git a/compiler/rustc_builtin_macros/src/pattern_type.rs b/compiler/rustc_builtin_macros/src/pattern_type.rs
index b61af0b0aaa..34faafdc07c 100644
--- a/compiler/rustc_builtin_macros/src/pattern_type.rs
+++ b/compiler/rustc_builtin_macros/src/pattern_type.rs
@@ -1,4 +1,3 @@
-use rustc_ast::ptr::P;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::{AnonConst, DUMMY_NODE_ID, Ty, TyPat, TyPatKind, ast, token};
 use rustc_errors::PResult;
@@ -22,7 +21,10 @@ pub(crate) fn expand<'cx>(
     ExpandResult::Ready(base::MacEager::ty(cx.ty(sp, ast::TyKind::Pat(ty, pat))))
 }
 
-fn parse_pat_ty<'a>(cx: &mut ExtCtxt<'a>, stream: TokenStream) -> PResult<'a, (P<Ty>, P<TyPat>)> {
+fn parse_pat_ty<'a>(
+    cx: &mut ExtCtxt<'a>,
+    stream: TokenStream,
+) -> PResult<'a, (Box<Ty>, Box<TyPat>)> {
     let mut parser = cx.new_parser_from_tts(stream);
 
     let ty = parser.parse_ty()?;
@@ -45,15 +47,15 @@ fn parse_pat_ty<'a>(cx: &mut ExtCtxt<'a>, stream: TokenStream) -> PResult<'a, (P
     Ok((ty, pat))
 }
 
-fn ty_pat(kind: TyPatKind, span: Span) -> P<TyPat> {
-    P(TyPat { id: DUMMY_NODE_ID, kind, span, tokens: None })
+fn ty_pat(kind: TyPatKind, span: Span) -> Box<TyPat> {
+    Box::new(TyPat { id: DUMMY_NODE_ID, kind, span, tokens: None })
 }
 
-fn pat_to_ty_pat(cx: &mut ExtCtxt<'_>, pat: ast::Pat) -> P<TyPat> {
+fn pat_to_ty_pat(cx: &mut ExtCtxt<'_>, pat: ast::Pat) -> Box<TyPat> {
     let kind = match pat.kind {
         ast::PatKind::Range(start, end, include_end) => TyPatKind::Range(
-            start.map(|value| P(AnonConst { id: DUMMY_NODE_ID, value })),
-            end.map(|value| P(AnonConst { id: DUMMY_NODE_ID, value })),
+            start.map(|value| Box::new(AnonConst { id: DUMMY_NODE_ID, value })),
+            end.map(|value| Box::new(AnonConst { id: DUMMY_NODE_ID, value })),
             include_end,
         ),
         ast::PatKind::Or(variants) => {
diff --git a/compiler/rustc_builtin_macros/src/proc_macro_harness.rs b/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
index df70c93c1c2..6ac3e17503d 100644
--- a/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
+++ b/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
@@ -1,6 +1,5 @@
 use std::{mem, slice};
 
-use rustc_ast::ptr::P;
 use rustc_ast::visit::{self, Visitor};
 use rustc_ast::{self as ast, HasNodeId, NodeId, attr};
 use rustc_ast_pretty::pprust;
@@ -232,12 +231,7 @@ impl<'a> Visitor<'a> for CollectProcMacros<'a> {
         let fn_ident = if let ast::ItemKind::Fn(fn_) = &item.kind {
             fn_.ident
         } else {
-            self.dcx
-                .create_err(errors::AttributeOnlyBeUsedOnBareFunctions {
-                    span: attr.span,
-                    path: &pprust::path_to_string(&attr.get_normal_item().path),
-                })
-                .emit();
+            // Error handled by general target checking logic
             return;
         };
 
@@ -286,7 +280,7 @@ impl<'a> Visitor<'a> for CollectProcMacros<'a> {
 //              // ...
 //          ];
 //      }
-fn mk_decls(cx: &mut ExtCtxt<'_>, macros: &[ProcMacro]) -> P<ast::Item> {
+fn mk_decls(cx: &mut ExtCtxt<'_>, macros: &[ProcMacro]) -> Box<ast::Item> {
     let expn_id = cx.resolver.expansion_for_ast_pass(
         DUMMY_SP,
         AstPass::ProcMacroHarness,
diff --git a/compiler/rustc_builtin_macros/src/source_util.rs b/compiler/rustc_builtin_macros/src/source_util.rs
index ecfd46a84ec..37bab5be542 100644
--- a/compiler/rustc_builtin_macros/src/source_util.rs
+++ b/compiler/rustc_builtin_macros/src/source_util.rs
@@ -3,7 +3,6 @@ use std::rc::Rc;
 use std::sync::Arc;
 
 use rustc_ast as ast;
-use rustc_ast::ptr::P;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::{join_path_idents, token};
 use rustc_ast_pretty::pprust;
@@ -144,7 +143,7 @@ pub(crate) fn expand_include<'cx>(
         node_id: ast::NodeId,
     }
     impl<'a> MacResult for ExpandInclude<'a> {
-        fn make_expr(mut self: Box<ExpandInclude<'a>>) -> Option<P<ast::Expr>> {
+        fn make_expr(mut self: Box<ExpandInclude<'a>>) -> Option<Box<ast::Expr>> {
             let expr = parse_expr(&mut self.p).ok()?;
             if self.p.token != token::Eof {
                 self.p.psess.buffer_lint(
@@ -157,7 +156,7 @@ pub(crate) fn expand_include<'cx>(
             Some(expr)
         }
 
-        fn make_items(mut self: Box<ExpandInclude<'a>>) -> Option<SmallVec<[P<ast::Item>; 1]>> {
+        fn make_items(mut self: Box<ExpandInclude<'a>>) -> Option<SmallVec<[Box<ast::Item>; 1]>> {
             let mut ret = SmallVec::new();
             loop {
                 match self.p.parse_item(ForceCollect::No) {
diff --git a/compiler/rustc_builtin_macros/src/test.rs b/compiler/rustc_builtin_macros/src/test.rs
index ba3d8368b2a..7a189ee1f4d 100644
--- a/compiler/rustc_builtin_macros/src/test.rs
+++ b/compiler/rustc_builtin_macros/src/test.rs
@@ -4,11 +4,13 @@
 use std::assert_matches::assert_matches;
 use std::iter;
 
-use rustc_ast::ptr::P;
-use rustc_ast::{self as ast, GenericParamKind, attr, join_path_idents};
+use rustc_ast::{self as ast, GenericParamKind, HasNodeId, attr, join_path_idents};
 use rustc_ast_pretty::pprust;
+use rustc_attr_parsing::AttributeParser;
 use rustc_errors::{Applicability, Diag, Level};
 use rustc_expand::base::*;
+use rustc_hir::Attribute;
+use rustc_hir::attrs::AttributeKind;
 use rustc_span::{ErrorGuaranteed, FileNameDisplayPreference, Ident, Span, Symbol, sym};
 use thin_vec::{ThinVec, thin_vec};
 use tracing::debug;
@@ -75,7 +77,7 @@ pub(crate) fn expand_test_case(
     }
 
     let ret = if is_stmt {
-        Annotatable::Stmt(P(ecx.stmt_item(item.span, item)))
+        Annotatable::Stmt(Box::new(ecx.stmt_item(item.span, item)))
     } else {
         Annotatable::Item(item)
     };
@@ -128,7 +130,7 @@ pub(crate) fn expand_test_or_bench(
     let ast::ItemKind::Fn(fn_) = &item.kind else {
         not_testable_error(cx, attr_sp, Some(&item));
         return if is_stmt {
-            vec![Annotatable::Stmt(P(cx.stmt_item(item.span, item)))]
+            vec![Annotatable::Stmt(Box::new(cx.stmt_item(item.span, item)))]
         } else {
             vec![Annotatable::Item(item)]
         };
@@ -152,7 +154,7 @@ pub(crate) fn expand_test_or_bench(
     };
     if check_result.is_err() {
         return if is_stmt {
-            vec![Annotatable::Stmt(P(cx.stmt_item(item.span, item)))]
+            vec![Annotatable::Stmt(Box::new(cx.stmt_item(item.span, item)))]
         } else {
             vec![Annotatable::Item(item)]
         };
@@ -198,7 +200,7 @@ pub(crate) fn expand_test_or_bench(
     // `-Cinstrument-coverage` builds.
     // This requires `#[allow_internal_unstable(coverage_attribute)]` on the
     // corresponding macro declaration in `core::macros`.
-    let coverage_off = |mut expr: P<ast::Expr>| {
+    let coverage_off = |mut expr: Box<ast::Expr>| {
         assert_matches!(expr.kind, ast::ExprKind::Closure(_));
         expr.attrs.push(cx.attr_nested_word(sym::coverage, sym::off, sp));
         expr
@@ -385,11 +387,11 @@ pub(crate) fn expand_test_or_bench(
     if is_stmt {
         vec![
             // Access to libtest under a hygienic name
-            Annotatable::Stmt(P(cx.stmt_item(sp, test_extern))),
+            Annotatable::Stmt(Box::new(cx.stmt_item(sp, test_extern))),
             // The generated test case
-            Annotatable::Stmt(P(cx.stmt_item(sp, test_const))),
+            Annotatable::Stmt(Box::new(cx.stmt_item(sp, test_const))),
             // The original item
-            Annotatable::Stmt(P(cx.stmt_item(sp, item))),
+            Annotatable::Stmt(Box::new(cx.stmt_item(sp, item))),
         ]
     } else {
         vec![
@@ -473,39 +475,19 @@ fn should_ignore_message(i: &ast::Item) -> Option<Symbol> {
 }
 
 fn should_panic(cx: &ExtCtxt<'_>, i: &ast::Item) -> ShouldPanic {
-    match attr::find_by_name(&i.attrs, sym::should_panic) {
-        Some(attr) => {
-            match attr.meta_item_list() {
-                // Handle #[should_panic(expected = "foo")]
-                Some(list) => {
-                    let msg = list
-                        .iter()
-                        .find(|mi| mi.has_name(sym::expected))
-                        .and_then(|mi| mi.meta_item())
-                        .and_then(|mi| mi.value_str());
-                    if list.len() != 1 || msg.is_none() {
-                        cx.dcx()
-                            .struct_span_warn(
-                                attr.span,
-                                "argument must be of the form: \
-                             `expected = \"error message\"`",
-                            )
-                            .with_note(
-                                "errors in this attribute were erroneously \
-                                allowed and will become a hard error in a \
-                                future release",
-                            )
-                            .emit();
-                        ShouldPanic::Yes(None)
-                    } else {
-                        ShouldPanic::Yes(msg)
-                    }
-                }
-                // Handle #[should_panic] and #[should_panic = "expected"]
-                None => ShouldPanic::Yes(attr.value_str()),
-            }
-        }
-        None => ShouldPanic::No,
+    if let Some(Attribute::Parsed(AttributeKind::ShouldPanic { reason, .. })) =
+        AttributeParser::parse_limited(
+            cx.sess,
+            &i.attrs,
+            sym::should_panic,
+            i.span,
+            i.node_id(),
+            None,
+        )
+    {
+        ShouldPanic::Yes(reason)
+    } else {
+        ShouldPanic::No
     }
 }
 
diff --git a/compiler/rustc_builtin_macros/src/test_harness.rs b/compiler/rustc_builtin_macros/src/test_harness.rs
index 111c85d49eb..e803f3be82b 100644
--- a/compiler/rustc_builtin_macros/src/test_harness.rs
+++ b/compiler/rustc_builtin_macros/src/test_harness.rs
@@ -5,7 +5,6 @@ use std::mem;
 use rustc_ast as ast;
 use rustc_ast::entry::EntryPointType;
 use rustc_ast::mut_visit::*;
-use rustc_ast::ptr::P;
 use rustc_ast::visit::Visitor;
 use rustc_ast::{ModKind, attr};
 use rustc_errors::DiagCtxtHandle;
@@ -284,7 +283,7 @@ fn generate_test_harness(
 /// [`TestCtxt::reexport_test_harness_main`] provides a different name for the `main`
 /// function and [`TestCtxt::test_runner`] provides a path that replaces
 /// `test::test_main_static`.
-fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
+fn mk_main(cx: &mut TestCtxt<'_>) -> Box<ast::Item> {
     let sp = cx.def_site;
     let ecx = &cx.ext_cx;
     let test_ident = Ident::new(sym::test, sp);
@@ -348,7 +347,7 @@ fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
         define_opaque: None,
     }));
 
-    let main = P(ast::Item {
+    let main = Box::new(ast::Item {
         attrs: thin_vec![main_attr, coverage_attr, doc_hidden_attr],
         id: ast::DUMMY_NODE_ID,
         kind: main,
@@ -364,7 +363,7 @@ fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
 
 /// Creates a slice containing every test like so:
 /// &[&test1, &test2]
-fn mk_tests_slice(cx: &TestCtxt<'_>, sp: Span) -> P<ast::Expr> {
+fn mk_tests_slice(cx: &TestCtxt<'_>, sp: Span) -> Box<ast::Expr> {
     debug!("building test vector from {} tests", cx.test_cases.len());
     let ecx = &cx.ext_cx;
 
diff --git a/compiler/rustc_builtin_macros/src/util.rs b/compiler/rustc_builtin_macros/src/util.rs
index 38fec2bff14..f00c170e485 100644
--- a/compiler/rustc_builtin_macros/src/util.rs
+++ b/compiler/rustc_builtin_macros/src/util.rs
@@ -1,4 +1,3 @@
-use rustc_ast::ptr::P;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::{self as ast, AttrStyle, Attribute, MetaItem, attr, token};
 use rustc_errors::{Applicability, Diag, ErrorGuaranteed};
@@ -83,7 +82,7 @@ type UnexpectedExprKind<'a> = Result<(Diag<'a>, bool /* has_suggestions */), Err
 #[allow(rustc::untranslatable_diagnostic)]
 pub(crate) fn expr_to_spanned_string<'a>(
     cx: &'a mut ExtCtxt<'_>,
-    expr: P<ast::Expr>,
+    expr: Box<ast::Expr>,
     err_msg: &'static str,
 ) -> ExpandResult<ExprToSpannedStringResult<'a>, ()> {
     if !cx.force_mode
@@ -135,7 +134,7 @@ pub(crate) fn expr_to_spanned_string<'a>(
 /// compilation on error, merely emits a non-fatal error and returns `Err`.
 pub(crate) fn expr_to_string(
     cx: &mut ExtCtxt<'_>,
-    expr: P<ast::Expr>,
+    expr: Box<ast::Expr>,
     err_msg: &'static str,
 ) -> ExpandResult<Result<(Symbol, ast::StrStyle), ErrorGuaranteed>, ()> {
     expr_to_spanned_string(cx, expr, err_msg).map(|res| {
@@ -158,7 +157,7 @@ pub(crate) fn check_zero_tts(cx: &ExtCtxt<'_>, span: Span, tts: TokenStream, nam
 }
 
 /// Parse an expression. On error, emit it, advancing to `Eof`, and return `Err`.
-pub(crate) fn parse_expr(p: &mut parser::Parser<'_>) -> Result<P<ast::Expr>, ErrorGuaranteed> {
+pub(crate) fn parse_expr(p: &mut parser::Parser<'_>) -> Result<Box<ast::Expr>, ErrorGuaranteed> {
     let guar = match p.parse_expr() {
         Ok(expr) => return Ok(expr),
         Err(err) => err.emit(),
@@ -209,7 +208,7 @@ pub(crate) fn get_single_expr_from_tts(
     span: Span,
     tts: TokenStream,
     name: &str,
-) -> ExpandResult<Result<P<ast::Expr>, ErrorGuaranteed>, ()> {
+) -> ExpandResult<Result<Box<ast::Expr>, ErrorGuaranteed>, ()> {
     let mut p = cx.new_parser_from_tts(tts);
     if p.token == token::Eof {
         let guar = cx.dcx().emit_err(errors::OnlyOneArgument { span, name });
@@ -232,7 +231,7 @@ pub(crate) fn get_single_expr_from_tts(
 pub(crate) fn get_exprs_from_tts(
     cx: &mut ExtCtxt<'_>,
     tts: TokenStream,
-) -> ExpandResult<Result<Vec<P<ast::Expr>>, ErrorGuaranteed>, ()> {
+) -> ExpandResult<Result<Vec<Box<ast::Expr>>, ErrorGuaranteed>, ()> {
     let mut p = cx.new_parser_from_tts(tts);
     let mut es = Vec::new();
     while p.token != token::Eof {
diff --git a/compiler/rustc_codegen_cranelift/src/constant.rs b/compiler/rustc_codegen_cranelift/src/constant.rs
index a04cfa27237..a56466750e7 100644
--- a/compiler/rustc_codegen_cranelift/src/constant.rs
+++ b/compiler/rustc_codegen_cranelift/src/constant.rs
@@ -281,8 +281,8 @@ fn data_id_for_static(
             .abi
             .bytes();
 
-        let linkage = if import_linkage == rustc_middle::mir::mono::Linkage::ExternalWeak
-            || import_linkage == rustc_middle::mir::mono::Linkage::WeakAny
+        let linkage = if import_linkage == rustc_hir::attrs::Linkage::ExternalWeak
+            || import_linkage == rustc_hir::attrs::Linkage::WeakAny
         {
             Linkage::Preemptible
         } else {
@@ -310,7 +310,10 @@ fn data_id_for_static(
         // `extern_with_linkage_foo` will instead be initialized to
         // zero.
 
-        let ref_name = format!("_rust_extern_with_linkage_{}", symbol_name);
+        let ref_name = format!(
+            "_rust_extern_with_linkage_{:016x}_{symbol_name}",
+            tcx.stable_crate_id(LOCAL_CRATE)
+        );
         let ref_data_id = module.declare_data(&ref_name, Linkage::Local, false, false).unwrap();
         let mut data = DataDescription::new();
         data.set_align(align);
@@ -329,8 +332,8 @@ fn data_id_for_static(
 
     let linkage = if definition {
         crate::linkage::get_static_linkage(tcx, def_id)
-    } else if attrs.linkage == Some(rustc_middle::mir::mono::Linkage::ExternalWeak)
-        || attrs.linkage == Some(rustc_middle::mir::mono::Linkage::WeakAny)
+    } else if attrs.linkage == Some(rustc_hir::attrs::Linkage::ExternalWeak)
+        || attrs.linkage == Some(rustc_hir::attrs::Linkage::WeakAny)
     {
         Linkage::Preemptible
     } else {
diff --git a/compiler/rustc_codegen_cranelift/src/driver/aot.rs b/compiler/rustc_codegen_cranelift/src/driver/aot.rs
index 8ec3599b63d..7e77781dc2f 100644
--- a/compiler/rustc_codegen_cranelift/src/driver/aot.rs
+++ b/compiler/rustc_codegen_cranelift/src/driver/aot.rs
@@ -18,12 +18,11 @@ use rustc_codegen_ssa::{
 use rustc_data_structures::profiling::SelfProfilerRef;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::{IntoDynSyncSend, par_map};
+use rustc_hir::attrs::Linkage as RLinkage;
 use rustc_metadata::fs::copy_to_stdout;
 use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
-use rustc_middle::mir::mono::{
-    CodegenUnit, Linkage as RLinkage, MonoItem, MonoItemData, Visibility,
-};
+use rustc_middle::mir::mono::{CodegenUnit, MonoItem, MonoItemData, Visibility};
 use rustc_session::Session;
 use rustc_session::config::{DebugInfo, OutFileName, OutputFilenames, OutputType};
 
diff --git a/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs b/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
index 4ff5773a06c..ed40901ac9b 100644
--- a/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
+++ b/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
@@ -969,7 +969,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
 
             let layout = amount.layout();
             match layout.ty.kind() {
-                ty::Uint(_) | ty::Int(_) | ty::RawPtr(..) => {}
+                ty::Uint(_) | ty::Int(_) => {}
                 _ => {
                     report_atomic_type_validation_error(fx, intrinsic, source_info.span, layout.ty);
                     return Ok(());
@@ -982,7 +982,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
             let old =
                 fx.bcx.ins().atomic_rmw(ty, MemFlags::trusted(), AtomicRmwOp::Add, ptr, amount);
 
-            let old = CValue::by_val(old, layout);
+            let old = CValue::by_val(old, ret.layout());
             ret.write_cvalue(fx, old);
         }
         sym::atomic_xsub => {
@@ -991,7 +991,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
 
             let layout = amount.layout();
             match layout.ty.kind() {
-                ty::Uint(_) | ty::Int(_) | ty::RawPtr(..) => {}
+                ty::Uint(_) | ty::Int(_) => {}
                 _ => {
                     report_atomic_type_validation_error(fx, intrinsic, source_info.span, layout.ty);
                     return Ok(());
@@ -1004,7 +1004,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
             let old =
                 fx.bcx.ins().atomic_rmw(ty, MemFlags::trusted(), AtomicRmwOp::Sub, ptr, amount);
 
-            let old = CValue::by_val(old, layout);
+            let old = CValue::by_val(old, ret.layout());
             ret.write_cvalue(fx, old);
         }
         sym::atomic_and => {
@@ -1013,7 +1013,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
 
             let layout = src.layout();
             match layout.ty.kind() {
-                ty::Uint(_) | ty::Int(_) | ty::RawPtr(..) => {}
+                ty::Uint(_) | ty::Int(_) => {}
                 _ => {
                     report_atomic_type_validation_error(fx, intrinsic, source_info.span, layout.ty);
                     return Ok(());
@@ -1025,7 +1025,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
 
             let old = fx.bcx.ins().atomic_rmw(ty, MemFlags::trusted(), AtomicRmwOp::And, ptr, src);
 
-            let old = CValue::by_val(old, layout);
+            let old = CValue::by_val(old, ret.layout());
             ret.write_cvalue(fx, old);
         }
         sym::atomic_or => {
@@ -1034,7 +1034,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
 
             let layout = src.layout();
             match layout.ty.kind() {
-                ty::Uint(_) | ty::Int(_) | ty::RawPtr(..) => {}
+                ty::Uint(_) | ty::Int(_) => {}
                 _ => {
                     report_atomic_type_validation_error(fx, intrinsic, source_info.span, layout.ty);
                     return Ok(());
@@ -1046,7 +1046,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
 
             let old = fx.bcx.ins().atomic_rmw(ty, MemFlags::trusted(), AtomicRmwOp::Or, ptr, src);
 
-            let old = CValue::by_val(old, layout);
+            let old = CValue::by_val(old, ret.layout());
             ret.write_cvalue(fx, old);
         }
         sym::atomic_xor => {
@@ -1055,7 +1055,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
 
             let layout = src.layout();
             match layout.ty.kind() {
-                ty::Uint(_) | ty::Int(_) | ty::RawPtr(..) => {}
+                ty::Uint(_) | ty::Int(_) => {}
                 _ => {
                     report_atomic_type_validation_error(fx, intrinsic, source_info.span, layout.ty);
                     return Ok(());
@@ -1067,7 +1067,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
 
             let old = fx.bcx.ins().atomic_rmw(ty, MemFlags::trusted(), AtomicRmwOp::Xor, ptr, src);
 
-            let old = CValue::by_val(old, layout);
+            let old = CValue::by_val(old, ret.layout());
             ret.write_cvalue(fx, old);
         }
         sym::atomic_nand => {
@@ -1076,7 +1076,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
 
             let layout = src.layout();
             match layout.ty.kind() {
-                ty::Uint(_) | ty::Int(_) | ty::RawPtr(..) => {}
+                ty::Uint(_) | ty::Int(_) => {}
                 _ => {
                     report_atomic_type_validation_error(fx, intrinsic, source_info.span, layout.ty);
                     return Ok(());
@@ -1088,7 +1088,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
 
             let old = fx.bcx.ins().atomic_rmw(ty, MemFlags::trusted(), AtomicRmwOp::Nand, ptr, src);
 
-            let old = CValue::by_val(old, layout);
+            let old = CValue::by_val(old, ret.layout());
             ret.write_cvalue(fx, old);
         }
         sym::atomic_max => {
diff --git a/compiler/rustc_codegen_cranelift/src/linkage.rs b/compiler/rustc_codegen_cranelift/src/linkage.rs
index ca853aac158..d76ab9d0109 100644
--- a/compiler/rustc_codegen_cranelift/src/linkage.rs
+++ b/compiler/rustc_codegen_cranelift/src/linkage.rs
@@ -1,4 +1,5 @@
-use rustc_middle::mir::mono::{Linkage as RLinkage, MonoItem, Visibility};
+use rustc_hir::attrs::Linkage as RLinkage;
+use rustc_middle::mir::mono::{MonoItem, Visibility};
 
 use crate::prelude::*;
 
diff --git a/compiler/rustc_codegen_gcc/src/base.rs b/compiler/rustc_codegen_gcc/src/base.rs
index c105916bbb2..e9d72e457a0 100644
--- a/compiler/rustc_codegen_gcc/src/base.rs
+++ b/compiler/rustc_codegen_gcc/src/base.rs
@@ -8,8 +8,8 @@ use rustc_codegen_ssa::ModuleCodegen;
 use rustc_codegen_ssa::base::maybe_create_entry_wrapper;
 use rustc_codegen_ssa::mono_item::MonoItemExt;
 use rustc_codegen_ssa::traits::DebugInfoCodegenMethods;
+use rustc_hir::attrs::Linkage;
 use rustc_middle::dep_graph;
-use rustc_middle::mir::mono::Linkage;
 #[cfg(feature = "master")]
 use rustc_middle::mir::mono::Visibility;
 use rustc_middle::ty::TyCtxt;
diff --git a/compiler/rustc_codegen_gcc/src/builder.rs b/compiler/rustc_codegen_gcc/src/builder.rs
index 34ade3d025f..f7a7a3f8c7e 100644
--- a/compiler/rustc_codegen_gcc/src/builder.rs
+++ b/compiler/rustc_codegen_gcc/src/builder.rs
@@ -1671,6 +1671,7 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
         dst: RValue<'gcc>,
         src: RValue<'gcc>,
         order: AtomicOrdering,
+        ret_ptr: bool,
     ) -> RValue<'gcc> {
         let size = get_maybe_pointer_size(src);
         let name = match op {
@@ -1698,6 +1699,9 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
         let atomic_function = self.context.get_builtin_function(name);
         let order = self.context.new_rvalue_from_int(self.i32_type, order.to_gcc());
 
+        // FIXME: If `ret_ptr` is true and `src` is an integer, we should really tell GCC
+        // that this is a pointer operation that needs to preserve provenance -- but like LLVM,
+        // GCC does not currently seems to support that.
         let void_ptr_type = self.context.new_type::<*mut ()>();
         let volatile_void_ptr_type = void_ptr_type.make_volatile();
         let dst = self.context.new_cast(self.location, dst, volatile_void_ptr_type);
@@ -1705,7 +1709,8 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
         let new_src_type = atomic_function.get_param(1).to_rvalue().get_type();
         let src = self.context.new_bitcast(self.location, src, new_src_type);
         let res = self.context.new_call(self.location, atomic_function, &[dst, src, order]);
-        self.context.new_cast(self.location, res, src.get_type())
+        let res_type = if ret_ptr { void_ptr_type } else { src.get_type() };
+        self.context.new_cast(self.location, res, res_type)
     }
 
     fn atomic_fence(&mut self, order: AtomicOrdering, scope: SynchronizationScope) {
diff --git a/compiler/rustc_codegen_gcc/src/consts.rs b/compiler/rustc_codegen_gcc/src/consts.rs
index c04c75e1b11..619277eba8b 100644
--- a/compiler/rustc_codegen_gcc/src/consts.rs
+++ b/compiler/rustc_codegen_gcc/src/consts.rs
@@ -5,12 +5,13 @@ use rustc_abi::{self as abi, Align, HasDataLayout, Primitive, Size, WrappingRang
 use rustc_codegen_ssa::traits::{
     BaseTypeCodegenMethods, ConstCodegenMethods, StaticCodegenMethods,
 };
+use rustc_hir::attrs::Linkage;
 use rustc_hir::def::DefKind;
+use rustc_hir::def_id::LOCAL_CRATE;
 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
 use rustc_middle::mir::interpret::{
     self, ConstAllocation, ErrorHandled, Scalar as InterpScalar, read_target_uint,
 };
-use rustc_middle::mir::mono::Linkage;
 use rustc_middle::ty::layout::LayoutOf;
 use rustc_middle::ty::{self, Instance};
 use rustc_middle::{bug, span_bug};
@@ -384,8 +385,8 @@ fn check_and_apply_linkage<'gcc, 'tcx>(
         // linkage and there are no definitions), then
         // `extern_with_linkage_foo` will instead be initialized to
         // zero.
-        let mut real_name = "_rust_extern_with_linkage_".to_string();
-        real_name.push_str(sym);
+        let real_name =
+            format!("_rust_extern_with_linkage_{:016x}_{sym}", cx.tcx.stable_crate_id(LOCAL_CRATE));
         let global2 = cx.define_global(&real_name, gcc_type, is_tls, attrs.link_section);
         // TODO(antoyo): set linkage.
         let value = cx.const_ptrcast(global1.get_address(None), gcc_type);
diff --git a/compiler/rustc_codegen_gcc/src/debuginfo.rs b/compiler/rustc_codegen_gcc/src/debuginfo.rs
index 4c0b6439523..4c8585192a1 100644
--- a/compiler/rustc_codegen_gcc/src/debuginfo.rs
+++ b/compiler/rustc_codegen_gcc/src/debuginfo.rs
@@ -254,8 +254,7 @@ impl<'gcc, 'tcx> DebugInfoCodegenMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
         // TODO(antoyo): implement.
     }
 
-    fn debuginfo_finalize(&mut self) {
-        // TODO: emit section `.debug_gdb_scripts`.
+    fn debuginfo_finalize(&self) {
         self.context.set_debug_info(true)
     }
 
diff --git a/compiler/rustc_codegen_gcc/src/lib.rs b/compiler/rustc_codegen_gcc/src/lib.rs
index b11f11d38e3..4025aba82da 100644
--- a/compiler/rustc_codegen_gcc/src/lib.rs
+++ b/compiler/rustc_codegen_gcc/src/lib.rs
@@ -93,7 +93,6 @@ use gccjit::{CType, Context, OptimizationLevel};
 #[cfg(feature = "master")]
 use gccjit::{TargetInfo, Version};
 use rustc_ast::expand::allocator::AllocatorKind;
-use rustc_ast::expand::autodiff_attrs::AutoDiffItem;
 use rustc_codegen_ssa::back::lto::{SerializedModule, ThinModule};
 use rustc_codegen_ssa::back::write::{
     CodegenContext, FatLtoInput, ModuleConfig, TargetMachineFactoryFn,
@@ -363,12 +362,7 @@ impl WriteBackendMethods for GccCodegenBackend {
         _exported_symbols_for_lto: &[String],
         each_linked_rlib_for_lto: &[PathBuf],
         modules: Vec<FatLtoInput<Self>>,
-        diff_functions: Vec<AutoDiffItem>,
     ) -> Result<ModuleCodegen<Self::Module>, FatalError> {
-        if !diff_functions.is_empty() {
-            unimplemented!();
-        }
-
         back::lto::run_fat(cgcx, each_linked_rlib_for_lto, modules)
     }
 
diff --git a/compiler/rustc_codegen_gcc/src/mono_item.rs b/compiler/rustc_codegen_gcc/src/mono_item.rs
index ff188c437da..35d44d21bcb 100644
--- a/compiler/rustc_codegen_gcc/src/mono_item.rs
+++ b/compiler/rustc_codegen_gcc/src/mono_item.rs
@@ -1,11 +1,12 @@
 #[cfg(feature = "master")]
 use gccjit::{FnAttribute, VarAttribute};
 use rustc_codegen_ssa::traits::PreDefineCodegenMethods;
+use rustc_hir::attrs::Linkage;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_middle::bug;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
-use rustc_middle::mir::mono::{Linkage, Visibility};
+use rustc_middle::mir::mono::Visibility;
 use rustc_middle::ty::layout::{FnAbiOf, HasTypingEnv, LayoutOf};
 use rustc_middle::ty::{self, Instance, TypeVisitableExt};
 
diff --git a/compiler/rustc_codegen_llvm/src/abi.rs b/compiler/rustc_codegen_llvm/src/abi.rs
index 009e7e2487b..043123fcab2 100644
--- a/compiler/rustc_codegen_llvm/src/abi.rs
+++ b/compiler/rustc_codegen_llvm/src/abi.rs
@@ -24,6 +24,7 @@ use crate::attributes::{self, llfn_attrs_from_instance};
 use crate::builder::Builder;
 use crate::context::CodegenCx;
 use crate::llvm::{self, Attribute, AttributePlace};
+use crate::llvm_util;
 use crate::type_::Type;
 use crate::type_of::LayoutLlvmExt;
 use crate::value::Value;
@@ -500,7 +501,16 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
                     }
                 }
                 PassMode::Indirect { attrs, meta_attrs: None, on_stack: false } => {
-                    apply(attrs);
+                    let i = apply(attrs);
+                    if cx.sess().opts.optimize != config::OptLevel::No
+                        && llvm_util::get_version() >= (21, 0, 0)
+                    {
+                        attributes::apply_to_llfn(
+                            llfn,
+                            llvm::AttributePlace::Argument(i),
+                            &[llvm::AttributeKind::DeadOnReturn.create_attr(cx.llcx)],
+                        );
+                    }
                 }
                 PassMode::Indirect { attrs, meta_attrs: Some(meta_attrs), on_stack } => {
                     assert!(!on_stack);
diff --git a/compiler/rustc_codegen_llvm/src/allocator.rs b/compiler/rustc_codegen_llvm/src/allocator.rs
index 2b5090ed6db..23610aa856c 100644
--- a/compiler/rustc_codegen_llvm/src/allocator.rs
+++ b/compiler/rustc_codegen_llvm/src/allocator.rs
@@ -8,11 +8,12 @@ use rustc_middle::bug;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::config::{DebugInfo, OomStrategy};
 use rustc_symbol_mangling::mangle_internal_symbol;
+use smallvec::SmallVec;
 
 use crate::builder::SBuilder;
 use crate::declare::declare_simple_fn;
 use crate::llvm::{self, False, True, Type, Value};
-use crate::{SimpleCx, attributes, debuginfo};
+use crate::{SimpleCx, attributes, debuginfo, llvm_util};
 
 pub(crate) unsafe fn codegen(
     tcx: TyCtxt<'_>,
@@ -147,6 +148,20 @@ fn create_wrapper_function(
         llvm::Visibility::from_generic(tcx.sess.default_visibility()),
         ty,
     );
+
+    let mut attrs = SmallVec::<[_; 2]>::new();
+
+    let target_cpu = llvm_util::target_cpu(tcx.sess);
+    let target_cpu_attr = llvm::CreateAttrStringValue(cx.llcx, "target-cpu", target_cpu);
+
+    let tune_cpu_attr = llvm_util::tune_cpu(tcx.sess)
+        .map(|tune_cpu| llvm::CreateAttrStringValue(cx.llcx, "tune-cpu", tune_cpu));
+
+    attrs.push(target_cpu_attr);
+    attrs.extend(tune_cpu_attr);
+
+    attributes::apply_to_llfn(llfn, llvm::AttributePlace::Function, &attrs);
+
     let no_return = if no_return {
         // -> ! DIFlagNoReturn
         let no_return = llvm::AttributeKind::NoReturn.create_attr(cx.llcx);
diff --git a/compiler/rustc_codegen_llvm/src/attributes.rs b/compiler/rustc_codegen_llvm/src/attributes.rs
index c548f467583..a6daacd95ef 100644
--- a/compiler/rustc_codegen_llvm/src/attributes.rs
+++ b/compiler/rustc_codegen_llvm/src/attributes.rs
@@ -28,22 +28,6 @@ pub(crate) fn apply_to_callsite(callsite: &Value, idx: AttributePlace, attrs: &[
     }
 }
 
-pub(crate) fn has_attr(llfn: &Value, idx: AttributePlace, attr: AttributeKind) -> bool {
-    llvm::HasAttributeAtIndex(llfn, idx, attr)
-}
-
-pub(crate) fn has_string_attr(llfn: &Value, name: &str) -> bool {
-    llvm::HasStringAttribute(llfn, name)
-}
-
-pub(crate) fn remove_from_llfn(llfn: &Value, place: AttributePlace, kind: AttributeKind) {
-    llvm::RemoveRustEnumAttributeAtIndex(llfn, place, kind);
-}
-
-pub(crate) fn remove_string_attr_from_llfn(llfn: &Value, name: &str) {
-    llvm::RemoveStringAttrFromFn(llfn, name);
-}
-
 /// Get LLVM attribute for the provided inline heuristic.
 #[inline]
 fn inline_attr<'ll>(cx: &CodegenCx<'ll, '_>, inline: InlineAttr) -> Option<&'ll Attribute> {
diff --git a/compiler/rustc_codegen_llvm/src/back/lto.rs b/compiler/rustc_codegen_llvm/src/back/lto.rs
index c269f11e931..853d0295238 100644
--- a/compiler/rustc_codegen_llvm/src/back/lto.rs
+++ b/compiler/rustc_codegen_llvm/src/back/lto.rs
@@ -24,9 +24,8 @@ use crate::back::write::{
     self, CodegenDiagnosticsStage, DiagnosticHandlers, bitcode_section_name, save_temp_bitcode,
 };
 use crate::errors::{LlvmError, LtoBitcodeFromRlib};
-use crate::llvm::AttributePlace::Function;
 use crate::llvm::{self, build_string};
-use crate::{LlvmCodegenBackend, ModuleLlvm, SimpleCx, attributes};
+use crate::{LlvmCodegenBackend, ModuleLlvm, SimpleCx};
 
 /// We keep track of the computed LTO cache keys from the previous
 /// session to determine which CGUs we can reuse.
@@ -593,31 +592,6 @@ pub(crate) fn run_pass_manager(
     }
 
     if cfg!(llvm_enzyme) && enable_ad && !thin {
-        let cx =
-            SimpleCx::new(module.module_llvm.llmod(), &module.module_llvm.llcx, cgcx.pointer_size);
-
-        for function in cx.get_functions() {
-            let enzyme_marker = "enzyme_marker";
-            if attributes::has_string_attr(function, enzyme_marker) {
-                // Sanity check: Ensure 'noinline' is present before replacing it.
-                assert!(
-                    attributes::has_attr(function, Function, llvm::AttributeKind::NoInline),
-                    "Expected __enzyme function to have 'noinline' before adding 'alwaysinline'"
-                );
-
-                attributes::remove_from_llfn(function, Function, llvm::AttributeKind::NoInline);
-                attributes::remove_string_attr_from_llfn(function, enzyme_marker);
-
-                assert!(
-                    !attributes::has_string_attr(function, enzyme_marker),
-                    "Expected function to not have 'enzyme_marker'"
-                );
-
-                let always_inline = llvm::AttributeKind::AlwaysInline.create_attr(cx.llcx);
-                attributes::apply_to_llfn(function, Function, &[always_inline]);
-            }
-        }
-
         let opt_stage = llvm::OptStage::FatLTO;
         let stage = write::AutodiffStage::PostAD;
         if !config.autodiff.contains(&config::AutoDiff::NoPostopt) {
diff --git a/compiler/rustc_codegen_llvm/src/back/write.rs b/compiler/rustc_codegen_llvm/src/back/write.rs
index 85a06f457eb..62998003ca1 100644
--- a/compiler/rustc_codegen_llvm/src/back/write.rs
+++ b/compiler/rustc_codegen_llvm/src/back/write.rs
@@ -862,7 +862,7 @@ pub(crate) fn codegen(
                     .generic_activity_with_arg("LLVM_module_codegen_embed_bitcode", &*module.name);
                 let thin_bc =
                     module.thin_lto_buffer.as_deref().expect("cannot find embedded bitcode");
-                embed_bitcode(cgcx, llcx, llmod, &config.bc_cmdline, &thin_bc);
+                embed_bitcode(cgcx, llcx, llmod, &thin_bc);
             }
         }
 
@@ -1058,7 +1058,6 @@ fn embed_bitcode(
     cgcx: &CodegenContext<LlvmCodegenBackend>,
     llcx: &llvm::Context,
     llmod: &llvm::Module,
-    cmdline: &str,
     bitcode: &[u8],
 ) {
     // We're adding custom sections to the output object file, but we definitely
@@ -1074,7 +1073,9 @@ fn embed_bitcode(
     // * Mach-O - this is for macOS. Inspecting the source code for the native
     //   linker here shows that the `.llvmbc` and `.llvmcmd` sections are
     //   automatically skipped by the linker. In that case there's nothing extra
-    //   that we need to do here.
+    //   that we need to do here. We do need to make sure that the
+    //   `__LLVM,__cmdline` section exists even though it is empty as otherwise
+    //   ld64 rejects the object file.
     //
     // * Wasm - the native LLD linker is hard-coded to skip `.llvmbc` and
     //   `.llvmcmd` sections, so there's nothing extra we need to do.
@@ -1111,7 +1112,7 @@ fn embed_bitcode(
         llvm::set_linkage(llglobal, llvm::Linkage::PrivateLinkage);
         llvm::LLVMSetGlobalConstant(llglobal, llvm::True);
 
-        let llconst = common::bytes_in_context(llcx, cmdline.as_bytes());
+        let llconst = common::bytes_in_context(llcx, &[]);
         let llglobal = llvm::add_global(llmod, common::val_ty(llconst), c"rustc.embedded.cmdline");
         llvm::set_initializer(llglobal, llconst);
         let section = if cgcx.target_is_like_darwin {
@@ -1128,7 +1129,7 @@ fn embed_bitcode(
         let section_flags = if cgcx.is_pe_coff { "n" } else { "e" };
         let asm = create_section_with_flags_asm(".llvmbc", section_flags, bitcode);
         llvm::append_module_inline_asm(llmod, &asm);
-        let asm = create_section_with_flags_asm(".llvmcmd", section_flags, cmdline.as_bytes());
+        let asm = create_section_with_flags_asm(".llvmcmd", section_flags, &[]);
         llvm::append_module_inline_asm(llmod, &asm);
     }
 }
diff --git a/compiler/rustc_codegen_llvm/src/base.rs b/compiler/rustc_codegen_llvm/src/base.rs
index d7da03bf490..9cc5d8dbc21 100644
--- a/compiler/rustc_codegen_llvm/src/base.rs
+++ b/compiler/rustc_codegen_llvm/src/base.rs
@@ -18,9 +18,10 @@ use rustc_codegen_ssa::base::maybe_create_entry_wrapper;
 use rustc_codegen_ssa::mono_item::MonoItemExt;
 use rustc_codegen_ssa::traits::*;
 use rustc_data_structures::small_c_str::SmallCStr;
+use rustc_hir::attrs::Linkage;
 use rustc_middle::dep_graph;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
-use rustc_middle::mir::mono::{Linkage, Visibility};
+use rustc_middle::mir::mono::Visibility;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::config::DebugInfo;
 use rustc_span::Symbol;
@@ -109,16 +110,11 @@ pub(crate) fn compile_codegen_unit(
             }
 
             // Finalize code coverage by injecting the coverage map. Note, the coverage map will
-            // also be added to the `llvm.compiler.used` variable, created below.
+            // also be added to the `llvm.compiler.used` variable, created next.
             if cx.sess().instrument_coverage() {
                 cx.coverageinfo_finalize();
             }
 
-            // Finalize debuginfo. This adds to `llvm.used`, created below.
-            if cx.sess().opts.debuginfo != DebugInfo::None {
-                cx.debuginfo_finalize();
-            }
-
             // Create the llvm.used and llvm.compiler.used variables.
             if !cx.used_statics.is_empty() {
                 cx.create_used_variable_impl(c"llvm.used", &cx.used_statics);
@@ -135,6 +131,11 @@ pub(crate) fn compile_codegen_unit(
                     llvm::LLVMDeleteGlobal(old_g);
                 }
             }
+
+            // Finalize debuginfo
+            if cx.sess().opts.debuginfo != DebugInfo::None {
+                cx.debuginfo_finalize();
+            }
         }
 
         ModuleCodegen::new_regular(cgu_name.to_string(), llvm_module)
diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs
index da2a153d819..cb98df59c1b 100644
--- a/compiler/rustc_codegen_llvm/src/builder.rs
+++ b/compiler/rustc_codegen_llvm/src/builder.rs
@@ -557,13 +557,25 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         let (size, signed) = ty.int_size_and_signed(self.tcx);
         let width = size.bits();
 
-        if oop == OverflowOp::Sub && !signed {
-            // Emit sub and icmp instead of llvm.usub.with.overflow. LLVM considers these
-            // to be the canonical form. It will attempt to reform llvm.usub.with.overflow
-            // in the backend if profitable.
-            let sub = self.sub(lhs, rhs);
-            let cmp = self.icmp(IntPredicate::IntULT, lhs, rhs);
-            return (sub, cmp);
+        if !signed {
+            match oop {
+                OverflowOp::Sub => {
+                    // Emit sub and icmp instead of llvm.usub.with.overflow. LLVM considers these
+                    // to be the canonical form. It will attempt to reform llvm.usub.with.overflow
+                    // in the backend if profitable.
+                    let sub = self.sub(lhs, rhs);
+                    let cmp = self.icmp(IntPredicate::IntULT, lhs, rhs);
+                    return (sub, cmp);
+                }
+                OverflowOp::Add => {
+                    // Like with sub above, using icmp is the preferred form. See
+                    // <https://rust-lang.zulipchat.com/#narrow/channel/187780-t-compiler.2Fllvm/topic/.60uadd.2Ewith.2Eoverflow.60.20.28again.29/near/533041085>
+                    let add = self.add(lhs, rhs);
+                    let cmp = self.icmp(IntPredicate::IntULT, add, lhs);
+                    return (add, cmp);
+                }
+                OverflowOp::Mul => {}
+            }
         }
 
         let oop_str = match oop {
@@ -1327,15 +1339,13 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         &mut self,
         op: rustc_codegen_ssa::common::AtomicRmwBinOp,
         dst: &'ll Value,
-        mut src: &'ll Value,
+        src: &'ll Value,
         order: rustc_middle::ty::AtomicOrdering,
+        ret_ptr: bool,
     ) -> &'ll Value {
-        // The only RMW operation that LLVM supports on pointers is compare-exchange.
-        let requires_cast_to_int = self.val_ty(src) == self.type_ptr()
-            && op != rustc_codegen_ssa::common::AtomicRmwBinOp::AtomicXchg;
-        if requires_cast_to_int {
-            src = self.ptrtoint(src, self.type_isize());
-        }
+        // FIXME: If `ret_ptr` is true and `src` is not a pointer, we *should* tell LLVM that the
+        // LHS is a pointer and the operation should be provenance-preserving, but LLVM does not
+        // currently support that (https://github.com/llvm/llvm-project/issues/120837).
         let mut res = unsafe {
             llvm::LLVMBuildAtomicRMW(
                 self.llbuilder,
@@ -1346,7 +1356,7 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
                 llvm::False, // SingleThreaded
             )
         };
-        if requires_cast_to_int {
+        if ret_ptr && self.val_ty(res) != self.type_ptr() {
             res = self.inttoptr(res, self.type_ptr());
         }
         res
@@ -1686,7 +1696,11 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
             return;
         }
 
-        self.call_intrinsic(intrinsic, &[self.val_ty(ptr)], &[self.cx.const_u64(size), ptr]);
+        if crate::llvm_util::get_version() >= (22, 0, 0) {
+            self.call_intrinsic(intrinsic, &[self.val_ty(ptr)], &[ptr]);
+        } else {
+            self.call_intrinsic(intrinsic, &[self.val_ty(ptr)], &[self.cx.const_u64(size), ptr]);
+        }
     }
 }
 impl<'a, 'll, CX: Borrow<SCx<'ll>>> GenericBuilder<'a, 'll, CX> {
@@ -1886,48 +1900,4 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
     ) {
         self.call_intrinsic("llvm.instrprof.increment", &[], &[fn_name, hash, num_counters, index]);
     }
-
-    /// Emits a call to `llvm.instrprof.mcdc.parameters`.
-    ///
-    /// This doesn't produce any code directly, but is used as input by
-    /// the LLVM pass that handles coverage instrumentation.
-    ///
-    /// (See clang's [`CodeGenPGO::emitMCDCParameters`] for comparison.)
-    ///
-    /// [`CodeGenPGO::emitMCDCParameters`]:
-    ///     https://github.com/rust-lang/llvm-project/blob/5399a24/clang/lib/CodeGen/CodeGenPGO.cpp#L1124
-    #[instrument(level = "debug", skip(self))]
-    pub(crate) fn mcdc_parameters(
-        &mut self,
-        fn_name: &'ll Value,
-        hash: &'ll Value,
-        bitmap_bits: &'ll Value,
-    ) {
-        self.call_intrinsic("llvm.instrprof.mcdc.parameters", &[], &[fn_name, hash, bitmap_bits]);
-    }
-
-    #[instrument(level = "debug", skip(self))]
-    pub(crate) fn mcdc_tvbitmap_update(
-        &mut self,
-        fn_name: &'ll Value,
-        hash: &'ll Value,
-        bitmap_index: &'ll Value,
-        mcdc_temp: &'ll Value,
-    ) {
-        let args = &[fn_name, hash, bitmap_index, mcdc_temp];
-        self.call_intrinsic("llvm.instrprof.mcdc.tvbitmap.update", &[], args);
-    }
-
-    #[instrument(level = "debug", skip(self))]
-    pub(crate) fn mcdc_condbitmap_reset(&mut self, mcdc_temp: &'ll Value) {
-        self.store(self.const_i32(0), mcdc_temp, self.tcx.data_layout.i32_align.abi);
-    }
-
-    #[instrument(level = "debug", skip(self))]
-    pub(crate) fn mcdc_condbitmap_update(&mut self, cond_index: &'ll Value, mcdc_temp: &'ll Value) {
-        let align = self.tcx.data_layout.i32_align.abi;
-        let current_tv_index = self.load(self.cx.type_i32(), mcdc_temp, align);
-        let new_tv_index = self.add(current_tv_index, cond_index);
-        self.store(new_tv_index, mcdc_temp, align);
-    }
 }
diff --git a/compiler/rustc_codegen_llvm/src/builder/autodiff.rs b/compiler/rustc_codegen_llvm/src/builder/autodiff.rs
index 829b3c513c2..e2df3265f6f 100644
--- a/compiler/rustc_codegen_llvm/src/builder/autodiff.rs
+++ b/compiler/rustc_codegen_llvm/src/builder/autodiff.rs
@@ -1,40 +1,92 @@
 use std::ptr;
 
-use rustc_ast::expand::autodiff_attrs::{AutoDiffAttrs, AutoDiffItem, DiffActivity, DiffMode};
-use rustc_codegen_ssa::ModuleCodegen;
+use rustc_ast::expand::autodiff_attrs::{AutoDiffAttrs, DiffActivity, DiffMode};
 use rustc_codegen_ssa::common::TypeKind;
-use rustc_codegen_ssa::traits::BaseTypeCodegenMethods;
-use rustc_errors::FatalError;
-use rustc_middle::bug;
-use tracing::{debug, trace};
+use rustc_codegen_ssa::traits::{BaseTypeCodegenMethods, BuilderMethods};
+use rustc_middle::ty::{PseudoCanonicalInput, Ty, TyCtxt, TypingEnv};
+use rustc_middle::{bug, ty};
+use tracing::debug;
 
-use crate::back::write::llvm_err;
-use crate::builder::{SBuilder, UNNAMED};
+use crate::builder::{Builder, PlaceRef, UNNAMED};
 use crate::context::SimpleCx;
 use crate::declare::declare_simple_fn;
-use crate::errors::{AutoDiffWithoutEnable, LlvmError};
-use crate::llvm::AttributePlace::Function;
-use crate::llvm::{Metadata, True};
+use crate::llvm;
+use crate::llvm::{Metadata, True, Type};
 use crate::value::Value;
-use crate::{CodegenContext, LlvmCodegenBackend, ModuleLlvm, attributes, llvm};
 
-fn get_params(fnc: &Value) -> Vec<&Value> {
-    let param_num = llvm::LLVMCountParams(fnc) as usize;
-    let mut fnc_args: Vec<&Value> = vec![];
-    fnc_args.reserve(param_num);
-    unsafe {
-        llvm::LLVMGetParams(fnc, fnc_args.as_mut_ptr());
-        fnc_args.set_len(param_num);
+pub(crate) fn adjust_activity_to_abi<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    fn_ty: Ty<'tcx>,
+    da: &mut Vec<DiffActivity>,
+) {
+    if !matches!(fn_ty.kind(), ty::FnDef(..)) {
+        bug!("expected fn def for autodiff, got {:?}", fn_ty);
     }
-    fnc_args
-}
 
-fn has_sret(fnc: &Value) -> bool {
-    let num_args = llvm::LLVMCountParams(fnc) as usize;
-    if num_args == 0 {
-        false
-    } else {
-        unsafe { llvm::LLVMRustHasAttributeAtIndex(fnc, 0, llvm::AttributeKind::StructRet) }
+    // We don't actually pass the types back into the type system.
+    // All we do is decide how to handle the arguments.
+    let sig = fn_ty.fn_sig(tcx).skip_binder();
+
+    let mut new_activities = vec![];
+    let mut new_positions = vec![];
+    for (i, ty) in sig.inputs().iter().enumerate() {
+        if let Some(inner_ty) = ty.builtin_deref(true) {
+            if inner_ty.is_slice() {
+                // Now we need to figure out the size of each slice element in memory to allow
+                // safety checks and usability improvements in the backend.
+                let sty = match inner_ty.builtin_index() {
+                    Some(sty) => sty,
+                    None => {
+                        panic!("slice element type unknown");
+                    }
+                };
+                let pci = PseudoCanonicalInput {
+                    typing_env: TypingEnv::fully_monomorphized(),
+                    value: sty,
+                };
+
+                let layout = tcx.layout_of(pci);
+                let elem_size = match layout {
+                    Ok(layout) => layout.size,
+                    Err(_) => {
+                        bug!("autodiff failed to compute slice element size");
+                    }
+                };
+                let elem_size: u32 = elem_size.bytes() as u32;
+
+                // We know that the length will be passed as extra arg.
+                if !da.is_empty() {
+                    // We are looking at a slice. The length of that slice will become an
+                    // extra integer on llvm level. Integers are always const.
+                    // However, if the slice get's duplicated, we want to know to later check the
+                    // size. So we mark the new size argument as FakeActivitySize.
+                    // There is one FakeActivitySize per slice, so for convenience we store the
+                    // slice element size in bytes in it. We will use the size in the backend.
+                    let activity = match da[i] {
+                        DiffActivity::DualOnly
+                        | DiffActivity::Dual
+                        | DiffActivity::Dualv
+                        | DiffActivity::DuplicatedOnly
+                        | DiffActivity::Duplicated => {
+                            DiffActivity::FakeActivitySize(Some(elem_size))
+                        }
+                        DiffActivity::Const => DiffActivity::Const,
+                        _ => bug!("unexpected activity for ptr/ref"),
+                    };
+                    new_activities.push(activity);
+                    new_positions.push(i + 1);
+                }
+
+                continue;
+            }
+        }
+    }
+    // now add the extra activities coming from slices
+    // Reverse order to not invalidate the indices
+    for _ in 0..new_activities.len() {
+        let pos = new_positions.pop().unwrap();
+        let activity = new_activities.pop().unwrap();
+        da.insert(pos, activity);
     }
 }
 
@@ -48,14 +100,13 @@ fn has_sret(fnc: &Value) -> bool {
 // need to match those.
 // FIXME(ZuseZ4): This logic is a bit more complicated than it should be, can we simplify it
 // using iterators and peek()?
-fn match_args_from_caller_to_enzyme<'ll>(
+fn match_args_from_caller_to_enzyme<'ll, 'tcx>(
     cx: &SimpleCx<'ll>,
-    builder: &SBuilder<'ll, 'll>,
+    builder: &mut Builder<'_, 'll, 'tcx>,
     width: u32,
     args: &mut Vec<&'ll llvm::Value>,
     inputs: &[DiffActivity],
     outer_args: &[&'ll llvm::Value],
-    has_sret: bool,
 ) {
     debug!("matching autodiff arguments");
     // We now handle the issue that Rust level arguments not always match the llvm-ir level
@@ -67,14 +118,6 @@ fn match_args_from_caller_to_enzyme<'ll>(
     let mut outer_pos: usize = 0;
     let mut activity_pos = 0;
 
-    if has_sret {
-        // Then the first outer arg is the sret pointer. Enzyme doesn't know about sret, so the
-        // inner function will still return something. We increase our outer_pos by one,
-        // and once we're done with all other args we will take the return of the inner call and
-        // update the sret pointer with it
-        outer_pos = 1;
-    }
-
     let enzyme_const = cx.create_metadata(b"enzyme_const");
     let enzyme_out = cx.create_metadata(b"enzyme_out");
     let enzyme_dup = cx.create_metadata(b"enzyme_dup");
@@ -193,92 +236,6 @@ fn match_args_from_caller_to_enzyme<'ll>(
     }
 }
 
-// On LLVM-IR, we can luckily declare __enzyme_ functions without specifying the input
-// arguments. We do however need to declare them with their correct return type.
-// We already figured the correct return type out in our frontend, when generating the outer_fn,
-// so we can now just go ahead and use that. This is not always trivial, e.g. because sret.
-// Beyond sret, this article describes our challenges nicely:
-// <https://yorickpeterse.com/articles/the-mess-that-is-handling-structure-arguments-and-returns-in-llvm/>
-// I.e. (i32, f32) will get merged into i64, but we don't handle that yet.
-fn compute_enzyme_fn_ty<'ll>(
-    cx: &SimpleCx<'ll>,
-    attrs: &AutoDiffAttrs,
-    fn_to_diff: &'ll Value,
-    outer_fn: &'ll Value,
-) -> &'ll llvm::Type {
-    let fn_ty = cx.get_type_of_global(outer_fn);
-    let mut ret_ty = cx.get_return_type(fn_ty);
-
-    let has_sret = has_sret(outer_fn);
-
-    if has_sret {
-        // Now we don't just forward the return type, so we have to figure it out based on the
-        // primal return type, in combination with the autodiff settings.
-        let fn_ty = cx.get_type_of_global(fn_to_diff);
-        let inner_ret_ty = cx.get_return_type(fn_ty);
-
-        let void_ty = unsafe { llvm::LLVMVoidTypeInContext(cx.llcx) };
-        if inner_ret_ty == void_ty {
-            // This indicates that even the inner function has an sret.
-            // Right now I only look for an sret in the outer function.
-            // This *probably* needs some extra handling, but I never ran
-            // into such a case. So I'll wait for user reports to have a test case.
-            bug!("sret in inner function");
-        }
-
-        if attrs.width == 1 {
-            // Enzyme returns a struct of style:
-            // `{ original_ret(if requested), float, float, ... }`
-            let mut struct_elements = vec![];
-            if attrs.has_primal_ret() {
-                struct_elements.push(inner_ret_ty);
-            }
-            // Next, we push the list of active floats, since they will be lowered to `enzyme_out`,
-            // and therefore part of the return struct.
-            let param_tys = cx.func_params_types(fn_ty);
-            for (act, param_ty) in attrs.input_activity.iter().zip(param_tys) {
-                if matches!(act, DiffActivity::Active) {
-                    // Now find the float type at position i based on the fn_ty,
-                    // to know what (f16/f32/f64/...) to add to the struct.
-                    struct_elements.push(param_ty);
-                }
-            }
-            ret_ty = cx.type_struct(&struct_elements, false);
-        } else {
-            // First we check if we also have to deal with the primal return.
-            match attrs.mode {
-                DiffMode::Forward => match attrs.ret_activity {
-                    DiffActivity::Dual => {
-                        let arr_ty =
-                            unsafe { llvm::LLVMArrayType2(inner_ret_ty, attrs.width as u64 + 1) };
-                        ret_ty = arr_ty;
-                    }
-                    DiffActivity::DualOnly => {
-                        let arr_ty =
-                            unsafe { llvm::LLVMArrayType2(inner_ret_ty, attrs.width as u64) };
-                        ret_ty = arr_ty;
-                    }
-                    DiffActivity::Const => {
-                        todo!("Not sure, do we need to do something here?");
-                    }
-                    _ => {
-                        bug!("unreachable");
-                    }
-                },
-                DiffMode::Reverse => {
-                    todo!("Handle sret for reverse mode");
-                }
-                _ => {
-                    bug!("unreachable");
-                }
-            }
-        }
-    }
-
-    // LLVM can figure out the input types on it's own, so we take a shortcut here.
-    unsafe { llvm::LLVMFunctionType(ret_ty, ptr::null(), 0, True) }
-}
-
 /// When differentiating `fn_to_diff`, take a `outer_fn` and generate another
 /// function with expected naming and calling conventions[^1] which will be
 /// discovered by the enzyme LLVM pass and its body populated with the differentiated
@@ -288,11 +245,15 @@ fn compute_enzyme_fn_ty<'ll>(
 /// [^1]: <https://enzyme.mit.edu/getting_started/CallingConvention/>
 // FIXME(ZuseZ4): `outer_fn` should include upstream safety checks to
 // cover some assumptions of enzyme/autodiff, which could lead to UB otherwise.
-fn generate_enzyme_call<'ll>(
+pub(crate) fn generate_enzyme_call<'ll, 'tcx>(
+    builder: &mut Builder<'_, 'll, 'tcx>,
     cx: &SimpleCx<'ll>,
     fn_to_diff: &'ll Value,
-    outer_fn: &'ll Value,
+    outer_name: &str,
+    ret_ty: &'ll Type,
+    fn_args: &[&'ll Value],
     attrs: AutoDiffAttrs,
+    dest: PlaceRef<'tcx, &'ll Value>,
 ) {
     // We have to pick the name depending on whether we want forward or reverse mode autodiff.
     let mut ad_name: String = match attrs.mode {
@@ -302,11 +263,9 @@ fn generate_enzyme_call<'ll>(
     }
     .to_string();
 
-    // add outer_fn name to ad_name to make it unique, in case users apply autodiff to multiple
+    // add outer_name to ad_name to make it unique, in case users apply autodiff to multiple
     // functions. Unwrap will only panic, if LLVM gave us an invalid string.
-    let name = llvm::get_value_name(outer_fn);
-    let outer_fn_name = std::str::from_utf8(&name).unwrap();
-    ad_name.push_str(outer_fn_name);
+    ad_name.push_str(outer_name);
 
     // Let us assume the user wrote the following function square:
     //
@@ -316,14 +275,8 @@ fn generate_enzyme_call<'ll>(
     //  %0 = fmul double %x, %x
     //  ret double %0
     // }
-    // ```
-    //
-    // The user now applies autodiff to the function square, in which case fn_to_diff will be `square`.
-    // Our macro generates the following placeholder code (slightly simplified):
     //
-    // ```llvm
     // define double @dsquare(double %x) {
-    //  ; placeholder code
     //  return 0.0;
     // }
     // ```
@@ -340,175 +293,44 @@ fn generate_enzyme_call<'ll>(
     //   ret double %0
     // }
     // ```
-    unsafe {
-        let enzyme_ty = compute_enzyme_fn_ty(cx, &attrs, fn_to_diff, outer_fn);
-
-        // FIXME(ZuseZ4): the CC/Addr/Vis values are best effort guesses, we should look at tests and
-        // think a bit more about what should go here.
-        let cc = llvm::LLVMGetFunctionCallConv(outer_fn);
-        let ad_fn = declare_simple_fn(
-            cx,
-            &ad_name,
-            llvm::CallConv::try_from(cc).expect("invalid callconv"),
-            llvm::UnnamedAddr::No,
-            llvm::Visibility::Default,
-            enzyme_ty,
-        );
-
-        // Otherwise LLVM might inline our temporary code before the enzyme pass has a chance to
-        // do it's work.
-        let attr = llvm::AttributeKind::NoInline.create_attr(cx.llcx);
-        attributes::apply_to_llfn(ad_fn, Function, &[attr]);
-
-        // We add a made-up attribute just such that we can recognize it after AD to update
-        // (no)-inline attributes. We'll then also remove this attribute.
-        let enzyme_marker_attr = llvm::CreateAttrString(cx.llcx, "enzyme_marker");
-        attributes::apply_to_llfn(outer_fn, Function, &[enzyme_marker_attr]);
-
-        // first, remove all calls from fnc
-        let entry = llvm::LLVMGetFirstBasicBlock(outer_fn);
-        let br = llvm::LLVMRustGetTerminator(entry);
-        llvm::LLVMRustEraseInstFromParent(br);
-
-        let last_inst = llvm::LLVMRustGetLastInstruction(entry).unwrap();
-        let mut builder = SBuilder::build(cx, entry);
-
-        let num_args = llvm::LLVMCountParams(&fn_to_diff);
-        let mut args = Vec::with_capacity(num_args as usize + 1);
-        args.push(fn_to_diff);
-
-        let enzyme_primal_ret = cx.create_metadata(b"enzyme_primal_return");
-        if matches!(attrs.ret_activity, DiffActivity::Dual | DiffActivity::Active) {
-            args.push(cx.get_metadata_value(enzyme_primal_ret));
-        }
-        if attrs.width > 1 {
-            let enzyme_width = cx.create_metadata(b"enzyme_width");
-            args.push(cx.get_metadata_value(enzyme_width));
-            args.push(cx.get_const_int(cx.type_i64(), attrs.width as u64));
-        }
-
-        let has_sret = has_sret(outer_fn);
-        let outer_args: Vec<&llvm::Value> = get_params(outer_fn);
-        match_args_from_caller_to_enzyme(
-            &cx,
-            &builder,
-            attrs.width,
-            &mut args,
-            &attrs.input_activity,
-            &outer_args,
-            has_sret,
-        );
-
-        let call = builder.call(enzyme_ty, ad_fn, &args, None);
-
-        // This part is a bit iffy. LLVM requires that a call to an inlineable function has some
-        // metadata attached to it, but we just created this code oota. Given that the
-        // differentiated function already has partly confusing metadata, and given that this
-        // affects nothing but the auttodiff IR, we take a shortcut and just steal metadata from the
-        // dummy code which we inserted at a higher level.
-        // FIXME(ZuseZ4): Work with Enzyme core devs to clarify what debug metadata issues we have,
-        // and how to best improve it for enzyme core and rust-enzyme.
-        let md_ty = cx.get_md_kind_id("dbg");
-        if llvm::LLVMRustHasMetadata(last_inst, md_ty) {
-            let md = llvm::LLVMRustDIGetInstMetadata(last_inst)
-                .expect("failed to get instruction metadata");
-            let md_todiff = cx.get_metadata_value(md);
-            llvm::LLVMSetMetadata(call, md_ty, md_todiff);
-        } else {
-            // We don't panic, since depending on whether we are in debug or release mode, we might
-            // have no debug info to copy, which would then be ok.
-            trace!("no dbg info");
-        }
-
-        // Now that we copied the metadata, get rid of dummy code.
-        llvm::LLVMRustEraseInstUntilInclusive(entry, last_inst);
-
-        if cx.val_ty(call) == cx.type_void() || has_sret {
-            if has_sret {
-                // This is what we already have in our outer_fn (shortened):
-                // define void @_foo(ptr <..> sret([32 x i8]) initializes((0, 32)) %0, <...>) {
-                //   %7 = call [4 x double] (...) @__enzyme_fwddiff_foo(ptr @square, metadata !"enzyme_width", i64 4, <...>)
-                //   <Here we are, we want to add the following two lines>
-                //   store [4 x double] %7, ptr %0, align 8
-                //   ret void
-                // }
-
-                // now store the result of the enzyme call into the sret pointer.
-                let sret_ptr = outer_args[0];
-                let call_ty = cx.val_ty(call);
-                if attrs.width == 1 {
-                    assert_eq!(cx.type_kind(call_ty), TypeKind::Struct);
-                } else {
-                    assert_eq!(cx.type_kind(call_ty), TypeKind::Array);
-                }
-                llvm::LLVMBuildStore(&builder.llbuilder, call, sret_ptr);
-            }
-            builder.ret_void();
-        } else {
-            builder.ret(call);
-        }
-
-        // Let's crash in case that we messed something up above and generated invalid IR.
-        llvm::LLVMRustVerifyFunction(
-            outer_fn,
-            llvm::LLVMRustVerifierFailureAction::LLVMAbortProcessAction,
-        );
-    }
-}
-
-pub(crate) fn differentiate<'ll>(
-    module: &'ll ModuleCodegen<ModuleLlvm>,
-    cgcx: &CodegenContext<LlvmCodegenBackend>,
-    diff_items: Vec<AutoDiffItem>,
-) -> Result<(), FatalError> {
-    for item in &diff_items {
-        trace!("{}", item);
+    let enzyme_ty = unsafe { llvm::LLVMFunctionType(ret_ty, ptr::null(), 0, True) };
+
+    // FIXME(ZuseZ4): the CC/Addr/Vis values are best effort guesses, we should look at tests and
+    // think a bit more about what should go here.
+    let cc = unsafe { llvm::LLVMGetFunctionCallConv(fn_to_diff) };
+    let ad_fn = declare_simple_fn(
+        cx,
+        &ad_name,
+        llvm::CallConv::try_from(cc).expect("invalid callconv"),
+        llvm::UnnamedAddr::No,
+        llvm::Visibility::Default,
+        enzyme_ty,
+    );
+
+    let num_args = llvm::LLVMCountParams(&fn_to_diff);
+    let mut args = Vec::with_capacity(num_args as usize + 1);
+    args.push(fn_to_diff);
+
+    let enzyme_primal_ret = cx.create_metadata(b"enzyme_primal_return");
+    if matches!(attrs.ret_activity, DiffActivity::Dual | DiffActivity::Active) {
+        args.push(cx.get_metadata_value(enzyme_primal_ret));
     }
-
-    let diag_handler = cgcx.create_dcx();
-
-    let cx = SimpleCx::new(module.module_llvm.llmod(), module.module_llvm.llcx, cgcx.pointer_size);
-
-    // First of all, did the user try to use autodiff without using the -Zautodiff=Enable flag?
-    if !diff_items.is_empty()
-        && !cgcx.opts.unstable_opts.autodiff.contains(&rustc_session::config::AutoDiff::Enable)
-    {
-        return Err(diag_handler.handle().emit_almost_fatal(AutoDiffWithoutEnable));
-    }
-
-    // Here we replace the placeholder code with the actual autodiff code, which calls Enzyme.
-    for item in diff_items.iter() {
-        let name = item.source.clone();
-        let fn_def: Option<&llvm::Value> = cx.get_function(&name);
-        let Some(fn_def) = fn_def else {
-            return Err(llvm_err(
-                diag_handler.handle(),
-                LlvmError::PrepareAutoDiff {
-                    src: item.source.clone(),
-                    target: item.target.clone(),
-                    error: "could not find source function".to_owned(),
-                },
-            ));
-        };
-        debug!(?item.target);
-        let fn_target: Option<&llvm::Value> = cx.get_function(&item.target);
-        let Some(fn_target) = fn_target else {
-            return Err(llvm_err(
-                diag_handler.handle(),
-                LlvmError::PrepareAutoDiff {
-                    src: item.source.clone(),
-                    target: item.target.clone(),
-                    error: "could not find target function".to_owned(),
-                },
-            ));
-        };
-
-        generate_enzyme_call(&cx, fn_def, fn_target, item.attrs.clone());
+    if attrs.width > 1 {
+        let enzyme_width = cx.create_metadata(b"enzyme_width");
+        args.push(cx.get_metadata_value(enzyme_width));
+        args.push(cx.get_const_int(cx.type_i64(), attrs.width as u64));
     }
 
-    // FIXME(ZuseZ4): support SanitizeHWAddress and prevent illegal/unsupported opts
+    match_args_from_caller_to_enzyme(
+        &cx,
+        builder,
+        attrs.width,
+        &mut args,
+        &attrs.input_activity,
+        fn_args,
+    );
 
-    trace!("done with differentiate()");
+    let call = builder.call(enzyme_ty, None, None, ad_fn, &args, None, None);
 
-    Ok(())
+    builder.store_to_place(call, dest.val);
 }
diff --git a/compiler/rustc_codegen_llvm/src/consts.rs b/compiler/rustc_codegen_llvm/src/consts.rs
index 0b96b63bc85..9ec7b0f80ae 100644
--- a/compiler/rustc_codegen_llvm/src/consts.rs
+++ b/compiler/rustc_codegen_llvm/src/consts.rs
@@ -4,14 +4,15 @@ use rustc_abi::{Align, HasDataLayout, Primitive, Scalar, Size, WrappingRange};
 use rustc_codegen_ssa::common;
 use rustc_codegen_ssa::traits::*;
 use rustc_hir::LangItem;
+use rustc_hir::attrs::Linkage;
 use rustc_hir::def::DefKind;
-use rustc_hir::def_id::DefId;
+use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
 use rustc_middle::mir::interpret::{
     Allocation, ConstAllocation, ErrorHandled, InitChunk, Pointer, Scalar as InterpScalar,
     read_target_uint,
 };
-use rustc_middle::mir::mono::{Linkage, MonoItem};
+use rustc_middle::mir::mono::MonoItem;
 use rustc_middle::ty::layout::{HasTypingEnv, LayoutOf};
 use rustc_middle::ty::{self, Instance};
 use rustc_middle::{bug, span_bug};
@@ -191,8 +192,8 @@ fn check_and_apply_linkage<'ll, 'tcx>(
         // linkage and there are no definitions), then
         // `extern_with_linkage_foo` will instead be initialized to
         // zero.
-        let mut real_name = "_rust_extern_with_linkage_".to_string();
-        real_name.push_str(sym);
+        let real_name =
+            format!("_rust_extern_with_linkage_{:016x}_{sym}", cx.tcx.stable_crate_id(LOCAL_CRATE));
         let g2 = cx.define_global(&real_name, llty).unwrap_or_else(|| {
             cx.sess().dcx().emit_fatal(SymbolAlreadyDefined {
                 span: cx.tcx.def_span(def_id),
diff --git a/compiler/rustc_codegen_llvm/src/context.rs b/compiler/rustc_codegen_llvm/src/context.rs
index ee77774c688..b0f3494ea68 100644
--- a/compiler/rustc_codegen_llvm/src/context.rs
+++ b/compiler/rustc_codegen_llvm/src/context.rs
@@ -8,7 +8,6 @@ use std::str;
 use rustc_abi::{HasDataLayout, Size, TargetDataLayout, VariantIdx};
 use rustc_codegen_ssa::back::versioned_llvm_target;
 use rustc_codegen_ssa::base::{wants_msvc_seh, wants_wasm_eh};
-use rustc_codegen_ssa::common::TypeKind;
 use rustc_codegen_ssa::errors as ssa_errors;
 use rustc_codegen_ssa::traits::*;
 use rustc_data_structures::base_n::{ALPHANUMERIC_ONLY, ToBaseN};
@@ -213,6 +212,12 @@ pub(crate) unsafe fn create_module<'ll>(
             target_data_layout = target_data_layout.replace("p8:128:128:128:48", "p8:128:128")
         }
     }
+    if llvm_version < (22, 0, 0) {
+        if sess.target.arch == "avr" {
+            // LLVM 22.0 updated the default layout on avr: https://github.com/llvm/llvm-project/pull/153010
+            target_data_layout = target_data_layout.replace("n8:16", "n8")
+        }
+    }
 
     // Ensure the data-layout values hardcoded remain the defaults.
     {
@@ -654,10 +659,6 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
     }
 }
 impl<'ll> SimpleCx<'ll> {
-    pub(crate) fn get_return_type(&self, ty: &'ll Type) -> &'ll Type {
-        assert_eq!(self.type_kind(ty), TypeKind::Function);
-        unsafe { llvm::LLVMGetReturnType(ty) }
-    }
     pub(crate) fn get_type_of_global(&self, val: &'ll Value) -> &'ll Type {
         unsafe { llvm::LLVMGlobalGetValueType(val) }
     }
@@ -721,16 +722,6 @@ impl<'ll, CX: Borrow<SCx<'ll>>> GenericCx<'ll, CX> {
             llvm::LLVMMDStringInContext2(self.llcx(), name.as_ptr() as *const c_char, name.len())
         }
     }
-
-    pub(crate) fn get_functions(&self) -> Vec<&'ll Value> {
-        let mut functions = vec![];
-        let mut func = unsafe { llvm::LLVMGetFirstFunction(self.llmod()) };
-        while let Some(f) = func {
-            functions.push(f);
-            func = unsafe { llvm::LLVMGetNextFunction(f) }
-        }
-        functions
-    }
 }
 
 impl<'ll, 'tcx> MiscCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/ffi.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/ffi.rs
index f6000e72840..a4b60d420f3 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/ffi.rs
@@ -73,48 +73,6 @@ pub(crate) struct CounterExpression {
     pub(crate) rhs: Counter,
 }
 
-pub(crate) mod mcdc {
-    use rustc_middle::mir::coverage::{ConditionId, ConditionInfo, DecisionInfo};
-
-    /// Must match the layout of `LLVMRustMCDCDecisionParameters`.
-    #[repr(C)]
-    #[derive(Clone, Copy, Debug, Default)]
-    pub(crate) struct DecisionParameters {
-        bitmap_idx: u32,
-        num_conditions: u16,
-    }
-
-    type LLVMConditionId = i16;
-
-    /// Must match the layout of `LLVMRustMCDCBranchParameters`.
-    #[repr(C)]
-    #[derive(Clone, Copy, Debug, Default)]
-    pub(crate) struct BranchParameters {
-        condition_id: LLVMConditionId,
-        condition_ids: [LLVMConditionId; 2],
-    }
-
-    impl From<ConditionInfo> for BranchParameters {
-        fn from(value: ConditionInfo) -> Self {
-            let to_llvm_cond_id = |cond_id: Option<ConditionId>| {
-                cond_id.and_then(|id| LLVMConditionId::try_from(id.as_usize()).ok()).unwrap_or(-1)
-            };
-            let ConditionInfo { condition_id, true_next_id, false_next_id } = value;
-            Self {
-                condition_id: to_llvm_cond_id(Some(condition_id)),
-                condition_ids: [to_llvm_cond_id(false_next_id), to_llvm_cond_id(true_next_id)],
-            }
-        }
-    }
-
-    impl From<DecisionInfo> for DecisionParameters {
-        fn from(info: DecisionInfo) -> Self {
-            let DecisionInfo { bitmap_idx, num_conditions } = info;
-            Self { bitmap_idx, num_conditions }
-        }
-    }
-}
-
 /// A span of source code coordinates to be embedded in coverage metadata.
 ///
 /// Must match the layout of `LLVMRustCoverageSpan`.
@@ -148,26 +106,14 @@ pub(crate) struct Regions {
     pub(crate) code_regions: Vec<CodeRegion>,
     pub(crate) expansion_regions: Vec<ExpansionRegion>,
     pub(crate) branch_regions: Vec<BranchRegion>,
-    pub(crate) mcdc_branch_regions: Vec<MCDCBranchRegion>,
-    pub(crate) mcdc_decision_regions: Vec<MCDCDecisionRegion>,
 }
 
 impl Regions {
     /// Returns true if none of this structure's tables contain any regions.
     pub(crate) fn has_no_regions(&self) -> bool {
-        let Self {
-            code_regions,
-            expansion_regions,
-            branch_regions,
-            mcdc_branch_regions,
-            mcdc_decision_regions,
-        } = self;
-
-        code_regions.is_empty()
-            && expansion_regions.is_empty()
-            && branch_regions.is_empty()
-            && mcdc_branch_regions.is_empty()
-            && mcdc_decision_regions.is_empty()
+        let Self { code_regions, expansion_regions, branch_regions } = self;
+
+        code_regions.is_empty() && expansion_regions.is_empty() && branch_regions.is_empty()
     }
 }
 
@@ -195,21 +141,3 @@ pub(crate) struct BranchRegion {
     pub(crate) true_counter: Counter,
     pub(crate) false_counter: Counter,
 }
-
-/// Must match the layout of `LLVMRustCoverageMCDCBranchRegion`.
-#[derive(Clone, Debug)]
-#[repr(C)]
-pub(crate) struct MCDCBranchRegion {
-    pub(crate) cov_span: CoverageSpan,
-    pub(crate) true_counter: Counter,
-    pub(crate) false_counter: Counter,
-    pub(crate) mcdc_branch_params: mcdc::BranchParameters,
-}
-
-/// Must match the layout of `LLVMRustCoverageMCDCDecisionRegion`.
-#[derive(Clone, Debug)]
-#[repr(C)]
-pub(crate) struct MCDCDecisionRegion {
-    pub(crate) cov_span: CoverageSpan,
-    pub(crate) mcdc_decision_params: mcdc::DecisionParameters,
-}
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/llvm_cov.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/llvm_cov.rs
index 907d6d41a1f..bc4f6bb6a82 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/llvm_cov.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/llvm_cov.rs
@@ -63,13 +63,7 @@ pub(crate) fn write_function_mappings_to_buffer(
     expressions: &[ffi::CounterExpression],
     regions: &ffi::Regions,
 ) -> Vec<u8> {
-    let ffi::Regions {
-        code_regions,
-        expansion_regions,
-        branch_regions,
-        mcdc_branch_regions,
-        mcdc_decision_regions,
-    } = regions;
+    let ffi::Regions { code_regions, expansion_regions, branch_regions } = regions;
 
     // SAFETY:
     // - All types are FFI-compatible and have matching representations in Rust/C++.
@@ -87,10 +81,6 @@ pub(crate) fn write_function_mappings_to_buffer(
             expansion_regions.len(),
             branch_regions.as_ptr(),
             branch_regions.len(),
-            mcdc_branch_regions.as_ptr(),
-            mcdc_branch_regions.len(),
-            mcdc_decision_regions.as_ptr(),
-            mcdc_decision_regions.len(),
             buffer,
         )
     })
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/covfun.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/covfun.rs
index fd1e7f7f160..e0da8d36876 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/covfun.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/covfun.rs
@@ -140,8 +140,6 @@ fn fill_region_tables<'tcx>(
         code_regions,
         expansion_regions: _, // FIXME(Zalathar): Fill out support for expansion regions
         branch_regions,
-        mcdc_branch_regions,
-        mcdc_decision_regions,
     } = &mut covfun.regions;
 
     // For each counter/region pair in this function+file, convert it to a
@@ -161,20 +159,6 @@ fn fill_region_tables<'tcx>(
                     false_counter: counter_for_bcb(false_bcb),
                 });
             }
-            MappingKind::MCDCBranch { true_bcb, false_bcb, mcdc_params } => {
-                mcdc_branch_regions.push(ffi::MCDCBranchRegion {
-                    cov_span,
-                    true_counter: counter_for_bcb(true_bcb),
-                    false_counter: counter_for_bcb(false_bcb),
-                    mcdc_branch_params: ffi::mcdc::BranchParameters::from(mcdc_params),
-                });
-            }
-            MappingKind::MCDCDecision(mcdc_decision_params) => {
-                mcdc_decision_regions.push(ffi::MCDCDecisionRegion {
-                    cov_span,
-                    mcdc_decision_params: ffi::mcdc::DecisionParameters::from(mcdc_decision_params),
-                });
-            }
         }
     }
 }
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
index 119237abd6b..6a58f495c9d 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
@@ -1,11 +1,10 @@
 use std::cell::{OnceCell, RefCell};
 use std::ffi::{CStr, CString};
 
-use rustc_abi::Size;
 use rustc_codegen_ssa::traits::{
-    BuilderMethods, ConstCodegenMethods, CoverageInfoBuilderMethods, MiscCodegenMethods,
+    ConstCodegenMethods, CoverageInfoBuilderMethods, MiscCodegenMethods,
 };
-use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
+use rustc_data_structures::fx::FxIndexMap;
 use rustc_middle::mir::coverage::CoverageKind;
 use rustc_middle::ty::Instance;
 use tracing::{debug, instrument};
@@ -28,34 +27,13 @@ pub(crate) struct CguCoverageContext<'ll, 'tcx> {
     /// symbol name, and `llvm-cov` will exit fatally if it can't resolve that
     /// hash back to an entry in the binary's `__llvm_prf_names` linker section.
     pub(crate) pgo_func_name_var_map: RefCell<FxIndexMap<Instance<'tcx>, &'ll llvm::Value>>,
-    pub(crate) mcdc_condition_bitmap_map: RefCell<FxHashMap<Instance<'tcx>, Vec<&'ll llvm::Value>>>,
 
     covfun_section_name: OnceCell<CString>,
 }
 
 impl<'ll, 'tcx> CguCoverageContext<'ll, 'tcx> {
     pub(crate) fn new() -> Self {
-        Self {
-            pgo_func_name_var_map: Default::default(),
-            mcdc_condition_bitmap_map: Default::default(),
-            covfun_section_name: Default::default(),
-        }
-    }
-
-    /// LLVM use a temp value to record evaluated mcdc test vector of each decision, which is
-    /// called condition bitmap. In order to handle nested decisions, several condition bitmaps can
-    /// be allocated for a function body. These values are named `mcdc.addr.{i}` and are a 32-bit
-    /// integers. They respectively hold the condition bitmaps for decisions with a depth of `i`.
-    fn try_get_mcdc_condition_bitmap(
-        &self,
-        instance: &Instance<'tcx>,
-        decision_depth: u16,
-    ) -> Option<&'ll llvm::Value> {
-        self.mcdc_condition_bitmap_map
-            .borrow()
-            .get(instance)
-            .and_then(|bitmap_map| bitmap_map.get(decision_depth as usize))
-            .copied() // Dereference Option<&&Value> to Option<&Value>
+        Self { pgo_func_name_var_map: Default::default(), covfun_section_name: Default::default() }
     }
 
     /// Returns the list of instances considered "used" in this CGU, as
@@ -105,38 +83,6 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
 }
 
 impl<'tcx> CoverageInfoBuilderMethods<'tcx> for Builder<'_, '_, 'tcx> {
-    fn init_coverage(&mut self, instance: Instance<'tcx>) {
-        let Some(function_coverage_info) =
-            self.tcx.instance_mir(instance.def).function_coverage_info.as_deref()
-        else {
-            return;
-        };
-
-        // If there are no MC/DC bitmaps to set up, return immediately.
-        if function_coverage_info.mcdc_bitmap_bits == 0 {
-            return;
-        }
-
-        let fn_name = self.ensure_pgo_func_name_var(instance);
-        let hash = self.const_u64(function_coverage_info.function_source_hash);
-        let bitmap_bits = self.const_u32(function_coverage_info.mcdc_bitmap_bits as u32);
-        self.mcdc_parameters(fn_name, hash, bitmap_bits);
-
-        // Create pointers named `mcdc.addr.{i}` to stack-allocated condition bitmaps.
-        let mut cond_bitmaps = vec![];
-        for i in 0..function_coverage_info.mcdc_num_condition_bitmaps {
-            // MC/DC intrinsics will perform loads/stores that use the ABI default
-            // alignment for i32, so our variable declaration should match.
-            let align = self.tcx.data_layout.i32_align.abi;
-            let cond_bitmap = self.alloca(Size::from_bytes(4), align);
-            llvm::set_value_name(cond_bitmap, format!("mcdc.addr.{i}").as_bytes());
-            self.store(self.const_i32(0), cond_bitmap, align);
-            cond_bitmaps.push(cond_bitmap);
-        }
-
-        self.coverage_cx().mcdc_condition_bitmap_map.borrow_mut().insert(instance, cond_bitmaps);
-    }
-
     #[instrument(level = "debug", skip(self))]
     fn add_coverage(&mut self, instance: Instance<'tcx>, kind: &CoverageKind) {
         // Our caller should have already taken care of inlining subtleties,
@@ -153,7 +99,7 @@ impl<'tcx> CoverageInfoBuilderMethods<'tcx> for Builder<'_, '_, 'tcx> {
         // When that happens, we currently just discard those statements, so
         // the corresponding code will be undercounted.
         // FIXME(Zalathar): Find a better solution for mixed-coverage builds.
-        let Some(coverage_cx) = &bx.cx.coverage_cx else { return };
+        let Some(_coverage_cx) = &bx.cx.coverage_cx else { return };
 
         let Some(function_coverage_info) =
             bx.tcx.instance_mir(instance.def).function_coverage_info.as_deref()
@@ -185,30 +131,6 @@ impl<'tcx> CoverageInfoBuilderMethods<'tcx> for Builder<'_, '_, 'tcx> {
             }
             // If a BCB doesn't have an associated physical counter, there's nothing to codegen.
             CoverageKind::VirtualCounter { .. } => {}
-            CoverageKind::CondBitmapUpdate { index, decision_depth } => {
-                let cond_bitmap = coverage_cx
-                    .try_get_mcdc_condition_bitmap(&instance, decision_depth)
-                    .expect("mcdc cond bitmap should have been allocated for updating");
-                let cond_index = bx.const_i32(index as i32);
-                bx.mcdc_condbitmap_update(cond_index, cond_bitmap);
-            }
-            CoverageKind::TestVectorBitmapUpdate { bitmap_idx, decision_depth } => {
-                let cond_bitmap =
-                    coverage_cx.try_get_mcdc_condition_bitmap(&instance, decision_depth).expect(
-                        "mcdc cond bitmap should have been allocated for merging \
-                        into the global bitmap",
-                    );
-                assert!(
-                    bitmap_idx as usize <= function_coverage_info.mcdc_bitmap_bits,
-                    "bitmap index of the decision out of range"
-                );
-
-                let fn_name = bx.ensure_pgo_func_name_var(instance);
-                let hash = bx.const_u64(function_coverage_info.function_source_hash);
-                let bitmap_index = bx.const_u32(bitmap_idx);
-                bx.mcdc_tvbitmap_update(fn_name, hash, bitmap_index, cond_bitmap);
-                bx.mcdc_condbitmap_reset(cond_bitmap);
-            }
         }
     }
 }
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs b/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs
index fccd32dec95..6eb7042da61 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs
@@ -1,13 +1,11 @@
 // .debug_gdb_scripts binary section.
 
-use std::collections::BTreeSet;
-use std::ffi::CString;
-
+use rustc_codegen_ssa::base::collect_debugger_visualizers_transitive;
 use rustc_codegen_ssa::traits::*;
 use rustc_hir::def_id::LOCAL_CRATE;
 use rustc_middle::bug;
 use rustc_middle::middle::debugger_visualizer::DebuggerVisualizerType;
-use rustc_session::config::DebugInfo;
+use rustc_session::config::{CrateType, DebugInfo};
 
 use crate::builder::Builder;
 use crate::common::CodegenCx;
@@ -33,12 +31,7 @@ pub(crate) fn insert_reference_to_gdb_debug_scripts_section_global(bx: &mut Buil
 pub(crate) fn get_or_insert_gdb_debug_scripts_section_global<'ll>(
     cx: &CodegenCx<'ll, '_>,
 ) -> &'ll Value {
-    let c_section_var_name = CString::new(format!(
-        "__rustc_debug_gdb_scripts_section_{}_{:08x}",
-        cx.tcx.crate_name(LOCAL_CRATE),
-        cx.tcx.stable_crate_id(LOCAL_CRATE),
-    ))
-    .unwrap();
+    let c_section_var_name = c"__rustc_debug_gdb_scripts_section__";
     let section_var_name = c_section_var_name.to_str().unwrap();
 
     let section_var = unsafe { llvm::LLVMGetNamedGlobal(cx.llmod, c_section_var_name.as_ptr()) };
@@ -51,14 +44,10 @@ pub(crate) fn get_or_insert_gdb_debug_scripts_section_global<'ll>(
 
         // Next, add the pretty printers that were specified via the `#[debugger_visualizer]`
         // attribute.
-        let visualizers = cx
-            .tcx
-            .debugger_visualizers(LOCAL_CRATE)
-            .iter()
-            .filter(|visualizer| {
-                visualizer.visualizer_type == DebuggerVisualizerType::GdbPrettyPrinter
-            })
-            .collect::<BTreeSet<_>>();
+        let visualizers = collect_debugger_visualizers_transitive(
+            cx.tcx,
+            DebuggerVisualizerType::GdbPrettyPrinter,
+        );
         let crate_name = cx.tcx.crate_name(LOCAL_CRATE);
         for (index, visualizer) in visualizers.iter().enumerate() {
             // The initial byte `4` instructs GDB that the following pretty printer
@@ -95,5 +84,35 @@ pub(crate) fn get_or_insert_gdb_debug_scripts_section_global<'ll>(
 }
 
 pub(crate) fn needs_gdb_debug_scripts_section(cx: &CodegenCx<'_, '_>) -> bool {
-    cx.sess().opts.debuginfo != DebugInfo::None && cx.sess().target.emit_debug_gdb_scripts
+    // To ensure the section `__rustc_debug_gdb_scripts_section__` will not create
+    // ODR violations at link time, this section will not be emitted for rlibs since
+    // each rlib could produce a different set of visualizers that would be embedded
+    // in the `.debug_gdb_scripts` section. For that reason, we make sure that the
+    // section is only emitted for leaf crates.
+    let embed_visualizers = cx.tcx.crate_types().iter().any(|&crate_type| match crate_type {
+        CrateType::Executable
+        | CrateType::Dylib
+        | CrateType::Cdylib
+        | CrateType::Staticlib
+        | CrateType::Sdylib => {
+            // These are crate types for which we will embed pretty printers since they
+            // are treated as leaf crates.
+            true
+        }
+        CrateType::ProcMacro => {
+            // We could embed pretty printers for proc macro crates too but it does not
+            // seem like a good default, since this is a rare use case and we don't
+            // want to slow down the common case.
+            false
+        }
+        CrateType::Rlib => {
+            // As per the above description, embedding pretty printers for rlibs could
+            // lead to ODR violations so we skip this crate type as well.
+            false
+        }
+    });
+
+    cx.sess().opts.debuginfo != DebugInfo::None
+        && cx.sess().target.emit_debug_gdb_scripts
+        && embed_visualizers
 }
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs b/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs
index c911435967c..2c3a84499ac 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs
@@ -30,7 +30,7 @@ use tracing::debug;
 
 use self::metadata::{UNKNOWN_COLUMN_NUMBER, UNKNOWN_LINE_NUMBER, file_metadata, type_di_node};
 use self::namespace::mangled_name_of_instance;
-use self::utils::{DIB, create_DIArray, debug_context, is_node_local_to_unit};
+use self::utils::{DIB, create_DIArray, is_node_local_to_unit};
 use crate::builder::Builder;
 use crate::common::{AsCCharPtr, CodegenCx};
 use crate::llvm;
@@ -131,28 +131,20 @@ impl<'ll, 'tcx> CodegenUnitDebugContext<'ll, 'tcx> {
 }
 
 /// Creates any deferred debug metadata nodes
-pub(crate) fn finalize(cx: &mut CodegenCx<'_, '_>) {
-    if cx.dbg_cx.is_none() {
-        return;
-    }
-
-    debug!("finalize");
-
-    if gdb::needs_gdb_debug_scripts_section(cx) {
-        // Add a .debug_gdb_scripts section to this compile-unit. This will
-        // cause GDB to try and load the gdb_load_rust_pretty_printers.py file,
-        // which activates the Rust pretty printers for binary this section is
-        // contained in.
-        let section_var = gdb::get_or_insert_gdb_debug_scripts_section_global(cx);
+pub(crate) fn finalize(cx: &CodegenCx<'_, '_>) {
+    if let Some(dbg_cx) = &cx.dbg_cx {
+        debug!("finalize");
+
+        if gdb::needs_gdb_debug_scripts_section(cx) {
+            // Add a .debug_gdb_scripts section to this compile-unit. This will
+            // cause GDB to try and load the gdb_load_rust_pretty_printers.py file,
+            // which activates the Rust pretty printers for binary this section is
+            // contained in.
+            gdb::get_or_insert_gdb_debug_scripts_section_global(cx);
+        }
 
-        // Make sure that the linker doesn't optimize the global away. Adding
-        // it to `llvm.used` has the advantage that it works even in no_std
-        // binaries, where we don't have a main shim and thus don't emit a
-        // volatile load to preserve the global.
-        cx.add_used_global(section_var);
+        dbg_cx.finalize(cx.sess());
     }
-
-    debug_context(cx).finalize(cx.sess());
 }
 
 impl<'ll> Builder<'_, 'll, '_> {
@@ -541,31 +533,26 @@ impl<'ll, 'tcx> DebugInfoCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
             // First, let's see if this is a method within an inherent impl. Because
             // if yes, we want to make the result subroutine DIE a child of the
             // subroutine's self-type.
-            if let Some(impl_def_id) = cx.tcx.impl_of_assoc(instance.def_id()) {
-                // If the method does *not* belong to a trait, proceed
-                if cx.tcx.trait_id_of_impl(impl_def_id).is_none() {
-                    let impl_self_ty = cx.tcx.instantiate_and_normalize_erasing_regions(
-                        instance.args,
-                        cx.typing_env(),
-                        cx.tcx.type_of(impl_def_id),
-                    );
-
-                    // Only "class" methods are generally understood by LLVM,
-                    // so avoid methods on other types (e.g., `<*mut T>::null`).
-                    if let ty::Adt(def, ..) = impl_self_ty.kind()
-                        && !def.is_box()
-                    {
-                        // Again, only create type information if full debuginfo is enabled
-                        if cx.sess().opts.debuginfo == DebugInfo::Full && !impl_self_ty.has_param()
-                        {
-                            return (type_di_node(cx, impl_self_ty), true);
-                        } else {
-                            return (namespace::item_namespace(cx, def.did()), false);
-                        }
+            // For trait method impls we still use the "parallel namespace"
+            // strategy
+            if let Some(imp_def_id) = cx.tcx.inherent_impl_of_assoc(instance.def_id()) {
+                let impl_self_ty = cx.tcx.instantiate_and_normalize_erasing_regions(
+                    instance.args,
+                    cx.typing_env(),
+                    cx.tcx.type_of(imp_def_id),
+                );
+
+                // Only "class" methods are generally understood by LLVM,
+                // so avoid methods on other types (e.g., `<*mut T>::null`).
+                if let ty::Adt(def, ..) = impl_self_ty.kind()
+                    && !def.is_box()
+                {
+                    // Again, only create type information if full debuginfo is enabled
+                    if cx.sess().opts.debuginfo == DebugInfo::Full && !impl_self_ty.has_param() {
+                        return (type_di_node(cx, impl_self_ty), true);
+                    } else {
+                        return (namespace::item_namespace(cx, def.did()), false);
                     }
-                } else {
-                    // For trait method impls we still use the "parallel namespace"
-                    // strategy
                 }
             }
 
@@ -622,7 +609,7 @@ impl<'ll, 'tcx> DebugInfoCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         metadata::extend_scope_to_file(self, scope_metadata, file)
     }
 
-    fn debuginfo_finalize(&mut self) {
+    fn debuginfo_finalize(&self) {
         finalize(self)
     }
 
diff --git a/compiler/rustc_codegen_llvm/src/intrinsic.rs b/compiler/rustc_codegen_llvm/src/intrinsic.rs
index 7b27e496986..4935f8d7dff 100644
--- a/compiler/rustc_codegen_llvm/src/intrinsic.rs
+++ b/compiler/rustc_codegen_llvm/src/intrinsic.rs
@@ -3,24 +3,29 @@ use std::cmp::Ordering;
 
 use rustc_abi::{Align, BackendRepr, ExternAbi, Float, HasDataLayout, Primitive, Size};
 use rustc_codegen_ssa::base::{compare_simd_types, wants_msvc_seh, wants_wasm_eh};
+use rustc_codegen_ssa::codegen_attrs::autodiff_attrs;
 use rustc_codegen_ssa::common::{IntPredicate, TypeKind};
 use rustc_codegen_ssa::errors::{ExpectedPointerMutability, InvalidMonomorphization};
 use rustc_codegen_ssa::mir::operand::{OperandRef, OperandValue};
 use rustc_codegen_ssa::mir::place::{PlaceRef, PlaceValue};
 use rustc_codegen_ssa::traits::*;
-use rustc_hir as hir;
+use rustc_hir::def_id::LOCAL_CRATE;
+use rustc_hir::{self as hir};
 use rustc_middle::mir::BinOp;
 use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt, HasTypingEnv, LayoutOf};
-use rustc_middle::ty::{self, GenericArgsRef, Ty};
+use rustc_middle::ty::{self, GenericArgsRef, Instance, Ty, TyCtxt, TypingEnv};
 use rustc_middle::{bug, span_bug};
 use rustc_span::{Span, Symbol, sym};
-use rustc_symbol_mangling::mangle_internal_symbol;
+use rustc_symbol_mangling::{mangle_internal_symbol, symbol_name_for_instance_in_crate};
+use rustc_target::callconv::PassMode;
 use rustc_target::spec::PanicStrategy;
 use tracing::debug;
 
 use crate::abi::FnAbiLlvmExt;
 use crate::builder::Builder;
+use crate::builder::autodiff::{adjust_activity_to_abi, generate_enzyme_call};
 use crate::context::CodegenCx;
+use crate::errors::AutoDiffWithoutEnable;
 use crate::llvm::{self, Metadata};
 use crate::type_::Type;
 use crate::type_of::LayoutLlvmExt;
@@ -189,6 +194,10 @@ impl<'ll, 'tcx> IntrinsicCallBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
                     &[ptr, args[1].immediate()],
                 )
             }
+            sym::autodiff => {
+                codegen_autodiff(self, tcx, instance, args, result);
+                return Ok(());
+            }
             sym::is_val_statically_known => {
                 if let OperandValue::Immediate(imm) = args[0].val {
                     self.call_intrinsic(
@@ -1113,6 +1122,143 @@ fn get_rust_try_fn<'a, 'll, 'tcx>(
     rust_try
 }
 
+fn codegen_autodiff<'ll, 'tcx>(
+    bx: &mut Builder<'_, 'll, 'tcx>,
+    tcx: TyCtxt<'tcx>,
+    instance: ty::Instance<'tcx>,
+    args: &[OperandRef<'tcx, &'ll Value>],
+    result: PlaceRef<'tcx, &'ll Value>,
+) {
+    if !tcx.sess.opts.unstable_opts.autodiff.contains(&rustc_session::config::AutoDiff::Enable) {
+        let _ = tcx.dcx().emit_almost_fatal(AutoDiffWithoutEnable);
+    }
+
+    let fn_args = instance.args;
+    let callee_ty = instance.ty(tcx, bx.typing_env());
+
+    let sig = callee_ty.fn_sig(tcx).skip_binder();
+
+    let ret_ty = sig.output();
+    let llret_ty = bx.layout_of(ret_ty).llvm_type(bx);
+
+    // Get source, diff, and attrs
+    let (source_id, source_args) = match fn_args.into_type_list(tcx)[0].kind() {
+        ty::FnDef(def_id, source_params) => (def_id, source_params),
+        _ => bug!("invalid autodiff intrinsic args"),
+    };
+
+    let fn_source = match Instance::try_resolve(tcx, bx.cx.typing_env(), *source_id, source_args) {
+        Ok(Some(instance)) => instance,
+        Ok(None) => bug!(
+            "could not resolve ({:?}, {:?}) to a specific autodiff instance",
+            source_id,
+            source_args
+        ),
+        Err(_) => {
+            // An error has already been emitted
+            return;
+        }
+    };
+
+    let source_symbol = symbol_name_for_instance_in_crate(tcx, fn_source.clone(), LOCAL_CRATE);
+    let Some(fn_to_diff) = bx.cx.get_function(&source_symbol) else {
+        bug!("could not find source function")
+    };
+
+    let (diff_id, diff_args) = match fn_args.into_type_list(tcx)[1].kind() {
+        ty::FnDef(def_id, diff_args) => (def_id, diff_args),
+        _ => bug!("invalid args"),
+    };
+
+    let fn_diff = match Instance::try_resolve(tcx, bx.cx.typing_env(), *diff_id, diff_args) {
+        Ok(Some(instance)) => instance,
+        Ok(None) => bug!(
+            "could not resolve ({:?}, {:?}) to a specific autodiff instance",
+            diff_id,
+            diff_args
+        ),
+        Err(_) => {
+            // An error has already been emitted
+            return;
+        }
+    };
+
+    let val_arr = get_args_from_tuple(bx, args[2], fn_diff);
+    let diff_symbol = symbol_name_for_instance_in_crate(tcx, fn_diff.clone(), LOCAL_CRATE);
+
+    let Some(mut diff_attrs) = autodiff_attrs(tcx, fn_diff.def_id()) else {
+        bug!("could not find autodiff attrs")
+    };
+
+    adjust_activity_to_abi(
+        tcx,
+        fn_source.ty(tcx, TypingEnv::fully_monomorphized()),
+        &mut diff_attrs.input_activity,
+    );
+
+    // Build body
+    generate_enzyme_call(
+        bx,
+        bx.cx,
+        fn_to_diff,
+        &diff_symbol,
+        llret_ty,
+        &val_arr,
+        diff_attrs.clone(),
+        result,
+    );
+}
+
+fn get_args_from_tuple<'ll, 'tcx>(
+    bx: &mut Builder<'_, 'll, 'tcx>,
+    tuple_op: OperandRef<'tcx, &'ll Value>,
+    fn_instance: Instance<'tcx>,
+) -> Vec<&'ll Value> {
+    let cx = bx.cx;
+    let fn_abi = cx.fn_abi_of_instance(fn_instance, ty::List::empty());
+
+    match tuple_op.val {
+        OperandValue::Immediate(val) => vec![val],
+        OperandValue::Pair(v1, v2) => vec![v1, v2],
+        OperandValue::Ref(ptr) => {
+            let tuple_place = PlaceRef { val: ptr, layout: tuple_op.layout };
+
+            let mut result = Vec::with_capacity(fn_abi.args.len());
+            let mut tuple_index = 0;
+
+            for arg in &fn_abi.args {
+                match arg.mode {
+                    PassMode::Ignore => {}
+                    PassMode::Direct(_) | PassMode::Cast { .. } => {
+                        let field = tuple_place.project_field(bx, tuple_index);
+                        let llvm_ty = field.layout.llvm_type(bx.cx);
+                        let val = bx.load(llvm_ty, field.val.llval, field.val.align);
+                        result.push(val);
+                        tuple_index += 1;
+                    }
+                    PassMode::Pair(_, _) => {
+                        let field = tuple_place.project_field(bx, tuple_index);
+                        let llvm_ty = field.layout.llvm_type(bx.cx);
+                        let pair_val = bx.load(llvm_ty, field.val.llval, field.val.align);
+                        result.push(bx.extract_value(pair_val, 0));
+                        result.push(bx.extract_value(pair_val, 1));
+                        tuple_index += 1;
+                    }
+                    PassMode::Indirect { .. } => {
+                        let field = tuple_place.project_field(bx, tuple_index);
+                        result.push(field.val.llval);
+                        tuple_index += 1;
+                    }
+                }
+            }
+
+            result
+        }
+
+        OperandValue::ZeroSized => vec![],
+    }
+}
+
 fn generic_simd_intrinsic<'ll, 'tcx>(
     bx: &mut Builder<'_, 'll, 'tcx>,
     name: Symbol,
diff --git a/compiler/rustc_codegen_llvm/src/lib.rs b/compiler/rustc_codegen_llvm/src/lib.rs
index ca84b6de8b1..79e80db6f55 100644
--- a/compiler/rustc_codegen_llvm/src/lib.rs
+++ b/compiler/rustc_codegen_llvm/src/lib.rs
@@ -30,7 +30,6 @@ use context::SimpleCx;
 use errors::ParseTargetMachineConfig;
 use llvm_util::target_config;
 use rustc_ast::expand::allocator::AllocatorKind;
-use rustc_ast::expand::autodiff_attrs::AutoDiffItem;
 use rustc_codegen_ssa::back::lto::{SerializedModule, ThinModule};
 use rustc_codegen_ssa::back::write::{
     CodegenContext, FatLtoInput, ModuleConfig, TargetMachineFactoryConfig, TargetMachineFactoryFn,
@@ -173,15 +172,10 @@ impl WriteBackendMethods for LlvmCodegenBackend {
         exported_symbols_for_lto: &[String],
         each_linked_rlib_for_lto: &[PathBuf],
         modules: Vec<FatLtoInput<Self>>,
-        diff_fncs: Vec<AutoDiffItem>,
     ) -> Result<ModuleCodegen<Self::Module>, FatalError> {
         let mut module =
             back::lto::run_fat(cgcx, exported_symbols_for_lto, each_linked_rlib_for_lto, modules)?;
 
-        if !diff_fncs.is_empty() {
-            builder::autodiff::differentiate(&module, cgcx, diff_fncs)?;
-        }
-
         let dcx = cgcx.create_dcx();
         let dcx = dcx.handle();
         back::lto::run_pass_manager(cgcx, dcx, &mut module, false)?;
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 2443194ff48..ad3c3d5932e 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -249,6 +249,7 @@ pub(crate) enum AttributeKind {
     FnRetThunkExtern = 41,
     Writable = 42,
     DeadOnUnwind = 43,
+    DeadOnReturn = 44,
 }
 
 /// LLVMIntPredicate
@@ -2056,10 +2057,6 @@ unsafe extern "C" {
         NumExpansionRegions: size_t,
         BranchRegions: *const crate::coverageinfo::ffi::BranchRegion,
         NumBranchRegions: size_t,
-        MCDCBranchRegions: *const crate::coverageinfo::ffi::MCDCBranchRegion,
-        NumMCDCBranchRegions: size_t,
-        MCDCDecisionRegions: *const crate::coverageinfo::ffi::MCDCDecisionRegion,
-        NumMCDCDecisionRegions: size_t,
         BufferOut: &RustString,
     );
 
diff --git a/compiler/rustc_codegen_llvm/src/llvm/mod.rs b/compiler/rustc_codegen_llvm/src/llvm/mod.rs
index 154ba4fd690..0ea0af0c9af 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/mod.rs
@@ -42,32 +42,6 @@ pub(crate) fn AddFunctionAttributes<'ll>(
     }
 }
 
-pub(crate) fn HasAttributeAtIndex<'ll>(
-    llfn: &'ll Value,
-    idx: AttributePlace,
-    kind: AttributeKind,
-) -> bool {
-    unsafe { LLVMRustHasAttributeAtIndex(llfn, idx.as_uint(), kind) }
-}
-
-pub(crate) fn HasStringAttribute<'ll>(llfn: &'ll Value, name: &str) -> bool {
-    unsafe { LLVMRustHasFnAttribute(llfn, name.as_c_char_ptr(), name.len()) }
-}
-
-pub(crate) fn RemoveStringAttrFromFn<'ll>(llfn: &'ll Value, name: &str) {
-    unsafe { LLVMRustRemoveFnAttribute(llfn, name.as_c_char_ptr(), name.len()) }
-}
-
-pub(crate) fn RemoveRustEnumAttributeAtIndex(
-    llfn: &Value,
-    place: AttributePlace,
-    kind: AttributeKind,
-) {
-    unsafe {
-        LLVMRustRemoveEnumAttributeAtIndex(llfn, place.as_uint(), kind);
-    }
-}
-
 pub(crate) fn AddCallSiteAttributes<'ll>(
     callsite: &'ll Value,
     idx: AttributePlace,
diff --git a/compiler/rustc_codegen_llvm/src/llvm_util.rs b/compiler/rustc_codegen_llvm/src/llvm_util.rs
index 53899da183a..28d2100f478 100644
--- a/compiler/rustc_codegen_llvm/src/llvm_util.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm_util.rs
@@ -262,6 +262,15 @@ pub(crate) fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> Option<LLVMFea
         // Filter out features that are not supported by the current LLVM version
         ("aarch64", "fpmr") => None, // only existed in 18
         ("arm", "fp16") => Some(LLVMFeature::new("fullfp16")),
+        // NVPTX targets added in LLVM 20
+        ("nvptx64", "sm_100") if get_version().0 < 20 => None,
+        ("nvptx64", "sm_100a") if get_version().0 < 20 => None,
+        ("nvptx64", "sm_101") if get_version().0 < 20 => None,
+        ("nvptx64", "sm_101a") if get_version().0 < 20 => None,
+        ("nvptx64", "sm_120") if get_version().0 < 20 => None,
+        ("nvptx64", "sm_120a") if get_version().0 < 20 => None,
+        ("nvptx64", "ptx86") if get_version().0 < 20 => None,
+        ("nvptx64", "ptx87") if get_version().0 < 20 => None,
         // Filter out features that are not supported by the current LLVM version
         ("loongarch64", "div32" | "lam-bh" | "lamcas" | "ld-seq-sa" | "scq")
             if get_version().0 < 20 =>
@@ -324,15 +333,12 @@ pub(crate) fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> Option<LLVMFea
 ///
 /// We do not have to worry about RUSTC_SPECIFIC_FEATURES here, those are handled outside codegen.
 pub(crate) fn target_config(sess: &Session) -> TargetConfig {
-    // Add base features for the target.
-    // We do *not* add the -Ctarget-features there, and instead duplicate the logic for that below.
-    // The reason is that if LLVM considers a feature implied but we do not, we don't want that to
-    // show up in `cfg`. That way, `cfg` is entirely under our control -- except for the handling of
-    // the target CPU, that is still expanded to target features (with all their implied features)
-    // by LLVM.
     let target_machine = create_informational_target_machine(sess, true);
 
     let (unstable_target_features, target_features) = cfg_target_feature(sess, |feature| {
+        // This closure determines whether the target CPU has the feature according to LLVM. We do
+        // *not* consider the `-Ctarget-feature`s here, as that will be handled later in
+        // `cfg_target_feature`.
         if let Some(feat) = to_llvm_features(sess, feature) {
             // All the LLVM features this expands to must be enabled.
             for llvm_feature in feat {
@@ -371,24 +377,25 @@ fn update_target_reliable_float_cfg(sess: &Session, cfg: &mut TargetConfig) {
     let target_abi = sess.target.options.abi.as_ref();
     let target_pointer_width = sess.target.pointer_width;
     let version = get_version();
+    let lt_20_1_1 = version < (20, 1, 1);
+    let lt_21_0_0 = version < (21, 0, 0);
 
     cfg.has_reliable_f16 = match (target_arch, target_os) {
-        // Selection failure <https://github.com/llvm/llvm-project/issues/50374>
-        ("s390x", _) => false,
-        // LLVM crash without neon <https://github.com/llvm/llvm-project/issues/129394> (now fixed)
+        // LLVM crash without neon <https://github.com/llvm/llvm-project/issues/129394> (fixed in llvm20)
         ("aarch64", _)
-            if !cfg.target_features.iter().any(|f| f.as_str() == "neon")
-                && version < (20, 1, 1) =>
+            if !cfg.target_features.iter().any(|f| f.as_str() == "neon") && lt_20_1_1 =>
         {
             false
         }
         // Unsupported <https://github.com/llvm/llvm-project/issues/94434>
         ("arm64ec", _) => false,
+        // Selection failure <https://github.com/llvm/llvm-project/issues/50374> (fixed in llvm21)
+        ("s390x", _) if lt_21_0_0 => false,
         // MinGW ABI bugs <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115054>
         ("x86_64", "windows") if target_env == "gnu" && target_abi != "llvm" => false,
         // Infinite recursion <https://github.com/llvm/llvm-project/issues/97981>
         ("csky", _) => false,
-        ("hexagon", _) => false,
+        ("hexagon", _) if lt_21_0_0 => false, // (fixed in llvm21)
         ("powerpc" | "powerpc64", _) => false,
         ("sparc" | "sparc64", _) => false,
         ("wasm32" | "wasm64", _) => false,
@@ -401,9 +408,10 @@ fn update_target_reliable_float_cfg(sess: &Session, cfg: &mut TargetConfig) {
     cfg.has_reliable_f128 = match (target_arch, target_os) {
         // Unsupported <https://github.com/llvm/llvm-project/issues/94434>
         ("arm64ec", _) => false,
-        // Selection bug <https://github.com/llvm/llvm-project/issues/96432>
-        ("mips64" | "mips64r6", _) => false,
-        // Selection bug <https://github.com/llvm/llvm-project/issues/95471>
+        // Selection bug <https://github.com/llvm/llvm-project/issues/96432> (fixed in llvm20)
+        ("mips64" | "mips64r6", _) if lt_20_1_1 => false,
+        // Selection bug <https://github.com/llvm/llvm-project/issues/95471>. This issue is closed
+        // but basic math still does not work.
         ("nvptx64", _) => false,
         // Unsupported https://github.com/llvm/llvm-project/issues/121122
         ("amdgpu", _) => false,
@@ -413,8 +421,8 @@ fn update_target_reliable_float_cfg(sess: &Session, cfg: &mut TargetConfig) {
         // ABI unsupported  <https://github.com/llvm/llvm-project/issues/41838>
         ("sparc", _) => false,
         // Stack alignment bug <https://github.com/llvm/llvm-project/issues/77401>. NB: tests may
-        // not fail if our compiler-builtins is linked.
-        ("x86", _) => false,
+        // not fail if our compiler-builtins is linked. (fixed in llvm21)
+        ("x86", _) if lt_21_0_0 => false,
         // MinGW ABI bugs <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115054>
         ("x86_64", "windows") if target_env == "gnu" && target_abi != "llvm" => false,
         // There are no known problems on other platforms, so the only requirement is that symbols
diff --git a/compiler/rustc_codegen_llvm/src/mono_item.rs b/compiler/rustc_codegen_llvm/src/mono_item.rs
index f9edaded60d..5075befae8a 100644
--- a/compiler/rustc_codegen_llvm/src/mono_item.rs
+++ b/compiler/rustc_codegen_llvm/src/mono_item.rs
@@ -1,8 +1,9 @@
 use rustc_codegen_ssa::traits::*;
+use rustc_hir::attrs::Linkage;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_middle::bug;
-use rustc_middle::mir::mono::{Linkage, Visibility};
+use rustc_middle::mir::mono::Visibility;
 use rustc_middle::ty::layout::{FnAbiOf, HasTypingEnv, LayoutOf};
 use rustc_middle::ty::{self, Instance, TypeVisitableExt};
 use rustc_session::config::CrateType;
diff --git a/compiler/rustc_codegen_ssa/Cargo.toml b/compiler/rustc_codegen_ssa/Cargo.toml
index 30956fd1855..6a8971de746 100644
--- a/compiler/rustc_codegen_ssa/Cargo.toml
+++ b/compiler/rustc_codegen_ssa/Cargo.toml
@@ -26,6 +26,7 @@ rustc_hashes = { path = "../rustc_hashes" }
 rustc_hir = { path = "../rustc_hir" }
 rustc_incremental = { path = "../rustc_incremental" }
 rustc_index = { path = "../rustc_index" }
+rustc_lint_defs = { path = "../rustc_lint_defs" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_metadata = { path = "../rustc_metadata" }
 rustc_middle = { path = "../rustc_middle" }
diff --git a/compiler/rustc_codegen_ssa/messages.ftl b/compiler/rustc_codegen_ssa/messages.ftl
index a70d0011d16..b6cfea88363 100644
--- a/compiler/rustc_codegen_ssa/messages.ftl
+++ b/compiler/rustc_codegen_ssa/messages.ftl
@@ -101,6 +101,8 @@ codegen_ssa_invalid_monomorphization_basic_float_type = invalid monomorphization
 
 codegen_ssa_invalid_monomorphization_basic_integer_type = invalid monomorphization of `{$name}` intrinsic: expected basic integer type, found `{$ty}`
 
+codegen_ssa_invalid_monomorphization_basic_integer_or_ptr_type = invalid monomorphization of `{$name}` intrinsic: expected basic integer or pointer type, found `{$ty}`
+
 codegen_ssa_invalid_monomorphization_cannot_return = invalid monomorphization of `{$name}` intrinsic: cannot return `{$ret_ty}`, expected `u{$expected_int_bits}` or `[u8; {$expected_bytes}]`
 
 codegen_ssa_invalid_monomorphization_cast_wide_pointer = invalid monomorphization of `{$name}` intrinsic: cannot cast wide pointer `{$ty}`
@@ -178,6 +180,10 @@ codegen_ssa_ld64_unimplemented_modifier = `as-needed` modifier not implemented y
 
 codegen_ssa_lib_def_write_failure = failed to write lib.def file: {$error}
 
+codegen_ssa_link_exe_status_stack_buffer_overrun = 0xc0000409 is `STATUS_STACK_BUFFER_OVERRUN`
+    .abort_note = this may have been caused by a program abort and not a stack buffer overrun
+    .event_log_note = consider checking the Application Event Log for Windows Error Reporting events to see the fail fast error code
+
 codegen_ssa_link_exe_unexpected_error = `link.exe` returned an unexpected error
 
 codegen_ssa_link_script_unavailable = can only use link script when linking with GNU-like linker
@@ -395,6 +401,9 @@ codegen_ssa_version_script_write_failure = failed to write version script: {$err
 
 codegen_ssa_visual_studio_not_installed = you may need to install Visual Studio build tools with the "C++ build tools" workload
 
+codegen_ssa_xcrun_about =
+    the SDK is needed by the linker to know where to find symbols in system libraries and for embedding the SDK version in the final object file
+
 codegen_ssa_xcrun_command_line_tools_insufficient =
     when compiling for iOS, tvOS, visionOS or watchOS, you need a full installation of Xcode
 
diff --git a/compiler/rustc_codegen_ssa/src/assert_module_sources.rs b/compiler/rustc_codegen_ssa/src/assert_module_sources.rs
index 3710625ac12..43e1e135a66 100644
--- a/compiler/rustc_codegen_ssa/src/assert_module_sources.rs
+++ b/compiler/rustc_codegen_ssa/src/assert_module_sources.rs
@@ -69,6 +69,15 @@ pub fn assert_module_sources(tcx: TyCtxt<'_>, set_reuse: &dyn Fn(&mut CguReuseTr
 
         set_reuse(&mut ams.cgu_reuse_tracker);
 
+        if tcx.sess.opts.unstable_opts.print_mono_items
+            && let Some(data) = &ams.cgu_reuse_tracker.data
+        {
+            data.actual_reuse.items().all(|(cgu, reuse)| {
+                println!("CGU_REUSE {cgu} {reuse}");
+                true
+            });
+        }
+
         ams.cgu_reuse_tracker.check_expected_reuse(tcx.sess);
     });
 }
diff --git a/compiler/rustc_codegen_ssa/src/back/apple.rs b/compiler/rustc_codegen_ssa/src/back/apple.rs
index d242efaf4fd..2274450e20e 100644
--- a/compiler/rustc_codegen_ssa/src/back/apple.rs
+++ b/compiler/rustc_codegen_ssa/src/back/apple.rs
@@ -17,7 +17,7 @@ mod tests;
 
 /// The canonical name of the desired SDK for a given target.
 pub(super) fn sdk_name(target: &Target) -> &'static str {
-    match (&*target.os, &*target.abi) {
+    match (&*target.os, &*target.env) {
         ("macos", "") => "MacOSX",
         ("ios", "") => "iPhoneOS",
         ("ios", "sim") => "iPhoneSimulator",
@@ -34,7 +34,7 @@ pub(super) fn sdk_name(target: &Target) -> &'static str {
 }
 
 pub(super) fn macho_platform(target: &Target) -> u32 {
-    match (&*target.os, &*target.abi) {
+    match (&*target.os, &*target.env) {
         ("macos", _) => object::macho::PLATFORM_MACOS,
         ("ios", "macabi") => object::macho::PLATFORM_MACCATALYST,
         ("ios", "sim") => object::macho::PLATFORM_IOSSIMULATOR,
@@ -160,6 +160,10 @@ pub(super) fn add_version_to_llvm_target(
 pub(super) fn get_sdk_root(sess: &Session) -> Option<PathBuf> {
     let sdk_name = sdk_name(&sess.target);
 
+    // Attempt to invoke `xcrun` to find the SDK.
+    //
+    // Note that when cross-compiling from e.g. Linux, the `xcrun` binary may sometimes be provided
+    // as a shim by a cross-compilation helper tool. It usually isn't, but we still try nonetheless.
     match xcrun_show_sdk_path(sdk_name, sess.verbose_internals()) {
         Ok((path, stderr)) => {
             // Emit extra stderr, such as if `-verbose` was passed, or if `xcrun` emitted a warning.
@@ -169,7 +173,19 @@ pub(super) fn get_sdk_root(sess: &Session) -> Option<PathBuf> {
             Some(path)
         }
         Err(err) => {
-            let mut diag = sess.dcx().create_err(err);
+            // Failure to find the SDK is not a hard error, since the user might have specified it
+            // in a manner unknown to us (moreso if cross-compiling):
+            // - A compiler driver like `zig cc` which links using an internally bundled SDK.
+            // - Extra linker arguments (`-Clink-arg=-syslibroot`).
+            // - A custom linker or custom compiler driver.
+            //
+            // Though we still warn, since such cases are uncommon, and it is very hard to debug if
+            // you do not know the details.
+            //
+            // FIXME(madsmtm): Make this a lint, to allow deny warnings to work.
+            // (Or fix <https://github.com/rust-lang/rust/issues/21204>).
+            let mut diag = sess.dcx().create_warn(err);
+            diag.note(fluent::codegen_ssa_xcrun_about);
 
             // Recognize common error cases, and give more Rust-specific error messages for those.
             if let Some(developer_dir) = xcode_select_developer_dir() {
@@ -209,6 +225,8 @@ fn xcrun_show_sdk_path(
     sdk_name: &'static str,
     verbose: bool,
 ) -> Result<(PathBuf, String), XcrunError> {
+    // Intentionally invoke the `xcrun` in PATH, since e.g. nixpkgs provide an `xcrun` shim, so we
+    // don't want to require `/usr/bin/xcrun`.
     let mut cmd = Command::new("xcrun");
     if verbose {
         cmd.arg("--verbose");
@@ -280,7 +298,7 @@ fn stdout_to_path(mut stdout: Vec<u8>) -> PathBuf {
     }
     #[cfg(unix)]
     let path = <OsString as std::os::unix::ffi::OsStringExt>::from_vec(stdout);
-    #[cfg(not(unix))] // Unimportant, this is only used on macOS
-    let path = OsString::from(String::from_utf8(stdout).unwrap());
+    #[cfg(not(unix))] // Not so important, this is mostly used on macOS
+    let path = OsString::from(String::from_utf8(stdout).expect("stdout must be UTF-8"));
     PathBuf::from(path)
 }
diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index b69fbf61185..4ebe59dc2a7 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -880,6 +880,14 @@ fn link_natively(
                             windows_registry::find_tool(&sess.target.arch, "link.exe").is_some();
 
                         sess.dcx().emit_note(errors::LinkExeUnexpectedError);
+
+                        // STATUS_STACK_BUFFER_OVERRUN is also used for fast abnormal program termination, e.g. abort().
+                        // Emit a special diagnostic to let people know that this most likely doesn't indicate a stack buffer overrun.
+                        const STATUS_STACK_BUFFER_OVERRUN: i32 = 0xc0000409u32 as _;
+                        if code == STATUS_STACK_BUFFER_OVERRUN {
+                            sess.dcx().emit_note(errors::LinkExeStatusStackBufferOverrun);
+                        }
+
                         if is_vs_installed && has_linker {
                             // the linker is broken
                             sess.dcx().emit_note(errors::RepairVSBuildTools);
@@ -3026,7 +3034,7 @@ pub(crate) fn are_upstream_rust_objects_already_included(sess: &Session) -> bool
 /// We need to communicate five things to the linker on Apple/Darwin targets:
 /// - The architecture.
 /// - The operating system (and that it's an Apple platform).
-/// - The environment / ABI.
+/// - The environment.
 /// - The deployment target.
 /// - The SDK version.
 fn add_apple_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
@@ -3040,7 +3048,7 @@ fn add_apple_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavo
     // `sess.target.arch` (`target_arch`) is not detailed enough.
     let llvm_arch = sess.target.llvm_target.split_once('-').expect("LLVM target must have arch").0;
     let target_os = &*sess.target.os;
-    let target_abi = &*sess.target.abi;
+    let target_env = &*sess.target.env;
 
     // The architecture name to forward to the linker.
     //
@@ -3091,14 +3099,14 @@ fn add_apple_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavo
         // > - visionos-simulator
         // > - xros-simulator
         // > - driverkit
-        let platform_name = match (target_os, target_abi) {
+        let platform_name = match (target_os, target_env) {
             (os, "") => os,
             ("ios", "macabi") => "mac-catalyst",
             ("ios", "sim") => "ios-simulator",
             ("tvos", "sim") => "tvos-simulator",
             ("watchos", "sim") => "watchos-simulator",
             ("visionos", "sim") => "visionos-simulator",
-            _ => bug!("invalid OS/ABI combination for Apple target: {target_os}, {target_abi}"),
+            _ => bug!("invalid OS/env combination for Apple target: {target_os}, {target_env}"),
         };
 
         let min_version = sess.apple_deployment_target().fmt_full().to_string();
@@ -3186,39 +3194,60 @@ fn add_apple_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavo
 }
 
 fn add_apple_sdk(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) -> Option<PathBuf> {
-    let os = &sess.target.os;
-    if sess.target.vendor != "apple"
-        || !matches!(os.as_ref(), "ios" | "tvos" | "watchos" | "visionos" | "macos")
-        || !matches!(flavor, LinkerFlavor::Darwin(..))
-    {
+    if !sess.target.is_like_darwin {
         return None;
     }
-
-    if os == "macos" && !matches!(flavor, LinkerFlavor::Darwin(Cc::No, _)) {
+    let LinkerFlavor::Darwin(cc, _) = flavor else {
         return None;
-    }
-
-    let sdk_root = sess.time("get_apple_sdk_root", || get_apple_sdk_root(sess))?;
+    };
 
-    match flavor {
-        LinkerFlavor::Darwin(Cc::Yes, _) => {
-            // Use `-isysroot` instead of `--sysroot`, as only the former
-            // makes Clang treat it as a platform SDK.
-            //
-            // This is admittedly a bit strange, as on most targets
-            // `-isysroot` only applies to include header files, but on Apple
-            // targets this also applies to libraries and frameworks.
-            cmd.cc_arg("-isysroot");
-            cmd.cc_arg(&sdk_root);
-        }
-        LinkerFlavor::Darwin(Cc::No, _) => {
-            cmd.link_arg("-syslibroot");
-            cmd.link_arg(&sdk_root);
-        }
-        _ => unreachable!(),
+    // The default compiler driver on macOS is at `/usr/bin/cc`. This is a trampoline binary that
+    // effectively invokes `xcrun cc` internally to look up both the compiler binary and the SDK
+    // root from the current Xcode installation. When cross-compiling, when `rustc` is invoked
+    // inside Xcode, or when invoking the linker directly, this default logic is unsuitable, so
+    // instead we invoke `xcrun` manually.
+    //
+    // (Note that this doesn't mean we get a duplicate lookup here - passing `SDKROOT` below will
+    // cause the trampoline binary to skip looking up the SDK itself).
+    let sdkroot = sess.time("get_apple_sdk_root", || get_apple_sdk_root(sess))?;
+
+    if cc == Cc::Yes {
+        // There are a few options to pass the SDK root when linking with a C/C++ compiler:
+        // - The `--sysroot` flag.
+        // - The `-isysroot` flag.
+        // - The `SDKROOT` environment variable.
+        //
+        // `--sysroot` isn't actually enough to get Clang to treat it as a platform SDK, you need
+        // to specify `-isysroot`. This is admittedly a bit strange, as on most targets `-isysroot`
+        // only applies to include header files, but on Apple targets it also applies to libraries
+        // and frameworks.
+        //
+        // This leaves the choice between `-isysroot` and `SDKROOT`. Both are supported by Clang and
+        // GCC, though they may not be supported by all compiler drivers. We choose `SDKROOT`,
+        // primarily because that is the same interface that is used when invoking the tool under
+        // `xcrun -sdk macosx $tool`.
+        //
+        // In that sense, if a given compiler driver does not support `SDKROOT`, the blame is fairly
+        // clearly in the tool in question, since they also don't support being run under `xcrun`.
+        //
+        // Additionally, `SDKROOT` is an environment variable and thus optional. It also has lower
+        // precedence than `-isysroot`, so a custom compiler driver that does not support it and
+        // instead figures out the SDK on their own can easily do so by using `-isysroot`.
+        //
+        // (This in particular affects Clang built with the `DEFAULT_SYSROOT` CMake flag, such as
+        // the one provided by some versions of Homebrew's `llvm` package. Those will end up
+        // ignoring the value we set here, and instead use their built-in sysroot).
+        cmd.cmd().env("SDKROOT", &sdkroot);
+    } else {
+        // When invoking the linker directly, we use the `-syslibroot` parameter. `SDKROOT` is not
+        // read by the linker, so it's really the only option.
+        //
+        // This is also what Clang does.
+        cmd.link_arg("-syslibroot");
+        cmd.link_arg(&sdkroot);
     }
 
-    Some(sdk_root)
+    Some(sdkroot)
 }
 
 fn get_apple_sdk_root(sess: &Session) -> Option<PathBuf> {
@@ -3247,7 +3276,13 @@ fn get_apple_sdk_root(sess: &Session) -> Option<PathBuf> {
             }
             "macosx"
                 if sdkroot.contains("iPhoneOS.platform")
-                    || sdkroot.contains("iPhoneSimulator.platform") => {}
+                    || sdkroot.contains("iPhoneSimulator.platform")
+                    || sdkroot.contains("AppleTVOS.platform")
+                    || sdkroot.contains("AppleTVSimulator.platform")
+                    || sdkroot.contains("WatchOS.platform")
+                    || sdkroot.contains("WatchSimulator.platform")
+                    || sdkroot.contains("XROS.platform")
+                    || sdkroot.contains("XRSimulator.platform") => {}
             "watchos"
                 if sdkroot.contains("WatchSimulator.platform")
                     || sdkroot.contains("MacOSX.platform") => {}
diff --git a/compiler/rustc_codegen_ssa/src/back/linker.rs b/compiler/rustc_codegen_ssa/src/back/linker.rs
index 050797354b4..df1e91b12f9 100644
--- a/compiler/rustc_codegen_ssa/src/back/linker.rs
+++ b/compiler/rustc_codegen_ssa/src/back/linker.rs
@@ -1805,11 +1805,18 @@ pub(crate) fn exported_symbols(
             .collect();
     }
 
-    if let CrateType::ProcMacro = crate_type {
+    let mut symbols = if let CrateType::ProcMacro = crate_type {
         exported_symbols_for_proc_macro_crate(tcx)
     } else {
         exported_symbols_for_non_proc_macro(tcx, crate_type)
+    };
+
+    if crate_type == CrateType::Dylib || crate_type == CrateType::ProcMacro {
+        let metadata_symbol_name = exported_symbols::metadata_symbol_name(tcx);
+        symbols.push((metadata_symbol_name, SymbolExportKind::Data));
     }
+
+    symbols
 }
 
 fn exported_symbols_for_non_proc_macro(
@@ -1842,12 +1849,8 @@ fn exported_symbols_for_proc_macro_crate(tcx: TyCtxt<'_>) -> Vec<(String, Symbol
 
     let stable_crate_id = tcx.stable_crate_id(LOCAL_CRATE);
     let proc_macro_decls_name = tcx.sess.generate_proc_macro_decls_symbol(stable_crate_id);
-    let metadata_symbol_name = exported_symbols::metadata_symbol_name(tcx);
 
-    vec![
-        (proc_macro_decls_name, SymbolExportKind::Data),
-        (metadata_symbol_name, SymbolExportKind::Data),
-    ]
+    vec![(proc_macro_decls_name, SymbolExportKind::Data)]
 }
 
 pub(crate) fn linked_symbols(
diff --git a/compiler/rustc_codegen_ssa/src/back/symbol_export.rs b/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
index 4b4b39f5353..77096822fdc 100644
--- a/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
+++ b/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
@@ -8,7 +8,7 @@ use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LOCAL_CRATE, LocalDefId};
 use rustc_middle::bug;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::middle::exported_symbols::{
-    ExportedSymbol, SymbolExportInfo, SymbolExportKind, SymbolExportLevel, metadata_symbol_name,
+    ExportedSymbol, SymbolExportInfo, SymbolExportKind, SymbolExportLevel,
 };
 use rustc_middle::query::LocalCrate;
 use rustc_middle::ty::{self, GenericArgKind, GenericArgsRef, Instance, SymbolName, Ty, TyCtxt};
@@ -289,23 +289,6 @@ fn exported_non_generic_symbols_provider_local<'tcx>(
         }));
     }
 
-    if tcx.crate_types().contains(&CrateType::Dylib)
-        || tcx.crate_types().contains(&CrateType::ProcMacro)
-    {
-        let symbol_name = metadata_symbol_name(tcx);
-        let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
-
-        symbols.push((
-            exported_symbol,
-            SymbolExportInfo {
-                level: SymbolExportLevel::C,
-                kind: SymbolExportKind::Data,
-                used: true,
-                rustc_std_internal_symbol: false,
-            },
-        ));
-    }
-
     // Sort so we get a stable incr. comp. hash.
     symbols.sort_by_cached_key(|s| s.0.symbol_name_for_local_instance(tcx));
 
@@ -323,7 +306,8 @@ fn exported_generic_symbols_provider_local<'tcx>(
     let mut symbols: Vec<_> = vec![];
 
     if tcx.local_crate_exports_generics() {
-        use rustc_middle::mir::mono::{Linkage, MonoItem, Visibility};
+        use rustc_hir::attrs::Linkage;
+        use rustc_middle::mir::mono::{MonoItem, Visibility};
         use rustc_middle::ty::InstanceKind;
 
         // Normally, we require that shared monomorphizations are not hidden,
@@ -586,7 +570,7 @@ fn symbol_export_level(tcx: TyCtxt<'_>, sym_def_id: DefId) -> SymbolExportLevel
     // core/std/allocators/etc. For example symbols used to hook up allocation
     // are not considered for export
     let codegen_fn_attrs = tcx.codegen_fn_attrs(sym_def_id);
-    let is_extern = codegen_fn_attrs.contains_extern_indicator();
+    let is_extern = codegen_fn_attrs.contains_extern_indicator(tcx, sym_def_id);
     let std_internal =
         codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL);
 
diff --git a/compiler/rustc_codegen_ssa/src/back/write.rs b/compiler/rustc_codegen_ssa/src/back/write.rs
index aa29afb7f5b..26d089a1171 100644
--- a/compiler/rustc_codegen_ssa/src/back/write.rs
+++ b/compiler/rustc_codegen_ssa/src/back/write.rs
@@ -7,7 +7,6 @@ use std::{fs, io, mem, str, thread};
 
 use rustc_abi::Size;
 use rustc_ast::attr;
-use rustc_ast::expand::autodiff_attrs::AutoDiffItem;
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::jobserver::{self, Acquired};
 use rustc_data_structures::memmap::Mmap;
@@ -38,7 +37,7 @@ use tracing::debug;
 use super::link::{self, ensure_removed};
 use super::lto::{self, SerializedModule};
 use crate::back::lto::check_lto_allowed;
-use crate::errors::{AutodiffWithoutLto, ErrorCreatingRemarkDir};
+use crate::errors::ErrorCreatingRemarkDir;
 use crate::traits::*;
 use crate::{
     CachedModuleCodegen, CodegenResults, CompiledModule, CrateInfo, ModuleCodegen, ModuleKind,
@@ -76,12 +75,9 @@ pub struct ModuleConfig {
     /// Names of additional optimization passes to run.
     pub passes: Vec<String>,
     /// Some(level) to optimize at a certain level, or None to run
-    /// absolutely no optimizations (used for the metadata module).
+    /// absolutely no optimizations (used for the allocator module).
     pub opt_level: Option<config::OptLevel>,
 
-    /// Some(level) to optimize binary size, or None to not affect program size.
-    pub opt_size: Option<config::OptLevel>,
-
     pub pgo_gen: SwitchWithOptPath,
     pub pgo_use: Option<PathBuf>,
     pub pgo_sample_use: Option<PathBuf>,
@@ -102,7 +98,6 @@ pub struct ModuleConfig {
     pub emit_obj: EmitObj,
     pub emit_thin_lto: bool,
     pub emit_thin_lto_summary: bool,
-    pub bc_cmdline: String,
 
     // Miscellaneous flags. These are mostly copied from command-line
     // options.
@@ -110,7 +105,6 @@ pub struct ModuleConfig {
     pub lint_llvm_ir: bool,
     pub no_prepopulate_passes: bool,
     pub no_builtins: bool,
-    pub time_module: bool,
     pub vectorize_loop: bool,
     pub vectorize_slp: bool,
     pub merge_functions: bool,
@@ -171,7 +165,6 @@ impl ModuleConfig {
             passes: if_regular!(sess.opts.cg.passes.clone(), vec![]),
 
             opt_level: opt_level_and_size,
-            opt_size: opt_level_and_size,
 
             pgo_gen: if_regular!(
                 sess.opts.cg.profile_generate.clone(),
@@ -221,17 +214,12 @@ impl ModuleConfig {
                 sess.opts.output_types.contains_key(&OutputType::ThinLinkBitcode),
                 false
             ),
-            bc_cmdline: sess.target.bitcode_llvm_cmdline.to_string(),
 
             verify_llvm_ir: sess.verify_llvm_ir(),
             lint_llvm_ir: sess.opts.unstable_opts.lint_llvm_ir,
             no_prepopulate_passes: sess.opts.cg.no_prepopulate_passes,
             no_builtins: no_builtins || sess.target.no_builtins,
 
-            // Exclude metadata and allocator modules from time_passes output,
-            // since they throw off the "LLVM passes" measurement.
-            time_module: if_regular!(true, false),
-
             // Copy what clang does by turning on loop vectorization at O2 and
             // slp vectorization at O3.
             vectorize_loop: !sess.opts.cg.no_vectorize_loops
@@ -454,7 +442,6 @@ pub(crate) fn start_async_codegen<B: ExtraBackendMethods>(
     backend: B,
     tcx: TyCtxt<'_>,
     target_cpu: String,
-    autodiff_items: &[AutoDiffItem],
 ) -> OngoingCodegen<B> {
     let (coordinator_send, coordinator_receive) = channel();
 
@@ -473,7 +460,6 @@ pub(crate) fn start_async_codegen<B: ExtraBackendMethods>(
         backend.clone(),
         tcx,
         &crate_info,
-        autodiff_items,
         shared_emitter,
         codegen_worker_send,
         coordinator_receive,
@@ -728,7 +714,6 @@ pub(crate) enum WorkItem<B: WriteBackendMethods> {
         each_linked_rlib_for_lto: Vec<PathBuf>,
         needs_fat_lto: Vec<FatLtoInput<B>>,
         import_only_modules: Vec<(SerializedModule<B::ModuleBuffer>, WorkProduct)>,
-        autodiff: Vec<AutoDiffItem>,
     },
     /// Performs thin-LTO on the given module.
     ThinLto(lto::ThinModule<B>),
@@ -1001,7 +986,6 @@ fn execute_fat_lto_work_item<B: ExtraBackendMethods>(
     each_linked_rlib_for_lto: &[PathBuf],
     mut needs_fat_lto: Vec<FatLtoInput<B>>,
     import_only_modules: Vec<(SerializedModule<B::ModuleBuffer>, WorkProduct)>,
-    autodiff: Vec<AutoDiffItem>,
     module_config: &ModuleConfig,
 ) -> Result<WorkItemResult<B>, FatalError> {
     for (module, wp) in import_only_modules {
@@ -1013,7 +997,6 @@ fn execute_fat_lto_work_item<B: ExtraBackendMethods>(
         exported_symbols_for_lto,
         each_linked_rlib_for_lto,
         needs_fat_lto,
-        autodiff,
     )?;
     let module = B::codegen(cgcx, module, module_config)?;
     Ok(WorkItemResult::Finished(module))
@@ -1105,7 +1088,6 @@ fn start_executing_work<B: ExtraBackendMethods>(
     backend: B,
     tcx: TyCtxt<'_>,
     crate_info: &CrateInfo,
-    autodiff_items: &[AutoDiffItem],
     shared_emitter: SharedEmitter,
     codegen_worker_send: Sender<CguMessage>,
     coordinator_receive: Receiver<Message<B>>,
@@ -1115,7 +1097,6 @@ fn start_executing_work<B: ExtraBackendMethods>(
 ) -> thread::JoinHandle<Result<CompiledModules, ()>> {
     let coordinator_send = tx_to_llvm_workers;
     let sess = tcx.sess;
-    let autodiff_items = autodiff_items.to_vec();
 
     let mut each_linked_rlib_for_lto = Vec::new();
     let mut each_linked_rlib_file_for_lto = Vec::new();
@@ -1448,7 +1429,6 @@ fn start_executing_work<B: ExtraBackendMethods>(
                                 each_linked_rlib_for_lto: each_linked_rlib_file_for_lto,
                                 needs_fat_lto,
                                 import_only_modules,
-                                autodiff: autodiff_items.clone(),
                             },
                             0,
                         ));
@@ -1456,11 +1436,6 @@ fn start_executing_work<B: ExtraBackendMethods>(
                             helper.request_token();
                         }
                     } else {
-                        if !autodiff_items.is_empty() {
-                            let dcx = cgcx.create_dcx();
-                            dcx.handle().emit_fatal(AutodiffWithoutLto {});
-                        }
-
                         for (work, cost) in generate_thin_lto_work(
                             &cgcx,
                             &exported_symbols_for_lto,
@@ -1740,7 +1715,7 @@ fn spawn_work<'a, B: ExtraBackendMethods>(
     llvm_start_time: &mut Option<VerboseTimingGuard<'a>>,
     work: WorkItem<B>,
 ) {
-    if cgcx.config(work.module_kind()).time_module && llvm_start_time.is_none() {
+    if llvm_start_time.is_none() {
         *llvm_start_time = Some(cgcx.prof.verbose_generic_activity("LLVM_passes"));
     }
 
@@ -1795,7 +1770,6 @@ fn spawn_work<'a, B: ExtraBackendMethods>(
                     each_linked_rlib_for_lto,
                     needs_fat_lto,
                     import_only_modules,
-                    autodiff,
                 } => {
                     let _timer = cgcx
                         .prof
@@ -1806,7 +1780,6 @@ fn spawn_work<'a, B: ExtraBackendMethods>(
                         &each_linked_rlib_for_lto,
                         needs_fat_lto,
                         import_only_modules,
-                        autodiff,
                         module_config,
                     )
                 }
diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs
index b4556ced0b3..67cd1f4cd41 100644
--- a/compiler/rustc_codegen_ssa/src/base.rs
+++ b/compiler/rustc_codegen_ssa/src/base.rs
@@ -647,7 +647,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
 ) -> OngoingCodegen<B> {
     // Skip crate items and just output metadata in -Z no-codegen mode.
     if tcx.sess.opts.unstable_opts.no_codegen || !tcx.sess.opts.output_types.should_codegen() {
-        let ongoing_codegen = start_async_codegen(backend, tcx, target_cpu, &[]);
+        let ongoing_codegen = start_async_codegen(backend, tcx, target_cpu);
 
         ongoing_codegen.codegen_finished(tcx);
 
@@ -665,8 +665,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
 
     // Run the monomorphization collector and partition the collected items into
     // codegen units.
-    let MonoItemPartitions { codegen_units, autodiff_items, .. } =
-        tcx.collect_and_partition_mono_items(());
+    let MonoItemPartitions { codegen_units, .. } = tcx.collect_and_partition_mono_items(());
 
     // Force all codegen_unit queries so they are already either red or green
     // when compile_codegen_unit accesses them. We are not able to re-execute
@@ -679,34 +678,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
         }
     }
 
-    let ongoing_codegen = start_async_codegen(backend.clone(), tcx, target_cpu, autodiff_items);
-
-    // Codegen an allocator shim, if necessary.
-    if let Some(kind) = allocator_kind_for_codegen(tcx) {
-        let llmod_id =
-            cgu_name_builder.build_cgu_name(LOCAL_CRATE, &["crate"], Some("allocator")).to_string();
-        let module_llvm = tcx.sess.time("write_allocator_module", || {
-            backend.codegen_allocator(
-                tcx,
-                &llmod_id,
-                kind,
-                // If allocator_kind is Some then alloc_error_handler_kind must
-                // also be Some.
-                tcx.alloc_error_handler_kind(()).unwrap(),
-            )
-        });
-
-        ongoing_codegen.wait_for_signal_to_codegen_item();
-        ongoing_codegen.check_for_errors(tcx.sess);
-
-        // These modules are generally cheap and won't throw off scheduling.
-        let cost = 0;
-        submit_codegened_module_to_llvm(
-            &ongoing_codegen.coordinator,
-            ModuleCodegen::new_allocator(llmod_id, module_llvm),
-            cost,
-        );
-    }
+    let ongoing_codegen = start_async_codegen(backend.clone(), tcx, target_cpu);
 
     // For better throughput during parallel processing by LLVM, we used to sort
     // CGUs largest to smallest. This would lead to better thread utilization
@@ -823,6 +795,35 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
         }
     }
 
+    // Codegen an allocator shim, if necessary.
+    // Do this last to ensure the LLVM_passes timer doesn't start while no CGUs have been codegened
+    // yet for the backend to optimize.
+    if let Some(kind) = allocator_kind_for_codegen(tcx) {
+        let llmod_id =
+            cgu_name_builder.build_cgu_name(LOCAL_CRATE, &["crate"], Some("allocator")).to_string();
+        let module_llvm = tcx.sess.time("write_allocator_module", || {
+            backend.codegen_allocator(
+                tcx,
+                &llmod_id,
+                kind,
+                // If allocator_kind is Some then alloc_error_handler_kind must
+                // also be Some.
+                tcx.alloc_error_handler_kind(()).unwrap(),
+            )
+        });
+
+        ongoing_codegen.wait_for_signal_to_codegen_item();
+        ongoing_codegen.check_for_errors(tcx.sess);
+
+        // These modules are generally cheap and won't throw off scheduling.
+        let cost = 0;
+        submit_codegened_module_to_llvm(
+            &ongoing_codegen.coordinator,
+            ModuleCodegen::new_allocator(llmod_id, module_llvm),
+            cost,
+        );
+    }
+
     ongoing_codegen.codegen_finished(tcx);
 
     // Since the main thread is sometimes blocked during codegen, we keep track
diff --git a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
index 7f54a47327a..af70f0deb07 100644
--- a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
+++ b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
@@ -11,7 +11,6 @@ use rustc_hir::{self as hir, Attribute, LangItem, find_attr, lang_items};
 use rustc_middle::middle::codegen_fn_attrs::{
     CodegenFnAttrFlags, CodegenFnAttrs, PatchableFunctionEntry,
 };
-use rustc_middle::mir::mono::Linkage;
 use rustc_middle::query::Providers;
 use rustc_middle::span_bug;
 use rustc_middle::ty::{self as ty, TyCtxt};
@@ -26,31 +25,6 @@ use crate::target_features::{
     check_target_feature_trait_unsafe, check_tied_features, from_target_feature_attr,
 };
 
-fn linkage_by_name(tcx: TyCtxt<'_>, def_id: LocalDefId, name: &str) -> Linkage {
-    use rustc_middle::mir::mono::Linkage::*;
-
-    // Use the names from src/llvm/docs/LangRef.rst here. Most types are only
-    // applicable to variable declarations and may not really make sense for
-    // Rust code in the first place but allow them anyway and trust that the
-    // user knows what they're doing. Who knows, unanticipated use cases may pop
-    // up in the future.
-    //
-    // ghost, dllimport, dllexport and linkonce_odr_autohide are not supported
-    // and don't have to be, LLVM treats them as no-ops.
-    match name {
-        "available_externally" => AvailableExternally,
-        "common" => Common,
-        "extern_weak" => ExternalWeak,
-        "external" => External,
-        "internal" => Internal,
-        "linkonce" => LinkOnceAny,
-        "linkonce_odr" => LinkOnceODR,
-        "weak" => WeakAny,
-        "weak_odr" => WeakODR,
-        _ => tcx.dcx().span_fatal(tcx.def_span(def_id), "invalid linkage specified"),
-    }
-}
-
 /// In some cases, attributes are only valid on functions, but it's the `check_attr`
 /// pass that checks that they aren't used anywhere else, rather than this module.
 /// In these cases, we bail from performing further checks that are only meaningful for
@@ -103,13 +77,6 @@ fn parse_instruction_set_attr(tcx: TyCtxt<'_>, attr: &Attribute) -> Option<Instr
     }
 }
 
-// FIXME(jdonszelmann): remove when linkage becomes a parsed attr
-fn parse_linkage_attr(tcx: TyCtxt<'_>, did: LocalDefId, attr: &Attribute) -> Option<Linkage> {
-    let val = attr.value_str()?;
-    let linkage = linkage_by_name(tcx, did, val.as_str());
-    Some(linkage)
-}
-
 // FIXME(jdonszelmann): remove when no_sanitize becomes a parsed attr
 fn parse_no_sanitize_attr(tcx: TyCtxt<'_>, attr: &Attribute) -> Option<SanitizerSet> {
     let list = attr.meta_item_list()?;
@@ -210,14 +177,6 @@ fn process_builtin_attrs(
     let mut interesting_spans = InterestingAttributeDiagnosticSpans::default();
     let rust_target_features = tcx.rust_target_features(LOCAL_CRATE);
 
-    // If our rustc version supports autodiff/enzyme, then we call our handler
-    // to check for any `#[rustc_autodiff(...)]` attributes.
-    // FIXME(jdonszelmann): merge with loop below
-    if cfg!(llvm_enzyme) {
-        let ad = autodiff_attrs(tcx, did.into());
-        codegen_fn_attrs.autodiff_item = ad;
-    }
-
     for attr in attrs.iter() {
         if let hir::Attribute::Parsed(p) = attr {
             match p {
@@ -332,6 +291,28 @@ fn process_builtin_attrs(
                 AttributeKind::StdInternalSymbol(_) => {
                     codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL
                 }
+                AttributeKind::Linkage(linkage, _) => {
+                    let linkage = Some(*linkage);
+
+                    if tcx.is_foreign_item(did) {
+                        codegen_fn_attrs.import_linkage = linkage;
+
+                        if tcx.is_mutable_static(did.into()) {
+                            let mut diag = tcx.dcx().struct_span_err(
+                                attr.span(),
+                                "extern mutable statics are not allowed with `#[linkage]`",
+                            );
+                            diag.note(
+                                "marking the extern static mutable would allow changing which \
+                                symbol the static references rather than make the target of the \
+                                symbol mutable",
+                            );
+                            diag.emit();
+                        }
+                    } else {
+                        codegen_fn_attrs.linkage = linkage;
+                    }
+                }
                 _ => {}
             }
         }
@@ -349,28 +330,6 @@ fn process_builtin_attrs(
                 codegen_fn_attrs.flags |= CodegenFnAttrFlags::ALLOCATOR_ZEROED
             }
             sym::thread_local => codegen_fn_attrs.flags |= CodegenFnAttrFlags::THREAD_LOCAL,
-            sym::linkage => {
-                let linkage = parse_linkage_attr(tcx, did, attr);
-
-                if tcx.is_foreign_item(did) {
-                    codegen_fn_attrs.import_linkage = linkage;
-
-                    if tcx.is_mutable_static(did.into()) {
-                        let mut diag = tcx.dcx().struct_span_err(
-                            attr.span(),
-                            "extern mutable statics are not allowed with `#[linkage]`",
-                        );
-                        diag.note(
-                            "marking the extern static mutable would allow changing which \
-                            symbol the static references rather than make the target of the \
-                            symbol mutable",
-                        );
-                        diag.emit();
-                    }
-                } else {
-                    codegen_fn_attrs.linkage = linkage;
-                }
-            }
             sym::no_sanitize => {
                 interesting_spans.no_sanitize = Some(attr.span());
                 codegen_fn_attrs.no_sanitize |=
@@ -443,6 +402,27 @@ fn apply_overrides(tcx: TyCtxt<'_>, did: LocalDefId, codegen_fn_attrs: &mut Code
     if tcx.should_inherit_track_caller(did) {
         codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER;
     }
+
+    // Foreign items by default use no mangling for their symbol name.
+    if tcx.is_foreign_item(did) {
+        // There's a few exceptions to this rule though:
+        if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
+            // * `#[rustc_std_internal_symbol]` mangles the symbol name in a special way
+            //   both for exports and imports through foreign items. This is handled further,
+            //   during symbol mangling logic.
+        } else if codegen_fn_attrs.link_name.is_some() {
+            // * This can be overridden with the `#[link_name]` attribute
+        } else {
+            // NOTE: there's one more exception that we cannot apply here. On wasm,
+            // some items cannot be `no_mangle`.
+            // However, we don't have enough information here to determine that.
+            // As such, no_mangle foreign items on wasm that have the same defid as some
+            // import will *still* be mangled despite this.
+            //
+            // if none of the exceptions apply; apply no_mangle
+            codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
+        }
+    }
 }
 
 fn check_result(
@@ -624,7 +604,7 @@ fn inherited_align<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Option<Align> {
 /// placeholder functions. We wrote the rustc_autodiff attributes ourself, so this should never
 /// panic, unless we introduced a bug when parsing the autodiff macro.
 //FIXME(jdonszelmann): put in the main loop. No need to have two..... :/ Let's do that when we make autodiff parsed.
-fn autodiff_attrs(tcx: TyCtxt<'_>, id: DefId) -> Option<AutoDiffAttrs> {
+pub fn autodiff_attrs(tcx: TyCtxt<'_>, id: DefId) -> Option<AutoDiffAttrs> {
     let attrs = tcx.get_attrs(id, sym::rustc_autodiff);
 
     let attrs = attrs.filter(|attr| attr.has_name(sym::rustc_autodiff)).collect::<Vec<_>>();
diff --git a/compiler/rustc_codegen_ssa/src/errors.rs b/compiler/rustc_codegen_ssa/src/errors.rs
index 3d787d8bdbd..7ac830bcda9 100644
--- a/compiler/rustc_codegen_ssa/src/errors.rs
+++ b/compiler/rustc_codegen_ssa/src/errors.rs
@@ -550,6 +550,18 @@ impl<G: EmissionGuarantee> Diagnostic<'_, G> for LinkingFailed<'_> {
 #[diag(codegen_ssa_link_exe_unexpected_error)]
 pub(crate) struct LinkExeUnexpectedError;
 
+pub(crate) struct LinkExeStatusStackBufferOverrun;
+
+impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for LinkExeStatusStackBufferOverrun {
+    fn into_diag(self, dcx: rustc_errors::DiagCtxtHandle<'a>, level: Level) -> Diag<'a, G> {
+        let mut diag =
+            Diag::new(dcx, level, fluent::codegen_ssa_link_exe_status_stack_buffer_overrun);
+        diag.note(fluent::codegen_ssa_abort_note);
+        diag.note(fluent::codegen_ssa_event_log_note);
+        diag
+    }
+}
+
 #[derive(Diagnostic)]
 #[diag(codegen_ssa_repair_vs_build_tools)]
 pub(crate) struct RepairVSBuildTools;
@@ -764,6 +776,14 @@ pub enum InvalidMonomorphization<'tcx> {
         ty: Ty<'tcx>,
     },
 
+    #[diag(codegen_ssa_invalid_monomorphization_basic_integer_or_ptr_type, code = E0511)]
+    BasicIntegerOrPtrType {
+        #[primary_span]
+        span: Span,
+        name: Symbol,
+        ty: Ty<'tcx>,
+    },
+
     #[diag(codegen_ssa_invalid_monomorphization_basic_float_type, code = E0511)]
     BasicFloatType {
         #[primary_span]
diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index e96590441fa..c3dc3e42b83 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -5,6 +5,7 @@ use rustc_ast as ast;
 use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
 use rustc_data_structures::packed::Pu128;
 use rustc_hir::lang_items::LangItem;
+use rustc_lint_defs::builtin::TAIL_CALL_TRACK_CALLER;
 use rustc_middle::mir::{self, AssertKind, InlineAsmMacro, SwitchTargets, UnwindTerminateReason};
 use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf, ValidityRequirement};
 use rustc_middle::ty::print::{with_no_trimmed_paths, with_no_visible_paths};
@@ -35,7 +36,7 @@ enum MergingSucc {
     True,
 }
 
-/// Indicates to the call terminator codegen whether a cal
+/// Indicates to the call terminator codegen whether a call
 /// is a normal call or an explicit tail call.
 #[derive(Debug, PartialEq)]
 enum CallKind {
@@ -906,7 +907,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     fn_span,
                 );
 
-                let instance = match instance.def {
+                match instance.def {
                     // We don't need AsyncDropGlueCtorShim here because it is not `noop func`,
                     // it is `func returning noop future`
                     ty::InstanceKind::DropGlue(_, None) => {
@@ -995,14 +996,35 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                                         intrinsic.name,
                                     );
                                 }
-                                instance
+                                (Some(instance), None)
                             }
                         }
                     }
-                    _ => instance,
-                };
 
-                (Some(instance), None)
+                    _ if kind == CallKind::Tail
+                        && instance.def.requires_caller_location(bx.tcx()) =>
+                    {
+                        if let Some(hir_id) =
+                            terminator.source_info.scope.lint_root(&self.mir.source_scopes)
+                        {
+                            let msg = "tail calling a function marked with `#[track_caller]` has no special effect";
+                            bx.tcx().node_lint(TAIL_CALL_TRACK_CALLER, hir_id, |d| {
+                                _ = d.primary_message(msg).span(fn_span)
+                            });
+                        }
+
+                        let instance = ty::Instance::resolve_for_fn_ptr(
+                            bx.tcx(),
+                            bx.typing_env(),
+                            def_id,
+                            generic_args,
+                        )
+                        .unwrap();
+
+                        (None, Some(bx.get_fn_addr(instance)))
+                    }
+                    _ => (Some(instance), None),
+                }
             }
             ty::FnPtr(..) => (None, Some(callee.immediate())),
             _ => bug!("{} is not callable", callee.layout.ty),
diff --git a/compiler/rustc_codegen_ssa/src/mir/intrinsic.rs b/compiler/rustc_codegen_ssa/src/mir/intrinsic.rs
index fc95f62b4a4..3c667b8e882 100644
--- a/compiler/rustc_codegen_ssa/src/mir/intrinsic.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/intrinsic.rs
@@ -92,6 +92,13 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         let invalid_monomorphization_int_type = |ty| {
             bx.tcx().dcx().emit_err(InvalidMonomorphization::BasicIntegerType { span, name, ty });
         };
+        let invalid_monomorphization_int_or_ptr_type = |ty| {
+            bx.tcx().dcx().emit_err(InvalidMonomorphization::BasicIntegerOrPtrType {
+                span,
+                name,
+                ty,
+            });
+        };
 
         let parse_atomic_ordering = |ord: ty::Value<'tcx>| {
             let discr = ord.valtree.unwrap_branch()[0].unwrap_leaf();
@@ -351,7 +358,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             sym::atomic_load => {
                 let ty = fn_args.type_at(0);
                 if !(int_type_width_signed(ty, bx.tcx()).is_some() || ty.is_raw_ptr()) {
-                    invalid_monomorphization_int_type(ty);
+                    invalid_monomorphization_int_or_ptr_type(ty);
                     return Ok(());
                 }
                 let ordering = fn_args.const_at(1).to_value();
@@ -367,7 +374,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             sym::atomic_store => {
                 let ty = fn_args.type_at(0);
                 if !(int_type_width_signed(ty, bx.tcx()).is_some() || ty.is_raw_ptr()) {
-                    invalid_monomorphization_int_type(ty);
+                    invalid_monomorphization_int_or_ptr_type(ty);
                     return Ok(());
                 }
                 let ordering = fn_args.const_at(1).to_value();
@@ -377,10 +384,11 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 bx.atomic_store(val, ptr, parse_atomic_ordering(ordering), size);
                 return Ok(());
             }
+            // These are all AtomicRMW ops
             sym::atomic_cxchg | sym::atomic_cxchgweak => {
                 let ty = fn_args.type_at(0);
                 if !(int_type_width_signed(ty, bx.tcx()).is_some() || ty.is_raw_ptr()) {
-                    invalid_monomorphization_int_type(ty);
+                    invalid_monomorphization_int_or_ptr_type(ty);
                     return Ok(());
                 }
                 let succ_ordering = fn_args.const_at(1).to_value();
@@ -407,7 +415,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
                 return Ok(());
             }
-            // These are all AtomicRMW ops
             sym::atomic_max | sym::atomic_min => {
                 let atom_op = if name == sym::atomic_max {
                     AtomicRmwBinOp::AtomicMax
@@ -420,7 +427,13 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     let ordering = fn_args.const_at(1).to_value();
                     let ptr = args[0].immediate();
                     let val = args[1].immediate();
-                    bx.atomic_rmw(atom_op, ptr, val, parse_atomic_ordering(ordering))
+                    bx.atomic_rmw(
+                        atom_op,
+                        ptr,
+                        val,
+                        parse_atomic_ordering(ordering),
+                        /* ret_ptr */ false,
+                    )
                 } else {
                     invalid_monomorphization_int_type(ty);
                     return Ok(());
@@ -438,21 +451,44 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     let ordering = fn_args.const_at(1).to_value();
                     let ptr = args[0].immediate();
                     let val = args[1].immediate();
-                    bx.atomic_rmw(atom_op, ptr, val, parse_atomic_ordering(ordering))
+                    bx.atomic_rmw(
+                        atom_op,
+                        ptr,
+                        val,
+                        parse_atomic_ordering(ordering),
+                        /* ret_ptr */ false,
+                    )
                 } else {
                     invalid_monomorphization_int_type(ty);
                     return Ok(());
                 }
             }
-            sym::atomic_xchg
-            | sym::atomic_xadd
+            sym::atomic_xchg => {
+                let ty = fn_args.type_at(0);
+                let ordering = fn_args.const_at(1).to_value();
+                if int_type_width_signed(ty, bx.tcx()).is_some() || ty.is_raw_ptr() {
+                    let ptr = args[0].immediate();
+                    let val = args[1].immediate();
+                    let atomic_op = AtomicRmwBinOp::AtomicXchg;
+                    bx.atomic_rmw(
+                        atomic_op,
+                        ptr,
+                        val,
+                        parse_atomic_ordering(ordering),
+                        /* ret_ptr */ ty.is_raw_ptr(),
+                    )
+                } else {
+                    invalid_monomorphization_int_or_ptr_type(ty);
+                    return Ok(());
+                }
+            }
+            sym::atomic_xadd
             | sym::atomic_xsub
             | sym::atomic_and
             | sym::atomic_nand
             | sym::atomic_or
             | sym::atomic_xor => {
                 let atom_op = match name {
-                    sym::atomic_xchg => AtomicRmwBinOp::AtomicXchg,
                     sym::atomic_xadd => AtomicRmwBinOp::AtomicAdd,
                     sym::atomic_xsub => AtomicRmwBinOp::AtomicSub,
                     sym::atomic_and => AtomicRmwBinOp::AtomicAnd,
@@ -462,14 +498,28 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     _ => unreachable!(),
                 };
 
-                let ty = fn_args.type_at(0);
-                if int_type_width_signed(ty, bx.tcx()).is_some() || ty.is_raw_ptr() {
-                    let ordering = fn_args.const_at(1).to_value();
-                    let ptr = args[0].immediate();
-                    let val = args[1].immediate();
-                    bx.atomic_rmw(atom_op, ptr, val, parse_atomic_ordering(ordering))
+                // The type of the in-memory data.
+                let ty_mem = fn_args.type_at(0);
+                // The type of the 2nd operand, given by-value.
+                let ty_op = fn_args.type_at(1);
+
+                let ordering = fn_args.const_at(2).to_value();
+                // We require either both arguments to have the same integer type, or the first to
+                // be a pointer and the second to be `usize`.
+                if (int_type_width_signed(ty_mem, bx.tcx()).is_some() && ty_op == ty_mem)
+                    || (ty_mem.is_raw_ptr() && ty_op == bx.tcx().types.usize)
+                {
+                    let ptr = args[0].immediate(); // of type "pointer to `ty_mem`"
+                    let val = args[1].immediate(); // of type `ty_op`
+                    bx.atomic_rmw(
+                        atom_op,
+                        ptr,
+                        val,
+                        parse_atomic_ordering(ordering),
+                        /* ret_ptr */ ty_mem.is_raw_ptr(),
+                    )
                 } else {
-                    invalid_monomorphization_int_type(ty);
+                    invalid_monomorphization_int_or_ptr_type(ty_mem);
                     return Ok(());
                 }
             }
diff --git a/compiler/rustc_codegen_ssa/src/mir/mod.rs b/compiler/rustc_codegen_ssa/src/mir/mod.rs
index 50d0f910744..06873313e2e 100644
--- a/compiler/rustc_codegen_ssa/src/mir/mod.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/mod.rs
@@ -296,10 +296,6 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     // Apply debuginfo to the newly allocated locals.
     fx.debug_introduce_locals(&mut start_bx, consts_debug_info.unwrap_or_default());
 
-    // If the backend supports coverage, and coverage is enabled for this function,
-    // do any necessary start-of-function codegen (e.g. locals for MC/DC bitmaps).
-    start_bx.init_coverage(instance);
-
     // The builders will be created separately for each basic block at `codegen_block`.
     // So drop the builder of `start_llbb` to avoid having two at the same time.
     drop(start_bx);
diff --git a/compiler/rustc_codegen_ssa/src/mir/naked_asm.rs b/compiler/rustc_codegen_ssa/src/mir/naked_asm.rs
index 2a9b5c9019b..31784cabf4a 100644
--- a/compiler/rustc_codegen_ssa/src/mir/naked_asm.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/naked_asm.rs
@@ -1,6 +1,6 @@
 use rustc_abi::{BackendRepr, Float, Integer, Primitive, RegKind};
-use rustc_hir::attrs::InstructionSetAttr;
-use rustc_middle::mir::mono::{Linkage, MonoItemData, Visibility};
+use rustc_hir::attrs::{InstructionSetAttr, Linkage};
+use rustc_middle::mir::mono::{MonoItemData, Visibility};
 use rustc_middle::mir::{InlineAsmOperand, START_BLOCK};
 use rustc_middle::ty::layout::{FnAbiOf, LayoutOf, TyAndLayout};
 use rustc_middle::ty::{Instance, Ty, TyCtxt, TypeVisitableExt};
diff --git a/compiler/rustc_codegen_ssa/src/mir/operand.rs b/compiler/rustc_codegen_ssa/src/mir/operand.rs
index 5459f95c186..d851c332980 100644
--- a/compiler/rustc_codegen_ssa/src/mir/operand.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/operand.rs
@@ -498,6 +498,35 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
                         bx.cx().const_uint(cast_to, niche_variants.start().as_u32() as u64);
                     (is_niche, tagged_discr, 0)
                 } else {
+                    // Thanks to parameter attributes and load metadata, LLVM already knows
+                    // the general valid range of the tag. It's possible, though, for there
+                    // to be an impossible value *in the middle*, which those ranges don't
+                    // communicate, so it's worth an `assume` to let the optimizer know.
+                    // Most importantly, this means when optimizing a variant test like
+                    // `SELECT(is_niche, complex, CONST) == CONST` it's ok to simplify that
+                    // to `!is_niche` because the `complex` part can't possibly match.
+                    //
+                    // This was previously asserted on `tagged_discr` below, where the
+                    // impossible value is more obvious, but that caused an intermediate
+                    // value to become multi-use and thus not optimize, so instead this
+                    // assumes on the original input which is always multi-use. See
+                    // <https://github.com/llvm/llvm-project/issues/134024#issuecomment-3131782555>
+                    //
+                    // FIXME: If we ever get range assume operand bundles in LLVM (so we
+                    // don't need the `icmp`s in the instruction stream any more), it
+                    // might be worth moving this back to being on the switch argument
+                    // where it's more obviously applicable.
+                    if niche_variants.contains(&untagged_variant)
+                        && bx.cx().sess().opts.optimize != OptLevel::No
+                    {
+                        let impossible = niche_start
+                            .wrapping_add(u128::from(untagged_variant.as_u32()))
+                            .wrapping_sub(u128::from(niche_variants.start().as_u32()));
+                        let impossible = bx.cx().const_uint_big(tag_llty, impossible);
+                        let ne = bx.icmp(IntPredicate::IntNE, tag, impossible);
+                        bx.assume(ne);
+                    }
+
                     // With multiple niched variants we'll have to actually compute
                     // the variant index from the stored tag.
                     //
@@ -588,20 +617,6 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
                 let untagged_variant_const =
                     bx.cx().const_uint(cast_to, u64::from(untagged_variant.as_u32()));
 
-                // Thanks to parameter attributes and load metadata, LLVM already knows
-                // the general valid range of the tag. It's possible, though, for there
-                // to be an impossible value *in the middle*, which those ranges don't
-                // communicate, so it's worth an `assume` to let the optimizer know.
-                // Most importantly, this means when optimizing a variant test like
-                // `SELECT(is_niche, complex, CONST) == CONST` it's ok to simplify that
-                // to `!is_niche` because the `complex` part can't possibly match.
-                if niche_variants.contains(&untagged_variant)
-                    && bx.cx().sess().opts.optimize != OptLevel::No
-                {
-                    let ne = bx.icmp(IntPredicate::IntNE, tagged_discr, untagged_variant_const);
-                    bx.assume(ne);
-                }
-
                 let discr = bx.select(is_niche, tagged_discr, untagged_variant_const);
 
                 // In principle we could insert assumes on the possible range of `discr`, but
diff --git a/compiler/rustc_codegen_ssa/src/mono_item.rs b/compiler/rustc_codegen_ssa/src/mono_item.rs
index b9040c330fb..8f03dc1e6b5 100644
--- a/compiler/rustc_codegen_ssa/src/mono_item.rs
+++ b/compiler/rustc_codegen_ssa/src/mono_item.rs
@@ -1,5 +1,6 @@
+use rustc_hir::attrs::Linkage;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
-use rustc_middle::mir::mono::{Linkage, MonoItem, MonoItemData, Visibility};
+use rustc_middle::mir::mono::{MonoItem, MonoItemData, Visibility};
 use rustc_middle::ty::layout::HasTyCtxt;
 use tracing::debug;
 
diff --git a/compiler/rustc_codegen_ssa/src/target_features.rs b/compiler/rustc_codegen_ssa/src/target_features.rs
index d984156c674..7e4341a8236 100644
--- a/compiler/rustc_codegen_ssa/src/target_features.rs
+++ b/compiler/rustc_codegen_ssa/src/target_features.rs
@@ -197,7 +197,10 @@ fn parse_rust_feature_flag<'a>(
 /// 2nd component of the return value, respectively).
 ///
 /// `target_base_has_feature` should check whether the given feature (a Rust feature name!) is
-/// enabled in the "base" target machine, i.e., without applying `-Ctarget-feature`.
+/// enabled in the "base" target machine, i.e., without applying `-Ctarget-feature`. Note that LLVM
+/// may consider features to be implied that we do not and vice-versa. We want `cfg` to be entirely
+/// consistent with Rust feature implications, and thus only consult LLVM to expand the target CPU
+/// to target features.
 ///
 /// We do not have to worry about RUSTC_SPECIFIC_FEATURES here, those are handled elsewhere.
 pub fn cfg_target_feature(
@@ -211,7 +214,15 @@ pub fn cfg_target_feature(
         .rust_target_features()
         .iter()
         .filter(|(feature, _, _)| target_base_has_feature(feature))
-        .map(|(feature, _, _)| Symbol::intern(feature))
+        .flat_map(|(base_feature, _, _)| {
+            // Expand the direct base feature into all transitively-implied features. Note that we
+            // cannot simply use the `implied` field of the tuple since that only contains
+            // directly-implied features.
+            //
+            // Iteration order is irrelevant because we're collecting into an `UnordSet`.
+            #[allow(rustc::potential_query_instability)]
+            sess.target.implied_target_features(base_feature).into_iter().map(|f| Symbol::intern(f))
+        })
         .collect();
 
     // Add enabled and remove disabled features.
diff --git a/compiler/rustc_codegen_ssa/src/traits/builder.rs b/compiler/rustc_codegen_ssa/src/traits/builder.rs
index 4b18146863b..f417d1a7bf7 100644
--- a/compiler/rustc_codegen_ssa/src/traits/builder.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/builder.rs
@@ -548,12 +548,15 @@ pub trait BuilderMethods<'a, 'tcx>:
         failure_order: AtomicOrdering,
         weak: bool,
     ) -> (Self::Value, Self::Value);
+    /// `ret_ptr` indicates whether the return type (which is also the type `dst` points to)
+    /// is a pointer or the same type as `src`.
     fn atomic_rmw(
         &mut self,
         op: AtomicRmwBinOp,
         dst: Self::Value,
         src: Self::Value,
         order: AtomicOrdering,
+        ret_ptr: bool,
     ) -> Self::Value;
     fn atomic_fence(&mut self, order: AtomicOrdering, scope: SynchronizationScope);
     fn set_invariant_load(&mut self, load: Self::Value);
diff --git a/compiler/rustc_codegen_ssa/src/traits/coverageinfo.rs b/compiler/rustc_codegen_ssa/src/traits/coverageinfo.rs
index 0b513dac503..31482a53b6d 100644
--- a/compiler/rustc_codegen_ssa/src/traits/coverageinfo.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/coverageinfo.rs
@@ -2,11 +2,6 @@ use rustc_middle::mir::coverage::CoverageKind;
 use rustc_middle::ty::Instance;
 
 pub trait CoverageInfoBuilderMethods<'tcx> {
-    /// Performs any start-of-function codegen needed for coverage instrumentation.
-    ///
-    /// Can be a no-op in backends that don't support coverage instrumentation.
-    fn init_coverage(&mut self, _instance: Instance<'tcx>) {}
-
     /// Handle the MIR coverage info in a backend-specific way.
     ///
     /// This can potentially be a no-op in backends that don't support
diff --git a/compiler/rustc_codegen_ssa/src/traits/debuginfo.rs b/compiler/rustc_codegen_ssa/src/traits/debuginfo.rs
index 30a3bd5abe4..b9d4950e0ad 100644
--- a/compiler/rustc_codegen_ssa/src/traits/debuginfo.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/debuginfo.rs
@@ -50,7 +50,7 @@ pub trait DebugInfoCodegenMethods<'tcx>: BackendTypes {
         scope_metadata: Self::DIScope,
         file: &SourceFile,
     ) -> Self::DIScope;
-    fn debuginfo_finalize(&mut self);
+    fn debuginfo_finalize(&self);
 
     // FIXME(eddyb) find a common convention for all of the debuginfo-related
     // names (choose between `dbg`, `debug`, `debuginfo`, `debug_info` etc.).
diff --git a/compiler/rustc_codegen_ssa/src/traits/declare.rs b/compiler/rustc_codegen_ssa/src/traits/declare.rs
index 9f735546558..8d5f0a5b939 100644
--- a/compiler/rustc_codegen_ssa/src/traits/declare.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/declare.rs
@@ -1,5 +1,6 @@
+use rustc_hir::attrs::Linkage;
 use rustc_hir::def_id::DefId;
-use rustc_middle::mir::mono::{Linkage, Visibility};
+use rustc_middle::mir::mono::Visibility;
 use rustc_middle::ty::Instance;
 
 pub trait PreDefineCodegenMethods<'tcx> {
diff --git a/compiler/rustc_codegen_ssa/src/traits/write.rs b/compiler/rustc_codegen_ssa/src/traits/write.rs
index f391c198e1a..c29ad90735b 100644
--- a/compiler/rustc_codegen_ssa/src/traits/write.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/write.rs
@@ -1,6 +1,5 @@
 use std::path::PathBuf;
 
-use rustc_ast::expand::autodiff_attrs::AutoDiffItem;
 use rustc_errors::{DiagCtxtHandle, FatalError};
 use rustc_middle::dep_graph::WorkProduct;
 
@@ -23,7 +22,6 @@ pub trait WriteBackendMethods: Clone + 'static {
         exported_symbols_for_lto: &[String],
         each_linked_rlib_for_lto: &[PathBuf],
         modules: Vec<FatLtoInput<Self>>,
-        diff_fncs: Vec<AutoDiffItem>,
     ) -> Result<ModuleCodegen<Self::Module>, FatalError>;
     /// Performs thin LTO by performing necessary global analysis and returning two
     /// lists, one of the modules that need optimization and another for modules that
diff --git a/compiler/rustc_const_eval/messages.ftl b/compiler/rustc_const_eval/messages.ftl
index 2985eafb63a..60518dafbf2 100644
--- a/compiler/rustc_const_eval/messages.ftl
+++ b/compiler/rustc_const_eval/messages.ftl
@@ -57,7 +57,7 @@ const_eval_const_context = {$kind ->
 }
 
 const_eval_const_heap_ptr_in_final = encountered `const_allocate` pointer in final value that was not made global
-    .note = use `const_make_global` to make allocated pointers immutable before returning
+    .note = use `const_make_global` to turn allocated pointers into immutable globals before returning
 
 const_eval_const_make_global_ptr_already_made_global = attempting to call `const_make_global` twice on the same allocation {$alloc}
 
@@ -231,6 +231,9 @@ const_eval_mutable_borrow_escaping =
 
 const_eval_mutable_ptr_in_final = encountered mutable pointer in final value of {const_eval_intern_kind}
 
+const_eval_partial_pointer_in_final = encountered partial pointer in final value of {const_eval_intern_kind}
+    .note = while pointers can be broken apart into individual bytes during const-evaluation, only complete pointers (with all their bytes in the right order) are supported in the final value
+
 const_eval_nested_static_in_thread_local = #[thread_local] does not support implicit nested statics, please create explicit static items and refer to them instead
 
 const_eval_non_const_await =
@@ -299,10 +302,8 @@ const_eval_panic = evaluation panicked: {$msg}
 
 const_eval_panic_non_str = argument to `panic!()` in a const context must have type `&str`
 
-const_eval_partial_pointer_copy =
-    unable to copy parts of a pointer from memory at {$ptr}
-const_eval_partial_pointer_overwrite =
-    unable to overwrite parts of a pointer in memory at {$ptr}
+const_eval_partial_pointer_read =
+    unable to read parts of a pointer from memory at {$ptr}
 const_eval_pointer_arithmetic_overflow =
     overflowing pointer arithmetic: the total offset in bytes does not fit in an `isize`
 
diff --git a/compiler/rustc_const_eval/src/check_consts/check.rs b/compiler/rustc_const_eval/src/check_consts/check.rs
index 8e2c138282a..ca707b50d50 100644
--- a/compiler/rustc_const_eval/src/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/check_consts/check.rs
@@ -827,7 +827,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
 
                 // At this point, we are calling a function, `callee`, whose `DefId` is known...
 
-                // `begin_panic` and `#[rustc_const_panic_str]` functions accept generic
+                // `begin_panic` and `panic_display` functions accept generic
                 // types other than str. Check to enforce that only str can be used in
                 // const-eval.
 
@@ -841,8 +841,8 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                     return;
                 }
 
-                // const-eval of `#[rustc_const_panic_str]` functions assumes the argument is `&&str`
-                if tcx.has_attr(callee, sym::rustc_const_panic_str) {
+                // const-eval of `panic_display` assumes the argument is `&&str`
+                if tcx.is_lang_item(callee, LangItem::PanicDisplay) {
                     match args[0].node.ty(&self.ccx.body.local_decls, tcx).kind() {
                         ty::Ref(_, ty, _) if matches!(ty.kind(), ty::Ref(_, ty, _) if ty.is_str()) =>
                             {}
diff --git a/compiler/rustc_const_eval/src/check_consts/ops.rs b/compiler/rustc_const_eval/src/check_consts/ops.rs
index 982e640fa92..79e32dcf105 100644
--- a/compiler/rustc_const_eval/src/check_consts/ops.rs
+++ b/compiler/rustc_const_eval/src/check_consts/ops.rs
@@ -142,7 +142,7 @@ impl<'tcx> NonConstOp<'tcx> for FnCallNonConst<'tcx> {
             |err, self_ty, trait_id| {
                 // FIXME(const_trait_impl): Do we need any of this on the non-const codepath?
 
-                let trait_ref = TraitRef::from_method(tcx, trait_id, self.args);
+                let trait_ref = TraitRef::from_assoc(tcx, trait_id, self.args);
 
                 match self_ty.kind() {
                     Param(param_ty) => {
diff --git a/compiler/rustc_const_eval/src/const_eval/eval_queries.rs b/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
index 5835660e1c3..4da2663319c 100644
--- a/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
+++ b/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
@@ -117,6 +117,13 @@ fn eval_body_using_ecx<'tcx, R: InterpretationResult<'tcx>>(
                 ecx.tcx.dcx().emit_err(errors::ConstHeapPtrInFinal { span: ecx.tcx.span }),
             )));
         }
+        Err(InternError::PartialPointer) => {
+            throw_inval!(AlreadyReported(ReportedErrorInfo::non_const_eval_error(
+                ecx.tcx
+                    .dcx()
+                    .emit_err(errors::PartialPtrInFinal { span: ecx.tcx.span, kind: intern_kind }),
+            )));
+        }
     }
 
     interp_ok(R::make_result(ret, ecx))
diff --git a/compiler/rustc_const_eval/src/const_eval/machine.rs b/compiler/rustc_const_eval/src/const_eval/machine.rs
index a18ae79f318..da954cf4ed7 100644
--- a/compiler/rustc_const_eval/src/const_eval/machine.rs
+++ b/compiler/rustc_const_eval/src/const_eval/machine.rs
@@ -237,7 +237,7 @@ impl<'tcx> CompileTimeInterpCx<'tcx> {
     ) -> InterpResult<'tcx, Option<ty::Instance<'tcx>>> {
         let def_id = instance.def_id();
 
-        if self.tcx.has_attr(def_id, sym::rustc_const_panic_str)
+        if self.tcx.is_lang_item(def_id, LangItem::PanicDisplay)
             || self.tcx.is_lang_item(def_id, LangItem::BeginPanic)
         {
             let args = self.copy_fn_args(args);
diff --git a/compiler/rustc_const_eval/src/errors.rs b/compiler/rustc_const_eval/src/errors.rs
index a4148cb145f..2d412ee5ec2 100644
--- a/compiler/rustc_const_eval/src/errors.rs
+++ b/compiler/rustc_const_eval/src/errors.rs
@@ -52,6 +52,15 @@ pub(crate) struct ConstHeapPtrInFinal {
 }
 
 #[derive(Diagnostic)]
+#[diag(const_eval_partial_pointer_in_final)]
+#[note]
+pub(crate) struct PartialPtrInFinal {
+    #[primary_span]
+    pub span: Span,
+    pub kind: InternKind,
+}
+
+#[derive(Diagnostic)]
 #[diag(const_eval_unstable_in_stable_exposed)]
 pub(crate) struct UnstableInStableExposed {
     pub gate: String,
@@ -836,8 +845,7 @@ impl ReportErrorExt for UnsupportedOpInfo {
             UnsupportedOpInfo::Unsupported(s) => s.clone().into(),
             UnsupportedOpInfo::ExternTypeField => const_eval_extern_type_field,
             UnsupportedOpInfo::UnsizedLocal => const_eval_unsized_local,
-            UnsupportedOpInfo::OverwritePartialPointer(_) => const_eval_partial_pointer_overwrite,
-            UnsupportedOpInfo::ReadPartialPointer(_) => const_eval_partial_pointer_copy,
+            UnsupportedOpInfo::ReadPartialPointer(_) => const_eval_partial_pointer_read,
             UnsupportedOpInfo::ReadPointerAsInt(_) => const_eval_read_pointer_as_int,
             UnsupportedOpInfo::ThreadLocalStatic(_) => const_eval_thread_local_static,
             UnsupportedOpInfo::ExternStatic(_) => const_eval_extern_static,
@@ -848,7 +856,7 @@ impl ReportErrorExt for UnsupportedOpInfo {
         use UnsupportedOpInfo::*;
 
         use crate::fluent_generated::*;
-        if let ReadPointerAsInt(_) | OverwritePartialPointer(_) | ReadPartialPointer(_) = self {
+        if let ReadPointerAsInt(_) | ReadPartialPointer(_) = self {
             diag.help(const_eval_ptr_as_bytes_1);
             diag.help(const_eval_ptr_as_bytes_2);
         }
@@ -860,7 +868,7 @@ impl ReportErrorExt for UnsupportedOpInfo {
             | UnsupportedOpInfo::ExternTypeField
             | Unsupported(_)
             | ReadPointerAsInt(_) => {}
-            OverwritePartialPointer(ptr) | ReadPartialPointer(ptr) => {
+            ReadPartialPointer(ptr) => {
                 diag.arg("ptr", ptr);
             }
             ThreadLocalStatic(did) | ExternStatic(did) => rustc_middle::ty::tls::with(|tcx| {
diff --git a/compiler/rustc_const_eval/src/interpret/call.rs b/compiler/rustc_const_eval/src/interpret/call.rs
index b8a65369825..64cb934ac8d 100644
--- a/compiler/rustc_const_eval/src/interpret/call.rs
+++ b/compiler/rustc_const_eval/src/interpret/call.rs
@@ -346,7 +346,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         destination: &PlaceTy<'tcx, M::Provenance>,
         mut cont: ReturnContinuation,
     ) -> InterpResult<'tcx> {
-        let _span = enter_trace_span!(M, step::init_stack_frame, %instance, tracing_separate_thread = Empty);
+        let _trace = enter_trace_span!(M, step::init_stack_frame, %instance, tracing_separate_thread = Empty);
 
         // Compute callee information.
         // FIXME: for variadic support, do we have to somehow determine callee's extra_args?
@@ -527,7 +527,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         target: Option<mir::BasicBlock>,
         unwind: mir::UnwindAction,
     ) -> InterpResult<'tcx> {
-        let _span =
+        let _trace =
             enter_trace_span!(M, step::init_fn_call, tracing_separate_thread = Empty, ?fn_val)
                 .or_if_tracing_disabled(|| trace!("init_fn_call: {:#?}", fn_val));
 
@@ -731,18 +731,21 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     ) {
         let tcx = *self.tcx;
 
-        let trait_def_id = tcx.trait_of_assoc(def_id).unwrap();
-        let virtual_trait_ref = ty::TraitRef::from_method(tcx, trait_def_id, virtual_instance.args);
+        let trait_def_id = tcx.parent(def_id);
+        let virtual_trait_ref = ty::TraitRef::from_assoc(tcx, trait_def_id, virtual_instance.args);
         let existential_trait_ref = ty::ExistentialTraitRef::erase_self_ty(tcx, virtual_trait_ref);
         let concrete_trait_ref = existential_trait_ref.with_self_ty(tcx, dyn_ty);
 
-        let concrete_method = Instance::expect_resolve_for_vtable(
-            tcx,
-            self.typing_env,
-            def_id,
-            virtual_instance.args.rebase_onto(tcx, trait_def_id, concrete_trait_ref.args),
-            self.cur_span(),
-        );
+        let concrete_method = {
+            let _trace = enter_trace_span!(M, resolve::expect_resolve_for_vtable, ?def_id);
+            Instance::expect_resolve_for_vtable(
+                tcx,
+                self.typing_env,
+                def_id,
+                virtual_instance.args.rebase_onto(tcx, trait_def_id, concrete_trait_ref.args),
+                self.cur_span(),
+            )
+        };
         assert_eq!(concrete_instance, concrete_method);
     }
 
@@ -825,7 +828,11 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 place
             }
         };
-        let instance = ty::Instance::resolve_drop_in_place(*self.tcx, place.layout.ty);
+        let instance = {
+            let _trace =
+                enter_trace_span!(M, resolve::resolve_drop_in_place, ty = ?place.layout.ty);
+            ty::Instance::resolve_drop_in_place(*self.tcx, place.layout.ty)
+        };
         let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty())?;
 
         let arg = self.mplace_to_ref(&place)?;
diff --git a/compiler/rustc_const_eval/src/interpret/cast.rs b/compiler/rustc_const_eval/src/interpret/cast.rs
index de4fbc7b475..e3afeda5b7c 100644
--- a/compiler/rustc_const_eval/src/interpret/cast.rs
+++ b/compiler/rustc_const_eval/src/interpret/cast.rs
@@ -16,8 +16,8 @@ use super::{
     FnVal, ImmTy, Immediate, InterpCx, Machine, OpTy, PlaceTy, err_inval, interp_ok, throw_ub,
     throw_ub_custom,
 };
-use crate::fluent_generated as fluent;
 use crate::interpret::Writeable;
+use crate::{enter_trace_span, fluent_generated as fluent};
 
 impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     pub fn cast(
@@ -81,13 +81,16 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 // The src operand does not matter, just its type
                 match *src.layout.ty.kind() {
                     ty::FnDef(def_id, args) => {
-                        let instance = ty::Instance::resolve_for_fn_ptr(
-                            *self.tcx,
-                            self.typing_env,
-                            def_id,
-                            args,
-                        )
-                        .ok_or_else(|| err_inval!(TooGeneric))?;
+                        let instance = {
+                            let _trace = enter_trace_span!(M, resolve::resolve_for_fn_ptr, ?def_id);
+                            ty::Instance::resolve_for_fn_ptr(
+                                *self.tcx,
+                                self.typing_env,
+                                def_id,
+                                args,
+                            )
+                            .ok_or_else(|| err_inval!(TooGeneric))?
+                        };
 
                         let fn_ptr = self.fn_ptr(FnVal::Instance(instance));
                         self.write_pointer(fn_ptr, dest)?;
@@ -114,12 +117,15 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 // The src operand does not matter, just its type
                 match *src.layout.ty.kind() {
                     ty::Closure(def_id, args) => {
-                        let instance = ty::Instance::resolve_closure(
-                            *self.tcx,
-                            def_id,
-                            args,
-                            ty::ClosureKind::FnOnce,
-                        );
+                        let instance = {
+                            let _trace = enter_trace_span!(M, resolve::resolve_closure, ?def_id);
+                            ty::Instance::resolve_closure(
+                                *self.tcx,
+                                def_id,
+                                args,
+                                ty::ClosureKind::FnOnce,
+                            )
+                        };
                         let fn_ptr = self.fn_ptr(FnVal::Instance(instance));
                         self.write_pointer(fn_ptr, dest)?;
                     }
diff --git a/compiler/rustc_const_eval/src/interpret/eval_context.rs b/compiler/rustc_const_eval/src/interpret/eval_context.rs
index c4b705d7124..a8a1ac1c980 100644
--- a/compiler/rustc_const_eval/src/interpret/eval_context.rs
+++ b/compiler/rustc_const_eval/src/interpret/eval_context.rs
@@ -113,7 +113,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     /// See [LayoutOf::layout_of] for the original documentation.
     #[inline(always)]
     pub fn layout_of(&self, ty: Ty<'tcx>) -> <Self as LayoutOfHelpers<'tcx>>::LayoutOfResult {
-        let _span = enter_trace_span!(M, layouting::layout_of, ty = ?ty.kind());
+        let _trace = enter_trace_span!(M, layouting::layout_of, ty = ?ty.kind());
         LayoutOf::layout_of(self, ty)
     }
 
@@ -126,7 +126,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         sig: ty::PolyFnSig<'tcx>,
         extra_args: &'tcx ty::List<Ty<'tcx>>,
     ) -> <Self as FnAbiOfHelpers<'tcx>>::FnAbiOfResult {
-        let _span = enter_trace_span!(M, layouting::fn_abi_of_fn_ptr, ?sig, ?extra_args);
+        let _trace = enter_trace_span!(M, layouting::fn_abi_of_fn_ptr, ?sig, ?extra_args);
         FnAbiOf::fn_abi_of_fn_ptr(self, sig, extra_args)
     }
 
@@ -139,7 +139,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         instance: ty::Instance<'tcx>,
         extra_args: &'tcx ty::List<Ty<'tcx>>,
     ) -> <Self as FnAbiOfHelpers<'tcx>>::FnAbiOfResult {
-        let _span = enter_trace_span!(M, layouting::fn_abi_of_instance, ?instance, ?extra_args);
+        let _trace = enter_trace_span!(M, layouting::fn_abi_of_instance, ?instance, ?extra_args);
         FnAbiOf::fn_abi_of_instance(self, instance, extra_args)
     }
 }
@@ -322,7 +322,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         frame: &Frame<'tcx, M::Provenance, M::FrameExtra>,
         value: T,
     ) -> Result<T, ErrorHandled> {
-        let _span = enter_trace_span!(
+        let _trace = enter_trace_span!(
             M,
             "instantiate_from_frame_and_normalize_erasing_regions",
             "{}",
@@ -344,6 +344,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         def: DefId,
         args: GenericArgsRef<'tcx>,
     ) -> InterpResult<'tcx, ty::Instance<'tcx>> {
+        let _trace = enter_trace_span!(M, resolve::try_resolve, def = ?def);
         trace!("resolve: {:?}, {:#?}", def, args);
         trace!("typing_env: {:#?}", self.typing_env);
         trace!("args: {:#?}", args);
diff --git a/compiler/rustc_const_eval/src/interpret/intern.rs b/compiler/rustc_const_eval/src/interpret/intern.rs
index bb59b9f5418..5d510a98352 100644
--- a/compiler/rustc_const_eval/src/interpret/intern.rs
+++ b/compiler/rustc_const_eval/src/interpret/intern.rs
@@ -19,9 +19,12 @@ use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
 use rustc_hir as hir;
 use rustc_hir::definitions::{DefPathData, DisambiguatorState};
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
-use rustc_middle::mir::interpret::{ConstAllocation, CtfeProvenance, InterpResult};
+use rustc_middle::mir::interpret::{
+    AllocBytes, ConstAllocation, CtfeProvenance, InterpResult, Provenance,
+};
 use rustc_middle::query::TyCtxtAt;
 use rustc_middle::span_bug;
+use rustc_middle::ty::TyCtxt;
 use rustc_middle::ty::layout::TyAndLayout;
 use rustc_span::def_id::LocalDefId;
 use tracing::{instrument, trace};
@@ -52,39 +55,30 @@ impl HasStaticRootDefId for const_eval::CompileTimeMachine<'_> {
     }
 }
 
-/// Intern an allocation. Returns `Err` if the allocation does not exist in the local memory.
-///
-/// `mutability` can be used to force immutable interning: if it is `Mutability::Not`, the
-/// allocation is interned immutably; if it is `Mutability::Mut`, then the allocation *must be*
-/// already mutable (as a sanity check).
-///
-/// Returns an iterator over all relocations referred to by this allocation.
-fn intern_shallow<'tcx, M: CompileTimeMachine<'tcx>>(
-    ecx: &mut InterpCx<'tcx, M>,
-    alloc_id: AllocId,
+fn prepare_alloc<'tcx, Prov: Provenance, Extra, Bytes: AllocBytes>(
+    tcx: TyCtxt<'tcx>,
+    kind: MemoryKind<const_eval::MemoryKind>,
+    alloc: &mut Allocation<Prov, Extra, Bytes>,
     mutability: Mutability,
-    disambiguator: Option<&mut DisambiguatorState>,
-) -> Result<impl Iterator<Item = CtfeProvenance> + 'tcx, InternError> {
-    trace!("intern_shallow {:?}", alloc_id);
-    // remove allocation
-    // FIXME(#120456) - is `swap_remove` correct?
-    let Some((kind, mut alloc)) = ecx.memory.alloc_map.swap_remove(&alloc_id) else {
-        return Err(InternError::DanglingPointer);
-    };
-
+) -> Result<(), InternError> {
     match kind {
         MemoryKind::Machine(const_eval::MemoryKind::Heap { was_made_global }) => {
             if !was_made_global {
                 // Attempting to intern a `const_allocate`d pointer that was not made global via
-                // `const_make_global`. We want to error here, but we have to first put the
-                // allocation back into the `alloc_map` to keep things in a consistent state.
-                ecx.memory.alloc_map.insert(alloc_id, (kind, alloc));
+                // `const_make_global`.
+                tcx.dcx().delayed_bug("non-global heap allocation in const value");
                 return Err(InternError::ConstAllocNotGlobal);
             }
         }
         MemoryKind::Stack | MemoryKind::CallerLocation => {}
     }
 
+    if !alloc.provenance_merge_bytes(&tcx) {
+        // Per-byte provenance is not supported by backends, so we cannot accept it here.
+        tcx.dcx().delayed_bug("partial pointer in const value");
+        return Err(InternError::PartialPointer);
+    }
+
     // Set allocation mutability as appropriate. This is used by LLVM to put things into
     // read-only memory, and also by Miri when evaluating other globals that
     // access this one.
@@ -97,6 +91,36 @@ fn intern_shallow<'tcx, M: CompileTimeMachine<'tcx>>(
             assert_eq!(alloc.mutability, Mutability::Mut);
         }
     }
+    Ok(())
+}
+
+/// Intern an allocation. Returns `Err` if the allocation does not exist in the local memory.
+///
+/// `mutability` can be used to force immutable interning: if it is `Mutability::Not`, the
+/// allocation is interned immutably; if it is `Mutability::Mut`, then the allocation *must be*
+/// already mutable (as a sanity check).
+///
+/// Returns an iterator over all relocations referred to by this allocation.
+fn intern_shallow<'tcx, M: CompileTimeMachine<'tcx>>(
+    ecx: &mut InterpCx<'tcx, M>,
+    alloc_id: AllocId,
+    mutability: Mutability,
+    disambiguator: Option<&mut DisambiguatorState>,
+) -> Result<impl Iterator<Item = CtfeProvenance> + 'tcx, InternError> {
+    trace!("intern_shallow {:?}", alloc_id);
+    // remove allocation
+    // FIXME(#120456) - is `swap_remove` correct?
+    let Some((kind, mut alloc)) = ecx.memory.alloc_map.swap_remove(&alloc_id) else {
+        return Err(InternError::DanglingPointer);
+    };
+
+    if let Err(err) = prepare_alloc(*ecx.tcx, kind, &mut alloc, mutability) {
+        // We want to error here, but we have to first put the
+        // allocation back into the `alloc_map` to keep things in a consistent state.
+        ecx.memory.alloc_map.insert(alloc_id, (kind, alloc));
+        return Err(err);
+    }
+
     // link the alloc id to the actual allocation
     let alloc = ecx.tcx.mk_const_alloc(alloc);
     if let Some(static_id) = ecx.machine.static_def_id() {
@@ -166,6 +190,7 @@ pub enum InternError {
     BadMutablePointer,
     DanglingPointer,
     ConstAllocNotGlobal,
+    PartialPointer,
 }
 
 /// Intern `ret` and everything it references.
@@ -221,13 +246,11 @@ pub fn intern_const_alloc_recursive<'tcx, M: CompileTimeMachine<'tcx>>(
     let mut todo: Vec<_> = if is_static {
         // Do not steal the root allocation, we need it later to create the return value of `eval_static_initializer`.
         // But still change its mutability to match the requested one.
-        let alloc = ecx.memory.alloc_map.get_mut(&base_alloc_id).unwrap();
-        alloc.1.mutability = base_mutability;
-        alloc.1.provenance().ptrs().iter().map(|&(_, prov)| prov).collect()
+        let (kind, alloc) = ecx.memory.alloc_map.get_mut(&base_alloc_id).unwrap();
+        prepare_alloc(*ecx.tcx, *kind, alloc, base_mutability)?;
+        alloc.provenance().ptrs().iter().map(|&(_, prov)| prov).collect()
     } else {
-        intern_shallow(ecx, base_alloc_id, base_mutability, Some(&mut disambiguator))
-            .unwrap()
-            .collect()
+        intern_shallow(ecx, base_alloc_id, base_mutability, Some(&mut disambiguator))?.collect()
     };
     // We need to distinguish "has just been interned" from "was already in `tcx`",
     // so we track this in a separate set.
@@ -235,7 +258,6 @@ pub fn intern_const_alloc_recursive<'tcx, M: CompileTimeMachine<'tcx>>(
     // Whether we encountered a bad mutable pointer.
     // We want to first report "dangling" and then "mutable", so we need to delay reporting these
     // errors.
-    let mut result = Ok(());
     let mut found_bad_mutable_ptr = false;
 
     // Keep interning as long as there are things to intern.
@@ -310,20 +332,15 @@ pub fn intern_const_alloc_recursive<'tcx, M: CompileTimeMachine<'tcx>>(
         // okay with losing some potential for immutability here. This can anyway only affect
         // `static mut`.
         just_interned.insert(alloc_id);
-        match intern_shallow(ecx, alloc_id, inner_mutability, Some(&mut disambiguator)) {
-            Ok(nested) => todo.extend(nested),
-            Err(err) => {
-                ecx.tcx.dcx().delayed_bug("error during const interning");
-                result = Err(err);
-            }
-        }
+        let next = intern_shallow(ecx, alloc_id, inner_mutability, Some(&mut disambiguator))?;
+        todo.extend(next);
     }
-    if found_bad_mutable_ptr && result.is_ok() {
+    if found_bad_mutable_ptr {
         // We found a mutable pointer inside a const where inner allocations should be immutable,
         // and there was no other error. This should usually never happen! However, this can happen
         // in unleash-miri mode, so report it as a normal error then.
         if ecx.tcx.sess.opts.unstable_opts.unleash_the_miri_inside_of_you {
-            result = Err(InternError::BadMutablePointer);
+            return Err(InternError::BadMutablePointer);
         } else {
             span_bug!(
                 ecx.tcx.span,
@@ -331,7 +348,7 @@ pub fn intern_const_alloc_recursive<'tcx, M: CompileTimeMachine<'tcx>>(
             );
         }
     }
-    result
+    Ok(())
 }
 
 /// Intern `ret`. This function assumes that `ret` references no other allocation.
diff --git a/compiler/rustc_const_eval/src/interpret/memory.rs b/compiler/rustc_const_eval/src/interpret/memory.rs
index 23b40894f16..2c1e5087e1c 100644
--- a/compiler/rustc_const_eval/src/interpret/memory.rs
+++ b/compiler/rustc_const_eval/src/interpret/memory.rs
@@ -1314,29 +1314,20 @@ impl<'a, 'tcx, Prov: Provenance, Extra, Bytes: AllocBytes>
     }
 
     /// Mark the given sub-range (relative to this allocation reference) as uninitialized.
-    pub fn write_uninit(&mut self, range: AllocRange) -> InterpResult<'tcx> {
+    pub fn write_uninit(&mut self, range: AllocRange) {
         let range = self.range.subrange(range);
 
-        self.alloc
-            .write_uninit(&self.tcx, range)
-            .map_err(|e| e.to_interp_error(self.alloc_id))
-            .into()
+        self.alloc.write_uninit(&self.tcx, range);
     }
 
     /// Mark the entire referenced range as uninitialized
-    pub fn write_uninit_full(&mut self) -> InterpResult<'tcx> {
-        self.alloc
-            .write_uninit(&self.tcx, self.range)
-            .map_err(|e| e.to_interp_error(self.alloc_id))
-            .into()
+    pub fn write_uninit_full(&mut self) {
+        self.alloc.write_uninit(&self.tcx, self.range);
     }
 
     /// Remove all provenance in the reference range.
-    pub fn clear_provenance(&mut self) -> InterpResult<'tcx> {
-        self.alloc
-            .clear_provenance(&self.tcx, self.range)
-            .map_err(|e| e.to_interp_error(self.alloc_id))
-            .into()
+    pub fn clear_provenance(&mut self) {
+        self.alloc.clear_provenance(&self.tcx, self.range);
     }
 }
 
@@ -1427,11 +1418,8 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
 
         // Side-step AllocRef and directly access the underlying bytes more efficiently.
         // (We are staying inside the bounds here and all bytes do get overwritten so all is good.)
-        let alloc_id = alloc_ref.alloc_id;
-        let bytes = alloc_ref
-            .alloc
-            .get_bytes_unchecked_for_overwrite(&alloc_ref.tcx, alloc_ref.range)
-            .map_err(move |e| e.to_interp_error(alloc_id))?;
+        let bytes =
+            alloc_ref.alloc.get_bytes_unchecked_for_overwrite(&alloc_ref.tcx, alloc_ref.range);
         // `zip` would stop when the first iterator ends; we want to definitely
         // cover all of `bytes`.
         for dest in bytes {
@@ -1513,10 +1501,8 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         // `get_bytes_mut` will clear the provenance, which is correct,
         // since we don't want to keep any provenance at the target.
         // This will also error if copying partial provenance is not supported.
-        let provenance = src_alloc
-            .provenance()
-            .prepare_copy(src_range, dest_offset, num_copies, self)
-            .map_err(|e| e.to_interp_error(src_alloc_id))?;
+        let provenance =
+            src_alloc.provenance().prepare_copy(src_range, dest_offset, num_copies, self);
         // Prepare a copy of the initialization mask.
         let init = src_alloc.init_mask().prepare_copy(src_range);
 
@@ -1534,10 +1520,8 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             dest_range,
         )?;
         // Yes we do overwrite all bytes in `dest_bytes`.
-        let dest_bytes = dest_alloc
-            .get_bytes_unchecked_for_overwrite_ptr(&tcx, dest_range)
-            .map_err(|e| e.to_interp_error(dest_alloc_id))?
-            .as_mut_ptr();
+        let dest_bytes =
+            dest_alloc.get_bytes_unchecked_for_overwrite_ptr(&tcx, dest_range).as_mut_ptr();
 
         if init.no_bytes_init() {
             // Fast path: If all bytes are `uninit` then there is nothing to copy. The target range
@@ -1546,9 +1530,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             // This also avoids writing to the target bytes so that the backing allocation is never
             // touched if the bytes stay uninitialized for the whole interpreter execution. On contemporary
             // operating system this can avoid physically allocating the page.
-            dest_alloc
-                .write_uninit(&tcx, dest_range)
-                .map_err(|e| e.to_interp_error(dest_alloc_id))?;
+            dest_alloc.write_uninit(&tcx, dest_range);
             // `write_uninit` also resets the provenance, so we are done.
             return interp_ok(());
         }
diff --git a/compiler/rustc_const_eval/src/interpret/operand.rs b/compiler/rustc_const_eval/src/interpret/operand.rs
index 14541809070..53a440b646b 100644
--- a/compiler/rustc_const_eval/src/interpret/operand.rs
+++ b/compiler/rustc_const_eval/src/interpret/operand.rs
@@ -773,7 +773,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         mir_place: mir::Place<'tcx>,
         layout: Option<TyAndLayout<'tcx>>,
     ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
-        let _span = enter_trace_span!(
+        let _trace = enter_trace_span!(
             M,
             step::eval_place_to_op,
             ?mir_place,
@@ -823,7 +823,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         mir_op: &mir::Operand<'tcx>,
         layout: Option<TyAndLayout<'tcx>>,
     ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
-        let _span =
+        let _trace =
             enter_trace_span!(M, step::eval_operand, ?mir_op, tracing_separate_thread = Empty);
 
         use rustc_middle::mir::Operand::*;
diff --git a/compiler/rustc_const_eval/src/interpret/place.rs b/compiler/rustc_const_eval/src/interpret/place.rs
index 45c4edb8503..3255ffa54aa 100644
--- a/compiler/rustc_const_eval/src/interpret/place.rs
+++ b/compiler/rustc_const_eval/src/interpret/place.rs
@@ -526,7 +526,7 @@ where
         &self,
         mir_place: mir::Place<'tcx>,
     ) -> InterpResult<'tcx, PlaceTy<'tcx, M::Provenance>> {
-        let _span =
+        let _trace =
             enter_trace_span!(M, step::eval_place, ?mir_place, tracing_separate_thread = Empty);
 
         let mut place = self.local_to_place(mir_place.local)?;
@@ -705,7 +705,7 @@ where
 
         match value {
             Immediate::Scalar(scalar) => {
-                alloc.write_scalar(alloc_range(Size::ZERO, scalar.size()), scalar)
+                alloc.write_scalar(alloc_range(Size::ZERO, scalar.size()), scalar)?;
             }
             Immediate::ScalarPair(a_val, b_val) => {
                 let BackendRepr::ScalarPair(a, b) = layout.backend_repr else {
@@ -725,10 +725,10 @@ where
                 alloc.write_scalar(alloc_range(Size::ZERO, a_val.size()), a_val)?;
                 alloc.write_scalar(alloc_range(b_offset, b_val.size()), b_val)?;
                 // We don't have to reset padding here, `write_immediate` will anyway do a validation run.
-                interp_ok(())
             }
             Immediate::Uninit => alloc.write_uninit_full(),
         }
+        interp_ok(())
     }
 
     pub fn write_uninit(
@@ -748,7 +748,7 @@ where
                     // Zero-sized access
                     return interp_ok(());
                 };
-                alloc.write_uninit_full()?;
+                alloc.write_uninit_full();
             }
         }
         interp_ok(())
@@ -772,7 +772,7 @@ where
                     // Zero-sized access
                     return interp_ok(());
                 };
-                alloc.clear_provenance()?;
+                alloc.clear_provenance();
             }
         }
         interp_ok(())
diff --git a/compiler/rustc_const_eval/src/interpret/step.rs b/compiler/rustc_const_eval/src/interpret/step.rs
index 9df49c0f4cc..f1995b3f132 100644
--- a/compiler/rustc_const_eval/src/interpret/step.rs
+++ b/compiler/rustc_const_eval/src/interpret/step.rs
@@ -76,7 +76,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     ///
     /// This does NOT move the statement counter forward, the caller has to do that!
     pub fn eval_statement(&mut self, stmt: &mir::Statement<'tcx>) -> InterpResult<'tcx> {
-        let _span = enter_trace_span!(
+        let _trace = enter_trace_span!(
             M,
             step::eval_statement,
             stmt = ?stmt.kind,
@@ -465,7 +465,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     }
 
     fn eval_terminator(&mut self, terminator: &mir::Terminator<'tcx>) -> InterpResult<'tcx> {
-        let _span = enter_trace_span!(
+        let _trace = enter_trace_span!(
             M,
             step::eval_terminator,
             terminator = ?terminator.kind,
@@ -560,7 +560,11 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                     "Async Drop must be expanded or reset to sync in runtime MIR"
                 );
                 let place = self.eval_place(place)?;
-                let instance = Instance::resolve_drop_in_place(*self.tcx, place.layout.ty);
+                let instance = {
+                    let _trace =
+                        enter_trace_span!(M, resolve::resolve_drop_in_place, ty = ?place.layout.ty);
+                    Instance::resolve_drop_in_place(*self.tcx, place.layout.ty)
+                };
                 if let ty::InstanceKind::DropGlue(_, None) = instance.def {
                     // This is the branch we enter if and only if the dropped type has no drop glue
                     // whatsoever. This can happen as a result of monomorphizing a drop of a
diff --git a/compiler/rustc_const_eval/src/interpret/util.rs b/compiler/rustc_const_eval/src/interpret/util.rs
index 71800950faa..72bee345406 100644
--- a/compiler/rustc_const_eval/src/interpret/util.rs
+++ b/compiler/rustc_const_eval/src/interpret/util.rs
@@ -85,11 +85,11 @@ impl EnteredTraceSpan for tracing::span::EnteredSpan {
 /// # let my_debug_var = String::new();
 /// // logs a span named "hello" with a field named "arg" of value 42 (works only because
 /// // 42 implements the tracing::Value trait, otherwise use one of the options below)
-/// let _span = enter_trace_span!(M, "hello", arg = 42);
+/// let _trace = enter_trace_span!(M, "hello", arg = 42);
 /// // logs a field called "my_display_var" using the Display implementation
-/// let _span = enter_trace_span!(M, "hello", %my_display_var);
+/// let _trace = enter_trace_span!(M, "hello", %my_display_var);
 /// // logs a field called "my_debug_var" using the Debug implementation
-/// let _span = enter_trace_span!(M, "hello", ?my_debug_var);
+/// let _trace = enter_trace_span!(M, "hello", ?my_debug_var);
 ///  ```
 ///
 /// ### `NAME::SUBNAME` syntax
@@ -107,8 +107,8 @@ impl EnteredTraceSpan for tracing::span::EnteredSpan {
 /// # use rustc_const_eval::enter_trace_span;
 /// # type M = rustc_const_eval::const_eval::CompileTimeMachine<'static>;
 /// // for example, the first will expand to the second
-/// let _span = enter_trace_span!(M, borrow_tracker::on_stack_pop, /* ... */);
-/// let _span = enter_trace_span!(M, "borrow_tracker", borrow_tracker = "on_stack_pop", /* ... */);
+/// let _trace = enter_trace_span!(M, borrow_tracker::on_stack_pop, /* ... */);
+/// let _trace = enter_trace_span!(M, "borrow_tracker", borrow_tracker = "on_stack_pop", /* ... */);
 /// ```
 ///
 /// ### `tracing_separate_thread` parameter
@@ -124,7 +124,7 @@ impl EnteredTraceSpan for tracing::span::EnteredSpan {
 /// ```rust
 /// # use rustc_const_eval::enter_trace_span;
 /// # type M = rustc_const_eval::const_eval::CompileTimeMachine<'static>;
-/// let _span = enter_trace_span!(M, step::eval_statement, tracing_separate_thread = tracing::field::Empty);
+/// let _trace = enter_trace_span!(M, step::eval_statement, tracing_separate_thread = tracing::field::Empty);
 /// ```
 ///
 /// ### Executing something else when tracing is disabled
@@ -136,7 +136,7 @@ impl EnteredTraceSpan for tracing::span::EnteredSpan {
 /// # use rustc_const_eval::enter_trace_span;
 /// # use rustc_const_eval::interpret::EnteredTraceSpan;
 /// # type M = rustc_const_eval::const_eval::CompileTimeMachine<'static>;
-/// let _span = enter_trace_span!(M, step::eval_statement)
+/// let _trace = enter_trace_span!(M, step::eval_statement)
 ///     .or_if_tracing_disabled(|| tracing::info!("eval_statement"));
 /// ```
 #[macro_export]
diff --git a/compiler/rustc_const_eval/src/interpret/validity.rs b/compiler/rustc_const_eval/src/interpret/validity.rs
index ed48f53c310..5e8bee65706 100644
--- a/compiler/rustc_const_eval/src/interpret/validity.rs
+++ b/compiler/rustc_const_eval/src/interpret/validity.rs
@@ -949,7 +949,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
                 let padding_size = offset - padding_cleared_until;
                 let range = alloc_range(padding_start, padding_size);
                 trace!("reset_padding on {}: resetting padding range {range:?}", mplace.layout.ty);
-                alloc.write_uninit(range)?;
+                alloc.write_uninit(range);
             }
             padding_cleared_until = offset + size;
         }
@@ -1239,7 +1239,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValueVisitor<'tcx, M> for ValidityVisitor<'rt,
                 if self.reset_provenance_and_padding {
                     // We can't share this with above as above, we might be looking at read-only memory.
                     let mut alloc = self.ecx.get_ptr_alloc_mut(mplace.ptr(), size)?.expect("we already excluded size 0");
-                    alloc.clear_provenance()?;
+                    alloc.clear_provenance();
                     // Also, mark this as containing data, not padding.
                     self.add_data_range(mplace.ptr(), size);
                 }
@@ -1415,7 +1415,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         recursive: bool,
         reset_provenance_and_padding: bool,
     ) -> InterpResult<'tcx> {
-        let _span = enter_trace_span!(
+        let _trace = enter_trace_span!(
             M,
             "validate_operand",
             "recursive={recursive}, reset_provenance_and_padding={reset_provenance_and_padding}, val={val:?}"
diff --git a/compiler/rustc_const_eval/src/lib.rs b/compiler/rustc_const_eval/src/lib.rs
index 3840cdf7575..8ace560d85d 100644
--- a/compiler/rustc_const_eval/src/lib.rs
+++ b/compiler/rustc_const_eval/src/lib.rs
@@ -1,6 +1,7 @@
 // tidy-alphabetical-start
 #![allow(internal_features)]
 #![allow(rustc::diagnostic_outside_of_impl)]
+#![cfg_attr(bootstrap, feature(strict_overflow_ops))]
 #![doc(rust_logo)]
 #![feature(array_try_map)]
 #![feature(assert_matches)]
@@ -10,7 +11,6 @@
 #![feature(never_type)]
 #![feature(rustdoc_internals)]
 #![feature(slice_ptr_get)]
-#![feature(strict_overflow_ops)]
 #![feature(trait_alias)]
 #![feature(try_blocks)]
 #![feature(unqualified_local_imports)]
diff --git a/compiler/rustc_const_eval/src/util/type_name.rs b/compiler/rustc_const_eval/src/util/type_name.rs
index e6b9759819f..13cc607135a 100644
--- a/compiler/rustc_const_eval/src/util/type_name.rs
+++ b/compiler/rustc_const_eval/src/util/type_name.rs
@@ -5,20 +5,23 @@ use rustc_hir::def_id::CrateNum;
 use rustc_hir::definitions::DisambiguatedDefPathData;
 use rustc_middle::bug;
 use rustc_middle::ty::print::{PrettyPrinter, PrintError, Printer};
-use rustc_middle::ty::{self, GenericArg, GenericArgKind, Ty, TyCtxt};
+use rustc_middle::ty::{self, GenericArg, Ty, TyCtxt};
 
-struct AbsolutePathPrinter<'tcx> {
+struct TypeNamePrinter<'tcx> {
     tcx: TyCtxt<'tcx>,
     path: String,
 }
 
-impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
+impl<'tcx> Printer<'tcx> for TypeNamePrinter<'tcx> {
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }
 
     fn print_region(&mut self, _region: ty::Region<'_>) -> Result<(), PrintError> {
-        unreachable!(); // because `<Self As PrettyPrinter>::should_print_region` returns false
+        // FIXME: most regions have been erased by the time this code runs.
+        // Just printing `'_` is a bit hacky but gives mostly good results, and
+        // doing better is difficult. See `should_print_optional_region`.
+        write!(self, "'_")
     }
 
     fn print_type(&mut self, ty: Ty<'tcx>) -> Result<(), PrintError> {
@@ -73,26 +76,26 @@ impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
         self.pretty_print_dyn_existential(predicates)
     }
 
-    fn path_crate(&mut self, cnum: CrateNum) -> Result<(), PrintError> {
+    fn print_crate_name(&mut self, cnum: CrateNum) -> Result<(), PrintError> {
         self.path.push_str(self.tcx.crate_name(cnum).as_str());
         Ok(())
     }
 
-    fn path_qualified(
+    fn print_path_with_qualified(
         &mut self,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
     ) -> Result<(), PrintError> {
-        self.pretty_path_qualified(self_ty, trait_ref)
+        self.pretty_print_path_with_qualified(self_ty, trait_ref)
     }
 
-    fn path_append_impl(
+    fn print_path_with_impl(
         &mut self,
         print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
     ) -> Result<(), PrintError> {
-        self.pretty_path_append_impl(
+        self.pretty_print_path_with_impl(
             |cx| {
                 print_prefix(cx)?;
 
@@ -105,7 +108,7 @@ impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
         )
     }
 
-    fn path_append(
+    fn print_path_with_simple(
         &mut self,
         print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
         disambiguated_data: &DisambiguatedDefPathData,
@@ -117,25 +120,30 @@ impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
         Ok(())
     }
 
-    fn path_generic_args(
+    fn print_path_with_generic_args(
         &mut self,
         print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
         args: &[GenericArg<'tcx>],
     ) -> Result<(), PrintError> {
         print_prefix(self)?;
-        let args =
-            args.iter().cloned().filter(|arg| !matches!(arg.kind(), GenericArgKind::Lifetime(_)));
-        if args.clone().next().is_some() {
-            self.generic_delimiters(|cx| cx.comma_sep(args))
+        if !args.is_empty() {
+            self.generic_delimiters(|cx| cx.comma_sep(args.iter().copied()))
         } else {
             Ok(())
         }
     }
 }
 
-impl<'tcx> PrettyPrinter<'tcx> for AbsolutePathPrinter<'tcx> {
-    fn should_print_region(&self, _region: ty::Region<'_>) -> bool {
-        false
+impl<'tcx> PrettyPrinter<'tcx> for TypeNamePrinter<'tcx> {
+    fn should_print_optional_region(&self, _region: ty::Region<'_>) -> bool {
+        // Bound regions are always printed (as `'_`), which gives some idea that they are special,
+        // even though the `for` is omitted by the pretty printer.
+        // E.g. `for<'a, 'b> fn(&'a u32, &'b u32)` is printed as "fn(&'_ u32, &'_ u32)".
+        match _region.kind() {
+            ty::ReErased => false,
+            ty::ReBound(..) => true,
+            _ => unreachable!(),
+        }
     }
 
     fn generic_delimiters(
@@ -157,7 +165,7 @@ impl<'tcx> PrettyPrinter<'tcx> for AbsolutePathPrinter<'tcx> {
     }
 }
 
-impl Write for AbsolutePathPrinter<'_> {
+impl Write for TypeNamePrinter<'_> {
     fn write_str(&mut self, s: &str) -> std::fmt::Result {
         self.path.push_str(s);
         Ok(())
@@ -165,7 +173,7 @@ impl Write for AbsolutePathPrinter<'_> {
 }
 
 pub fn type_name<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> String {
-    let mut p = AbsolutePathPrinter { tcx, path: String::new() };
+    let mut p = TypeNamePrinter { tcx, path: String::new() };
     p.print_type(ty).unwrap();
     p.path
 }
diff --git a/compiler/rustc_error_codes/src/error_codes/E0518.md b/compiler/rustc_error_codes/src/error_codes/E0518.md
index f04329bc4e6..87dc231578a 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0518.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0518.md
@@ -1,9 +1,11 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 An `#[inline(..)]` attribute was incorrectly placed on something other than a
 function or method.
 
 Example of erroneous code:
 
-```compile_fail,E0518
+```ignore (no longer emitted)
 #[inline(always)]
 struct Foo;
 
diff --git a/compiler/rustc_error_codes/src/error_codes/E0578.md b/compiler/rustc_error_codes/src/error_codes/E0578.md
index fca89757287..78fabe855bb 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0578.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0578.md
@@ -1,8 +1,10 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 A module cannot be found and therefore, the visibility cannot be determined.
 
 Erroneous code example:
 
-```compile_fail,E0578,edition2018
+```ignore (no longer emitted)
 foo!();
 
 pub (in ::Sea) struct Shark; // error!
diff --git a/compiler/rustc_error_codes/src/error_codes/E0701.md b/compiler/rustc_error_codes/src/error_codes/E0701.md
index 4965e643105..e1be0e915f4 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0701.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0701.md
@@ -1,9 +1,11 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 This error indicates that a `#[non_exhaustive]` attribute was incorrectly placed
 on something other than a struct or enum.
 
 Erroneous code example:
 
-```compile_fail,E0701
+```ignore (no longer emitted)
 #[non_exhaustive]
 trait Foo { }
 ```
diff --git a/compiler/rustc_error_codes/src/error_codes/E0739.md b/compiler/rustc_error_codes/src/error_codes/E0739.md
index 406d3d52779..5403405ca9d 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0739.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0739.md
@@ -1,8 +1,10 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 `#[track_caller]` must  be applied to a function
 
 Erroneous code example:
 
-```compile_fail,E0739
+```ignore (no longer emitted)
 #[track_caller]
 struct Bar {
     a: u8,
diff --git a/compiler/rustc_error_codes/src/error_codes/E0755.md b/compiler/rustc_error_codes/src/error_codes/E0755.md
index b67f078c78e..bd93626a8db 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0755.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0755.md
@@ -1,8 +1,10 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 The `ffi_pure` attribute was used on a non-foreign function.
 
 Erroneous code example:
 
-```compile_fail,E0755
+```ignore (no longer emitted)
 #![feature(ffi_pure)]
 
 #[unsafe(ffi_pure)] // error!
diff --git a/compiler/rustc_error_codes/src/error_codes/E0756.md b/compiler/rustc_error_codes/src/error_codes/E0756.md
index aadde038d12..daafc2a5ac0 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0756.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0756.md
@@ -1,9 +1,11 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 The `ffi_const` attribute was used on something other than a foreign function
 declaration.
 
 Erroneous code example:
 
-```compile_fail,E0756
+```ignore (no longer emitted)
 #![feature(ffi_const)]
 
 #[unsafe(ffi_const)] // error!
diff --git a/compiler/rustc_error_codes/src/error_codes/E0788.md b/compiler/rustc_error_codes/src/error_codes/E0788.md
index ba138aed2d1..1afa961f9b7 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0788.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0788.md
@@ -1,3 +1,5 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 A `#[coverage(off|on)]` attribute was found in a position where it is not
 allowed.
 
@@ -10,7 +12,7 @@ Coverage attributes can be applied to:
 
 Example of erroneous code:
 
-```compile_fail,E0788
+```ignore (no longer emitted)
 unsafe extern "C" {
     #[coverage(off)]
     fn foreign_fn();
diff --git a/compiler/rustc_error_codes/src/error_codes/E0793.md b/compiler/rustc_error_codes/src/error_codes/E0793.md
index ccd1b43bd19..2722dac104b 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0793.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0793.md
@@ -1,4 +1,9 @@
-An unaligned reference to a field of a [packed] struct got created.
+An unaligned reference to a field of a [packed] `struct` or `union` was created.
+
+The `#[repr(packed)]` attribute removes padding between fields, which can
+cause fields to be stored at unaligned memory addresses. Creating references
+to such fields violates Rust's memory safety guarantees and can lead to
+undefined behavior in optimized code.
 
 Erroneous code example:
 
@@ -45,9 +50,36 @@ unsafe {
     // For formatting, we can create a copy to avoid the direct reference.
     let copy = foo.field1;
     println!("{}", copy);
+
     // Creating a copy can be written in a single line with curly braces.
     // (This is equivalent to the two lines above.)
     println!("{}", { foo.field1 });
+
+    // A reference to a field that will always be sufficiently aligned is safe:
+    println!("{}", foo.field2);
+}
+```
+
+### Unions
+
+Although creating a reference to a `union` field is `unsafe`, this error
+will still be triggered if the referenced field is not sufficiently
+aligned. Use `addr_of!` and raw pointers in the same way as for struct fields.
+
+```compile_fail,E0793
+#[repr(packed)]
+pub union Foo {
+    field1: u64,
+    field2: u8,
+}
+
+unsafe {
+    let foo = Foo { field1: 0 };
+    // Accessing the field directly is fine.
+    let val = foo.field1;
+
+    // A reference to a packed union field causes an error.
+    let val = &foo.field1; // ERROR
 }
 ```
 
diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index 96c7ba6ed27..e579370ce4e 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -847,17 +847,18 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
         self
     }
 
+    with_fn! { with_span_help,
     /// Prints the span with some help above it.
     /// This is like [`Diag::help()`], but it gets its own span.
     #[rustc_lint_diagnostics]
-    pub fn span_help<S: Into<MultiSpan>>(
+    pub fn span_help(
         &mut self,
-        sp: S,
+        sp: impl Into<MultiSpan>,
         msg: impl Into<SubdiagMessage>,
     ) -> &mut Self {
         self.sub(Level::Help, msg, sp.into());
         self
-    }
+    } }
 
     /// Disallow attaching suggestions to this diagnostic.
     /// Any suggestions attached e.g. with the `span_suggestion_*` methods
@@ -1112,7 +1113,7 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
             .map(|snippet| {
                 debug_assert!(
                     !(sp.is_empty() && snippet.is_empty()),
-                    "Span must not be empty and have no suggestion"
+                    "Span `{sp:?}` must not be empty and have no suggestion"
                 );
                 Substitution { parts: vec![SubstitutionPart { snippet, span: sp }] }
             })
@@ -1382,6 +1383,11 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
         &mut self.long_ty_path
     }
 
+    pub fn with_long_ty_path(mut self, long_ty_path: Option<PathBuf>) -> Self {
+        self.long_ty_path = long_ty_path;
+        self
+    }
+
     /// Most `emit_producing_guarantee` functions use this as a starting point.
     fn emit_producing_nothing(mut self) {
         let diag = self.take_diag();
diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index 84970e7c162..97c47fa9b9a 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -409,7 +409,7 @@ pub trait Emitter {
                 if !redundant_span || always_backtrace {
                     let msg: Cow<'static, _> = match trace.kind {
                         ExpnKind::Macro(MacroKind::Attr, _) => {
-                            "this procedural macro expansion".into()
+                            "this attribute macro expansion".into()
                         }
                         ExpnKind::Macro(MacroKind::Derive, _) => {
                             "this derive macro expansion".into()
@@ -3546,7 +3546,7 @@ pub fn detect_confusion_type(sm: &SourceMap, suggested: &str, sp: Span) -> Confu
 
         for (f, s) in iter::zip(found.chars(), suggested.chars()) {
             if f != s {
-                if f.to_lowercase().to_string() == s.to_lowercase().to_string() {
+                if f.eq_ignore_ascii_case(&s) {
                     // Check for case differences (any character that differs only in case)
                     if ascii_confusables.contains(&f) || ascii_confusables.contains(&s) {
                         has_case_diff = true;
diff --git a/compiler/rustc_expand/messages.ftl b/compiler/rustc_expand/messages.ftl
index 5a53670c865..1f8f3be6809 100644
--- a/compiler/rustc_expand/messages.ftl
+++ b/compiler/rustc_expand/messages.ftl
@@ -70,6 +70,9 @@ expand_invalid_fragment_specifier =
     invalid fragment specifier `{$fragment}`
     .help = {$help}
 
+expand_macro_args_bad_delim = macro attribute argument matchers require parentheses
+expand_macro_args_bad_delim_sugg = the delimiters should be `(` and `)`
+
 expand_macro_body_stability =
     macros cannot have body stability attributes
     .label = invalid body stability attribute
diff --git a/compiler/rustc_expand/src/base.rs b/compiler/rustc_expand/src/base.rs
index 1a9832b2fe2..f2c15071532 100644
--- a/compiler/rustc_expand/src/base.rs
+++ b/compiler/rustc_expand/src/base.rs
@@ -7,7 +7,6 @@ use std::rc::Rc;
 use std::sync::Arc;
 
 use rustc_ast::attr::{AttributeExt, MarkedAttrs};
-use rustc_ast::ptr::P;
 use rustc_ast::token::MetaVarKind;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::visit::{AssocCtxt, Visitor};
@@ -18,6 +17,7 @@ use rustc_errors::{DiagCtxtHandle, ErrorGuaranteed, PResult};
 use rustc_feature::Features;
 use rustc_hir as hir;
 use rustc_hir::attrs::{AttributeKind, CfgEntry, Deprecation};
+use rustc_hir::def::MacroKinds;
 use rustc_hir::{Stability, find_attr};
 use rustc_lint_defs::{BufferedEarlyLint, RegisteredTools};
 use rustc_parse::MACRO_ARGUMENTS;
@@ -45,11 +45,11 @@ use crate::stats::MacroStat;
 // to use `assign_id!`
 #[derive(Debug, Clone)]
 pub enum Annotatable {
-    Item(P<ast::Item>),
-    AssocItem(P<ast::AssocItem>, AssocCtxt),
-    ForeignItem(P<ast::ForeignItem>),
-    Stmt(P<ast::Stmt>),
-    Expr(P<ast::Expr>),
+    Item(Box<ast::Item>),
+    AssocItem(Box<ast::AssocItem>, AssocCtxt),
+    ForeignItem(Box<ast::ForeignItem>),
+    Stmt(Box<ast::Stmt>),
+    Expr(Box<ast::Expr>),
     Arm(ast::Arm),
     ExprField(ast::ExprField),
     PatField(ast::PatField),
@@ -141,28 +141,28 @@ impl Annotatable {
         }
     }
 
-    pub fn expect_item(self) -> P<ast::Item> {
+    pub fn expect_item(self) -> Box<ast::Item> {
         match self {
             Annotatable::Item(i) => i,
             _ => panic!("expected Item"),
         }
     }
 
-    pub fn expect_trait_item(self) -> P<ast::AssocItem> {
+    pub fn expect_trait_item(self) -> Box<ast::AssocItem> {
         match self {
             Annotatable::AssocItem(i, AssocCtxt::Trait) => i,
             _ => panic!("expected Item"),
         }
     }
 
-    pub fn expect_impl_item(self) -> P<ast::AssocItem> {
+    pub fn expect_impl_item(self) -> Box<ast::AssocItem> {
         match self {
             Annotatable::AssocItem(i, AssocCtxt::Impl { .. }) => i,
             _ => panic!("expected Item"),
         }
     }
 
-    pub fn expect_foreign_item(self) -> P<ast::ForeignItem> {
+    pub fn expect_foreign_item(self) -> Box<ast::ForeignItem> {
         match self {
             Annotatable::ForeignItem(i) => i,
             _ => panic!("expected foreign item"),
@@ -176,7 +176,7 @@ impl Annotatable {
         }
     }
 
-    pub fn expect_expr(self) -> P<ast::Expr> {
+    pub fn expect_expr(self) -> Box<ast::Expr> {
         match self {
             Annotatable::Expr(expr) => expr,
             _ => panic!("expected expression"),
@@ -412,37 +412,37 @@ macro_rules! make_stmts_default {
 /// methods are spliced into the AST at the callsite of the macro.
 pub trait MacResult {
     /// Creates an expression.
-    fn make_expr(self: Box<Self>) -> Option<P<ast::Expr>> {
+    fn make_expr(self: Box<Self>) -> Option<Box<ast::Expr>> {
         None
     }
 
     /// Creates zero or more items.
-    fn make_items(self: Box<Self>) -> Option<SmallVec<[P<ast::Item>; 1]>> {
+    fn make_items(self: Box<Self>) -> Option<SmallVec<[Box<ast::Item>; 1]>> {
         None
     }
 
     /// Creates zero or more impl items.
-    fn make_impl_items(self: Box<Self>) -> Option<SmallVec<[P<ast::AssocItem>; 1]>> {
+    fn make_impl_items(self: Box<Self>) -> Option<SmallVec<[Box<ast::AssocItem>; 1]>> {
         None
     }
 
     /// Creates zero or more impl items.
-    fn make_trait_impl_items(self: Box<Self>) -> Option<SmallVec<[P<ast::AssocItem>; 1]>> {
+    fn make_trait_impl_items(self: Box<Self>) -> Option<SmallVec<[Box<ast::AssocItem>; 1]>> {
         None
     }
 
     /// Creates zero or more trait items.
-    fn make_trait_items(self: Box<Self>) -> Option<SmallVec<[P<ast::AssocItem>; 1]>> {
+    fn make_trait_items(self: Box<Self>) -> Option<SmallVec<[Box<ast::AssocItem>; 1]>> {
         None
     }
 
     /// Creates zero or more items in an `extern {}` block
-    fn make_foreign_items(self: Box<Self>) -> Option<SmallVec<[P<ast::ForeignItem>; 1]>> {
+    fn make_foreign_items(self: Box<Self>) -> Option<SmallVec<[Box<ast::ForeignItem>; 1]>> {
         None
     }
 
     /// Creates a pattern.
-    fn make_pat(self: Box<Self>) -> Option<P<ast::Pat>> {
+    fn make_pat(self: Box<Self>) -> Option<Box<ast::Pat>> {
         None
     }
 
@@ -454,7 +454,7 @@ pub trait MacResult {
         make_stmts_default!(self)
     }
 
-    fn make_ty(self: Box<Self>) -> Option<P<ast::Ty>> {
+    fn make_ty(self: Box<Self>) -> Option<Box<ast::Ty>> {
         None
     }
 
@@ -521,38 +521,38 @@ macro_rules! make_MacEager {
 }
 
 make_MacEager! {
-    expr: P<ast::Expr>,
-    pat: P<ast::Pat>,
-    items: SmallVec<[P<ast::Item>; 1]>,
-    impl_items: SmallVec<[P<ast::AssocItem>; 1]>,
-    trait_items: SmallVec<[P<ast::AssocItem>; 1]>,
-    foreign_items: SmallVec<[P<ast::ForeignItem>; 1]>,
+    expr: Box<ast::Expr>,
+    pat: Box<ast::Pat>,
+    items: SmallVec<[Box<ast::Item>; 1]>,
+    impl_items: SmallVec<[Box<ast::AssocItem>; 1]>,
+    trait_items: SmallVec<[Box<ast::AssocItem>; 1]>,
+    foreign_items: SmallVec<[Box<ast::ForeignItem>; 1]>,
     stmts: SmallVec<[ast::Stmt; 1]>,
-    ty: P<ast::Ty>,
+    ty: Box<ast::Ty>,
 }
 
 impl MacResult for MacEager {
-    fn make_expr(self: Box<Self>) -> Option<P<ast::Expr>> {
+    fn make_expr(self: Box<Self>) -> Option<Box<ast::Expr>> {
         self.expr
     }
 
-    fn make_items(self: Box<Self>) -> Option<SmallVec<[P<ast::Item>; 1]>> {
+    fn make_items(self: Box<Self>) -> Option<SmallVec<[Box<ast::Item>; 1]>> {
         self.items
     }
 
-    fn make_impl_items(self: Box<Self>) -> Option<SmallVec<[P<ast::AssocItem>; 1]>> {
+    fn make_impl_items(self: Box<Self>) -> Option<SmallVec<[Box<ast::AssocItem>; 1]>> {
         self.impl_items
     }
 
-    fn make_trait_impl_items(self: Box<Self>) -> Option<SmallVec<[P<ast::AssocItem>; 1]>> {
+    fn make_trait_impl_items(self: Box<Self>) -> Option<SmallVec<[Box<ast::AssocItem>; 1]>> {
         self.impl_items
     }
 
-    fn make_trait_items(self: Box<Self>) -> Option<SmallVec<[P<ast::AssocItem>; 1]>> {
+    fn make_trait_items(self: Box<Self>) -> Option<SmallVec<[Box<ast::AssocItem>; 1]>> {
         self.trait_items
     }
 
-    fn make_foreign_items(self: Box<Self>) -> Option<SmallVec<[P<ast::ForeignItem>; 1]>> {
+    fn make_foreign_items(self: Box<Self>) -> Option<SmallVec<[Box<ast::ForeignItem>; 1]>> {
         self.foreign_items
     }
 
@@ -563,13 +563,13 @@ impl MacResult for MacEager {
         }
     }
 
-    fn make_pat(self: Box<Self>) -> Option<P<ast::Pat>> {
+    fn make_pat(self: Box<Self>) -> Option<Box<ast::Pat>> {
         if let Some(p) = self.pat {
             return Some(p);
         }
         if let Some(e) = self.expr {
             if matches!(e.kind, ast::ExprKind::Lit(_) | ast::ExprKind::IncludedBytes(_)) {
-                return Some(P(ast::Pat {
+                return Some(Box::new(ast::Pat {
                     id: ast::DUMMY_NODE_ID,
                     span: e.span,
                     kind: PatKind::Expr(e),
@@ -580,7 +580,7 @@ impl MacResult for MacEager {
         None
     }
 
-    fn make_ty(self: Box<Self>) -> Option<P<ast::Ty>> {
+    fn make_ty(self: Box<Self>) -> Option<Box<ast::Ty>> {
         self.ty
     }
 }
@@ -608,8 +608,8 @@ impl DummyResult {
     }
 
     /// A plain dummy expression.
-    pub fn raw_expr(sp: Span, guar: Option<ErrorGuaranteed>) -> P<ast::Expr> {
-        P(ast::Expr {
+    pub fn raw_expr(sp: Span, guar: Option<ErrorGuaranteed>) -> Box<ast::Expr> {
+        Box::new(ast::Expr {
             id: ast::DUMMY_NODE_ID,
             kind: if let Some(guar) = guar {
                 ast::ExprKind::Err(guar)
@@ -624,12 +624,12 @@ impl DummyResult {
 }
 
 impl MacResult for DummyResult {
-    fn make_expr(self: Box<DummyResult>) -> Option<P<ast::Expr>> {
+    fn make_expr(self: Box<DummyResult>) -> Option<Box<ast::Expr>> {
         Some(DummyResult::raw_expr(self.span, self.guar))
     }
 
-    fn make_pat(self: Box<DummyResult>) -> Option<P<ast::Pat>> {
-        Some(P(ast::Pat {
+    fn make_pat(self: Box<DummyResult>) -> Option<Box<ast::Pat>> {
+        Some(Box::new(ast::Pat {
             id: ast::DUMMY_NODE_ID,
             kind: PatKind::Wild,
             span: self.span,
@@ -637,23 +637,23 @@ impl MacResult for DummyResult {
         }))
     }
 
-    fn make_items(self: Box<DummyResult>) -> Option<SmallVec<[P<ast::Item>; 1]>> {
+    fn make_items(self: Box<DummyResult>) -> Option<SmallVec<[Box<ast::Item>; 1]>> {
         Some(SmallVec::new())
     }
 
-    fn make_impl_items(self: Box<DummyResult>) -> Option<SmallVec<[P<ast::AssocItem>; 1]>> {
+    fn make_impl_items(self: Box<DummyResult>) -> Option<SmallVec<[Box<ast::AssocItem>; 1]>> {
         Some(SmallVec::new())
     }
 
-    fn make_trait_impl_items(self: Box<DummyResult>) -> Option<SmallVec<[P<ast::AssocItem>; 1]>> {
+    fn make_trait_impl_items(self: Box<DummyResult>) -> Option<SmallVec<[Box<ast::AssocItem>; 1]>> {
         Some(SmallVec::new())
     }
 
-    fn make_trait_items(self: Box<DummyResult>) -> Option<SmallVec<[P<ast::AssocItem>; 1]>> {
+    fn make_trait_items(self: Box<DummyResult>) -> Option<SmallVec<[Box<ast::AssocItem>; 1]>> {
         Some(SmallVec::new())
     }
 
-    fn make_foreign_items(self: Box<Self>) -> Option<SmallVec<[P<ast::ForeignItem>; 1]>> {
+    fn make_foreign_items(self: Box<Self>) -> Option<SmallVec<[Box<ast::ForeignItem>; 1]>> {
         Some(SmallVec::new())
     }
 
@@ -665,11 +665,11 @@ impl MacResult for DummyResult {
         }])
     }
 
-    fn make_ty(self: Box<DummyResult>) -> Option<P<ast::Ty>> {
+    fn make_ty(self: Box<DummyResult>) -> Option<Box<ast::Ty>> {
         // FIXME(nnethercote): you might expect `ast::TyKind::Dummy` to be used here, but some
         // values produced here end up being lowered to HIR, which `ast::TyKind::Dummy` does not
         // support, so we use an empty tuple instead.
-        Some(P(ast::Ty {
+        Some(Box::new(ast::Ty {
             id: ast::DUMMY_NODE_ID,
             kind: ast::TyKind::Tup(ThinVec::new()),
             span: self.span,
@@ -719,6 +719,9 @@ impl MacResult for DummyResult {
 /// A syntax extension kind.
 #[derive(Clone)]
 pub enum SyntaxExtensionKind {
+    /// A `macro_rules!` macro that can work as any `MacroKind`
+    MacroRules(Arc<crate::MacroRulesMacroExpander>),
+
     /// A token-based function-like macro.
     Bang(
         /// An expander with signature TokenStream -> TokenStream.
@@ -773,9 +776,39 @@ pub enum SyntaxExtensionKind {
     ),
 
     /// A glob delegation.
+    ///
+    /// This is for delegated function implementations, and has nothing to do with glob imports.
     GlobDelegation(Arc<dyn GlobDelegationExpander + sync::DynSync + sync::DynSend>),
 }
 
+impl SyntaxExtensionKind {
+    /// Returns `Some(expander)` for a macro usable as a `LegacyBang`; otherwise returns `None`
+    ///
+    /// This includes a `MacroRules` with function-like rules.
+    pub fn as_legacy_bang(&self) -> Option<&(dyn TTMacroExpander + sync::DynSync + sync::DynSend)> {
+        match self {
+            SyntaxExtensionKind::LegacyBang(exp) => Some(exp.as_ref()),
+            SyntaxExtensionKind::MacroRules(exp) if exp.kinds().contains(MacroKinds::BANG) => {
+                Some(exp.as_ref())
+            }
+            _ => None,
+        }
+    }
+
+    /// Returns `Some(expander)` for a macro usable as an `Attr`; otherwise returns `None`
+    ///
+    /// This includes a `MacroRules` with `attr` rules.
+    pub fn as_attr(&self) -> Option<&(dyn AttrProcMacro + sync::DynSync + sync::DynSend)> {
+        match self {
+            SyntaxExtensionKind::Attr(exp) => Some(exp.as_ref()),
+            SyntaxExtensionKind::MacroRules(exp) if exp.kinds().contains(MacroKinds::ATTR) => {
+                Some(exp.as_ref())
+            }
+            _ => None,
+        }
+    }
+}
+
 /// A struct representing a macro definition in "lowered" form ready for expansion.
 pub struct SyntaxExtension {
     /// A syntax extension kind.
@@ -805,18 +838,19 @@ pub struct SyntaxExtension {
 }
 
 impl SyntaxExtension {
-    /// Returns which kind of macro calls this syntax extension.
-    pub fn macro_kind(&self) -> MacroKind {
+    /// Returns which kinds of macro call this syntax extension.
+    pub fn macro_kinds(&self) -> MacroKinds {
         match self.kind {
             SyntaxExtensionKind::Bang(..)
             | SyntaxExtensionKind::LegacyBang(..)
-            | SyntaxExtensionKind::GlobDelegation(..) => MacroKind::Bang,
+            | SyntaxExtensionKind::GlobDelegation(..) => MacroKinds::BANG,
             SyntaxExtensionKind::Attr(..)
             | SyntaxExtensionKind::LegacyAttr(..)
-            | SyntaxExtensionKind::NonMacroAttr => MacroKind::Attr,
+            | SyntaxExtensionKind::NonMacroAttr => MacroKinds::ATTR,
             SyntaxExtensionKind::Derive(..) | SyntaxExtensionKind::LegacyDerive(..) => {
-                MacroKind::Derive
+                MacroKinds::DERIVE
             }
+            SyntaxExtensionKind::MacroRules(ref m) => m.kinds(),
         }
     }
 
@@ -905,10 +939,7 @@ impl SyntaxExtension {
             find_attr!(attrs, AttributeKind::AllowInternalUnstable(i, _) => i)
                 .map(|i| i.as_slice())
                 .unwrap_or_default();
-        // FIXME(jdonszelman): allow_internal_unsafe isn't yet new-style
-        // let allow_internal_unsafe = find_attr!(attrs, AttributeKind::AllowInternalUnsafe);
-        let allow_internal_unsafe =
-            ast::attr::find_by_name(attrs, sym::allow_internal_unsafe).is_some();
+        let allow_internal_unsafe = find_attr!(attrs, AttributeKind::AllowInternalUnsafe(_));
 
         let local_inner_macros = ast::attr::find_by_name(attrs, sym::macro_export)
             .and_then(|macro_export| macro_export.meta_item_list())
@@ -1028,11 +1059,12 @@ impl SyntaxExtension {
         parent: LocalExpnId,
         call_site: Span,
         descr: Symbol,
+        kind: MacroKind,
         macro_def_id: Option<DefId>,
         parent_module: Option<DefId>,
     ) -> ExpnData {
         ExpnData::new(
-            ExpnKind::Macro(self.macro_kind(), descr),
+            ExpnKind::Macro(kind, descr),
             parent.to_expn_id(),
             call_site,
             self.span,
@@ -1162,7 +1194,7 @@ pub trait LintStoreExpand {
         registered_tools: &RegisteredTools,
         node_id: NodeId,
         attrs: &[Attribute],
-        items: &[P<Item>],
+        items: &[Box<Item>],
         name: Symbol,
     );
 }
diff --git a/compiler/rustc_expand/src/build.rs b/compiler/rustc_expand/src/build.rs
index 51d6e43ab67..c3e86ec0614 100644
--- a/compiler/rustc_expand/src/build.rs
+++ b/compiler/rustc_expand/src/build.rs
@@ -1,4 +1,3 @@
-use rustc_ast::ptr::P;
 use rustc_ast::token::Delimiter;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::util::literal;
@@ -59,10 +58,10 @@ impl<'a> ExtCtxt<'a> {
         path: ast::Path,
         delim: Delimiter,
         tokens: TokenStream,
-    ) -> P<ast::MacCall> {
-        P(ast::MacCall {
+    ) -> Box<ast::MacCall> {
+        Box::new(ast::MacCall {
             path,
-            args: P(ast::DelimArgs {
+            args: Box::new(ast::DelimArgs {
                 dspan: tokenstream::DelimSpan { open: span, close: span },
                 delim,
                 tokens,
@@ -70,32 +69,32 @@ impl<'a> ExtCtxt<'a> {
         })
     }
 
-    pub fn ty_mt(&self, ty: P<ast::Ty>, mutbl: ast::Mutability) -> ast::MutTy {
+    pub fn ty_mt(&self, ty: Box<ast::Ty>, mutbl: ast::Mutability) -> ast::MutTy {
         ast::MutTy { ty, mutbl }
     }
 
-    pub fn ty(&self, span: Span, kind: ast::TyKind) -> P<ast::Ty> {
-        P(ast::Ty { id: ast::DUMMY_NODE_ID, span, kind, tokens: None })
+    pub fn ty(&self, span: Span, kind: ast::TyKind) -> Box<ast::Ty> {
+        Box::new(ast::Ty { id: ast::DUMMY_NODE_ID, span, kind, tokens: None })
     }
 
-    pub fn ty_infer(&self, span: Span) -> P<ast::Ty> {
+    pub fn ty_infer(&self, span: Span) -> Box<ast::Ty> {
         self.ty(span, ast::TyKind::Infer)
     }
 
-    pub fn ty_path(&self, path: ast::Path) -> P<ast::Ty> {
+    pub fn ty_path(&self, path: ast::Path) -> Box<ast::Ty> {
         self.ty(path.span, ast::TyKind::Path(None, path))
     }
 
     // Might need to take bounds as an argument in the future, if you ever want
     // to generate a bounded existential trait type.
-    pub fn ty_ident(&self, span: Span, ident: Ident) -> P<ast::Ty> {
+    pub fn ty_ident(&self, span: Span, ident: Ident) -> Box<ast::Ty> {
         self.ty_path(self.path_ident(span, ident))
     }
 
     pub fn anon_const(&self, span: Span, kind: ast::ExprKind) -> ast::AnonConst {
         ast::AnonConst {
             id: ast::DUMMY_NODE_ID,
-            value: P(ast::Expr {
+            value: Box::new(ast::Expr {
                 id: ast::DUMMY_NODE_ID,
                 kind,
                 span,
@@ -112,14 +111,14 @@ impl<'a> ExtCtxt<'a> {
     pub fn ty_ref(
         &self,
         span: Span,
-        ty: P<ast::Ty>,
+        ty: Box<ast::Ty>,
         lifetime: Option<ast::Lifetime>,
         mutbl: ast::Mutability,
-    ) -> P<ast::Ty> {
+    ) -> Box<ast::Ty> {
         self.ty(span, ast::TyKind::Ref(lifetime, self.ty_mt(ty, mutbl)))
     }
 
-    pub fn ty_ptr(&self, span: Span, ty: P<ast::Ty>, mutbl: ast::Mutability) -> P<ast::Ty> {
+    pub fn ty_ptr(&self, span: Span, ty: Box<ast::Ty>, mutbl: ast::Mutability) -> Box<ast::Ty> {
         self.ty(span, ast::TyKind::Ptr(self.ty_mt(ty, mutbl)))
     }
 
@@ -128,7 +127,7 @@ impl<'a> ExtCtxt<'a> {
         span: Span,
         ident: Ident,
         bounds: ast::GenericBounds,
-        default: Option<P<ast::Ty>>,
+        default: Option<Box<ast::Ty>>,
     ) -> ast::GenericParam {
         ast::GenericParam {
             ident: ident.with_span_pos(span),
@@ -163,7 +162,7 @@ impl<'a> ExtCtxt<'a> {
         span: Span,
         ident: Ident,
         bounds: ast::GenericBounds,
-        ty: P<ast::Ty>,
+        ty: Box<ast::Ty>,
         default: Option<AnonConst>,
     ) -> ast::GenericParam {
         ast::GenericParam {
@@ -211,11 +210,11 @@ impl<'a> ExtCtxt<'a> {
         self.lifetime(span, Ident::new(kw::StaticLifetime, span))
     }
 
-    pub fn stmt_expr(&self, expr: P<ast::Expr>) -> ast::Stmt {
+    pub fn stmt_expr(&self, expr: Box<ast::Expr>) -> ast::Stmt {
         ast::Stmt { id: ast::DUMMY_NODE_ID, span: expr.span, kind: ast::StmtKind::Expr(expr) }
     }
 
-    pub fn stmt_let(&self, sp: Span, mutbl: bool, ident: Ident, ex: P<ast::Expr>) -> ast::Stmt {
+    pub fn stmt_let(&self, sp: Span, mutbl: bool, ident: Ident, ex: Box<ast::Expr>) -> ast::Stmt {
         self.stmt_let_ty(sp, mutbl, ident, None, ex)
     }
 
@@ -224,15 +223,15 @@ impl<'a> ExtCtxt<'a> {
         sp: Span,
         mutbl: bool,
         ident: Ident,
-        ty: Option<P<ast::Ty>>,
-        ex: P<ast::Expr>,
+        ty: Option<Box<ast::Ty>>,
+        ex: Box<ast::Expr>,
     ) -> ast::Stmt {
         let pat = if mutbl {
             self.pat_ident_binding_mode(sp, ident, ast::BindingMode::MUT)
         } else {
             self.pat_ident(sp, ident)
         };
-        let local = P(ast::Local {
+        let local = Box::new(ast::Local {
             super_: None,
             pat,
             ty,
@@ -247,8 +246,8 @@ impl<'a> ExtCtxt<'a> {
     }
 
     /// Generates `let _: Type;`, which is usually used for type assertions.
-    pub fn stmt_let_type_only(&self, span: Span, ty: P<ast::Ty>) -> ast::Stmt {
-        let local = P(ast::Local {
+    pub fn stmt_let_type_only(&self, span: Span, ty: Box<ast::Ty>) -> ast::Stmt {
+        let local = Box::new(ast::Local {
             super_: None,
             pat: self.pat_wild(span),
             ty: Some(ty),
@@ -262,19 +261,19 @@ impl<'a> ExtCtxt<'a> {
         self.stmt_local(local, span)
     }
 
-    pub fn stmt_semi(&self, expr: P<ast::Expr>) -> ast::Stmt {
+    pub fn stmt_semi(&self, expr: Box<ast::Expr>) -> ast::Stmt {
         ast::Stmt { id: ast::DUMMY_NODE_ID, span: expr.span, kind: ast::StmtKind::Semi(expr) }
     }
 
-    pub fn stmt_local(&self, local: P<ast::Local>, span: Span) -> ast::Stmt {
+    pub fn stmt_local(&self, local: Box<ast::Local>, span: Span) -> ast::Stmt {
         ast::Stmt { id: ast::DUMMY_NODE_ID, kind: ast::StmtKind::Let(local), span }
     }
 
-    pub fn stmt_item(&self, sp: Span, item: P<ast::Item>) -> ast::Stmt {
+    pub fn stmt_item(&self, sp: Span, item: Box<ast::Item>) -> ast::Stmt {
         ast::Stmt { id: ast::DUMMY_NODE_ID, kind: ast::StmtKind::Item(item), span: sp }
     }
 
-    pub fn block_expr(&self, expr: P<ast::Expr>) -> P<ast::Block> {
+    pub fn block_expr(&self, expr: Box<ast::Expr>) -> Box<ast::Block> {
         self.block(
             expr.span,
             thin_vec![ast::Stmt {
@@ -284,8 +283,8 @@ impl<'a> ExtCtxt<'a> {
             }],
         )
     }
-    pub fn block(&self, span: Span, stmts: ThinVec<ast::Stmt>) -> P<ast::Block> {
-        P(ast::Block {
+    pub fn block(&self, span: Span, stmts: ThinVec<ast::Stmt>) -> Box<ast::Block> {
+        Box::new(ast::Block {
             stmts,
             id: ast::DUMMY_NODE_ID,
             rules: BlockCheckMode::Default,
@@ -294,22 +293,28 @@ impl<'a> ExtCtxt<'a> {
         })
     }
 
-    pub fn expr(&self, span: Span, kind: ast::ExprKind) -> P<ast::Expr> {
-        P(ast::Expr { id: ast::DUMMY_NODE_ID, kind, span, attrs: AttrVec::new(), tokens: None })
+    pub fn expr(&self, span: Span, kind: ast::ExprKind) -> Box<ast::Expr> {
+        Box::new(ast::Expr {
+            id: ast::DUMMY_NODE_ID,
+            kind,
+            span,
+            attrs: AttrVec::new(),
+            tokens: None,
+        })
     }
 
-    pub fn expr_path(&self, path: ast::Path) -> P<ast::Expr> {
+    pub fn expr_path(&self, path: ast::Path) -> Box<ast::Expr> {
         self.expr(path.span, ast::ExprKind::Path(None, path))
     }
 
-    pub fn expr_ident(&self, span: Span, id: Ident) -> P<ast::Expr> {
+    pub fn expr_ident(&self, span: Span, id: Ident) -> Box<ast::Expr> {
         self.expr_path(self.path_ident(span, id))
     }
-    pub fn expr_self(&self, span: Span) -> P<ast::Expr> {
+    pub fn expr_self(&self, span: Span) -> Box<ast::Expr> {
         self.expr_ident(span, Ident::with_dummy_span(kw::SelfLower))
     }
 
-    pub fn expr_macro_call(&self, span: Span, call: P<ast::MacCall>) -> P<ast::Expr> {
+    pub fn expr_macro_call(&self, span: Span, call: Box<ast::MacCall>) -> Box<ast::Expr> {
         self.expr(span, ast::ExprKind::MacCall(call))
     }
 
@@ -317,31 +322,31 @@ impl<'a> ExtCtxt<'a> {
         &self,
         sp: Span,
         op: ast::BinOpKind,
-        lhs: P<ast::Expr>,
-        rhs: P<ast::Expr>,
-    ) -> P<ast::Expr> {
+        lhs: Box<ast::Expr>,
+        rhs: Box<ast::Expr>,
+    ) -> Box<ast::Expr> {
         self.expr(sp, ast::ExprKind::Binary(Spanned { node: op, span: sp }, lhs, rhs))
     }
 
-    pub fn expr_deref(&self, sp: Span, e: P<ast::Expr>) -> P<ast::Expr> {
+    pub fn expr_deref(&self, sp: Span, e: Box<ast::Expr>) -> Box<ast::Expr> {
         self.expr(sp, ast::ExprKind::Unary(UnOp::Deref, e))
     }
 
-    pub fn expr_addr_of(&self, sp: Span, e: P<ast::Expr>) -> P<ast::Expr> {
+    pub fn expr_addr_of(&self, sp: Span, e: Box<ast::Expr>) -> Box<ast::Expr> {
         self.expr(sp, ast::ExprKind::AddrOf(ast::BorrowKind::Ref, ast::Mutability::Not, e))
     }
 
-    pub fn expr_paren(&self, sp: Span, e: P<ast::Expr>) -> P<ast::Expr> {
+    pub fn expr_paren(&self, sp: Span, e: Box<ast::Expr>) -> Box<ast::Expr> {
         self.expr(sp, ast::ExprKind::Paren(e))
     }
 
     pub fn expr_method_call(
         &self,
         span: Span,
-        expr: P<ast::Expr>,
+        expr: Box<ast::Expr>,
         ident: Ident,
-        args: ThinVec<P<ast::Expr>>,
-    ) -> P<ast::Expr> {
+        args: ThinVec<Box<ast::Expr>>,
+    ) -> Box<ast::Expr> {
         let seg = ast::PathSegment::from_ident(ident);
         self.expr(
             span,
@@ -357,38 +362,38 @@ impl<'a> ExtCtxt<'a> {
     pub fn expr_call(
         &self,
         span: Span,
-        expr: P<ast::Expr>,
-        args: ThinVec<P<ast::Expr>>,
-    ) -> P<ast::Expr> {
+        expr: Box<ast::Expr>,
+        args: ThinVec<Box<ast::Expr>>,
+    ) -> Box<ast::Expr> {
         self.expr(span, ast::ExprKind::Call(expr, args))
     }
-    pub fn expr_loop(&self, sp: Span, block: P<ast::Block>) -> P<ast::Expr> {
+    pub fn expr_loop(&self, sp: Span, block: Box<ast::Block>) -> Box<ast::Expr> {
         self.expr(sp, ast::ExprKind::Loop(block, None, sp))
     }
-    pub fn expr_asm(&self, sp: Span, expr: P<ast::InlineAsm>) -> P<ast::Expr> {
+    pub fn expr_asm(&self, sp: Span, expr: Box<ast::InlineAsm>) -> Box<ast::Expr> {
         self.expr(sp, ast::ExprKind::InlineAsm(expr))
     }
     pub fn expr_call_ident(
         &self,
         span: Span,
         id: Ident,
-        args: ThinVec<P<ast::Expr>>,
-    ) -> P<ast::Expr> {
+        args: ThinVec<Box<ast::Expr>>,
+    ) -> Box<ast::Expr> {
         self.expr(span, ast::ExprKind::Call(self.expr_ident(span, id), args))
     }
     pub fn expr_call_global(
         &self,
         sp: Span,
         fn_path: Vec<Ident>,
-        args: ThinVec<P<ast::Expr>>,
-    ) -> P<ast::Expr> {
+        args: ThinVec<Box<ast::Expr>>,
+    ) -> Box<ast::Expr> {
         let pathexpr = self.expr_path(self.path_global(sp, fn_path));
         self.expr_call(sp, pathexpr, args)
     }
-    pub fn expr_block(&self, b: P<ast::Block>) -> P<ast::Expr> {
+    pub fn expr_block(&self, b: Box<ast::Block>) -> Box<ast::Expr> {
         self.expr(b.span, ast::ExprKind::Block(b, None))
     }
-    pub fn field_imm(&self, span: Span, ident: Ident, e: P<ast::Expr>) -> ast::ExprField {
+    pub fn field_imm(&self, span: Span, ident: Ident, e: Box<ast::Expr>) -> ast::ExprField {
         ast::ExprField {
             ident: ident.with_span_pos(span),
             expr: e,
@@ -404,10 +409,10 @@ impl<'a> ExtCtxt<'a> {
         span: Span,
         path: ast::Path,
         fields: ThinVec<ast::ExprField>,
-    ) -> P<ast::Expr> {
+    ) -> Box<ast::Expr> {
         self.expr(
             span,
-            ast::ExprKind::Struct(P(ast::StructExpr {
+            ast::ExprKind::Struct(Box::new(ast::StructExpr {
                 qself: None,
                 path,
                 fields,
@@ -420,61 +425,61 @@ impl<'a> ExtCtxt<'a> {
         span: Span,
         id: Ident,
         fields: ThinVec<ast::ExprField>,
-    ) -> P<ast::Expr> {
+    ) -> Box<ast::Expr> {
         self.expr_struct(span, self.path_ident(span, id), fields)
     }
 
-    pub fn expr_usize(&self, span: Span, n: usize) -> P<ast::Expr> {
+    pub fn expr_usize(&self, span: Span, n: usize) -> Box<ast::Expr> {
         let suffix = Some(ast::UintTy::Usize.name());
         let lit = token::Lit::new(token::Integer, sym::integer(n), suffix);
         self.expr(span, ast::ExprKind::Lit(lit))
     }
 
-    pub fn expr_u32(&self, span: Span, n: u32) -> P<ast::Expr> {
+    pub fn expr_u32(&self, span: Span, n: u32) -> Box<ast::Expr> {
         let suffix = Some(ast::UintTy::U32.name());
         let lit = token::Lit::new(token::Integer, sym::integer(n), suffix);
         self.expr(span, ast::ExprKind::Lit(lit))
     }
 
-    pub fn expr_bool(&self, span: Span, value: bool) -> P<ast::Expr> {
+    pub fn expr_bool(&self, span: Span, value: bool) -> Box<ast::Expr> {
         let lit = token::Lit::new(token::Bool, if value { kw::True } else { kw::False }, None);
         self.expr(span, ast::ExprKind::Lit(lit))
     }
 
-    pub fn expr_str(&self, span: Span, s: Symbol) -> P<ast::Expr> {
+    pub fn expr_str(&self, span: Span, s: Symbol) -> Box<ast::Expr> {
         let lit = token::Lit::new(token::Str, literal::escape_string_symbol(s), None);
         self.expr(span, ast::ExprKind::Lit(lit))
     }
 
-    pub fn expr_byte_str(&self, span: Span, bytes: Vec<u8>) -> P<ast::Expr> {
+    pub fn expr_byte_str(&self, span: Span, bytes: Vec<u8>) -> Box<ast::Expr> {
         let lit = token::Lit::new(token::ByteStr, literal::escape_byte_str_symbol(&bytes), None);
         self.expr(span, ast::ExprKind::Lit(lit))
     }
 
     /// `[expr1, expr2, ...]`
-    pub fn expr_array(&self, sp: Span, exprs: ThinVec<P<ast::Expr>>) -> P<ast::Expr> {
+    pub fn expr_array(&self, sp: Span, exprs: ThinVec<Box<ast::Expr>>) -> Box<ast::Expr> {
         self.expr(sp, ast::ExprKind::Array(exprs))
     }
 
     /// `&[expr1, expr2, ...]`
-    pub fn expr_array_ref(&self, sp: Span, exprs: ThinVec<P<ast::Expr>>) -> P<ast::Expr> {
+    pub fn expr_array_ref(&self, sp: Span, exprs: ThinVec<Box<ast::Expr>>) -> Box<ast::Expr> {
         self.expr_addr_of(sp, self.expr_array(sp, exprs))
     }
 
-    pub fn expr_some(&self, sp: Span, expr: P<ast::Expr>) -> P<ast::Expr> {
+    pub fn expr_some(&self, sp: Span, expr: Box<ast::Expr>) -> Box<ast::Expr> {
         let some = self.std_path(&[sym::option, sym::Option, sym::Some]);
         self.expr_call_global(sp, some, thin_vec![expr])
     }
 
-    pub fn expr_none(&self, sp: Span) -> P<ast::Expr> {
+    pub fn expr_none(&self, sp: Span) -> Box<ast::Expr> {
         let none = self.std_path(&[sym::option, sym::Option, sym::None]);
         self.expr_path(self.path_global(sp, none))
     }
-    pub fn expr_tuple(&self, sp: Span, exprs: ThinVec<P<ast::Expr>>) -> P<ast::Expr> {
+    pub fn expr_tuple(&self, sp: Span, exprs: ThinVec<Box<ast::Expr>>) -> Box<ast::Expr> {
         self.expr(sp, ast::ExprKind::Tup(exprs))
     }
 
-    pub fn expr_unreachable(&self, span: Span) -> P<ast::Expr> {
+    pub fn expr_unreachable(&self, span: Span) -> Box<ast::Expr> {
         self.expr_macro_call(
             span,
             self.macro_call(
@@ -489,12 +494,12 @@ impl<'a> ExtCtxt<'a> {
         )
     }
 
-    pub fn expr_ok(&self, sp: Span, expr: P<ast::Expr>) -> P<ast::Expr> {
+    pub fn expr_ok(&self, sp: Span, expr: Box<ast::Expr>) -> Box<ast::Expr> {
         let ok = self.std_path(&[sym::result, sym::Result, sym::Ok]);
         self.expr_call_global(sp, ok, thin_vec![expr])
     }
 
-    pub fn expr_try(&self, sp: Span, head: P<ast::Expr>) -> P<ast::Expr> {
+    pub fn expr_try(&self, sp: Span, head: Box<ast::Expr>) -> Box<ast::Expr> {
         let ok = self.std_path(&[sym::result, sym::Result, sym::Ok]);
         let ok_path = self.path_global(sp, ok);
         let err = self.std_path(&[sym::result, sym::Result, sym::Err]);
@@ -523,16 +528,16 @@ impl<'a> ExtCtxt<'a> {
         self.expr_match(sp, head, thin_vec![ok_arm, err_arm])
     }
 
-    pub fn pat(&self, span: Span, kind: PatKind) -> P<ast::Pat> {
-        P(ast::Pat { id: ast::DUMMY_NODE_ID, kind, span, tokens: None })
+    pub fn pat(&self, span: Span, kind: PatKind) -> Box<ast::Pat> {
+        Box::new(ast::Pat { id: ast::DUMMY_NODE_ID, kind, span, tokens: None })
     }
-    pub fn pat_wild(&self, span: Span) -> P<ast::Pat> {
+    pub fn pat_wild(&self, span: Span) -> Box<ast::Pat> {
         self.pat(span, PatKind::Wild)
     }
-    pub fn pat_lit(&self, span: Span, expr: P<ast::Expr>) -> P<ast::Pat> {
+    pub fn pat_lit(&self, span: Span, expr: Box<ast::Expr>) -> Box<ast::Pat> {
         self.pat(span, PatKind::Expr(expr))
     }
-    pub fn pat_ident(&self, span: Span, ident: Ident) -> P<ast::Pat> {
+    pub fn pat_ident(&self, span: Span, ident: Ident) -> Box<ast::Pat> {
         self.pat_ident_binding_mode(span, ident, ast::BindingMode::NONE)
     }
 
@@ -541,19 +546,19 @@ impl<'a> ExtCtxt<'a> {
         span: Span,
         ident: Ident,
         ann: ast::BindingMode,
-    ) -> P<ast::Pat> {
+    ) -> Box<ast::Pat> {
         let pat = PatKind::Ident(ann, ident.with_span_pos(span), None);
         self.pat(span, pat)
     }
-    pub fn pat_path(&self, span: Span, path: ast::Path) -> P<ast::Pat> {
+    pub fn pat_path(&self, span: Span, path: ast::Path) -> Box<ast::Pat> {
         self.pat(span, PatKind::Path(None, path))
     }
     pub fn pat_tuple_struct(
         &self,
         span: Span,
         path: ast::Path,
-        subpats: ThinVec<P<ast::Pat>>,
-    ) -> P<ast::Pat> {
+        subpats: ThinVec<Box<ast::Pat>>,
+    ) -> Box<ast::Pat> {
         self.pat(span, PatKind::TupleStruct(None, path, subpats))
     }
     pub fn pat_struct(
@@ -561,20 +566,20 @@ impl<'a> ExtCtxt<'a> {
         span: Span,
         path: ast::Path,
         field_pats: ThinVec<ast::PatField>,
-    ) -> P<ast::Pat> {
+    ) -> Box<ast::Pat> {
         self.pat(span, PatKind::Struct(None, path, field_pats, ast::PatFieldsRest::None))
     }
-    pub fn pat_tuple(&self, span: Span, pats: ThinVec<P<ast::Pat>>) -> P<ast::Pat> {
+    pub fn pat_tuple(&self, span: Span, pats: ThinVec<Box<ast::Pat>>) -> Box<ast::Pat> {
         self.pat(span, PatKind::Tuple(pats))
     }
 
-    pub fn pat_some(&self, span: Span, pat: P<ast::Pat>) -> P<ast::Pat> {
+    pub fn pat_some(&self, span: Span, pat: Box<ast::Pat>) -> Box<ast::Pat> {
         let some = self.std_path(&[sym::option, sym::Option, sym::Some]);
         let path = self.path_global(span, some);
         self.pat_tuple_struct(span, path, thin_vec![pat])
     }
 
-    pub fn arm(&self, span: Span, pat: P<ast::Pat>, expr: P<ast::Expr>) -> ast::Arm {
+    pub fn arm(&self, span: Span, pat: Box<ast::Pat>, expr: Box<ast::Expr>) -> ast::Arm {
         ast::Arm {
             attrs: AttrVec::new(),
             pat,
@@ -590,22 +595,27 @@ impl<'a> ExtCtxt<'a> {
         self.arm(span, self.pat_wild(span), self.expr_unreachable(span))
     }
 
-    pub fn expr_match(&self, span: Span, arg: P<ast::Expr>, arms: ThinVec<ast::Arm>) -> P<Expr> {
+    pub fn expr_match(
+        &self,
+        span: Span,
+        arg: Box<ast::Expr>,
+        arms: ThinVec<ast::Arm>,
+    ) -> Box<Expr> {
         self.expr(span, ast::ExprKind::Match(arg, arms, MatchKind::Prefix))
     }
 
     pub fn expr_if(
         &self,
         span: Span,
-        cond: P<ast::Expr>,
-        then: P<ast::Expr>,
-        els: Option<P<ast::Expr>>,
-    ) -> P<ast::Expr> {
+        cond: Box<ast::Expr>,
+        then: Box<ast::Expr>,
+        els: Option<Box<ast::Expr>>,
+    ) -> Box<ast::Expr> {
         let els = els.map(|x| self.expr_block(self.block_expr(x)));
         self.expr(span, ast::ExprKind::If(cond, self.block_expr(then), els))
     }
 
-    pub fn lambda(&self, span: Span, ids: Vec<Ident>, body: P<ast::Expr>) -> P<ast::Expr> {
+    pub fn lambda(&self, span: Span, ids: Vec<Ident>, body: Box<ast::Expr>) -> Box<ast::Expr> {
         let fn_decl = self.fn_decl(
             ids.iter().map(|id| self.param(span, *id, self.ty(span, ast::TyKind::Infer))).collect(),
             ast::FnRetTy::Default(span),
@@ -633,11 +643,11 @@ impl<'a> ExtCtxt<'a> {
         )
     }
 
-    pub fn lambda0(&self, span: Span, body: P<ast::Expr>) -> P<ast::Expr> {
+    pub fn lambda0(&self, span: Span, body: Box<ast::Expr>) -> Box<ast::Expr> {
         self.lambda(span, Vec::new(), body)
     }
 
-    pub fn lambda1(&self, span: Span, body: P<ast::Expr>, ident: Ident) -> P<ast::Expr> {
+    pub fn lambda1(&self, span: Span, body: Box<ast::Expr>, ident: Ident) -> Box<ast::Expr> {
         self.lambda(span, vec![ident], body)
     }
 
@@ -646,11 +656,11 @@ impl<'a> ExtCtxt<'a> {
         span: Span,
         stmts: ThinVec<ast::Stmt>,
         ident: Ident,
-    ) -> P<ast::Expr> {
+    ) -> Box<ast::Expr> {
         self.lambda1(span, self.expr_block(self.block(span, stmts)), ident)
     }
 
-    pub fn param(&self, span: Span, ident: Ident, ty: P<ast::Ty>) -> ast::Param {
+    pub fn param(&self, span: Span, ident: Ident, ty: Box<ast::Ty>) -> ast::Param {
         let arg_pat = self.pat_ident(span, ident);
         ast::Param {
             attrs: AttrVec::default(),
@@ -663,12 +673,12 @@ impl<'a> ExtCtxt<'a> {
     }
 
     // `self` is unused but keep it as method for the convenience use.
-    pub fn fn_decl(&self, inputs: ThinVec<ast::Param>, output: ast::FnRetTy) -> P<ast::FnDecl> {
-        P(ast::FnDecl { inputs, output })
+    pub fn fn_decl(&self, inputs: ThinVec<ast::Param>, output: ast::FnRetTy) -> Box<ast::FnDecl> {
+        Box::new(ast::FnDecl { inputs, output })
     }
 
-    pub fn item(&self, span: Span, attrs: ast::AttrVec, kind: ast::ItemKind) -> P<ast::Item> {
-        P(ast::Item {
+    pub fn item(&self, span: Span, attrs: ast::AttrVec, kind: ast::ItemKind) -> Box<ast::Item> {
+        Box::new(ast::Item {
             attrs,
             id: ast::DUMMY_NODE_ID,
             kind,
@@ -686,10 +696,10 @@ impl<'a> ExtCtxt<'a> {
         &self,
         span: Span,
         ident: Ident,
-        ty: P<ast::Ty>,
+        ty: Box<ast::Ty>,
         mutability: ast::Mutability,
-        expr: P<ast::Expr>,
-    ) -> P<ast::Item> {
+        expr: Box<ast::Expr>,
+    ) -> Box<ast::Item> {
         self.item(
             span,
             AttrVec::new(),
@@ -711,9 +721,9 @@ impl<'a> ExtCtxt<'a> {
         &self,
         span: Span,
         ident: Ident,
-        ty: P<ast::Ty>,
-        expr: P<ast::Expr>,
-    ) -> P<ast::Item> {
+        ty: Box<ast::Ty>,
+        expr: Box<ast::Expr>,
+    ) -> Box<ast::Item> {
         let defaultness = ast::Defaultness::Final;
         self.item(
             span,
diff --git a/compiler/rustc_expand/src/errors.rs b/compiler/rustc_expand/src/errors.rs
index fd1391a554a..e58269991fc 100644
--- a/compiler/rustc_expand/src/errors.rs
+++ b/compiler/rustc_expand/src/errors.rs
@@ -482,3 +482,21 @@ mod metavar_exprs {
         pub key: MacroRulesNormalizedIdent,
     }
 }
+
+#[derive(Diagnostic)]
+#[diag(expand_macro_args_bad_delim)]
+pub(crate) struct MacroArgsBadDelim {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sugg: MacroArgsBadDelimSugg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(expand_macro_args_bad_delim_sugg, applicability = "machine-applicable")]
+pub(crate) struct MacroArgsBadDelimSugg {
+    #[suggestion_part(code = "(")]
+    pub open: Span,
+    #[suggestion_part(code = ")")]
+    pub close: Span,
+}
diff --git a/compiler/rustc_expand/src/expand.rs b/compiler/rustc_expand/src/expand.rs
index f02aa6c120f..670f5c91bb9 100644
--- a/compiler/rustc_expand/src/expand.rs
+++ b/compiler/rustc_expand/src/expand.rs
@@ -4,7 +4,6 @@ use std::sync::Arc;
 use std::{iter, mem};
 
 use rustc_ast::mut_visit::*;
-use rustc_ast::ptr::P;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::visit::{self, AssocCtxt, Visitor, VisitorResult, try_visit, walk_list};
 use rustc_ast::{
@@ -65,8 +64,8 @@ macro_rules! ast_fragments {
         /// A fragment of AST that can be produced by a single macro expansion.
         /// Can also serve as an input and intermediate result for macro expansion operations.
         pub enum AstFragment {
-            OptExpr(Option<P<ast::Expr>>),
-            MethodReceiverExpr(P<ast::Expr>),
+            OptExpr(Option<Box<ast::Expr>>),
+            MethodReceiverExpr(Box<ast::Expr>),
             $($Kind($AstTy),)*
         }
 
@@ -112,14 +111,14 @@ macro_rules! ast_fragments {
                 }
             }
 
-            pub(crate) fn make_opt_expr(self) -> Option<P<ast::Expr>> {
+            pub(crate) fn make_opt_expr(self) -> Option<Box<ast::Expr>> {
                 match self {
                     AstFragment::OptExpr(expr) => expr,
                     _ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
                 }
             }
 
-            pub(crate) fn make_method_receiver_expr(self) -> P<ast::Expr> {
+            pub(crate) fn make_method_receiver_expr(self) -> Box<ast::Expr> {
                 match self {
                     AstFragment::MethodReceiverExpr(expr) => expr,
                     _ => panic!("AstFragment::make_* called on the wrong kind of fragment"),
@@ -188,17 +187,17 @@ macro_rules! ast_fragments {
 }
 
 ast_fragments! {
-    Expr(P<ast::Expr>) {
+    Expr(Box<ast::Expr>) {
         "expression";
         one fn visit_expr; fn visit_expr; fn pprust::expr_to_string;
         fn make_expr;
     }
-    Pat(P<ast::Pat>) {
+    Pat(Box<ast::Pat>) {
         "pattern";
         one fn visit_pat; fn visit_pat; fn pprust::pat_to_string;
         fn make_pat;
     }
-    Ty(P<ast::Ty>) {
+    Ty(Box<ast::Ty>) {
         "type";
         one fn visit_ty; fn visit_ty; fn pprust::ty_to_string;
         fn make_ty;
@@ -208,30 +207,30 @@ ast_fragments! {
         many fn flat_map_stmt; fn visit_stmt(); fn pprust::stmt_to_string;
         fn make_stmts;
     }
-    Items(SmallVec<[P<ast::Item>; 1]>) {
+    Items(SmallVec<[Box<ast::Item>; 1]>) {
         "item";
         many fn flat_map_item; fn visit_item(); fn pprust::item_to_string;
         fn make_items;
     }
-    TraitItems(SmallVec<[P<ast::AssocItem>; 1]>) {
+    TraitItems(SmallVec<[Box<ast::AssocItem>; 1]>) {
         "trait item";
         many fn flat_map_assoc_item; fn visit_assoc_item(AssocCtxt::Trait);
             fn pprust::assoc_item_to_string;
         fn make_trait_items;
     }
-    ImplItems(SmallVec<[P<ast::AssocItem>; 1]>) {
+    ImplItems(SmallVec<[Box<ast::AssocItem>; 1]>) {
         "impl item";
         many fn flat_map_assoc_item; fn visit_assoc_item(AssocCtxt::Impl { of_trait: false });
             fn pprust::assoc_item_to_string;
         fn make_impl_items;
     }
-    TraitImplItems(SmallVec<[P<ast::AssocItem>; 1]>) {
+    TraitImplItems(SmallVec<[Box<ast::AssocItem>; 1]>) {
         "impl item";
         many fn flat_map_assoc_item; fn visit_assoc_item(AssocCtxt::Impl { of_trait: true });
             fn pprust::assoc_item_to_string;
         fn make_trait_impl_items;
     }
-    ForeignItems(SmallVec<[P<ast::ForeignItem>; 1]>) {
+    ForeignItems(SmallVec<[Box<ast::ForeignItem>; 1]>) {
         "foreign item";
         many fn flat_map_foreign_item; fn visit_foreign_item(); fn pprust::foreign_item_to_string;
         fn make_foreign_items;
@@ -392,7 +391,7 @@ pub struct Invocation {
 
 pub enum InvocationKind {
     Bang {
-        mac: P<ast::MacCall>,
+        mac: Box<ast::MacCall>,
         span: Span,
     },
     Attr {
@@ -409,7 +408,7 @@ pub enum InvocationKind {
         item: Annotatable,
     },
     GlobDelegation {
-        item: P<ast::AssocItem>,
+        item: Box<ast::AssocItem>,
         /// Whether this is a trait impl or an inherent impl
         of_trait: bool,
     },
@@ -737,8 +736,8 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
 
         let (fragment_kind, span) = (invoc.fragment_kind, invoc.span());
         ExpandResult::Ready(match invoc.kind {
-            InvocationKind::Bang { mac, span } => match ext {
-                SyntaxExtensionKind::Bang(expander) => {
+            InvocationKind::Bang { mac, span } => {
+                if let SyntaxExtensionKind::Bang(expander) = ext {
                     match expander.expand(self.cx, span, mac.args.tokens.clone()) {
                         Ok(tok_result) => {
                             let fragment =
@@ -756,8 +755,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                         }
                         Err(guar) => return ExpandResult::Ready(fragment_kind.dummy(span, guar)),
                     }
-                }
-                SyntaxExtensionKind::LegacyBang(expander) => {
+                } else if let Some(expander) = ext.as_legacy_bang() {
                     let tok_result = match expander.expand(self.cx, span, mac.args.tokens.clone()) {
                         ExpandResult::Ready(tok_result) => tok_result,
                         ExpandResult::Retry(_) => {
@@ -777,11 +775,12 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                         let guar = self.error_wrong_fragment_kind(fragment_kind, &mac, span);
                         fragment_kind.dummy(span, guar)
                     }
+                } else {
+                    unreachable!();
                 }
-                _ => unreachable!(),
-            },
-            InvocationKind::Attr { attr, pos, mut item, derives } => match ext {
-                SyntaxExtensionKind::Attr(expander) => {
+            }
+            InvocationKind::Attr { attr, pos, mut item, derives } => {
+                if let Some(expander) = ext.as_attr() {
                     self.gate_proc_macro_input(&item);
                     self.gate_proc_macro_attr_item(span, &item);
                     let tokens = match &item {
@@ -836,8 +835,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                         }
                         Err(guar) => return ExpandResult::Ready(fragment_kind.dummy(span, guar)),
                     }
-                }
-                SyntaxExtensionKind::LegacyAttr(expander) => {
+                } else if let SyntaxExtensionKind::LegacyAttr(expander) = ext {
                     match validate_attr::parse_meta(&self.cx.sess.psess, &attr) {
                         Ok(meta) => {
                             let item_clone = macro_stats.then(|| item.clone());
@@ -879,15 +877,15 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                             fragment_kind.expect_from_annotatables(iter::once(item))
                         }
                     }
-                }
-                SyntaxExtensionKind::NonMacroAttr => {
+                } else if let SyntaxExtensionKind::NonMacroAttr = ext {
                     // `-Zmacro-stats` ignores these because they don't do any real expansion.
                     self.cx.expanded_inert_attrs.mark(&attr);
                     item.visit_attrs(|attrs| attrs.insert(pos, attr));
                     fragment_kind.expect_from_annotatables(iter::once(item))
+                } else {
+                    unreachable!();
                 }
-                _ => unreachable!(),
-            },
+            }
             InvocationKind::Derive { path, item, is_const } => match ext {
                 SyntaxExtensionKind::Derive(expander)
                 | SyntaxExtensionKind::LegacyDerive(expander) => {
@@ -948,15 +946,14 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                     _ => unreachable!(),
                 };
 
-                type Node = AstNodeWrapper<P<ast::AssocItem>, ImplItemTag>;
+                type Node = AstNodeWrapper<Box<ast::AssocItem>, ImplItemTag>;
                 let single_delegations = build_single_delegations::<Node>(
                     self.cx, deleg, &item, &suffixes, item.span, true,
                 );
                 // `-Zmacro-stats` ignores these because they don't seem important.
-                fragment_kind.expect_from_annotatables(
-                    single_delegations
-                        .map(|item| Annotatable::AssocItem(P(item), AssocCtxt::Impl { of_trait })),
-                )
+                fragment_kind.expect_from_annotatables(single_delegations.map(|item| {
+                    Annotatable::AssocItem(Box::new(item), AssocCtxt::Impl { of_trait })
+                }))
             }
         })
     }
@@ -1228,7 +1225,7 @@ trait InvocationCollectorNode: HasAttrs + HasNodeId + Sized {
     fn is_mac_call(&self) -> bool {
         false
     }
-    fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
+    fn take_mac_call(self) -> (Box<ast::MacCall>, ast::AttrVec, AddSemicolon) {
         unreachable!()
     }
     fn delegation(&self) -> Option<(&ast::DelegationMac, &ast::Item<Self::ItemKind>)> {
@@ -1269,7 +1266,7 @@ trait InvocationCollectorNode: HasAttrs + HasNodeId + Sized {
     }
 }
 
-impl InvocationCollectorNode for P<ast::Item> {
+impl InvocationCollectorNode for Box<ast::Item> {
     const KIND: AstFragmentKind = AstFragmentKind::Items;
     fn to_annotatable(self) -> Annotatable {
         Annotatable::Item(self)
@@ -1283,7 +1280,7 @@ impl InvocationCollectorNode for P<ast::Item> {
     fn is_mac_call(&self) -> bool {
         matches!(self.kind, ItemKind::MacCall(..))
     }
-    fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
+    fn take_mac_call(self) -> (Box<ast::MacCall>, ast::AttrVec, AddSemicolon) {
         match self.kind {
             ItemKind::MacCall(mac) => (mac, self.attrs, AddSemicolon::No),
             _ => unreachable!(),
@@ -1299,7 +1296,7 @@ impl InvocationCollectorNode for P<ast::Item> {
         ItemKind::Delegation(deleg)
     }
     fn from_item(item: ast::Item<Self::ItemKind>) -> Self {
-        P(item)
+        Box::new(item)
     }
     fn flatten_outputs(items: impl Iterator<Item = Self::OutputTy>) -> Self::OutputTy {
         items.flatten().collect()
@@ -1421,8 +1418,8 @@ impl InvocationCollectorNode for P<ast::Item> {
 }
 
 struct TraitItemTag;
-impl InvocationCollectorNode for AstNodeWrapper<P<ast::AssocItem>, TraitItemTag> {
-    type OutputTy = SmallVec<[P<ast::AssocItem>; 1]>;
+impl InvocationCollectorNode for AstNodeWrapper<Box<ast::AssocItem>, TraitItemTag> {
+    type OutputTy = SmallVec<[Box<ast::AssocItem>; 1]>;
     type ItemKind = AssocItemKind;
     const KIND: AstFragmentKind = AstFragmentKind::TraitItems;
     fn to_annotatable(self) -> Annotatable {
@@ -1437,7 +1434,7 @@ impl InvocationCollectorNode for AstNodeWrapper<P<ast::AssocItem>, TraitItemTag>
     fn is_mac_call(&self) -> bool {
         matches!(self.wrapped.kind, AssocItemKind::MacCall(..))
     }
-    fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
+    fn take_mac_call(self) -> (Box<ast::MacCall>, ast::AttrVec, AddSemicolon) {
         let item = self.wrapped;
         match item.kind {
             AssocItemKind::MacCall(mac) => (mac, item.attrs, AddSemicolon::No),
@@ -1454,7 +1451,7 @@ impl InvocationCollectorNode for AstNodeWrapper<P<ast::AssocItem>, TraitItemTag>
         AssocItemKind::Delegation(deleg)
     }
     fn from_item(item: ast::Item<Self::ItemKind>) -> Self {
-        AstNodeWrapper::new(P(item), TraitItemTag)
+        AstNodeWrapper::new(Box::new(item), TraitItemTag)
     }
     fn flatten_outputs(items: impl Iterator<Item = Self::OutputTy>) -> Self::OutputTy {
         items.flatten().collect()
@@ -1462,8 +1459,8 @@ impl InvocationCollectorNode for AstNodeWrapper<P<ast::AssocItem>, TraitItemTag>
 }
 
 struct ImplItemTag;
-impl InvocationCollectorNode for AstNodeWrapper<P<ast::AssocItem>, ImplItemTag> {
-    type OutputTy = SmallVec<[P<ast::AssocItem>; 1]>;
+impl InvocationCollectorNode for AstNodeWrapper<Box<ast::AssocItem>, ImplItemTag> {
+    type OutputTy = SmallVec<[Box<ast::AssocItem>; 1]>;
     type ItemKind = AssocItemKind;
     const KIND: AstFragmentKind = AstFragmentKind::ImplItems;
     fn to_annotatable(self) -> Annotatable {
@@ -1478,7 +1475,7 @@ impl InvocationCollectorNode for AstNodeWrapper<P<ast::AssocItem>, ImplItemTag>
     fn is_mac_call(&self) -> bool {
         matches!(self.wrapped.kind, AssocItemKind::MacCall(..))
     }
-    fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
+    fn take_mac_call(self) -> (Box<ast::MacCall>, ast::AttrVec, AddSemicolon) {
         let item = self.wrapped;
         match item.kind {
             AssocItemKind::MacCall(mac) => (mac, item.attrs, AddSemicolon::No),
@@ -1495,7 +1492,7 @@ impl InvocationCollectorNode for AstNodeWrapper<P<ast::AssocItem>, ImplItemTag>
         AssocItemKind::Delegation(deleg)
     }
     fn from_item(item: ast::Item<Self::ItemKind>) -> Self {
-        AstNodeWrapper::new(P(item), ImplItemTag)
+        AstNodeWrapper::new(Box::new(item), ImplItemTag)
     }
     fn flatten_outputs(items: impl Iterator<Item = Self::OutputTy>) -> Self::OutputTy {
         items.flatten().collect()
@@ -1503,8 +1500,8 @@ impl InvocationCollectorNode for AstNodeWrapper<P<ast::AssocItem>, ImplItemTag>
 }
 
 struct TraitImplItemTag;
-impl InvocationCollectorNode for AstNodeWrapper<P<ast::AssocItem>, TraitImplItemTag> {
-    type OutputTy = SmallVec<[P<ast::AssocItem>; 1]>;
+impl InvocationCollectorNode for AstNodeWrapper<Box<ast::AssocItem>, TraitImplItemTag> {
+    type OutputTy = SmallVec<[Box<ast::AssocItem>; 1]>;
     type ItemKind = AssocItemKind;
     const KIND: AstFragmentKind = AstFragmentKind::TraitImplItems;
     fn to_annotatable(self) -> Annotatable {
@@ -1519,7 +1516,7 @@ impl InvocationCollectorNode for AstNodeWrapper<P<ast::AssocItem>, TraitImplItem
     fn is_mac_call(&self) -> bool {
         matches!(self.wrapped.kind, AssocItemKind::MacCall(..))
     }
-    fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
+    fn take_mac_call(self) -> (Box<ast::MacCall>, ast::AttrVec, AddSemicolon) {
         let item = self.wrapped;
         match item.kind {
             AssocItemKind::MacCall(mac) => (mac, item.attrs, AddSemicolon::No),
@@ -1536,14 +1533,14 @@ impl InvocationCollectorNode for AstNodeWrapper<P<ast::AssocItem>, TraitImplItem
         AssocItemKind::Delegation(deleg)
     }
     fn from_item(item: ast::Item<Self::ItemKind>) -> Self {
-        AstNodeWrapper::new(P(item), TraitImplItemTag)
+        AstNodeWrapper::new(Box::new(item), TraitImplItemTag)
     }
     fn flatten_outputs(items: impl Iterator<Item = Self::OutputTy>) -> Self::OutputTy {
         items.flatten().collect()
     }
 }
 
-impl InvocationCollectorNode for P<ast::ForeignItem> {
+impl InvocationCollectorNode for Box<ast::ForeignItem> {
     const KIND: AstFragmentKind = AstFragmentKind::ForeignItems;
     fn to_annotatable(self) -> Annotatable {
         Annotatable::ForeignItem(self)
@@ -1557,7 +1554,7 @@ impl InvocationCollectorNode for P<ast::ForeignItem> {
     fn is_mac_call(&self) -> bool {
         matches!(self.kind, ForeignItemKind::MacCall(..))
     }
-    fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
+    fn take_mac_call(self) -> (Box<ast::MacCall>, ast::AttrVec, AddSemicolon) {
         match self.kind {
             ForeignItemKind::MacCall(mac) => (mac, self.attrs, AddSemicolon::No),
             _ => unreachable!(),
@@ -1672,7 +1669,7 @@ impl InvocationCollectorNode for ast::Arm {
 impl InvocationCollectorNode for ast::Stmt {
     const KIND: AstFragmentKind = AstFragmentKind::Stmts;
     fn to_annotatable(self) -> Annotatable {
-        Annotatable::Stmt(P(self))
+        Annotatable::Stmt(Box::new(self))
     }
     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
         fragment.make_stmts()
@@ -1689,7 +1686,7 @@ impl InvocationCollectorNode for ast::Stmt {
             StmtKind::Let(..) | StmtKind::Empty => false,
         }
     }
-    fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
+    fn take_mac_call(self) -> (Box<ast::MacCall>, ast::AttrVec, AddSemicolon) {
         // We pull macro invocations (both attributes and fn-like macro calls) out of their
         // `StmtKind`s and treat them as statement macro invocations, not as items or expressions.
         let (add_semicolon, mac, attrs) = match self.kind {
@@ -1726,7 +1723,7 @@ impl InvocationCollectorNode for ast::Stmt {
         ItemKind::Delegation(deleg)
     }
     fn from_item(item: ast::Item<Self::ItemKind>) -> Self {
-        ast::Stmt { id: ast::DUMMY_NODE_ID, span: item.span, kind: StmtKind::Item(P(item)) }
+        ast::Stmt { id: ast::DUMMY_NODE_ID, span: item.span, kind: StmtKind::Item(Box::new(item)) }
     }
     fn flatten_outputs(items: impl Iterator<Item = Self::OutputTy>) -> Self::OutputTy {
         items.flatten().collect()
@@ -1769,7 +1766,7 @@ impl InvocationCollectorNode for ast::Crate {
 }
 
 impl InvocationCollectorNode for ast::Ty {
-    type OutputTy = P<ast::Ty>;
+    type OutputTy = Box<ast::Ty>;
     const KIND: AstFragmentKind = AstFragmentKind::Ty;
     fn to_annotatable(self) -> Annotatable {
         unreachable!()
@@ -1793,7 +1790,7 @@ impl InvocationCollectorNode for ast::Ty {
     fn is_mac_call(&self) -> bool {
         matches!(self.kind, ast::TyKind::MacCall(..))
     }
-    fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
+    fn take_mac_call(self) -> (Box<ast::MacCall>, ast::AttrVec, AddSemicolon) {
         match self.kind {
             TyKind::MacCall(mac) => (mac, AttrVec::new(), AddSemicolon::No),
             _ => unreachable!(),
@@ -1802,7 +1799,7 @@ impl InvocationCollectorNode for ast::Ty {
 }
 
 impl InvocationCollectorNode for ast::Pat {
-    type OutputTy = P<ast::Pat>;
+    type OutputTy = Box<ast::Pat>;
     const KIND: AstFragmentKind = AstFragmentKind::Pat;
     fn to_annotatable(self) -> Annotatable {
         unreachable!()
@@ -1816,7 +1813,7 @@ impl InvocationCollectorNode for ast::Pat {
     fn is_mac_call(&self) -> bool {
         matches!(self.kind, PatKind::MacCall(..))
     }
-    fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
+    fn take_mac_call(self) -> (Box<ast::MacCall>, ast::AttrVec, AddSemicolon) {
         match self.kind {
             PatKind::MacCall(mac) => (mac, AttrVec::new(), AddSemicolon::No),
             _ => unreachable!(),
@@ -1825,10 +1822,10 @@ impl InvocationCollectorNode for ast::Pat {
 }
 
 impl InvocationCollectorNode for ast::Expr {
-    type OutputTy = P<ast::Expr>;
+    type OutputTy = Box<ast::Expr>;
     const KIND: AstFragmentKind = AstFragmentKind::Expr;
     fn to_annotatable(self) -> Annotatable {
-        Annotatable::Expr(P(self))
+        Annotatable::Expr(Box::new(self))
     }
     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
         fragment.make_expr()
@@ -1842,7 +1839,7 @@ impl InvocationCollectorNode for ast::Expr {
     fn is_mac_call(&self) -> bool {
         matches!(self.kind, ExprKind::MacCall(..))
     }
-    fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
+    fn take_mac_call(self) -> (Box<ast::MacCall>, ast::AttrVec, AddSemicolon) {
         match self.kind {
             ExprKind::MacCall(mac) => (mac, self.attrs, AddSemicolon::No),
             _ => unreachable!(),
@@ -1851,8 +1848,8 @@ impl InvocationCollectorNode for ast::Expr {
 }
 
 struct OptExprTag;
-impl InvocationCollectorNode for AstNodeWrapper<P<ast::Expr>, OptExprTag> {
-    type OutputTy = Option<P<ast::Expr>>;
+impl InvocationCollectorNode for AstNodeWrapper<Box<ast::Expr>, OptExprTag> {
+    type OutputTy = Option<Box<ast::Expr>>;
     const KIND: AstFragmentKind = AstFragmentKind::OptExpr;
     fn to_annotatable(self) -> Annotatable {
         Annotatable::Expr(self.wrapped)
@@ -1867,7 +1864,7 @@ impl InvocationCollectorNode for AstNodeWrapper<P<ast::Expr>, OptExprTag> {
     fn is_mac_call(&self) -> bool {
         matches!(self.wrapped.kind, ast::ExprKind::MacCall(..))
     }
-    fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
+    fn take_mac_call(self) -> (Box<ast::MacCall>, ast::AttrVec, AddSemicolon) {
         let node = self.wrapped;
         match node.kind {
             ExprKind::MacCall(mac) => (mac, node.attrs, AddSemicolon::No),
@@ -1884,13 +1881,13 @@ impl InvocationCollectorNode for AstNodeWrapper<P<ast::Expr>, OptExprTag> {
 struct MethodReceiverTag;
 
 impl InvocationCollectorNode for AstNodeWrapper<ast::Expr, MethodReceiverTag> {
-    type OutputTy = AstNodeWrapper<P<ast::Expr>, MethodReceiverTag>;
+    type OutputTy = AstNodeWrapper<Box<ast::Expr>, MethodReceiverTag>;
     const KIND: AstFragmentKind = AstFragmentKind::MethodReceiverExpr;
     fn descr() -> &'static str {
         "an expression"
     }
     fn to_annotatable(self) -> Annotatable {
-        Annotatable::Expr(P(self.wrapped))
+        Annotatable::Expr(Box::new(self.wrapped))
     }
     fn fragment_to_output(fragment: AstFragment) -> Self::OutputTy {
         AstNodeWrapper::new(fragment.make_method_receiver_expr(), MethodReceiverTag)
@@ -1901,7 +1898,7 @@ impl InvocationCollectorNode for AstNodeWrapper<ast::Expr, MethodReceiverTag> {
     fn is_mac_call(&self) -> bool {
         matches!(self.wrapped.kind, ast::ExprKind::MacCall(..))
     }
-    fn take_mac_call(self) -> (P<ast::MacCall>, ast::AttrVec, AddSemicolon) {
+    fn take_mac_call(self) -> (Box<ast::MacCall>, ast::AttrVec, AddSemicolon) {
         let node = self.wrapped;
         match node.kind {
             ExprKind::MacCall(mac) => (mac, node.attrs, AddSemicolon::No),
@@ -2038,7 +2035,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
         placeholder(fragment_kind, NodeId::placeholder_from_expn_id(expn_id), vis)
     }
 
-    fn collect_bang(&mut self, mac: P<ast::MacCall>, kind: AstFragmentKind) -> AstFragment {
+    fn collect_bang(&mut self, mac: Box<ast::MacCall>, kind: AstFragmentKind) -> AstFragment {
         // cache the macro call span so that it can be
         // easily adjusted for incremental compilation
         let span = mac.span();
@@ -2056,7 +2053,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
 
     fn collect_glob_delegation(
         &mut self,
-        item: P<ast::AssocItem>,
+        item: Box<ast::AssocItem>,
         of_trait: bool,
         kind: AstFragmentKind,
     ) -> AstFragment {
@@ -2157,6 +2154,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                             attr_name,
                             macro_name: pprust::path_to_string(&call.path),
                             invoc_span: call.path.span,
+                            attr_span: attr.span,
                         },
                     );
                 }
@@ -2328,15 +2326,15 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
 }
 
 impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
-    fn flat_map_item(&mut self, node: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
+    fn flat_map_item(&mut self, node: Box<ast::Item>) -> SmallVec<[Box<ast::Item>; 1]> {
         self.flat_map_node(node)
     }
 
     fn flat_map_assoc_item(
         &mut self,
-        node: P<ast::AssocItem>,
+        node: Box<ast::AssocItem>,
         ctxt: AssocCtxt,
-    ) -> SmallVec<[P<ast::AssocItem>; 1]> {
+    ) -> SmallVec<[Box<ast::AssocItem>; 1]> {
         match ctxt {
             AssocCtxt::Trait => self.flat_map_node(AstNodeWrapper::new(node, TraitItemTag)),
             AssocCtxt::Impl { of_trait: false } => {
@@ -2350,8 +2348,8 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
 
     fn flat_map_foreign_item(
         &mut self,
-        node: P<ast::ForeignItem>,
-    ) -> SmallVec<[P<ast::ForeignItem>; 1]> {
+        node: Box<ast::ForeignItem>,
+    ) -> SmallVec<[Box<ast::ForeignItem>; 1]> {
         self.flat_map_node(node)
     }
 
@@ -2446,7 +2444,7 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
         self.visit_node(AstNodeWrapper::from_mut(node, MethodReceiverTag))
     }
 
-    fn filter_map_expr(&mut self, node: P<ast::Expr>) -> Option<P<ast::Expr>> {
+    fn filter_map_expr(&mut self, node: Box<ast::Expr>) -> Option<Box<ast::Expr>> {
         self.flat_map_node(AstNodeWrapper::new(node, OptExprTag))
     }
 
diff --git a/compiler/rustc_expand/src/mbe/diagnostics.rs b/compiler/rustc_expand/src/mbe/diagnostics.rs
index 7a280d671f4..80433b7be91 100644
--- a/compiler/rustc_expand/src/mbe/diagnostics.rs
+++ b/compiler/rustc_expand/src/mbe/diagnostics.rs
@@ -7,29 +7,40 @@ use rustc_macros::Subdiagnostic;
 use rustc_parse::parser::{Parser, Recovery, token_descr};
 use rustc_session::parse::ParseSess;
 use rustc_span::source_map::SourceMap;
-use rustc_span::{ErrorGuaranteed, Ident, Span};
+use rustc_span::{DUMMY_SP, ErrorGuaranteed, Ident, Span};
 use tracing::debug;
 
 use super::macro_rules::{MacroRule, NoopTracker, parser_from_cx};
 use crate::expand::{AstFragmentKind, parse_ast_fragment};
 use crate::mbe::macro_parser::ParseResult::*;
 use crate::mbe::macro_parser::{MatcherLoc, NamedParseResult, TtParser};
-use crate::mbe::macro_rules::{Tracker, try_match_macro};
+use crate::mbe::macro_rules::{Tracker, try_match_macro, try_match_macro_attr};
 
 pub(super) fn failed_to_match_macro(
     psess: &ParseSess,
     sp: Span,
     def_span: Span,
     name: Ident,
-    arg: TokenStream,
+    attr_args: Option<&TokenStream>,
+    body: &TokenStream,
     rules: &[MacroRule],
 ) -> (Span, ErrorGuaranteed) {
     debug!("failed to match macro");
+    let def_head_span = if !def_span.is_dummy() && !psess.source_map().is_imported(def_span) {
+        psess.source_map().guess_head_span(def_span)
+    } else {
+        DUMMY_SP
+    };
+
     // An error occurred, try the expansion again, tracking the expansion closely for better
     // diagnostics.
     let mut tracker = CollectTrackerAndEmitter::new(psess.dcx(), sp);
 
-    let try_success_result = try_match_macro(psess, name, &arg, rules, &mut tracker);
+    let try_success_result = if let Some(attr_args) = attr_args {
+        try_match_macro_attr(psess, name, attr_args, body, rules, &mut tracker)
+    } else {
+        try_match_macro(psess, name, body, rules, &mut tracker)
+    };
 
     if try_success_result.is_ok() {
         // Nonterminal parser recovery might turn failed matches into successful ones,
@@ -54,8 +65,8 @@ pub(super) fn failed_to_match_macro(
 
     let mut err = psess.dcx().struct_span_err(span, parse_failure_msg(&token, None));
     err.span_label(span, label);
-    if !def_span.is_dummy() && !psess.source_map().is_imported(def_span) {
-        err.span_label(psess.source_map().guess_head_span(def_span), "when calling this macro");
+    if !def_head_span.is_dummy() {
+        err.span_label(def_head_span, "when calling this macro");
     }
 
     annotate_doc_comment(&mut err, psess.source_map(), span);
@@ -79,13 +90,16 @@ pub(super) fn failed_to_match_macro(
     }
 
     // Check whether there's a missing comma in this macro call, like `println!("{}" a);`
-    if let Some((arg, comma_span)) = arg.add_comma() {
+    if attr_args.is_none()
+        && let Some((body, comma_span)) = body.add_comma()
+    {
         for rule in rules {
-            let parser = parser_from_cx(psess, arg.clone(), Recovery::Allowed);
+            let MacroRule::Func { lhs, .. } = rule else { continue };
+            let parser = parser_from_cx(psess, body.clone(), Recovery::Allowed);
             let mut tt_parser = TtParser::new(name);
 
             if let Success(_) =
-                tt_parser.parse_tt(&mut Cow::Borrowed(&parser), &rule.lhs, &mut NoopTracker)
+                tt_parser.parse_tt(&mut Cow::Borrowed(&parser), lhs, &mut NoopTracker)
             {
                 if comma_span.is_dummy() {
                     err.note("you might be missing a comma");
@@ -116,13 +130,13 @@ struct CollectTrackerAndEmitter<'dcx, 'matcher> {
 
 struct BestFailure {
     token: Token,
-    position_in_tokenstream: u32,
+    position_in_tokenstream: (bool, u32),
     msg: &'static str,
     remaining_matcher: MatcherLoc,
 }
 
 impl BestFailure {
-    fn is_better_position(&self, position: u32) -> bool {
+    fn is_better_position(&self, position: (bool, u32)) -> bool {
         position > self.position_in_tokenstream
     }
 }
@@ -142,7 +156,7 @@ impl<'dcx, 'matcher> Tracker<'matcher> for CollectTrackerAndEmitter<'dcx, 'match
         }
     }
 
-    fn after_arm(&mut self, result: &NamedParseResult<Self::Failure>) {
+    fn after_arm(&mut self, in_body: bool, result: &NamedParseResult<Self::Failure>) {
         match result {
             Success(_) => {
                 // Nonterminal parser recovery might turn failed matches into successful ones,
@@ -155,14 +169,15 @@ impl<'dcx, 'matcher> Tracker<'matcher> for CollectTrackerAndEmitter<'dcx, 'match
             Failure((token, approx_position, msg)) => {
                 debug!(?token, ?msg, "a new failure of an arm");
 
+                let position_in_tokenstream = (in_body, *approx_position);
                 if self
                     .best_failure
                     .as_ref()
-                    .is_none_or(|failure| failure.is_better_position(*approx_position))
+                    .is_none_or(|failure| failure.is_better_position(position_in_tokenstream))
                 {
                     self.best_failure = Some(BestFailure {
                         token: *token,
-                        position_in_tokenstream: *approx_position,
+                        position_in_tokenstream,
                         msg,
                         remaining_matcher: self
                             .remaining_matcher
diff --git a/compiler/rustc_expand/src/mbe/macro_check.rs b/compiler/rustc_expand/src/mbe/macro_check.rs
index bbdff866feb..faeae1f494e 100644
--- a/compiler/rustc_expand/src/mbe/macro_check.rs
+++ b/compiler/rustc_expand/src/mbe/macro_check.rs
@@ -193,15 +193,19 @@ struct MacroState<'a> {
 /// Arguments:
 /// - `psess` is used to emit diagnostics and lints
 /// - `node_id` is used to emit lints
-/// - `lhs` and `rhs` represent the rule
+/// - `args`, `lhs`, and `rhs` represent the rule
 pub(super) fn check_meta_variables(
     psess: &ParseSess,
     node_id: NodeId,
+    args: Option<&TokenTree>,
     lhs: &TokenTree,
     rhs: &TokenTree,
 ) -> Result<(), ErrorGuaranteed> {
     let mut guar = None;
     let mut binders = Binders::default();
+    if let Some(args) = args {
+        check_binders(psess, node_id, args, &Stack::Empty, &mut binders, &Stack::Empty, &mut guar);
+    }
     check_binders(psess, node_id, lhs, &Stack::Empty, &mut binders, &Stack::Empty, &mut guar);
     check_occurrences(psess, node_id, rhs, &Stack::Empty, &binders, &Stack::Empty, &mut guar);
     guar.map_or(Ok(()), Err)
@@ -353,10 +357,10 @@ enum NestedMacroState {
     /// The token `macro_rules` was processed.
     MacroRules,
     /// The tokens `macro_rules!` were processed.
-    MacroRulesNot,
+    MacroRulesBang,
     /// The tokens `macro_rules!` followed by a name were processed. The name may be either directly
     /// an identifier or a meta-variable (that hopefully would be instantiated by an identifier).
-    MacroRulesNotName,
+    MacroRulesBangName,
     /// The keyword `macro` was processed.
     Macro,
     /// The keyword `macro` followed by a name was processed.
@@ -404,24 +408,24 @@ fn check_nested_occurrences(
                 NestedMacroState::MacroRules,
                 &TokenTree::Token(Token { kind: TokenKind::Bang, .. }),
             ) => {
-                state = NestedMacroState::MacroRulesNot;
+                state = NestedMacroState::MacroRulesBang;
             }
             (
-                NestedMacroState::MacroRulesNot,
+                NestedMacroState::MacroRulesBang,
                 &TokenTree::Token(Token { kind: TokenKind::Ident(..), .. }),
             ) => {
-                state = NestedMacroState::MacroRulesNotName;
+                state = NestedMacroState::MacroRulesBangName;
             }
-            (NestedMacroState::MacroRulesNot, &TokenTree::MetaVar(..)) => {
-                state = NestedMacroState::MacroRulesNotName;
+            (NestedMacroState::MacroRulesBang, &TokenTree::MetaVar(..)) => {
+                state = NestedMacroState::MacroRulesBangName;
                 // We check that the meta-variable is correctly used.
                 check_occurrences(psess, node_id, tt, macros, binders, ops, guar);
             }
-            (NestedMacroState::MacroRulesNotName, TokenTree::Delimited(.., del))
+            (NestedMacroState::MacroRulesBangName, TokenTree::Delimited(.., del))
             | (NestedMacroState::MacroName, TokenTree::Delimited(.., del))
                 if del.delim == Delimiter::Brace =>
             {
-                let macro_rules = state == NestedMacroState::MacroRulesNotName;
+                let macro_rules = state == NestedMacroState::MacroRulesBangName;
                 state = NestedMacroState::Empty;
                 let rest =
                     check_nested_macro(psess, node_id, macro_rules, &del.tts, &nested_macros, guar);
diff --git a/compiler/rustc_expand/src/mbe/macro_rules.rs b/compiler/rustc_expand/src/mbe/macro_rules.rs
index 52d38c35f98..334f57f9d62 100644
--- a/compiler/rustc_expand/src/mbe/macro_rules.rs
+++ b/compiler/rustc_expand/src/mbe/macro_rules.rs
@@ -6,15 +6,16 @@ use std::{mem, slice};
 use ast::token::IdentIsRaw;
 use rustc_ast::token::NtPatKind::*;
 use rustc_ast::token::TokenKind::*;
-use rustc_ast::token::{self, NonterminalKind, Token, TokenKind};
-use rustc_ast::tokenstream::{DelimSpan, TokenStream};
+use rustc_ast::token::{self, Delimiter, NonterminalKind, Token, TokenKind};
+use rustc_ast::tokenstream::{self, DelimSpan, TokenStream};
 use rustc_ast::{self as ast, DUMMY_NODE_ID, NodeId};
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
-use rustc_errors::{Applicability, Diag, ErrorGuaranteed};
+use rustc_errors::{Applicability, Diag, ErrorGuaranteed, MultiSpan};
 use rustc_feature::Features;
 use rustc_hir as hir;
 use rustc_hir::attrs::AttributeKind;
+use rustc_hir::def::MacroKinds;
 use rustc_hir::find_attr;
 use rustc_lint_defs::BuiltinLintDiag;
 use rustc_lint_defs::builtin::{
@@ -23,23 +24,26 @@ use rustc_lint_defs::builtin::{
 use rustc_parse::exp;
 use rustc_parse::parser::{Parser, Recovery};
 use rustc_session::Session;
-use rustc_session::parse::ParseSess;
+use rustc_session::parse::{ParseSess, feature_err};
 use rustc_span::edition::Edition;
 use rustc_span::hygiene::Transparency;
 use rustc_span::{Ident, Span, kw, sym};
 use tracing::{debug, instrument, trace, trace_span};
 
+use super::diagnostics::failed_to_match_macro;
 use super::macro_parser::{NamedMatches, NamedParseResult};
 use super::{SequenceRepetition, diagnostics};
 use crate::base::{
-    DummyResult, ExpandResult, ExtCtxt, MacResult, MacroExpanderResult, SyntaxExtension,
-    SyntaxExtensionKind, TTMacroExpander,
+    AttrProcMacro, DummyResult, ExpandResult, ExtCtxt, MacResult, MacroExpanderResult,
+    SyntaxExtension, SyntaxExtensionKind, TTMacroExpander,
 };
+use crate::errors;
 use crate::expand::{AstFragment, AstFragmentKind, ensure_complete_parse, parse_ast_fragment};
+use crate::mbe::macro_check::check_meta_variables;
 use crate::mbe::macro_parser::{Error, ErrorReported, Failure, MatcherLoc, Success, TtParser};
 use crate::mbe::quoted::{RulePart, parse_one_tt};
 use crate::mbe::transcribe::transcribe;
-use crate::mbe::{self, KleeneOp, macro_check};
+use crate::mbe::{self, KleeneOp};
 
 pub(crate) struct ParserAnyMacro<'a> {
     parser: Parser<'a>,
@@ -123,10 +127,17 @@ impl<'a> ParserAnyMacro<'a> {
     }
 }
 
-pub(super) struct MacroRule {
-    pub(super) lhs: Vec<MatcherLoc>,
-    lhs_span: Span,
-    rhs: mbe::TokenTree,
+pub(super) enum MacroRule {
+    /// A function-style rule, for use with `m!()`
+    Func { lhs: Vec<MatcherLoc>, lhs_span: Span, rhs: mbe::TokenTree },
+    /// An attr rule, for use with `#[m]`
+    Attr {
+        args: Vec<MatcherLoc>,
+        args_span: Span,
+        body: Vec<MatcherLoc>,
+        body_span: Span,
+        rhs: mbe::TokenTree,
+    },
 }
 
 pub struct MacroRulesMacroExpander {
@@ -134,14 +145,24 @@ pub struct MacroRulesMacroExpander {
     name: Ident,
     span: Span,
     transparency: Transparency,
+    kinds: MacroKinds,
     rules: Vec<MacroRule>,
 }
 
 impl MacroRulesMacroExpander {
-    pub fn get_unused_rule(&self, rule_i: usize) -> Option<(&Ident, Span)> {
+    pub fn get_unused_rule(&self, rule_i: usize) -> Option<(&Ident, MultiSpan)> {
         // If the rhs contains an invocation like `compile_error!`, don't report it as unused.
-        let rule = &self.rules[rule_i];
-        if has_compile_error_macro(&rule.rhs) { None } else { Some((&self.name, rule.lhs_span)) }
+        let (span, rhs) = match self.rules[rule_i] {
+            MacroRule::Func { lhs_span, ref rhs, .. } => (MultiSpan::from_span(lhs_span), rhs),
+            MacroRule::Attr { args_span, body_span, ref rhs, .. } => {
+                (MultiSpan::from_spans(vec![args_span, body_span]), rhs)
+            }
+        };
+        if has_compile_error_macro(rhs) { None } else { Some((&self.name, span)) }
+    }
+
+    pub fn kinds(&self) -> MacroKinds {
+        self.kinds
     }
 }
 
@@ -165,6 +186,28 @@ impl TTMacroExpander for MacroRulesMacroExpander {
     }
 }
 
+impl AttrProcMacro for MacroRulesMacroExpander {
+    fn expand(
+        &self,
+        cx: &mut ExtCtxt<'_>,
+        sp: Span,
+        args: TokenStream,
+        body: TokenStream,
+    ) -> Result<TokenStream, ErrorGuaranteed> {
+        expand_macro_attr(
+            cx,
+            sp,
+            self.span,
+            self.node_id,
+            self.name,
+            self.transparency,
+            args,
+            body,
+            &self.rules,
+        )
+    }
+}
+
 struct DummyExpander(ErrorGuaranteed);
 
 impl TTMacroExpander for DummyExpander {
@@ -197,7 +240,7 @@ pub(super) trait Tracker<'matcher> {
 
     /// This is called after an arm has been parsed, either successfully or unsuccessfully. When
     /// this is called, `before_match_loc` was called at least once (with a `MatcherLoc::Eof`).
-    fn after_arm(&mut self, _result: &NamedParseResult<Self::Failure>) {}
+    fn after_arm(&mut self, _in_body: bool, _result: &NamedParseResult<Self::Failure>) {}
 
     /// For tracing.
     fn description() -> &'static str;
@@ -245,14 +288,17 @@ fn expand_macro<'cx>(
 
     match try_success_result {
         Ok((rule_index, rule, named_matches)) => {
-            let mbe::TokenTree::Delimited(rhs_span, _, ref rhs) = rule.rhs else {
+            let MacroRule::Func { rhs, .. } = rule else {
+                panic!("try_match_macro returned non-func rule");
+            };
+            let mbe::TokenTree::Delimited(rhs_span, _, rhs) = rhs else {
                 cx.dcx().span_bug(sp, "malformed macro rhs");
             };
-            let arm_span = rule.rhs.span();
+            let arm_span = rhs_span.entire();
 
             // rhs has holes ( `$id` and `$(...)` that need filled)
             let id = cx.current_expansion.id;
-            let tts = match transcribe(psess, &named_matches, rhs, rhs_span, transparency, id) {
+            let tts = match transcribe(psess, &named_matches, rhs, *rhs_span, transparency, id) {
                 Ok(tts) => tts,
                 Err(err) => {
                     let guar = err.emit();
@@ -280,13 +326,76 @@ fn expand_macro<'cx>(
         Err(CanRetry::Yes) => {
             // Retry and emit a better error.
             let (span, guar) =
-                diagnostics::failed_to_match_macro(cx.psess(), sp, def_span, name, arg, rules);
+                failed_to_match_macro(cx.psess(), sp, def_span, name, None, &arg, rules);
             cx.macro_error_and_trace_macros_diag();
             DummyResult::any(span, guar)
         }
     }
 }
 
+/// Expands the rules based macro defined by `rules` for a given attribute `args` and `body`.
+#[instrument(skip(cx, transparency, args, body, rules))]
+fn expand_macro_attr(
+    cx: &mut ExtCtxt<'_>,
+    sp: Span,
+    def_span: Span,
+    node_id: NodeId,
+    name: Ident,
+    transparency: Transparency,
+    args: TokenStream,
+    body: TokenStream,
+    rules: &[MacroRule],
+) -> Result<TokenStream, ErrorGuaranteed> {
+    let psess = &cx.sess.psess;
+    // Macros defined in the current crate have a real node id,
+    // whereas macros from an external crate have a dummy id.
+    let is_local = node_id != DUMMY_NODE_ID;
+
+    if cx.trace_macros() {
+        let msg = format!(
+            "expanding `#[{name}({})] {}`",
+            pprust::tts_to_string(&args),
+            pprust::tts_to_string(&body),
+        );
+        trace_macros_note(&mut cx.expansions, sp, msg);
+    }
+
+    // Track nothing for the best performance.
+    match try_match_macro_attr(psess, name, &args, &body, rules, &mut NoopTracker) {
+        Ok((i, rule, named_matches)) => {
+            let MacroRule::Attr { rhs, .. } = rule else {
+                panic!("try_macro_match_attr returned non-attr rule");
+            };
+            let mbe::TokenTree::Delimited(rhs_span, _, rhs) = rhs else {
+                cx.dcx().span_bug(sp, "malformed macro rhs");
+            };
+
+            let id = cx.current_expansion.id;
+            let tts = transcribe(psess, &named_matches, rhs, *rhs_span, transparency, id)
+                .map_err(|e| e.emit())?;
+
+            if cx.trace_macros() {
+                let msg = format!("to `{}`", pprust::tts_to_string(&tts));
+                trace_macros_note(&mut cx.expansions, sp, msg);
+            }
+
+            if is_local {
+                cx.resolver.record_macro_rule_usage(node_id, i);
+            }
+
+            Ok(tts)
+        }
+        Err(CanRetry::No(guar)) => Err(guar),
+        Err(CanRetry::Yes) => {
+            // Retry and emit a better error.
+            let (_, guar) =
+                failed_to_match_macro(cx.psess(), sp, def_span, name, Some(&args), &body, rules);
+            cx.trace_macros_diag();
+            Err(guar)
+        }
+    }
+}
+
 pub(super) enum CanRetry {
     Yes,
     /// We are not allowed to retry macro expansion as a fatal error has been emitted already.
@@ -327,6 +436,7 @@ pub(super) fn try_match_macro<'matcher, T: Tracker<'matcher>>(
     // Try each arm's matchers.
     let mut tt_parser = TtParser::new(name);
     for (i, rule) in rules.iter().enumerate() {
+        let MacroRule::Func { lhs, .. } = rule else { continue };
         let _tracing_span = trace_span!("Matching arm", %i);
 
         // Take a snapshot of the state of pre-expansion gating at this point.
@@ -335,9 +445,9 @@ pub(super) fn try_match_macro<'matcher, T: Tracker<'matcher>>(
         // are not recorded. On the first `Success(..)`ful matcher, the spans are merged.
         let mut gated_spans_snapshot = mem::take(&mut *psess.gated_spans.spans.borrow_mut());
 
-        let result = tt_parser.parse_tt(&mut Cow::Borrowed(&parser), &rule.lhs, track);
+        let result = tt_parser.parse_tt(&mut Cow::Borrowed(&parser), lhs, track);
 
-        track.after_arm(&result);
+        track.after_arm(true, &result);
 
         match result {
             Success(named_matches) => {
@@ -372,6 +482,60 @@ pub(super) fn try_match_macro<'matcher, T: Tracker<'matcher>>(
     Err(CanRetry::Yes)
 }
 
+/// Try expanding the macro attribute. Returns the index of the successful arm and its
+/// named_matches if it was successful, and nothing if it failed. On failure, it's the caller's job
+/// to use `track` accordingly to record all errors correctly.
+#[instrument(level = "debug", skip(psess, attr_args, attr_body, rules, track), fields(tracking = %T::description()))]
+pub(super) fn try_match_macro_attr<'matcher, T: Tracker<'matcher>>(
+    psess: &ParseSess,
+    name: Ident,
+    attr_args: &TokenStream,
+    attr_body: &TokenStream,
+    rules: &'matcher [MacroRule],
+    track: &mut T,
+) -> Result<(usize, &'matcher MacroRule, NamedMatches), CanRetry> {
+    // This uses the same strategy as `try_match_macro`
+    let args_parser = parser_from_cx(psess, attr_args.clone(), T::recovery());
+    let body_parser = parser_from_cx(psess, attr_body.clone(), T::recovery());
+    let mut tt_parser = TtParser::new(name);
+    for (i, rule) in rules.iter().enumerate() {
+        let MacroRule::Attr { args, body, .. } = rule else { continue };
+
+        let mut gated_spans_snapshot = mem::take(&mut *psess.gated_spans.spans.borrow_mut());
+
+        let result = tt_parser.parse_tt(&mut Cow::Borrowed(&args_parser), args, track);
+        track.after_arm(false, &result);
+
+        let mut named_matches = match result {
+            Success(named_matches) => named_matches,
+            Failure(_) => {
+                mem::swap(&mut gated_spans_snapshot, &mut psess.gated_spans.spans.borrow_mut());
+                continue;
+            }
+            Error(_, _) => return Err(CanRetry::Yes),
+            ErrorReported(guar) => return Err(CanRetry::No(guar)),
+        };
+
+        let result = tt_parser.parse_tt(&mut Cow::Borrowed(&body_parser), body, track);
+        track.after_arm(true, &result);
+
+        match result {
+            Success(body_named_matches) => {
+                psess.gated_spans.merge(gated_spans_snapshot);
+                named_matches.extend(body_named_matches);
+                return Ok((i, rule, named_matches));
+            }
+            Failure(_) => {
+                mem::swap(&mut gated_spans_snapshot, &mut psess.gated_spans.spans.borrow_mut())
+            }
+            Error(_, _) => return Err(CanRetry::Yes),
+            ErrorReported(guar) => return Err(CanRetry::No(guar)),
+        }
+    }
+
+    Err(CanRetry::Yes)
+}
+
 /// Converts a macro item into a syntax extension.
 pub fn compile_declarative_macro(
     sess: &Session,
@@ -383,12 +547,12 @@ pub fn compile_declarative_macro(
     node_id: NodeId,
     edition: Edition,
 ) -> (SyntaxExtension, usize) {
-    let mk_syn_ext = |expander| {
-        let kind = SyntaxExtensionKind::LegacyBang(expander);
+    let mk_syn_ext = |kind| {
         let is_local = is_defined_in_current_crate(node_id);
         SyntaxExtension::new(sess, kind, span, Vec::new(), edition, ident.name, attrs, is_local)
     };
-    let dummy_syn_ext = |guar| (mk_syn_ext(Arc::new(DummyExpander(guar))), 0);
+    let dummy_syn_ext =
+        |guar| (mk_syn_ext(SyntaxExtensionKind::LegacyBang(Arc::new(DummyExpander(guar)))), 0);
 
     let macro_rules = macro_def.macro_rules;
     let exp_sep = if macro_rules { exp!(Semi) } else { exp!(Comma) };
@@ -401,9 +565,31 @@ pub fn compile_declarative_macro(
     let mut guar = None;
     let mut check_emission = |ret: Result<(), ErrorGuaranteed>| guar = guar.or(ret.err());
 
+    let mut kinds = MacroKinds::empty();
     let mut rules = Vec::new();
 
     while p.token != token::Eof {
+        let args = if p.eat_keyword_noexpect(sym::attr) {
+            kinds |= MacroKinds::ATTR;
+            if !features.macro_attr() {
+                feature_err(sess, sym::macro_attr, span, "`macro_rules!` attributes are unstable")
+                    .emit();
+            }
+            if let Some(guar) = check_no_eof(sess, &p, "expected macro attr args") {
+                return dummy_syn_ext(guar);
+            }
+            let args = p.parse_token_tree();
+            check_args_parens(sess, &args);
+            let args = parse_one_tt(args, RulePart::Pattern, sess, node_id, features, edition);
+            check_emission(check_lhs(sess, node_id, &args));
+            if let Some(guar) = check_no_eof(sess, &p, "expected macro attr body") {
+                return dummy_syn_ext(guar);
+            }
+            Some(args)
+        } else {
+            kinds |= MacroKinds::BANG;
+            None
+        };
         let lhs_tt = p.parse_token_tree();
         let lhs_tt = parse_one_tt(lhs_tt, RulePart::Pattern, sess, node_id, features, edition);
         check_emission(check_lhs(sess, node_id, &lhs_tt));
@@ -416,7 +602,7 @@ pub fn compile_declarative_macro(
         let rhs_tt = p.parse_token_tree();
         let rhs_tt = parse_one_tt(rhs_tt, RulePart::Body, sess, node_id, features, edition);
         check_emission(check_rhs(sess, &rhs_tt));
-        check_emission(macro_check::check_meta_variables(&sess.psess, node_id, &lhs_tt, &rhs_tt));
+        check_emission(check_meta_variables(&sess.psess, node_id, args.as_ref(), &lhs_tt, &rhs_tt));
         let lhs_span = lhs_tt.span();
         // Convert the lhs into `MatcherLoc` form, which is better for doing the
         // actual matching.
@@ -425,7 +611,17 @@ pub fn compile_declarative_macro(
         } else {
             return dummy_syn_ext(guar.unwrap());
         };
-        rules.push(MacroRule { lhs, lhs_span, rhs: rhs_tt });
+        if let Some(args) = args {
+            let args_span = args.span();
+            let mbe::TokenTree::Delimited(.., delimited) = args else {
+                return dummy_syn_ext(guar.unwrap());
+            };
+            let args = mbe::macro_parser::compute_locs(&delimited.tts);
+            let body_span = lhs_span;
+            rules.push(MacroRule::Attr { args, args_span, body: lhs, body_span, rhs: rhs_tt });
+        } else {
+            rules.push(MacroRule::Func { lhs, lhs_span, rhs: rhs_tt });
+        }
         if p.token == token::Eof {
             break;
         }
@@ -438,6 +634,7 @@ pub fn compile_declarative_macro(
         let guar = sess.dcx().span_err(span, "macros must contain at least one rule");
         return dummy_syn_ext(guar);
     }
+    assert!(!kinds.is_empty());
 
     let transparency = find_attr!(attrs, AttributeKind::MacroTransparency(x) => *x)
         .unwrap_or(Transparency::fallback(macro_rules));
@@ -451,9 +648,8 @@ pub fn compile_declarative_macro(
     // Return the number of rules for unused rule linting, if this is a local macro.
     let nrules = if is_defined_in_current_crate(node_id) { rules.len() } else { 0 };
 
-    let expander =
-        Arc::new(MacroRulesMacroExpander { name: ident, span, node_id, transparency, rules });
-    (mk_syn_ext(expander), nrules)
+    let exp = MacroRulesMacroExpander { name: ident, kinds, span, node_id, transparency, rules };
+    (mk_syn_ext(SyntaxExtensionKind::MacroRules(Arc::new(exp))), nrules)
 }
 
 fn check_no_eof(sess: &Session, p: &Parser<'_>, msg: &'static str) -> Option<ErrorGuaranteed> {
@@ -469,6 +665,18 @@ fn check_no_eof(sess: &Session, p: &Parser<'_>, msg: &'static str) -> Option<Err
     None
 }
 
+fn check_args_parens(sess: &Session, args: &tokenstream::TokenTree) {
+    // This does not handle the non-delimited case; that gets handled separately by `check_lhs`.
+    if let tokenstream::TokenTree::Delimited(dspan, _, delim, _) = args
+        && *delim != Delimiter::Parenthesis
+    {
+        sess.dcx().emit_err(errors::MacroArgsBadDelim {
+            span: dspan.entire(),
+            sugg: errors::MacroArgsBadDelimSugg { open: dspan.open, close: dspan.close },
+        });
+    }
+}
+
 fn check_lhs(sess: &Session, node_id: NodeId, lhs: &mbe::TokenTree) -> Result<(), ErrorGuaranteed> {
     let e1 = check_lhs_nt_follows(sess, node_id, lhs);
     let e2 = check_lhs_no_empty_seq(sess, slice::from_ref(lhs));
diff --git a/compiler/rustc_expand/src/module.rs b/compiler/rustc_expand/src/module.rs
index e925052c607..662c67f2d3f 100644
--- a/compiler/rustc_expand/src/module.rs
+++ b/compiler/rustc_expand/src/module.rs
@@ -1,7 +1,6 @@
 use std::iter::once;
 use std::path::{self, Path, PathBuf};
 
-use rustc_ast::ptr::P;
 use rustc_ast::{AttrVec, Attribute, Inline, Item, ModSpans};
 use rustc_errors::{Diag, ErrorGuaranteed};
 use rustc_parse::{exp, new_parser_from_file, unwrap_or_emit_fatal, validate_attr};
@@ -31,7 +30,7 @@ pub struct ModulePathSuccess {
 }
 
 pub(crate) struct ParsedExternalMod {
-    pub items: ThinVec<P<Item>>,
+    pub items: ThinVec<Box<Item>>,
     pub spans: ModSpans,
     pub file_path: PathBuf,
     pub dir_path: PathBuf,
diff --git a/compiler/rustc_expand/src/placeholders.rs b/compiler/rustc_expand/src/placeholders.rs
index 6e1c6df4bcb..05f9a5aa43f 100644
--- a/compiler/rustc_expand/src/placeholders.rs
+++ b/compiler/rustc_expand/src/placeholders.rs
@@ -1,5 +1,4 @@
 use rustc_ast::mut_visit::*;
-use rustc_ast::ptr::P;
 use rustc_ast::token::Delimiter;
 use rustc_ast::visit::AssocCtxt;
 use rustc_ast::{self as ast, Safety};
@@ -15,10 +14,10 @@ pub(crate) fn placeholder(
     id: ast::NodeId,
     vis: Option<ast::Visibility>,
 ) -> AstFragment {
-    fn mac_placeholder() -> P<ast::MacCall> {
-        P(ast::MacCall {
+    fn mac_placeholder() -> Box<ast::MacCall> {
+        Box::new(ast::MacCall {
             path: ast::Path { span: DUMMY_SP, segments: ThinVec::new(), tokens: None },
-            args: P(ast::DelimArgs {
+            args: Box::new(ast::DelimArgs {
                 dspan: ast::tokenstream::DelimSpan::dummy(),
                 delim: Delimiter::Parenthesis,
                 tokens: ast::tokenstream::TokenStream::new(Vec::new()),
@@ -35,7 +34,7 @@ pub(crate) fn placeholder(
     });
     let span = DUMMY_SP;
     let expr_placeholder = || {
-        P(ast::Expr {
+        Box::new(ast::Expr {
             id,
             span,
             attrs: ast::AttrVec::new(),
@@ -43,10 +42,17 @@ pub(crate) fn placeholder(
             tokens: None,
         })
     };
-    let ty =
-        || P(ast::Ty { id, kind: ast::TyKind::MacCall(mac_placeholder()), span, tokens: None });
-    let pat =
-        || P(ast::Pat { id, kind: ast::PatKind::MacCall(mac_placeholder()), span, tokens: None });
+    let ty = || {
+        Box::new(ast::Ty { id, kind: ast::TyKind::MacCall(mac_placeholder()), span, tokens: None })
+    };
+    let pat = || {
+        Box::new(ast::Pat {
+            id,
+            kind: ast::PatKind::MacCall(mac_placeholder()),
+            span,
+            tokens: None,
+        })
+    };
 
     match kind {
         AstFragmentKind::Crate => AstFragment::Crate(ast::Crate {
@@ -59,7 +65,7 @@ pub(crate) fn placeholder(
         AstFragmentKind::Expr => AstFragment::Expr(expr_placeholder()),
         AstFragmentKind::OptExpr => AstFragment::OptExpr(Some(expr_placeholder())),
         AstFragmentKind::MethodReceiverExpr => AstFragment::MethodReceiverExpr(expr_placeholder()),
-        AstFragmentKind::Items => AstFragment::Items(smallvec![P(ast::Item {
+        AstFragmentKind::Items => AstFragment::Items(smallvec![Box::new(ast::Item {
             id,
             span,
             vis,
@@ -67,15 +73,17 @@ pub(crate) fn placeholder(
             kind: ast::ItemKind::MacCall(mac_placeholder()),
             tokens: None,
         })]),
-        AstFragmentKind::TraitItems => AstFragment::TraitItems(smallvec![P(ast::AssocItem {
-            id,
-            span,
-            vis,
-            attrs,
-            kind: ast::AssocItemKind::MacCall(mac_placeholder()),
-            tokens: None,
-        })]),
-        AstFragmentKind::ImplItems => AstFragment::ImplItems(smallvec![P(ast::AssocItem {
+        AstFragmentKind::TraitItems => {
+            AstFragment::TraitItems(smallvec![Box::new(ast::AssocItem {
+                id,
+                span,
+                vis,
+                attrs,
+                kind: ast::AssocItemKind::MacCall(mac_placeholder()),
+                tokens: None,
+            })])
+        }
+        AstFragmentKind::ImplItems => AstFragment::ImplItems(smallvec![Box::new(ast::AssocItem {
             id,
             span,
             vis,
@@ -84,7 +92,7 @@ pub(crate) fn placeholder(
             tokens: None,
         })]),
         AstFragmentKind::TraitImplItems => {
-            AstFragment::TraitImplItems(smallvec![P(ast::AssocItem {
+            AstFragment::TraitImplItems(smallvec![Box::new(ast::AssocItem {
                 id,
                 span,
                 vis,
@@ -94,7 +102,7 @@ pub(crate) fn placeholder(
             })])
         }
         AstFragmentKind::ForeignItems => {
-            AstFragment::ForeignItems(smallvec![P(ast::ForeignItem {
+            AstFragment::ForeignItems(smallvec![Box::new(ast::ForeignItem {
                 id,
                 span,
                 vis,
@@ -103,20 +111,20 @@ pub(crate) fn placeholder(
                 tokens: None,
             })])
         }
-        AstFragmentKind::Pat => AstFragment::Pat(P(ast::Pat {
+        AstFragmentKind::Pat => AstFragment::Pat(Box::new(ast::Pat {
             id,
             span,
             kind: ast::PatKind::MacCall(mac_placeholder()),
             tokens: None,
         })),
-        AstFragmentKind::Ty => AstFragment::Ty(P(ast::Ty {
+        AstFragmentKind::Ty => AstFragment::Ty(Box::new(ast::Ty {
             id,
             span,
             kind: ast::TyKind::MacCall(mac_placeholder()),
             tokens: None,
         })),
         AstFragmentKind::Stmts => AstFragment::Stmts(smallvec![{
-            let mac = P(ast::MacCallStmt {
+            let mac = Box::new(ast::MacCallStmt {
                 mac: mac_placeholder(),
                 style: ast::MacStmtStyle::Braces,
                 attrs: ast::AttrVec::new(),
@@ -297,7 +305,7 @@ impl MutVisitor for PlaceholderExpander {
         }
     }
 
-    fn flat_map_item(&mut self, item: P<ast::Item>) -> SmallVec<[P<ast::Item>; 1]> {
+    fn flat_map_item(&mut self, item: Box<ast::Item>) -> SmallVec<[Box<ast::Item>; 1]> {
         match item.kind {
             ast::ItemKind::MacCall(_) => self.remove(item.id).make_items(),
             _ => walk_flat_map_item(self, item),
@@ -306,9 +314,9 @@ impl MutVisitor for PlaceholderExpander {
 
     fn flat_map_assoc_item(
         &mut self,
-        item: P<ast::AssocItem>,
+        item: Box<ast::AssocItem>,
         ctxt: AssocCtxt,
-    ) -> SmallVec<[P<ast::AssocItem>; 1]> {
+    ) -> SmallVec<[Box<ast::AssocItem>; 1]> {
         match item.kind {
             ast::AssocItemKind::MacCall(_) => {
                 let it = self.remove(item.id);
@@ -324,8 +332,8 @@ impl MutVisitor for PlaceholderExpander {
 
     fn flat_map_foreign_item(
         &mut self,
-        item: P<ast::ForeignItem>,
-    ) -> SmallVec<[P<ast::ForeignItem>; 1]> {
+        item: Box<ast::ForeignItem>,
+    ) -> SmallVec<[Box<ast::ForeignItem>; 1]> {
         match item.kind {
             ast::ForeignItemKind::MacCall(_) => self.remove(item.id).make_foreign_items(),
             _ => walk_flat_map_foreign_item(self, item),
@@ -346,7 +354,7 @@ impl MutVisitor for PlaceholderExpander {
         }
     }
 
-    fn filter_map_expr(&mut self, expr: P<ast::Expr>) -> Option<P<ast::Expr>> {
+    fn filter_map_expr(&mut self, expr: Box<ast::Expr>) -> Option<Box<ast::Expr>> {
         match expr.kind {
             ast::ExprKind::MacCall(_) => self.remove(expr.id).make_opt_expr(),
             _ => walk_filter_map_expr(self, expr),
diff --git a/compiler/rustc_expand/src/proc_macro.rs b/compiler/rustc_expand/src/proc_macro.rs
index 84fbbbef061..9bfda8764f5 100644
--- a/compiler/rustc_expand/src/proc_macro.rs
+++ b/compiler/rustc_expand/src/proc_macro.rs
@@ -1,4 +1,3 @@
-use rustc_ast::ptr::P;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_errors::ErrorGuaranteed;
 use rustc_parse::parser::{ForceCollect, Parser};
@@ -161,7 +160,7 @@ impl MultiItemModifier for DeriveProcMacro {
                 Ok(None) => break,
                 Ok(Some(item)) => {
                     if is_stmt {
-                        items.push(Annotatable::Stmt(P(ecx.stmt_item(span, item))));
+                        items.push(Annotatable::Stmt(Box::new(ecx.stmt_item(span, item))));
                     } else {
                         items.push(Annotatable::Item(item));
                     }
diff --git a/compiler/rustc_expand/src/stats.rs b/compiler/rustc_expand/src/stats.rs
index b4c4eac028f..3e40632275b 100644
--- a/compiler/rustc_expand/src/stats.rs
+++ b/compiler/rustc_expand/src/stats.rs
@@ -1,6 +1,5 @@
 use std::iter;
 
-use rustc_ast::ptr::P;
 use rustc_ast::{self as ast, DUMMY_NODE_ID, Expr, ExprKind};
 use rustc_ast_pretty::pprust;
 use rustc_span::hygiene::{ExpnKind, MacroKind};
@@ -41,7 +40,7 @@ pub(crate) fn update_bang_macro_stats(
     ecx: &mut ExtCtxt<'_>,
     fragment_kind: AstFragmentKind,
     span: Span,
-    mac: P<ast::MacCall>,
+    mac: Box<ast::MacCall>,
     fragment: &AstFragment,
 ) {
     // Does this path match any of the include macros, e.g. `include!`?
diff --git a/compiler/rustc_feature/src/accepted.rs b/compiler/rustc_feature/src/accepted.rs
index 83be3241b12..9fe55216f93 100644
--- a/compiler/rustc_feature/src/accepted.rs
+++ b/compiler/rustc_feature/src/accepted.rs
@@ -396,6 +396,8 @@ declare_features! (
     (accepted, slice_patterns, "1.42.0", Some(62254)),
     /// Allows use of `&foo[a..b]` as a slicing syntax.
     (accepted, slicing_syntax, "1.0.0", None),
+    /// Allows use of `sse4a` target feature.
+    (accepted, sse4a_target_feature, "CURRENT_RUSTC_VERSION", Some(44839)),
     /// Allows elision of `'static` lifetimes in `static`s and `const`s.
     (accepted, static_in_const, "1.17.0", Some(35897)),
     /// Allows the definition recursive static items.
@@ -408,6 +410,8 @@ declare_features! (
     (accepted, target_feature, "1.27.0", None),
     /// Allows the use of `#[target_feature]` on safe functions.
     (accepted, target_feature_11, "1.86.0", Some(69098)),
+    /// Allows use of `tbm` target feature.
+    (accepted, tbm_target_feature, "CURRENT_RUSTC_VERSION", Some(44839)),
     /// Allows `fn main()` with return types which implements `Termination` (RFC 1937).
     (accepted, termination_trait, "1.26.0", Some(43301)),
     /// Allows `#[test]` functions where the return type implements `Termination` (RFC 1937).
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
index 5c63d4808db..6fbedaf5b10 100644
--- a/compiler/rustc_feature/src/builtin_attrs.rs
+++ b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -120,13 +120,15 @@ pub struct AttributeTemplate {
     /// If `true`, the attribute is allowed to be a bare word like `#[test]`.
     pub word: bool,
     /// If `Some`, the attribute is allowed to take a list of items like `#[allow(..)]`.
-    pub list: Option<&'static str>,
+    pub list: Option<&'static [&'static str]>,
     /// If non-empty, the attribute is allowed to take a list containing exactly
     /// one of the listed words, like `#[coverage(off)]`.
     pub one_of: &'static [Symbol],
     /// If `Some`, the attribute is allowed to be a name/value pair where the
     /// value is a string, like `#[must_use = "reason"]`.
-    pub name_value_str: Option<&'static str>,
+    pub name_value_str: Option<&'static [&'static str]>,
+    /// A link to the document for this attribute.
+    pub docs: Option<&'static str>,
 }
 
 impl AttributeTemplate {
@@ -137,11 +139,15 @@ impl AttributeTemplate {
             suggestions.push(format!("#{inner}[{name}]"));
         }
         if let Some(descr) = self.list {
-            suggestions.push(format!("#{inner}[{name}({descr})]"));
+            for descr in descr {
+                suggestions.push(format!("#{inner}[{name}({descr})]"));
+            }
         }
         suggestions.extend(self.one_of.iter().map(|&word| format!("#{inner}[{name}({word})]")));
         if let Some(descr) = self.name_value_str {
-            suggestions.push(format!("#{inner}[{name} = \"{descr}\"]"));
+            for descr in descr {
+                suggestions.push(format!("#{inner}[{name} = \"{descr}\"]"));
+            }
         }
         suggestions.sort();
 
@@ -205,20 +211,33 @@ pub enum AttributeDuplicates {
 /// supports forms `#[attr]` and `#[attr(description)]`.
 #[macro_export]
 macro_rules! template {
-    (Word) => { $crate::template!(@ true, None, &[], None) };
-    (List: $descr: expr) => { $crate::template!(@ false, Some($descr), &[], None) };
-    (OneOf: $one_of: expr) => { $crate::template!(@ false, None, $one_of, None) };
-    (NameValueStr: $descr: expr) => { $crate::template!(@ false, None, &[], Some($descr)) };
-    (Word, List: $descr: expr) => { $crate::template!(@ true, Some($descr), &[], None) };
-    (Word, NameValueStr: $descr: expr) => { $crate::template!(@ true, None, &[], Some($descr)) };
+    (Word) => { $crate::template!(@ true, None, &[], None, None) };
+    (Word, $link: literal) => { $crate::template!(@ true, None, &[], None, Some($link)) };
+    (List: $descr: expr) => { $crate::template!(@ false, Some($descr), &[], None, None) };
+    (List: $descr: expr, $link: literal) => { $crate::template!(@ false, Some($descr), &[], None, Some($link)) };
+    (OneOf: $one_of: expr) => { $crate::template!(@ false, None, $one_of, None, None) };
+    (NameValueStr: [$($descr: literal),* $(,)?]) => { $crate::template!(@ false, None, &[], Some(&[$($descr,)*]), None) };
+    (NameValueStr: [$($descr: literal),* $(,)?], $link: literal) => { $crate::template!(@ false, None, &[], Some(&[$($descr,)*]), Some($link)) };
+    (NameValueStr: $descr: literal) => { $crate::template!(@ false, None, &[], Some(&[$descr]), None) };
+    (NameValueStr: $descr: literal, $link: literal) => { $crate::template!(@ false, None, &[], Some(&[$descr]), Some($link)) };
+    (Word, List: $descr: expr) => { $crate::template!(@ true, Some($descr), &[], None, None) };
+    (Word, List: $descr: expr, $link: literal) => { $crate::template!(@ true, Some($descr), &[], None, Some($link)) };
+    (Word, NameValueStr: $descr: expr) => { $crate::template!(@ true, None, &[], Some(&[$descr]), None) };
+    (Word, NameValueStr: $descr: expr, $link: literal) => { $crate::template!(@ true, None, &[], Some(&[$descr]), Some($link)) };
     (List: $descr1: expr, NameValueStr: $descr2: expr) => {
-        $crate::template!(@ false, Some($descr1), &[], Some($descr2))
+        $crate::template!(@ false, Some($descr1), &[], Some(&[$descr2]), None)
+    };
+    (List: $descr1: expr, NameValueStr: $descr2: expr, $link: literal) => {
+        $crate::template!(@ false, Some($descr1), &[], Some(&[$descr2]), Some($link))
     };
     (Word, List: $descr1: expr, NameValueStr: $descr2: expr) => {
-        $crate::template!(@ true, Some($descr1), &[], Some($descr2))
+        $crate::template!(@ true, Some($descr1), &[], Some(&[$descr2]), None)
     };
-    (@ $word: expr, $list: expr, $one_of: expr, $name_value_str: expr) => { $crate::AttributeTemplate {
-        word: $word, list: $list, one_of: $one_of, name_value_str: $name_value_str
+    (Word, List: $descr1: expr, NameValueStr: $descr2: expr, $link: literal) => {
+        $crate::template!(@ true, Some($descr1), &[], Some(&[$descr2]), Some($link))
+    };
+    (@ $word: expr, $list: expr, $one_of: expr, $name_value_str: expr, $link: expr) => { $crate::AttributeTemplate {
+        word: $word, list: $list, one_of: $one_of, name_value_str: $name_value_str, docs: $link,
     } };
 }
 
@@ -391,18 +410,42 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // ==========================================================================
 
     // Conditional compilation:
-    ungated!(cfg, Normal, template!(List: "predicate"), DuplicatesOk, EncodeCrossCrate::Yes),
-    ungated!(cfg_attr, Normal, template!(List: "predicate, attr1, attr2, ..."), DuplicatesOk, EncodeCrossCrate::Yes),
+    ungated!(
+        cfg, Normal,
+        template!(
+            List: &["predicate"],
+            "https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg-attribute"
+        ),
+        DuplicatesOk, EncodeCrossCrate::Yes
+    ),
+    ungated!(
+        cfg_attr, Normal,
+        template!(
+            List: &["predicate, attr1, attr2, ..."],
+            "https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg_attr-attribute"
+        ),
+        DuplicatesOk, EncodeCrossCrate::Yes
+    ),
 
     // Testing:
     ungated!(
-        ignore, Normal, template!(Word, NameValueStr: "reason"), WarnFollowing,
-        EncodeCrossCrate::No,
+        ignore, Normal,
+        template!(
+            Word,
+            NameValueStr: "reason",
+            "https://doc.rust-lang.org/reference/attributes/testing.html#the-ignore-attribute"
+        ),
+        WarnFollowing, EncodeCrossCrate::No,
     ),
     ungated!(
         should_panic, Normal,
-        template!(Word, List: r#"expected = "reason""#, NameValueStr: "reason"), FutureWarnFollowing,
-        EncodeCrossCrate::No,
+        template!(
+            Word,
+            List: &[r#"expected = "reason""#],
+            NameValueStr: "reason",
+            "https://doc.rust-lang.org/reference/attributes/testing.html#the-should_panic-attribute"
+        ),
+        FutureWarnFollowing, EncodeCrossCrate::No,
     ),
     // FIXME(Centril): This can be used on stable but shouldn't.
     ungated!(
@@ -411,46 +454,102 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
 
     // Macros:
-    ungated!(automatically_derived, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::Yes),
     ungated!(
-        macro_use, Normal, template!(Word, List: "name1, name2, ..."), WarnFollowingWordOnly,
-        EncodeCrossCrate::No,
+        automatically_derived, Normal,
+        template!(
+            Word,
+            "https://doc.rust-lang.org/reference/attributes/derive.html#the-automatically_derived-attribute"
+        ),
+        WarnFollowing, EncodeCrossCrate::Yes
+    ),
+    ungated!(
+        macro_use, Normal,
+        template!(
+            Word,
+            List: &["name1, name2, ..."],
+            "https://doc.rust-lang.org/reference/macros-by-example.html#the-macro_use-attribute"
+        ),
+        WarnFollowingWordOnly, EncodeCrossCrate::No,
     ),
     ungated!(macro_escape, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No), // Deprecated synonym for `macro_use`.
     ungated!(
-        macro_export, Normal, template!(Word, List: "local_inner_macros"),
+        macro_export, Normal,
+        template!(
+            Word,
+            List: &["local_inner_macros"],
+            "https://doc.rust-lang.org/reference/macros-by-example.html#path-based-scope"
+        ),
         WarnFollowing, EncodeCrossCrate::Yes
     ),
-    ungated!(proc_macro, Normal, template!(Word), ErrorFollowing, EncodeCrossCrate::No),
     ungated!(
-        proc_macro_derive, Normal, template!(List: "TraitName, /*opt*/ attributes(name1, name2, ...)"),
+        proc_macro, Normal,
+        template!(
+            Word,
+            "https://doc.rust-lang.org/reference/procedural-macros.html#function-like-procedural-macros"),
+        ErrorFollowing, EncodeCrossCrate::No
+    ),
+    ungated!(
+        proc_macro_derive, Normal,
+        template!(
+            List: &["TraitName", "TraitName, attributes(name1, name2, ...)"],
+            "https://doc.rust-lang.org/reference/procedural-macros.html#derive-macros"
+        ),
         ErrorFollowing, EncodeCrossCrate::No,
     ),
-    ungated!(proc_macro_attribute, Normal, template!(Word), ErrorFollowing, EncodeCrossCrate::No),
+    ungated!(
+        proc_macro_attribute, Normal,
+        template!(Word, "https://doc.rust-lang.org/reference/procedural-macros.html#attribute-macros"),
+        ErrorFollowing, EncodeCrossCrate::No
+    ),
 
     // Lints:
     ungated!(
-        warn, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
+        warn, Normal,
+        template!(
+            List: &["lint1", "lint1, lint2, ...", r#"lint1, lint2, lint3, reason = "...""#],
+            "https://doc.rust-lang.org/reference/attributes/diagnostics.html#lint-check-attributes"
+        ),
         DuplicatesOk, EncodeCrossCrate::No,
     ),
     ungated!(
-        allow, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
+        allow, Normal,
+        template!(
+            List: &["lint1", "lint1, lint2, ...", r#"lint1, lint2, lint3, reason = "...""#],
+            "https://doc.rust-lang.org/reference/attributes/diagnostics.html#lint-check-attributes"
+        ),
         DuplicatesOk, EncodeCrossCrate::No,
     ),
     ungated!(
-        expect, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
+        expect, Normal,
+        template!(
+            List: &["lint1", "lint1, lint2, ...", r#"lint1, lint2, lint3, reason = "...""#],
+            "https://doc.rust-lang.org/reference/attributes/diagnostics.html#lint-check-attributes"
+        ),
         DuplicatesOk, EncodeCrossCrate::No,
     ),
     ungated!(
-        forbid, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
+        forbid, Normal,
+        template!(
+            List: &["lint1", "lint1, lint2, ...", r#"lint1, lint2, lint3, reason = "...""#],
+            "https://doc.rust-lang.org/reference/attributes/diagnostics.html#lint-check-attributes"
+        ),
         DuplicatesOk, EncodeCrossCrate::No
     ),
     ungated!(
-        deny, Normal, template!(List: r#"lint1, lint2, ..., /*opt*/ reason = "...""#),
+        deny, Normal,
+        template!(
+            List: &["lint1", "lint1, lint2, ...", r#"lint1, lint2, lint3, reason = "...""#],
+            "https://doc.rust-lang.org/reference/attributes/diagnostics.html#lint-check-attributes"
+        ),
         DuplicatesOk, EncodeCrossCrate::No
     ),
     ungated!(
-        must_use, Normal, template!(Word, NameValueStr: "reason"),
+        must_use, Normal,
+        template!(
+            Word,
+            NameValueStr: "reason",
+            "https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-must_use-attribute"
+        ),
         FutureWarnFollowing, EncodeCrossCrate::Yes
     ),
     gated!(
@@ -461,52 +560,104 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         deprecated, Normal,
         template!(
             Word,
-            List: r#"/*opt*/ since = "version", /*opt*/ note = "reason""#,
-            NameValueStr: "reason"
+            List: &[r#"/*opt*/ since = "version", /*opt*/ note = "reason""#],
+            NameValueStr: "reason",
+            "https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-deprecated-attribute"
         ),
         ErrorFollowing, EncodeCrossCrate::Yes
     ),
 
     // Crate properties:
     ungated!(
-        crate_name, CrateLevel, template!(NameValueStr: "name"), FutureWarnFollowing,
-        EncodeCrossCrate::No,
+        crate_name, CrateLevel,
+        template!(
+            NameValueStr: "name",
+            "https://doc.rust-lang.org/reference/crates-and-source-files.html#the-crate_name-attribute"
+        ),
+        FutureWarnFollowing, EncodeCrossCrate::No,
     ),
     ungated!(
-        crate_type, CrateLevel, template!(NameValueStr: "bin|lib|..."), DuplicatesOk,
-        EncodeCrossCrate::No,
+        crate_type, CrateLevel,
+        template!(
+            NameValueStr: ["bin", "lib", "dylib", "cdylib", "rlib", "staticlib", "sdylib", "proc-macro"],
+            "https://doc.rust-lang.org/reference/linkage.html"
+        ),
+        DuplicatesOk, EncodeCrossCrate::No,
     ),
 
     // ABI, linking, symbols, and FFI
     ungated!(
         link, Normal,
-        template!(List: r#"name = "...", /*opt*/ kind = "dylib|static|...", /*opt*/ wasm_import_module = "...", /*opt*/ import_name_type = "decorated|noprefix|undecorated""#),
-        DuplicatesOk,
-        EncodeCrossCrate::No,
+        template!(List: &[
+            r#"name = "...""#,
+            r#"name = "...", kind = "dylib|static|...""#,
+            r#"name = "...", wasm_import_module = "...""#,
+            r#"name = "...", import_name_type = "decorated|noprefix|undecorated""#,
+            r#"name = "...", kind = "dylib|static|...", wasm_import_module = "...", import_name_type = "decorated|noprefix|undecorated""#,
+        ], "https://doc.rust-lang.org/reference/items/external-blocks.html#the-link-attribute"),
+        DuplicatesOk, EncodeCrossCrate::No,
     ),
     ungated!(
-        link_name, Normal, template!(NameValueStr: "name"),
+        link_name, Normal,
+        template!(NameValueStr: "name", "https://doc.rust-lang.org/reference/items/external-blocks.html#the-link_name-attribute"),
         FutureWarnPreceding, EncodeCrossCrate::Yes
     ),
-    ungated!(no_link, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No),
-    ungated!(repr, Normal, template!(List: "C"), DuplicatesOk, EncodeCrossCrate::No),
+    ungated!(
+        no_link, Normal,
+        template!(Word, "https://doc.rust-lang.org/reference/items/extern-crates.html#the-no_link-attribute"),
+        WarnFollowing, EncodeCrossCrate::No
+    ),
+    ungated!(
+        repr, Normal,
+        template!(
+            List: &["C", "Rust", "transparent", "align(...)", "packed(...)", "<integer type>"],
+            "https://doc.rust-lang.org/reference/type-layout.html#representations"
+        ),
+        DuplicatesOk, EncodeCrossCrate::No
+    ),
     // FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
-    gated!(rustc_align, Normal, template!(List: "alignment"), DuplicatesOk, EncodeCrossCrate::No, fn_align, experimental!(rustc_align)),
-    ungated!(unsafe(Edition2024) export_name, Normal, template!(NameValueStr: "name"), FutureWarnPreceding, EncodeCrossCrate::No),
-    ungated!(unsafe(Edition2024) link_section, Normal, template!(NameValueStr: "name"), FutureWarnPreceding, EncodeCrossCrate::No),
-    ungated!(unsafe(Edition2024) no_mangle, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No),
-    ungated!(used, Normal, template!(Word, List: "compiler|linker"), WarnFollowing, EncodeCrossCrate::No),
-    ungated!(link_ordinal, Normal, template!(List: "ordinal"), ErrorPreceding, EncodeCrossCrate::Yes),
-    ungated!(unsafe naked, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No),
+    gated!(rustc_align, Normal, template!(List: &["alignment"]), DuplicatesOk, EncodeCrossCrate::No, fn_align, experimental!(rustc_align)),
+    ungated!(
+        unsafe(Edition2024) export_name, Normal,
+        template!(NameValueStr: "name", "https://doc.rust-lang.org/reference/abi.html#the-export_name-attribute"),
+        FutureWarnPreceding, EncodeCrossCrate::No
+    ),
+    ungated!(
+        unsafe(Edition2024) link_section, Normal,
+        template!(NameValueStr: "name", "https://doc.rust-lang.org/reference/abi.html#the-link_section-attribute"),
+        FutureWarnPreceding, EncodeCrossCrate::No
+    ),
+    ungated!(
+        unsafe(Edition2024) no_mangle, Normal,
+        template!(Word, "https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute"),
+        WarnFollowing, EncodeCrossCrate::No
+    ),
+    ungated!(
+        used, Normal,
+        template!(Word, List: &["compiler", "linker"], "https://doc.rust-lang.org/reference/abi.html#the-used-attribute"),
+        WarnFollowing, EncodeCrossCrate::No
+    ),
+    ungated!(
+        link_ordinal, Normal,
+        template!(List: &["ordinal"], "https://doc.rust-lang.org/reference/items/external-blocks.html#the-link_ordinal-attribute"),
+        ErrorPreceding, EncodeCrossCrate::Yes
+    ),
+    ungated!(
+        unsafe naked, Normal,
+        template!(Word, "https://doc.rust-lang.org/reference/attributes/codegen.html#the-naked-attribute"),
+        WarnFollowing, EncodeCrossCrate::No
+    ),
 
     // Limits:
     ungated!(
-        recursion_limit, CrateLevel, template!(NameValueStr: "N"), FutureWarnFollowing,
-        EncodeCrossCrate::No
+        recursion_limit, CrateLevel,
+        template!(NameValueStr: "N", "https://doc.rust-lang.org/reference/attributes/limits.html#the-recursion_limit-attribute"),
+        FutureWarnFollowing, EncodeCrossCrate::No
     ),
     ungated!(
-        type_length_limit, CrateLevel, template!(NameValueStr: "N"), FutureWarnFollowing,
-        EncodeCrossCrate::No
+        type_length_limit, CrateLevel,
+        template!(NameValueStr: "N", "https://doc.rust-lang.org/reference/attributes/limits.html#the-type_length_limit-attribute"),
+        FutureWarnFollowing, EncodeCrossCrate::No
     ),
     gated!(
         move_size_limit, CrateLevel, template!(NameValueStr: "N"), ErrorFollowing,
@@ -514,35 +665,84 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
 
     // Entry point:
-    ungated!(no_main, CrateLevel, template!(Word), WarnFollowing, EncodeCrossCrate::No),
+    ungated!(
+        no_main, CrateLevel,
+        template!(Word, "https://doc.rust-lang.org/reference/crates-and-source-files.html#the-no_main-attribute"),
+        WarnFollowing, EncodeCrossCrate::No
+    ),
 
     // Modules, prelude, and resolution:
-    ungated!(path, Normal, template!(NameValueStr: "file"), FutureWarnFollowing, EncodeCrossCrate::No),
-    ungated!(no_std, CrateLevel, template!(Word), WarnFollowing, EncodeCrossCrate::No),
-    ungated!(no_implicit_prelude, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No),
-    ungated!(non_exhaustive, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::Yes),
+    ungated!(
+        path, Normal,
+        template!(NameValueStr: "file", "https://doc.rust-lang.org/reference/items/modules.html#the-path-attribute"),
+        FutureWarnFollowing, EncodeCrossCrate::No
+    ),
+    ungated!(
+        no_std, CrateLevel,
+        template!(Word, "https://doc.rust-lang.org/reference/names/preludes.html#the-no_std-attribute"),
+        WarnFollowing, EncodeCrossCrate::No
+    ),
+    ungated!(
+        no_implicit_prelude, Normal,
+        template!(Word, "https://doc.rust-lang.org/reference/names/preludes.html#the-no_implicit_prelude-attribute"),
+        WarnFollowing, EncodeCrossCrate::No
+    ),
+    ungated!(
+        non_exhaustive, Normal,
+        template!(Word, "https://doc.rust-lang.org/reference/attributes/type_system.html#the-non_exhaustive-attribute"),
+        WarnFollowing, EncodeCrossCrate::Yes
+    ),
 
     // Runtime
     ungated!(
         windows_subsystem, CrateLevel,
-        template!(NameValueStr: "windows|console"), FutureWarnFollowing,
-        EncodeCrossCrate::No
+        template!(NameValueStr: ["windows", "console"], "https://doc.rust-lang.org/reference/runtime.html#the-windows_subsystem-attribute"),
+        FutureWarnFollowing, EncodeCrossCrate::No
+    ),
+    ungated!( // RFC 2070
+        panic_handler, Normal,
+        template!(Word, "https://doc.rust-lang.org/reference/panic.html#the-panic_handler-attribute"),
+        WarnFollowing, EncodeCrossCrate::Yes
     ),
-    ungated!(panic_handler, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::Yes), // RFC 2070
 
     // Code generation:
-    ungated!(inline, Normal, template!(Word, List: "always|never"), FutureWarnFollowing, EncodeCrossCrate::No),
-    ungated!(cold, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No),
-    ungated!(no_builtins, CrateLevel, template!(Word), WarnFollowing, EncodeCrossCrate::Yes),
     ungated!(
-        target_feature, Normal, template!(List: r#"enable = "name""#),
+        inline, Normal,
+        template!(
+            Word,
+            List: &["always", "never"],
+            "https://doc.rust-lang.org/reference/attributes/codegen.html#the-inline-attribute"
+        ),
+        FutureWarnFollowing, EncodeCrossCrate::No
+    ),
+    ungated!(
+        cold, Normal,
+        template!(Word, "https://doc.rust-lang.org/reference/attributes/codegen.html#the-cold-attribute"),
+        WarnFollowing, EncodeCrossCrate::No
+    ),
+    ungated!(
+        no_builtins, CrateLevel,
+        template!(Word, "https://doc.rust-lang.org/reference/attributes/codegen.html#the-no_builtins-attribute"),
+        WarnFollowing, EncodeCrossCrate::Yes
+    ),
+    ungated!(
+        target_feature, Normal,
+        template!(List: &[r#"enable = "name""#], "https://doc.rust-lang.org/reference/attributes/codegen.html#the-target_feature-attribute"),
         DuplicatesOk, EncodeCrossCrate::No,
     ),
-    ungated!(track_caller, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::Yes),
-    ungated!(instruction_set, Normal, template!(List: "set"), ErrorPreceding, EncodeCrossCrate::No),
+    ungated!(
+        track_caller, Normal,
+        template!(Word, "https://doc.rust-lang.org/reference/attributes/codegen.html#the-track_caller-attribute"),
+        WarnFollowing, EncodeCrossCrate::Yes
+    ),
+    ungated!(
+        instruction_set, Normal,
+        template!(List: &["set"], "https://doc.rust-lang.org/reference/attributes/codegen.html#the-instruction_set-attribute"),
+        ErrorPreceding, EncodeCrossCrate::No
+    ),
     gated!(
         no_sanitize, Normal,
-        template!(List: "address, kcfi, memory, thread"), DuplicatesOk,
+        template!(List: &["address, kcfi, memory, thread"]), DuplicatesOk,
         EncodeCrossCrate::No, experimental!(no_sanitize)
     ),
     gated!(
@@ -552,18 +752,31 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
 
     ungated!(
-        doc, Normal, template!(List: "hidden|inline|...", NameValueStr: "string"), DuplicatesOk,
-        EncodeCrossCrate::Yes
+        doc, Normal,
+        template!(
+            List: &["hidden", "inline"],
+            NameValueStr: "string",
+            "https://doc.rust-lang.org/rustdoc/write-documentation/the-doc-attribute.html"
+        ),
+        DuplicatesOk, EncodeCrossCrate::Yes
     ),
 
     // Debugging
     ungated!(
         debugger_visualizer, Normal,
-        template!(List: r#"natvis_file = "...", gdb_script_file = "...""#),
+        template!(
+            List: &[r#"natvis_file = "...", gdb_script_file = "...""#],
+            "https://doc.rust-lang.org/reference/attributes/debugger.html#the-debugger_visualizer-attribute"
+        ),
         DuplicatesOk, EncodeCrossCrate::No
     ),
-    ungated!(collapse_debuginfo, Normal, template!(List: "no|external|yes"), ErrorFollowing,
-        EncodeCrossCrate::Yes
+    ungated!(
+        collapse_debuginfo, Normal,
+        template!(
+            List: &["no", "external", "yes"],
+            "https://doc.rust-lang.org/reference/attributes/debugger.html#the-collapse_debuginfo-attribute"
+        ),
+        ErrorFollowing, EncodeCrossCrate::Yes
     ),
 
     // ==========================================================================
@@ -578,7 +791,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
 
     // Testing:
     gated!(
-        test_runner, CrateLevel, template!(List: "path"), ErrorFollowing,
+        test_runner, CrateLevel, template!(List: &["path"]), ErrorFollowing,
         EncodeCrossCrate::Yes, custom_test_frameworks,
         "custom test frameworks are an unstable feature",
     ),
@@ -597,7 +810,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
     // RFC 2412
     gated!(
-        optimize, Normal, template!(List: "none|size|speed"), ErrorPreceding,
+        optimize, Normal, template!(List: &["none", "size", "speed"]), ErrorPreceding,
         EncodeCrossCrate::No, optimize_attribute, experimental!(optimize)
     ),
 
@@ -610,7 +823,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         EncodeCrossCrate::No, experimental!(ffi_const)
     ),
     gated!(
-        register_tool, CrateLevel, template!(List: "tool1, tool2, ..."), DuplicatesOk,
+        register_tool, CrateLevel, template!(List: &["tool1, tool2, ..."]), DuplicatesOk,
         EncodeCrossCrate::No, experimental!(register_tool),
     ),
 
@@ -624,7 +837,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
     // lang-team MCP 147
     gated!(
-        deprecated_safe, Normal, template!(List: r#"since = "version", note = "...""#), ErrorFollowing,
+        deprecated_safe, Normal, template!(List: &[r#"since = "version", note = "...""#]), ErrorFollowing,
         EncodeCrossCrate::Yes, experimental!(deprecated_safe),
     ),
 
@@ -643,7 +856,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // RFC 3543
     // `#[patchable_function_entry(prefix_nops = m, entry_nops = n)]`
     gated!(
-        patchable_function_entry, Normal, template!(List: "prefix_nops = m, entry_nops = n"), ErrorPreceding,
+        patchable_function_entry, Normal, template!(List: &["prefix_nops = m, entry_nops = n"]), ErrorPreceding,
         EncodeCrossCrate::Yes, experimental!(patchable_function_entry)
     ),
 
@@ -673,37 +886,37 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
 
     ungated!(
         feature, CrateLevel,
-        template!(List: "name1, name2, ..."), DuplicatesOk, EncodeCrossCrate::No,
+        template!(List: &["name1, name2, ..."]), DuplicatesOk, EncodeCrossCrate::No,
     ),
     // DuplicatesOk since it has its own validation
     ungated!(
         stable, Normal,
-        template!(List: r#"feature = "name", since = "version""#), DuplicatesOk, EncodeCrossCrate::No,
+        template!(List: &[r#"feature = "name", since = "version""#]), DuplicatesOk, EncodeCrossCrate::No,
     ),
     ungated!(
         unstable, Normal,
-        template!(List: r#"feature = "name", reason = "...", issue = "N""#), DuplicatesOk,
+        template!(List: &[r#"feature = "name", reason = "...", issue = "N""#]), DuplicatesOk,
         EncodeCrossCrate::Yes
     ),
     ungated!(
-        unstable_feature_bound, Normal, template!(Word, List: "feat1, feat2, ..."),
+        unstable_feature_bound, Normal, template!(Word, List: &["feat1, feat2, ..."]),
         DuplicatesOk, EncodeCrossCrate::No,
     ),
     ungated!(
-        rustc_const_unstable, Normal, template!(List: r#"feature = "name""#),
+        rustc_const_unstable, Normal, template!(List: &[r#"feature = "name""#]),
         DuplicatesOk, EncodeCrossCrate::Yes
     ),
     ungated!(
         rustc_const_stable, Normal,
-        template!(List: r#"feature = "name""#), DuplicatesOk, EncodeCrossCrate::No,
+        template!(List: &[r#"feature = "name""#]), DuplicatesOk, EncodeCrossCrate::No,
     ),
     ungated!(
         rustc_default_body_unstable, Normal,
-        template!(List: r#"feature = "name", reason = "...", issue = "N""#),
+        template!(List: &[r#"feature = "name", reason = "...", issue = "N""#]),
         DuplicatesOk, EncodeCrossCrate::No
     ),
     gated!(
-        allow_internal_unstable, Normal, template!(Word, List: "feat1, feat2, ..."),
+        allow_internal_unstable, Normal, template!(Word, List: &["feat1, feat2, ..."]),
         DuplicatesOk, EncodeCrossCrate::Yes,
         "allow_internal_unstable side-steps feature gating and stability checks",
     ),
@@ -718,7 +931,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         through unstable paths"
     ),
     rustc_attr!(
-        rustc_deprecated_safe_2024, Normal, template!(List: r#"audit_that = "...""#),
+        rustc_deprecated_safe_2024, Normal, template!(List: &[r#"audit_that = "...""#]),
         ErrorFollowing, EncodeCrossCrate::Yes,
         "`#[rustc_deprecated_safe_2024]` is used to declare functions unsafe across the edition 2024 boundary",
     ),
@@ -743,7 +956,13 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     rustc_attr!(
         rustc_never_type_options,
         Normal,
-        template!(List: r#"/*opt*/ fallback = "unit|niko|never|no""#),
+        template!(List: &[
+            "",
+            r#"fallback = "unit""#,
+            r#"fallback = "niko""#,
+            r#"fallback = "never""#,
+            r#"fallback = "no""#,
+        ]),
         ErrorFollowing,
         EncodeCrossCrate::No,
         "`rustc_never_type_options` is used to experiment with never type fallback and work on \
@@ -808,7 +1027,17 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // ==========================================================================
 
     gated!(
-        linkage, Normal, template!(NameValueStr: "external|internal|..."),
+        linkage, Normal, template!(NameValueStr: [
+            "available_externally",
+            "common",
+            "extern_weak",
+            "external",
+            "internal",
+            "linkonce",
+            "linkonce_odr",
+            "weak",
+            "weak_odr",
+        ], "https://doc.rust-lang.org/reference/linkage.html"),
         ErrorPreceding, EncodeCrossCrate::No,
         "the `linkage` attribute is experimental and not portable across platforms",
     ),
@@ -823,7 +1052,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
 
     rustc_attr!(
         rustc_builtin_macro, Normal,
-        template!(Word, List: "name, /*opt*/ attributes(name1, name2, ...)"), ErrorFollowing,
+        template!(Word, List: &["name", "name, /*opt*/ attributes(name1, name2, ...)"]), ErrorFollowing,
         EncodeCrossCrate::Yes,
     ),
     rustc_attr!(
@@ -832,12 +1061,12 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
     rustc_attr!(
         rustc_macro_transparency, Normal,
-        template!(NameValueStr: "transparent|semiopaque|opaque"), ErrorFollowing,
+        template!(NameValueStr: ["transparent", "semiopaque", "opaque"]), ErrorFollowing,
         EncodeCrossCrate::Yes, "used internally for testing macro hygiene",
     ),
     rustc_attr!(
         rustc_autodiff, Normal,
-        template!(Word, List: r#""...""#), DuplicatesOk,
+        template!(Word, List: &[r#""...""#]), DuplicatesOk,
         EncodeCrossCrate::Yes,
     ),
     // Traces that are left when `cfg` and `cfg_attr` attributes are expanded.
@@ -860,7 +1089,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     rustc_attr!(
         rustc_on_unimplemented, Normal,
         template!(
-            List: r#"/*opt*/ message = "...", /*opt*/ label = "...", /*opt*/ note = "...""#,
+            List: &[r#"/*opt*/ message = "...", /*opt*/ label = "...", /*opt*/ note = "...""#],
             NameValueStr: "message"
         ),
         ErrorFollowing, EncodeCrossCrate::Yes,
@@ -868,7 +1097,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
     rustc_attr!(
         rustc_confusables, Normal,
-        template!(List: r#""name1", "name2", ..."#),
+        template!(List: &[r#""name1", "name2", ..."#]),
         ErrorFollowing, EncodeCrossCrate::Yes,
     ),
     // Enumerates "identity-like" conversion methods to suggest on type mismatch.
@@ -909,7 +1138,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // Used by the `rustc::bad_opt_access` lint on fields
     // types (as well as any others in future).
     rustc_attr!(
-        rustc_lint_opt_deny_field_access, Normal, template!(List: "message"),
+        rustc_lint_opt_deny_field_access, Normal, template!(List: &["message"]),
         WarnFollowing, EncodeCrossCrate::Yes,
     ),
 
@@ -921,7 +1150,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         rustc_promotable, Normal, template!(Word), WarnFollowing,
         EncodeCrossCrate::No, ),
     rustc_attr!(
-        rustc_legacy_const_generics, Normal, template!(List: "N"), ErrorFollowing,
+        rustc_legacy_const_generics, Normal, template!(List: &["N"]), ErrorFollowing,
         EncodeCrossCrate::Yes,
     ),
     // Do not const-check this function's body. It will always get replaced during CTFE via `hook_special_const_fn`.
@@ -930,10 +1159,6 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         EncodeCrossCrate::Yes, "`#[rustc_do_not_const_check]` skips const-check for this function's body",
     ),
     rustc_attr!(
-        rustc_const_panic_str, Normal, template!(Word), WarnFollowing,
-        EncodeCrossCrate::Yes, "`#[rustc_const_panic_str]` ensures the argument to this function is &&str during const-check",
-    ),
-    rustc_attr!(
         rustc_const_stable_indirect, Normal,
         template!(Word),
         WarnFollowing,
@@ -946,7 +1171,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
     gated!(
         rustc_allow_const_fn_unstable, Normal,
-        template!(Word, List: "feat1, feat2, ..."), DuplicatesOk, EncodeCrossCrate::No,
+        template!(Word, List: &["feat1, feat2, ..."]), DuplicatesOk, EncodeCrossCrate::No,
         "rustc_allow_const_fn_unstable side-steps feature gating and stability checks"
     ),
 
@@ -955,13 +1180,13 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // ==========================================================================
 
     rustc_attr!(
-        rustc_layout_scalar_valid_range_start, Normal, template!(List: "value"), ErrorFollowing,
+        rustc_layout_scalar_valid_range_start, Normal, template!(List: &["value"]), ErrorFollowing,
         EncodeCrossCrate::Yes,
         "the `#[rustc_layout_scalar_valid_range_start]` attribute is just used to enable \
         niche optimizations in the standard library",
     ),
     rustc_attr!(
-        rustc_layout_scalar_valid_range_end, Normal, template!(List: "value"), ErrorFollowing,
+        rustc_layout_scalar_valid_range_end, Normal, template!(List: &["value"]), ErrorFollowing,
         EncodeCrossCrate::Yes,
         "the `#[rustc_layout_scalar_valid_range_end]` attribute is just used to enable \
         niche optimizations in the standard library",
@@ -1097,14 +1322,14 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         "the `#[rustc_main]` attribute is used internally to specify test entry point function",
     ),
     rustc_attr!(
-        rustc_skip_during_method_dispatch, Normal, template!(List: "array, boxed_slice"), ErrorFollowing,
+        rustc_skip_during_method_dispatch, Normal, template!(List: &["array, boxed_slice"]), ErrorFollowing,
         EncodeCrossCrate::No,
         "the `#[rustc_skip_during_method_dispatch]` attribute is used to exclude a trait \
         from method dispatch when the receiver is of the following type, for compatibility in \
         editions < 2021 (array) or editions < 2024 (boxed_slice)."
     ),
     rustc_attr!(
-        rustc_must_implement_one_of, Normal, template!(List: "function1, function2, ..."),
+        rustc_must_implement_one_of, Normal, template!(List: &["function1, function2, ..."]),
         ErrorFollowing, EncodeCrossCrate::No,
         "the `#[rustc_must_implement_one_of]` attribute is used to change minimal complete \
         definition of a trait. Its syntax and semantics are highly experimental and will be \
@@ -1166,11 +1391,11 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         WarnFollowing, EncodeCrossCrate::No
     ),
     rustc_attr!(
-        TEST, rustc_layout, Normal, template!(List: "field1, field2, ..."),
+        TEST, rustc_layout, Normal, template!(List: &["field1, field2, ..."]),
         WarnFollowing, EncodeCrossCrate::Yes
     ),
     rustc_attr!(
-        TEST, rustc_abi, Normal, template!(List: "field1, field2, ..."),
+        TEST, rustc_abi, Normal, template!(List: &["field1, field2, ..."]),
         WarnFollowing, EncodeCrossCrate::No
     ),
     rustc_attr!(
@@ -1191,29 +1416,29 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         EncodeCrossCrate::Yes
     ),
     rustc_attr!(
-        TEST, rustc_if_this_changed, Normal, template!(Word, List: "DepNode"), DuplicatesOk,
+        TEST, rustc_if_this_changed, Normal, template!(Word, List: &["DepNode"]), DuplicatesOk,
         EncodeCrossCrate::No
     ),
     rustc_attr!(
-        TEST, rustc_then_this_would_need, Normal, template!(List: "DepNode"), DuplicatesOk,
+        TEST, rustc_then_this_would_need, Normal, template!(List: &["DepNode"]), DuplicatesOk,
         EncodeCrossCrate::No
     ),
     rustc_attr!(
         TEST, rustc_clean, Normal,
-        template!(List: r#"cfg = "...", /*opt*/ label = "...", /*opt*/ except = "...""#),
+        template!(List: &[r#"cfg = "...", /*opt*/ label = "...", /*opt*/ except = "...""#]),
         DuplicatesOk, EncodeCrossCrate::No
     ),
     rustc_attr!(
         TEST, rustc_partition_reused, Normal,
-        template!(List: r#"cfg = "...", module = "...""#), DuplicatesOk, EncodeCrossCrate::No
+        template!(List: &[r#"cfg = "...", module = "...""#]), DuplicatesOk, EncodeCrossCrate::No
     ),
     rustc_attr!(
         TEST, rustc_partition_codegened, Normal,
-        template!(List: r#"cfg = "...", module = "...""#), DuplicatesOk, EncodeCrossCrate::No
+        template!(List: &[r#"cfg = "...", module = "...""#]), DuplicatesOk, EncodeCrossCrate::No
     ),
     rustc_attr!(
         TEST, rustc_expected_cgu_reuse, Normal,
-        template!(List: r#"cfg = "...", module = "...", kind = "...""#), DuplicatesOk,
+        template!(List: &[r#"cfg = "...", module = "...", kind = "...""#]), DuplicatesOk,
         EncodeCrossCrate::No
     ),
     rustc_attr!(
@@ -1225,11 +1450,11 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         WarnFollowing, EncodeCrossCrate::No
     ),
     rustc_attr!(
-        TEST, rustc_mir, Normal, template!(List: "arg1, arg2, ..."),
+        TEST, rustc_mir, Normal, template!(List: &["arg1, arg2, ..."]),
         DuplicatesOk, EncodeCrossCrate::Yes
     ),
     gated!(
-        custom_mir, Normal, template!(List: r#"dialect = "...", phase = "...""#),
+        custom_mir, Normal, template!(List: &[r#"dialect = "...", phase = "...""#]),
         ErrorFollowing, EncodeCrossCrate::No,
         "the `#[custom_mir]` attribute is just used for the Rust test suite",
     ),
diff --git a/compiler/rustc_feature/src/removed.rs b/compiler/rustc_feature/src/removed.rs
index 4eee79a2a71..04f261ada06 100644
--- a/compiler/rustc_feature/src/removed.rs
+++ b/compiler/rustc_feature/src/removed.rs
@@ -54,7 +54,7 @@ declare_features! (
 
     /// Allows using the `amdgpu-kernel` ABI.
     (removed, abi_amdgpu_kernel, "1.77.0", Some(51575), None, 120495),
-    (removed, abi_c_cmse_nonsecure_call, "CURRENT_RUSTC_VERSION", Some(81391), Some("renamed to abi_cmse_nonsecure_call"), 142146),
+    (removed, abi_c_cmse_nonsecure_call, "1.90.0", Some(81391), Some("renamed to abi_cmse_nonsecure_call"), 142146),
     (removed, advanced_slice_patterns, "1.42.0", Some(62254),
      Some("merged into `#![feature(slice_patterns)]`"), 67712),
     (removed, allocator, "1.0.0", None, None),
@@ -300,7 +300,7 @@ declare_features! (
     // FIXME(#141617): we should have a better way to track removed library features, but we reuse
     // the infrastructure here so users still get hints. The symbols used here can be remove from
     // `symbol.rs` when that happens.
-    (removed, concat_idents, "CURRENT_RUSTC_VERSION", Some(29599),
+    (removed, concat_idents, "1.90.0", Some(29599),
      Some("use the `${concat(..)}` metavariable expression instead"), 142704),
     // -------------------------------------------------------------------------
     // feature-group-end: removed library features
diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
index 1303b3317e0..07f928b8c88 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -327,14 +327,13 @@ declare_features! (
     (unstable, m68k_target_feature, "1.85.0", Some(134328)),
     (unstable, mips_target_feature, "1.27.0", Some(44839)),
     (unstable, movrs_target_feature, "1.88.0", Some(137976)),
+    (unstable, nvptx_target_feature, "CURRENT_RUSTC_VERSION", Some(44839)),
     (unstable, powerpc_target_feature, "1.27.0", Some(44839)),
     (unstable, prfchw_target_feature, "1.78.0", Some(44839)),
     (unstable, riscv_target_feature, "1.45.0", Some(44839)),
     (unstable, rtm_target_feature, "1.35.0", Some(44839)),
     (unstable, s390x_target_feature, "1.82.0", Some(44839)),
     (unstable, sparc_target_feature, "1.84.0", Some(132783)),
-    (unstable, sse4a_target_feature, "1.27.0", Some(44839)),
-    (unstable, tbm_target_feature, "1.27.0", Some(44839)),
     (unstable, wasm_target_feature, "1.30.0", Some(44839)),
     (unstable, x87_target_feature, "1.85.0", Some(44839)),
     // !!!!    !!!!    !!!!    !!!!   !!!!    !!!!    !!!!    !!!!    !!!!    !!!!    !!!!
@@ -352,7 +351,7 @@ declare_features! (
     /// Allows `extern "avr-interrupt" fn()` and `extern "avr-non-blocking-interrupt" fn()`.
     (unstable, abi_avr_interrupt, "1.45.0", Some(69664)),
     /// Allows `extern "cmse-nonsecure-call" fn()`.
-    (unstable, abi_cmse_nonsecure_call, "CURRENT_RUSTC_VERSION", Some(81391)),
+    (unstable, abi_cmse_nonsecure_call, "1.90.0", Some(81391)),
     /// Allows `extern "custom" fn()`.
     (unstable, abi_custom, "1.89.0", Some(140829)),
     /// Allows `extern "gpu-kernel" fn()`.
@@ -471,6 +470,8 @@ declare_features! (
     (unstable, deprecated_suggestion, "1.61.0", Some(94785)),
     /// Allows deref patterns.
     (incomplete, deref_patterns, "1.79.0", Some(87121)),
+    /// Allows deriving the From trait on single-field structs.
+    (unstable, derive_from, "CURRENT_RUSTC_VERSION", Some(144889)),
     /// Tells rustdoc to automatically generate `#[doc(cfg(...))]`.
     (unstable, doc_auto_cfg, "1.58.0", Some(43781)),
     /// Allows `#[doc(cfg(...))]`.
@@ -544,7 +545,7 @@ declare_features! (
     (incomplete, inherent_associated_types, "1.52.0", Some(8995)),
     /// Allows using `pointer` and `reference` in intra-doc links
     (unstable, intra_doc_pointers, "1.51.0", Some(80896)),
-    // Allows setting the threshold for the `large_assignments` lint.
+    /// Allows setting the threshold for the `large_assignments` lint.
     (unstable, large_assignments, "1.52.0", Some(83518)),
     /// Allow to have type alias types for inter-crate use.
     (incomplete, lazy_type_alias, "1.72.0", Some(112792)),
@@ -552,7 +553,9 @@ declare_features! (
     /// to pass custom arguments to the linker.
     (unstable, link_arg_attribute, "1.76.0", Some(99427)),
     /// Allows fused `loop`/`match` for direct intraprocedural jumps.
-    (incomplete, loop_match, "CURRENT_RUSTC_VERSION", Some(132306)),
+    (incomplete, loop_match, "1.90.0", Some(132306)),
+    /// Allow `macro_rules!` attribute rules
+    (unstable, macro_attr, "CURRENT_RUSTC_VERSION", Some(83527)),
     /// Give access to additional metadata about declarative macro meta-variables.
     (unstable, macro_metavar_expr, "1.61.0", Some(83527)),
     /// Provides a way to concatenate identifiers using metavariable expressions.
diff --git a/compiler/rustc_hir/Cargo.toml b/compiler/rustc_hir/Cargo.toml
index 539d2e6f0b1..71496b7ec32 100644
--- a/compiler/rustc_hir/Cargo.toml
+++ b/compiler/rustc_hir/Cargo.toml
@@ -5,6 +5,7 @@ edition = "2024"
 
 [dependencies]
 # tidy-alphabetical-start
+bitflags = "2.9.1"
 odht = { version = "0.3.1", features = ["nightly"] }
 rustc_abi = { path = "../rustc_abi" }
 rustc_arena = { path = "../rustc_arena" }
diff --git a/compiler/rustc_hir/src/attrs/data_structures.rs b/compiler/rustc_hir/src/attrs/data_structures.rs
index d9d2ec48948..510fc832978 100644
--- a/compiler/rustc_hir/src/attrs/data_structures.rs
+++ b/compiler/rustc_hir/src/attrs/data_structures.rs
@@ -187,6 +187,24 @@ pub enum CfgEntry {
     Version(Option<RustcVersion>, Span),
 }
 
+/// Possible values for the `#[linkage]` attribute, allowing to specify the
+/// linkage type for a `MonoItem`.
+///
+/// See <https://llvm.org/docs/LangRef.html#linkage-types> for more details about these variants.
+#[derive(Encodable, Decodable, Clone, Copy, Debug, PartialEq, Eq, Hash)]
+#[derive(HashStable_Generic, PrintAttribute)]
+pub enum Linkage {
+    AvailableExternally,
+    Common,
+    ExternalWeak,
+    External,
+    Internal,
+    LinkOnceAny,
+    LinkOnceODR,
+    WeakAny,
+    WeakODR,
+}
+
 /// Represents parsed *built-in* inert attributes.
 ///
 /// ## Overview
@@ -249,6 +267,9 @@ pub enum AttributeKind {
     /// Represents `#[rustc_allow_incoherent_impl]`.
     AllowIncoherentImpl(Span),
 
+    /// Represents `#[allow_internal_unsafe]`.
+    AllowInternalUnsafe(Span),
+
     /// Represents `#[allow_internal_unstable]`.
     AllowInternalUnstable(ThinVec<(Symbol, Span)>, Span),
 
@@ -357,6 +378,9 @@ pub enum AttributeKind {
     /// Represents [`#[link_section]`](https://doc.rust-lang.org/reference/abi.html#the-link_section-attribute)
     LinkSection { name: Symbol, span: Span },
 
+    /// Represents `#[linkage]`.
+    Linkage(Linkage, Span),
+
     /// Represents `#[loop_match]`.
     LoopMatch(Span),
 
@@ -436,6 +460,9 @@ pub enum AttributeKind {
     /// Represents `#[rustc_object_lifetime_default]`.
     RustcObjectLifetimeDefault,
 
+    /// Represents `#[should_panic]`
+    ShouldPanic { reason: Option<Symbol>, span: Span },
+
     /// Represents `#[rustc_skip_during_method_dispatch]`.
     SkipDuringMethodDispatch { array: bool, boxed_slice: bool, span: Span },
 
diff --git a/compiler/rustc_hir/src/attrs/encode_cross_crate.rs b/compiler/rustc_hir/src/attrs/encode_cross_crate.rs
index b66e5bbeabe..84a975523f2 100644
--- a/compiler/rustc_hir/src/attrs/encode_cross_crate.rs
+++ b/compiler/rustc_hir/src/attrs/encode_cross_crate.rs
@@ -16,6 +16,7 @@ impl AttributeKind {
             Align { .. } => No,
             AllowConstFnUnstable(..) => No,
             AllowIncoherentImpl(..) => No,
+            AllowInternalUnsafe(..) => Yes,
             AllowInternalUnstable(..) => Yes,
             AsPtr(..) => Yes,
             AutomaticallyDerived(..) => Yes,
@@ -45,6 +46,7 @@ impl AttributeKind {
             LinkName { .. } => Yes, // Needed for rustdoc
             LinkOrdinal { .. } => No,
             LinkSection { .. } => Yes, // Needed for rustdoc
+            Linkage(..) => No,
             LoopMatch(..) => No,
             MacroEscape(..) => No,
             MacroTransparency(..) => Yes,
@@ -70,6 +72,7 @@ impl AttributeKind {
             RustcLayoutScalarValidRangeEnd(..) => Yes,
             RustcLayoutScalarValidRangeStart(..) => Yes,
             RustcObjectLifetimeDefault => No,
+            ShouldPanic { .. } => No,
             SkipDuringMethodDispatch { .. } => No,
             SpecializationTrait(..) => No,
             Stability { .. } => Yes,
diff --git a/compiler/rustc_hir/src/def.rs b/compiler/rustc_hir/src/def.rs
index 2201d493f2d..79319e24266 100644
--- a/compiler/rustc_hir/src/def.rs
+++ b/compiler/rustc_hir/src/def.rs
@@ -31,6 +31,53 @@ pub enum CtorKind {
     Const,
 }
 
+/// A set of macro kinds, for macros that can have more than one kind
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Encodable, Decodable, Hash, Debug)]
+#[derive(HashStable_Generic)]
+pub struct MacroKinds(u8);
+bitflags::bitflags! {
+    impl MacroKinds: u8 {
+        const BANG = 1 << 0;
+        const ATTR = 1 << 1;
+        const DERIVE = 1 << 2;
+    }
+}
+
+impl From<MacroKind> for MacroKinds {
+    fn from(kind: MacroKind) -> Self {
+        match kind {
+            MacroKind::Bang => Self::BANG,
+            MacroKind::Attr => Self::ATTR,
+            MacroKind::Derive => Self::DERIVE,
+        }
+    }
+}
+
+impl MacroKinds {
+    /// Convert the MacroKinds to a static string.
+    ///
+    /// This hardcodes all the possibilities, in order to return a static string.
+    pub fn descr(self) -> &'static str {
+        match self {
+            // FIXME: change this to "function-like macro" and fix all tests
+            Self::BANG => "macro",
+            Self::ATTR => "attribute macro",
+            Self::DERIVE => "derive macro",
+            _ if self == (Self::ATTR | Self::BANG) => "attribute/function macro",
+            _ if self == (Self::DERIVE | Self::BANG) => "derive/function macro",
+            _ if self == (Self::ATTR | Self::DERIVE) => "attribute/derive macro",
+            _ if self.is_all() => "attribute/derive/function macro",
+            _ if self.is_empty() => "useless macro",
+            _ => unreachable!(),
+        }
+    }
+
+    /// Return an indefinite article (a/an) for use with `descr()`
+    pub fn article(self) -> &'static str {
+        if self.contains(Self::ATTR) { "an" } else { "a" }
+    }
+}
+
 /// An attribute that is not a macro; e.g., `#[inline]` or `#[rustfmt::skip]`.
 #[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug, HashStable_Generic)]
 pub enum NonMacroAttrKind {
@@ -101,7 +148,7 @@ pub enum DefKind {
     AssocConst,
 
     // Macro namespace
-    Macro(MacroKind),
+    Macro(MacroKinds),
 
     // Not namespaced (or they are, but we don't treat them so)
     ExternCrate,
@@ -177,7 +224,7 @@ impl DefKind {
             DefKind::AssocConst => "associated constant",
             DefKind::TyParam => "type parameter",
             DefKind::ConstParam => "const parameter",
-            DefKind::Macro(macro_kind) => macro_kind.descr(),
+            DefKind::Macro(kinds) => kinds.descr(),
             DefKind::LifetimeParam => "lifetime parameter",
             DefKind::Use => "import",
             DefKind::ForeignMod => "foreign module",
@@ -208,7 +255,7 @@ impl DefKind {
             | DefKind::Use
             | DefKind::InlineConst
             | DefKind::ExternCrate => "an",
-            DefKind::Macro(macro_kind) => macro_kind.article(),
+            DefKind::Macro(kinds) => kinds.article(),
             _ => "a",
         }
     }
@@ -306,6 +353,11 @@ impl DefKind {
     }
 
     #[inline]
+    pub fn is_adt(self) -> bool {
+        matches!(self, DefKind::Struct | DefKind::Union | DefKind::Enum)
+    }
+
+    #[inline]
     pub fn is_fn_like(self) -> bool {
         matches!(
             self,
@@ -313,6 +365,43 @@ impl DefKind {
         )
     }
 
+    /// Whether the corresponding item has generic parameters, ie. the `generics_of` query works.
+    pub fn has_generics(self) -> bool {
+        match self {
+            DefKind::AnonConst
+            | DefKind::AssocConst
+            | DefKind::AssocFn
+            | DefKind::AssocTy
+            | DefKind::Closure
+            | DefKind::Const
+            | DefKind::Ctor(..)
+            | DefKind::Enum
+            | DefKind::Field
+            | DefKind::Fn
+            | DefKind::ForeignTy
+            | DefKind::Impl { .. }
+            | DefKind::InlineConst
+            | DefKind::OpaqueTy
+            | DefKind::Static { .. }
+            | DefKind::Struct
+            | DefKind::SyntheticCoroutineBody
+            | DefKind::Trait
+            | DefKind::TraitAlias
+            | DefKind::TyAlias
+            | DefKind::Union
+            | DefKind::Variant => true,
+            DefKind::ConstParam
+            | DefKind::ExternCrate
+            | DefKind::ForeignMod
+            | DefKind::GlobalAsm
+            | DefKind::LifetimeParam
+            | DefKind::Macro(_)
+            | DefKind::Mod
+            | DefKind::TyParam
+            | DefKind::Use => false,
+        }
+    }
+
     /// Whether `query get_codegen_attrs` should be used with this definition.
     pub fn has_codegen_attrs(self) -> bool {
         match self {
@@ -803,10 +892,10 @@ impl<Id> Res<Id> {
         )
     }
 
-    pub fn macro_kind(self) -> Option<MacroKind> {
+    pub fn macro_kinds(self) -> Option<MacroKinds> {
         match self {
-            Res::Def(DefKind::Macro(kind), _) => Some(kind),
-            Res::NonMacroAttr(..) => Some(MacroKind::Attr),
+            Res::Def(DefKind::Macro(kinds), _) => Some(kinds),
+            Res::NonMacroAttr(..) => Some(MacroKinds::ATTR),
             _ => None,
         }
     }
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index c30c830f9af..2c8986b7c7d 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -20,7 +20,6 @@ use rustc_data_structures::tagged_ptr::TaggedRef;
 use rustc_index::IndexVec;
 use rustc_macros::{Decodable, Encodable, HashStable_Generic};
 use rustc_span::def_id::LocalDefId;
-use rustc_span::hygiene::MacroKind;
 use rustc_span::source_map::Spanned;
 use rustc_span::{BytePos, DUMMY_SP, ErrorGuaranteed, Ident, Span, Symbol, kw, sym};
 use rustc_target::asm::InlineAsmRegOrRegClass;
@@ -30,7 +29,7 @@ use tracing::debug;
 
 use crate::LangItem;
 use crate::attrs::AttributeKind;
-use crate::def::{CtorKind, DefKind, PerNS, Res};
+use crate::def::{CtorKind, DefKind, MacroKinds, PerNS, Res};
 use crate::def_id::{DefId, LocalDefIdMap};
 pub(crate) use crate::hir_id::{HirId, ItemLocalId, ItemLocalMap, OwnerId};
 use crate::intravisit::{FnKind, VisitorExt};
@@ -1233,6 +1232,13 @@ impl Attribute {
             _ => None,
         }
     }
+
+    pub fn is_parsed_attr(&self) -> bool {
+        match self {
+            Attribute::Parsed(_) => true,
+            Attribute::Unparsed(_) => false,
+        }
+    }
 }
 
 impl AttributeExt for Attribute {
@@ -1303,12 +1309,10 @@ impl AttributeExt for Attribute {
         match &self {
             Attribute::Unparsed(u) => u.span,
             // FIXME: should not be needed anymore when all attrs are parsed
-            Attribute::Parsed(AttributeKind::Deprecation { span, .. }) => *span,
             Attribute::Parsed(AttributeKind::DocComment { span, .. }) => *span,
-            Attribute::Parsed(AttributeKind::MacroUse { span, .. }) => *span,
-            Attribute::Parsed(AttributeKind::MayDangle(span)) => *span,
-            Attribute::Parsed(AttributeKind::Ignore { span, .. }) => *span,
-            Attribute::Parsed(AttributeKind::AutomaticallyDerived(span)) => *span,
+            Attribute::Parsed(AttributeKind::Deprecation { span, .. }) => *span,
+            Attribute::Parsed(AttributeKind::AllowInternalUnsafe(span)) => *span,
+            Attribute::Parsed(AttributeKind::Linkage(_, span)) => *span,
             a => panic!("can't get the span of an arbitrary parsed attribute: {a:?}"),
         }
     }
@@ -4155,7 +4159,7 @@ impl<'hir> Item<'hir> {
         expect_fn, (Ident, &FnSig<'hir>, &'hir Generics<'hir>, BodyId),
             ItemKind::Fn { ident, sig, generics, body, .. }, (*ident, sig, generics, *body);
 
-        expect_macro, (Ident, &ast::MacroDef, MacroKind),
+        expect_macro, (Ident, &ast::MacroDef, MacroKinds),
             ItemKind::Macro(ident, def, mk), (*ident, def, *mk);
 
         expect_mod, (Ident, &'hir Mod<'hir>), ItemKind::Mod(ident, m), (*ident, m);
@@ -4193,7 +4197,7 @@ impl<'hir> Item<'hir> {
         expect_trait_alias, (Ident, &'hir Generics<'hir>, GenericBounds<'hir>),
             ItemKind::TraitAlias(ident, generics, bounds), (*ident, generics, bounds);
 
-        expect_impl, &'hir Impl<'hir>, ItemKind::Impl(imp), imp;
+        expect_impl, &Impl<'hir>, ItemKind::Impl(imp), imp;
     }
 }
 
@@ -4334,7 +4338,7 @@ pub enum ItemKind<'hir> {
         has_body: bool,
     },
     /// A MBE macro definition (`macro_rules!` or `macro`).
-    Macro(Ident, &'hir ast::MacroDef, MacroKind),
+    Macro(Ident, &'hir ast::MacroDef, MacroKinds),
     /// A module.
     Mod(Ident, &'hir Mod<'hir>),
     /// An external module, e.g. `extern { .. }`.
@@ -4371,7 +4375,7 @@ pub enum ItemKind<'hir> {
     TraitAlias(Ident, &'hir Generics<'hir>, GenericBounds<'hir>),
 
     /// An implementation, e.g., `impl<A> Trait for Foo { .. }`.
-    Impl(&'hir Impl<'hir>),
+    Impl(Impl<'hir>),
 }
 
 /// Represents an impl block declaration.
@@ -4380,6 +4384,14 @@ pub enum ItemKind<'hir> {
 /// Refer to [`ImplItem`] for an associated item within an impl block.
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
 pub struct Impl<'hir> {
+    pub generics: &'hir Generics<'hir>,
+    pub of_trait: Option<&'hir TraitImplHeader<'hir>>,
+    pub self_ty: &'hir Ty<'hir>,
+    pub items: &'hir [ImplItemId],
+}
+
+#[derive(Debug, Clone, Copy, HashStable_Generic)]
+pub struct TraitImplHeader<'hir> {
     pub constness: Constness,
     pub safety: Safety,
     pub polarity: ImplPolarity,
@@ -4387,13 +4399,7 @@ pub struct Impl<'hir> {
     // We do not put a `Span` in `Defaultness` because it breaks foreign crate metadata
     // decoding as `Span`s cannot be decoded when a `Session` is not available.
     pub defaultness_span: Option<Span>,
-    pub generics: &'hir Generics<'hir>,
-
-    /// The trait being implemented, if any.
-    pub of_trait: Option<TraitRef<'hir>>,
-
-    pub self_ty: &'hir Ty<'hir>,
-    pub items: &'hir [ImplItemId],
+    pub trait_ref: TraitRef<'hir>,
 }
 
 impl ItemKind<'_> {
@@ -4755,8 +4761,8 @@ impl<'hir> Node<'hir> {
     /// Get a `hir::Impl` if the node is an impl block for the given `trait_def_id`.
     pub fn impl_block_of_trait(self, trait_def_id: DefId) -> Option<&'hir Impl<'hir>> {
         if let Node::Item(Item { kind: ItemKind::Impl(impl_block), .. }) = self
-            && let Some(trait_ref) = impl_block.of_trait
-            && let Some(trait_id) = trait_ref.trait_def_id()
+            && let Some(of_trait) = impl_block.of_trait
+            && let Some(trait_id) = of_trait.trait_ref.trait_def_id()
             && trait_id == trait_def_id
         {
             Some(impl_block)
@@ -4951,7 +4957,7 @@ mod size_asserts {
     static_assert_size!(GenericArg<'_>, 16);
     static_assert_size!(GenericBound<'_>, 64);
     static_assert_size!(Generics<'_>, 56);
-    static_assert_size!(Impl<'_>, 80);
+    static_assert_size!(Impl<'_>, 40);
     static_assert_size!(ImplItem<'_>, 96);
     static_assert_size!(ImplItemKind<'_>, 40);
     static_assert_size!(Item<'_>, 88);
@@ -4966,6 +4972,7 @@ mod size_asserts {
     static_assert_size!(Res, 12);
     static_assert_size!(Stmt<'_>, 32);
     static_assert_size!(StmtKind<'_>, 16);
+    static_assert_size!(TraitImplHeader<'_>, 48);
     static_assert_size!(TraitItem<'_>, 88);
     static_assert_size!(TraitItemKind<'_>, 48);
     static_assert_size!(Ty<'_>, 48);
diff --git a/compiler/rustc_hir/src/intravisit.rs b/compiler/rustc_hir/src/intravisit.rs
index 23fa466859a..9b2f8ae75fa 100644
--- a/compiler/rustc_hir/src/intravisit.rs
+++ b/compiler/rustc_hir/src/intravisit.rs
@@ -590,21 +590,21 @@ pub fn walk_item<'v, V: Visitor<'v>>(visitor: &mut V, item: &'v Item<'v>) -> V::
             try_visit!(visitor.visit_generics(generics));
             try_visit!(visitor.visit_enum_def(enum_definition));
         }
-        ItemKind::Impl(Impl {
-            constness: _,
-            safety: _,
-            defaultness: _,
-            polarity: _,
-            defaultness_span: _,
-            generics,
-            of_trait,
-            self_ty,
-            items,
-        }) => {
+        ItemKind::Impl(Impl { generics, of_trait, self_ty, items }) => {
             try_visit!(visitor.visit_generics(generics));
-            visit_opt!(visitor, visit_trait_ref, of_trait);
+            if let Some(TraitImplHeader {
+                constness: _,
+                safety: _,
+                polarity: _,
+                defaultness: _,
+                defaultness_span: _,
+                trait_ref,
+            }) = of_trait
+            {
+                try_visit!(visitor.visit_trait_ref(trait_ref));
+            }
             try_visit!(visitor.visit_ty_unambig(self_ty));
-            walk_list!(visitor, visit_impl_item_ref, *items);
+            walk_list!(visitor, visit_impl_item_ref, items);
         }
         ItemKind::Struct(ident, ref generics, ref struct_definition)
         | ItemKind::Union(ident, ref generics, ref struct_definition) => {
diff --git a/compiler/rustc_hir/src/lang_items.rs b/compiler/rustc_hir/src/lang_items.rs
index 75c04b23ed6..905b84a8cbe 100644
--- a/compiler/rustc_hir/src/lang_items.rs
+++ b/compiler/rustc_hir/src/lang_items.rs
@@ -286,6 +286,7 @@ language_item_table! {
     Panic,                   sym::panic,               panic_fn,                   Target::Fn,             GenericRequirement::Exact(0);
     PanicNounwind,           sym::panic_nounwind,      panic_nounwind,             Target::Fn,             GenericRequirement::Exact(0);
     PanicFmt,                sym::panic_fmt,           panic_fmt,                  Target::Fn,             GenericRequirement::None;
+    PanicDisplay,            sym::panic_display,       panic_display,              Target::Fn,             GenericRequirement::None;
     ConstPanicFmt,           sym::const_panic_fmt,     const_panic_fmt,            Target::Fn,             GenericRequirement::None;
     PanicBoundsCheck,        sym::panic_bounds_check,  panic_bounds_check_fn,      Target::Fn,             GenericRequirement::Exact(0);
     PanicMisalignedPointerDereference, sym::panic_misaligned_pointer_dereference, panic_misaligned_pointer_dereference_fn, Target::Fn, GenericRequirement::Exact(0);
diff --git a/compiler/rustc_hir/src/lints.rs b/compiler/rustc_hir/src/lints.rs
index c55a41eb2b7..e3cde2d3bb6 100644
--- a/compiler/rustc_hir/src/lints.rs
+++ b/compiler/rustc_hir/src/lints.rs
@@ -1,8 +1,8 @@
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_macros::HashStable_Generic;
-use rustc_span::Span;
+use rustc_span::{Span, Symbol};
 
-use crate::HirId;
+use crate::{HirId, Target};
 
 #[derive(Debug)]
 pub struct DelayedLints {
@@ -34,4 +34,5 @@ pub enum AttributeLintKind {
     UnusedDuplicate { this: Span, other: Span, warning: bool },
     IllFormedAttributeInput { suggestions: Vec<String> },
     EmptyAttribute { first_span: Span },
+    InvalidTarget { name: Symbol, target: Target, applied: String, only: &'static str },
 }
diff --git a/compiler/rustc_hir/src/target.rs b/compiler/rustc_hir/src/target.rs
index d617f44f8d8..f68dad3a5e8 100644
--- a/compiler/rustc_hir/src/target.rs
+++ b/compiler/rustc_hir/src/target.rs
@@ -6,23 +6,34 @@
 
 use std::fmt::{self, Display};
 
+use rustc_ast::visit::AssocCtxt;
+use rustc_ast::{AssocItemKind, ForeignItemKind, ast};
+use rustc_macros::HashStable_Generic;
+
 use crate::def::DefKind;
 use crate::{Item, ItemKind, TraitItem, TraitItemKind, hir};
 
-#[derive(Copy, Clone, PartialEq, Debug)]
+#[derive(Copy, Clone, PartialEq, Debug, Eq, HashStable_Generic)]
 pub enum GenericParamKind {
     Type,
     Lifetime,
     Const,
 }
 
-#[derive(Copy, Clone, PartialEq, Debug)]
+#[derive(Copy, Clone, PartialEq, Debug, Eq, HashStable_Generic)]
 pub enum MethodKind {
-    Trait { body: bool },
+    /// Method in a `trait Trait` block
+    Trait {
+        /// Whether a default is provided for this method
+        body: bool,
+    },
+    /// Method in a `impl Trait for Type` block
+    TraitImpl,
+    /// Method in a `impl Type` block
     Inherent,
 }
 
-#[derive(Copy, Clone, PartialEq, Debug)]
+#[derive(Copy, Clone, PartialEq, Debug, Eq, HashStable_Generic)]
 pub enum Target {
     ExternCrate,
     Use,
@@ -57,6 +68,9 @@ pub enum Target {
     PatField,
     ExprField,
     WherePredicate,
+    MacroCall,
+    Crate,
+    Delegation { mac: bool },
 }
 
 impl Display for Target {
@@ -98,7 +112,10 @@ impl Target {
             | Target::Param
             | Target::PatField
             | Target::ExprField
-            | Target::WherePredicate => false,
+            | Target::MacroCall
+            | Target::Crate
+            | Target::WherePredicate
+            | Target::Delegation { .. } => false,
         }
     }
 
@@ -146,6 +163,39 @@ impl Target {
         }
     }
 
+    pub fn from_ast_item(item: &ast::Item) -> Target {
+        match item.kind {
+            ast::ItemKind::ExternCrate(..) => Target::ExternCrate,
+            ast::ItemKind::Use(..) => Target::Use,
+            ast::ItemKind::Static { .. } => Target::Static,
+            ast::ItemKind::Const(..) => Target::Const,
+            ast::ItemKind::Fn { .. } => Target::Fn,
+            ast::ItemKind::Mod(..) => Target::Mod,
+            ast::ItemKind::ForeignMod { .. } => Target::ForeignMod,
+            ast::ItemKind::GlobalAsm { .. } => Target::GlobalAsm,
+            ast::ItemKind::TyAlias(..) => Target::TyAlias,
+            ast::ItemKind::Enum(..) => Target::Enum,
+            ast::ItemKind::Struct(..) => Target::Struct,
+            ast::ItemKind::Union(..) => Target::Union,
+            ast::ItemKind::Trait(..) => Target::Trait,
+            ast::ItemKind::TraitAlias(..) => Target::TraitAlias,
+            ast::ItemKind::Impl(ref i) => Target::Impl { of_trait: i.of_trait.is_some() },
+            ast::ItemKind::MacCall(..) => Target::MacroCall,
+            ast::ItemKind::MacroDef(..) => Target::MacroDef,
+            ast::ItemKind::Delegation(..) => Target::Delegation { mac: false },
+            ast::ItemKind::DelegationMac(..) => Target::Delegation { mac: true },
+        }
+    }
+
+    pub fn from_foreign_item_kind(kind: &ast::ForeignItemKind) -> Target {
+        match kind {
+            ForeignItemKind::Static(_) => Target::ForeignStatic,
+            ForeignItemKind::Fn(_) => Target::ForeignFn,
+            ForeignItemKind::TyAlias(_) => Target::ForeignTy,
+            ForeignItemKind::MacCall(_) => Target::MacroCall,
+        }
+    }
+
     pub fn from_trait_item(trait_item: &TraitItem<'_>) -> Target {
         match trait_item.kind {
             TraitItemKind::Const(..) => Target::AssocConst,
@@ -183,12 +233,40 @@ impl Target {
         }
     }
 
+    pub fn from_assoc_item_kind(kind: &ast::AssocItemKind, assoc_ctxt: AssocCtxt) -> Target {
+        match kind {
+            AssocItemKind::Const(_) => Target::AssocConst,
+            AssocItemKind::Fn(f) => Target::Method(match assoc_ctxt {
+                AssocCtxt::Trait => MethodKind::Trait { body: f.body.is_some() },
+                AssocCtxt::Impl { of_trait } => {
+                    if of_trait {
+                        MethodKind::TraitImpl
+                    } else {
+                        MethodKind::Inherent
+                    }
+                }
+            }),
+            AssocItemKind::Type(_) => Target::AssocTy,
+            AssocItemKind::Delegation(_) => Target::Delegation { mac: false },
+            AssocItemKind::DelegationMac(_) => Target::Delegation { mac: true },
+            AssocItemKind::MacCall(_) => Target::MacroCall,
+        }
+    }
+
+    pub fn from_expr(expr: &ast::Expr) -> Self {
+        match &expr.kind {
+            ast::ExprKind::Closure(..) | ast::ExprKind::Gen(..) => Self::Closure,
+            ast::ExprKind::Paren(e) => Self::from_expr(&e),
+            _ => Self::Expression,
+        }
+    }
+
     pub fn name(self) -> &'static str {
         match self {
             Target::ExternCrate => "extern crate",
             Target::Use => "use",
-            Target::Static => "static item",
-            Target::Const => "constant item",
+            Target::Static => "static",
+            Target::Const => "constant",
             Target::Fn => "function",
             Target::Closure => "closure",
             Target::Mod => "module",
@@ -202,8 +280,7 @@ impl Target {
             Target::Union => "union",
             Target::Trait => "trait",
             Target::TraitAlias => "trait alias",
-            Target::Impl { of_trait: false } => "inherent implementation block",
-            Target::Impl { of_trait: true } => "trait implementation block",
+            Target::Impl { .. } => "implementation block",
             Target::Expression => "expression",
             Target::Statement => "statement",
             Target::Arm => "match arm",
@@ -212,12 +289,13 @@ impl Target {
                 MethodKind::Inherent => "inherent method",
                 MethodKind::Trait { body: false } => "required trait method",
                 MethodKind::Trait { body: true } => "provided trait method",
+                MethodKind::TraitImpl => "trait method in an impl block",
             },
             Target::AssocTy => "associated type",
             Target::ForeignFn => "foreign function",
             Target::ForeignStatic => "foreign static item",
             Target::ForeignTy => "foreign type",
-            Target::GenericParam { kind, has_default: _ } => match kind {
+            Target::GenericParam { kind, .. } => match kind {
                 GenericParamKind::Type => "type parameter",
                 GenericParamKind::Lifetime => "lifetime parameter",
                 GenericParamKind::Const => "const parameter",
@@ -227,6 +305,60 @@ impl Target {
             Target::PatField => "pattern field",
             Target::ExprField => "struct field",
             Target::WherePredicate => "where predicate",
+            Target::MacroCall => "macro call",
+            Target::Crate => "crate",
+            Target::Delegation { .. } => "delegation",
+        }
+    }
+
+    pub fn plural_name(self) -> &'static str {
+        match self {
+            Target::ExternCrate => "extern crates",
+            Target::Use => "use statements",
+            Target::Static => "statics",
+            Target::Const => "constants",
+            Target::Fn => "functions",
+            Target::Closure => "closures",
+            Target::Mod => "modules",
+            Target::ForeignMod => "foreign modules",
+            Target::GlobalAsm => "global asms",
+            Target::TyAlias => "type aliases",
+            Target::Enum => "enums",
+            Target::Variant => "enum variants",
+            Target::Struct => "structs",
+            Target::Field => "struct fields",
+            Target::Union => "unions",
+            Target::Trait => "traits",
+            Target::TraitAlias => "trait aliases",
+            Target::Impl { of_trait: false } => "inherent impl blocks",
+            Target::Impl { of_trait: true } => "trait impl blocks",
+            Target::Expression => "expressions",
+            Target::Statement => "statements",
+            Target::Arm => "match arms",
+            Target::AssocConst => "associated consts",
+            Target::Method(kind) => match kind {
+                MethodKind::Inherent => "inherent methods",
+                MethodKind::Trait { body: false } => "required trait methods",
+                MethodKind::Trait { body: true } => "provided trait methods",
+                MethodKind::TraitImpl => "trait methods in impl blocks",
+            },
+            Target::AssocTy => "associated types",
+            Target::ForeignFn => "foreign functions",
+            Target::ForeignStatic => "foreign statics",
+            Target::ForeignTy => "foreign types",
+            Target::GenericParam { kind, has_default: _ } => match kind {
+                GenericParamKind::Type => "type parameters",
+                GenericParamKind::Lifetime => "lifetime parameters",
+                GenericParamKind::Const => "const parameters",
+            },
+            Target::MacroDef => "macro defs",
+            Target::Param => "function params",
+            Target::PatField => "pattern fields",
+            Target::ExprField => "struct fields",
+            Target::WherePredicate => "where predicates",
+            Target::MacroCall => "macro calls",
+            Target::Crate => "crates",
+            Target::Delegation { .. } => "delegations",
         }
     }
 }
diff --git a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
index 6767e5ed88d..e4827256193 100644
--- a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
+++ b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
@@ -445,10 +445,10 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
     tcx: TyCtxt<'tcx>,
     impl_m_def_id: LocalDefId,
 ) -> Result<&'tcx DefIdMap<ty::EarlyBinder<'tcx, Ty<'tcx>>>, ErrorGuaranteed> {
-    let impl_m = tcx.opt_associated_item(impl_m_def_id.to_def_id()).unwrap();
-    let trait_m = tcx.opt_associated_item(impl_m.trait_item_def_id.unwrap()).unwrap();
+    let impl_m = tcx.associated_item(impl_m_def_id.to_def_id());
+    let trait_m = tcx.associated_item(impl_m.trait_item_def_id.unwrap());
     let impl_trait_ref =
-        tcx.impl_trait_ref(impl_m.impl_container(tcx).unwrap()).unwrap().instantiate_identity();
+        tcx.impl_trait_ref(tcx.parent(impl_m_def_id.to_def_id())).unwrap().instantiate_identity();
     // First, check a few of the same things as `compare_impl_method`,
     // just so we don't ICE during instantiation later.
     check_method_is_structurally_compatible(tcx, impl_m, trait_m, impl_trait_ref, true)?;
diff --git a/compiler/rustc_hir_analysis/src/check/intrinsic.rs b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
index 6e5fe3823ab..f50aed0b3c2 100644
--- a/compiler/rustc_hir_analysis/src/check/intrinsic.rs
+++ b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
@@ -135,6 +135,7 @@ fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: LocalDefId) -> hi
         | sym::round_ties_even_f32
         | sym::round_ties_even_f64
         | sym::round_ties_even_f128
+        | sym::autodiff
         | sym::const_eval_select => hir::Safety::Safe,
         _ => hir::Safety::Unsafe,
     };
@@ -198,6 +199,7 @@ pub(crate) fn check_intrinsic_type(
     let safety = intrinsic_operation_unsafety(tcx, intrinsic_id);
     let n_lts = 0;
     let (n_tps, n_cts, inputs, output) = match intrinsic_name {
+        sym::autodiff => (4, 0, vec![param(0), param(1), param(2)], param(3)),
         sym::abort => (0, 0, vec![], tcx.types.never),
         sym::unreachable => (0, 0, vec![], tcx.types.never),
         sym::breakpoint => (0, 0, vec![], tcx.types.unit),
@@ -652,16 +654,16 @@ pub(crate) fn check_intrinsic_type(
         sym::atomic_store => (1, 1, vec![Ty::new_mut_ptr(tcx, param(0)), param(0)], tcx.types.unit),
 
         sym::atomic_xchg
-        | sym::atomic_xadd
-        | sym::atomic_xsub
-        | sym::atomic_and
-        | sym::atomic_nand
-        | sym::atomic_or
-        | sym::atomic_xor
         | sym::atomic_max
         | sym::atomic_min
         | sym::atomic_umax
         | sym::atomic_umin => (1, 1, vec![Ty::new_mut_ptr(tcx, param(0)), param(0)], param(0)),
+        sym::atomic_xadd
+        | sym::atomic_xsub
+        | sym::atomic_and
+        | sym::atomic_nand
+        | sym::atomic_or
+        | sym::atomic_xor => (2, 1, vec![Ty::new_mut_ptr(tcx, param(0)), param(1)], param(0)),
         sym::atomic_fence | sym::atomic_singlethreadfence => (0, 1, Vec::new(), tcx.types.unit),
 
         other => {
diff --git a/compiler/rustc_hir_analysis/src/check/region.rs b/compiler/rustc_hir_analysis/src/check/region.rs
index 95f6fba6487..f5770b7312d 100644
--- a/compiler/rustc_hir_analysis/src/check/region.rs
+++ b/compiler/rustc_hir_analysis/src/check/region.rs
@@ -199,6 +199,11 @@ fn resolve_arm<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, arm: &'tcx hir:
 
     resolve_pat(visitor, arm.pat);
     if let Some(guard) = arm.guard {
+        // We introduce a new scope to contain bindings and temporaries from `if let` guards, to
+        // ensure they're dropped before the arm's pattern's bindings. This extends to the end of
+        // the arm body and is the scope of its locals as well.
+        visitor.enter_scope(Scope { local_id: arm.hir_id.local_id, data: ScopeData::MatchGuard });
+        visitor.cx.var_parent = visitor.cx.parent;
         resolve_cond(visitor, guard);
     }
     resolve_expr(visitor, arm.body, false);
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index a62efed13bc..e6a1f6d8d8b 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -244,48 +244,48 @@ pub(super) fn check_item<'tcx>(
         //
         // won't be allowed unless there's an *explicit* implementation of `Send`
         // for `T`
-        hir::ItemKind::Impl(impl_) => {
-            let header = tcx.impl_trait_header(def_id);
-            let is_auto = header
-                .is_some_and(|header| tcx.trait_is_auto(header.trait_ref.skip_binder().def_id));
-
+        hir::ItemKind::Impl(ref impl_) => {
             crate::impl_wf_check::check_impl_wf(tcx, def_id)?;
             let mut res = Ok(());
-            if let (hir::Defaultness::Default { .. }, true) = (impl_.defaultness, is_auto) {
-                let sp = impl_.of_trait.as_ref().map_or(item.span, |t| t.path.span);
-                res = Err(tcx
-                    .dcx()
-                    .struct_span_err(sp, "impls of auto traits cannot be default")
-                    .with_span_labels(impl_.defaultness_span, "default because of this")
-                    .with_span_label(sp, "auto trait")
-                    .emit());
-            }
-            // We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span.
-            match header.map(|h| h.polarity) {
-                // `None` means this is an inherent impl
-                Some(ty::ImplPolarity::Positive) | None => {
-                    res = res.and(check_impl(tcx, item, impl_.self_ty, &impl_.of_trait));
-                }
-                Some(ty::ImplPolarity::Negative) => {
-                    let ast::ImplPolarity::Negative(span) = impl_.polarity else {
-                        bug!("impl_polarity query disagrees with impl's polarity in HIR");
-                    };
-                    // FIXME(#27579): what amount of WF checking do we need for neg impls?
-                    if let hir::Defaultness::Default { .. } = impl_.defaultness {
-                        let mut spans = vec![span];
-                        spans.extend(impl_.defaultness_span);
-                        res = Err(struct_span_code_err!(
-                            tcx.dcx(),
-                            spans,
-                            E0750,
-                            "negative impls cannot be default impls"
-                        )
+            if let Some(of_trait) = impl_.of_trait {
+                let header = tcx.impl_trait_header(def_id).unwrap();
+                let is_auto = tcx.trait_is_auto(header.trait_ref.skip_binder().def_id);
+                if let (hir::Defaultness::Default { .. }, true) = (of_trait.defaultness, is_auto) {
+                    let sp = of_trait.trait_ref.path.span;
+                    res = Err(tcx
+                        .dcx()
+                        .struct_span_err(sp, "impls of auto traits cannot be default")
+                        .with_span_labels(of_trait.defaultness_span, "default because of this")
+                        .with_span_label(sp, "auto trait")
                         .emit());
-                    }
                 }
-                Some(ty::ImplPolarity::Reservation) => {
-                    // FIXME: what amount of WF checking do we need for reservation impls?
+                match header.polarity {
+                    ty::ImplPolarity::Positive => {
+                        res = res.and(check_impl(tcx, item, impl_));
+                    }
+                    ty::ImplPolarity::Negative => {
+                        let ast::ImplPolarity::Negative(span) = of_trait.polarity else {
+                            bug!("impl_polarity query disagrees with impl's polarity in HIR");
+                        };
+                        // FIXME(#27579): what amount of WF checking do we need for neg impls?
+                        if let hir::Defaultness::Default { .. } = of_trait.defaultness {
+                            let mut spans = vec![span];
+                            spans.extend(of_trait.defaultness_span);
+                            res = Err(struct_span_code_err!(
+                                tcx.dcx(),
+                                spans,
+                                E0750,
+                                "negative impls cannot be default impls"
+                            )
+                            .emit());
+                        }
+                    }
+                    ty::ImplPolarity::Reservation => {
+                        // FIXME: what amount of WF checking do we need for reservation impls?
+                    }
                 }
+            } else {
+                res = res.and(check_impl(tcx, item, impl_));
             }
             res
         }
@@ -1258,16 +1258,15 @@ pub(crate) fn check_const_item(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Result<()
     })
 }
 
-#[instrument(level = "debug", skip(tcx, hir_self_ty, hir_trait_ref))]
+#[instrument(level = "debug", skip(tcx, impl_))]
 fn check_impl<'tcx>(
     tcx: TyCtxt<'tcx>,
     item: &'tcx hir::Item<'tcx>,
-    hir_self_ty: &hir::Ty<'_>,
-    hir_trait_ref: &Option<hir::TraitRef<'_>>,
+    impl_: &hir::Impl<'_>,
 ) -> Result<(), ErrorGuaranteed> {
     enter_wf_checking_ctxt(tcx, item.owner_id.def_id, |wfcx| {
-        match hir_trait_ref {
-            Some(hir_trait_ref) => {
+        match impl_.of_trait {
+            Some(of_trait) => {
                 // `#[rustc_reservation_impl]` impls are not real impls and
                 // therefore don't need to be WF (the trait's `Self: Trait` predicate
                 // won't hold).
@@ -1275,7 +1274,7 @@ fn check_impl<'tcx>(
                 // Avoid bogus "type annotations needed `Foo: Bar`" errors on `impl Bar for Foo` in case
                 // other `Foo` impls are incoherent.
                 tcx.ensure_ok().coherent_trait(trait_ref.def_id)?;
-                let trait_span = hir_trait_ref.path.span;
+                let trait_span = of_trait.trait_ref.path.span;
                 let trait_ref = wfcx.deeply_normalize(
                     trait_span,
                     Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)),
@@ -1299,12 +1298,12 @@ fn check_impl<'tcx>(
                     if let Some(pred) = obligation.predicate.as_trait_clause()
                         && pred.skip_binder().self_ty() == trait_ref.self_ty()
                     {
-                        obligation.cause.span = hir_self_ty.span;
+                        obligation.cause.span = impl_.self_ty.span;
                     }
                     if let Some(pred) = obligation.predicate.as_projection_clause()
                         && pred.skip_binder().self_ty() == trait_ref.self_ty()
                     {
-                        obligation.cause.span = hir_self_ty.span;
+                        obligation.cause.span = impl_.self_ty.span;
                     }
                 }
 
@@ -1321,7 +1320,7 @@ fn check_impl<'tcx>(
                         wfcx.register_obligation(Obligation::new(
                             tcx,
                             ObligationCause::new(
-                                hir_self_ty.span,
+                                impl_.self_ty.span,
                                 wfcx.body_def_id,
                                 ObligationCauseCode::WellFormed(None),
                             ),
@@ -1342,7 +1341,7 @@ fn check_impl<'tcx>(
                     self_ty,
                 );
                 wfcx.register_wf_obligation(
-                    hir_self_ty.span,
+                    impl_.self_ty.span,
                     Some(WellFormedLoc::Ty(item.hir_id().expect_owner().def_id)),
                     self_ty.into(),
                 );
@@ -2288,8 +2287,7 @@ fn lint_redundant_lifetimes<'tcx>(
             // Proceed
         }
         DefKind::AssocFn | DefKind::AssocTy | DefKind::AssocConst => {
-            let parent_def_id = tcx.local_parent(owner_id);
-            if matches!(tcx.def_kind(parent_def_id), DefKind::Impl { of_trait: true }) {
+            if tcx.trait_impl_of_assoc(owner_id.to_def_id()).is_some() {
                 // Don't check for redundant lifetimes for associated items of trait
                 // implementations, since the signature is required to be compatible
                 // with the trait, even if the implementation implies some lifetimes
diff --git a/compiler/rustc_hir_analysis/src/coherence/builtin.rs b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
index 27948f50a4a..32b175611ce 100644
--- a/compiler/rustc_hir_analysis/src/coherence/builtin.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
@@ -531,8 +531,10 @@ pub(crate) fn coerce_unsized_info<'tcx>(
                 }));
             } else if diff_fields.len() > 1 {
                 let item = tcx.hir_expect_item(impl_did);
-                let span = if let ItemKind::Impl(hir::Impl { of_trait: Some(t), .. }) = &item.kind {
-                    t.path.span
+                let span = if let ItemKind::Impl(hir::Impl { of_trait: Some(of_trait), .. }) =
+                    &item.kind
+                {
+                    of_trait.trait_ref.path.span
                 } else {
                     tcx.def_span(impl_did)
                 };
diff --git a/compiler/rustc_hir_analysis/src/coherence/orphan.rs b/compiler/rustc_hir_analysis/src/coherence/orphan.rs
index c75fef9f716..f707196c816 100644
--- a/compiler/rustc_hir_analysis/src/coherence/orphan.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/orphan.rs
@@ -384,7 +384,7 @@ fn emit_orphan_check_error<'tcx>(
         traits::OrphanCheckErr::NonLocalInputType(tys) => {
             let item = tcx.hir_expect_item(impl_def_id);
             let impl_ = item.expect_impl();
-            let hir_trait_ref = impl_.of_trait.as_ref().unwrap();
+            let of_trait = impl_.of_trait.unwrap();
 
             let span = tcx.def_span(impl_def_id);
             let mut diag = tcx.dcx().create_err(match trait_ref.self_ty().kind() {
@@ -401,7 +401,7 @@ fn emit_orphan_check_error<'tcx>(
                     impl_.self_ty.span
                 } else {
                     // Point at `C<B>` in `impl<A, B> for C<B> in D<A>`
-                    hir_trait_ref.path.span
+                    of_trait.trait_ref.path.span
                 };
 
                 ty = tcx.erase_regions(ty);
diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
index 8ccbfbbb3b4..b72e743f95b 100644
--- a/compiler/rustc_hir_analysis/src/collect.rs
+++ b/compiler/rustc_hir_analysis/src/collect.rs
@@ -1295,18 +1295,22 @@ fn impl_trait_header(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<ty::ImplTrai
     let icx = ItemCtxt::new(tcx, def_id);
     let item = tcx.hir_expect_item(def_id);
     let impl_ = item.expect_impl();
-    impl_.of_trait.as_ref().map(|ast_trait_ref| {
+    let is_rustc_reservation = tcx.has_attr(def_id, sym::rustc_reservation_impl);
+    if is_rustc_reservation && impl_.of_trait.is_none() {
+        tcx.dcx().span_err(item.span, "reservation impls can't be inherent");
+    }
+    impl_.of_trait.map(|of_trait| {
         let selfty = tcx.type_of(def_id).instantiate_identity();
 
-        check_impl_constness(tcx, impl_.constness, ast_trait_ref);
+        check_impl_constness(tcx, of_trait.constness, &of_trait.trait_ref);
 
-        let trait_ref = icx.lowerer().lower_impl_trait_ref(ast_trait_ref, selfty);
+        let trait_ref = icx.lowerer().lower_impl_trait_ref(&of_trait.trait_ref, selfty);
 
         ty::ImplTraitHeader {
             trait_ref: ty::EarlyBinder::bind(trait_ref),
-            safety: impl_.safety,
-            polarity: polarity_of_impl(tcx, def_id, impl_, item.span),
-            constness: impl_.constness,
+            safety: of_trait.safety,
+            polarity: polarity_of_impl(tcx, of_trait, is_rustc_reservation),
+            constness: of_trait.constness,
         }
     })
 }
@@ -1350,26 +1354,18 @@ fn check_impl_constness(
 
 fn polarity_of_impl(
     tcx: TyCtxt<'_>,
-    def_id: LocalDefId,
-    impl_: &hir::Impl<'_>,
-    span: Span,
+    of_trait: &hir::TraitImplHeader<'_>,
+    is_rustc_reservation: bool,
 ) -> ty::ImplPolarity {
-    let is_rustc_reservation = tcx.has_attr(def_id, sym::rustc_reservation_impl);
-    match &impl_ {
-        hir::Impl { polarity: hir::ImplPolarity::Negative(span), of_trait, .. } => {
+    match of_trait.polarity {
+        hir::ImplPolarity::Negative(span) => {
             if is_rustc_reservation {
-                let span = span.to(of_trait.as_ref().map_or(*span, |t| t.path.span));
+                let span = span.to(of_trait.trait_ref.path.span);
                 tcx.dcx().span_err(span, "reservation impls can't be negative");
             }
             ty::ImplPolarity::Negative
         }
-        hir::Impl { polarity: hir::ImplPolarity::Positive, of_trait: None, .. } => {
-            if is_rustc_reservation {
-                tcx.dcx().span_err(span, "reservation impls can't be inherent");
-            }
-            ty::ImplPolarity::Positive
-        }
-        hir::Impl { polarity: hir::ImplPolarity::Positive, of_trait: Some(_), .. } => {
+        hir::ImplPolarity::Positive => {
             if is_rustc_reservation {
                 ty::ImplPolarity::Reservation
             } else {
diff --git a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
index 522409a5ee5..b59dc4bd132 100644
--- a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
@@ -158,7 +158,9 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
     if let Node::Item(item) = node {
         match item.kind {
             ItemKind::Impl(impl_) => {
-                if impl_.defaultness.is_default() {
+                if let Some(of_trait) = impl_.of_trait
+                    && of_trait.defaultness.is_default()
+                {
                     is_default_impl_trait = tcx
                         .impl_trait_ref(def_id)
                         .map(|t| ty::Binder::dummy(t.instantiate_identity()));
@@ -517,8 +519,7 @@ pub(super) fn explicit_predicates_of<'tcx>(
                 projection.args == trait_identity_args
                     // FIXME(return_type_notation): This check should be more robust
                     && !tcx.is_impl_trait_in_trait(projection.def_id)
-                    && tcx.associated_item(projection.def_id).container_id(tcx)
-                        == def_id.to_def_id()
+                    && tcx.parent(projection.def_id) == def_id.to_def_id()
             } else {
                 false
             }
diff --git a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
index eb3492f5de6..8133f9f6823 100644
--- a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
+++ b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
@@ -604,13 +604,10 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
 
     #[instrument(level = "debug", skip(self))]
     fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
-        match &item.kind {
-            hir::ItemKind::Impl(hir::Impl { of_trait, .. }) => {
-                if let Some(of_trait) = of_trait {
-                    self.record_late_bound_vars(of_trait.hir_ref_id, Vec::default());
-                }
-            }
-            _ => {}
+        if let hir::ItemKind::Impl(impl_) = item.kind
+            && let Some(of_trait) = impl_.of_trait
+        {
+            self.record_late_bound_vars(of_trait.trait_ref.hir_ref_id, Vec::default());
         }
         match item.kind {
             hir::ItemKind::Fn { generics, .. } => {
@@ -636,7 +633,7 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
             | hir::ItemKind::Union(_, generics, _)
             | hir::ItemKind::Trait(_, _, _, _, generics, ..)
             | hir::ItemKind::TraitAlias(_, generics, ..)
-            | hir::ItemKind::Impl(&hir::Impl { generics, .. }) => {
+            | hir::ItemKind::Impl(hir::Impl { generics, .. }) => {
                 // These kinds of items have only early-bound lifetime parameters.
                 self.visit_early(item.hir_id(), generics, |this| intravisit::walk_item(this, item));
             }
@@ -2106,7 +2103,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
                     // If we have a self type alias (in an impl), try to resolve an
                     // associated item from one of the supertraits of the impl's trait.
                     Res::SelfTyAlias { alias_to: impl_def_id, is_trait_impl: true, .. } => {
-                        let hir::ItemKind::Impl(hir::Impl { of_trait: Some(trait_ref), .. }) = self
+                        let hir::ItemKind::Impl(hir::Impl { of_trait: Some(of_trait), .. }) = self
                             .tcx
                             .hir_node_by_def_id(impl_def_id.expect_local())
                             .expect_item()
@@ -2114,7 +2111,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
                         else {
                             return;
                         };
-                        let Some(trait_def_id) = trait_ref.trait_def_id() else {
+                        let Some(trait_def_id) = of_trait.trait_ref.trait_def_id() else {
                             return;
                         };
                         let Some((bound_vars, assoc_item)) = BoundVarContext::supertrait_hrtb_vars(
diff --git a/compiler/rustc_hir_analysis/src/collect/type_of.rs b/compiler/rustc_hir_analysis/src/collect/type_of.rs
index 22fb02714dd..62125c99d80 100644
--- a/compiler/rustc_hir_analysis/src/collect/type_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/type_of.rs
@@ -251,7 +251,7 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<'_
                         .emit_err(crate::errors::SelfInImplSelf { span: spans.into(), note: () });
                     Ty::new_error(tcx, guar)
                 }
-                _ => icx.lower_ty(*self_ty),
+                _ => icx.lower_ty(self_ty),
             },
             ItemKind::Fn { .. } => {
                 let args = ty::GenericArgs::identity_for_item(tcx, def_id);
diff --git a/compiler/rustc_hir_analysis/src/errors/wrong_number_of_generic_args.rs b/compiler/rustc_hir_analysis/src/errors/wrong_number_of_generic_args.rs
index 835f8e8cdae..8a9f9130fea 100644
--- a/compiler/rustc_hir_analysis/src/errors/wrong_number_of_generic_args.rs
+++ b/compiler/rustc_hir_analysis/src/errors/wrong_number_of_generic_args.rs
@@ -147,7 +147,11 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
             let hir::Node::Item(hir::Item {
                 kind:
                     hir::ItemKind::Impl(hir::Impl {
-                        of_trait: Some(hir::TraitRef { hir_ref_id: id_in_of_trait, .. }),
+                        of_trait:
+                            Some(hir::TraitImplHeader {
+                                trait_ref: hir::TraitRef { hir_ref_id: id_in_of_trait, .. },
+                                ..
+                            }),
                         ..
                     }),
                 ..
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
index 386e1091ac4..d14aef8ace4 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
@@ -199,12 +199,10 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             //        However, this can easily get out of sync! Ideally, we would perform this step
             //        where we are guaranteed to catch *all* bounds like in
             //        `Self::lower_poly_trait_ref`. List of concrete issues:
-            //        FIXME(more_maybe_bounds): We don't call this for e.g., trait object tys or
-            //                                  supertrait bounds!
+            //        FIXME(more_maybe_bounds): We don't call this for trait object tys, supertrait
+            //                                  bounds or associated type bounds (ATB)!
             //        FIXME(trait_alias, #143122): We don't call it for the RHS. Arguably however,
-            //                                       AST lowering should reject them outright.
-            //        FIXME(associated_type_bounds): We don't call this for them. However, AST
-            //                                       lowering should reject them outright (#135229).
+            //                                     AST lowering should reject them outright.
             let bounds = collect_relaxed_bounds(hir_bounds, self_ty_where_predicates);
             self.check_and_report_invalid_relaxed_bounds(bounds);
         }
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
index 3e446b7c656..93b82acf621 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs
@@ -755,7 +755,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         let limit = if candidates.len() == 5 { 5 } else { 4 };
 
         for (index, &item) in candidates.iter().take(limit).enumerate() {
-            let impl_ = tcx.impl_of_assoc(item).unwrap();
+            let impl_ = tcx.parent(item);
 
             let note_span = if item.is_local() {
                 Some(tcx.def_span(item))
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/lint.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/lint.rs
index 646ff3ca08d..56998b5b53c 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/lint.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/lint.rs
@@ -200,7 +200,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         }) = tcx.hir_node_by_def_id(parent_id)
             && self_ty.hir_id == impl_self_ty.hir_id
         {
-            let Some(of_trait_ref) = of_trait else {
+            let Some(of_trait) = of_trait else {
                 diag.span_suggestion_verbose(
                     impl_self_ty.span.shrink_to_hi(),
                     "you might have intended to implement this trait for a given type",
@@ -209,10 +209,10 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 );
                 return;
             };
-            if !of_trait_ref.trait_def_id().is_some_and(|def_id| def_id.is_local()) {
+            if !of_trait.trait_ref.trait_def_id().is_some_and(|def_id| def_id.is_local()) {
                 return;
             }
-            let of_trait_span = of_trait_ref.path.span;
+            let of_trait_span = of_trait.trait_ref.path.span;
             // make sure that we are not calling unwrap to abort during the compilation
             let Ok(of_trait_name) = tcx.sess.source_map().span_to_snippet(of_trait_span) else {
                 return;
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
index 7e2bfa9f920..c7b984d9b25 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -1135,9 +1135,10 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                         );
                     }
                 } else {
+                    let trait_ =
+                        tcx.short_string(bound.print_only_trait_path(), err.long_ty_path());
                     err.note(format!(
-                        "associated {assoc_kind_str} `{assoc_ident}` could derive from `{}`",
-                        bound.print_only_trait_path(),
+                        "associated {assoc_kind_str} `{assoc_ident}` could derive from `{trait_}`",
                     ));
                 }
             }
@@ -2731,7 +2732,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         };
         let i = tcx.parent_hir_node(fn_hir_id).expect_item().expect_impl();
 
-        let trait_ref = self.lower_impl_trait_ref(i.of_trait.as_ref()?, self.lower_ty(i.self_ty));
+        let trait_ref = self.lower_impl_trait_ref(&i.of_trait?.trait_ref, self.lower_ty(i.self_ty));
 
         let assoc = tcx.associated_items(trait_ref.def_id).find_by_ident_and_kind(
             tcx,
diff --git a/compiler/rustc_hir_analysis/src/hir_wf_check.rs b/compiler/rustc_hir_analysis/src/hir_wf_check.rs
index 3fddaee8cef..d8578970adc 100644
--- a/compiler/rustc_hir_analysis/src/hir_wf_check.rs
+++ b/compiler/rustc_hir_analysis/src/hir_wf_check.rs
@@ -154,8 +154,9 @@ pub(super) fn diagnostic_hir_wf_check<'tcx>(
                 hir::ItemKind::TyAlias(_, _, ty)
                 | hir::ItemKind::Static(_, _, ty, _)
                 | hir::ItemKind::Const(_, _, ty, _) => vec![ty],
-                hir::ItemKind::Impl(impl_) => match &impl_.of_trait {
-                    Some(t) => t
+                hir::ItemKind::Impl(impl_) => match impl_.of_trait {
+                    Some(of_trait) => of_trait
+                        .trait_ref
                         .path
                         .segments
                         .last()
diff --git a/compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs b/compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs
index 0043f0c7117..b38639ed8c6 100644
--- a/compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs
+++ b/compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs
@@ -390,45 +390,13 @@ fn check_predicates<'tcx>(
 
     let mut res = Ok(());
     for (clause, span) in impl1_predicates {
-        if !impl2_predicates.iter().any(|pred2| trait_predicates_eq(clause.as_predicate(), *pred2))
-        {
+        if !impl2_predicates.iter().any(|&pred2| clause.as_predicate() == pred2) {
             res = res.and(check_specialization_on(tcx, clause, span))
         }
     }
     res
 }
 
-/// Checks if some predicate on the specializing impl (`predicate1`) is the same
-/// as some predicate on the base impl (`predicate2`).
-///
-/// This basically just checks syntactic equivalence, but is a little more
-/// forgiving since we want to equate `T: Tr` with `T: [const] Tr` so this can work:
-///
-/// ```ignore (illustrative)
-/// #[rustc_specialization_trait]
-/// trait Specialize { }
-///
-/// impl<T: Bound> Tr for T { }
-/// impl<T: [const] Bound + Specialize> const Tr for T { }
-/// ```
-///
-/// However, we *don't* want to allow the reverse, i.e., when the bound on the
-/// specializing impl is not as const as the bound on the base impl:
-///
-/// ```ignore (illustrative)
-/// impl<T: [const] Bound> const Tr for T { }
-/// impl<T: Bound + Specialize> const Tr for T { } // should be T: [const] Bound
-/// ```
-///
-/// So we make that check in this function and try to raise a helpful error message.
-fn trait_predicates_eq<'tcx>(
-    predicate1: ty::Predicate<'tcx>,
-    predicate2: ty::Predicate<'tcx>,
-) -> bool {
-    // FIXME(const_trait_impl)
-    predicate1 == predicate2
-}
-
 #[instrument(level = "debug", skip(tcx))]
 fn check_specialization_on<'tcx>(
     tcx: TyCtxt<'tcx>,
diff --git a/compiler/rustc_hir_pretty/src/lib.rs b/compiler/rustc_hir_pretty/src/lib.rs
index 235eec96d74..be5859b57c5 100644
--- a/compiler/rustc_hir_pretty/src/lib.rs
+++ b/compiler/rustc_hir_pretty/src/lib.rs
@@ -690,39 +690,44 @@ impl<'a> State<'a> {
                 let (cb, ib) = self.head("union");
                 self.print_struct(ident.name, generics, struct_def, item.span, true, cb, ib);
             }
-            hir::ItemKind::Impl(&hir::Impl {
-                constness,
-                safety,
-                polarity,
-                defaultness,
-                defaultness_span: _,
-                generics,
-                ref of_trait,
-                self_ty,
-                items,
-            }) => {
+            hir::ItemKind::Impl(hir::Impl { generics, of_trait, self_ty, items }) => {
                 let (cb, ib) = self.head("");
-                self.print_defaultness(defaultness);
-                self.print_safety(safety);
-                self.word_nbsp("impl");
 
-                if let hir::Constness::Const = constness {
-                    self.word_nbsp("const");
-                }
+                let impl_generics = |this: &mut Self| {
+                    this.word_nbsp("impl");
+                    if !generics.params.is_empty() {
+                        this.print_generic_params(generics.params);
+                        this.space();
+                    }
+                };
 
-                if !generics.params.is_empty() {
-                    self.print_generic_params(generics.params);
-                    self.space();
-                }
+                match of_trait {
+                    None => impl_generics(self),
+                    Some(&hir::TraitImplHeader {
+                        constness,
+                        safety,
+                        polarity,
+                        defaultness,
+                        defaultness_span: _,
+                        ref trait_ref,
+                    }) => {
+                        self.print_defaultness(defaultness);
+                        self.print_safety(safety);
+
+                        impl_generics(self);
+
+                        if let hir::Constness::Const = constness {
+                            self.word_nbsp("const");
+                        }
 
-                if let hir::ImplPolarity::Negative(_) = polarity {
-                    self.word("!");
-                }
+                        if let hir::ImplPolarity::Negative(_) = polarity {
+                            self.word("!");
+                        }
 
-                if let Some(t) = of_trait {
-                    self.print_trait_ref(t);
-                    self.space();
-                    self.word_space("for");
+                        self.print_trait_ref(trait_ref);
+                        self.space();
+                        self.word_space("for");
+                    }
                 }
 
                 self.print_type(self_ty);
diff --git a/compiler/rustc_hir_typeck/messages.ftl b/compiler/rustc_hir_typeck/messages.ftl
index bac4d70103c..1ed0756fdd6 100644
--- a/compiler/rustc_hir_typeck/messages.ftl
+++ b/compiler/rustc_hir_typeck/messages.ftl
@@ -159,7 +159,7 @@ hir_typeck_lossy_provenance_ptr2int =
     .suggestion = use `.addr()` to obtain the address of a pointer
     .help = if you can't comply with strict provenance and need to expose the pointer provenance you can use `.expose_provenance()` instead
 
-hir_typeck_missing_parentheses_in_range = can't call method `{$method_name}` on type `{$ty_str}`
+hir_typeck_missing_parentheses_in_range = can't call method `{$method_name}` on type `{$ty}`
 
 hir_typeck_naked_asm_outside_naked_fn =
     the `naked_asm!` macro can only be used in functions marked with `#[unsafe(naked)]`
@@ -184,7 +184,7 @@ hir_typeck_never_type_fallback_flowing_into_unsafe_path = never type fallback af
 hir_typeck_never_type_fallback_flowing_into_unsafe_union_field = never type fallback affects this union access
     .help = specify the type explicitly
 
-hir_typeck_no_associated_item = no {$item_kind} named `{$item_ident}` found for {$ty_prefix} `{$ty_str}`{$trait_missing_method ->
+hir_typeck_no_associated_item = no {$item_kind} named `{$item_ident}` found for {$ty_prefix} `{$ty}`{$trait_missing_method ->
     [true] {""}
     *[other] {" "}in the current scope
 }
diff --git a/compiler/rustc_hir_typeck/src/callee.rs b/compiler/rustc_hir_typeck/src/callee.rs
index 48bb45de53e..7afc555b598 100644
--- a/compiler/rustc_hir_typeck/src/callee.rs
+++ b/compiler/rustc_hir_typeck/src/callee.rs
@@ -910,7 +910,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // const stability checking here too, I guess.
         if self.tcx.is_conditionally_const(callee_did) {
             let q = self.tcx.const_conditions(callee_did);
-            // FIXME(const_trait_impl): Use this span with a better cause code.
             for (idx, (cond, pred_span)) in
                 q.instantiate(self.tcx, callee_args).into_iter().enumerate()
             {
diff --git a/compiler/rustc_hir_typeck/src/demand.rs b/compiler/rustc_hir_typeck/src/demand.rs
index e5684f8cbe6..fb6ebe066a8 100644
--- a/compiler/rustc_hir_typeck/src/demand.rs
+++ b/compiler/rustc_hir_typeck/src/demand.rs
@@ -698,7 +698,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ) {
         match (self.tcx.parent_hir_node(expr.hir_id), error) {
             (hir::Node::LetStmt(hir::LetStmt { ty: Some(ty), init: Some(init), .. }), _)
-                if init.hir_id == expr.hir_id =>
+                if init.hir_id == expr.hir_id && !ty.span.source_equal(init.span) =>
             {
                 // Point at `let` assignment type.
                 err.span_label(ty.span, "expected due to this");
diff --git a/compiler/rustc_hir_typeck/src/errors.rs b/compiler/rustc_hir_typeck/src/errors.rs
index a8bb6956f10..d15d092b7d3 100644
--- a/compiler/rustc_hir_typeck/src/errors.rs
+++ b/compiler/rustc_hir_typeck/src/errors.rs
@@ -200,11 +200,11 @@ pub(crate) enum ExplicitDestructorCallSugg {
 
 #[derive(Diagnostic)]
 #[diag(hir_typeck_missing_parentheses_in_range, code = E0689)]
-pub(crate) struct MissingParenthesesInRange {
+pub(crate) struct MissingParenthesesInRange<'tcx> {
     #[primary_span]
     #[label(hir_typeck_missing_parentheses_in_range)]
     pub span: Span,
-    pub ty_str: String,
+    pub ty: Ty<'tcx>,
     pub method_name: String,
     #[subdiagnostic]
     pub add_missing_parentheses: Option<AddMissingParenthesesInRange>,
@@ -828,13 +828,13 @@ pub(crate) struct UnlabeledCfInWhileCondition<'a> {
 
 #[derive(Diagnostic)]
 #[diag(hir_typeck_no_associated_item, code = E0599)]
-pub(crate) struct NoAssociatedItem {
+pub(crate) struct NoAssociatedItem<'tcx> {
     #[primary_span]
     pub span: Span,
     pub item_kind: &'static str,
     pub item_ident: Ident,
     pub ty_prefix: Cow<'static, str>,
-    pub ty_str: String,
+    pub ty: Ty<'tcx>,
     pub trait_missing_method: bool,
 }
 
diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/compiler/rustc_hir_typeck/src/expr.rs
index 454ec7ddcaf..0498a938366 100644
--- a/compiler/rustc_hir_typeck/src/expr.rs
+++ b/compiler/rustc_hir_typeck/src/expr.rs
@@ -2745,6 +2745,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 let available_field_names = self.available_field_names(variant, expr, skip_fields);
                 if let Some(field_name) =
                     find_best_match_for_name(&available_field_names, field.ident.name, None)
+                    && !(field.ident.name.as_str().parse::<usize>().is_ok()
+                        && field_name.as_str().parse::<usize>().is_ok())
                 {
                     err.span_label(field.ident.span, "unknown field");
                     err.span_suggestion_verbose(
@@ -3321,18 +3323,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         } else {
             (base_ty, "")
         };
-        for (found_fields, args) in
+        for found_fields in
             self.get_field_candidates_considering_privacy_for_diag(span, ty, mod_id, expr.hir_id)
         {
-            let field_names = found_fields.iter().map(|field| field.name).collect::<Vec<_>>();
+            let field_names = found_fields.iter().map(|field| field.0.name).collect::<Vec<_>>();
             let mut candidate_fields: Vec<_> = found_fields
                 .into_iter()
                 .filter_map(|candidate_field| {
                     self.check_for_nested_field_satisfying_condition_for_diag(
                         span,
-                        &|candidate_field, _| candidate_field.ident(self.tcx()) == field,
+                        &|candidate_field, _| candidate_field == field,
                         candidate_field,
-                        args,
                         vec![],
                         mod_id,
                         expr.hir_id,
@@ -3361,6 +3362,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 );
             } else if let Some(field_name) =
                 find_best_match_for_name(&field_names, field.name, None)
+                && !(field.name.as_str().parse::<usize>().is_ok()
+                    && field_name.as_str().parse::<usize>().is_ok())
             {
                 err.span_suggestion_verbose(
                     field.span,
@@ -3396,7 +3399,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         base_ty: Ty<'tcx>,
         mod_id: DefId,
         hir_id: HirId,
-    ) -> Vec<(Vec<&'tcx ty::FieldDef>, GenericArgsRef<'tcx>)> {
+    ) -> Vec<Vec<(Ident, Ty<'tcx>)>> {
         debug!("get_field_candidates(span: {:?}, base_t: {:?}", span, base_ty);
 
         let mut autoderef = self.autoderef(span, base_ty).silence_errors();
@@ -3422,7 +3425,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         if fields.iter().all(|field| !field.vis.is_accessible_from(mod_id, tcx)) {
                             return None;
                         }
-                        return Some((
+                        return Some(
                             fields
                                 .iter()
                                 .filter(move |field| {
@@ -3431,9 +3434,25 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                 })
                                 // For compile-time reasons put a limit on number of fields we search
                                 .take(100)
+                                .map(|field_def| {
+                                    (
+                                        field_def.ident(self.tcx).normalize_to_macros_2_0(),
+                                        field_def.ty(self.tcx, args),
+                                    )
+                                })
+                                .collect::<Vec<_>>(),
+                        );
+                    }
+                    ty::Tuple(types) => {
+                        return Some(
+                            types
+                                .iter()
+                                .enumerate()
+                                // For compile-time reasons put a limit on number of fields we search
+                                .take(100)
+                                .map(|(i, ty)| (Ident::from_str(&i.to_string()), ty))
                                 .collect::<Vec<_>>(),
-                            *args,
-                        ));
+                        );
                     }
                     _ => None,
                 }
@@ -3443,56 +3462,46 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
     /// This method is called after we have encountered a missing field error to recursively
     /// search for the field
+    #[instrument(skip(self, matches, mod_id, hir_id), level = "debug")]
     pub(crate) fn check_for_nested_field_satisfying_condition_for_diag(
         &self,
         span: Span,
-        matches: &impl Fn(&ty::FieldDef, Ty<'tcx>) -> bool,
-        candidate_field: &ty::FieldDef,
-        subst: GenericArgsRef<'tcx>,
+        matches: &impl Fn(Ident, Ty<'tcx>) -> bool,
+        (candidate_name, candidate_ty): (Ident, Ty<'tcx>),
         mut field_path: Vec<Ident>,
         mod_id: DefId,
         hir_id: HirId,
     ) -> Option<Vec<Ident>> {
-        debug!(
-            "check_for_nested_field_satisfying(span: {:?}, candidate_field: {:?}, field_path: {:?}",
-            span, candidate_field, field_path
-        );
-
         if field_path.len() > 3 {
             // For compile-time reasons and to avoid infinite recursion we only check for fields
             // up to a depth of three
-            None
-        } else {
-            field_path.push(candidate_field.ident(self.tcx).normalize_to_macros_2_0());
-            let field_ty = candidate_field.ty(self.tcx, subst);
-            if matches(candidate_field, field_ty) {
-                return Some(field_path);
-            } else {
-                for (nested_fields, subst) in self
-                    .get_field_candidates_considering_privacy_for_diag(
-                        span, field_ty, mod_id, hir_id,
-                    )
-                {
-                    // recursively search fields of `candidate_field` if it's a ty::Adt
-                    for field in nested_fields {
-                        if let Some(field_path) = self
-                            .check_for_nested_field_satisfying_condition_for_diag(
-                                span,
-                                matches,
-                                field,
-                                subst,
-                                field_path.clone(),
-                                mod_id,
-                                hir_id,
-                            )
-                        {
-                            return Some(field_path);
-                        }
-                    }
+            return None;
+        }
+        field_path.push(candidate_name);
+        if matches(candidate_name, candidate_ty) {
+            return Some(field_path);
+        }
+        for nested_fields in self.get_field_candidates_considering_privacy_for_diag(
+            span,
+            candidate_ty,
+            mod_id,
+            hir_id,
+        ) {
+            // recursively search fields of `candidate_field` if it's a ty::Adt
+            for field in nested_fields {
+                if let Some(field_path) = self.check_for_nested_field_satisfying_condition_for_diag(
+                    span,
+                    matches,
+                    field,
+                    field_path.clone(),
+                    mod_id,
+                    hir_id,
+                ) {
+                    return Some(field_path);
                 }
             }
-            None
         }
+        None
     }
 
     fn check_expr_index(
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
index 36abd7c8555..b80a2af3100 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
@@ -1589,26 +1589,64 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // e.g. `reuse HasSelf::method;` should suggest `reuse HasSelf::method($args);`.
                 full_call_span.shrink_to_hi()
             };
+
+            // Controls how the arguments should be listed in the suggestion.
+            enum ArgumentsFormatting {
+                SingleLine,
+                Multiline { fallback_indent: String, brace_indent: String },
+            }
+            let arguments_formatting = {
+                let mut provided_inputs = matched_inputs.iter().filter_map(|a| *a);
+                if let Some(brace_indent) = source_map.indentation_before(suggestion_span)
+                    && let Some(first_idx) = provided_inputs.by_ref().next()
+                    && let Some(last_idx) = provided_inputs.by_ref().next()
+                    && let (_, first_span) = provided_arg_tys[first_idx]
+                    && let (_, last_span) = provided_arg_tys[last_idx]
+                    && source_map.is_multiline(first_span.to(last_span))
+                    && let Some(fallback_indent) = source_map.indentation_before(first_span)
+                {
+                    ArgumentsFormatting::Multiline { fallback_indent, brace_indent }
+                } else {
+                    ArgumentsFormatting::SingleLine
+                }
+            };
+
             let mut suggestion = "(".to_owned();
             let mut needs_comma = false;
             for (expected_idx, provided_idx) in matched_inputs.iter_enumerated() {
                 if needs_comma {
-                    suggestion += ", ";
-                } else {
-                    needs_comma = true;
+                    suggestion += ",";
+                }
+                match &arguments_formatting {
+                    ArgumentsFormatting::SingleLine if needs_comma => suggestion += " ",
+                    ArgumentsFormatting::SingleLine => {}
+                    ArgumentsFormatting::Multiline { .. } => suggestion += "\n",
                 }
-                let suggestion_text = if let Some(provided_idx) = provided_idx
+                needs_comma = true;
+                let (suggestion_span, suggestion_text) = if let Some(provided_idx) = provided_idx
                     && let (_, provided_span) = provided_arg_tys[*provided_idx]
                     && let Ok(arg_text) = source_map.span_to_snippet(provided_span)
                 {
-                    arg_text
+                    (Some(provided_span), arg_text)
                 } else {
                     // Propose a placeholder of the correct type
                     let (_, expected_ty) = formal_and_expected_inputs[expected_idx];
-                    ty_to_snippet(expected_ty, expected_idx)
+                    (None, ty_to_snippet(expected_ty, expected_idx))
                 };
+                if let ArgumentsFormatting::Multiline { fallback_indent, .. } =
+                    &arguments_formatting
+                {
+                    let indent = suggestion_span
+                        .and_then(|span| source_map.indentation_before(span))
+                        .unwrap_or_else(|| fallback_indent.clone());
+                    suggestion += &indent;
+                }
                 suggestion += &suggestion_text;
             }
+            if let ArgumentsFormatting::Multiline { brace_indent, .. } = arguments_formatting {
+                suggestion += ",\n";
+                suggestion += &brace_indent;
+            }
             suggestion += ")";
             err.span_suggestion_verbose(
                 suggestion_span,
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
index 2345cdab208..aca3840712e 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
@@ -936,7 +936,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             Node::ImplItem(item) => {
                 // If it doesn't impl a trait, we can add a return type
                 let Node::Item(&hir::Item {
-                    kind: hir::ItemKind::Impl(&hir::Impl { of_trait, .. }),
+                    kind: hir::ItemKind::Impl(hir::Impl { of_trait, .. }),
                     ..
                 }) = self.tcx.parent_hir_node(item.hir_id())
                 else {
@@ -2378,6 +2378,15 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 .filter_map(|variant| {
                     let sole_field = &variant.single_field();
 
+                    // When expected_ty and expr_ty are the same ADT, we prefer to compare their internal generic params,
+                    // When the current variant has a sole field whose type is still an unresolved inference variable,
+                    // suggestions would be often wrong. So suppress the suggestion. See #145294.
+                    if let (ty::Adt(exp_adt, _), ty::Adt(act_adt, _)) = (expected.kind(), expr_ty.kind())
+                        && exp_adt.did() == act_adt.did()
+                        && sole_field.ty(self.tcx, args).is_ty_var() {
+                            return None;
+                    }
+
                     let field_is_local = sole_field.did.is_local();
                     let field_is_accessible =
                         sole_field.vis.is_accessible_from(expr.hir_id.owner.def_id, self.tcx)
diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index 0c0cc752b01..824d592fa6c 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -376,16 +376,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
-    fn suggest_missing_writer(&self, rcvr_ty: Ty<'tcx>, rcvr_expr: &hir::Expr<'tcx>) -> Diag<'_> {
-        let mut file = None;
+    fn suggest_missing_writer(
+        &self,
+        rcvr_ty: Ty<'tcx>,
+        rcvr_expr: &hir::Expr<'tcx>,
+        mut long_ty_path: Option<PathBuf>,
+    ) -> Diag<'_> {
         let mut err = struct_span_code_err!(
             self.dcx(),
             rcvr_expr.span,
             E0599,
             "cannot write into `{}`",
-            self.tcx.short_string(rcvr_ty, &mut file),
+            self.tcx.short_string(rcvr_ty, &mut long_ty_path),
         );
-        *err.long_ty_path() = file;
+        *err.long_ty_path() = long_ty_path;
         err.span_note(
             rcvr_expr.span,
             "must implement `io::Write`, `fmt::Write`, or have a `write_fmt` method",
@@ -403,7 +407,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         &self,
         self_source: SelfSource<'tcx>,
         method_name: Ident,
-        ty_str_reported: &str,
+        ty: Ty<'tcx>,
         err: &mut Diag<'_>,
     ) {
         #[derive(Debug)]
@@ -478,7 +482,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
 
                 // If the shadowed binding has an itializer expression,
-                // use the initializer expression'ty to try to find the method again.
+                // use the initializer expression's ty to try to find the method again.
                 // For example like:  `let mut x = Vec::new();`,
                 // `Vec::new()` is the itializer expression.
                 if let Some(self_ty) = self.fcx.node_ty_opt(binding.init_hir_id)
@@ -566,17 +570,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     let mut span = MultiSpan::from_span(sugg_let.span);
                     span.push_span_label(sugg_let.span,
                             format!("`{rcvr_name}` of type `{self_ty}` that has method `{method_name}` defined earlier here"));
+
+                    let ty = self.tcx.short_string(ty, err.long_ty_path());
                     span.push_span_label(
                         self.tcx.hir_span(recv_id),
-                        format!(
-                            "earlier `{rcvr_name}` shadowed here with type `{ty_str_reported}`"
-                        ),
+                        format!("earlier `{rcvr_name}` shadowed here with type `{ty}`"),
                     );
                     err.span_note(
                         span,
                         format!(
                             "there's an earlier shadowed binding `{rcvr_name}` of type `{self_ty}` \
-                                    that has method `{method_name}` available"
+                             that has method `{method_name}` available"
                         ),
                     );
                 }
@@ -602,15 +606,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let tcx = self.tcx;
         let rcvr_ty = self.resolve_vars_if_possible(rcvr_ty);
         let mut ty_file = None;
-        let (ty_str, short_ty_str) =
-            if trait_missing_method && let ty::Dynamic(predicates, _, _) = rcvr_ty.kind() {
-                (predicates.to_string(), with_forced_trimmed_paths!(predicates.to_string()))
-            } else {
-                (
-                    tcx.short_string(rcvr_ty, &mut ty_file),
-                    with_forced_trimmed_paths!(rcvr_ty.to_string()),
-                )
-            };
         let is_method = mode == Mode::MethodCall;
         let unsatisfied_predicates = &no_match_data.unsatisfied_predicates;
         let similar_candidate = no_match_data.similar_candidate;
@@ -629,15 +624,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // We could pass the file for long types into these two, but it isn't strictly necessary
         // given how targeted they are.
-        if let Err(guar) = self.report_failed_method_call_on_range_end(
-            tcx,
-            rcvr_ty,
-            source,
-            span,
-            item_ident,
-            &short_ty_str,
-            &mut ty_file,
-        ) {
+        if let Err(guar) =
+            self.report_failed_method_call_on_range_end(tcx, rcvr_ty, source, span, item_ident)
+        {
             return guar;
         }
         if let Err(guar) = self.report_failed_method_call_on_numerical_infer_var(
@@ -647,44 +636,42 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             span,
             item_kind,
             item_ident,
-            &short_ty_str,
             &mut ty_file,
         ) {
             return guar;
         }
         span = item_ident.span;
 
-        // Don't show generic arguments when the method can't be found in any implementation (#81576).
-        let mut ty_str_reported = ty_str.clone();
-        if let ty::Adt(_, generics) = rcvr_ty.kind() {
-            if generics.len() > 0 {
-                let mut autoderef = self.autoderef(span, rcvr_ty).silence_errors();
-                let candidate_found = autoderef.any(|(ty, _)| {
-                    if let ty::Adt(adt_def, _) = ty.kind() {
-                        self.tcx
-                            .inherent_impls(adt_def.did())
-                            .into_iter()
-                            .any(|def_id| self.associated_value(*def_id, item_ident).is_some())
-                    } else {
-                        false
-                    }
-                });
-                let has_deref = autoderef.step_count() > 0;
-                if !candidate_found && !has_deref && unsatisfied_predicates.is_empty() {
-                    if let Some((path_string, _)) = ty_str.split_once('<') {
-                        ty_str_reported = path_string.to_string();
-                    }
-                }
-            }
-        }
-
         let is_write = sugg_span.ctxt().outer_expn_data().macro_def_id.is_some_and(|def_id| {
             tcx.is_diagnostic_item(sym::write_macro, def_id)
                 || tcx.is_diagnostic_item(sym::writeln_macro, def_id)
         }) && item_ident.name == sym::write_fmt;
         let mut err = if is_write && let SelfSource::MethodCall(rcvr_expr) = source {
-            self.suggest_missing_writer(rcvr_ty, rcvr_expr)
+            self.suggest_missing_writer(rcvr_ty, rcvr_expr, ty_file)
         } else {
+            // Don't show expanded generic arguments when the method can't be found in any
+            // implementation (#81576).
+            let mut ty = rcvr_ty;
+            if let ty::Adt(def, generics) = rcvr_ty.kind() {
+                if generics.len() > 0 {
+                    let mut autoderef = self.autoderef(span, rcvr_ty).silence_errors();
+                    let candidate_found = autoderef.any(|(ty, _)| {
+                        if let ty::Adt(adt_def, _) = ty.kind() {
+                            self.tcx
+                                .inherent_impls(adt_def.did())
+                                .into_iter()
+                                .any(|def_id| self.associated_value(*def_id, item_ident).is_some())
+                        } else {
+                            false
+                        }
+                    });
+                    let has_deref = autoderef.step_count() > 0;
+                    if !candidate_found && !has_deref && unsatisfied_predicates.is_empty() {
+                        ty = self.tcx.at(span).type_of(def.did()).instantiate_identity();
+                    }
+                }
+            }
+
             let mut err = self.dcx().create_err(NoAssociatedItem {
                 span,
                 item_kind,
@@ -695,16 +682,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 } else {
                     rcvr_ty.prefix_string(self.tcx)
                 },
-                ty_str: ty_str_reported.clone(),
+                ty,
                 trait_missing_method,
             });
 
             if is_method {
                 self.suggest_use_shadowed_binding_with_method(
-                    source,
-                    item_ident,
-                    &ty_str_reported,
-                    &mut err,
+                    source, item_ident, rcvr_ty, &mut err,
                 );
             }
 
@@ -734,6 +718,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
             err
         };
+
         if tcx.sess.source_map().is_multiline(sugg_span) {
             err.span_label(sugg_span.with_hi(span.lo()), "");
         }
@@ -750,6 +735,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
 
         if tcx.ty_is_opaque_future(rcvr_ty) && item_ident.name == sym::poll {
+            let ty_str = self.tcx.short_string(rcvr_ty, err.long_ty_path());
             err.help(format!(
                 "method `poll` found on `Pin<&mut {ty_str}>`, \
                 see documentation for `std::pin::Pin`"
@@ -1117,7 +1103,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         self_ty.span.ctxt().outer_expn_data().kind,
                         ExpnKind::Macro(MacroKind::Derive, _)
                     ) || matches!(
-                        of_trait.as_ref().map(|t| t.path.span.ctxt().outer_expn_data().kind),
+                        of_trait.map(|t| t.trait_ref.path.span.ctxt().outer_expn_data().kind),
                         Some(ExpnKind::Macro(MacroKind::Derive, _))
                     ) =>
                     {
@@ -1179,13 +1165,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             entry.0.insert(cause_span);
                             entry.1.insert((cause_span, "unsatisfied trait bound introduced here"));
                         } else {
-                            if let Some(trait_ref) = of_trait {
-                                entry.0.insert(trait_ref.path.span);
+                            if let Some(of_trait) = of_trait {
+                                entry.0.insert(of_trait.trait_ref.path.span);
                             }
                             entry.0.insert(self_ty.span);
                         };
-                        if let Some(trait_ref) = of_trait {
-                            entry.1.insert((trait_ref.path.span, ""));
+                        if let Some(of_trait) = of_trait {
+                            entry.1.insert((of_trait.trait_ref.path.span, ""));
                         }
                         entry.1.insert((self_ty.span, ""));
                     }
@@ -1339,7 +1325,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             }
                             let OnUnimplementedNote { message, label, notes, .. } = self
                                 .err_ctxt()
-                                .on_unimplemented_note(trait_ref, &obligation, &mut ty_file);
+                                .on_unimplemented_note(trait_ref, &obligation, err.long_ty_path());
                             (message, label, notes)
                         })
                         .unwrap()
@@ -1347,6 +1333,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     (None, None, Vec::new())
                 };
                 let primary_message = primary_message.unwrap_or_else(|| {
+                    let ty_str = self.tcx.short_string(rcvr_ty, err.long_ty_path());
                     format!(
                         "the {item_kind} `{item_ident}` exists for {actual_prefix} `{ty_str}`, \
                          but its trait bounds were not satisfied"
@@ -1409,6 +1396,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let mut find_candidate_for_method = false;
 
         let mut label_span_not_found = |err: &mut Diag<'_>| {
+            let ty_str = self.tcx.short_string(rcvr_ty, err.long_ty_path());
             if unsatisfied_predicates.is_empty() {
                 err.span_label(span, format!("{item_kind} not found in `{ty_str}`"));
                 let is_string_or_ref_str = match rcvr_ty.kind() {
@@ -2520,8 +2508,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         source: SelfSource<'tcx>,
         span: Span,
         item_name: Ident,
-        ty_str: &str,
-        long_ty_path: &mut Option<PathBuf>,
     ) -> Result<(), ErrorGuaranteed> {
         if let SelfSource::MethodCall(expr) = source {
             for (_, parent) in tcx.hir_parent_iter(expr.hir_id).take(5) {
@@ -2583,18 +2569,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     );
                     if pick.is_ok() {
                         let range_span = parent_expr.span.with_hi(expr.span.hi());
-                        let mut err = self.dcx().create_err(errors::MissingParenthesesInRange {
+                        return Err(self.dcx().emit_err(errors::MissingParenthesesInRange {
                             span,
-                            ty_str: ty_str.to_string(),
+                            ty: actual,
                             method_name: item_name.as_str().to_string(),
                             add_missing_parentheses: Some(errors::AddMissingParenthesesInRange {
                                 func_name: item_name.name.as_str().to_string(),
                                 left: range_span.shrink_to_lo(),
                                 right: range_span.shrink_to_hi(),
                             }),
-                        });
-                        *err.long_ty_path() = long_ty_path.take();
-                        return Err(err.emit());
+                        }));
                     }
                 }
             }
@@ -2610,7 +2594,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         span: Span,
         item_kind: &str,
         item_name: Ident,
-        ty_str: &str,
         long_ty_path: &mut Option<PathBuf>,
     ) -> Result<(), ErrorGuaranteed> {
         let found_candidate = all_traits(self.tcx)
@@ -2643,14 +2626,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             && !actual.has_concrete_skeleton()
             && let SelfSource::MethodCall(expr) = source
         {
+            let ty_str = self.tcx.short_string(actual, long_ty_path);
             let mut err = struct_span_code_err!(
                 self.dcx(),
                 span,
                 E0689,
-                "can't call {} `{}` on ambiguous numeric type `{}`",
-                item_kind,
-                item_name,
-                ty_str
+                "can't call {item_kind} `{item_name}` on ambiguous numeric type `{ty_str}`"
             );
             *err.long_ty_path() = long_ty_path.take();
             let concrete_type = if actual.is_integral() { "i32" } else { "f32" };
@@ -2792,7 +2773,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ) {
         if let SelfSource::MethodCall(expr) = source {
             let mod_id = self.tcx.parent_module(expr.hir_id).to_def_id();
-            for (fields, args) in self.get_field_candidates_considering_privacy_for_diag(
+            for fields in self.get_field_candidates_considering_privacy_for_diag(
                 span,
                 actual,
                 mod_id,
@@ -2831,7 +2812,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                 })
                             },
                             candidate_field,
-                            args,
                             vec![],
                             mod_id,
                             expr.hir_id,
@@ -3671,7 +3651,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         )
                     {
                         debug!("try_alt_rcvr: pick candidate {:?}", pick);
-                        let did = Some(pick.item.container_id(self.tcx));
+                        let did = pick.item.trait_container(self.tcx);
                         // We don't want to suggest a container type when the missing
                         // method is `.clone()` or `.deref()` otherwise we'd suggest
                         // `Arc::new(foo).clone()`, which is far from what the user wants.
@@ -3720,8 +3700,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     && !alt_rcvr_sugg
                     // `T: !Unpin`
                     && !unpin
-                    // The method isn't `as_ref`, as it would provide a wrong suggestion for `Pin`.
-                    && sym::as_ref != item_name.name
                     // Either `Pin::as_ref` or `Pin::as_mut`.
                     && let Some(pin_call) = pin_call
                     // Search for `item_name` as a method accessible on `Pin<T>`.
@@ -3735,6 +3713,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     // We skip some common traits that we don't want to consider because autoderefs
                     // would take care of them.
                     && !skippable.contains(&Some(pick.item.container_id(self.tcx)))
+                    // Do not suggest pinning when the method is directly on `Pin`.
+                    && pick.item.impl_container(self.tcx).map_or(true, |did| {
+                        match self.tcx.type_of(did).skip_binder().kind() {
+                            ty::Adt(def, _) => Some(def.did()) != self.tcx.lang_items().pin_type(),
+                            _ => true,
+                        }
+                    })
                     // We don't want to go through derefs.
                     && pick.autoderefs == 0
                     // Check that the method of the same name that was found on the new `Pin<T>`
diff --git a/compiler/rustc_hir_typeck/src/pat.rs b/compiler/rustc_hir_typeck/src/pat.rs
index bf4611e1e34..7dc736e5e6b 100644
--- a/compiler/rustc_hir_typeck/src/pat.rs
+++ b/compiler/rustc_hir_typeck/src/pat.rs
@@ -1756,7 +1756,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let missing_parentheses = match (expected.kind(), fields, had_err) {
             // #67037: only do this if we could successfully type-check the expected type against
             // the tuple struct pattern. Otherwise the args could get out of range on e.g.,
-            // `let P() = U;` where `P != U` with `struct P<T>(T);`.
+            // `let P() = U;` where `P != U` with `struct Box<T>(T);`.
             (ty::Adt(_, args), [field], Ok(())) => {
                 let field_ty = self.field_ty(pat_span, field, args);
                 match field_ty.kind() {
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index 7379df7c7c7..82d4856df39 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -484,17 +484,7 @@ pub enum NllRegionVariableOrigin {
     Placeholder(ty::PlaceholderRegion),
 
     Existential {
-        /// If this is true, then this variable was created to represent a lifetime
-        /// bound in a `for` binder. For example, it might have been created to
-        /// represent the lifetime `'a` in a type like `for<'a> fn(&'a u32)`.
-        /// Such variables are created when we are trying to figure out if there
-        /// is any valid instantiation of `'a` that could fit into some scenario.
-        ///
-        /// This is used to inform error reporting: in the case that we are trying to
-        /// determine whether there is any valid instantiation of a `'a` variable that meets
-        /// some constraint C, we want to blame the "source" of that `for` type,
-        /// rather than blaming the source of the constraint C.
-        from_forall: bool,
+        name: Option<Symbol>,
     },
 }
 
diff --git a/compiler/rustc_interface/src/passes.rs b/compiler/rustc_interface/src/passes.rs
index 8dec8069bc7..3ba224723e3 100644
--- a/compiler/rustc_interface/src/passes.rs
+++ b/compiler/rustc_interface/src/passes.rs
@@ -108,7 +108,7 @@ impl LintStoreExpand for LintStoreExpandImpl<'_> {
         registered_tools: &RegisteredTools,
         node_id: ast::NodeId,
         attrs: &[ast::Attribute],
-        items: &[rustc_ast::ptr::P<ast::Item>],
+        items: &[Box<ast::Item>],
         name: Symbol,
     ) {
         pre_expansion_lint(sess, features, self.0, registered_tools, (node_id, attrs, items), name);
@@ -371,7 +371,7 @@ fn print_macro_stats(ecx: &ExtCtxt<'_>) {
             // The name won't abut or overlap with the uses value, but it does
             // overlap with the empty part of the uses column. Shrink the width
             // of the uses column to account for the excess name length.
-            uses_w = uses_with_underscores.len() + 1
+            uses_w -= name.len() - name_w;
         };
 
         _ = writeln!(
diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
index 86faab62d03..0a764808f95 100644
--- a/compiler/rustc_interface/src/tests.rs
+++ b/compiler/rustc_interface/src/tests.rs
@@ -689,6 +689,7 @@ fn test_unstable_options_tracking_hash() {
     // Make sure that changing an [UNTRACKED] option leaves the hash unchanged.
     // tidy-alphabetical-start
     untracked!(assert_incr_state, Some(String::from("loaded")));
+    untracked!(codegen_source_order, true);
     untracked!(deduplicate_diagnostics, false);
     untracked!(dump_dep_graph, true);
     untracked!(dump_mir, Some(String::from("abc")));
@@ -777,7 +778,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(
         coverage_options,
         CoverageOptions {
-            level: CoverageLevel::Mcdc,
+            level: CoverageLevel::Branch,
             // (don't collapse test-only options onto the same line)
             discard_all_spans_in_codegen: true,
         }
diff --git a/compiler/rustc_lint/messages.ftl b/compiler/rustc_lint/messages.ftl
index 4d0c0c94a81..c485e6fc849 100644
--- a/compiler/rustc_lint/messages.ftl
+++ b/compiler/rustc_lint/messages.ftl
@@ -349,6 +349,7 @@ lint_ill_formed_attribute_input = {$num_suggestions ->
         [1] attribute must be of the form {$suggestions}
         *[other] valid forms for the attribute are {$suggestions}
     }
+    .note = for more information, visit <{$docs}>
 
 lint_impl_trait_overcaptures = `{$self_ty}` will capture more lifetimes than possibly intended in edition 2024
     .note = specifically, {$num_captured ->
@@ -982,6 +983,7 @@ lint_unused_allocation_mut = unnecessary allocation, use `&mut` instead
 
 lint_unused_builtin_attribute = unused attribute `{$attr_name}`
     .note = the built-in attribute `{$attr_name}` will be ignored, since it's applied to the macro invocation `{$macro_name}`
+    .suggestion = remove the attribute
 
 lint_unused_closure =
     unused {$pre}{$count ->
diff --git a/compiler/rustc_lint/src/builtin.rs b/compiler/rustc_lint/src/builtin.rs
index c893b723375..8006cfcf30f 100644
--- a/compiler/rustc_lint/src/builtin.rs
+++ b/compiler/rustc_lint/src/builtin.rs
@@ -21,6 +21,7 @@ use rustc_ast::tokenstream::{TokenStream, TokenTree};
 use rustc_ast::visit::{FnCtxt, FnKind};
 use rustc_ast::{self as ast, *};
 use rustc_ast_pretty::pprust::expr_to_string;
+use rustc_attr_parsing::AttributeParser;
 use rustc_errors::{Applicability, LintDiagnostic};
 use rustc_feature::GateIssue;
 use rustc_hir as hir;
@@ -248,12 +249,6 @@ impl UnsafeCode {
 }
 
 impl EarlyLintPass for UnsafeCode {
-    fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
-        if attr.has_name(sym::allow_internal_unsafe) {
-            self.report_unsafe(cx, attr.span, BuiltinUnsafe::AllowInternalUnsafe);
-        }
-    }
-
     #[inline]
     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
         if let ast::ExprKind::Block(ref blk, _) = e.kind {
@@ -270,7 +265,10 @@ impl EarlyLintPass for UnsafeCode {
                 self.report_unsafe(cx, it.span, BuiltinUnsafe::UnsafeTrait);
             }
 
-            ast::ItemKind::Impl(box ast::Impl { safety: ast::Safety::Unsafe(_), .. }) => {
+            ast::ItemKind::Impl(ast::Impl {
+                of_trait: Some(box ast::TraitImplHeader { safety: ast::Safety::Unsafe(_), .. }),
+                ..
+            }) => {
                 self.report_unsafe(cx, it.span, BuiltinUnsafe::UnsafeImpl);
             }
 
@@ -312,6 +310,19 @@ impl EarlyLintPass for UnsafeCode {
                 }
             }
 
+            ast::ItemKind::MacroDef(..) => {
+                if let Some(attr) = AttributeParser::parse_limited(
+                    cx.builder.sess(),
+                    &it.attrs,
+                    sym::allow_internal_unsafe,
+                    it.span,
+                    DUMMY_NODE_ID,
+                    Some(cx.builder.features()),
+                ) {
+                    self.report_unsafe(cx, attr.span(), BuiltinUnsafe::AllowInternalUnsafe);
+                }
+            }
+
             _ => {}
         }
     }
diff --git a/compiler/rustc_lint/src/context.rs b/compiler/rustc_lint/src/context.rs
index 11181d10af5..cb159a0b914 100644
--- a/compiler/rustc_lint/src/context.rs
+++ b/compiler/rustc_lint/src/context.rs
@@ -745,41 +745,41 @@ impl<'tcx> LateContext<'tcx> {
     /// }
     /// ```
     pub fn get_def_path(&self, def_id: DefId) -> Vec<Symbol> {
-        struct AbsolutePathPrinter<'tcx> {
+        struct LintPathPrinter<'tcx> {
             tcx: TyCtxt<'tcx>,
             path: Vec<Symbol>,
         }
 
-        impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
+        impl<'tcx> Printer<'tcx> for LintPathPrinter<'tcx> {
             fn tcx(&self) -> TyCtxt<'tcx> {
                 self.tcx
             }
 
             fn print_region(&mut self, _region: ty::Region<'_>) -> Result<(), PrintError> {
-                unreachable!(); // because `path_generic_args` ignores the `GenericArgs`
+                unreachable!(); // because `print_path_with_generic_args` ignores the `GenericArgs`
             }
 
             fn print_type(&mut self, _ty: Ty<'tcx>) -> Result<(), PrintError> {
-                unreachable!(); // because `path_generic_args` ignores the `GenericArgs`
+                unreachable!(); // because `print_path_with_generic_args` ignores the `GenericArgs`
             }
 
             fn print_dyn_existential(
                 &mut self,
                 _predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
             ) -> Result<(), PrintError> {
-                unreachable!(); // because `path_generic_args` ignores the `GenericArgs`
+                unreachable!(); // because `print_path_with_generic_args` ignores the `GenericArgs`
             }
 
             fn print_const(&mut self, _ct: ty::Const<'tcx>) -> Result<(), PrintError> {
-                unreachable!(); // because `path_generic_args` ignores the `GenericArgs`
+                unreachable!(); // because `print_path_with_generic_args` ignores the `GenericArgs`
             }
 
-            fn path_crate(&mut self, cnum: CrateNum) -> Result<(), PrintError> {
+            fn print_crate_name(&mut self, cnum: CrateNum) -> Result<(), PrintError> {
                 self.path = vec![self.tcx.crate_name(cnum)];
                 Ok(())
             }
 
-            fn path_qualified(
+            fn print_path_with_qualified(
                 &mut self,
                 self_ty: Ty<'tcx>,
                 trait_ref: Option<ty::TraitRef<'tcx>>,
@@ -800,7 +800,7 @@ impl<'tcx> LateContext<'tcx> {
                 })
             }
 
-            fn path_append_impl(
+            fn print_path_with_impl(
                 &mut self,
                 print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
                 self_ty: Ty<'tcx>,
@@ -825,7 +825,7 @@ impl<'tcx> LateContext<'tcx> {
                 Ok(())
             }
 
-            fn path_append(
+            fn print_path_with_simple(
                 &mut self,
                 print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
                 disambiguated_data: &DisambiguatedDefPathData,
@@ -844,7 +844,7 @@ impl<'tcx> LateContext<'tcx> {
                 Ok(())
             }
 
-            fn path_generic_args(
+            fn print_path_with_generic_args(
                 &mut self,
                 print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
                 _args: &[GenericArg<'tcx>],
@@ -853,7 +853,7 @@ impl<'tcx> LateContext<'tcx> {
             }
         }
 
-        let mut p = AbsolutePathPrinter { tcx: self.tcx, path: vec![] };
+        let mut p = LintPathPrinter { tcx: self.tcx, path: vec![] };
         p.print_def_path(def_id, &[]).unwrap();
         p.path
     }
diff --git a/compiler/rustc_lint/src/default_could_be_derived.rs b/compiler/rustc_lint/src/default_could_be_derived.rs
index 7c39d8917ce..1d92cfbc039 100644
--- a/compiler/rustc_lint/src/default_could_be_derived.rs
+++ b/compiler/rustc_lint/src/default_could_be_derived.rs
@@ -62,8 +62,7 @@ impl<'tcx> LateLintPass<'tcx> for DefaultCouldBeDerived {
         // Look for manual implementations of `Default`.
         let Some(default_def_id) = cx.tcx.get_diagnostic_item(sym::Default) else { return };
         let hir::ImplItemKind::Fn(_sig, body_id) = impl_item.kind else { return };
-        let assoc = cx.tcx.associated_item(impl_item.owner_id);
-        let parent = assoc.container_id(cx.tcx);
+        let parent = cx.tcx.parent(impl_item.owner_id.to_def_id());
         if find_attr!(cx.tcx.get_all_attrs(parent), AttributeKind::AutomaticallyDerived(..)) {
             // We don't care about what `#[derive(Default)]` produces in this lint.
             return;
diff --git a/compiler/rustc_lint/src/deref_into_dyn_supertrait.rs b/compiler/rustc_lint/src/deref_into_dyn_supertrait.rs
index dd16117db1c..943fcc0801b 100644
--- a/compiler/rustc_lint/src/deref_into_dyn_supertrait.rs
+++ b/compiler/rustc_lint/src/deref_into_dyn_supertrait.rs
@@ -61,8 +61,8 @@ impl<'tcx> LateLintPass<'tcx> for DerefIntoDynSupertrait {
         // `Deref` is being implemented for `t`
         if let hir::ItemKind::Impl(impl_) = item.kind
             // the trait is a `Deref` implementation
-            && let Some(trait_) = &impl_.of_trait
-            && let Some(did) = trait_.trait_def_id()
+            && let Some(of_trait) = &impl_.of_trait
+            && let Some(did) = of_trait.trait_ref.trait_def_id()
             && tcx.is_lang_item(did, LangItem::Deref)
             // the self type is `dyn t_principal`
             && let self_ty = tcx.type_of(item.owner_id).instantiate_identity()
diff --git a/compiler/rustc_lint/src/drop_forget_useless.rs b/compiler/rustc_lint/src/drop_forget_useless.rs
index 7f098893f7d..c2d137986ce 100644
--- a/compiler/rustc_lint/src/drop_forget_useless.rs
+++ b/compiler/rustc_lint/src/drop_forget_useless.rs
@@ -151,7 +151,7 @@ impl<'tcx> LateLintPass<'tcx> for DropForgetUseless {
                     && let Node::Stmt(stmt) = node
                     && let StmtKind::Semi(e) = stmt.kind
                     && e.hir_id == expr.hir_id
-                    && let Some(arg_span) = arg.span.find_ancestor_inside(expr.span)
+                    && let Some(arg_span) = arg.span.find_ancestor_inside_same_ctxt(expr.span)
                 {
                     UseLetUnderscoreIgnoreSuggestion::Suggestion {
                         start_span: expr.span.shrink_to_lo().until(arg_span),
diff --git a/compiler/rustc_lint/src/early.rs b/compiler/rustc_lint/src/early.rs
index 48e3bbb79fa..58205087def 100644
--- a/compiler/rustc_lint/src/early.rs
+++ b/compiler/rustc_lint/src/early.rs
@@ -4,7 +4,6 @@
 //! resolution, just before AST lowering. These lints are for purely
 //! syntactical lints.
 
-use rustc_ast::ptr::P;
 use rustc_ast::visit::{self as ast_visit, Visitor, walk_list};
 use rustc_ast::{self as ast, HasAttrs};
 use rustc_data_structures::stack::ensure_sufficient_stack;
@@ -297,7 +296,7 @@ impl<'a> EarlyCheckNode<'a> for (&'a ast::Crate, &'a [ast::Attribute]) {
     }
 }
 
-impl<'a> EarlyCheckNode<'a> for (ast::NodeId, &'a [ast::Attribute], &'a [P<ast::Item>]) {
+impl<'a> EarlyCheckNode<'a> for (ast::NodeId, &'a [ast::Attribute], &'a [Box<ast::Item>]) {
     fn id(self) -> ast::NodeId {
         self.0
     }
diff --git a/compiler/rustc_lint/src/early/diagnostics.rs b/compiler/rustc_lint/src/early/diagnostics.rs
index f0fbf5bc81e..678d3d1f8ed 100644
--- a/compiler/rustc_lint/src/early/diagnostics.rs
+++ b/compiler/rustc_lint/src/early/diagnostics.rs
@@ -205,8 +205,14 @@ pub fn decorate_builtin_lint(
             }
             .decorate_lint(diag);
         }
-        BuiltinLintDiag::UnusedBuiltinAttribute { attr_name, macro_name, invoc_span } => {
-            lints::UnusedBuiltinAttribute { invoc_span, attr_name, macro_name }.decorate_lint(diag);
+        BuiltinLintDiag::UnusedBuiltinAttribute {
+            attr_name,
+            macro_name,
+            invoc_span,
+            attr_span,
+        } => {
+            lints::UnusedBuiltinAttribute { invoc_span, attr_name, macro_name, attr_span }
+                .decorate_lint(diag);
         }
         BuiltinLintDiag::TrailingMacro(is_trailing, name) => {
             lints::TrailingMacro { is_trailing, name }.decorate_lint(diag);
@@ -447,12 +453,14 @@ pub fn decorate_builtin_lint(
         BuiltinLintDiag::UnusedCrateDependency { extern_crate, local_crate } => {
             lints::UnusedCrateDependency { extern_crate, local_crate }.decorate_lint(diag)
         }
-        BuiltinLintDiag::IllFormedAttributeInput { suggestions } => {
+        BuiltinLintDiag::IllFormedAttributeInput { suggestions, docs } => {
             lints::IllFormedAttributeInput {
                 num_suggestions: suggestions.len(),
                 suggestions: DiagArgValue::StrListSepByAnd(
                     suggestions.into_iter().map(|s| format!("`{s}`").into()).collect(),
                 ),
+                has_docs: docs.is_some(),
+                docs: docs.unwrap_or(""),
             }
             .decorate_lint(diag)
         }
diff --git a/compiler/rustc_lint/src/internal.rs b/compiler/rustc_lint/src/internal.rs
index 7dafcc199a3..016ff17f5d7 100644
--- a/compiler/rustc_lint/src/internal.rs
+++ b/compiler/rustc_lint/src/internal.rs
@@ -411,11 +411,11 @@ declare_lint_pass!(LintPassImpl => [LINT_PASS_IMPL_WITHOUT_MACRO]);
 
 impl EarlyLintPass for LintPassImpl {
     fn check_item(&mut self, cx: &EarlyContext<'_>, item: &ast::Item) {
-        if let ast::ItemKind::Impl(box ast::Impl { of_trait: Some(lint_pass), .. }) = &item.kind
-            && let Some(last) = lint_pass.path.segments.last()
+        if let ast::ItemKind::Impl(ast::Impl { of_trait: Some(of_trait), .. }) = &item.kind
+            && let Some(last) = of_trait.trait_ref.path.segments.last()
             && last.ident.name == sym::LintPass
         {
-            let expn_data = lint_pass.path.span.ctxt().outer_expn_data();
+            let expn_data = of_trait.trait_ref.path.span.ctxt().outer_expn_data();
             let call_site = expn_data.call_site;
             if expn_data.kind != ExpnKind::Macro(MacroKind::Bang, sym::impl_lint_pass)
                 && call_site.ctxt().outer_expn_data().kind
@@ -423,7 +423,7 @@ impl EarlyLintPass for LintPassImpl {
             {
                 cx.emit_span_lint(
                     LINT_PASS_IMPL_WITHOUT_MACRO,
-                    lint_pass.path.span,
+                    of_trait.trait_ref.path.span,
                     LintPassByHand,
                 );
             }
@@ -582,8 +582,8 @@ impl Diagnostics {
         for (_hir_id, parent) in cx.tcx.hir_parent_iter(current_id) {
             debug!(?parent);
             if let hir::Node::Item(hir::Item { kind: hir::ItemKind::Impl(impl_), .. }) = parent
-                && let hir::Impl { of_trait: Some(of_trait), .. } = impl_
-                && let Some(def_id) = of_trait.trait_def_id()
+                && let Some(of_trait) = impl_.of_trait
+                && let Some(def_id) = of_trait.trait_ref.trait_def_id()
                 && let Some(name) = cx.tcx.get_diagnostic_name(def_id)
                 && matches!(name, sym::Diagnostic | sym::Subdiagnostic | sym::LintDiagnostic)
             {
diff --git a/compiler/rustc_lint/src/lifetime_syntax.rs b/compiler/rustc_lint/src/lifetime_syntax.rs
index 2a5a34cdc6e..464f4fc34b9 100644
--- a/compiler/rustc_lint/src/lifetime_syntax.rs
+++ b/compiler/rustc_lint/src/lifetime_syntax.rs
@@ -434,7 +434,7 @@ fn emit_mismatch_diagnostic<'tcx>(
         lints::MismatchedLifetimeSyntaxesSuggestion::Mixed {
             implicit_suggestions,
             explicit_anonymous_suggestions,
-            tool_only: false,
+            optional_alternative: false,
         }
     });
 
@@ -455,7 +455,10 @@ fn emit_mismatch_diagnostic<'tcx>(
     let implicit_suggestion = should_suggest_implicit.then(|| {
         let suggestions = make_implicit_suggestions(&suggest_change_to_implicit);
 
-        lints::MismatchedLifetimeSyntaxesSuggestion::Implicit { suggestions, tool_only: false }
+        lints::MismatchedLifetimeSyntaxesSuggestion::Implicit {
+            suggestions,
+            optional_alternative: false,
+        }
     });
 
     tracing::debug!(
@@ -508,7 +511,7 @@ fn build_mismatch_suggestion(
     lints::MismatchedLifetimeSyntaxesSuggestion::Explicit {
         lifetime_name,
         suggestions,
-        tool_only: false,
+        optional_alternative: false,
     }
 }
 
diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs
index ef63c0dee8c..a6d59af6900 100644
--- a/compiler/rustc_lint/src/lints.rs
+++ b/compiler/rustc_lint/src/lints.rs
@@ -902,9 +902,8 @@ pub(crate) struct MappingToUnit {
     pub argument_label: Span,
     #[label(lint_map_label)]
     pub map_label: Span,
-    #[suggestion(style = "verbose", code = "{replace}", applicability = "maybe-incorrect")]
+    #[suggestion(style = "verbose", code = "for_each", applicability = "maybe-incorrect")]
     pub suggestion: Span,
-    pub replace: String,
 }
 
 // internal.rs
@@ -2686,6 +2685,9 @@ pub(crate) struct UnusedCrateDependency {
 pub(crate) struct IllFormedAttributeInput {
     pub num_suggestions: usize,
     pub suggestions: DiagArgValue,
+    #[note]
+    pub has_docs: bool,
+    pub docs: &'static str,
 }
 
 #[derive(LintDiagnostic)]
@@ -2936,9 +2938,10 @@ pub(crate) struct RawPrefix {
 pub(crate) struct UnusedBuiltinAttribute {
     #[note]
     pub invoc_span: Span,
-
     pub attr_name: Symbol,
     pub macro_name: String,
+    #[suggestion(code = "", applicability = "machine-applicable", style = "tool-only")]
+    pub attr_span: Span,
 }
 
 #[derive(LintDiagnostic)]
@@ -3292,7 +3295,7 @@ impl<'a, G: EmissionGuarantee> LintDiagnostic<'a, G> for MismatchedLifetimeSynta
             diag.subdiagnostic(s);
 
             for mut s in suggestions {
-                s.make_tool_only();
+                s.make_optional_alternative();
                 diag.subdiagnostic(s);
             }
         }
@@ -3303,33 +3306,33 @@ impl<'a, G: EmissionGuarantee> LintDiagnostic<'a, G> for MismatchedLifetimeSynta
 pub(crate) enum MismatchedLifetimeSyntaxesSuggestion {
     Implicit {
         suggestions: Vec<Span>,
-        tool_only: bool,
+        optional_alternative: bool,
     },
 
     Mixed {
         implicit_suggestions: Vec<Span>,
         explicit_anonymous_suggestions: Vec<(Span, String)>,
-        tool_only: bool,
+        optional_alternative: bool,
     },
 
     Explicit {
         lifetime_name: String,
         suggestions: Vec<(Span, String)>,
-        tool_only: bool,
+        optional_alternative: bool,
     },
 }
 
 impl MismatchedLifetimeSyntaxesSuggestion {
-    fn make_tool_only(&mut self) {
+    fn make_optional_alternative(&mut self) {
         use MismatchedLifetimeSyntaxesSuggestion::*;
 
-        let tool_only = match self {
-            Implicit { tool_only, .. } | Mixed { tool_only, .. } | Explicit { tool_only, .. } => {
-                tool_only
-            }
+        let optional_alternative = match self {
+            Implicit { optional_alternative, .. }
+            | Mixed { optional_alternative, .. }
+            | Explicit { optional_alternative, .. } => optional_alternative,
         };
 
-        *tool_only = true;
+        *optional_alternative = true;
     }
 }
 
@@ -3337,22 +3340,40 @@ impl Subdiagnostic for MismatchedLifetimeSyntaxesSuggestion {
     fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
         use MismatchedLifetimeSyntaxesSuggestion::*;
 
-        let style = |tool_only| {
-            if tool_only { SuggestionStyle::CompletelyHidden } else { SuggestionStyle::ShowAlways }
+        let style = |optional_alternative| {
+            if optional_alternative {
+                SuggestionStyle::CompletelyHidden
+            } else {
+                SuggestionStyle::ShowAlways
+            }
+        };
+
+        let applicability = |optional_alternative| {
+            // `cargo fix` can't handle more than one fix for the same issue,
+            // so hide alternative suggestions from it by marking them as maybe-incorrect
+            if optional_alternative {
+                Applicability::MaybeIncorrect
+            } else {
+                Applicability::MachineApplicable
+            }
         };
 
         match self {
-            Implicit { suggestions, tool_only } => {
+            Implicit { suggestions, optional_alternative } => {
                 let suggestions = suggestions.into_iter().map(|s| (s, String::new())).collect();
                 diag.multipart_suggestion_with_style(
                     fluent::lint_mismatched_lifetime_syntaxes_suggestion_implicit,
                     suggestions,
-                    Applicability::MaybeIncorrect,
-                    style(tool_only),
+                    applicability(optional_alternative),
+                    style(optional_alternative),
                 );
             }
 
-            Mixed { implicit_suggestions, explicit_anonymous_suggestions, tool_only } => {
+            Mixed {
+                implicit_suggestions,
+                explicit_anonymous_suggestions,
+                optional_alternative,
+            } => {
                 let message = if implicit_suggestions.is_empty() {
                     fluent::lint_mismatched_lifetime_syntaxes_suggestion_mixed_only_paths
                 } else {
@@ -3368,12 +3389,12 @@ impl Subdiagnostic for MismatchedLifetimeSyntaxesSuggestion {
                 diag.multipart_suggestion_with_style(
                     message,
                     suggestions,
-                    Applicability::MaybeIncorrect,
-                    style(tool_only),
+                    applicability(optional_alternative),
+                    style(optional_alternative),
                 );
             }
 
-            Explicit { lifetime_name, suggestions, tool_only } => {
+            Explicit { lifetime_name, suggestions, optional_alternative } => {
                 diag.arg("lifetime_name", lifetime_name);
                 let msg = diag.eagerly_translate(
                     fluent::lint_mismatched_lifetime_syntaxes_suggestion_explicit,
@@ -3382,8 +3403,8 @@ impl Subdiagnostic for MismatchedLifetimeSyntaxesSuggestion {
                 diag.multipart_suggestion_with_style(
                     msg,
                     suggestions,
-                    Applicability::MaybeIncorrect,
-                    style(tool_only),
+                    applicability(optional_alternative),
+                    style(optional_alternative),
                 );
             }
         }
diff --git a/compiler/rustc_lint/src/map_unit_fn.rs b/compiler/rustc_lint/src/map_unit_fn.rs
index 34210137bde..18a947dc1ee 100644
--- a/compiler/rustc_lint/src/map_unit_fn.rs
+++ b/compiler/rustc_lint/src/map_unit_fn.rs
@@ -1,6 +1,7 @@
-use rustc_hir::{Expr, ExprKind, HirId, Stmt, StmtKind};
-use rustc_middle::ty::{self, Ty};
+use rustc_hir::{Expr, ExprKind, Stmt, StmtKind};
+use rustc_middle::ty::{self};
 use rustc_session::{declare_lint, declare_lint_pass};
+use rustc_span::sym;
 
 use crate::lints::MappingToUnit;
 use crate::{LateContext, LateLintPass, LintContext};
@@ -39,58 +40,43 @@ declare_lint_pass!(MapUnitFn => [MAP_UNIT_FN]);
 
 impl<'tcx> LateLintPass<'tcx> for MapUnitFn {
     fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &Stmt<'_>) {
-        if stmt.span.from_expansion() {
+        let StmtKind::Semi(expr) = stmt.kind else {
             return;
-        }
-
-        if let StmtKind::Semi(expr) = stmt.kind
-            && let ExprKind::MethodCall(path, receiver, args, span) = expr.kind
+        };
+        let ExprKind::MethodCall(path, receiver, [arg], span) = expr.kind else {
+            return;
+        };
+        if path.ident.name != sym::map
+            || stmt.span.from_expansion()
+            || receiver.span.from_expansion()
+            || arg.span.from_expansion()
+            || !is_impl_slice(cx, receiver)
+            || !cx
+                .typeck_results()
+                .type_dependent_def_id(expr.hir_id)
+                .is_some_and(|id| cx.tcx.is_diagnostic_item(sym::IteratorMap, id))
         {
-            if path.ident.name.as_str() == "map" {
-                if receiver.span.from_expansion()
-                    || args.iter().any(|e| e.span.from_expansion())
-                    || !is_impl_slice(cx, receiver)
-                    || !is_diagnostic_name(cx, expr.hir_id, "IteratorMap")
-                {
-                    return;
-                }
-                let arg_ty = cx.typeck_results().expr_ty(&args[0]);
-                let default_span = args[0].span;
-                if let ty::FnDef(id, _) = arg_ty.kind() {
-                    let fn_ty = cx.tcx.fn_sig(id).skip_binder();
-                    let ret_ty = fn_ty.output().skip_binder();
-                    if is_unit_type(ret_ty) {
-                        cx.emit_span_lint(
-                            MAP_UNIT_FN,
-                            span,
-                            MappingToUnit {
-                                function_label: cx.tcx.span_of_impl(*id).unwrap_or(default_span),
-                                argument_label: args[0].span,
-                                map_label: span,
-                                suggestion: path.ident.span,
-                                replace: "for_each".to_string(),
-                            },
-                        )
-                    }
-                } else if let ty::Closure(id, subs) = arg_ty.kind() {
-                    let cl_ty = subs.as_closure().sig();
-                    let ret_ty = cl_ty.output().skip_binder();
-                    if is_unit_type(ret_ty) {
-                        cx.emit_span_lint(
-                            MAP_UNIT_FN,
-                            span,
-                            MappingToUnit {
-                                function_label: cx.tcx.span_of_impl(*id).unwrap_or(default_span),
-                                argument_label: args[0].span,
-                                map_label: span,
-                                suggestion: path.ident.span,
-                                replace: "for_each".to_string(),
-                            },
-                        )
-                    }
-                }
-            }
+            return;
         }
+        let (id, sig) = match *cx.typeck_results().expr_ty(arg).kind() {
+            ty::Closure(id, subs) => (id, subs.as_closure().sig()),
+            ty::FnDef(id, _) => (id, cx.tcx.fn_sig(id).skip_binder()),
+            _ => return,
+        };
+        let ret_ty = sig.output().skip_binder();
+        if !(ret_ty.is_unit() || ret_ty.is_never()) {
+            return;
+        }
+        cx.emit_span_lint(
+            MAP_UNIT_FN,
+            span,
+            MappingToUnit {
+                function_label: cx.tcx.span_of_impl(id).unwrap_or(arg.span),
+                argument_label: arg.span,
+                map_label: span,
+                suggestion: path.ident.span,
+            },
+        );
     }
 }
 
@@ -102,18 +88,3 @@ fn is_impl_slice(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
     }
     false
 }
-
-fn is_unit_type(ty: Ty<'_>) -> bool {
-    ty.is_unit() || ty.is_never()
-}
-
-fn is_diagnostic_name(cx: &LateContext<'_>, id: HirId, name: &str) -> bool {
-    if let Some(def_id) = cx.typeck_results().type_dependent_def_id(id)
-        && let Some(item) = cx.tcx.get_diagnostic_name(def_id)
-    {
-        if item.as_str() == name {
-            return true;
-        }
-    }
-    false
-}
diff --git a/compiler/rustc_lint/src/non_local_def.rs b/compiler/rustc_lint/src/non_local_def.rs
index b877f909fc0..dca22b986ff 100644
--- a/compiler/rustc_lint/src/non_local_def.rs
+++ b/compiler/rustc_lint/src/non_local_def.rs
@@ -5,7 +5,7 @@ use rustc_hir::{Body, HirId, Item, ItemKind, Node, Path, TyKind};
 use rustc_middle::ty::TyCtxt;
 use rustc_session::{declare_lint, impl_lint_pass};
 use rustc_span::def_id::{DefId, LOCAL_CRATE};
-use rustc_span::{ExpnKind, MacroKind, Span, kw, sym};
+use rustc_span::{ExpnKind, Span, kw, sym};
 
 use crate::lints::{NonLocalDefinitionsCargoUpdateNote, NonLocalDefinitionsDiag};
 use crate::{LateContext, LateLintPass, LintContext, fluent_generated as fluent};
@@ -129,8 +129,8 @@ impl<'tcx> LateLintPass<'tcx> for NonLocalDefinitions {
                 // of the `impl` definition
                 let mut collector = PathCollector { paths: Vec::new() };
                 collector.visit_ty_unambig(&impl_.self_ty);
-                if let Some(of_trait) = &impl_.of_trait {
-                    collector.visit_trait_ref(of_trait);
+                if let Some(of_trait) = impl_.of_trait {
+                    collector.visit_trait_ref(&of_trait.trait_ref);
                 }
 
                 // 1.5. Remove any path that doesn't resolve to a `DefId` or if it resolve to a
@@ -240,7 +240,7 @@ impl<'tcx> LateLintPass<'tcx> for NonLocalDefinitions {
                     },
                 )
             }
-            ItemKind::Macro(_, _macro, MacroKind::Bang)
+            ItemKind::Macro(_, _macro, _kinds)
                 if cx.tcx.has_attr(item.owner_id.def_id, sym::macro_export) =>
             {
                 cx.emit_span_lint(
diff --git a/compiler/rustc_lint/src/nonstandard_style.rs b/compiler/rustc_lint/src/nonstandard_style.rs
index 7e5f43ba77f..8fafaa33d0c 100644
--- a/compiler/rustc_lint/src/nonstandard_style.rs
+++ b/compiler/rustc_lint/src/nonstandard_style.rs
@@ -187,7 +187,7 @@ impl EarlyLintPass for NonCamelCaseTypes {
 
             // N.B. This check is only for inherent associated types, so that we don't lint against
             // trait impls where we should have warned for the trait definition already.
-            ast::ItemKind::Impl(box ast::Impl { of_trait: None, items, .. }) => {
+            ast::ItemKind::Impl(ast::Impl { of_trait: None, items, .. }) => {
                 for it in items {
                     // FIXME: this doesn't respect `#[allow(..)]` on the item itself.
                     if let ast::AssocItemKind::Type(alias) = &it.kind {
diff --git a/compiler/rustc_lint/src/pass_by_value.rs b/compiler/rustc_lint/src/pass_by_value.rs
index 4f65acd8001..29006732aad 100644
--- a/compiler/rustc_lint/src/pass_by_value.rs
+++ b/compiler/rustc_lint/src/pass_by_value.rs
@@ -24,10 +24,8 @@ impl<'tcx> LateLintPass<'tcx> for PassByValue {
     fn check_ty(&mut self, cx: &LateContext<'_>, ty: &'tcx hir::Ty<'tcx, AmbigArg>) {
         match &ty.kind {
             TyKind::Ref(_, hir::MutTy { ty: inner_ty, mutbl: hir::Mutability::Not }) => {
-                if let Some(impl_did) = cx.tcx.impl_of_assoc(ty.hir_id.owner.to_def_id()) {
-                    if cx.tcx.impl_trait_ref(impl_did).is_some() {
-                        return;
-                    }
+                if cx.tcx.trait_impl_of_assoc(ty.hir_id.owner.to_def_id()).is_some() {
+                    return;
                 }
                 if let Some(t) = path_for_pass_by_value(cx, inner_ty) {
                     cx.emit_span_lint(
diff --git a/compiler/rustc_lint/src/types.rs b/compiler/rustc_lint/src/types.rs
index b0afc333ebe..f8a692313f0 100644
--- a/compiler/rustc_lint/src/types.rs
+++ b/compiler/rustc_lint/src/types.rs
@@ -1904,10 +1904,9 @@ impl InvalidAtomicOrdering {
         if let ExprKind::MethodCall(method_path, _, args, _) = &expr.kind
             && recognized_names.contains(&method_path.ident.name)
             && let Some(m_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id)
-            && let Some(impl_did) = cx.tcx.impl_of_assoc(m_def_id)
-            && let Some(adt) = cx.tcx.type_of(impl_did).instantiate_identity().ty_adt_def()
             // skip extension traits, only lint functions from the standard library
-            && cx.tcx.trait_id_of_impl(impl_did).is_none()
+            && let Some(impl_did) = cx.tcx.inherent_impl_of_assoc(m_def_id)
+            && let Some(adt) = cx.tcx.type_of(impl_did).instantiate_identity().ty_adt_def()
             && let parent = cx.tcx.parent(adt.did())
             && cx.tcx.is_diagnostic_item(sym::atomic_mod, parent)
             && ATOMIC_TYPES.contains(&cx.tcx.item_name(adt.did()))
diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
index 3b84c6b6110..a0083a7df3d 100644
--- a/compiler/rustc_lint_defs/src/builtin.rs
+++ b/compiler/rustc_lint_defs/src/builtin.rs
@@ -217,6 +217,7 @@ declare_lint! {
     @future_incompatible = FutureIncompatibleInfo {
         reason: FutureIncompatibilityReason::FutureReleaseError,
         reference: "issue #57571 <https://github.com/rust-lang/rust/issues/57571>",
+        report_in_deps: true,
     };
     crate_level_only
 }
@@ -2156,6 +2157,7 @@ declare_lint! {
     @future_incompatible = FutureIncompatibleInfo {
         reason: FutureIncompatibilityReason::FutureReleaseError,
         reference: "issue #52234 <https://github.com/rust-lang/rust/issues/52234>",
+        report_in_deps: true,
     };
     crate_level_only
 }
@@ -2839,7 +2841,7 @@ declare_lint! {
     /// [issue #79813]: https://github.com/rust-lang/rust/issues/79813
     /// [future-incompatible]: ../index.md#future-incompatible-lints
     pub SEMICOLON_IN_EXPRESSIONS_FROM_MACROS,
-    Warn,
+    Deny,
     "trailing semicolon in macro body used as expression",
     @future_incompatible = FutureIncompatibleInfo {
         reason: FutureIncompatibilityReason::FutureReleaseError,
@@ -2887,11 +2889,12 @@ declare_lint! {
     /// struct S { /* fields */ }
     /// ```
     pub LEGACY_DERIVE_HELPERS,
-    Warn,
+    Deny,
     "detects derive helper attributes that are used before they are introduced",
     @future_incompatible = FutureIncompatibleInfo {
         reason: FutureIncompatibilityReason::FutureReleaseError,
         reference: "issue #79202 <https://github.com/rust-lang/rust/issues/79202>",
+        report_in_deps: true,
     };
 }
 
@@ -4624,11 +4627,12 @@ declare_lint! {
     ///
     /// [future-incompatible]: ../index.md#future-incompatible-lints
     pub PRIVATE_MACRO_USE,
-    Warn,
+    Deny,
     "detects certain macro bindings that should not be re-exported",
     @future_incompatible = FutureIncompatibleInfo {
         reason: FutureIncompatibilityReason::FutureReleaseError,
         reference: "issue #120192 <https://github.com/rust-lang/rust/issues/120192>",
+        report_in_deps: true,
     };
 }
 
@@ -4828,7 +4832,7 @@ declare_lint! {
     ///
     /// ### Example
     ///
-    /// ```rust
+    /// ```rust,compile_fail
     /// #![doc = in_root!()]
     ///
     /// macro_rules! in_root { () => { "" } }
@@ -4853,11 +4857,12 @@ declare_lint! {
     ///
     /// [future-incompatible]: ../index.md#future-incompatible-lints
     pub OUT_OF_SCOPE_MACRO_CALLS,
-    Warn,
+    Deny,
     "detects out of scope calls to `macro_rules` in key-value attributes",
     @future_incompatible = FutureIncompatibleInfo {
         reason: FutureIncompatibilityReason::FutureReleaseError,
         reference: "issue #124535 <https://github.com/rust-lang/rust/issues/124535>",
+        report_in_deps: true,
     };
 }
 
@@ -5100,3 +5105,36 @@ declare_lint! {
         report_in_deps: true,
     };
 }
+
+declare_lint! {
+    /// The `tail_call_track_caller` lint detects usage of `become` attempting to tail call
+    /// a function marked with `#[track_caller]`.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// #![feature(explicit_tail_calls)]
+    /// #![expect(incomplete_features)]
+    ///
+    /// #[track_caller]
+    /// fn f() {}
+    ///
+    /// fn g() {
+    ///     become f();
+    /// }
+    ///
+    /// g();
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// Due to implementation details of tail calls and `#[track_caller]` attribute, calls to
+    /// functions marked with `#[track_caller]` cannot become tail calls. As such using `become`
+    /// is no different than a normal call (except for changes in drop order).
+    pub TAIL_CALL_TRACK_CALLER,
+    Warn,
+    "detects tail calls of functions marked with `#[track_caller]`",
+    @feature_gate = explicit_tail_calls;
+}
diff --git a/compiler/rustc_lint_defs/src/lib.rs b/compiler/rustc_lint_defs/src/lib.rs
index fe068d96b74..3bb7bbce567 100644
--- a/compiler/rustc_lint_defs/src/lib.rs
+++ b/compiler/rustc_lint_defs/src/lib.rs
@@ -647,6 +647,7 @@ pub enum BuiltinLintDiag {
         attr_name: Symbol,
         macro_name: String,
         invoc_span: Span,
+        attr_span: Span,
     },
     PatternsInFnsWithoutBody {
         span: Span,
@@ -793,6 +794,7 @@ pub enum BuiltinLintDiag {
     },
     IllFormedAttributeInput {
         suggestions: Vec<String>,
+        docs: Option<&'static str>,
     },
     InnerAttributeUnstable {
         is_macro: bool,
diff --git a/compiler/rustc_llvm/build.rs b/compiler/rustc_llvm/build.rs
index 069b684ad09..1394edcee6b 100644
--- a/compiler/rustc_llvm/build.rs
+++ b/compiler/rustc_llvm/build.rs
@@ -171,6 +171,16 @@ fn main() {
     let cxxflags = output(&mut cmd);
     let mut cfg = cc::Build::new();
     cfg.warnings(false);
+
+    // Prevent critical warnings when we're compiling from rust-lang/rust CI,
+    // except on MSVC, as the compiler throws warnings that are only reported
+    // for this platform. See https://github.com/rust-lang/rust/pull/145031#issuecomment-3162677202
+    // FIXME(llvm22): It looks like the specific problem code has been removed
+    // in https://github.com/llvm/llvm-project/commit/e8fc808bf8e78a3c80d1f8e293a92677b92366dd,
+    // retry msvc once we bump our LLVM version.
+    if std::env::var_os("CI").is_some() && !target.contains("msvc") {
+        cfg.warnings_into_errors(true);
+    }
     for flag in cxxflags.split_whitespace() {
         // Ignore flags like `-m64` when we're doing a cross build
         if is_crossed && flag.starts_with("-m") {
@@ -245,7 +255,7 @@ fn main() {
         println!("cargo:rustc-link-lib=kstat");
     }
 
-    if (target.starts_with("arm") && !target.contains("freebsd")) && !target.contains("ohos")
+    if (target.starts_with("arm") && !target.contains("freebsd") && !target.contains("ohos"))
         || target.starts_with("mips-")
         || target.starts_with("mipsel-")
         || target.starts_with("powerpc-")
diff --git a/compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp
index 4695de8ea09..22e7c7a160f 100644
--- a/compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp
@@ -37,28 +37,6 @@ static coverage::Counter fromRust(LLVMRustCounter Counter) {
   report_fatal_error("Bad LLVMRustCounterKind!");
 }
 
-struct LLVMRustMCDCDecisionParameters {
-  uint32_t BitmapIdx;
-  uint16_t NumConditions;
-};
-
-struct LLVMRustMCDCBranchParameters {
-  int16_t ConditionID;
-  int16_t ConditionIDs[2];
-};
-
-static coverage::mcdc::BranchParameters
-fromRust(LLVMRustMCDCBranchParameters Params) {
-  return coverage::mcdc::BranchParameters(
-      Params.ConditionID, {Params.ConditionIDs[0], Params.ConditionIDs[1]});
-}
-
-static coverage::mcdc::DecisionParameters
-fromRust(LLVMRustMCDCDecisionParameters Params) {
-  return coverage::mcdc::DecisionParameters(Params.BitmapIdx,
-                                            Params.NumConditions);
-}
-
 // Must match the layout of
 // `rustc_codegen_llvm::coverageinfo::ffi::CoverageSpan`.
 struct LLVMRustCoverageSpan {
@@ -90,22 +68,6 @@ struct LLVMRustCoverageBranchRegion {
   LLVMRustCounter FalseCount;
 };
 
-// Must match the layout of
-// `rustc_codegen_llvm::coverageinfo::ffi::MCDCBranchRegion`.
-struct LLVMRustCoverageMCDCBranchRegion {
-  LLVMRustCoverageSpan Span;
-  LLVMRustCounter TrueCount;
-  LLVMRustCounter FalseCount;
-  LLVMRustMCDCBranchParameters MCDCBranchParams;
-};
-
-// Must match the layout of
-// `rustc_codegen_llvm::coverageinfo::ffi::MCDCDecisionRegion`.
-struct LLVMRustCoverageMCDCDecisionRegion {
-  LLVMRustCoverageSpan Span;
-  LLVMRustMCDCDecisionParameters MCDCDecisionParams;
-};
-
 // FFI equivalent of enum `llvm::coverage::CounterExpression::ExprKind`
 // https://github.com/rust-lang/llvm-project/blob/ea6fa9c2/llvm/include/llvm/ProfileData/Coverage/CoverageMapping.h#L154
 enum class LLVMRustCounterExprKind {
@@ -159,10 +121,7 @@ extern "C" void LLVMRustCoverageWriteFunctionMappingsToBuffer(
     const LLVMRustCoverageExpansionRegion *ExpansionRegions,
     size_t NumExpansionRegions,
     const LLVMRustCoverageBranchRegion *BranchRegions, size_t NumBranchRegions,
-    const LLVMRustCoverageMCDCBranchRegion *MCDCBranchRegions,
-    size_t NumMCDCBranchRegions,
-    const LLVMRustCoverageMCDCDecisionRegion *MCDCDecisionRegions,
-    size_t NumMCDCDecisionRegions, RustStringRef BufferOut) {
+    RustStringRef BufferOut) {
   // Convert from FFI representation to LLVM representation.
 
   // Expressions:
@@ -176,8 +135,8 @@ extern "C" void LLVMRustCoverageWriteFunctionMappingsToBuffer(
   }
 
   std::vector<coverage::CounterMappingRegion> MappingRegions;
-  MappingRegions.reserve(NumCodeRegions + NumBranchRegions +
-                         NumMCDCBranchRegions + NumMCDCDecisionRegions);
+  MappingRegions.reserve(NumCodeRegions + NumExpansionRegions +
+                         NumBranchRegions);
 
   // Code regions:
   for (const auto &Region : ArrayRef(CodeRegions, NumCodeRegions)) {
@@ -201,24 +160,6 @@ extern "C" void LLVMRustCoverageWriteFunctionMappingsToBuffer(
         Region.Span.LineEnd, Region.Span.ColumnEnd));
   }
 
-  // MC/DC branch regions:
-  for (const auto &Region : ArrayRef(MCDCBranchRegions, NumMCDCBranchRegions)) {
-    MappingRegions.push_back(coverage::CounterMappingRegion::makeBranchRegion(
-        fromRust(Region.TrueCount), fromRust(Region.FalseCount),
-        Region.Span.FileID, Region.Span.LineStart, Region.Span.ColumnStart,
-        Region.Span.LineEnd, Region.Span.ColumnEnd,
-        fromRust(Region.MCDCBranchParams)));
-  }
-
-  // MC/DC decision regions:
-  for (const auto &Region :
-       ArrayRef(MCDCDecisionRegions, NumMCDCDecisionRegions)) {
-    MappingRegions.push_back(coverage::CounterMappingRegion::makeDecisionRegion(
-        fromRust(Region.MCDCDecisionParams), Region.Span.FileID,
-        Region.Span.LineStart, Region.Span.ColumnStart, Region.Span.LineEnd,
-        Region.Span.ColumnEnd));
-  }
-
   // Write the converted expressions and mappings to a byte buffer.
   auto CoverageMappingWriter = coverage::CoverageMappingWriter(
       ArrayRef<unsigned>(VirtualFileMappingIDs, NumVirtualFileMappingIDs),
diff --git a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
index 588d867bbbf..cd4f80f808c 100644
--- a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
@@ -277,6 +277,7 @@ enum class LLVMRustAttributeKind {
   FnRetThunkExtern = 41,
   Writable = 42,
   DeadOnUnwind = 43,
+  DeadOnReturn = 44,
 };
 
 static Attribute::AttrKind fromRust(LLVMRustAttributeKind Kind) {
@@ -369,6 +370,12 @@ static Attribute::AttrKind fromRust(LLVMRustAttributeKind Kind) {
     return Attribute::Writable;
   case LLVMRustAttributeKind::DeadOnUnwind:
     return Attribute::DeadOnUnwind;
+  case LLVMRustAttributeKind::DeadOnReturn:
+#if LLVM_VERSION_GE(21, 0)
+    return Attribute::DeadOnReturn;
+#else
+    report_fatal_error("DeadOnReturn attribute requires LLVM 21 or later");
+#endif
   }
   report_fatal_error("bad LLVMRustAttributeKind");
 }
diff --git a/compiler/rustc_macros/src/diagnostics/utils.rs b/compiler/rustc_macros/src/diagnostics/utils.rs
index 060799e981d..c310b99d535 100644
--- a/compiler/rustc_macros/src/diagnostics/utils.rs
+++ b/compiler/rustc_macros/src/diagnostics/utils.rs
@@ -146,7 +146,7 @@ impl<'ty> FieldInnerTy<'ty> {
             };
 
             let path = &ty_path.path;
-            let ty = path.segments.iter().last().unwrap();
+            let ty = path.segments.last().unwrap();
             let syn::PathArguments::AngleBracketed(bracketed) = &ty.arguments else {
                 panic!("expected bracketed generic arguments");
             };
diff --git a/compiler/rustc_metadata/src/native_libs.rs b/compiler/rustc_metadata/src/native_libs.rs
index 8855766ca98..958e314efab 100644
--- a/compiler/rustc_metadata/src/native_libs.rs
+++ b/compiler/rustc_metadata/src/native_libs.rs
@@ -83,7 +83,7 @@ pub fn walk_native_lib_search_dirs<R>(
     // Mac Catalyst uses the macOS SDK, but to link to iOS-specific frameworks
     // we must have the support library stubs in the library search path (#121430).
     if let Some(sdk_root) = apple_sdk_root
-        && sess.target.llvm_target.contains("macabi")
+        && sess.target.env == "macabi"
     {
         f(&sdk_root.join("System/iOSSupport/usr/lib"), false)?;
         f(&sdk_root.join("System/iOSSupport/System/Library/Frameworks"), true)?;
diff --git a/compiler/rustc_metadata/src/rmeta/decoder.rs b/compiler/rustc_metadata/src/rmeta/decoder.rs
index 00c97a2f738..548c56a97bc 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder.rs
@@ -1530,7 +1530,7 @@ impl<'a> CrateMetadataRef<'a> {
                 let macro_rules = self.root.tables.is_macro_rules.get(self, id);
                 let body =
                     self.root.tables.macro_definition.get(self, id).unwrap().decode((self, sess));
-                ast::MacroDef { macro_rules, body: ast::ptr::P(body) }
+                ast::MacroDef { macro_rules, body: Box::new(body) }
             }
             _ => bug!(),
         }
diff --git a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
index 0f3896fd9be..11fef3be5d0 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
@@ -75,24 +75,6 @@ impl<'a, 'tcx, T: Copy + Decodable<DecodeContext<'a, 'tcx>>> ProcessQueryValue<'
 }
 
 impl<'a, 'tcx, T: Copy + Decodable<DecodeContext<'a, 'tcx>>>
-    ProcessQueryValue<'tcx, ty::EarlyBinder<'tcx, &'tcx [T]>>
-    for Option<DecodeIterator<'a, 'tcx, T>>
-{
-    #[inline(always)]
-    fn process_decoded(
-        self,
-        tcx: TyCtxt<'tcx>,
-        err: impl Fn() -> !,
-    ) -> ty::EarlyBinder<'tcx, &'tcx [T]> {
-        ty::EarlyBinder::bind(if let Some(iter) = self {
-            tcx.arena.alloc_from_iter(iter)
-        } else {
-            err()
-        })
-    }
-}
-
-impl<'a, 'tcx, T: Copy + Decodable<DecodeContext<'a, 'tcx>>>
     ProcessQueryValue<'tcx, Option<&'tcx [T]>> for Option<DecodeIterator<'a, 'tcx, T>>
 {
     #[inline(always)]
@@ -413,6 +395,7 @@ provide! { tcx, def_id, other, cdata,
 
     crate_extern_paths => { cdata.source().paths().cloned().collect() }
     expn_that_defined => { cdata.get_expn_that_defined(def_id.index, tcx.sess) }
+    default_field => { cdata.get_default_field(def_id.index) }
     is_doc_hidden => { cdata.get_attr_flags(def_id.index).contains(AttrFlags::IS_DOC_HIDDEN) }
     doc_link_resolutions => { tcx.arena.alloc(cdata.get_doc_link_resolutions(def_id.index)) }
     doc_link_traits_in_scope => {
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index ff9f77be945..a7e7e9985f4 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -19,13 +19,12 @@ use rustc_hir::find_attr;
 use rustc_hir_pretty::id_to_string;
 use rustc_middle::dep_graph::WorkProductId;
 use rustc_middle::middle::dependency_format::Linkage;
-use rustc_middle::middle::exported_symbols::metadata_symbol_name;
 use rustc_middle::mir::interpret;
 use rustc_middle::query::Providers;
 use rustc_middle::traits::specialization_graph;
+use rustc_middle::ty::AssocItemContainer;
 use rustc_middle::ty::codec::TyEncoder;
 use rustc_middle::ty::fast_reject::{self, TreatParams};
-use rustc_middle::ty::{AssocItemContainer, SymbolName};
 use rustc_middle::{bug, span_bug};
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder, opaque};
 use rustc_session::config::{CrateType, OptLevel, TargetModifier};
@@ -1982,7 +1981,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                 def_key.disambiguated_data.data = DefPathData::MacroNs(name);
 
                 let def_id = id.to_def_id();
-                self.tables.def_kind.set_some(def_id.index, DefKind::Macro(macro_kind));
+                self.tables.def_kind.set_some(def_id.index, DefKind::Macro(macro_kind.into()));
                 self.tables.proc_macro.set_some(def_id.index, macro_kind);
                 self.encode_attrs(id);
                 record!(self.tables.def_keys[def_id] <- def_key);
@@ -2207,19 +2206,8 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         exported_symbols: &[(ExportedSymbol<'tcx>, SymbolExportInfo)],
     ) -> LazyArray<(ExportedSymbol<'static>, SymbolExportInfo)> {
         empty_proc_macro!(self);
-        // The metadata symbol name is special. It should not show up in
-        // downstream crates.
-        let metadata_symbol_name = SymbolName::new(self.tcx, &metadata_symbol_name(self.tcx));
 
-        self.lazy_array(
-            exported_symbols
-                .iter()
-                .filter(|&(exported_symbol, _)| match *exported_symbol {
-                    ExportedSymbol::NoDefId(symbol_name) => symbol_name != metadata_symbol_name,
-                    _ => true,
-                })
-                .cloned(),
-        )
+        self.lazy_array(exported_symbols.iter().cloned())
     }
 
     fn encode_dylib_dependency_formats(&mut self) -> LazyArray<Option<LinkagePreference>> {
diff --git a/compiler/rustc_metadata/src/rmeta/mod.rs b/compiler/rustc_metadata/src/rmeta/mod.rs
index 99174e4ad2f..1f7d142d330 100644
--- a/compiler/rustc_metadata/src/rmeta/mod.rs
+++ b/compiler/rustc_metadata/src/rmeta/mod.rs
@@ -11,7 +11,7 @@ use rustc_abi::{FieldIdx, ReprOptions, VariantIdx};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::svh::Svh;
 use rustc_hir::attrs::StrippedCfgItem;
-use rustc_hir::def::{CtorKind, DefKind, DocLinkResMap};
+use rustc_hir::def::{CtorKind, DefKind, DocLinkResMap, MacroKinds};
 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, DefIndex, DefPathHash, StableCrateId};
 use rustc_hir::definitions::DefKey;
 use rustc_hir::lang_items::LangItem;
diff --git a/compiler/rustc_metadata/src/rmeta/parameterized.rs b/compiler/rustc_metadata/src/rmeta/parameterized.rs
index d632e65104a..34180001f80 100644
--- a/compiler/rustc_metadata/src/rmeta/parameterized.rs
+++ b/compiler/rustc_metadata/src/rmeta/parameterized.rs
@@ -6,7 +6,7 @@ use rustc_index::{Idx, IndexVec};
 use rustc_middle::ty::{Binder, EarlyBinder};
 use rustc_span::Symbol;
 
-use crate::rmeta::{LazyArray, LazyTable, LazyValue};
+use crate::rmeta::{LazyArray, LazyValue};
 
 pub(crate) trait ParameterizedOverTcx: 'static {
     type Value<'tcx>;
@@ -48,10 +48,6 @@ impl<T: ParameterizedOverTcx> ParameterizedOverTcx for LazyArray<T> {
     type Value<'tcx> = LazyArray<T::Value<'tcx>>;
 }
 
-impl<I: 'static, T: ParameterizedOverTcx> ParameterizedOverTcx for LazyTable<I, T> {
-    type Value<'tcx> = LazyTable<I, T::Value<'tcx>>;
-}
-
 macro_rules! trivially_parameterized_over_tcx {
     ($($ty:ty),+ $(,)?) => {
         $(
@@ -154,7 +150,6 @@ parameterized_over_tcx! {
     rustc_middle::mir::CoroutineLayout,
     rustc_middle::mir::interpret::ConstAllocation,
     rustc_middle::ty::Clause,
-    rustc_middle::ty::ClauseKind,
     rustc_middle::ty::Const,
     rustc_middle::ty::ConstConditions,
     rustc_middle::ty::FnSig,
diff --git a/compiler/rustc_metadata/src/rmeta/table.rs b/compiler/rustc_metadata/src/rmeta/table.rs
index 28f406fbc96..2cb07a28a8a 100644
--- a/compiler/rustc_metadata/src/rmeta/table.rs
+++ b/compiler/rustc_metadata/src/rmeta/table.rs
@@ -66,22 +66,6 @@ pub(super) trait FixedSizeEncoding: IsDefault {
     fn write_to_bytes(self, b: &mut Self::ByteArray);
 }
 
-/// This implementation is not used generically, but for reading/writing
-/// concrete `u32` fields in `Lazy*` structures, which may be zero.
-impl FixedSizeEncoding for u32 {
-    type ByteArray = [u8; 4];
-
-    #[inline]
-    fn from_bytes(b: &[u8; 4]) -> Self {
-        Self::from_le_bytes(*b)
-    }
-
-    #[inline]
-    fn write_to_bytes(self, b: &mut [u8; 4]) {
-        *b = self.to_le_bytes();
-    }
-}
-
 impl FixedSizeEncoding for u64 {
     type ByteArray = [u8; 8];
 
@@ -97,7 +81,7 @@ impl FixedSizeEncoding for u64 {
 }
 
 macro_rules! fixed_size_enum {
-    ($ty:ty { $(($($pat:tt)*))* }) => {
+    ($ty:ty { $(($($pat:tt)*))* } $( unreachable { $(($($upat:tt)*))+ } )?) => {
         impl FixedSizeEncoding for Option<$ty> {
             type ByteArray = [u8;1];
 
@@ -119,12 +103,24 @@ macro_rules! fixed_size_enum {
                 b[0] = match self {
                     None => unreachable!(),
                     $(Some($($pat)*) => 1 + ${index()},)*
+                    $(Some($($($upat)*)|+) => unreachable!(),)?
                 }
             }
         }
     }
 }
 
+// Workaround; need const traits to construct bitflags in a const
+macro_rules! const_macro_kinds {
+    ($($name:ident),+$(,)?) => (MacroKinds::from_bits_truncate($(MacroKinds::$name.bits())|+))
+}
+const MACRO_KINDS_ATTR_BANG: MacroKinds = const_macro_kinds!(ATTR, BANG);
+const MACRO_KINDS_DERIVE_BANG: MacroKinds = const_macro_kinds!(DERIVE, BANG);
+const MACRO_KINDS_DERIVE_ATTR: MacroKinds = const_macro_kinds!(DERIVE, ATTR);
+const MACRO_KINDS_DERIVE_ATTR_BANG: MacroKinds = const_macro_kinds!(DERIVE, ATTR, BANG);
+// Ensure that we get a compilation error if MacroKinds gets extended without updating metadata.
+const _: () = assert!(MACRO_KINDS_DERIVE_ATTR_BANG.is_all());
+
 fixed_size_enum! {
     DefKind {
         ( Mod                                      )
@@ -167,18 +163,16 @@ fixed_size_enum! {
         ( Ctor(CtorOf::Struct, CtorKind::Const)    )
         ( Ctor(CtorOf::Variant, CtorKind::Fn)      )
         ( Ctor(CtorOf::Variant, CtorKind::Const)   )
-        ( Macro(MacroKind::Bang)                   )
-        ( Macro(MacroKind::Attr)                   )
-        ( Macro(MacroKind::Derive)                 )
+        ( Macro(MacroKinds::BANG)                  )
+        ( Macro(MacroKinds::ATTR)                  )
+        ( Macro(MacroKinds::DERIVE)                )
+        ( Macro(MACRO_KINDS_ATTR_BANG)             )
+        ( Macro(MACRO_KINDS_DERIVE_ATTR)           )
+        ( Macro(MACRO_KINDS_DERIVE_BANG)           )
+        ( Macro(MACRO_KINDS_DERIVE_ATTR_BANG)      )
         ( SyntheticCoroutineBody                   )
-    }
-}
-
-fixed_size_enum! {
-    ty::ImplPolarity {
-        ( Positive    )
-        ( Negative    )
-        ( Reservation )
+    } unreachable {
+        ( Macro(_)                                 )
     }
 }
 
@@ -306,45 +300,6 @@ impl FixedSizeEncoding for bool {
     }
 }
 
-impl FixedSizeEncoding for Option<bool> {
-    type ByteArray = [u8; 1];
-
-    #[inline]
-    fn from_bytes(b: &[u8; 1]) -> Self {
-        match b[0] {
-            0 => Some(false),
-            1 => Some(true),
-            2 => None,
-            _ => unreachable!(),
-        }
-    }
-
-    #[inline]
-    fn write_to_bytes(self, b: &mut [u8; 1]) {
-        debug_assert!(!self.is_default());
-        b[0] = match self {
-            Some(false) => 0,
-            Some(true) => 1,
-            None => 2,
-        };
-    }
-}
-
-impl FixedSizeEncoding for UnusedGenericParams {
-    type ByteArray = [u8; 4];
-
-    #[inline]
-    fn from_bytes(b: &[u8; 4]) -> Self {
-        let x: u32 = u32::from_bytes(b);
-        UnusedGenericParams::from_bits(x)
-    }
-
-    #[inline]
-    fn write_to_bytes(self, b: &mut [u8; 4]) {
-        self.bits().write_to_bytes(b);
-    }
-}
-
 // NOTE(eddyb) there could be an impl for `usize`, which would enable a more
 // generic `LazyValue<T>` impl, but in the general case we might not need / want
 // to fit every `usize` in `u32`.
diff --git a/compiler/rustc_middle/messages.ftl b/compiler/rustc_middle/messages.ftl
index 69aa4383f13..69adb2fe391 100644
--- a/compiler/rustc_middle/messages.ftl
+++ b/compiler/rustc_middle/messages.ftl
@@ -122,8 +122,6 @@ middle_strict_coherence_needs_negative_coherence =
     to use `strict_coherence` on this trait, the `with_negative_coherence` feature must be enabled
     .label = due to this attribute
 
-middle_type_length_limit = reached the type-length limit while instantiating `{$shrunk}`
+middle_type_length_limit = reached the type-length limit while instantiating `{$instance}`
 
 middle_unsupported_union = we don't support unions yet: '{$ty_name}'
-
-middle_written_to_path = the full type name has been written to '{$path}'
diff --git a/compiler/rustc_middle/src/error.rs b/compiler/rustc_middle/src/error.rs
index f36ae831653..7520bc262c6 100644
--- a/compiler/rustc_middle/src/error.rs
+++ b/compiler/rustc_middle/src/error.rs
@@ -1,4 +1,4 @@
-use std::path::{Path, PathBuf};
+use std::path::Path;
 use std::{fmt, io};
 
 use rustc_errors::codes::*;
@@ -6,7 +6,7 @@ use rustc_errors::{DiagArgName, DiagArgValue, DiagMessage};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::{Span, Symbol};
 
-use crate::ty::Ty;
+use crate::ty::{Instance, Ty};
 
 #[derive(Diagnostic)]
 #[diag(middle_drop_check_overflow, code = E0320)]
@@ -161,13 +161,10 @@ pub(crate) struct ErroneousConstant {
 #[derive(Diagnostic)]
 #[diag(middle_type_length_limit)]
 #[help(middle_consider_type_length_limit)]
-pub(crate) struct TypeLengthLimit {
+pub(crate) struct TypeLengthLimit<'tcx> {
     #[primary_span]
     pub span: Span,
-    pub shrunk: String,
-    #[note(middle_written_to_path)]
-    pub was_written: bool,
-    pub path: PathBuf,
+    pub instance: Instance<'tcx>,
     pub type_length: usize,
 }
 
diff --git a/compiler/rustc_middle/src/middle/codegen_fn_attrs.rs b/compiler/rustc_middle/src/middle/codegen_fn_attrs.rs
index 94384e64afd..7d2fc0995aa 100644
--- a/compiler/rustc_middle/src/middle/codegen_fn_attrs.rs
+++ b/compiler/rustc_middle/src/middle/codegen_fn_attrs.rs
@@ -1,13 +1,12 @@
 use std::borrow::Cow;
 
 use rustc_abi::Align;
-use rustc_ast::expand::autodiff_attrs::AutoDiffAttrs;
-use rustc_hir::attrs::{InlineAttr, InstructionSetAttr, OptimizeAttr};
+use rustc_hir::attrs::{InlineAttr, InstructionSetAttr, Linkage, OptimizeAttr};
+use rustc_hir::def_id::DefId;
 use rustc_macros::{HashStable, TyDecodable, TyEncodable};
 use rustc_span::Symbol;
 use rustc_target::spec::SanitizerSet;
 
-use crate::mir::mono::Linkage;
 use crate::ty::{InstanceKind, TyCtxt};
 
 impl<'tcx> TyCtxt<'tcx> {
@@ -75,8 +74,6 @@ pub struct CodegenFnAttrs {
     /// The `#[patchable_function_entry(...)]` attribute. Indicates how many nops should be around
     /// the function entry.
     pub patchable_function_entry: Option<PatchableFunctionEntry>,
-    /// For the `#[autodiff]` macros.
-    pub autodiff_item: Option<AutoDiffAttrs>,
 }
 
 #[derive(Copy, Clone, Debug, TyEncodable, TyDecodable, HashStable)]
@@ -182,7 +179,6 @@ impl CodegenFnAttrs {
             instruction_set: None,
             alignment: None,
             patchable_function_entry: None,
-            autodiff_item: None,
         }
     }
 
@@ -193,7 +189,11 @@ impl CodegenFnAttrs {
     /// * `#[linkage]` is present
     ///
     /// Keep this in sync with the logic for the unused_attributes for `#[inline]` lint.
-    pub fn contains_extern_indicator(&self) -> bool {
+    pub fn contains_extern_indicator(&self, tcx: TyCtxt<'_>, did: DefId) -> bool {
+        if tcx.is_foreign_item(did) {
+            return false;
+        }
+
         self.flags.contains(CodegenFnAttrFlags::NO_MANGLE)
             || self.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
             || self.export_name.is_some()
diff --git a/compiler/rustc_middle/src/middle/privacy.rs b/compiler/rustc_middle/src/middle/privacy.rs
index 785ddd1ee29..e3e04c9d180 100644
--- a/compiler/rustc_middle/src/middle/privacy.rs
+++ b/compiler/rustc_middle/src/middle/privacy.rs
@@ -181,11 +181,7 @@ impl EffectiveVisibilities {
             // nominal visibility. For some items nominal visibility doesn't make sense so we
             // don't check this condition for them.
             let is_impl = matches!(tcx.def_kind(def_id), DefKind::Impl { .. });
-            let is_associated_item_in_trait_impl = tcx
-                .impl_of_assoc(def_id.to_def_id())
-                .and_then(|impl_id| tcx.trait_id_of_impl(impl_id))
-                .is_some();
-            if !is_impl && !is_associated_item_in_trait_impl {
+            if !is_impl && tcx.trait_impl_of_assoc(def_id.to_def_id()).is_none() {
                 let nominal_vis = tcx.visibility(def_id);
                 if !nominal_vis.is_at_least(ev.reachable, tcx) {
                     span_bug!(
diff --git a/compiler/rustc_middle/src/middle/region.rs b/compiler/rustc_middle/src/middle/region.rs
index 800c1af660a..857d041224f 100644
--- a/compiler/rustc_middle/src/middle/region.rs
+++ b/compiler/rustc_middle/src/middle/region.rs
@@ -96,6 +96,7 @@ impl fmt::Debug for Scope {
             ScopeData::Destruction => write!(fmt, "Destruction({:?})", self.local_id),
             ScopeData::IfThen => write!(fmt, "IfThen({:?})", self.local_id),
             ScopeData::IfThenRescope => write!(fmt, "IfThen[edition2024]({:?})", self.local_id),
+            ScopeData::MatchGuard => write!(fmt, "MatchGuard({:?})", self.local_id),
             ScopeData::Remainder(fsi) => write!(
                 fmt,
                 "Remainder {{ block: {:?}, first_statement_index: {}}}",
@@ -131,6 +132,11 @@ pub enum ScopeData {
     /// whose lifetimes do not cross beyond this scope.
     IfThenRescope,
 
+    /// Scope of the condition and body of a match arm with a guard
+    /// Used for variables introduced in an if-let guard,
+    /// whose lifetimes do not cross beyond this scope.
+    MatchGuard,
+
     /// Scope following a `let id = expr;` binding in a block.
     Remainder(FirstStatementIndex),
 }
diff --git a/compiler/rustc_middle/src/mir/consts.rs b/compiler/rustc_middle/src/mir/consts.rs
index 96131d47a17..164433aede2 100644
--- a/compiler/rustc_middle/src/mir/consts.rs
+++ b/compiler/rustc_middle/src/mir/consts.rs
@@ -448,6 +448,11 @@ impl<'tcx> Const<'tcx> {
         Self::Val(val, ty)
     }
 
+    #[inline]
+    pub fn from_ty_value(tcx: TyCtxt<'tcx>, val: ty::Value<'tcx>) -> Self {
+        Self::Ty(val.ty, ty::Const::new_value(tcx, val.valtree, val.ty))
+    }
+
     pub fn from_bits(
         tcx: TyCtxt<'tcx>,
         bits: u128,
diff --git a/compiler/rustc_middle/src/mir/coverage.rs b/compiler/rustc_middle/src/mir/coverage.rs
index e26575b552e..fd4c64b9a61 100644
--- a/compiler/rustc_middle/src/mir/coverage.rs
+++ b/compiler/rustc_middle/src/mir/coverage.rs
@@ -50,25 +50,6 @@ rustc_index::newtype_index! {
     pub struct ExpressionId {}
 }
 
-rustc_index::newtype_index! {
-    /// ID of a mcdc condition. Used by llvm to check mcdc coverage.
-    ///
-    /// Note for future: the max limit of 0xFFFF is probably too loose. Actually llvm does not
-    /// support decisions with too many conditions (7 and more at LLVM 18 while may be hundreds at 19)
-    /// and represents it with `int16_t`. This max value may be changed once we could
-    /// figure out an accurate limit.
-    #[derive(HashStable)]
-    #[encodable]
-    #[orderable]
-    #[max = 0xFFFF]
-    #[debug_format = "ConditionId({})"]
-    pub struct ConditionId {}
-}
-
-impl ConditionId {
-    pub const START: Self = Self::from_usize(0);
-}
-
 /// Enum that can hold a constant zero value, the ID of an physical coverage
 /// counter, or the ID of a coverage-counter expression.
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
@@ -109,16 +90,6 @@ pub enum CoverageKind {
     /// During codegen, this might be lowered to `llvm.instrprof.increment` or
     /// to a no-op, depending on the outcome of counter-creation.
     VirtualCounter { bcb: BasicCoverageBlock },
-
-    /// Marks the point in MIR control flow represented by a evaluated condition.
-    ///
-    /// This is eventually lowered to instruments updating mcdc temp variables.
-    CondBitmapUpdate { index: u32, decision_depth: u16 },
-
-    /// Marks the point in MIR control flow represented by a evaluated decision.
-    ///
-    /// This is eventually lowered to `llvm.instrprof.mcdc.tvbitmap.update` in LLVM IR.
-    TestVectorBitmapUpdate { bitmap_idx: u32, decision_depth: u16 },
 }
 
 impl Debug for CoverageKind {
@@ -128,12 +99,6 @@ impl Debug for CoverageKind {
             SpanMarker => write!(fmt, "SpanMarker"),
             BlockMarker { id } => write!(fmt, "BlockMarker({:?})", id.index()),
             VirtualCounter { bcb } => write!(fmt, "VirtualCounter({bcb:?})"),
-            CondBitmapUpdate { index, decision_depth } => {
-                write!(fmt, "CondBitmapUpdate(index={:?}, depth={:?})", index, decision_depth)
-            }
-            TestVectorBitmapUpdate { bitmap_idx, decision_depth } => {
-                write!(fmt, "TestVectorUpdate({:?}, depth={:?})", bitmap_idx, decision_depth)
-            }
         }
     }
 }
@@ -170,14 +135,6 @@ pub enum MappingKind {
     Code { bcb: BasicCoverageBlock },
     /// Associates a branch region with separate counters for true and false.
     Branch { true_bcb: BasicCoverageBlock, false_bcb: BasicCoverageBlock },
-    /// Associates a branch region with separate counters for true and false.
-    MCDCBranch {
-        true_bcb: BasicCoverageBlock,
-        false_bcb: BasicCoverageBlock,
-        mcdc_params: ConditionInfo,
-    },
-    /// Associates a decision region with a bitmap and number of conditions.
-    MCDCDecision(DecisionInfo),
 }
 
 #[derive(Clone, Debug)]
@@ -201,11 +158,6 @@ pub struct FunctionCoverageInfo {
     pub priority_list: Vec<BasicCoverageBlock>,
 
     pub mappings: Vec<Mapping>,
-
-    pub mcdc_bitmap_bits: usize,
-    /// The depth of the deepest decision is used to know how many
-    /// temp condbitmaps should be allocated for the function.
-    pub mcdc_num_condition_bitmaps: usize,
 }
 
 /// Coverage information for a function, recorded during MIR building and
@@ -222,10 +174,6 @@ pub struct CoverageInfoHi {
     /// data structures without having to scan the entire body first.
     pub num_block_markers: usize,
     pub branch_spans: Vec<BranchSpan>,
-    /// Branch spans generated by mcdc. Because of some limits mcdc builder give up generating
-    /// decisions including them so that they are handled as normal branch spans.
-    pub mcdc_degraded_branch_spans: Vec<MCDCBranchSpan>,
-    pub mcdc_spans: Vec<(MCDCDecisionSpan, Vec<MCDCBranchSpan>)>,
 }
 
 #[derive(Clone, Debug)]
@@ -236,39 +184,6 @@ pub struct BranchSpan {
     pub false_marker: BlockMarkerId,
 }
 
-#[derive(Copy, Clone, Debug)]
-#[derive(TyEncodable, TyDecodable, Hash, HashStable)]
-pub struct ConditionInfo {
-    pub condition_id: ConditionId,
-    pub true_next_id: Option<ConditionId>,
-    pub false_next_id: Option<ConditionId>,
-}
-
-#[derive(Clone, Debug)]
-#[derive(TyEncodable, TyDecodable, Hash, HashStable)]
-pub struct MCDCBranchSpan {
-    pub span: Span,
-    pub condition_info: ConditionInfo,
-    pub true_marker: BlockMarkerId,
-    pub false_marker: BlockMarkerId,
-}
-
-#[derive(Copy, Clone, Debug)]
-#[derive(TyEncodable, TyDecodable, Hash, HashStable)]
-pub struct DecisionInfo {
-    pub bitmap_idx: u32,
-    pub num_conditions: u16,
-}
-
-#[derive(Clone, Debug)]
-#[derive(TyEncodable, TyDecodable, Hash, HashStable)]
-pub struct MCDCDecisionSpan {
-    pub span: Span,
-    pub end_markers: Vec<BlockMarkerId>,
-    pub decision_depth: u16,
-    pub num_conditions: usize,
-}
-
 /// Contains information needed during codegen, obtained by inspecting the
 /// function's MIR after MIR optimizations.
 ///
diff --git a/compiler/rustc_middle/src/mir/interpret/allocation.rs b/compiler/rustc_middle/src/mir/interpret/allocation.rs
index 27ead514531..2ea92a39d48 100644
--- a/compiler/rustc_middle/src/mir/interpret/allocation.rs
+++ b/compiler/rustc_middle/src/mir/interpret/allocation.rs
@@ -306,8 +306,6 @@ pub enum AllocError {
     ScalarSizeMismatch(ScalarSizeMismatch),
     /// Encountered a pointer where we needed raw bytes.
     ReadPointerAsInt(Option<BadBytesAccess>),
-    /// Partially overwriting a pointer.
-    OverwritePartialPointer(Size),
     /// Partially copying a pointer.
     ReadPartialPointer(Size),
     /// Using uninitialized data where it is not allowed.
@@ -331,9 +329,6 @@ impl AllocError {
             ReadPointerAsInt(info) => InterpErrorKind::Unsupported(
                 UnsupportedOpInfo::ReadPointerAsInt(info.map(|b| (alloc_id, b))),
             ),
-            OverwritePartialPointer(offset) => InterpErrorKind::Unsupported(
-                UnsupportedOpInfo::OverwritePartialPointer(Pointer::new(alloc_id, offset)),
-            ),
             ReadPartialPointer(offset) => InterpErrorKind::Unsupported(
                 UnsupportedOpInfo::ReadPartialPointer(Pointer::new(alloc_id, offset)),
             ),
@@ -633,11 +628,11 @@ impl<Prov: Provenance, Extra, Bytes: AllocBytes> Allocation<Prov, Extra, Bytes>
         &mut self,
         cx: &impl HasDataLayout,
         range: AllocRange,
-    ) -> AllocResult<&mut [u8]> {
+    ) -> &mut [u8] {
         self.mark_init(range, true);
-        self.provenance.clear(range, cx)?;
+        self.provenance.clear(range, cx);
 
-        Ok(&mut self.bytes[range.start.bytes_usize()..range.end().bytes_usize()])
+        &mut self.bytes[range.start.bytes_usize()..range.end().bytes_usize()]
     }
 
     /// A raw pointer variant of `get_bytes_unchecked_for_overwrite` that avoids invalidating existing immutable aliases
@@ -646,15 +641,15 @@ impl<Prov: Provenance, Extra, Bytes: AllocBytes> Allocation<Prov, Extra, Bytes>
         &mut self,
         cx: &impl HasDataLayout,
         range: AllocRange,
-    ) -> AllocResult<*mut [u8]> {
+    ) -> *mut [u8] {
         self.mark_init(range, true);
-        self.provenance.clear(range, cx)?;
+        self.provenance.clear(range, cx);
 
         assert!(range.end().bytes_usize() <= self.bytes.len()); // need to do our own bounds-check
         // Crucially, we go via `AllocBytes::as_mut_ptr`, not `AllocBytes::deref_mut`.
         let begin_ptr = self.bytes.as_mut_ptr().wrapping_add(range.start.bytes_usize());
         let len = range.end().bytes_usize() - range.start.bytes_usize();
-        Ok(ptr::slice_from_raw_parts_mut(begin_ptr, len))
+        ptr::slice_from_raw_parts_mut(begin_ptr, len)
     }
 
     /// This gives direct mutable access to the entire buffer, just exposing their internal state
@@ -723,26 +718,45 @@ impl<Prov: Provenance, Extra, Bytes: AllocBytes> Allocation<Prov, Extra, Bytes>
                 let ptr = Pointer::new(prov, Size::from_bytes(bits));
                 return Ok(Scalar::from_pointer(ptr, cx));
             }
-
-            // If we can work on pointers byte-wise, join the byte-wise provenances.
-            if Prov::OFFSET_IS_ADDR {
-                let mut prov = self.provenance.get(range.start, cx);
+            // The other easy case is total absence of provenance.
+            if self.provenance.range_empty(range, cx) {
+                return Ok(Scalar::from_uint(bits, range.size));
+            }
+            // If we get here, we have to check per-byte provenance, and join them together.
+            let prov = 'prov: {
+                // Initialize with first fragment. Must have index 0.
+                let Some((mut joint_prov, 0)) = self.provenance.get_byte(range.start, cx) else {
+                    break 'prov None;
+                };
+                // Update with the remaining fragments.
                 for offset in Size::from_bytes(1)..range.size {
-                    let this_prov = self.provenance.get(range.start + offset, cx);
-                    prov = Prov::join(prov, this_prov);
+                    // Ensure there is provenance here and it has the right index.
+                    let Some((frag_prov, frag_idx)) =
+                        self.provenance.get_byte(range.start + offset, cx)
+                    else {
+                        break 'prov None;
+                    };
+                    // Wildcard provenance is allowed to come with any index (this is needed
+                    // for Miri's native-lib mode to work).
+                    if u64::from(frag_idx) != offset.bytes() && Some(frag_prov) != Prov::WILDCARD {
+                        break 'prov None;
+                    }
+                    // Merge this byte's provenance with the previous ones.
+                    joint_prov = match Prov::join(joint_prov, frag_prov) {
+                        Some(prov) => prov,
+                        None => break 'prov None,
+                    };
                 }
-                // Now use this provenance.
-                let ptr = Pointer::new(prov, Size::from_bytes(bits));
-                return Ok(Scalar::from_maybe_pointer(ptr, cx));
-            } else {
-                // Without OFFSET_IS_ADDR, the only remaining case we can handle is total absence of
-                // provenance.
-                if self.provenance.range_empty(range, cx) {
-                    return Ok(Scalar::from_uint(bits, range.size));
-                }
-                // Else we have mixed provenance, that doesn't work.
+                break 'prov Some(joint_prov);
+            };
+            if prov.is_none() && !Prov::OFFSET_IS_ADDR {
+                // There are some bytes with provenance here but overall the provenance does not add up.
+                // We need `OFFSET_IS_ADDR` to fall back to no-provenance here; without that option, we must error.
                 return Err(AllocError::ReadPartialPointer(range.start));
             }
+            // We can use this provenance.
+            let ptr = Pointer::new(prov, Size::from_bytes(bits));
+            return Ok(Scalar::from_maybe_pointer(ptr, cx));
         } else {
             // We are *not* reading a pointer.
             // If we can just ignore provenance or there is none, that's easy.
@@ -782,7 +796,7 @@ impl<Prov: Provenance, Extra, Bytes: AllocBytes> Allocation<Prov, Extra, Bytes>
 
         let endian = cx.data_layout().endian;
         // Yes we do overwrite all the bytes in `dst`.
-        let dst = self.get_bytes_unchecked_for_overwrite(cx, range)?;
+        let dst = self.get_bytes_unchecked_for_overwrite(cx, range);
         write_target_uint(endian, dst, bytes).unwrap();
 
         // See if we have to also store some provenance.
@@ -795,10 +809,9 @@ impl<Prov: Provenance, Extra, Bytes: AllocBytes> Allocation<Prov, Extra, Bytes>
     }
 
     /// Write "uninit" to the given memory range.
-    pub fn write_uninit(&mut self, cx: &impl HasDataLayout, range: AllocRange) -> AllocResult {
+    pub fn write_uninit(&mut self, cx: &impl HasDataLayout, range: AllocRange) {
         self.mark_init(range, false);
-        self.provenance.clear(range, cx)?;
-        Ok(())
+        self.provenance.clear(range, cx);
     }
 
     /// Mark all bytes in the given range as initialised and reset the provenance
@@ -817,9 +830,12 @@ impl<Prov: Provenance, Extra, Bytes: AllocBytes> Allocation<Prov, Extra, Bytes>
     }
 
     /// Remove all provenance in the given memory range.
-    pub fn clear_provenance(&mut self, cx: &impl HasDataLayout, range: AllocRange) -> AllocResult {
-        self.provenance.clear(range, cx)?;
-        return Ok(());
+    pub fn clear_provenance(&mut self, cx: &impl HasDataLayout, range: AllocRange) {
+        self.provenance.clear(range, cx);
+    }
+
+    pub fn provenance_merge_bytes(&mut self, cx: &impl HasDataLayout) -> bool {
+        self.provenance.merge_bytes(cx)
     }
 
     /// Applies a previously prepared provenance copy.
diff --git a/compiler/rustc_middle/src/mir/interpret/allocation/provenance_map.rs b/compiler/rustc_middle/src/mir/interpret/allocation/provenance_map.rs
index 119d4be64e6..ea8596ea286 100644
--- a/compiler/rustc_middle/src/mir/interpret/allocation/provenance_map.rs
+++ b/compiler/rustc_middle/src/mir/interpret/allocation/provenance_map.rs
@@ -10,7 +10,7 @@ use rustc_macros::HashStable;
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use tracing::trace;
 
-use super::{AllocError, AllocRange, AllocResult, CtfeProvenance, Provenance, alloc_range};
+use super::{AllocRange, CtfeProvenance, Provenance, alloc_range};
 
 /// Stores the provenance information of pointers stored in memory.
 #[derive(Clone, PartialEq, Eq, Hash, Debug)]
@@ -19,25 +19,25 @@ pub struct ProvenanceMap<Prov = CtfeProvenance> {
     /// `Provenance` in this map applies from the given offset for an entire pointer-size worth of
     /// bytes. Two entries in this map are always at least a pointer size apart.
     ptrs: SortedMap<Size, Prov>,
-    /// Provenance in this map only applies to the given single byte.
-    /// This map is disjoint from the previous. It will always be empty when
-    /// `Prov::OFFSET_IS_ADDR` is false.
-    bytes: Option<Box<SortedMap<Size, Prov>>>,
+    /// This stores byte-sized provenance fragments.
+    /// The `u8` indicates the position of this byte inside its original pointer.
+    /// If the bytes are re-assembled in their original order, the pointer can be used again.
+    /// Wildcard provenance is allowed to have index 0 everywhere.
+    bytes: Option<Box<SortedMap<Size, (Prov, u8)>>>,
 }
 
 // These impls are generic over `Prov` since `CtfeProvenance` is only decodable/encodable
 // for some particular `D`/`S`.
 impl<D: Decoder, Prov: Provenance + Decodable<D>> Decodable<D> for ProvenanceMap<Prov> {
     fn decode(d: &mut D) -> Self {
-        assert!(!Prov::OFFSET_IS_ADDR); // only `CtfeProvenance` is ever serialized
+        // `bytes` is not in the serialized format
         Self { ptrs: Decodable::decode(d), bytes: None }
     }
 }
 impl<S: Encoder, Prov: Provenance + Encodable<S>> Encodable<S> for ProvenanceMap<Prov> {
     fn encode(&self, s: &mut S) {
         let Self { ptrs, bytes } = self;
-        assert!(!Prov::OFFSET_IS_ADDR); // only `CtfeProvenance` is ever serialized
-        debug_assert!(bytes.is_none()); // without `OFFSET_IS_ADDR`, this is always empty
+        assert!(bytes.is_none()); // interning refuses allocations with pointer fragments
         ptrs.encode(s)
     }
 }
@@ -58,10 +58,10 @@ impl ProvenanceMap {
     /// Give access to the ptr-sized provenances (which can also be thought of as relocations, and
     /// indeed that is how codegen treats them).
     ///
-    /// Only exposed with `CtfeProvenance` provenance, since it panics if there is bytewise provenance.
+    /// Only use on interned allocations, as other allocations may have per-byte provenance!
     #[inline]
     pub fn ptrs(&self) -> &SortedMap<Size, CtfeProvenance> {
-        debug_assert!(self.bytes.is_none()); // `CtfeProvenance::OFFSET_IS_ADDR` is false so this cannot fail
+        assert!(self.bytes.is_none(), "`ptrs()` called on non-interned allocation");
         &self.ptrs
     }
 }
@@ -88,12 +88,12 @@ impl<Prov: Provenance> ProvenanceMap<Prov> {
     }
 
     /// `pm.range_ptrs_is_empty(r, cx)` == `pm.range_ptrs_get(r, cx).is_empty()`, but is faster.
-    pub(super) fn range_ptrs_is_empty(&self, range: AllocRange, cx: &impl HasDataLayout) -> bool {
+    fn range_ptrs_is_empty(&self, range: AllocRange, cx: &impl HasDataLayout) -> bool {
         self.ptrs.range_is_empty(Self::adjusted_range_ptrs(range, cx))
     }
 
     /// Returns all byte-wise provenance in the given range.
-    fn range_bytes_get(&self, range: AllocRange) -> &[(Size, Prov)] {
+    fn range_bytes_get(&self, range: AllocRange) -> &[(Size, (Prov, u8))] {
         if let Some(bytes) = self.bytes.as_ref() {
             bytes.range(range.start..range.end())
         } else {
@@ -107,19 +107,47 @@ impl<Prov: Provenance> ProvenanceMap<Prov> {
     }
 
     /// Get the provenance of a single byte.
-    pub fn get(&self, offset: Size, cx: &impl HasDataLayout) -> Option<Prov> {
+    pub fn get_byte(&self, offset: Size, cx: &impl HasDataLayout) -> Option<(Prov, u8)> {
         let prov = self.range_ptrs_get(alloc_range(offset, Size::from_bytes(1)), cx);
         debug_assert!(prov.len() <= 1);
         if let Some(entry) = prov.first() {
             // If it overlaps with this byte, it is on this byte.
             debug_assert!(self.bytes.as_ref().is_none_or(|b| !b.contains_key(&offset)));
-            Some(entry.1)
+            Some((entry.1, (offset - entry.0).bytes() as u8))
         } else {
             // Look up per-byte provenance.
             self.bytes.as_ref().and_then(|b| b.get(&offset).copied())
         }
     }
 
+    /// Attempt to merge per-byte provenance back into ptr chunks, if the right fragments
+    /// sit next to each other. Return `false` is that is not possible due to partial pointers.
+    pub fn merge_bytes(&mut self, cx: &impl HasDataLayout) -> bool {
+        let Some(bytes) = self.bytes.as_deref_mut() else {
+            return true;
+        };
+        let ptr_size = cx.data_layout().pointer_size();
+        while let Some((offset, (prov, _))) = bytes.iter().next().copied() {
+            // Check if this fragment starts a pointer.
+            let range = offset..offset + ptr_size;
+            let frags = bytes.range(range.clone());
+            if frags.len() != ptr_size.bytes_usize() {
+                return false;
+            }
+            for (idx, (_offset, (frag_prov, frag_idx))) in frags.iter().copied().enumerate() {
+                if frag_prov != prov || frag_idx != idx as u8 {
+                    return false;
+                }
+            }
+            // Looks like a pointer! Move it over to the ptr provenance map.
+            bytes.remove_range(range);
+            self.ptrs.insert(offset, prov);
+        }
+        // We managed to convert everything into whole pointers.
+        self.bytes = None;
+        true
+    }
+
     /// Check if there is ptr-sized provenance at the given index.
     /// Does not mean anything for bytewise provenance! But can be useful as an optimization.
     pub fn get_ptr(&self, offset: Size) -> Option<Prov> {
@@ -137,7 +165,7 @@ impl<Prov: Provenance> ProvenanceMap<Prov> {
 
     /// Yields all the provenances stored in this map.
     pub fn provenances(&self) -> impl Iterator<Item = Prov> {
-        let bytes = self.bytes.iter().flat_map(|b| b.values());
+        let bytes = self.bytes.iter().flat_map(|b| b.values().map(|(p, _i)| p));
         self.ptrs.values().chain(bytes).copied()
     }
 
@@ -148,16 +176,12 @@ impl<Prov: Provenance> ProvenanceMap<Prov> {
 
     /// Removes all provenance inside the given range.
     /// If there is provenance overlapping with the edges, might result in an error.
-    pub fn clear(&mut self, range: AllocRange, cx: &impl HasDataLayout) -> AllocResult {
+    pub fn clear(&mut self, range: AllocRange, cx: &impl HasDataLayout) {
         let start = range.start;
         let end = range.end();
         // Clear the bytewise part -- this is easy.
-        if Prov::OFFSET_IS_ADDR {
-            if let Some(bytes) = self.bytes.as_mut() {
-                bytes.remove_range(start..end);
-            }
-        } else {
-            debug_assert!(self.bytes.is_none());
+        if let Some(bytes) = self.bytes.as_mut() {
+            bytes.remove_range(start..end);
         }
 
         let pointer_size = cx.data_layout().pointer_size();
@@ -168,7 +192,7 @@ impl<Prov: Provenance> ProvenanceMap<Prov> {
             // Find all provenance overlapping the given range.
             if self.range_ptrs_is_empty(range, cx) {
                 // No provenance in this range, we are done. This is the common case.
-                return Ok(());
+                return;
             }
 
             // This redoes some of the work of `range_get_ptrs_is_empty`, but this path is much
@@ -179,28 +203,20 @@ impl<Prov: Provenance> ProvenanceMap<Prov> {
 
         // We need to handle clearing the provenance from parts of a pointer.
         if first < start {
-            if !Prov::OFFSET_IS_ADDR {
-                // We can't split up the provenance into less than a pointer.
-                return Err(AllocError::OverwritePartialPointer(first));
-            }
             // Insert the remaining part in the bytewise provenance.
             let prov = self.ptrs[&first];
             let bytes = self.bytes.get_or_insert_with(Box::default);
             for offset in first..start {
-                bytes.insert(offset, prov);
+                bytes.insert(offset, (prov, (offset - first).bytes() as u8));
             }
         }
         if last > end {
             let begin_of_last = last - pointer_size;
-            if !Prov::OFFSET_IS_ADDR {
-                // We can't split up the provenance into less than a pointer.
-                return Err(AllocError::OverwritePartialPointer(begin_of_last));
-            }
             // Insert the remaining part in the bytewise provenance.
             let prov = self.ptrs[&begin_of_last];
             let bytes = self.bytes.get_or_insert_with(Box::default);
             for offset in end..last {
-                bytes.insert(offset, prov);
+                bytes.insert(offset, (prov, (offset - begin_of_last).bytes() as u8));
             }
         }
 
@@ -208,8 +224,6 @@ impl<Prov: Provenance> ProvenanceMap<Prov> {
         // Since provenance do not overlap, we know that removing until `last` (exclusive) is fine,
         // i.e., this will not remove any other provenance just after the ones we care about.
         self.ptrs.remove_range(first..last);
-
-        Ok(())
     }
 
     /// Overwrites all provenance in the given range with wildcard provenance.
@@ -218,10 +232,6 @@ impl<Prov: Provenance> ProvenanceMap<Prov> {
     ///
     /// Provided for usage in Miri and panics otherwise.
     pub fn write_wildcards(&mut self, cx: &impl HasDataLayout, range: AllocRange) {
-        assert!(
-            Prov::OFFSET_IS_ADDR,
-            "writing wildcard provenance is not supported when `OFFSET_IS_ADDR` is false"
-        );
         let wildcard = Prov::WILDCARD.unwrap();
 
         let bytes = self.bytes.get_or_insert_with(Box::default);
@@ -229,21 +239,22 @@ impl<Prov: Provenance> ProvenanceMap<Prov> {
         // Remove pointer provenances that overlap with the range, then readd the edge ones bytewise.
         let ptr_range = Self::adjusted_range_ptrs(range, cx);
         let ptrs = self.ptrs.range(ptr_range.clone());
-        if let Some((offset, prov)) = ptrs.first() {
-            for byte_ofs in *offset..range.start {
-                bytes.insert(byte_ofs, *prov);
+        if let Some((offset, prov)) = ptrs.first().copied() {
+            for byte_ofs in offset..range.start {
+                bytes.insert(byte_ofs, (prov, (byte_ofs - offset).bytes() as u8));
             }
         }
-        if let Some((offset, prov)) = ptrs.last() {
-            for byte_ofs in range.end()..*offset + cx.data_layout().pointer_size() {
-                bytes.insert(byte_ofs, *prov);
+        if let Some((offset, prov)) = ptrs.last().copied() {
+            for byte_ofs in range.end()..offset + cx.data_layout().pointer_size() {
+                bytes.insert(byte_ofs, (prov, (byte_ofs - offset).bytes() as u8));
             }
         }
         self.ptrs.remove_range(ptr_range);
 
         // Overwrite bytewise provenance.
         for offset in range.start..range.end() {
-            bytes.insert(offset, wildcard);
+            // The fragment index does not matter for wildcard provenance.
+            bytes.insert(offset, (wildcard, 0));
         }
     }
 }
@@ -253,7 +264,7 @@ impl<Prov: Provenance> ProvenanceMap<Prov> {
 /// Offsets are already adjusted to the destination allocation.
 pub struct ProvenanceCopy<Prov> {
     dest_ptrs: Option<Box<[(Size, Prov)]>>,
-    dest_bytes: Option<Box<[(Size, Prov)]>>,
+    dest_bytes: Option<Box<[(Size, (Prov, u8))]>>,
 }
 
 impl<Prov: Provenance> ProvenanceMap<Prov> {
@@ -263,7 +274,7 @@ impl<Prov: Provenance> ProvenanceMap<Prov> {
         dest: Size,
         count: u64,
         cx: &impl HasDataLayout,
-    ) -> AllocResult<ProvenanceCopy<Prov>> {
+    ) -> ProvenanceCopy<Prov> {
         let shift_offset = move |idx, offset| {
             // compute offset for current repetition
             let dest_offset = dest + src.size * idx; // `Size` operations
@@ -301,24 +312,16 @@ impl<Prov: Provenance> ProvenanceMap<Prov> {
         let mut dest_bytes_box = None;
         let begin_overlap = self.range_ptrs_get(alloc_range(src.start, Size::ZERO), cx).first();
         let end_overlap = self.range_ptrs_get(alloc_range(src.end(), Size::ZERO), cx).first();
-        if !Prov::OFFSET_IS_ADDR {
-            // There can't be any bytewise provenance, and we cannot split up the begin/end overlap.
-            if let Some(entry) = begin_overlap {
-                return Err(AllocError::ReadPartialPointer(entry.0));
-            }
-            if let Some(entry) = end_overlap {
-                return Err(AllocError::ReadPartialPointer(entry.0));
-            }
-            debug_assert!(self.bytes.is_none());
-        } else {
-            let mut bytes = Vec::new();
+        // We only need to go here if there is some overlap or some bytewise provenance.
+        if begin_overlap.is_some() || end_overlap.is_some() || self.bytes.is_some() {
+            let mut bytes: Vec<(Size, (Prov, u8))> = Vec::new();
             // First, if there is a part of a pointer at the start, add that.
             if let Some(entry) = begin_overlap {
                 trace!("start overlapping entry: {entry:?}");
                 // For really small copies, make sure we don't run off the end of the `src` range.
                 let entry_end = cmp::min(entry.0 + ptr_size, src.end());
                 for offset in src.start..entry_end {
-                    bytes.push((offset, entry.1));
+                    bytes.push((offset, (entry.1, (offset - entry.0).bytes() as u8)));
                 }
             } else {
                 trace!("no start overlapping entry");
@@ -334,8 +337,9 @@ impl<Prov: Provenance> ProvenanceMap<Prov> {
                 let entry_start = cmp::max(entry.0, src.start);
                 for offset in entry_start..src.end() {
                     if bytes.last().is_none_or(|bytes_entry| bytes_entry.0 < offset) {
-                        // The last entry, if it exists, has a lower offset than us.
-                        bytes.push((offset, entry.1));
+                        // The last entry, if it exists, has a lower offset than us, so we
+                        // can add it at the end and remain sorted.
+                        bytes.push((offset, (entry.1, (offset - entry.0).bytes() as u8)));
                     } else {
                         // There already is an entry for this offset in there! This can happen when the
                         // start and end range checks actually end up hitting the same pointer, so we
@@ -358,7 +362,7 @@ impl<Prov: Provenance> ProvenanceMap<Prov> {
             dest_bytes_box = Some(dest_bytes.into_boxed_slice());
         }
 
-        Ok(ProvenanceCopy { dest_ptrs: dest_ptrs_box, dest_bytes: dest_bytes_box })
+        ProvenanceCopy { dest_ptrs: dest_ptrs_box, dest_bytes: dest_bytes_box }
     }
 
     /// Applies a provenance copy.
@@ -368,14 +372,10 @@ impl<Prov: Provenance> ProvenanceMap<Prov> {
         if let Some(dest_ptrs) = copy.dest_ptrs {
             self.ptrs.insert_presorted(dest_ptrs.into());
         }
-        if Prov::OFFSET_IS_ADDR {
-            if let Some(dest_bytes) = copy.dest_bytes
-                && !dest_bytes.is_empty()
-            {
-                self.bytes.get_or_insert_with(Box::default).insert_presorted(dest_bytes.into());
-            }
-        } else {
-            debug_assert!(copy.dest_bytes.is_none());
+        if let Some(dest_bytes) = copy.dest_bytes
+            && !dest_bytes.is_empty()
+        {
+            self.bytes.get_or_insert_with(Box::default).insert_presorted(dest_bytes.into());
         }
     }
 }
diff --git a/compiler/rustc_middle/src/mir/interpret/error.rs b/compiler/rustc_middle/src/mir/interpret/error.rs
index 77427a12d11..7c72a8ec243 100644
--- a/compiler/rustc_middle/src/mir/interpret/error.rs
+++ b/compiler/rustc_middle/src/mir/interpret/error.rs
@@ -582,9 +582,6 @@ pub enum UnsupportedOpInfo {
     //
     // The variants below are only reachable from CTFE/const prop, miri will never emit them.
     //
-    /// Overwriting parts of a pointer; without knowing absolute addresses, the resulting state
-    /// cannot be represented by the CTFE interpreter.
-    OverwritePartialPointer(Pointer<AllocId>),
     /// Attempting to read or copy parts of a pointer to somewhere else; without knowing absolute
     /// addresses, the resulting state cannot be represented by the CTFE interpreter.
     ReadPartialPointer(Pointer<AllocId>),
diff --git a/compiler/rustc_middle/src/mir/interpret/pointer.rs b/compiler/rustc_middle/src/mir/interpret/pointer.rs
index e25ff7651f6..c581b2ebf09 100644
--- a/compiler/rustc_middle/src/mir/interpret/pointer.rs
+++ b/compiler/rustc_middle/src/mir/interpret/pointer.rs
@@ -56,7 +56,7 @@ impl<T: HasDataLayout> PointerArithmetic for T {}
 /// mostly opaque; the `Machine` trait extends it with some more operations that also have access to
 /// some global state.
 /// The `Debug` rendering is used to display bare provenance, and for the default impl of `fmt`.
-pub trait Provenance: Copy + fmt::Debug + 'static {
+pub trait Provenance: Copy + PartialEq + fmt::Debug + 'static {
     /// Says whether the `offset` field of `Pointer`s with this provenance is the actual physical address.
     /// - If `false`, the offset *must* be relative. This means the bytes representing a pointer are
     ///   different from what the Abstract Machine prescribes, so the interpreter must prevent any
@@ -79,7 +79,7 @@ pub trait Provenance: Copy + fmt::Debug + 'static {
     fn get_alloc_id(self) -> Option<AllocId>;
 
     /// Defines the 'join' of provenance: what happens when doing a pointer load and different bytes have different provenance.
-    fn join(left: Option<Self>, right: Option<Self>) -> Option<Self>;
+    fn join(left: Self, right: Self) -> Option<Self>;
 }
 
 /// The type of provenance in the compile-time interpreter.
@@ -192,8 +192,8 @@ impl Provenance for CtfeProvenance {
         Some(self.alloc_id())
     }
 
-    fn join(_left: Option<Self>, _right: Option<Self>) -> Option<Self> {
-        panic!("merging provenance is not supported when `OFFSET_IS_ADDR` is false")
+    fn join(left: Self, right: Self) -> Option<Self> {
+        if left == right { Some(left) } else { None }
     }
 }
 
@@ -224,8 +224,8 @@ impl Provenance for AllocId {
         Some(self)
     }
 
-    fn join(_left: Option<Self>, _right: Option<Self>) -> Option<Self> {
-        panic!("merging provenance is not supported when `OFFSET_IS_ADDR` is false")
+    fn join(_left: Self, _right: Self) -> Option<Self> {
+        unreachable!()
     }
 }
 
diff --git a/compiler/rustc_middle/src/mir/mono.rs b/compiler/rustc_middle/src/mir/mono.rs
index e5864660575..0e6f797b1e4 100644
--- a/compiler/rustc_middle/src/mir/mono.rs
+++ b/compiler/rustc_middle/src/mir/mono.rs
@@ -2,7 +2,6 @@ use std::borrow::Cow;
 use std::fmt;
 use std::hash::Hash;
 
-use rustc_ast::expand::autodiff_attrs::AutoDiffItem;
 use rustc_data_structures::base_n::{BaseNString, CASE_INSENSITIVE, ToBaseN};
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::FxIndexMap;
@@ -10,9 +9,8 @@ use rustc_data_structures::stable_hasher::{HashStable, StableHasher, ToStableHas
 use rustc_data_structures::unord::UnordMap;
 use rustc_hashes::Hash128;
 use rustc_hir::ItemId;
-use rustc_hir::attrs::InlineAttr;
+use rustc_hir::attrs::{InlineAttr, Linkage};
 use rustc_hir::def_id::{CrateNum, DefId, DefIdSet, LOCAL_CRATE};
-use rustc_index::Idx;
 use rustc_macros::{HashStable, TyDecodable, TyEncodable};
 use rustc_query_system::ich::StableHashingContext;
 use rustc_session::config::OptLevel;
@@ -151,7 +149,7 @@ impl<'tcx> MonoItem<'tcx> {
         // instantiation:
         // We emit an unused_attributes lint for this case, which should be kept in sync if possible.
         let codegen_fn_attrs = tcx.codegen_instance_attrs(instance.def);
-        if codegen_fn_attrs.contains_extern_indicator()
+        if codegen_fn_attrs.contains_extern_indicator(tcx, instance.def.def_id())
             || codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED)
         {
             return InstantiationMode::GloballyShared { may_conflict: false };
@@ -337,7 +335,6 @@ impl ToStableHashKey<StableHashingContext<'_>> for MonoItem<'_> {
 pub struct MonoItemPartitions<'tcx> {
     pub codegen_units: &'tcx [CodegenUnit<'tcx>],
     pub all_mono_items: &'tcx DefIdSet,
-    pub autodiff_items: &'tcx [AutoDiffItem],
 }
 
 #[derive(Debug, HashStable)]
@@ -369,22 +366,6 @@ pub struct MonoItemData {
     pub size_estimate: usize,
 }
 
-/// Specifies the linkage type for a `MonoItem`.
-///
-/// See <https://llvm.org/docs/LangRef.html#linkage-types> for more details about these variants.
-#[derive(Copy, Clone, PartialEq, Debug, TyEncodable, TyDecodable, HashStable)]
-pub enum Linkage {
-    External,
-    AvailableExternally,
-    LinkOnceAny,
-    LinkOnceODR,
-    WeakAny,
-    WeakODR,
-    Internal,
-    ExternalWeak,
-    Common,
-}
-
 /// Specifies the symbol visibility with regards to dynamic linking.
 ///
 /// Visibility doesn't have any effect when linkage is internal.
@@ -526,44 +507,50 @@ impl<'tcx> CodegenUnit<'tcx> {
         tcx: TyCtxt<'tcx>,
     ) -> Vec<(MonoItem<'tcx>, MonoItemData)> {
         // The codegen tests rely on items being process in the same order as
-        // they appear in the file, so for local items, we sort by node_id first
+        // they appear in the file, so for local items, we sort by span first
         #[derive(PartialEq, Eq, PartialOrd, Ord)]
-        struct ItemSortKey<'tcx>(Option<usize>, SymbolName<'tcx>);
-
+        struct ItemSortKey<'tcx>(Option<Span>, SymbolName<'tcx>);
+
+        // We only want to take HirIds of user-defines instances into account.
+        // The others don't matter for the codegen tests and can even make item
+        // order unstable.
+        fn local_item_id<'tcx>(item: MonoItem<'tcx>) -> Option<DefId> {
+            match item {
+                MonoItem::Fn(ref instance) => match instance.def {
+                    InstanceKind::Item(def) => def.as_local().map(|_| def),
+                    InstanceKind::VTableShim(..)
+                    | InstanceKind::ReifyShim(..)
+                    | InstanceKind::Intrinsic(..)
+                    | InstanceKind::FnPtrShim(..)
+                    | InstanceKind::Virtual(..)
+                    | InstanceKind::ClosureOnceShim { .. }
+                    | InstanceKind::ConstructCoroutineInClosureShim { .. }
+                    | InstanceKind::DropGlue(..)
+                    | InstanceKind::CloneShim(..)
+                    | InstanceKind::ThreadLocalShim(..)
+                    | InstanceKind::FnPtrAddrShim(..)
+                    | InstanceKind::AsyncDropGlue(..)
+                    | InstanceKind::FutureDropPollShim(..)
+                    | InstanceKind::AsyncDropGlueCtorShim(..) => None,
+                },
+                MonoItem::Static(def_id) => def_id.as_local().map(|_| def_id),
+                MonoItem::GlobalAsm(item_id) => Some(item_id.owner_id.def_id.to_def_id()),
+            }
+        }
         fn item_sort_key<'tcx>(tcx: TyCtxt<'tcx>, item: MonoItem<'tcx>) -> ItemSortKey<'tcx> {
             ItemSortKey(
-                match item {
-                    MonoItem::Fn(ref instance) => {
-                        match instance.def {
-                            // We only want to take HirIds of user-defined
-                            // instances into account. The others don't matter for
-                            // the codegen tests and can even make item order
-                            // unstable.
-                            InstanceKind::Item(def) => def.as_local().map(Idx::index),
-                            InstanceKind::VTableShim(..)
-                            | InstanceKind::ReifyShim(..)
-                            | InstanceKind::Intrinsic(..)
-                            | InstanceKind::FnPtrShim(..)
-                            | InstanceKind::Virtual(..)
-                            | InstanceKind::ClosureOnceShim { .. }
-                            | InstanceKind::ConstructCoroutineInClosureShim { .. }
-                            | InstanceKind::DropGlue(..)
-                            | InstanceKind::CloneShim(..)
-                            | InstanceKind::ThreadLocalShim(..)
-                            | InstanceKind::FnPtrAddrShim(..)
-                            | InstanceKind::AsyncDropGlue(..)
-                            | InstanceKind::FutureDropPollShim(..)
-                            | InstanceKind::AsyncDropGlueCtorShim(..) => None,
-                        }
-                    }
-                    MonoItem::Static(def_id) => def_id.as_local().map(Idx::index),
-                    MonoItem::GlobalAsm(item_id) => Some(item_id.owner_id.def_id.index()),
-                },
+                local_item_id(item)
+                    .map(|def_id| tcx.def_span(def_id).find_ancestor_not_from_macro())
+                    .flatten(),
                 item.symbol_name(tcx),
             )
         }
 
         let mut items: Vec<_> = self.items().iter().map(|(&i, &data)| (i, data)).collect();
+        if !tcx.sess.opts.unstable_opts.codegen_source_order {
+            // It's already deterministic, so we can just use it.
+            return items;
+        }
         items.sort_by_cached_key(|&(i, _)| item_sort_key(tcx, i));
         items
     }
diff --git a/compiler/rustc_middle/src/mir/pretty.rs b/compiler/rustc_middle/src/mir/pretty.rs
index ed067d49127..f2d5b13cbc8 100644
--- a/compiler/rustc_middle/src/mir/pretty.rs
+++ b/compiler/rustc_middle/src/mir/pretty.rs
@@ -585,12 +585,7 @@ fn write_coverage_info_hi(
     coverage_info_hi: &coverage::CoverageInfoHi,
     w: &mut dyn io::Write,
 ) -> io::Result<()> {
-    let coverage::CoverageInfoHi {
-        num_block_markers: _,
-        branch_spans,
-        mcdc_degraded_branch_spans,
-        mcdc_spans,
-    } = coverage_info_hi;
+    let coverage::CoverageInfoHi { num_block_markers: _, branch_spans } = coverage_info_hi;
 
     // Only add an extra trailing newline if we printed at least one thing.
     let mut did_print = false;
@@ -603,38 +598,6 @@ fn write_coverage_info_hi(
         did_print = true;
     }
 
-    for coverage::MCDCBranchSpan { span, true_marker, false_marker, .. } in
-        mcdc_degraded_branch_spans
-    {
-        writeln!(
-            w,
-            "{INDENT}coverage branch {{ true: {true_marker:?}, false: {false_marker:?} }} => {span:?}",
-        )?;
-        did_print = true;
-    }
-
-    for (
-        coverage::MCDCDecisionSpan { span, end_markers, decision_depth, num_conditions: _ },
-        conditions,
-    ) in mcdc_spans
-    {
-        let num_conditions = conditions.len();
-        writeln!(
-            w,
-            "{INDENT}coverage mcdc decision {{ num_conditions: {num_conditions:?}, end: {end_markers:?}, depth: {decision_depth:?} }} => {span:?}"
-        )?;
-        for coverage::MCDCBranchSpan { span, condition_info, true_marker, false_marker } in
-            conditions
-        {
-            writeln!(
-                w,
-                "{INDENT}coverage mcdc branch {{ condition_id: {:?}, true: {true_marker:?}, false: {false_marker:?} }} => {span:?}",
-                condition_info.condition_id
-            )?;
-        }
-        did_print = true;
-    }
-
     if did_print {
         writeln!(w)?;
     }
@@ -1826,7 +1789,7 @@ pub fn write_allocation_bytes<'tcx, Prov: Provenance, Extra, Bytes: AllocBytes>(
                 ascii.push('╼');
                 i += ptr_size;
             }
-        } else if let Some(prov) = alloc.provenance().get(i, &tcx) {
+        } else if let Some((prov, idx)) = alloc.provenance().get_byte(i, &tcx) {
             // Memory with provenance must be defined
             assert!(
                 alloc.init_mask().is_range_initialized(alloc_range(i, Size::from_bytes(1))).is_ok()
@@ -1836,7 +1799,7 @@ pub fn write_allocation_bytes<'tcx, Prov: Provenance, Extra, Bytes: AllocBytes>(
             // Format is similar to "oversized" above.
             let j = i.bytes_usize();
             let c = alloc.inspect_with_uninit_and_ptr_outside_interpreter(j..j + 1)[0];
-            write!(w, "╾{c:02x}{prov:#?} (1 ptr byte)╼")?;
+            write!(w, "╾{c:02x}{prov:#?} (ptr fragment {idx})╼")?;
             i += Size::from_bytes(1);
         } else if alloc
             .init_mask()
@@ -1969,7 +1932,7 @@ fn pretty_print_const_value_tcx<'tcx>(
                         let args = tcx.lift(args).unwrap();
                         let mut p = FmtPrinter::new(tcx, Namespace::ValueNS);
                         p.print_alloc_ids = true;
-                        p.print_value_path(variant_def.def_id, args)?;
+                        p.pretty_print_value_path(variant_def.def_id, args)?;
                         fmt.write_str(&p.into_buffer())?;
 
                         match variant_def.ctor_kind() {
@@ -2011,7 +1974,7 @@ fn pretty_print_const_value_tcx<'tcx>(
         (ConstValue::ZeroSized, ty::FnDef(d, s)) => {
             let mut p = FmtPrinter::new(tcx, Namespace::ValueNS);
             p.print_alloc_ids = true;
-            p.print_value_path(*d, s)?;
+            p.pretty_print_value_path(*d, s)?;
             fmt.write_str(&p.into_buffer())?;
             return Ok(());
         }
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index a4589576594..f4d0120a2e7 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -1864,6 +1864,12 @@ rustc_queries! {
         feedable
     }
 
+    /// Returns whether the field corresponding to the `DefId` has a default field value.
+    query default_field(def_id: DefId) -> Option<DefId> {
+        desc { |tcx| "looking up the `const` corresponding to the default for `{}`", tcx.def_path_str(def_id) }
+        separate_provide_extern
+    }
+
     query check_well_formed(key: LocalDefId) -> Result<(), ErrorGuaranteed> {
         desc { |tcx| "checking that `{}` is well-formed", tcx.def_path_str(key) }
         return_result_from_ensure_ok
diff --git a/compiler/rustc_middle/src/thir.rs b/compiler/rustc_middle/src/thir.rs
index 3dd6d2c8928..f1d19800a78 100644
--- a/compiler/rustc_middle/src/thir.rs
+++ b/compiler/rustc_middle/src/thir.rs
@@ -832,17 +832,17 @@ pub enum PatKind<'tcx> {
     },
 
     /// One of the following:
-    /// * `&str` (represented as a valtree), which will be handled as a string pattern and thus
+    /// * `&str`, which will be handled as a string pattern and thus
     ///   exhaustiveness checking will detect if you use the same string twice in different
     ///   patterns.
-    /// * integer, bool, char or float (represented as a valtree), which will be handled by
+    /// * integer, bool, char or float, which will be handled by
     ///   exhaustiveness to cover exactly its own value, similar to `&str`, but these values are
     ///   much simpler.
     /// * raw pointers derived from integers, other raw pointers will have already resulted in an
     //    error.
     /// * `String`, if `string_deref_patterns` is enabled.
     Constant {
-        value: mir::Const<'tcx>,
+        value: ty::Value<'tcx>,
     },
 
     /// Pattern obtained by converting a constant (inline or named) to its pattern
@@ -935,7 +935,7 @@ impl<'tcx> PatRange<'tcx> {
         let lo_is_min = match self.lo {
             PatRangeBoundary::NegInfinity => true,
             PatRangeBoundary::Finite(value) => {
-                let lo = value.try_to_bits(size).unwrap() ^ bias;
+                let lo = value.try_to_scalar_int().unwrap().to_bits(size) ^ bias;
                 lo <= min
             }
             PatRangeBoundary::PosInfinity => false,
@@ -944,7 +944,7 @@ impl<'tcx> PatRange<'tcx> {
             let hi_is_max = match self.hi {
                 PatRangeBoundary::NegInfinity => false,
                 PatRangeBoundary::Finite(value) => {
-                    let hi = value.try_to_bits(size).unwrap() ^ bias;
+                    let hi = value.try_to_scalar_int().unwrap().to_bits(size) ^ bias;
                     hi > max || hi == max && self.end == RangeEnd::Included
                 }
                 PatRangeBoundary::PosInfinity => true,
@@ -957,22 +957,17 @@ impl<'tcx> PatRange<'tcx> {
     }
 
     #[inline]
-    pub fn contains(
-        &self,
-        value: mir::Const<'tcx>,
-        tcx: TyCtxt<'tcx>,
-        typing_env: ty::TypingEnv<'tcx>,
-    ) -> Option<bool> {
+    pub fn contains(&self, value: ty::Value<'tcx>, tcx: TyCtxt<'tcx>) -> Option<bool> {
         use Ordering::*;
-        debug_assert_eq!(self.ty, value.ty());
+        debug_assert_eq!(value.ty, self.ty);
         let ty = self.ty;
-        let value = PatRangeBoundary::Finite(value);
+        let value = PatRangeBoundary::Finite(value.valtree);
         // For performance, it's important to only do the second comparison if necessary.
         Some(
-            match self.lo.compare_with(value, ty, tcx, typing_env)? {
+            match self.lo.compare_with(value, ty, tcx)? {
                 Less | Equal => true,
                 Greater => false,
-            } && match value.compare_with(self.hi, ty, tcx, typing_env)? {
+            } && match value.compare_with(self.hi, ty, tcx)? {
                 Less => true,
                 Equal => self.end == RangeEnd::Included,
                 Greater => false,
@@ -981,21 +976,16 @@ impl<'tcx> PatRange<'tcx> {
     }
 
     #[inline]
-    pub fn overlaps(
-        &self,
-        other: &Self,
-        tcx: TyCtxt<'tcx>,
-        typing_env: ty::TypingEnv<'tcx>,
-    ) -> Option<bool> {
+    pub fn overlaps(&self, other: &Self, tcx: TyCtxt<'tcx>) -> Option<bool> {
         use Ordering::*;
         debug_assert_eq!(self.ty, other.ty);
         // For performance, it's important to only do the second comparison if necessary.
         Some(
-            match other.lo.compare_with(self.hi, self.ty, tcx, typing_env)? {
+            match other.lo.compare_with(self.hi, self.ty, tcx)? {
                 Less => true,
                 Equal => self.end == RangeEnd::Included,
                 Greater => false,
-            } && match self.lo.compare_with(other.hi, self.ty, tcx, typing_env)? {
+            } && match self.lo.compare_with(other.hi, self.ty, tcx)? {
                 Less => true,
                 Equal => other.end == RangeEnd::Included,
                 Greater => false,
@@ -1006,11 +996,13 @@ impl<'tcx> PatRange<'tcx> {
 
 impl<'tcx> fmt::Display for PatRange<'tcx> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        if let PatRangeBoundary::Finite(value) = &self.lo {
+        if let &PatRangeBoundary::Finite(valtree) = &self.lo {
+            let value = ty::Value { ty: self.ty, valtree };
             write!(f, "{value}")?;
         }
-        if let PatRangeBoundary::Finite(value) = &self.hi {
+        if let &PatRangeBoundary::Finite(valtree) = &self.hi {
             write!(f, "{}", self.end)?;
+            let value = ty::Value { ty: self.ty, valtree };
             write!(f, "{value}")?;
         } else {
             // `0..` is parsed as an inclusive range, we must display it correctly.
@@ -1024,7 +1016,8 @@ impl<'tcx> fmt::Display for PatRange<'tcx> {
 /// If present, the const must be of a numeric type.
 #[derive(Copy, Clone, Debug, PartialEq, HashStable, TypeVisitable)]
 pub enum PatRangeBoundary<'tcx> {
-    Finite(mir::Const<'tcx>),
+    /// The type of this valtree is stored in the surrounding `PatRange`.
+    Finite(ty::ValTree<'tcx>),
     NegInfinity,
     PosInfinity,
 }
@@ -1035,20 +1028,15 @@ impl<'tcx> PatRangeBoundary<'tcx> {
         matches!(self, Self::Finite(..))
     }
     #[inline]
-    pub fn as_finite(self) -> Option<mir::Const<'tcx>> {
+    pub fn as_finite(self) -> Option<ty::ValTree<'tcx>> {
         match self {
             Self::Finite(value) => Some(value),
             Self::NegInfinity | Self::PosInfinity => None,
         }
     }
-    pub fn eval_bits(
-        self,
-        ty: Ty<'tcx>,
-        tcx: TyCtxt<'tcx>,
-        typing_env: ty::TypingEnv<'tcx>,
-    ) -> u128 {
+    pub fn to_bits(self, ty: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> u128 {
         match self {
-            Self::Finite(value) => value.eval_bits(tcx, typing_env),
+            Self::Finite(value) => value.try_to_scalar_int().unwrap().to_bits_unchecked(),
             Self::NegInfinity => {
                 // Unwrap is ok because the type is known to be numeric.
                 ty.numeric_min_and_max_as_bits(tcx).unwrap().0
@@ -1060,14 +1048,8 @@ impl<'tcx> PatRangeBoundary<'tcx> {
         }
     }
 
-    #[instrument(skip(tcx, typing_env), level = "debug", ret)]
-    pub fn compare_with(
-        self,
-        other: Self,
-        ty: Ty<'tcx>,
-        tcx: TyCtxt<'tcx>,
-        typing_env: ty::TypingEnv<'tcx>,
-    ) -> Option<Ordering> {
+    #[instrument(skip(tcx), level = "debug", ret)]
+    pub fn compare_with(self, other: Self, ty: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<Ordering> {
         use PatRangeBoundary::*;
         match (self, other) {
             // When comparing with infinities, we must remember that `0u8..` and `0u8..=255`
@@ -1095,8 +1077,8 @@ impl<'tcx> PatRangeBoundary<'tcx> {
             _ => {}
         }
 
-        let a = self.eval_bits(ty, tcx, typing_env);
-        let b = other.eval_bits(ty, tcx, typing_env);
+        let a = self.to_bits(ty, tcx);
+        let b = other.to_bits(ty, tcx);
 
         match ty.kind() {
             ty::Float(ty::FloatTy::F16) => {
diff --git a/compiler/rustc_middle/src/ty/consts/valtree.rs b/compiler/rustc_middle/src/ty/consts/valtree.rs
index d95006dcf4a..a14e47d7082 100644
--- a/compiler/rustc_middle/src/ty/consts/valtree.rs
+++ b/compiler/rustc_middle/src/ty/consts/valtree.rs
@@ -2,10 +2,12 @@ use std::fmt;
 use std::ops::Deref;
 
 use rustc_data_structures::intern::Interned;
+use rustc_hir::def::Namespace;
 use rustc_macros::{HashStable, Lift, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable};
 
 use super::ScalarInt;
 use crate::mir::interpret::{ErrorHandled, Scalar};
+use crate::ty::print::{FmtPrinter, PrettyPrinter};
 use crate::ty::{self, Ty, TyCtxt};
 
 /// This datastructure is used to represent the value of constants used in the type system.
@@ -133,6 +135,8 @@ pub type ConstToValTreeResult<'tcx> = Result<Result<ValTree<'tcx>, Ty<'tcx>>, Er
 /// A type-level constant value.
 ///
 /// Represents a typed, fully evaluated constant.
+/// Note that this is also used by pattern elaboration to represent values which cannot occur in types,
+/// such as raw pointers and floats.
 #[derive(Copy, Clone, Debug, Hash, Eq, PartialEq)]
 #[derive(HashStable, TyEncodable, TyDecodable, TypeFoldable, TypeVisitable, Lift)]
 pub struct Value<'tcx> {
@@ -203,3 +207,14 @@ impl<'tcx> rustc_type_ir::inherent::ValueConst<TyCtxt<'tcx>> for Value<'tcx> {
         self.valtree
     }
 }
+
+impl<'tcx> fmt::Display for Value<'tcx> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        ty::tls::with(move |tcx| {
+            let cv = tcx.lift(*self).unwrap();
+            let mut p = FmtPrinter::new(tcx, Namespace::ValueNS);
+            p.pretty_print_const_valtree(cv, /*print_ty*/ true)?;
+            f.write_str(&p.into_buffer())
+        })
+    }
+}
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index db56082c71a..49a4733de3b 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -290,11 +290,8 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
         debug_assert_matches!(self.def_kind(def_id), DefKind::AssocTy | DefKind::AssocConst);
         let trait_def_id = self.parent(def_id);
         debug_assert_matches!(self.def_kind(trait_def_id), DefKind::Trait);
-        let trait_generics = self.generics_of(trait_def_id);
-        (
-            ty::TraitRef::new_from_args(self, trait_def_id, args.truncate_to(self, trait_generics)),
-            &args[trait_generics.count()..],
-        )
+        let trait_ref = ty::TraitRef::from_assoc(self, trait_def_id, args);
+        (trait_ref, &args[trait_ref.args.len()..])
     }
 
     fn mk_args(self, args: &[Self::GenericArg]) -> ty::GenericArgsRef<'tcx> {
diff --git a/compiler/rustc_middle/src/ty/diagnostics.rs b/compiler/rustc_middle/src/ty/diagnostics.rs
index b122ada0925..b3042904a29 100644
--- a/compiler/rustc_middle/src/ty/diagnostics.rs
+++ b/compiler/rustc_middle/src/ty/diagnostics.rs
@@ -7,14 +7,14 @@ use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::{
     Applicability, Diag, DiagArgValue, IntoDiagArg, into_diag_arg_using_display, listify, pluralize,
 };
-use rustc_hir::def::DefKind;
+use rustc_hir::def::{DefKind, Namespace};
 use rustc_hir::def_id::DefId;
 use rustc_hir::{self as hir, AmbigArg, LangItem, PredicateOrigin, WherePredicateKind};
 use rustc_span::{BytePos, Span};
 use rustc_type_ir::TyKind::*;
 
 use crate::ty::{
-    self, AliasTy, Const, ConstKind, FallibleTypeFolder, InferConst, InferTy, Opaque,
+    self, AliasTy, Const, ConstKind, FallibleTypeFolder, InferConst, InferTy, Instance, Opaque,
     PolyTraitPredicate, Projection, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable,
     TypeSuperVisitable, TypeVisitable, TypeVisitor,
 };
@@ -28,6 +28,15 @@ impl IntoDiagArg for Ty<'_> {
     }
 }
 
+impl IntoDiagArg for Instance<'_> {
+    fn into_diag_arg(self, path: &mut Option<std::path::PathBuf>) -> rustc_errors::DiagArgValue {
+        ty::tls::with(|tcx| {
+            let instance = tcx.short_string_namespace(self, path, Namespace::ValueNS);
+            rustc_errors::DiagArgValue::Str(std::borrow::Cow::Owned(instance))
+        })
+    }
+}
+
 into_diag_arg_using_display! {
     ty::Region<'_>,
 }
diff --git a/compiler/rustc_middle/src/ty/error.rs b/compiler/rustc_middle/src/ty/error.rs
index c24dc983d21..3f854038651 100644
--- a/compiler/rustc_middle/src/ty/error.rs
+++ b/compiler/rustc_middle/src/ty/error.rs
@@ -160,7 +160,11 @@ impl<'tcx> Ty<'tcx> {
             _ => {
                 let width = tcx.sess.diagnostic_width();
                 let length_limit = std::cmp::max(width / 4, 40);
-                format!("`{}`", tcx.string_with_limit(self, length_limit)).into()
+                format!(
+                    "`{}`",
+                    tcx.string_with_limit(self, length_limit, hir::def::Namespace::TypeNS)
+                )
+                .into()
             }
         }
     }
@@ -213,12 +217,12 @@ impl<'tcx> Ty<'tcx> {
 }
 
 impl<'tcx> TyCtxt<'tcx> {
-    pub fn string_with_limit<T>(self, t: T, length_limit: usize) -> String
+    pub fn string_with_limit<T>(self, t: T, length_limit: usize, ns: hir::def::Namespace) -> String
     where
         T: Copy + for<'a, 'b> Lift<TyCtxt<'b>, Lifted: Print<'b, FmtPrinter<'a, 'b>>>,
     {
         let mut type_limit = 50;
-        let regular = FmtPrinter::print_string(self, hir::def::Namespace::TypeNS, |p| {
+        let regular = FmtPrinter::print_string(self, ns, |p| {
             self.lift(t).expect("could not lift for printing").print(p)
         })
         .expect("could not write to `String`");
@@ -229,11 +233,7 @@ impl<'tcx> TyCtxt<'tcx> {
         loop {
             // Look for the longest properly trimmed path that still fits in length_limit.
             short = with_forced_trimmed_paths!({
-                let mut p = FmtPrinter::new_with_limit(
-                    self,
-                    hir::def::Namespace::TypeNS,
-                    rustc_session::Limit(type_limit),
-                );
+                let mut p = FmtPrinter::new_with_limit(self, ns, rustc_session::Limit(type_limit));
                 self.lift(t)
                     .expect("could not lift for printing")
                     .print(&mut p)
@@ -251,12 +251,28 @@ impl<'tcx> TyCtxt<'tcx> {
     /// When calling this after a `Diag` is constructed, the preferred way of doing so is
     /// `tcx.short_string(ty, diag.long_ty_path())`. The diagnostic itself is the one that keeps
     /// the existence of a "long type" anywhere in the diagnostic, so the note telling the user
-    /// where we wrote the file to is only printed once.
+    /// where we wrote the file to is only printed once. The path will use the type namespace.
     pub fn short_string<T>(self, t: T, path: &mut Option<PathBuf>) -> String
     where
         T: Copy + Hash + for<'a, 'b> Lift<TyCtxt<'b>, Lifted: Print<'b, FmtPrinter<'a, 'b>>>,
     {
-        let regular = FmtPrinter::print_string(self, hir::def::Namespace::TypeNS, |p| {
+        self.short_string_namespace(t, path, hir::def::Namespace::TypeNS)
+    }
+
+    /// When calling this after a `Diag` is constructed, the preferred way of doing so is
+    /// `tcx.short_string(ty, diag.long_ty_path())`. The diagnostic itself is the one that keeps
+    /// the existence of a "long type" anywhere in the diagnostic, so the note telling the user
+    /// where we wrote the file to is only printed once.
+    pub fn short_string_namespace<T>(
+        self,
+        t: T,
+        path: &mut Option<PathBuf>,
+        namespace: hir::def::Namespace,
+    ) -> String
+    where
+        T: Copy + Hash + for<'a, 'b> Lift<TyCtxt<'b>, Lifted: Print<'b, FmtPrinter<'a, 'b>>>,
+    {
+        let regular = FmtPrinter::print_string(self, namespace, |p| {
             self.lift(t).expect("could not lift for printing").print(p)
         })
         .expect("could not write to `String`");
@@ -270,7 +286,7 @@ impl<'tcx> TyCtxt<'tcx> {
         if regular.len() <= width * 2 / 3 {
             return regular;
         }
-        let short = self.string_with_limit(t, length_limit);
+        let short = self.string_with_limit(t, length_limit, namespace);
         if regular == short {
             return regular;
         }
diff --git a/compiler/rustc_middle/src/ty/generic_args.rs b/compiler/rustc_middle/src/ty/generic_args.rs
index b02abb5ab43..3ade3a3ef51 100644
--- a/compiler/rustc_middle/src/ty/generic_args.rs
+++ b/compiler/rustc_middle/src/ty/generic_args.rs
@@ -527,21 +527,28 @@ impl<'tcx> GenericArgs<'tcx> {
     #[inline]
     #[track_caller]
     pub fn type_at(&self, i: usize) -> Ty<'tcx> {
-        self[i].as_type().unwrap_or_else(|| bug!("expected type for param #{} in {:?}", i, self))
+        self[i].as_type().unwrap_or_else(
+            #[track_caller]
+            || bug!("expected type for param #{} in {:?}", i, self),
+        )
     }
 
     #[inline]
     #[track_caller]
     pub fn region_at(&self, i: usize) -> ty::Region<'tcx> {
-        self[i]
-            .as_region()
-            .unwrap_or_else(|| bug!("expected region for param #{} in {:?}", i, self))
+        self[i].as_region().unwrap_or_else(
+            #[track_caller]
+            || bug!("expected region for param #{} in {:?}", i, self),
+        )
     }
 
     #[inline]
     #[track_caller]
     pub fn const_at(&self, i: usize) -> ty::Const<'tcx> {
-        self[i].as_const().unwrap_or_else(|| bug!("expected const for param #{} in {:?}", i, self))
+        self[i].as_const().unwrap_or_else(
+            #[track_caller]
+            || bug!("expected const for param #{} in {:?}", i, self),
+        )
     }
 
     #[inline]
@@ -578,6 +585,9 @@ impl<'tcx> GenericArgs<'tcx> {
         tcx.mk_args_from_iter(target_args.iter().chain(self.iter().skip(defs.count())))
     }
 
+    /// Truncates this list of generic args to have at most the number of args in `generics`.
+    ///
+    /// You might be looking for [`TraitRef::from_assoc`](super::TraitRef::from_assoc).
     pub fn truncate_to(&self, tcx: TyCtxt<'tcx>, generics: &ty::Generics) -> GenericArgsRef<'tcx> {
         tcx.mk_args(&self[..generics.count()])
     }
diff --git a/compiler/rustc_middle/src/ty/instance.rs b/compiler/rustc_middle/src/ty/instance.rs
index 16873b6ee21..3a51f79f121 100644
--- a/compiler/rustc_middle/src/ty/instance.rs
+++ b/compiler/rustc_middle/src/ty/instance.rs
@@ -1,6 +1,5 @@
 use std::assert_matches::assert_matches;
 use std::fmt;
-use std::path::PathBuf;
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::ErrorGuaranteed;
@@ -17,7 +16,7 @@ use tracing::{debug, instrument};
 use crate::error;
 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use crate::ty::normalize_erasing_regions::NormalizationError;
-use crate::ty::print::{FmtPrinter, Printer, shrunk_instance_name};
+use crate::ty::print::{FmtPrinter, Print};
 use crate::ty::{
     self, EarlyBinder, GenericArgs, GenericArgsRef, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable,
     TypeVisitable, TypeVisitableExt, TypeVisitor,
@@ -389,59 +388,15 @@ fn type_length<'tcx>(item: impl TypeVisitable<TyCtxt<'tcx>>) -> usize {
     visitor.type_length
 }
 
-pub fn fmt_instance(
-    f: &mut fmt::Formatter<'_>,
-    instance: Instance<'_>,
-    type_length: Option<rustc_session::Limit>,
-) -> fmt::Result {
-    ty::tls::with(|tcx| {
-        let args = tcx.lift(instance.args).expect("could not lift for printing");
-
-        let mut p = if let Some(type_length) = type_length {
-            FmtPrinter::new_with_limit(tcx, Namespace::ValueNS, type_length)
-        } else {
-            FmtPrinter::new(tcx, Namespace::ValueNS)
-        };
-        p.print_def_path(instance.def_id(), args)?;
-        let s = p.into_buffer();
-        f.write_str(&s)
-    })?;
-
-    match instance.def {
-        InstanceKind::Item(_) => Ok(()),
-        InstanceKind::VTableShim(_) => write!(f, " - shim(vtable)"),
-        InstanceKind::ReifyShim(_, None) => write!(f, " - shim(reify)"),
-        InstanceKind::ReifyShim(_, Some(ReifyReason::FnPtr)) => write!(f, " - shim(reify-fnptr)"),
-        InstanceKind::ReifyShim(_, Some(ReifyReason::Vtable)) => write!(f, " - shim(reify-vtable)"),
-        InstanceKind::ThreadLocalShim(_) => write!(f, " - shim(tls)"),
-        InstanceKind::Intrinsic(_) => write!(f, " - intrinsic"),
-        InstanceKind::Virtual(_, num) => write!(f, " - virtual#{num}"),
-        InstanceKind::FnPtrShim(_, ty) => write!(f, " - shim({ty})"),
-        InstanceKind::ClosureOnceShim { .. } => write!(f, " - shim"),
-        InstanceKind::ConstructCoroutineInClosureShim { .. } => write!(f, " - shim"),
-        InstanceKind::DropGlue(_, None) => write!(f, " - shim(None)"),
-        InstanceKind::DropGlue(_, Some(ty)) => write!(f, " - shim(Some({ty}))"),
-        InstanceKind::CloneShim(_, ty) => write!(f, " - shim({ty})"),
-        InstanceKind::FnPtrAddrShim(_, ty) => write!(f, " - shim({ty})"),
-        InstanceKind::FutureDropPollShim(_, proxy_ty, impl_ty) => {
-            write!(f, " - dropshim({proxy_ty}-{impl_ty})")
-        }
-        InstanceKind::AsyncDropGlue(_, ty) => write!(f, " - shim({ty})"),
-        InstanceKind::AsyncDropGlueCtorShim(_, ty) => write!(f, " - shim(Some({ty}))"),
-    }
-}
-
-pub struct ShortInstance<'tcx>(pub Instance<'tcx>, pub usize);
-
-impl<'tcx> fmt::Display for ShortInstance<'tcx> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt_instance(f, self.0, Some(rustc_session::Limit(self.1)))
-    }
-}
-
 impl<'tcx> fmt::Display for Instance<'tcx> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt_instance(f, *self, None)
+        ty::tls::with(|tcx| {
+            let mut p = FmtPrinter::new(tcx, Namespace::ValueNS);
+            let instance = tcx.lift(*self).expect("could not lift for printing");
+            instance.print(&mut p)?;
+            let s = p.into_buffer();
+            f.write_str(&s)
+        })
     }
 }
 
@@ -610,23 +565,12 @@ impl<'tcx> Instance<'tcx> {
             Ok(None) => {
                 let type_length = type_length(args);
                 if !tcx.type_length_limit().value_within_limit(type_length) {
-                    let (shrunk, written_to_path) =
-                        shrunk_instance_name(tcx, Instance::new_raw(def_id, args));
-                    let mut path = PathBuf::new();
-                    let was_written = if let Some(path2) = written_to_path {
-                        path = path2;
-                        true
-                    } else {
-                        false
-                    };
                     tcx.dcx().emit_fatal(error::TypeLengthLimit {
                         // We don't use `def_span(def_id)` so that diagnostics point
                         // to the crate root during mono instead of to foreign items.
                         // This is arguably better.
                         span: span_or_local_def_span(),
-                        shrunk,
-                        was_written,
-                        path,
+                        instance: Instance::new_raw(def_id, args),
                         type_length,
                     });
                 } else {
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 0deb2482c6f..e70c98ab704 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -82,7 +82,7 @@ pub use self::context::{
     TyCtxtFeed, tls,
 };
 pub use self::fold::*;
-pub use self::instance::{Instance, InstanceKind, ReifyReason, ShortInstance, UnusedGenericParams};
+pub use self::instance::{Instance, InstanceKind, ReifyReason, UnusedGenericParams};
 pub use self::list::{List, ListWithCachedTypeInfo};
 pub use self::opaque_types::OpaqueTypeKey;
 pub use self::pattern::{Pattern, PatternKind};
@@ -1031,6 +1031,8 @@ pub struct ParamEnvAnd<'tcx, T> {
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
 #[derive(TypeVisitable, TypeFoldable)]
 pub struct TypingEnv<'tcx> {
+    #[type_foldable(identity)]
+    #[type_visitable(ignore)]
     pub typing_mode: TypingMode<'tcx>,
     pub param_env: ParamEnv<'tcx>,
 }
@@ -1923,21 +1925,50 @@ impl<'tcx> TyCtxt<'tcx> {
         self.impl_trait_ref(def_id).map(|tr| tr.skip_binder().def_id)
     }
 
-    /// If the given `DefId` is an associated item, returns the `DefId` of the parent trait or impl.
-    pub fn assoc_parent(self, def_id: DefId) -> Option<DefId> {
-        self.def_kind(def_id).is_assoc().then(|| self.parent(def_id))
+    /// If the given `DefId` is an associated item, returns the `DefId` and `DefKind` of the parent trait or impl.
+    pub fn assoc_parent(self, def_id: DefId) -> Option<(DefId, DefKind)> {
+        if !self.def_kind(def_id).is_assoc() {
+            return None;
+        }
+        let parent = self.parent(def_id);
+        let def_kind = self.def_kind(parent);
+        Some((parent, def_kind))
     }
 
     /// If the given `DefId` is an associated item of a trait,
     /// returns the `DefId` of the trait; otherwise, returns `None`.
     pub fn trait_of_assoc(self, def_id: DefId) -> Option<DefId> {
-        self.assoc_parent(def_id).filter(|id| self.def_kind(id) == DefKind::Trait)
+        match self.assoc_parent(def_id) {
+            Some((id, DefKind::Trait)) => Some(id),
+            _ => None,
+        }
     }
 
     /// If the given `DefId` is an associated item of an impl,
     /// returns the `DefId` of the impl; otherwise returns `None`.
     pub fn impl_of_assoc(self, def_id: DefId) -> Option<DefId> {
-        self.assoc_parent(def_id).filter(|id| matches!(self.def_kind(id), DefKind::Impl { .. }))
+        match self.assoc_parent(def_id) {
+            Some((id, DefKind::Impl { .. })) => Some(id),
+            _ => None,
+        }
+    }
+
+    /// If the given `DefId` is an associated item of an inherent impl,
+    /// returns the `DefId` of the impl; otherwise, returns `None`.
+    pub fn inherent_impl_of_assoc(self, def_id: DefId) -> Option<DefId> {
+        match self.assoc_parent(def_id) {
+            Some((id, DefKind::Impl { of_trait: false })) => Some(id),
+            _ => None,
+        }
+    }
+
+    /// If the given `DefId` is an associated item of a trait impl,
+    /// returns the `DefId` of the impl; otherwise, returns `None`.
+    pub fn trait_impl_of_assoc(self, def_id: DefId) -> Option<DefId> {
+        match self.assoc_parent(def_id) {
+            Some((id, DefKind::Impl { of_trait: true })) => Some(id),
+            _ => None,
+        }
     }
 
     pub fn is_exportable(self, def_id: DefId) -> bool {
diff --git a/compiler/rustc_middle/src/ty/predicate.rs b/compiler/rustc_middle/src/ty/predicate.rs
index 73a6f1829af..59e00f85957 100644
--- a/compiler/rustc_middle/src/ty/predicate.rs
+++ b/compiler/rustc_middle/src/ty/predicate.rs
@@ -6,8 +6,7 @@ use rustc_macros::{HashStable, extension};
 use rustc_type_ir as ir;
 
 use crate::ty::{
-    self, DebruijnIndex, EarlyBinder, PredicatePolarity, Ty, TyCtxt, TypeFlags, Upcast, UpcastFrom,
-    WithCachedTypeInfo,
+    self, DebruijnIndex, EarlyBinder, Ty, TyCtxt, TypeFlags, Upcast, UpcastFrom, WithCachedTypeInfo,
 };
 
 pub type TraitRef<'tcx> = ir::TraitRef<TyCtxt<'tcx>>;
@@ -536,15 +535,6 @@ impl<'tcx> UpcastFrom<TyCtxt<'tcx>, ty::Binder<'tcx, TraitRef<'tcx>>> for Clause
     }
 }
 
-impl<'tcx> UpcastFrom<TyCtxt<'tcx>, ty::Binder<'tcx, TraitRef<'tcx>>> for PolyTraitPredicate<'tcx> {
-    fn upcast_from(from: ty::Binder<'tcx, TraitRef<'tcx>>, _tcx: TyCtxt<'tcx>) -> Self {
-        from.map_bound(|trait_ref| TraitPredicate {
-            trait_ref,
-            polarity: PredicatePolarity::Positive,
-        })
-    }
-}
-
 impl<'tcx> UpcastFrom<TyCtxt<'tcx>, TraitPredicate<'tcx>> for Predicate<'tcx> {
     fn upcast_from(from: TraitPredicate<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
         PredicateKind::Clause(ClauseKind::Trait(from)).upcast(tcx)
diff --git a/compiler/rustc_middle/src/ty/print/mod.rs b/compiler/rustc_middle/src/ty/print/mod.rs
index 8a125c7fe28..e6feafea122 100644
--- a/compiler/rustc_middle/src/ty/print/mod.rs
+++ b/compiler/rustc_middle/src/ty/print/mod.rs
@@ -1,5 +1,3 @@
-use std::path::PathBuf;
-
 use hir::def::Namespace;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::sso::SsoHashSet;
@@ -8,7 +6,7 @@ use rustc_hir::def_id::{CrateNum, DefId, LocalDefId};
 use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
 use tracing::{debug, instrument, trace};
 
-use crate::ty::{self, GenericArg, ShortInstance, Ty, TyCtxt};
+use crate::ty::{self, GenericArg, Ty, TyCtxt};
 
 // `pretty` is a separate module only for organization.
 mod pretty;
@@ -21,18 +19,16 @@ pub trait Print<'tcx, P> {
     fn print(&self, p: &mut P) -> Result<(), PrintError>;
 }
 
-/// Interface for outputting user-facing "type-system entities"
-/// (paths, types, lifetimes, constants, etc.) as a side-effect
-/// (e.g. formatting, like `PrettyPrinter` implementors do) or by
-/// constructing some alternative representation (e.g. an AST),
-/// which the associated types allow passing through the methods.
-///
-/// For pretty-printing/formatting in particular, see `PrettyPrinter`.
-//
-// FIXME(eddyb) find a better name; this is more general than "printing".
+/// A trait that "prints" user-facing type system entities: paths, types, lifetimes, constants,
+/// etc. "Printing" here means building up a representation of the entity's path, usually as a
+/// `String` (e.g. "std::io::Read") or a `Vec<Symbol>` (e.g. `[sym::std, sym::io, sym::Read]`). The
+/// representation is built up by appending one or more pieces. The specific details included in
+/// the built-up representation depend on the purpose of the printer. The more advanced printers
+/// also rely on the `PrettyPrinter` sub-trait.
 pub trait Printer<'tcx>: Sized {
     fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
 
+    /// Appends a representation of an entity with a normal path, e.g. "std::io::Read".
     fn print_def_path(
         &mut self,
         def_id: DefId,
@@ -41,6 +37,7 @@ pub trait Printer<'tcx>: Sized {
         self.default_print_def_path(def_id, args)
     }
 
+    /// Like `print_def_path`, but for `DefPathData::Impl`.
     fn print_impl_path(
         &mut self,
         impl_def_id: DefId,
@@ -66,48 +63,67 @@ pub trait Printer<'tcx>: Sized {
         self.default_print_impl_path(impl_def_id, self_ty, impl_trait_ref)
     }
 
+    /// Appends a representation of a region.
     fn print_region(&mut self, region: ty::Region<'tcx>) -> Result<(), PrintError>;
 
+    /// Appends a representation of a type.
     fn print_type(&mut self, ty: Ty<'tcx>) -> Result<(), PrintError>;
 
+    /// Appends a representation of a list of `PolyExistentialPredicate`s.
     fn print_dyn_existential(
         &mut self,
         predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
     ) -> Result<(), PrintError>;
 
+    /// Appends a representation of a const.
     fn print_const(&mut self, ct: ty::Const<'tcx>) -> Result<(), PrintError>;
 
-    fn path_crate(&mut self, cnum: CrateNum) -> Result<(), PrintError>;
+    /// Appends a representation of a crate name, e.g. `std`, or even ``.
+    fn print_crate_name(&mut self, cnum: CrateNum) -> Result<(), PrintError>;
 
-    fn path_qualified(
+    /// Appends a representation of a (full or partial) simple path, in two parts. `print_prefix`,
+    /// when called, appends the representation of the leading segments. The rest of the method
+    /// appends the representation of the final segment, the details of which are in
+    /// `disambiguated_data`.
+    ///
+    /// E.g. `std::io` + `Read` -> `std::io::Read`.
+    fn print_path_with_simple(
         &mut self,
-        self_ty: Ty<'tcx>,
-        trait_ref: Option<ty::TraitRef<'tcx>>,
+        print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
+        disambiguated_data: &DisambiguatedDefPathData,
     ) -> Result<(), PrintError>;
 
-    fn path_append_impl(
+    /// Similar to `print_path_with_simple`, but the final segment is an `impl` segment.
+    ///
+    /// E.g. `slice` + `<impl [T]>` -> `slice::<impl [T]>`, which may then be further appended to,
+    /// giving a longer path representation such as `slice::<impl [T]>::to_vec_in::ConvertVec`.
+    fn print_path_with_impl(
         &mut self,
         print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
     ) -> Result<(), PrintError>;
 
-    fn path_append(
+    /// Appends a representation of a path ending in generic args, in two parts. `print_prefix`,
+    /// when called, appends the leading segments. The rest of the method appends the
+    /// representation of the generic args. (Some printers choose to skip appending the generic
+    /// args.)
+    ///
+    /// E.g. `ImplementsTraitForUsize` + `<usize>` -> `ImplementsTraitForUsize<usize>`.
+    fn print_path_with_generic_args(
         &mut self,
         print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
-        disambiguated_data: &DisambiguatedDefPathData,
+        args: &[GenericArg<'tcx>],
     ) -> Result<(), PrintError>;
 
-    fn path_generic_args(
+    /// Appends a representation of a qualified path segment, e.g. `<OsString as From<&T>>`.
+    /// If `trait_ref` is `None`, it may fall back to simpler forms, e.g. `<Vec<T>>` or just `Foo`.
+    fn print_path_with_qualified(
         &mut self,
-        print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
-        args: &[GenericArg<'tcx>],
+        self_ty: Ty<'tcx>,
+        trait_ref: Option<ty::TraitRef<'tcx>>,
     ) -> Result<(), PrintError>;
 
-    fn should_truncate(&mut self) -> bool {
-        false
-    }
-
     // Defaults (should not be overridden):
 
     #[instrument(skip(self), level = "debug")]
@@ -122,7 +138,7 @@ pub trait Printer<'tcx>: Sized {
         match key.disambiguated_data.data {
             DefPathData::CrateRoot => {
                 assert!(key.parent.is_none());
-                self.path_crate(def_id.krate)
+                self.print_crate_name(def_id.krate)
             }
 
             DefPathData::Impl => self.print_impl_path(def_id, args),
@@ -146,7 +162,7 @@ pub trait Printer<'tcx>: Sized {
                             )) = self.tcx().coroutine_kind(def_id)
                                 && args.len() > parent_args.len()
                             {
-                                return self.path_generic_args(
+                                return self.print_path_with_generic_args(
                                     |p| p.print_def_path(def_id, parent_args),
                                     &args[..parent_args.len() + 1][..1],
                                 );
@@ -168,7 +184,7 @@ pub trait Printer<'tcx>: Sized {
                         _ => {
                             if !generics.is_own_empty() && args.len() >= generics.count() {
                                 let args = generics.own_args_no_defaults(self.tcx(), args);
-                                return self.path_generic_args(
+                                return self.print_path_with_generic_args(
                                     |p| p.print_def_path(def_id, parent_args),
                                     args,
                                 );
@@ -184,7 +200,7 @@ pub trait Printer<'tcx>: Sized {
                         && self.tcx().generics_of(parent_def_id).parent_count == 0;
                 }
 
-                self.path_append(
+                self.print_path_with_simple(
                     |p: &mut Self| {
                         if trait_qualify_parent {
                             let trait_ref = ty::TraitRef::new(
@@ -192,7 +208,7 @@ pub trait Printer<'tcx>: Sized {
                                 parent_def_id,
                                 parent_args.iter().copied(),
                             );
-                            p.path_qualified(trait_ref.self_ty(), Some(trait_ref))
+                            p.print_path_with_qualified(trait_ref.self_ty(), Some(trait_ref))
                         } else {
                             p.print_def_path(parent_def_id, parent_args)
                         }
@@ -235,11 +251,15 @@ pub trait Printer<'tcx>: Sized {
             // If the impl is not co-located with either self-type or
             // trait-type, then fallback to a format that identifies
             // the module more clearly.
-            self.path_append_impl(|p| p.print_def_path(parent_def_id, &[]), self_ty, impl_trait_ref)
+            self.print_path_with_impl(
+                |p| p.print_def_path(parent_def_id, &[]),
+                self_ty,
+                impl_trait_ref,
+            )
         } else {
             // Otherwise, try to give a good form that would be valid language
             // syntax. Preferably using associated item notation.
-            self.path_qualified(self_ty, impl_trait_ref)
+            self.print_path_with_qualified(self_ty, impl_trait_ref)
         }
     }
 }
@@ -317,6 +337,43 @@ impl<'tcx, P: Printer<'tcx>> Print<'tcx, P> for Ty<'tcx> {
     }
 }
 
+impl<'tcx, P: Printer<'tcx> + std::fmt::Write> Print<'tcx, P> for ty::Instance<'tcx> {
+    fn print(&self, cx: &mut P) -> Result<(), PrintError> {
+        cx.print_def_path(self.def_id(), self.args)?;
+        match self.def {
+            ty::InstanceKind::Item(_) => {}
+            ty::InstanceKind::VTableShim(_) => cx.write_str(" - shim(vtable)")?,
+            ty::InstanceKind::ReifyShim(_, None) => cx.write_str(" - shim(reify)")?,
+            ty::InstanceKind::ReifyShim(_, Some(ty::ReifyReason::FnPtr)) => {
+                cx.write_str(" - shim(reify-fnptr)")?
+            }
+            ty::InstanceKind::ReifyShim(_, Some(ty::ReifyReason::Vtable)) => {
+                cx.write_str(" - shim(reify-vtable)")?
+            }
+            ty::InstanceKind::ThreadLocalShim(_) => cx.write_str(" - shim(tls)")?,
+            ty::InstanceKind::Intrinsic(_) => cx.write_str(" - intrinsic")?,
+            ty::InstanceKind::Virtual(_, num) => cx.write_str(&format!(" - virtual#{num}"))?,
+            ty::InstanceKind::FnPtrShim(_, ty) => cx.write_str(&format!(" - shim({ty})"))?,
+            ty::InstanceKind::ClosureOnceShim { .. } => cx.write_str(" - shim")?,
+            ty::InstanceKind::ConstructCoroutineInClosureShim { .. } => cx.write_str(" - shim")?,
+            ty::InstanceKind::DropGlue(_, None) => cx.write_str(" - shim(None)")?,
+            ty::InstanceKind::DropGlue(_, Some(ty)) => {
+                cx.write_str(&format!(" - shim(Some({ty}))"))?
+            }
+            ty::InstanceKind::CloneShim(_, ty) => cx.write_str(&format!(" - shim({ty})"))?,
+            ty::InstanceKind::FnPtrAddrShim(_, ty) => cx.write_str(&format!(" - shim({ty})"))?,
+            ty::InstanceKind::FutureDropPollShim(_, proxy_ty, impl_ty) => {
+                cx.write_str(&format!(" - dropshim({proxy_ty}-{impl_ty})"))?
+            }
+            ty::InstanceKind::AsyncDropGlue(_, ty) => cx.write_str(&format!(" - shim({ty})"))?,
+            ty::InstanceKind::AsyncDropGlueCtorShim(_, ty) => {
+                cx.write_str(&format!(" - shim(Some({ty}))"))?
+            }
+        };
+        Ok(())
+    }
+}
+
 impl<'tcx, P: Printer<'tcx>> Print<'tcx, P> for &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>> {
     fn print(&self, p: &mut P) -> Result<(), PrintError> {
         p.print_dyn_existential(self)
@@ -356,31 +413,3 @@ where
         with_no_trimmed_paths!(Self::print(t, fmt))
     }
 }
-
-/// Format instance name that is already known to be too long for rustc.
-/// Show only the first 2 types if it is longer than 32 characters to avoid blasting
-/// the user's terminal with thousands of lines of type-name.
-///
-/// If the type name is longer than before+after, it will be written to a file.
-pub fn shrunk_instance_name<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    instance: ty::Instance<'tcx>,
-) -> (String, Option<PathBuf>) {
-    let s = instance.to_string();
-
-    // Only use the shrunk version if it's really shorter.
-    // This also avoids the case where before and after slices overlap.
-    if s.chars().nth(33).is_some() {
-        let shrunk = format!("{}", ShortInstance(instance, 4));
-        if shrunk == s {
-            return (s, None);
-        }
-
-        let path = tcx.output_filenames(()).temp_path_for_diagnostic("long-type.txt");
-        let written_to_path = std::fs::write(&path, s).ok().map(|_| path);
-
-        (shrunk, written_to_path)
-    } else {
-        (s, None)
-    }
-}
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index b381d62be47..74caee7336a 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -245,7 +245,7 @@ impl<'tcx> RegionHighlightMode<'tcx> {
 /// Trait for printers that pretty-print using `fmt::Write` to the printer.
 pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
     /// Like `print_def_path` but for value paths.
-    fn print_value_path(
+    fn pretty_print_value_path(
         &mut self,
         def_id: DefId,
         args: &'tcx [GenericArg<'tcx>],
@@ -253,7 +253,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
         self.print_def_path(def_id, args)
     }
 
-    fn print_in_binder<T>(&mut self, value: &ty::Binder<'tcx, T>) -> Result<(), PrintError>
+    fn pretty_print_in_binder<T>(&mut self, value: &ty::Binder<'tcx, T>) -> Result<(), PrintError>
     where
         T: Print<'tcx, Self> + TypeFoldable<TyCtxt<'tcx>>,
     {
@@ -333,10 +333,14 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
         f: impl FnOnce(&mut Self) -> Result<(), PrintError>,
     ) -> Result<(), PrintError>;
 
-    /// Returns `true` if the region should be printed in
-    /// optional positions, e.g., `&'a T` or `dyn Tr + 'b`.
-    /// This is typically the case for all non-`'_` regions.
-    fn should_print_region(&self, region: ty::Region<'tcx>) -> bool;
+    fn should_truncate(&mut self) -> bool {
+        false
+    }
+
+    /// Returns `true` if the region should be printed in optional positions,
+    /// e.g., `&'a T` or `dyn Tr + 'b`. (Regions like the one in `Cow<'static, T>`
+    /// will always be printed.)
+    fn should_print_optional_region(&self, region: ty::Region<'tcx>) -> bool;
 
     fn reset_type_limit(&mut self) {}
 
@@ -470,7 +474,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
         // path to the crate followed by the path to the item within the crate.
         if let Some(cnum) = def_id.as_crate_root() {
             if cnum == LOCAL_CRATE {
-                self.path_crate(cnum)?;
+                self.print_crate_name(cnum)?;
                 return Ok(true);
             }
 
@@ -494,7 +498,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                         // or avoid ending up with `ExternCrateSource::Extern`,
                         // for the injected `std`/`core`.
                         if span.is_dummy() {
-                            self.path_crate(cnum)?;
+                            self.print_crate_name(cnum)?;
                             return Ok(true);
                         }
 
@@ -508,13 +512,13 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                         return Ok(true);
                     }
                     (ExternCrateSource::Path, LOCAL_CRATE) => {
-                        self.path_crate(cnum)?;
+                        self.print_crate_name(cnum)?;
                         return Ok(true);
                     }
                     _ => {}
                 },
                 None => {
-                    self.path_crate(cnum)?;
+                    self.print_crate_name(cnum)?;
                     return Ok(true);
                 }
             }
@@ -624,7 +628,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
             return Ok(false);
         }
         callers.push(visible_parent);
-        // HACK(eddyb) this bypasses `path_append`'s prefix printing to avoid
+        // HACK(eddyb) this bypasses `print_path_with_simple`'s prefix printing to avoid
         // knowing ahead of time whether the entire path will succeed or not.
         // To support printers that do not implement `PrettyPrinter`, a `Vec` or
         // linked list on the stack would need to be built, before any printing.
@@ -633,11 +637,14 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
             true => {}
         }
         callers.pop();
-        self.path_append(|_| Ok(()), &DisambiguatedDefPathData { data, disambiguator: 0 })?;
+        self.print_path_with_simple(
+            |_| Ok(()),
+            &DisambiguatedDefPathData { data, disambiguator: 0 },
+        )?;
         Ok(true)
     }
 
-    fn pretty_path_qualified(
+    fn pretty_print_path_with_qualified(
         &mut self,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
@@ -672,7 +679,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
         })
     }
 
-    fn pretty_path_append_impl(
+    fn pretty_print_path_with_impl(
         &mut self,
         print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
         self_ty: Ty<'tcx>,
@@ -710,7 +717,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
             }
             ty::Ref(r, ty, mutbl) => {
                 write!(self, "&")?;
-                if self.should_print_region(r) {
+                if self.should_print_optional_region(r) {
                     r.print(self)?;
                     write!(self, " ")?;
                 }
@@ -739,7 +746,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                     }
                     sig.print(self)?;
                     write!(self, " {{")?;
-                    self.print_value_path(def_id, args)?;
+                    self.pretty_print_value_path(def_id, args)?;
                     write!(self, "}}")?;
                 }
             }
@@ -778,7 +785,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
             },
             ty::Adt(def, args) => self.print_def_path(def.did(), args)?,
             ty::Dynamic(data, r, repr) => {
-                let print_r = self.should_print_region(r);
+                let print_r = self.should_print_optional_region(r);
                 if print_r {
                     write!(self, "(")?;
                 }
@@ -1308,10 +1315,10 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
         alias_ty: ty::AliasTerm<'tcx>,
     ) -> Result<(), PrintError> {
         let def_key = self.tcx().def_key(alias_ty.def_id);
-        self.path_generic_args(
+        self.print_path_with_generic_args(
             |p| {
-                p.path_append(
-                    |p| p.path_qualified(alias_ty.self_ty(), None),
+                p.print_path_with_simple(
+                    |p| p.print_path_with_qualified(alias_ty.self_ty(), None),
                     &def_key.disambiguated_data,
                 )
             },
@@ -1386,7 +1393,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                     if let ty::Tuple(tys) = principal.args.type_at(0).kind() {
                         let mut projections = predicates.projection_bounds();
                         if let (Some(proj), None) = (projections.next(), projections.next()) {
-                            p.pretty_fn_sig(
+                            p.pretty_print_fn_sig(
                                 tys,
                                 false,
                                 proj.skip_binder().term.as_type().expect("Return type was a const"),
@@ -1396,7 +1403,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                     }
                 }
 
-                // HACK(eddyb) this duplicates `FmtPrinter`'s `path_generic_args`,
+                // HACK(eddyb) this duplicates `FmtPrinter`'s `print_path_with_generic_args`,
                 // in order to place the projections inside the `<...>`.
                 if !resugared {
                     let principal_with_self =
@@ -1488,7 +1495,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
         Ok(())
     }
 
-    fn pretty_fn_sig(
+    fn pretty_print_fn_sig(
         &mut self,
         inputs: &[Ty<'tcx>],
         c_variadic: bool,
@@ -1525,7 +1532,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
             ty::ConstKind::Unevaluated(ty::UnevaluatedConst { def, args }) => {
                 match self.tcx().def_kind(def) {
                     DefKind::Const | DefKind::AssocConst => {
-                        self.print_value_path(def, args)?;
+                        self.pretty_print_value_path(def, args)?;
                     }
                     DefKind::AnonConst => {
                         if def.is_local()
@@ -1534,13 +1541,13 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                         {
                             write!(self, "{snip}")?;
                         } else {
-                            // Do not call `print_value_path` as if a parent of this anon const is
-                            // an impl it will attempt to print out the impl trait ref i.e. `<T as
-                            // Trait>::{constant#0}`. This would cause printing to enter an
-                            // infinite recursion if the anon const is in the self type i.e.
-                            // `impl<T: Default> Default for [T; 32 - 1 - 1 - 1] {` where we would
-                            // try to print
-                            // `<[T; /* print constant#0 again */] as // Default>::{constant#0}`.
+                            // Do not call `pretty_print_value_path` as if a parent of this anon
+                            // const is an impl it will attempt to print out the impl trait ref
+                            // i.e. `<T as Trait>::{constant#0}`. This would cause printing to
+                            // enter an infinite recursion if the anon const is in the self type
+                            // i.e. `impl<T: Default> Default for [T; 32 - 1 - 1 - 1] {` where we
+                            // would try to print `<[T; /* print constant#0 again */] as //
+                            // Default>::{constant#0}`.
                             write!(
                                 self,
                                 "{}::{}",
@@ -1742,7 +1749,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                     self.tcx().try_get_global_alloc(prov.alloc_id())
                 {
                     self.typed_value(
-                        |this| this.print_value_path(instance.def_id(), instance.args),
+                        |this| this.pretty_print_value_path(instance.def_id(), instance.args),
                         |this| this.print_type(ty),
                         " as ",
                     )?;
@@ -1936,7 +1943,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                         let variant_idx =
                             contents.variant.expect("destructed const of adt without variant idx");
                         let variant_def = &def.variant(variant_idx);
-                        self.print_value_path(variant_def.def_id, args)?;
+                        self.pretty_print_value_path(variant_def.def_id, args)?;
                         match variant_def.ctor_kind() {
                             Some(CtorKind::Const) => {}
                             Some(CtorKind::Fn) => {
@@ -1972,7 +1979,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
             }
             (_, ty::FnDef(def_id, args)) => {
                 // Never allowed today, but we still encounter them in invalid const args.
-                self.print_value_path(def_id, args)?;
+                self.pretty_print_value_path(def_id, args)?;
                 return Ok(());
             }
             // FIXME(oli-obk): also pretty print arrays and other aggregate constants by reading
@@ -1993,7 +2000,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
         Ok(())
     }
 
-    fn pretty_closure_as_impl(
+    fn pretty_print_closure_as_impl(
         &mut self,
         closure: ty::ClosureArgs<TyCtxt<'tcx>>,
     ) -> Result<(), PrintError> {
@@ -2131,8 +2138,6 @@ impl<'a, 'tcx> FmtPrinter<'a, 'tcx> {
     }
 }
 
-// HACK(eddyb) get rid of `def_path_str` and/or pass `Namespace` explicitly always
-// (but also some things just print a `DefId` generally so maybe we need this?)
 fn guess_def_namespace(tcx: TyCtxt<'_>, def_id: DefId) -> Namespace {
     match tcx.def_key(def_id).disambiguated_data.data {
         DefPathData::TypeNs(..) | DefPathData::CrateRoot | DefPathData::OpaqueTy => {
@@ -2157,6 +2162,7 @@ impl<'t> TyCtxt<'t> {
         self.def_path_str_with_args(def_id, &[])
     }
 
+    /// For this one we determine the appropriate namespace for the `def_id`.
     pub fn def_path_str_with_args(
         self,
         def_id: impl IntoQueryParam<DefId>,
@@ -2169,16 +2175,17 @@ impl<'t> TyCtxt<'t> {
         FmtPrinter::print_string(self, ns, |p| p.print_def_path(def_id, args)).unwrap()
     }
 
+    /// For this one we always use value namespace.
     pub fn value_path_str_with_args(
         self,
         def_id: impl IntoQueryParam<DefId>,
         args: &'t [GenericArg<'t>],
     ) -> String {
         let def_id = def_id.into_query_param();
-        let ns = guess_def_namespace(self, def_id);
+        let ns = Namespace::ValueNS;
         debug!("value_path_str: def_id={:?}, ns={:?}", def_id, ns);
 
-        FmtPrinter::print_string(self, ns, |p| p.print_value_path(def_id, args)).unwrap()
+        FmtPrinter::print_string(self, ns, |p| p.print_def_path(def_id, args)).unwrap()
     }
 }
 
@@ -2230,7 +2237,7 @@ impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
 
                 self.print_def_path(parent_def_id, &[])?;
 
-                // HACK(eddyb) copy of `path_append` to avoid
+                // HACK(eddyb) copy of `print_path_with_simple` to avoid
                 // constructing a `DisambiguatedDefPathData`.
                 if !self.empty_path {
                     write!(self, "::")?;
@@ -2295,10 +2302,6 @@ impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
         }
     }
 
-    fn should_truncate(&mut self) -> bool {
-        !self.type_length_limit.value_within_limit(self.printed_type_count)
-    }
-
     fn print_dyn_existential(
         &mut self,
         predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
@@ -2310,7 +2313,7 @@ impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
         self.pretty_print_const(ct, false)
     }
 
-    fn path_crate(&mut self, cnum: CrateNum) -> Result<(), PrintError> {
+    fn print_crate_name(&mut self, cnum: CrateNum) -> Result<(), PrintError> {
         self.empty_path = true;
         if cnum == LOCAL_CRATE {
             if self.tcx.sess.at_least_rust_2018() {
@@ -2327,23 +2330,23 @@ impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
         Ok(())
     }
 
-    fn path_qualified(
+    fn print_path_with_qualified(
         &mut self,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
     ) -> Result<(), PrintError> {
-        self.pretty_path_qualified(self_ty, trait_ref)?;
+        self.pretty_print_path_with_qualified(self_ty, trait_ref)?;
         self.empty_path = false;
         Ok(())
     }
 
-    fn path_append_impl(
+    fn print_path_with_impl(
         &mut self,
         print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
     ) -> Result<(), PrintError> {
-        self.pretty_path_append_impl(
+        self.pretty_print_path_with_impl(
             |p| {
                 print_prefix(p)?;
                 if !p.empty_path {
@@ -2359,7 +2362,7 @@ impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
         Ok(())
     }
 
-    fn path_append(
+    fn print_path_with_simple(
         &mut self,
         print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
         disambiguated_data: &DisambiguatedDefPathData,
@@ -2390,7 +2393,7 @@ impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
         Ok(())
     }
 
-    fn path_generic_args(
+    fn print_path_with_generic_args(
         &mut self,
         print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
         args: &[GenericArg<'tcx>],
@@ -2421,7 +2424,7 @@ impl<'tcx> PrettyPrinter<'tcx> for FmtPrinter<'_, 'tcx> {
         self.0.const_infer_name_resolver.as_ref().and_then(|func| func(id))
     }
 
-    fn print_value_path(
+    fn pretty_print_value_path(
         &mut self,
         def_id: DefId,
         args: &'tcx [GenericArg<'tcx>],
@@ -2433,7 +2436,7 @@ impl<'tcx> PrettyPrinter<'tcx> for FmtPrinter<'_, 'tcx> {
         Ok(())
     }
 
-    fn print_in_binder<T>(&mut self, value: &ty::Binder<'tcx, T>) -> Result<(), PrintError>
+    fn pretty_print_in_binder<T>(&mut self, value: &ty::Binder<'tcx, T>) -> Result<(), PrintError>
     where
         T: Print<'tcx, Self> + TypeFoldable<TyCtxt<'tcx>>,
     {
@@ -2487,7 +2490,11 @@ impl<'tcx> PrettyPrinter<'tcx> for FmtPrinter<'_, 'tcx> {
         Ok(())
     }
 
-    fn should_print_region(&self, region: ty::Region<'tcx>) -> bool {
+    fn should_truncate(&mut self) -> bool {
+        !self.type_length_limit.value_within_limit(self.printed_type_count)
+    }
+
+    fn should_print_optional_region(&self, region: ty::Region<'tcx>) -> bool {
         let highlight = self.region_highlight_mode;
         if highlight.region_highlighted(region).is_some() {
             return true;
@@ -2892,7 +2899,7 @@ where
     T: Print<'tcx, P> + TypeFoldable<TyCtxt<'tcx>>,
 {
     fn print(&self, p: &mut P) -> Result<(), PrintError> {
-        p.print_in_binder(self)
+        p.pretty_print_in_binder(self)
     }
 }
 
@@ -2987,7 +2994,7 @@ impl<'tcx> ty::Binder<'tcx, ty::TraitRef<'tcx>> {
     }
 }
 
-#[derive(Copy, Clone, TypeFoldable, TypeVisitable, Lift)]
+#[derive(Copy, Clone, TypeFoldable, TypeVisitable, Lift, Hash)]
 pub struct TraitPredPrintModifiersAndPath<'tcx>(ty::TraitPredicate<'tcx>);
 
 impl<'tcx> fmt::Debug for TraitPredPrintModifiersAndPath<'tcx> {
@@ -3090,7 +3097,7 @@ define_print! {
         }
 
         write!(p, "fn")?;
-        p.pretty_fn_sig(self.inputs(), self.c_variadic, self.output())?;
+        p.pretty_print_fn_sig(self.inputs(), self.c_variadic, self.output())?;
     }
 
     ty::TraitRef<'tcx> {
@@ -3225,7 +3232,7 @@ define_print! {
         // The args don't contain the self ty (as it has been erased) but the corresp.
         // generics do as the trait always has a self ty param. We need to offset.
         let args = &self.args[p.tcx().generics_of(self.def_id).parent_count - 1..];
-        p.path_generic_args(|p| write!(p, "{name}"), args)?;
+        p.print_path_with_generic_args(|p| write!(p, "{name}"), args)?;
         write!(p, " = ")?;
         self.term.print(p)?;
     }
@@ -3314,7 +3321,7 @@ define_print_and_forward_display! {
     }
 
     PrintClosureAsImpl<'tcx> {
-        p.pretty_closure_as_impl(self.closure)?;
+        p.pretty_print_closure_as_impl(self.closure)?;
     }
 
     ty::ParamTy {
diff --git a/compiler/rustc_middle/src/ty/rvalue_scopes.rs b/compiler/rustc_middle/src/ty/rvalue_scopes.rs
index 9bf6e3a7590..7dfe2d28051 100644
--- a/compiler/rustc_middle/src/ty/rvalue_scopes.rs
+++ b/compiler/rustc_middle/src/ty/rvalue_scopes.rs
@@ -44,7 +44,7 @@ impl RvalueScopes {
                     debug!("temporary_scope({expr_id:?}) = {id:?} [enclosing]");
                     return (Some(id), backwards_incompatible);
                 }
-                ScopeData::IfThenRescope => {
+                ScopeData::IfThenRescope | ScopeData::MatchGuard => {
                     debug!("temporary_scope({expr_id:?}) = {p:?} [enclosing]");
                     return (Some(p), backwards_incompatible);
                 }
diff --git a/compiler/rustc_middle/src/ty/structural_impls.rs b/compiler/rustc_middle/src/ty/structural_impls.rs
index 0e2aff6f9bd..89ef46b1ae5 100644
--- a/compiler/rustc_middle/src/ty/structural_impls.rs
+++ b/compiler/rustc_middle/src/ty/structural_impls.rs
@@ -12,7 +12,6 @@ use rustc_hir::def_id::LocalDefId;
 use rustc_span::source_map::Spanned;
 use rustc_type_ir::{ConstKind, TypeFolder, VisitorResult, try_visit};
 
-use super::print::PrettyPrinter;
 use super::{GenericArg, GenericArgKind, Pattern, Region};
 use crate::mir::PlaceElem;
 use crate::ty::print::{FmtPrinter, Printer, with_no_trimmed_paths};
@@ -168,15 +167,11 @@ impl<'tcx> fmt::Debug for ty::Const<'tcx> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         // If this is a value, we spend some effort to make it look nice.
         if let ConstKind::Value(cv) = self.kind() {
-            return ty::tls::with(move |tcx| {
-                let cv = tcx.lift(cv).unwrap();
-                let mut p = FmtPrinter::new(tcx, Namespace::ValueNS);
-                p.pretty_print_const_valtree(cv, /*print_ty*/ true)?;
-                f.write_str(&p.into_buffer())
-            });
+            write!(f, "{}", cv)
+        } else {
+            // Fall back to something verbose.
+            write!(f, "{:?}", self.kind())
         }
-        // Fall back to something verbose.
-        write!(f, "{:?}", self.kind())
     }
 }
 
diff --git a/compiler/rustc_mir_build/messages.ftl b/compiler/rustc_mir_build/messages.ftl
index 287639de663..83fbcb30dd9 100644
--- a/compiler/rustc_mir_build/messages.ftl
+++ b/compiler/rustc_mir_build/messages.ftl
@@ -121,8 +121,6 @@ mir_build_deref_raw_pointer_requires_unsafe_unsafe_op_in_unsafe_fn_allowed =
     .note = raw pointers may be null, dangling or unaligned; they can violate aliasing rules and cause data races: all of these are undefined behavior
     .label = dereference of raw pointer
 
-mir_build_exceeds_mcdc_condition_limit = number of conditions in decision ({$num_conditions}) exceeds limit ({$max_conditions}), so MC/DC analysis will not count this expression
-
 mir_build_extern_static_requires_unsafe =
     use of extern static is unsafe and requires unsafe block
     .note = extern statics are not controlled by the Rust type system: invalid data, aliasing violations or data races will cause undefined behavior
diff --git a/compiler/rustc_mir_build/src/builder/block.rs b/compiler/rustc_mir_build/src/builder/block.rs
index a71196f79d7..566d89f4269 100644
--- a/compiler/rustc_mir_build/src/builder/block.rs
+++ b/compiler/rustc_mir_build/src/builder/block.rs
@@ -6,7 +6,7 @@ use rustc_span::Span;
 use tracing::debug;
 
 use crate::builder::ForGuard::OutsideGuard;
-use crate::builder::matches::{DeclareLetBindings, EmitStorageLive, ScheduleDrops};
+use crate::builder::matches::{DeclareLetBindings, ScheduleDrops};
 use crate::builder::{BlockAnd, BlockAndExtension, BlockFrame, Builder};
 
 impl<'a, 'tcx> Builder<'a, 'tcx> {
@@ -199,15 +199,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                             None,
                             Some((Some(&destination), initializer_span)),
                         );
-                        this.visit_primary_bindings(pattern, &mut |this, node, span| {
-                            this.storage_live_binding(
-                                block,
-                                node,
-                                span,
-                                OutsideGuard,
-                                ScheduleDrops::Yes,
-                            );
-                        });
                         let else_block_span = this.thir[*else_block].span;
                         let (matching, failure) =
                             this.in_if_then_scope(last_remainder_scope, else_block_span, |this| {
@@ -218,7 +209,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                                     None,
                                     initializer_span,
                                     DeclareLetBindings::No,
-                                    EmitStorageLive::No,
                                 )
                             });
                         matching.and(failure)
diff --git a/compiler/rustc_mir_build/src/builder/coverageinfo.rs b/compiler/rustc_mir_build/src/builder/coverageinfo.rs
index aa43b273cff..14199c20921 100644
--- a/compiler/rustc_mir_build/src/builder/coverageinfo.rs
+++ b/compiler/rustc_mir_build/src/builder/coverageinfo.rs
@@ -8,11 +8,8 @@ use rustc_middle::thir::{ExprId, ExprKind, Pat, Thir};
 use rustc_middle::ty::TyCtxt;
 use rustc_span::def_id::LocalDefId;
 
-use crate::builder::coverageinfo::mcdc::MCDCInfoBuilder;
 use crate::builder::{Builder, CFG};
 
-mod mcdc;
-
 /// Collects coverage-related information during MIR building, to eventually be
 /// turned into a function's [`CoverageInfoHi`] when MIR building is complete.
 pub(crate) struct CoverageInfoBuilder {
@@ -23,8 +20,6 @@ pub(crate) struct CoverageInfoBuilder {
 
     /// Present if branch coverage is enabled.
     branch_info: Option<BranchInfo>,
-    /// Present if MC/DC coverage is enabled.
-    mcdc_info: Option<MCDCInfoBuilder>,
 }
 
 #[derive(Default)]
@@ -83,7 +78,6 @@ impl CoverageInfoBuilder {
             nots: FxHashMap::default(),
             markers: BlockMarkerGen::default(),
             branch_info: tcx.sess.instrument_coverage_branch().then(BranchInfo::default),
-            mcdc_info: tcx.sess.instrument_coverage_mcdc().then(MCDCInfoBuilder::new),
         })
     }
 
@@ -135,26 +129,11 @@ impl CoverageInfoBuilder {
 
     fn register_two_way_branch<'tcx>(
         &mut self,
-        tcx: TyCtxt<'tcx>,
         cfg: &mut CFG<'tcx>,
         source_info: SourceInfo,
         true_block: BasicBlock,
         false_block: BasicBlock,
     ) {
-        // Separate path for handling branches when MC/DC is enabled.
-        if let Some(mcdc_info) = self.mcdc_info.as_mut() {
-            let inject_block_marker =
-                |source_info, block| self.markers.inject_block_marker(cfg, source_info, block);
-            mcdc_info.visit_evaluated_condition(
-                tcx,
-                source_info,
-                true_block,
-                false_block,
-                inject_block_marker,
-            );
-            return;
-        }
-
         // Bail out if branch coverage is not enabled.
         let Some(branch_info) = self.branch_info.as_mut() else { return };
 
@@ -169,23 +148,14 @@ impl CoverageInfoBuilder {
     }
 
     pub(crate) fn into_done(self) -> Box<CoverageInfoHi> {
-        let Self { nots: _, markers: BlockMarkerGen { num_block_markers }, branch_info, mcdc_info } =
-            self;
+        let Self { nots: _, markers: BlockMarkerGen { num_block_markers }, branch_info } = self;
 
         let branch_spans =
             branch_info.map(|branch_info| branch_info.branch_spans).unwrap_or_default();
 
-        let (mcdc_spans, mcdc_degraded_branch_spans) =
-            mcdc_info.map(MCDCInfoBuilder::into_done).unwrap_or_default();
-
         // For simplicity, always return an info struct (without Option), even
         // if there's nothing interesting in it.
-        Box::new(CoverageInfoHi {
-            num_block_markers,
-            branch_spans,
-            mcdc_degraded_branch_spans,
-            mcdc_spans,
-        })
+        Box::new(CoverageInfoHi { num_block_markers, branch_spans })
     }
 }
 
@@ -238,14 +208,7 @@ impl<'tcx> Builder<'_, 'tcx> {
             mir::TerminatorKind::if_(mir::Operand::Copy(place), true_block, false_block),
         );
 
-        // Separate path for handling branches when MC/DC is enabled.
-        coverage_info.register_two_way_branch(
-            self.tcx,
-            &mut self.cfg,
-            source_info,
-            true_block,
-            false_block,
-        );
+        coverage_info.register_two_way_branch(&mut self.cfg, source_info, true_block, false_block);
 
         let join_block = self.cfg.start_new_block();
         self.cfg.goto(true_block, source_info, join_block);
@@ -276,13 +239,7 @@ impl<'tcx> Builder<'_, 'tcx> {
 
         let source_info = SourceInfo { span: self.thir[expr_id].span, scope: self.source_scope };
 
-        coverage_info.register_two_way_branch(
-            self.tcx,
-            &mut self.cfg,
-            source_info,
-            then_block,
-            else_block,
-        );
+        coverage_info.register_two_way_branch(&mut self.cfg, source_info, then_block, else_block);
     }
 
     /// If branch coverage is enabled, inject marker statements into `true_block`
@@ -299,12 +256,6 @@ impl<'tcx> Builder<'_, 'tcx> {
         let Some(coverage_info) = self.coverage_info.as_mut() else { return };
 
         let source_info = SourceInfo { span: pattern.span, scope: self.source_scope };
-        coverage_info.register_two_way_branch(
-            self.tcx,
-            &mut self.cfg,
-            source_info,
-            true_block,
-            false_block,
-        );
+        coverage_info.register_two_way_branch(&mut self.cfg, source_info, true_block, false_block);
     }
 }
diff --git a/compiler/rustc_mir_build/src/builder/coverageinfo/mcdc.rs b/compiler/rustc_mir_build/src/builder/coverageinfo/mcdc.rs
deleted file mode 100644
index 6b4871dc1fc..00000000000
--- a/compiler/rustc_mir_build/src/builder/coverageinfo/mcdc.rs
+++ /dev/null
@@ -1,295 +0,0 @@
-use std::collections::VecDeque;
-
-use rustc_middle::bug;
-use rustc_middle::mir::coverage::{
-    BlockMarkerId, ConditionId, ConditionInfo, MCDCBranchSpan, MCDCDecisionSpan,
-};
-use rustc_middle::mir::{BasicBlock, SourceInfo};
-use rustc_middle::thir::LogicalOp;
-use rustc_middle::ty::TyCtxt;
-use rustc_span::Span;
-
-use crate::builder::Builder;
-use crate::errors::MCDCExceedsConditionLimit;
-
-/// LLVM uses `i16` to represent condition id. Hence `i16::MAX` is the hard limit for number of
-/// conditions in a decision.
-const MAX_CONDITIONS_IN_DECISION: usize = i16::MAX as usize;
-
-#[derive(Default)]
-struct MCDCDecisionCtx {
-    /// To construct condition evaluation tree.
-    decision_stack: VecDeque<ConditionInfo>,
-    processing_decision: Option<MCDCDecisionSpan>,
-    conditions: Vec<MCDCBranchSpan>,
-}
-
-struct MCDCState {
-    decision_ctx_stack: Vec<MCDCDecisionCtx>,
-}
-
-impl MCDCState {
-    fn new() -> Self {
-        Self { decision_ctx_stack: vec![MCDCDecisionCtx::default()] }
-    }
-
-    /// Decision depth is given as a u16 to reduce the size of the `CoverageKind`,
-    /// as it is very unlikely that the depth ever reaches 2^16.
-    #[inline]
-    fn decision_depth(&self) -> u16 {
-        match u16::try_from(self.decision_ctx_stack.len())
-            .expect(
-                "decision depth did not fit in u16, this is likely to be an instrumentation error",
-            )
-            .checked_sub(1)
-        {
-            Some(d) => d,
-            None => bug!("Unexpected empty decision stack"),
-        }
-    }
-
-    // At first we assign ConditionIds for each sub expression.
-    // If the sub expression is composite, re-assign its ConditionId to its LHS and generate a new ConditionId for its RHS.
-    //
-    // Example: "x = (A && B) || (C && D) || (D && F)"
-    //
-    //      Visit Depth1:
-    //              (A && B) || (C && D) || (D && F)
-    //              ^-------LHS--------^    ^-RHS--^
-    //                      ID=1              ID=2
-    //
-    //      Visit LHS-Depth2:
-    //              (A && B) || (C && D)
-    //              ^-LHS--^    ^-RHS--^
-    //                ID=1        ID=3
-    //
-    //      Visit LHS-Depth3:
-    //               (A && B)
-    //               LHS   RHS
-    //               ID=1  ID=4
-    //
-    //      Visit RHS-Depth3:
-    //                         (C && D)
-    //                         LHS   RHS
-    //                         ID=3  ID=5
-    //
-    //      Visit RHS-Depth2:              (D && F)
-    //                                     LHS   RHS
-    //                                     ID=2  ID=6
-    //
-    //      Visit Depth1:
-    //              (A && B)  || (C && D)  || (D && F)
-    //              ID=1  ID=4   ID=3  ID=5   ID=2  ID=6
-    //
-    // A node ID of '0' always means MC/DC isn't being tracked.
-    //
-    // If a "next" node ID is '0', it means it's the end of the test vector.
-    //
-    // As the compiler tracks expression in pre-order, we can ensure that condition info of parents are always properly assigned when their children are visited.
-    // - If the op is AND, the "false_next" of LHS and RHS should be the parent's "false_next". While "true_next" of the LHS is the RHS, the "true next" of RHS is the parent's "true_next".
-    // - If the op is OR, the "true_next" of LHS and RHS should be the parent's "true_next". While "false_next" of the LHS is the RHS, the "false next" of RHS is the parent's "false_next".
-    fn record_conditions(&mut self, op: LogicalOp, span: Span) {
-        let decision_depth = self.decision_depth();
-        let Some(decision_ctx) = self.decision_ctx_stack.last_mut() else {
-            bug!("Unexpected empty decision_ctx_stack")
-        };
-        let decision = match decision_ctx.processing_decision.as_mut() {
-            Some(decision) => {
-                decision.span = decision.span.to(span);
-                decision
-            }
-            None => decision_ctx.processing_decision.insert(MCDCDecisionSpan {
-                span,
-                num_conditions: 0,
-                end_markers: vec![],
-                decision_depth,
-            }),
-        };
-
-        let parent_condition = decision_ctx.decision_stack.pop_back().unwrap_or_else(|| {
-            assert_eq!(
-                decision.num_conditions, 0,
-                "decision stack must be empty only for empty decision"
-            );
-            decision.num_conditions += 1;
-            ConditionInfo {
-                condition_id: ConditionId::START,
-                true_next_id: None,
-                false_next_id: None,
-            }
-        });
-        let lhs_id = parent_condition.condition_id;
-
-        let rhs_condition_id = ConditionId::from(decision.num_conditions);
-        decision.num_conditions += 1;
-        let (lhs, rhs) = match op {
-            LogicalOp::And => {
-                let lhs = ConditionInfo {
-                    condition_id: lhs_id,
-                    true_next_id: Some(rhs_condition_id),
-                    false_next_id: parent_condition.false_next_id,
-                };
-                let rhs = ConditionInfo {
-                    condition_id: rhs_condition_id,
-                    true_next_id: parent_condition.true_next_id,
-                    false_next_id: parent_condition.false_next_id,
-                };
-                (lhs, rhs)
-            }
-            LogicalOp::Or => {
-                let lhs = ConditionInfo {
-                    condition_id: lhs_id,
-                    true_next_id: parent_condition.true_next_id,
-                    false_next_id: Some(rhs_condition_id),
-                };
-                let rhs = ConditionInfo {
-                    condition_id: rhs_condition_id,
-                    true_next_id: parent_condition.true_next_id,
-                    false_next_id: parent_condition.false_next_id,
-                };
-                (lhs, rhs)
-            }
-        };
-        // We visit expressions tree in pre-order, so place the left-hand side on the top.
-        decision_ctx.decision_stack.push_back(rhs);
-        decision_ctx.decision_stack.push_back(lhs);
-    }
-
-    fn try_finish_decision(
-        &mut self,
-        span: Span,
-        true_marker: BlockMarkerId,
-        false_marker: BlockMarkerId,
-        degraded_branches: &mut Vec<MCDCBranchSpan>,
-    ) -> Option<(MCDCDecisionSpan, Vec<MCDCBranchSpan>)> {
-        let Some(decision_ctx) = self.decision_ctx_stack.last_mut() else {
-            bug!("Unexpected empty decision_ctx_stack")
-        };
-        let Some(condition_info) = decision_ctx.decision_stack.pop_back() else {
-            let branch = MCDCBranchSpan {
-                span,
-                condition_info: ConditionInfo {
-                    condition_id: ConditionId::START,
-                    true_next_id: None,
-                    false_next_id: None,
-                },
-                true_marker,
-                false_marker,
-            };
-            degraded_branches.push(branch);
-            return None;
-        };
-        let Some(decision) = decision_ctx.processing_decision.as_mut() else {
-            bug!("Processing decision should have been created before any conditions are taken");
-        };
-        if condition_info.true_next_id.is_none() {
-            decision.end_markers.push(true_marker);
-        }
-        if condition_info.false_next_id.is_none() {
-            decision.end_markers.push(false_marker);
-        }
-        decision_ctx.conditions.push(MCDCBranchSpan {
-            span,
-            condition_info,
-            true_marker,
-            false_marker,
-        });
-
-        if decision_ctx.decision_stack.is_empty() {
-            let conditions = std::mem::take(&mut decision_ctx.conditions);
-            decision_ctx.processing_decision.take().map(|decision| (decision, conditions))
-        } else {
-            None
-        }
-    }
-}
-
-pub(crate) struct MCDCInfoBuilder {
-    degraded_spans: Vec<MCDCBranchSpan>,
-    mcdc_spans: Vec<(MCDCDecisionSpan, Vec<MCDCBranchSpan>)>,
-    state: MCDCState,
-}
-
-impl MCDCInfoBuilder {
-    pub(crate) fn new() -> Self {
-        Self { degraded_spans: vec![], mcdc_spans: vec![], state: MCDCState::new() }
-    }
-
-    pub(crate) fn visit_evaluated_condition(
-        &mut self,
-        tcx: TyCtxt<'_>,
-        source_info: SourceInfo,
-        true_block: BasicBlock,
-        false_block: BasicBlock,
-        mut inject_block_marker: impl FnMut(SourceInfo, BasicBlock) -> BlockMarkerId,
-    ) {
-        let true_marker = inject_block_marker(source_info, true_block);
-        let false_marker = inject_block_marker(source_info, false_block);
-
-        // take_condition() returns Some for decision_result when the decision stack
-        // is empty, i.e. when all the conditions of the decision were instrumented,
-        // and the decision is "complete".
-        if let Some((decision, conditions)) = self.state.try_finish_decision(
-            source_info.span,
-            true_marker,
-            false_marker,
-            &mut self.degraded_spans,
-        ) {
-            let num_conditions = conditions.len();
-            assert_eq!(
-                num_conditions, decision.num_conditions,
-                "final number of conditions is not correct"
-            );
-            match num_conditions {
-                0 => {
-                    unreachable!("Decision with no condition is not expected");
-                }
-                1..=MAX_CONDITIONS_IN_DECISION => {
-                    self.mcdc_spans.push((decision, conditions));
-                }
-                _ => {
-                    self.degraded_spans.extend(conditions);
-
-                    tcx.dcx().emit_warn(MCDCExceedsConditionLimit {
-                        span: decision.span,
-                        num_conditions,
-                        max_conditions: MAX_CONDITIONS_IN_DECISION,
-                    });
-                }
-            }
-        }
-    }
-
-    pub(crate) fn into_done(
-        self,
-    ) -> (Vec<(MCDCDecisionSpan, Vec<MCDCBranchSpan>)>, Vec<MCDCBranchSpan>) {
-        (self.mcdc_spans, self.degraded_spans)
-    }
-}
-
-impl Builder<'_, '_> {
-    pub(crate) fn visit_coverage_branch_operation(&mut self, logical_op: LogicalOp, span: Span) {
-        if let Some(coverage_info) = self.coverage_info.as_mut()
-            && let Some(mcdc_info) = coverage_info.mcdc_info.as_mut()
-        {
-            mcdc_info.state.record_conditions(logical_op, span);
-        }
-    }
-
-    pub(crate) fn mcdc_increment_depth_if_enabled(&mut self) {
-        if let Some(coverage_info) = self.coverage_info.as_mut()
-            && let Some(mcdc_info) = coverage_info.mcdc_info.as_mut()
-        {
-            mcdc_info.state.decision_ctx_stack.push(MCDCDecisionCtx::default());
-        };
-    }
-
-    pub(crate) fn mcdc_decrement_depth_if_enabled(&mut self) {
-        if let Some(coverage_info) = self.coverage_info.as_mut()
-            && let Some(mcdc_info) = coverage_info.mcdc_info.as_mut()
-            && mcdc_info.state.decision_ctx_stack.pop().is_none()
-        {
-            bug!("Unexpected empty decision stack");
-        };
-    }
-}
diff --git a/compiler/rustc_mir_build/src/builder/custom/parse/instruction.rs b/compiler/rustc_mir_build/src/builder/custom/parse/instruction.rs
index 9825b947fe0..41d3aefcbe6 100644
--- a/compiler/rustc_mir_build/src/builder/custom/parse/instruction.rs
+++ b/compiler/rustc_mir_build/src/builder/custom/parse/instruction.rs
@@ -160,7 +160,7 @@ impl<'a, 'tcx> ParseCtxt<'a, 'tcx> {
                     });
                 }
             };
-            values.push(value.eval_bits(self.tcx, self.typing_env));
+            values.push(value.valtree.unwrap_leaf().to_bits_unchecked());
             targets.push(self.parse_block(arm.body)?);
         }
 
diff --git a/compiler/rustc_mir_build/src/builder/expr/into.rs b/compiler/rustc_mir_build/src/builder/expr/into.rs
index 82b883a99a1..eb99c184bd2 100644
--- a/compiler/rustc_mir_build/src/builder/expr/into.rs
+++ b/compiler/rustc_mir_build/src/builder/expr/into.rs
@@ -159,8 +159,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let condition_scope = this.local_scope();
                 let source_info = this.source_info(expr.span);
 
-                this.visit_coverage_branch_operation(op, expr.span);
-
                 // We first evaluate the left-hand side of the predicate ...
                 let (then_block, else_block) =
                     this.in_if_then_scope(condition_scope, expr.span, |this| {
diff --git a/compiler/rustc_mir_build/src/builder/matches/match_pair.rs b/compiler/rustc_mir_build/src/builder/matches/match_pair.rs
index 3a7854a5e11..7a848536d0e 100644
--- a/compiler/rustc_mir_build/src/builder/matches/match_pair.rs
+++ b/compiler/rustc_mir_build/src/builder/matches/match_pair.rs
@@ -124,9 +124,19 @@ impl<'tcx> MatchPairTree<'tcx> {
         let test_case = match pattern.kind {
             PatKind::Missing | PatKind::Wild | PatKind::Error(_) => None,
 
-            PatKind::Or { ref pats } => Some(TestCase::Or {
-                pats: pats.iter().map(|pat| FlatPat::new(place_builder.clone(), pat, cx)).collect(),
-            }),
+            PatKind::Or { ref pats } => {
+                let pats: Box<[FlatPat<'tcx>]> =
+                    pats.iter().map(|pat| FlatPat::new(place_builder.clone(), pat, cx)).collect();
+                if !pats[0].extra_data.bindings.is_empty() {
+                    // Hold a place for any bindings established in (possibly-nested) or-patterns.
+                    // By only holding a place when bindings are present, we skip over any
+                    // or-patterns that will be simplified by `merge_trivial_subcandidates`. In
+                    // other words, we can assume this expands into subcandidates.
+                    // FIXME(@dianne): this needs updating/removing if we always merge or-patterns
+                    extra_data.bindings.push(super::SubpatternBindings::FromOrPattern);
+                }
+                Some(TestCase::Or { pats })
+            }
 
             PatKind::Range(ref range) => {
                 if range.is_full_range(cx.tcx) == Some(true) {
@@ -194,12 +204,12 @@ impl<'tcx> MatchPairTree<'tcx> {
 
                 // Then push this binding, after any bindings in the subpattern.
                 if let Some(source) = place {
-                    extra_data.bindings.push(super::Binding {
+                    extra_data.bindings.push(super::SubpatternBindings::One(super::Binding {
                         span: pattern.span,
                         source,
                         var_id: var,
                         binding_mode: mode,
-                    });
+                    }));
                 }
 
                 None
diff --git a/compiler/rustc_mir_build/src/builder/matches/mod.rs b/compiler/rustc_mir_build/src/builder/matches/mod.rs
index 2c29b862841..6ee9674bb08 100644
--- a/compiler/rustc_mir_build/src/builder/matches/mod.rs
+++ b/compiler/rustc_mir_build/src/builder/matches/mod.rs
@@ -5,18 +5,18 @@
 //! This also includes code for pattern bindings in `let` statements and
 //! function parameters.
 
-use std::assert_matches::assert_matches;
 use std::borrow::Borrow;
 use std::mem;
 use std::sync::Arc;
 
+use itertools::{Itertools, Position};
 use rustc_abi::VariantIdx;
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_hir::{BindingMode, ByRef, LetStmt, LocalSource, Node};
 use rustc_middle::bug;
 use rustc_middle::middle::region;
-use rustc_middle::mir::{self, *};
+use rustc_middle::mir::*;
 use rustc_middle::thir::{self, *};
 use rustc_middle::ty::{self, CanonicalUserTypeAnnotation, Ty, ValTree, ValTreeKind};
 use rustc_pattern_analysis::constructor::RangeEnd;
@@ -69,18 +69,6 @@ pub(crate) enum DeclareLetBindings {
     LetNotPermitted,
 }
 
-/// Used by [`Builder::bind_matched_candidate_for_arm_body`] to determine
-/// whether or not to call [`Builder::storage_live_binding`] to emit
-/// [`StatementKind::StorageLive`].
-#[derive(Clone, Copy)]
-pub(crate) enum EmitStorageLive {
-    /// Yes, emit `StorageLive` as normal.
-    Yes,
-    /// No, don't emit `StorageLive`. The caller has taken responsibility for
-    /// emitting `StorageLive` as appropriate.
-    No,
-}
-
 /// Used by [`Builder::storage_live_binding`] and [`Builder::bind_matched_candidate_for_arm_body`]
 /// to decide whether to schedule drops.
 #[derive(Clone, Copy, Debug)]
@@ -125,15 +113,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let expr_span = expr.span;
 
         match expr.kind {
-            ExprKind::LogicalOp { op: op @ LogicalOp::And, lhs, rhs } => {
-                this.visit_coverage_branch_operation(op, expr_span);
+            ExprKind::LogicalOp { op: LogicalOp::And, lhs, rhs } => {
                 let lhs_then_block = this.then_else_break_inner(block, lhs, args).into_block();
                 let rhs_then_block =
                     this.then_else_break_inner(lhs_then_block, rhs, args).into_block();
                 rhs_then_block.unit()
             }
-            ExprKind::LogicalOp { op: op @ LogicalOp::Or, lhs, rhs } => {
-                this.visit_coverage_branch_operation(op, expr_span);
+            ExprKind::LogicalOp { op: LogicalOp::Or, lhs, rhs } => {
                 let local_scope = this.local_scope();
                 let (lhs_success_block, failure_block) =
                     this.in_if_then_scope(local_scope, expr_span, |this| {
@@ -207,16 +193,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 Some(args.variable_source_info.scope),
                 args.variable_source_info.span,
                 args.declare_let_bindings,
-                EmitStorageLive::Yes,
             ),
             _ => {
                 let mut block = block;
                 let temp_scope = args.temp_scope_override.unwrap_or_else(|| this.local_scope());
                 let mutability = Mutability::Mut;
 
-                // Increment the decision depth, in case we encounter boolean expressions
-                // further down.
-                this.mcdc_increment_depth_if_enabled();
                 let place = unpack!(
                     block = this.as_temp(
                         block,
@@ -228,7 +210,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         mutability
                     )
                 );
-                this.mcdc_decrement_depth_if_enabled();
 
                 let operand = Operand::Move(Place::from(place));
 
@@ -447,48 +428,53 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let arm_source_info = self.source_info(arm.span);
                 let arm_scope = (arm.scope, arm_source_info);
                 let match_scope = self.local_scope();
+                let guard_scope = arm
+                    .guard
+                    .map(|_| region::Scope { data: region::ScopeData::MatchGuard, ..arm.scope });
                 self.in_scope(arm_scope, arm.lint_level, |this| {
-                    let old_dedup_scope =
-                        mem::replace(&mut this.fixed_temps_scope, Some(arm.scope));
-
-                    // `try_to_place` may fail if it is unable to resolve the given
-                    // `PlaceBuilder` inside a closure. In this case, we don't want to include
-                    // a scrutinee place. `scrutinee_place_builder` will fail to be resolved
-                    // if the only match arm is a wildcard (`_`).
-                    // Example:
-                    // ```
-                    // let foo = (0, 1);
-                    // let c = || {
-                    //    match foo { _ => () };
-                    // };
-                    // ```
-                    let scrutinee_place = scrutinee_place_builder.try_to_place(this);
-                    let opt_scrutinee_place =
-                        scrutinee_place.as_ref().map(|place| (Some(place), scrutinee_span));
-                    let scope = this.declare_bindings(
-                        None,
-                        arm.span,
-                        &arm.pattern,
-                        arm.guard,
-                        opt_scrutinee_place,
-                    );
+                    this.opt_in_scope(guard_scope.map(|scope| (scope, arm_source_info)), |this| {
+                        // `if let` guard temps needing deduplicating will be in the guard scope.
+                        let old_dedup_scope =
+                            mem::replace(&mut this.fixed_temps_scope, guard_scope);
+
+                        // `try_to_place` may fail if it is unable to resolve the given
+                        // `PlaceBuilder` inside a closure. In this case, we don't want to include
+                        // a scrutinee place. `scrutinee_place_builder` will fail to be resolved
+                        // if the only match arm is a wildcard (`_`).
+                        // Example:
+                        // ```
+                        // let foo = (0, 1);
+                        // let c = || {
+                        //    match foo { _ => () };
+                        // };
+                        // ```
+                        let scrutinee_place = scrutinee_place_builder.try_to_place(this);
+                        let opt_scrutinee_place =
+                            scrutinee_place.as_ref().map(|place| (Some(place), scrutinee_span));
+                        let scope = this.declare_bindings(
+                            None,
+                            arm.span,
+                            &arm.pattern,
+                            arm.guard,
+                            opt_scrutinee_place,
+                        );
 
-                    let arm_block = this.bind_pattern(
-                        outer_source_info,
-                        branch,
-                        &built_match_tree.fake_borrow_temps,
-                        scrutinee_span,
-                        Some((arm, match_scope)),
-                        EmitStorageLive::Yes,
-                    );
+                        let arm_block = this.bind_pattern(
+                            outer_source_info,
+                            branch,
+                            &built_match_tree.fake_borrow_temps,
+                            scrutinee_span,
+                            Some((arm, match_scope)),
+                        );
 
-                    this.fixed_temps_scope = old_dedup_scope;
+                        this.fixed_temps_scope = old_dedup_scope;
 
-                    if let Some(source_scope) = scope {
-                        this.source_scope = source_scope;
-                    }
+                        if let Some(source_scope) = scope {
+                            this.source_scope = source_scope;
+                        }
 
-                    this.expr_into_dest(destination, arm_block, arm.body)
+                        this.expr_into_dest(destination, arm_block, arm.body)
+                    })
                 })
                 .into_block()
             })
@@ -533,7 +519,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         fake_borrow_temps: &[(Place<'tcx>, Local, FakeBorrowKind)],
         scrutinee_span: Span,
         arm_match_scope: Option<(&Arm<'tcx>, region::Scope)>,
-        emit_storage_live: EmitStorageLive,
     ) -> BasicBlock {
         if branch.sub_branches.len() == 1 {
             let [sub_branch] = branch.sub_branches.try_into().unwrap();
@@ -544,7 +529,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 scrutinee_span,
                 arm_match_scope,
                 ScheduleDrops::Yes,
-                emit_storage_live,
             )
         } else {
             // It's helpful to avoid scheduling drops multiple times to save
@@ -561,27 +545,20 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             // return: it isn't bound by move until right before enter the arm.
             // To handle this we instead unschedule it's drop after each time
             // we lower the guard.
+            // As a result, we end up with the drop order of the last sub-branch we lower. To use
+            // the drop order for the first sub-branch, we lower sub-branches in reverse (#142163).
             let target_block = self.cfg.start_new_block();
-            let mut schedule_drops = ScheduleDrops::Yes;
-            let arm = arm_match_scope.unzip().0;
-            // We keep a stack of all of the bindings and type ascriptions
-            // from the parent candidates that we visit, that also need to
-            // be bound for each candidate.
-            for sub_branch in branch.sub_branches {
-                if let Some(arm) = arm {
-                    self.clear_top_scope(arm.scope);
-                }
+            for (pos, sub_branch) in branch.sub_branches.into_iter().rev().with_position() {
+                debug_assert!(pos != Position::Only);
+                let schedule_drops =
+                    if pos == Position::Last { ScheduleDrops::Yes } else { ScheduleDrops::No };
                 let binding_end = self.bind_and_guard_matched_candidate(
                     sub_branch,
                     fake_borrow_temps,
                     scrutinee_span,
                     arm_match_scope,
                     schedule_drops,
-                    emit_storage_live,
                 );
-                if arm.is_none() {
-                    schedule_drops = ScheduleDrops::No;
-                }
                 self.cfg.goto(binding_end, outer_source_info, target_block);
             }
 
@@ -741,7 +718,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             &[],
             irrefutable_pat.span,
             None,
-            EmitStorageLive::Yes,
         )
         .unit()
     }
@@ -996,7 +972,7 @@ struct PatternExtraData<'tcx> {
     span: Span,
 
     /// Bindings that must be established.
-    bindings: Vec<Binding<'tcx>>,
+    bindings: Vec<SubpatternBindings<'tcx>>,
 
     /// Types that must be asserted.
     ascriptions: Vec<Ascription<'tcx>>,
@@ -1011,6 +987,15 @@ impl<'tcx> PatternExtraData<'tcx> {
     }
 }
 
+#[derive(Debug, Clone)]
+enum SubpatternBindings<'tcx> {
+    /// A single binding.
+    One(Binding<'tcx>),
+    /// Holds the place for an or-pattern's bindings. This ensures their drops are scheduled in the
+    /// order the primary bindings appear. See rust-lang/rust#142163 for more information.
+    FromOrPattern,
+}
+
 /// A pattern in a form suitable for lowering the match tree, with all irrefutable
 /// patterns simplified away.
 ///
@@ -1226,7 +1211,7 @@ fn traverse_candidate<'tcx, C, T, I>(
     }
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Copy, Debug)]
 struct Binding<'tcx> {
     span: Span,
     source: Place<'tcx>,
@@ -1260,7 +1245,7 @@ struct Ascription<'tcx> {
 #[derive(Debug, Clone)]
 enum TestCase<'tcx> {
     Variant { adt_def: ty::AdtDef<'tcx>, variant_index: VariantIdx },
-    Constant { value: mir::Const<'tcx> },
+    Constant { value: ty::Value<'tcx> },
     Range(Arc<PatRange<'tcx>>),
     Slice { len: usize, variable_length: bool },
     Deref { temp: Place<'tcx>, mutability: Mutability },
@@ -1331,13 +1316,13 @@ enum TestKind<'tcx> {
     If,
 
     /// Test for equality with value, possibly after an unsizing coercion to
-    /// `ty`,
+    /// `cast_ty`,
     Eq {
-        value: Const<'tcx>,
+        value: ty::Value<'tcx>,
         // Integer types are handled by `SwitchInt`, and constants with ADT
         // types and `&[T]` types are converted back into patterns, so this can
-        // only be `&str`, `f32` or `f64`.
-        ty: Ty<'tcx>,
+        // only be `&str` or floats.
+        cast_ty: Ty<'tcx>,
     },
 
     /// Test whether the value falls within an inclusive or exclusive range.
@@ -1372,8 +1357,8 @@ pub(crate) struct Test<'tcx> {
 enum TestBranch<'tcx> {
     /// Success branch, used for tests with two possible outcomes.
     Success,
-    /// Branch corresponding to this constant.
-    Constant(Const<'tcx>, u128),
+    /// Branch corresponding to this constant. Must be a scalar.
+    Constant(ty::Value<'tcx>),
     /// Branch corresponding to this variant.
     Variant(VariantIdx),
     /// Failure branch for tests with two possible outcomes, and "otherwise" branch for other tests.
@@ -1381,8 +1366,8 @@ enum TestBranch<'tcx> {
 }
 
 impl<'tcx> TestBranch<'tcx> {
-    fn as_constant(&self) -> Option<&Const<'tcx>> {
-        if let Self::Constant(v, _) = self { Some(v) } else { None }
+    fn as_constant(&self) -> Option<ty::Value<'tcx>> {
+        if let Self::Constant(v) = self { Some(*v) } else { None }
     }
 }
 
@@ -1452,12 +1437,7 @@ impl<'tcx> MatchTreeSubBranch<'tcx> {
             span: candidate.extra_data.span,
             success_block: candidate.pre_binding_block.unwrap(),
             otherwise_block: candidate.otherwise_block.unwrap(),
-            bindings: parent_data
-                .iter()
-                .flat_map(|d| &d.bindings)
-                .chain(&candidate.extra_data.bindings)
-                .cloned()
-                .collect(),
+            bindings: sub_branch_bindings(parent_data, &candidate.extra_data.bindings),
             ascriptions: parent_data
                 .iter()
                 .flat_map(|d| &d.ascriptions)
@@ -1490,6 +1470,68 @@ impl<'tcx> MatchTreeBranch<'tcx> {
     }
 }
 
+/// Collects the bindings for a [`MatchTreeSubBranch`], preserving the order they appear in the
+/// pattern, as though the or-alternatives chosen in this sub-branch were inlined.
+fn sub_branch_bindings<'tcx>(
+    parents: &[PatternExtraData<'tcx>],
+    leaf_bindings: &[SubpatternBindings<'tcx>],
+) -> Vec<Binding<'tcx>> {
+    // In the common case, all bindings will be in leaves. Allocate to fit the leaf's bindings.
+    let mut all_bindings = Vec::with_capacity(leaf_bindings.len());
+    let mut remainder = parents
+        .iter()
+        .map(|parent| parent.bindings.as_slice())
+        .chain([leaf_bindings])
+        // Skip over unsimplified or-patterns without bindings.
+        .filter(|bindings| !bindings.is_empty());
+    if let Some(candidate_bindings) = remainder.next() {
+        push_sub_branch_bindings(&mut all_bindings, candidate_bindings, &mut remainder);
+    }
+    // Make sure we've included all bindings. For ill-formed patterns like `(x, _ | y)`, we may not
+    // have collected all bindings yet, since we only check the first alternative when determining
+    // whether to inline subcandidates' bindings.
+    // FIXME(@dianne): prevent ill-formed patterns from getting here
+    while let Some(candidate_bindings) = remainder.next() {
+        ty::tls::with(|tcx| {
+            tcx.dcx().delayed_bug("mismatched or-pattern bindings but no error emitted")
+        });
+        // To recover, we collect the rest in an arbitrary order.
+        push_sub_branch_bindings(&mut all_bindings, candidate_bindings, &mut remainder);
+    }
+    all_bindings
+}
+
+/// Helper for [`sub_branch_bindings`]. Collects bindings from `candidate_bindings` into
+/// `flattened`. Bindings in or-patterns are collected recursively from `remainder`.
+fn push_sub_branch_bindings<'c, 'tcx: 'c>(
+    flattened: &mut Vec<Binding<'tcx>>,
+    candidate_bindings: &'c [SubpatternBindings<'tcx>],
+    remainder: &mut impl Iterator<Item = &'c [SubpatternBindings<'tcx>]>,
+) {
+    for subpat_bindings in candidate_bindings {
+        match subpat_bindings {
+            SubpatternBindings::One(binding) => flattened.push(*binding),
+            SubpatternBindings::FromOrPattern => {
+                // Inline bindings from an or-pattern. By construction, this always
+                // corresponds to a subcandidate and its closest descendants (i.e. those
+                // from nested or-patterns, but not adjacent or-patterns). To handle
+                // adjacent or-patterns, e.g. `(x | x, y | y)`, we update the `remainder` to
+                // point to the first descendant candidate from outside this or-pattern.
+                if let Some(subcandidate_bindings) = remainder.next() {
+                    push_sub_branch_bindings(flattened, subcandidate_bindings, remainder);
+                } else {
+                    // For ill-formed patterns like `x | _`, we may not have any subcandidates left
+                    // to inline bindings from.
+                    // FIXME(@dianne): prevent ill-formed patterns from getting here
+                    ty::tls::with(|tcx| {
+                        tcx.dcx().delayed_bug("mismatched or-pattern bindings but no error emitted")
+                    });
+                };
+            }
+        }
+    }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub(crate) enum HasMatchGuard {
     Yes,
@@ -2364,7 +2406,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         source_scope: Option<SourceScope>,
         scope_span: Span,
         declare_let_bindings: DeclareLetBindings,
-        emit_storage_live: EmitStorageLive,
     ) -> BlockAnd<()> {
         let expr_span = self.thir[expr_id].span;
         let scrutinee = unpack!(block = self.lower_scrutinee(block, expr_id, expr_span));
@@ -2398,14 +2439,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             }
         }
 
-        let success = self.bind_pattern(
-            self.source_info(pat.span),
-            branch,
-            &[],
-            expr_span,
-            None,
-            emit_storage_live,
-        );
+        let success = self.bind_pattern(self.source_info(pat.span), branch, &[], expr_span, None);
 
         // If branch coverage is enabled, record this branch.
         self.visit_coverage_conditional_let(pat, success, built_tree.otherwise_block);
@@ -2428,7 +2462,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         scrutinee_span: Span,
         arm_match_scope: Option<(&Arm<'tcx>, region::Scope)>,
         schedule_drops: ScheduleDrops,
-        emit_storage_live: EmitStorageLive,
     ) -> BasicBlock {
         debug!("bind_and_guard_matched_candidate(subbranch={:?})", sub_branch);
 
@@ -2453,11 +2486,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
             // Bindings for guards require some extra handling to automatically
             // insert implicit references/dereferences.
-            self.bind_matched_candidate_for_guard(
-                block,
-                schedule_drops,
-                sub_branch.bindings.iter(),
-            );
+            // This always schedules storage drops, so we may need to unschedule them below.
+            self.bind_matched_candidate_for_guard(block, sub_branch.bindings.iter());
             let guard_frame = GuardFrame {
                 locals: sub_branch
                     .bindings
@@ -2489,6 +2519,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     )
                 });
 
+            // If this isn't the final sub-branch being lowered, we need to unschedule drops of
+            // bindings and temporaries created for and by the guard. As a result, the drop order
+            // for the arm will correspond to the binding order of the final sub-branch lowered.
+            if matches!(schedule_drops, ScheduleDrops::No) {
+                self.clear_match_arm_and_guard_scopes(arm.scope);
+            }
+
             let source_info = self.source_info(guard_span);
             let guard_end = self.source_info(tcx.sess.source_map().end_point(guard_span));
             let guard_frame = self.guard_context.pop().unwrap();
@@ -2538,16 +2575,11 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let cause = FakeReadCause::ForGuardBinding;
                 self.cfg.push_fake_read(post_guard_block, guard_end, cause, Place::from(local_id));
             }
-            assert_matches!(
-                schedule_drops,
-                ScheduleDrops::Yes,
-                "patterns with guards must schedule drops"
-            );
+            // Only schedule drops for the last sub-branch we lower.
             self.bind_matched_candidate_for_arm_body(
                 post_guard_block,
-                ScheduleDrops::Yes,
+                schedule_drops,
                 by_value_bindings,
-                emit_storage_live,
             );
 
             post_guard_block
@@ -2559,7 +2591,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 block,
                 schedule_drops,
                 sub_branch.bindings.iter(),
-                emit_storage_live,
             );
             block
         }
@@ -2671,7 +2702,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     fn bind_matched_candidate_for_guard<'b>(
         &mut self,
         block: BasicBlock,
-        schedule_drops: ScheduleDrops,
         bindings: impl IntoIterator<Item = &'b Binding<'tcx>>,
     ) where
         'tcx: 'b,
@@ -2690,12 +2720,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             // a reference R: &T pointing to the location matched by
             // the pattern, and every occurrence of P within a guard
             // denotes *R.
+            // Drops must be scheduled to emit `StorageDead` on the guard's failure/break branches.
             let ref_for_guard = self.storage_live_binding(
                 block,
                 binding.var_id,
                 binding.span,
                 RefWithinGuard,
-                schedule_drops,
+                ScheduleDrops::Yes,
             );
             match binding.binding_mode.0 {
                 ByRef::No => {
@@ -2705,13 +2736,14 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     self.cfg.push_assign(block, source_info, ref_for_guard, rvalue);
                 }
                 ByRef::Yes(mutbl) => {
-                    // The arm binding will be by reference, so eagerly create it now.
+                    // The arm binding will be by reference, so eagerly create it now. Drops must
+                    // be scheduled to emit `StorageDead` on the guard's failure/break branches.
                     let value_for_arm = self.storage_live_binding(
                         block,
                         binding.var_id,
                         binding.span,
                         OutsideGuard,
-                        schedule_drops,
+                        ScheduleDrops::Yes,
                     );
 
                     let rvalue =
@@ -2730,7 +2762,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         block: BasicBlock,
         schedule_drops: ScheduleDrops,
         bindings: impl IntoIterator<Item = &'b Binding<'tcx>>,
-        emit_storage_live: EmitStorageLive,
     ) where
         'tcx: 'b,
     {
@@ -2740,19 +2771,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         // Assign each of the bindings. This may trigger moves out of the candidate.
         for binding in bindings {
             let source_info = self.source_info(binding.span);
-            let local = match emit_storage_live {
-                // Here storages are already alive, probably because this is a binding
-                // from let-else.
-                // We just need to schedule drop for the value.
-                EmitStorageLive::No => self.var_local_id(binding.var_id, OutsideGuard).into(),
-                EmitStorageLive::Yes => self.storage_live_binding(
-                    block,
-                    binding.var_id,
-                    binding.span,
-                    OutsideGuard,
-                    schedule_drops,
-                ),
-            };
+            let local = self.storage_live_binding(
+                block,
+                binding.var_id,
+                binding.span,
+                OutsideGuard,
+                schedule_drops,
+            );
             if matches!(schedule_drops, ScheduleDrops::Yes) {
                 self.schedule_drop_for_binding(binding.var_id, binding.span, OutsideGuard);
             }
diff --git a/compiler/rustc_mir_build/src/builder/matches/test.rs b/compiler/rustc_mir_build/src/builder/matches/test.rs
index a4609a6053e..d03794fe2d5 100644
--- a/compiler/rustc_mir_build/src/builder/matches/test.rs
+++ b/compiler/rustc_mir_build/src/builder/matches/test.rs
@@ -35,7 +35,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
             TestCase::Constant { .. } if match_pair.pattern_ty.is_bool() => TestKind::If,
             TestCase::Constant { .. } if is_switch_ty(match_pair.pattern_ty) => TestKind::SwitchInt,
-            TestCase::Constant { value } => TestKind::Eq { value, ty: match_pair.pattern_ty },
+            TestCase::Constant { value } => TestKind::Eq { value, cast_ty: match_pair.pattern_ty },
 
             TestCase::Range(ref range) => {
                 assert_eq!(range.ty, match_pair.pattern_ty);
@@ -112,7 +112,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let otherwise_block = target_block(TestBranch::Failure);
                 let switch_targets = SwitchTargets::new(
                     target_blocks.iter().filter_map(|(&branch, &block)| {
-                        if let TestBranch::Constant(_, bits) = branch {
+                        if let TestBranch::Constant(value) = branch {
+                            let bits = value.valtree.unwrap_leaf().to_bits_unchecked();
                             Some((bits, block))
                         } else {
                             None
@@ -135,17 +136,17 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 self.cfg.terminate(block, self.source_info(match_start_span), terminator);
             }
 
-            TestKind::Eq { value, mut ty } => {
+            TestKind::Eq { value, mut cast_ty } => {
                 let tcx = self.tcx;
                 let success_block = target_block(TestBranch::Success);
                 let fail_block = target_block(TestBranch::Failure);
 
-                let mut expect_ty = value.ty();
-                let mut expect = self.literal_operand(test.span, value);
+                let mut expect_ty = value.ty;
+                let mut expect = self.literal_operand(test.span, Const::from_ty_value(tcx, value));
 
                 let mut place = place;
                 let mut block = block;
-                match ty.kind() {
+                match cast_ty.kind() {
                     ty::Str => {
                         // String literal patterns may have type `str` if `deref_patterns` is
                         // enabled, in order to allow `deref!("..."): String`. In this case, `value`
@@ -167,7 +168,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                             Rvalue::Ref(re_erased, BorrowKind::Shared, place),
                         );
                         place = ref_place;
-                        ty = ref_str_ty;
+                        cast_ty = ref_str_ty;
                     }
                     ty::Adt(def, _) if tcx.is_lang_item(def.did(), LangItem::String) => {
                         if !tcx.features().string_deref_patterns() {
@@ -186,7 +187,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                             eq_block,
                             place,
                             Mutability::Not,
-                            ty,
+                            cast_ty,
                             ref_str,
                             test.span,
                         );
@@ -195,10 +196,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         // Similarly, the normal test code should be generated for the `&str`, instead of the `String`.
                         block = eq_block;
                         place = ref_str;
-                        ty = ref_str_ty;
+                        cast_ty = ref_str_ty;
                     }
                     &ty::Pat(base, _) => {
-                        assert_eq!(ty, value.ty());
+                        assert_eq!(cast_ty, value.ty);
                         assert!(base.is_trivially_pure_clone_copy());
 
                         let transmuted_place = self.temp(base, test.span);
@@ -219,14 +220,14 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
                         place = transmuted_place;
                         expect = Operand::Copy(transmuted_expect);
-                        ty = base;
+                        cast_ty = base;
                         expect_ty = base;
                     }
                     _ => {}
                 }
 
-                assert_eq!(expect_ty, ty);
-                if !ty.is_scalar() {
+                assert_eq!(expect_ty, cast_ty);
+                if !cast_ty.is_scalar() {
                     // Use `PartialEq::eq` instead of `BinOp::Eq`
                     // (the binop can only handle primitives)
                     // Make sure that we do *not* call any user-defined code here.
@@ -234,10 +235,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     // comparison defined in `core`.
                     // (Interestingly this means that exhaustiveness analysis relies, for soundness,
                     // on the `PartialEq` impl for `str` to b correct!)
-                    match *ty.kind() {
+                    match *cast_ty.kind() {
                         ty::Ref(_, deref_ty, _) if deref_ty == self.tcx.types.str_ => {}
                         _ => {
-                            span_bug!(source_info.span, "invalid type for non-scalar compare: {ty}")
+                            span_bug!(
+                                source_info.span,
+                                "invalid type for non-scalar compare: {cast_ty}"
+                            )
                         }
                     };
                     self.string_compare(
@@ -276,7 +280,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 };
 
                 if let Some(lo) = range.lo.as_finite() {
-                    let lo = self.literal_operand(test.span, lo);
+                    let lo = ty::Value { ty: range.ty, valtree: lo };
+                    let lo = self.literal_operand(test.span, Const::from_ty_value(self.tcx, lo));
                     self.compare(
                         block,
                         intermediate_block,
@@ -289,7 +294,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 };
 
                 if let Some(hi) = range.hi.as_finite() {
-                    let hi = self.literal_operand(test.span, hi);
+                    let hi = ty::Value { ty: range.ty, valtree: hi };
+                    let hi = self.literal_operand(test.span, Const::from_ty_value(self.tcx, hi));
                     let op = match range.end {
                         RangeEnd::Included => BinOp::Le,
                         RangeEnd::Excluded => BinOp::Lt,
@@ -555,10 +561,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 // not to add such values here.
                 let is_covering_range = |test_case: &TestCase<'tcx>| {
                     test_case.as_range().is_some_and(|range| {
-                        matches!(
-                            range.contains(value, self.tcx, self.typing_env()),
-                            None | Some(true)
-                        )
+                        matches!(range.contains(value, self.tcx), None | Some(true))
                     })
                 };
                 let is_conflicting_candidate = |candidate: &&mut Candidate<'tcx>| {
@@ -575,8 +578,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     None
                 } else {
                     fully_matched = true;
-                    let bits = value.eval_bits(self.tcx, self.typing_env());
-                    Some(TestBranch::Constant(value, bits))
+                    Some(TestBranch::Constant(value))
                 }
             }
             (TestKind::SwitchInt, TestCase::Range(range)) => {
@@ -585,12 +587,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 // the values being tested. (This restricts what values can be
                 // added to the test by subsequent candidates.)
                 fully_matched = false;
-                let not_contained =
-                    sorted_candidates.keys().filter_map(|br| br.as_constant()).copied().all(
-                        |val| {
-                            matches!(range.contains(val, self.tcx, self.typing_env()), Some(false))
-                        },
-                    );
+                let not_contained = sorted_candidates
+                    .keys()
+                    .filter_map(|br| br.as_constant())
+                    .all(|val| matches!(range.contains(val, self.tcx), Some(false)));
 
                 not_contained.then(|| {
                     // No switch values are contained in the pattern range,
@@ -601,7 +601,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
             (TestKind::If, TestCase::Constant { value }) => {
                 fully_matched = true;
-                let value = value.try_eval_bool(self.tcx, self.typing_env()).unwrap_or_else(|| {
+                let value = value.try_to_bool().unwrap_or_else(|| {
                     span_bug!(test.span, "expected boolean value but got {value:?}")
                 });
                 Some(if value { TestBranch::Success } else { TestBranch::Failure })
@@ -681,16 +681,12 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     fully_matched = false;
                     // If the testing range does not overlap with pattern range,
                     // the pattern can be matched only if this test fails.
-                    if !test.overlaps(pat, self.tcx, self.typing_env())? {
-                        Some(TestBranch::Failure)
-                    } else {
-                        None
-                    }
+                    if !test.overlaps(pat, self.tcx)? { Some(TestBranch::Failure) } else { None }
                 }
             }
             (TestKind::Range(range), &TestCase::Constant { value }) => {
                 fully_matched = false;
-                if !range.contains(value, self.tcx, self.typing_env())? {
+                if !range.contains(value, self.tcx)? {
                     // `value` is not contained in the testing range,
                     // so `value` can be matched only if this test fails.
                     Some(TestBranch::Failure)
diff --git a/compiler/rustc_mir_build/src/builder/matches/util.rs b/compiler/rustc_mir_build/src/builder/matches/util.rs
index 589e350a03f..2c8ad95b6af 100644
--- a/compiler/rustc_mir_build/src/builder/matches/util.rs
+++ b/compiler/rustc_mir_build/src/builder/matches/util.rs
@@ -138,7 +138,9 @@ impl<'a, 'b, 'tcx> FakeBorrowCollector<'a, 'b, 'tcx> {
 
     fn visit_candidate(&mut self, candidate: &Candidate<'tcx>) {
         for binding in &candidate.extra_data.bindings {
-            self.visit_binding(binding);
+            if let super::SubpatternBindings::One(binding) = binding {
+                self.visit_binding(binding);
+            }
         }
         for match_pair in &candidate.match_pairs {
             self.visit_match_pair(match_pair);
@@ -147,7 +149,9 @@ impl<'a, 'b, 'tcx> FakeBorrowCollector<'a, 'b, 'tcx> {
 
     fn visit_flat_pat(&mut self, flat_pat: &FlatPat<'tcx>) {
         for binding in &flat_pat.extra_data.bindings {
-            self.visit_binding(binding);
+            if let super::SubpatternBindings::One(binding) = binding {
+                self.visit_binding(binding);
+            }
         }
         for match_pair in &flat_pat.match_pairs {
             self.visit_match_pair(match_pair);
diff --git a/compiler/rustc_mir_build/src/builder/scope.rs b/compiler/rustc_mir_build/src/builder/scope.rs
index 1240b34cf9d..96659873622 100644
--- a/compiler/rustc_mir_build/src/builder/scope.rs
+++ b/compiler/rustc_mir_build/src/builder/scope.rs
@@ -697,6 +697,20 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         block.and(rv)
     }
 
+    /// Convenience wrapper that executes `f` either within the current scope or a new scope.
+    /// Used for pattern matching, which introduces an additional scope for patterns with guards.
+    pub(crate) fn opt_in_scope<R>(
+        &mut self,
+        opt_region_scope: Option<(region::Scope, SourceInfo)>,
+        f: impl FnOnce(&mut Builder<'a, 'tcx>) -> BlockAnd<R>,
+    ) -> BlockAnd<R> {
+        if let Some(region_scope) = opt_region_scope {
+            self.in_scope(region_scope, LintLevel::Inherited, f)
+        } else {
+            f(self)
+        }
+    }
+
     /// Push a scope onto the stack. You can then build code in this
     /// scope and call `pop_scope` afterwards. Note that these two
     /// calls must be paired; using `in_scope` as a convenience
@@ -1750,17 +1764,24 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         success_block
     }
 
-    /// Unschedules any drops in the top scope.
+    /// Unschedules any drops in the top two scopes.
     ///
-    /// This is only needed for `match` arm scopes, because they have one
-    /// entrance per pattern, but only one exit.
-    pub(crate) fn clear_top_scope(&mut self, region_scope: region::Scope) {
-        let top_scope = self.scopes.scopes.last_mut().unwrap();
+    /// This is only needed for pattern-matches combining guards and or-patterns: or-patterns lead
+    /// to guards being lowered multiple times before lowering the arm body, so we unschedle drops
+    /// for guards' temporaries and bindings between lowering each instance of an match arm's guard.
+    pub(crate) fn clear_match_arm_and_guard_scopes(&mut self, region_scope: region::Scope) {
+        let [.., arm_scope, guard_scope] = &mut *self.scopes.scopes else {
+            bug!("matches with guards should introduce separate scopes for the pattern and guard");
+        };
 
-        assert_eq!(top_scope.region_scope, region_scope);
+        assert_eq!(arm_scope.region_scope, region_scope);
+        assert_eq!(guard_scope.region_scope.data, region::ScopeData::MatchGuard);
+        assert_eq!(guard_scope.region_scope.local_id, region_scope.local_id);
 
-        top_scope.drops.clear();
-        top_scope.invalidate_cache();
+        arm_scope.drops.clear();
+        arm_scope.invalidate_cache();
+        guard_scope.drops.clear();
+        guard_scope.invalidate_cache();
     }
 }
 
diff --git a/compiler/rustc_mir_build/src/check_tail_calls.rs b/compiler/rustc_mir_build/src/check_tail_calls.rs
index 3ecccb422c4..d4b6da2c14b 100644
--- a/compiler/rustc_mir_build/src/check_tail_calls.rs
+++ b/compiler/rustc_mir_build/src/check_tail_calls.rs
@@ -3,6 +3,7 @@ use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_errors::Applicability;
 use rustc_hir::LangItem;
 use rustc_hir::def::DefKind;
+use rustc_hir::def_id::CRATE_DEF_ID;
 use rustc_middle::span_bug;
 use rustc_middle::thir::visit::{self, Visitor};
 use rustc_middle::thir::{BodyTy, Expr, ExprId, ExprKind, Thir};
@@ -136,7 +137,15 @@ impl<'tcx> TailCallCkVisitor<'_, 'tcx> {
 
         if caller_sig.inputs_and_output != callee_sig.inputs_and_output {
             if caller_sig.inputs() != callee_sig.inputs() {
-                self.report_arguments_mismatch(expr.span, caller_sig, callee_sig);
+                self.report_arguments_mismatch(
+                    expr.span,
+                    self.tcx.liberate_late_bound_regions(
+                        CRATE_DEF_ID.to_def_id(),
+                        self.caller_ty.fn_sig(self.tcx),
+                    ),
+                    self.tcx
+                        .liberate_late_bound_regions(CRATE_DEF_ID.to_def_id(), ty.fn_sig(self.tcx)),
+                );
             }
 
             // FIXME(explicit_tail_calls): this currently fails for cases where opaques are used.
diff --git a/compiler/rustc_mir_build/src/errors.rs b/compiler/rustc_mir_build/src/errors.rs
index 1a52c6c85cb..58c3de4a8b5 100644
--- a/compiler/rustc_mir_build/src/errors.rs
+++ b/compiler/rustc_mir_build/src/errors.rs
@@ -976,15 +976,6 @@ pub(crate) struct NonEmptyNeverPattern<'tcx> {
 }
 
 #[derive(Diagnostic)]
-#[diag(mir_build_exceeds_mcdc_condition_limit)]
-pub(crate) struct MCDCExceedsConditionLimit {
-    #[primary_span]
-    pub(crate) span: Span,
-    pub(crate) num_conditions: usize,
-    pub(crate) max_conditions: usize,
-}
-
-#[derive(Diagnostic)]
 #[diag(mir_build_pattern_not_covered, code = E0005)]
 pub(crate) struct PatternNotCovered<'s, 'tcx> {
     #[primary_span]
diff --git a/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs b/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
index a501cdf88c2..d46c4678bcf 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
@@ -11,11 +11,11 @@ use rustc_index::Idx;
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::traits::Obligation;
 use rustc_middle::mir::interpret::ErrorHandled;
+use rustc_middle::span_bug;
 use rustc_middle::thir::{FieldPat, Pat, PatKind};
 use rustc_middle::ty::{
     self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitableExt, TypeVisitor, ValTree,
 };
-use rustc_middle::{mir, span_bug};
 use rustc_span::def_id::DefId;
 use rustc_span::{DUMMY_SP, Span};
 use rustc_trait_selection::traits::ObligationCause;
@@ -288,16 +288,12 @@ impl<'tcx> ConstToPat<'tcx> {
                 // when lowering to MIR in `Builder::perform_test`, treat the constant as a `&str`.
                 // This works because `str` and `&str` have the same valtree representation.
                 let ref_str_ty = Ty::new_imm_ref(tcx, tcx.lifetimes.re_erased, ty);
-                PatKind::Constant {
-                    value: mir::Const::Ty(ref_str_ty, ty::Const::new_value(tcx, cv, ref_str_ty)),
-                }
+                PatKind::Constant { value: ty::Value { ty: ref_str_ty, valtree: cv } }
             }
             ty::Ref(_, pointee_ty, ..) => match *pointee_ty.kind() {
                 // `&str` is represented as a valtree, let's keep using this
                 // optimization for now.
-                ty::Str => PatKind::Constant {
-                    value: mir::Const::Ty(ty, ty::Const::new_value(tcx, cv, ty)),
-                },
+                ty::Str => PatKind::Constant { value: ty::Value { ty, valtree: cv } },
                 // All other references are converted into deref patterns and then recursively
                 // convert the dereferenced constant to a pattern that is the sub-pattern of the
                 // deref pattern.
@@ -326,15 +322,13 @@ impl<'tcx> ConstToPat<'tcx> {
                     // Also see <https://github.com/rust-lang/rfcs/pull/3535>.
                     return self.mk_err(tcx.dcx().create_err(NaNPattern { span }), ty);
                 } else {
-                    PatKind::Constant {
-                        value: mir::Const::Ty(ty, ty::Const::new_value(tcx, cv, ty)),
-                    }
+                    PatKind::Constant { value: ty::Value { ty, valtree: cv } }
                 }
             }
             ty::Pat(..) | ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::RawPtr(..) => {
                 // The raw pointers we see here have been "vetted" by valtree construction to be
                 // just integers, so we simply allow them.
-                PatKind::Constant { value: mir::Const::Ty(ty, ty::Const::new_value(tcx, cv, ty)) }
+                PatKind::Constant { value: ty::Value { ty, valtree: cv } }
             }
             ty::FnPtr(..) => {
                 unreachable!(
diff --git a/compiler/rustc_mir_build/src/thir/pattern/mod.rs b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
index a44afed5492..166e64a5fcb 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/mod.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
@@ -161,8 +161,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
                 format!("found bad range pattern endpoint `{expr:?}` outside of error recovery");
             return Err(self.tcx.dcx().span_delayed_bug(expr.span, msg));
         };
-
-        Ok(Some(PatRangeBoundary::Finite(value)))
+        Ok(Some(PatRangeBoundary::Finite(value.valtree)))
     }
 
     /// Overflowing literals are linted against in a late pass. This is mostly fine, except when we
@@ -235,7 +234,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
         let lo = lower_endpoint(lo_expr)?.unwrap_or(PatRangeBoundary::NegInfinity);
         let hi = lower_endpoint(hi_expr)?.unwrap_or(PatRangeBoundary::PosInfinity);
 
-        let cmp = lo.compare_with(hi, ty, self.tcx, self.typing_env);
+        let cmp = lo.compare_with(hi, ty, self.tcx);
         let mut kind = PatKind::Range(Arc::new(PatRange { lo, hi, end, ty }));
         match (end, cmp) {
             // `x..y` where `x < y`.
@@ -244,7 +243,8 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
             (RangeEnd::Included, Some(Ordering::Less)) => {}
             // `x..=y` where `x == y` and `x` and `y` are finite.
             (RangeEnd::Included, Some(Ordering::Equal)) if lo.is_finite() && hi.is_finite() => {
-                kind = PatKind::Constant { value: lo.as_finite().unwrap() };
+                let value = ty::Value { ty, valtree: lo.as_finite().unwrap() };
+                kind = PatKind::Constant { value };
             }
             // `..=x` where `x == ty::MIN`.
             (RangeEnd::Included, Some(Ordering::Equal)) if !lo.is_finite() => {}
diff --git a/compiler/rustc_mir_build/src/thir/print.rs b/compiler/rustc_mir_build/src/thir/print.rs
index 5efc4be2de2..b7e8d6fea40 100644
--- a/compiler/rustc_mir_build/src/thir/print.rs
+++ b/compiler/rustc_mir_build/src/thir/print.rs
@@ -763,7 +763,7 @@ impl<'a, 'tcx> ThirPrinter<'a, 'tcx> {
             }
             PatKind::Constant { value } => {
                 print_indented!(self, "Constant {", depth_lvl + 1);
-                print_indented!(self, format!("value: {:?}", value), depth_lvl + 2);
+                print_indented!(self, format!("value: {}", value), depth_lvl + 2);
                 print_indented!(self, "}", depth_lvl + 1);
             }
             PatKind::ExpandedConstant { def_id, subpattern } => {
diff --git a/compiler/rustc_mir_dataflow/src/framework/graphviz.rs b/compiler/rustc_mir_dataflow/src/framework/graphviz.rs
index a7d5422a3d7..f86a15a8f92 100644
--- a/compiler/rustc_mir_dataflow/src/framework/graphviz.rs
+++ b/compiler/rustc_mir_dataflow/src/framework/graphviz.rs
@@ -800,6 +800,7 @@ where
     let re = regex!("\t?\u{001f}([+-])");
 
     let raw_diff = format!("{:#?}", DebugDiffWithAdapter { new, old, ctxt });
+    let raw_diff = dot::escape_html(&raw_diff);
 
     // Replace newlines in the `Debug` output with `<br/>`
     let raw_diff = raw_diff.replace('\n', r#"<br align="left"/>"#);
diff --git a/compiler/rustc_mir_transform/messages.ftl b/compiler/rustc_mir_transform/messages.ftl
index ae3062f07de..2e08f50e8a9 100644
--- a/compiler/rustc_mir_transform/messages.ftl
+++ b/compiler/rustc_mir_transform/messages.ftl
@@ -9,8 +9,6 @@ mir_transform_const_mut_borrow = taking a mutable reference to a `const` item
     .note2 = the mutable reference will refer to this temporary, not the original `const` item
     .note3 = mutable reference created due to call to this method
 
-mir_transform_exceeds_mcdc_test_vector_limit = number of total test vectors in one function will exceed limit ({$max_num_test_vectors}) if this decision is instrumented, so MC/DC analysis ignores it
-
 mir_transform_ffi_unwind_call = call to {$foreign ->
     [true] foreign function
     *[false] function pointer
diff --git a/compiler/rustc_mir_transform/src/check_call_recursion.rs b/compiler/rustc_mir_transform/src/check_call_recursion.rs
index 6d61ac2dd80..a9acb1da5a3 100644
--- a/compiler/rustc_mir_transform/src/check_call_recursion.rs
+++ b/compiler/rustc_mir_transform/src/check_call_recursion.rs
@@ -43,8 +43,8 @@ impl<'tcx> MirLint<'tcx> for CheckDropRecursion {
 
         // First check if `body` is an `fn drop()` of `Drop`
         if let DefKind::AssocFn = tcx.def_kind(def_id)
-        && let Some(trait_ref) =
-            tcx.impl_of_assoc(def_id.to_def_id()).and_then(|def_id| tcx.impl_trait_ref(def_id))
+        && let Some(impl_id) = tcx.trait_impl_of_assoc(def_id.to_def_id())
+        && let trait_ref = tcx.impl_trait_ref(impl_id).unwrap()
         && tcx.is_lang_item(trait_ref.instantiate_identity().def_id, LangItem::Drop)
         // avoid erroneous `Drop` impls from causing ICEs below
         && let sig = tcx.fn_sig(def_id).instantiate_identity()
diff --git a/compiler/rustc_mir_transform/src/check_inline.rs b/compiler/rustc_mir_transform/src/check_inline.rs
index af6da209081..8d28cb3ca00 100644
--- a/compiler/rustc_mir_transform/src/check_inline.rs
+++ b/compiler/rustc_mir_transform/src/check_inline.rs
@@ -45,12 +45,6 @@ pub(super) fn is_inline_valid_on_fn<'tcx>(
         return Err("#[rustc_no_mir_inline]");
     }
 
-    // FIXME(#127234): Coverage instrumentation currently doesn't handle inlined
-    // MIR correctly when Modified Condition/Decision Coverage is enabled.
-    if tcx.sess.instrument_coverage_mcdc() {
-        return Err("incompatible with MC/DC coverage");
-    }
-
     let ty = tcx.type_of(def_id);
     if match ty.instantiate_identity().kind() {
         ty::FnDef(..) => tcx.fn_sig(def_id).instantiate_identity().c_variadic(),
diff --git a/compiler/rustc_mir_transform/src/check_packed_ref.rs b/compiler/rustc_mir_transform/src/check_packed_ref.rs
index dcb812c7899..100104e9de0 100644
--- a/compiler/rustc_mir_transform/src/check_packed_ref.rs
+++ b/compiler/rustc_mir_transform/src/check_packed_ref.rs
@@ -40,7 +40,7 @@ impl<'tcx> Visitor<'tcx> for PackedRefChecker<'_, 'tcx> {
         if context.is_borrow() && util::is_disaligned(self.tcx, self.body, self.typing_env, *place)
         {
             let def_id = self.body.source.instance.def_id();
-            if let Some(impl_def_id) = self.tcx.impl_of_assoc(def_id)
+            if let Some(impl_def_id) = self.tcx.trait_impl_of_assoc(def_id)
                 && self.tcx.is_builtin_derived(impl_def_id)
             {
                 // If we ever reach here it means that the generated derive
diff --git a/compiler/rustc_mir_transform/src/coverage/hir_info.rs b/compiler/rustc_mir_transform/src/coverage/hir_info.rs
new file mode 100644
index 00000000000..28fdc52b06c
--- /dev/null
+++ b/compiler/rustc_mir_transform/src/coverage/hir_info.rs
@@ -0,0 +1,128 @@
+use rustc_hir as hir;
+use rustc_hir::intravisit::{Visitor, walk_expr};
+use rustc_middle::hir::nested_filter;
+use rustc_middle::ty::TyCtxt;
+use rustc_span::Span;
+use rustc_span::def_id::LocalDefId;
+
+/// Function information extracted from HIR by the coverage instrumentor.
+#[derive(Debug)]
+pub(crate) struct ExtractedHirInfo {
+    pub(crate) function_source_hash: u64,
+    pub(crate) is_async_fn: bool,
+    /// The span of the function's signature, if available.
+    /// Must have the same context and filename as the body span.
+    pub(crate) fn_sig_span: Option<Span>,
+    pub(crate) body_span: Span,
+    /// "Holes" are regions within the function body (or its expansions) that
+    /// should not be included in coverage spans for this function
+    /// (e.g. closures and nested items).
+    pub(crate) hole_spans: Vec<Span>,
+}
+
+pub(crate) fn extract_hir_info<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> ExtractedHirInfo {
+    // FIXME(#79625): Consider improving MIR to provide the information needed, to avoid going back
+    // to HIR for it.
+
+    // HACK: For synthetic MIR bodies (async closures), use the def id of the HIR body.
+    if tcx.is_synthetic_mir(def_id) {
+        return extract_hir_info(tcx, tcx.local_parent(def_id));
+    }
+
+    let hir_node = tcx.hir_node_by_def_id(def_id);
+    let fn_body_id = hir_node.body_id().expect("HIR node is a function with body");
+    let hir_body = tcx.hir_body(fn_body_id);
+
+    let maybe_fn_sig = hir_node.fn_sig();
+    let is_async_fn = maybe_fn_sig.is_some_and(|fn_sig| fn_sig.header.is_async());
+
+    let mut body_span = hir_body.value.span;
+
+    use hir::{Closure, Expr, ExprKind, Node};
+    // Unexpand a closure's body span back to the context of its declaration.
+    // This helps with closure bodies that consist of just a single bang-macro,
+    // and also with closure bodies produced by async desugaring.
+    if let Node::Expr(&Expr { kind: ExprKind::Closure(&Closure { fn_decl_span, .. }), .. }) =
+        hir_node
+    {
+        body_span = body_span.find_ancestor_in_same_ctxt(fn_decl_span).unwrap_or(body_span);
+    }
+
+    // The actual signature span is only used if it has the same context and
+    // filename as the body, and precedes the body.
+    let fn_sig_span = maybe_fn_sig.map(|fn_sig| fn_sig.span).filter(|&fn_sig_span| {
+        let source_map = tcx.sess.source_map();
+        let file_idx = |span: Span| source_map.lookup_source_file_idx(span.lo());
+
+        fn_sig_span.eq_ctxt(body_span)
+            && fn_sig_span.hi() <= body_span.lo()
+            && file_idx(fn_sig_span) == file_idx(body_span)
+    });
+
+    let function_source_hash = hash_mir_source(tcx, hir_body);
+
+    let hole_spans = extract_hole_spans_from_hir(tcx, hir_body);
+
+    ExtractedHirInfo { function_source_hash, is_async_fn, fn_sig_span, body_span, hole_spans }
+}
+
+fn hash_mir_source<'tcx>(tcx: TyCtxt<'tcx>, hir_body: &'tcx hir::Body<'tcx>) -> u64 {
+    let owner = hir_body.id().hir_id.owner;
+    tcx.hir_owner_nodes(owner)
+        .opt_hash_including_bodies
+        .expect("hash should be present when coverage instrumentation is enabled")
+        .to_smaller_hash()
+        .as_u64()
+}
+
+fn extract_hole_spans_from_hir<'tcx>(tcx: TyCtxt<'tcx>, hir_body: &hir::Body<'tcx>) -> Vec<Span> {
+    struct HolesVisitor<'tcx> {
+        tcx: TyCtxt<'tcx>,
+        hole_spans: Vec<Span>,
+    }
+
+    impl<'tcx> Visitor<'tcx> for HolesVisitor<'tcx> {
+        /// We have special handling for nested items, but we still want to
+        /// traverse into nested bodies of things that are not considered items,
+        /// such as "anon consts" (e.g. array lengths).
+        type NestedFilter = nested_filter::OnlyBodies;
+
+        fn maybe_tcx(&mut self) -> TyCtxt<'tcx> {
+            self.tcx
+        }
+
+        /// We override `visit_nested_item` instead of `visit_item` because we
+        /// only need the item's span, not the item itself.
+        fn visit_nested_item(&mut self, id: hir::ItemId) -> Self::Result {
+            let span = self.tcx.def_span(id.owner_id.def_id);
+            self.visit_hole_span(span);
+            // Having visited this item, we don't care about its children,
+            // so don't call `walk_item`.
+        }
+
+        // We override `visit_expr` instead of the more specific expression
+        // visitors, so that we have direct access to the expression span.
+        fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
+            match expr.kind {
+                hir::ExprKind::Closure(_) | hir::ExprKind::ConstBlock(_) => {
+                    self.visit_hole_span(expr.span);
+                    // Having visited this expression, we don't care about its
+                    // children, so don't call `walk_expr`.
+                }
+
+                // For other expressions, recursively visit as normal.
+                _ => walk_expr(self, expr),
+            }
+        }
+    }
+    impl HolesVisitor<'_> {
+        fn visit_hole_span(&mut self, hole_span: Span) {
+            self.hole_spans.push(hole_span);
+        }
+    }
+
+    let mut visitor = HolesVisitor { tcx, hole_spans: vec![] };
+
+    visitor.visit_body(hir_body);
+    visitor.hole_spans
+}
diff --git a/compiler/rustc_mir_transform/src/coverage/mappings.rs b/compiler/rustc_mir_transform/src/coverage/mappings.rs
index b0e24cf2bdb..8dbe564f517 100644
--- a/compiler/rustc_mir_transform/src/coverage/mappings.rs
+++ b/compiler/rustc_mir_transform/src/coverage/mappings.rs
@@ -1,109 +1,36 @@
-use std::collections::BTreeSet;
-
-use rustc_data_structures::fx::FxIndexMap;
 use rustc_index::IndexVec;
 use rustc_middle::mir::coverage::{
-    BlockMarkerId, BranchSpan, ConditionId, ConditionInfo, CoverageInfoHi, CoverageKind,
+    BlockMarkerId, BranchSpan, CoverageInfoHi, CoverageKind, Mapping, MappingKind,
 };
 use rustc_middle::mir::{self, BasicBlock, StatementKind};
 use rustc_middle::ty::TyCtxt;
-use rustc_span::Span;
 
-use crate::coverage::ExtractedHirInfo;
-use crate::coverage::graph::{BasicCoverageBlock, CoverageGraph};
+use crate::coverage::graph::CoverageGraph;
+use crate::coverage::hir_info::ExtractedHirInfo;
 use crate::coverage::spans::extract_refined_covspans;
 use crate::coverage::unexpand::unexpand_into_body_span;
-use crate::errors::MCDCExceedsTestVectorLimit;
-
-/// Associates an ordinary executable code span with its corresponding BCB.
-#[derive(Debug)]
-pub(super) struct CodeMapping {
-    pub(super) span: Span,
-    pub(super) bcb: BasicCoverageBlock,
-}
-
-/// This is separate from [`MCDCBranch`] to help prepare for larger changes
-/// that will be needed for improved branch coverage in the future.
-/// (See <https://github.com/rust-lang/rust/pull/124217>.)
-#[derive(Debug)]
-pub(super) struct BranchPair {
-    pub(super) span: Span,
-    pub(super) true_bcb: BasicCoverageBlock,
-    pub(super) false_bcb: BasicCoverageBlock,
-}
-
-/// Associates an MC/DC branch span with condition info besides fields for normal branch.
-#[derive(Debug)]
-pub(super) struct MCDCBranch {
-    pub(super) span: Span,
-    pub(super) true_bcb: BasicCoverageBlock,
-    pub(super) false_bcb: BasicCoverageBlock,
-    pub(super) condition_info: ConditionInfo,
-    // Offset added to test vector idx if this branch is evaluated to true.
-    pub(super) true_index: usize,
-    // Offset added to test vector idx if this branch is evaluated to false.
-    pub(super) false_index: usize,
-}
-
-/// Associates an MC/DC decision with its join BCBs.
-#[derive(Debug)]
-pub(super) struct MCDCDecision {
-    pub(super) span: Span,
-    pub(super) end_bcbs: BTreeSet<BasicCoverageBlock>,
-    pub(super) bitmap_idx: usize,
-    pub(super) num_test_vectors: usize,
-    pub(super) decision_depth: u16,
-}
-
-// LLVM uses `i32` to index the bitmap. Thus `i32::MAX` is the hard limit for number of all test vectors
-// in a function.
-const MCDC_MAX_BITMAP_SIZE: usize = i32::MAX as usize;
 
 #[derive(Default)]
-pub(super) struct ExtractedMappings {
-    pub(super) code_mappings: Vec<CodeMapping>,
-    pub(super) branch_pairs: Vec<BranchPair>,
-    pub(super) mcdc_bitmap_bits: usize,
-    pub(super) mcdc_degraded_branches: Vec<MCDCBranch>,
-    pub(super) mcdc_mappings: Vec<(MCDCDecision, Vec<MCDCBranch>)>,
+pub(crate) struct ExtractedMappings {
+    pub(crate) mappings: Vec<Mapping>,
 }
 
-/// Extracts coverage-relevant spans from MIR, and associates them with
-/// their corresponding BCBs.
-pub(super) fn extract_all_mapping_info_from_mir<'tcx>(
+/// Extracts coverage-relevant spans from MIR, and uses them to create
+/// coverage mapping data for inclusion in MIR.
+pub(crate) fn extract_mappings_from_mir<'tcx>(
     tcx: TyCtxt<'tcx>,
     mir_body: &mir::Body<'tcx>,
     hir_info: &ExtractedHirInfo,
     graph: &CoverageGraph,
 ) -> ExtractedMappings {
-    let mut code_mappings = vec![];
-    let mut branch_pairs = vec![];
-    let mut mcdc_bitmap_bits = 0;
-    let mut mcdc_degraded_branches = vec![];
-    let mut mcdc_mappings = vec![];
+    let mut mappings = vec![];
 
     // Extract ordinary code mappings from MIR statement/terminator spans.
-    extract_refined_covspans(tcx, mir_body, hir_info, graph, &mut code_mappings);
-
-    branch_pairs.extend(extract_branch_pairs(mir_body, hir_info, graph));
+    extract_refined_covspans(tcx, mir_body, hir_info, graph, &mut mappings);
 
-    extract_mcdc_mappings(
-        mir_body,
-        tcx,
-        hir_info.body_span,
-        graph,
-        &mut mcdc_bitmap_bits,
-        &mut mcdc_degraded_branches,
-        &mut mcdc_mappings,
-    );
+    extract_branch_mappings(mir_body, hir_info, graph, &mut mappings);
 
-    ExtractedMappings {
-        code_mappings,
-        branch_pairs,
-        mcdc_bitmap_bits,
-        mcdc_degraded_branches,
-        mcdc_mappings,
-    }
+    ExtractedMappings { mappings }
 }
 
 fn resolve_block_markers(
@@ -127,25 +54,18 @@ fn resolve_block_markers(
     block_markers
 }
 
-// FIXME: There is currently a lot of redundancy between
-// `extract_branch_pairs` and `extract_mcdc_mappings`. This is needed so
-// that they can each be modified without interfering with the other, but in
-// the long term we should try to bring them together again when branch coverage
-// and MC/DC coverage support are more mature.
-
-pub(super) fn extract_branch_pairs(
+pub(super) fn extract_branch_mappings(
     mir_body: &mir::Body<'_>,
     hir_info: &ExtractedHirInfo,
     graph: &CoverageGraph,
-) -> Vec<BranchPair> {
-    let Some(coverage_info_hi) = mir_body.coverage_info_hi.as_deref() else { return vec![] };
+    mappings: &mut Vec<Mapping>,
+) {
+    let Some(coverage_info_hi) = mir_body.coverage_info_hi.as_deref() else { return };
 
     let block_markers = resolve_block_markers(coverage_info_hi, mir_body);
 
-    coverage_info_hi
-        .branch_spans
-        .iter()
-        .filter_map(|&BranchSpan { span: raw_span, true_marker, false_marker }| {
+    mappings.extend(coverage_info_hi.branch_spans.iter().filter_map(
+        |&BranchSpan { span: raw_span, true_marker, false_marker }| try {
             // For now, ignore any branch span that was introduced by
             // expansion. This makes things like assert macros less noisy.
             if !raw_span.ctxt().outer_expn_data().is_root() {
@@ -158,179 +78,7 @@ pub(super) fn extract_branch_pairs(
             let true_bcb = bcb_from_marker(true_marker)?;
             let false_bcb = bcb_from_marker(false_marker)?;
 
-            Some(BranchPair { span, true_bcb, false_bcb })
-        })
-        .collect::<Vec<_>>()
-}
-
-pub(super) fn extract_mcdc_mappings(
-    mir_body: &mir::Body<'_>,
-    tcx: TyCtxt<'_>,
-    body_span: Span,
-    graph: &CoverageGraph,
-    mcdc_bitmap_bits: &mut usize,
-    mcdc_degraded_branches: &mut impl Extend<MCDCBranch>,
-    mcdc_mappings: &mut impl Extend<(MCDCDecision, Vec<MCDCBranch>)>,
-) {
-    let Some(coverage_info_hi) = mir_body.coverage_info_hi.as_deref() else { return };
-
-    let block_markers = resolve_block_markers(coverage_info_hi, mir_body);
-
-    let bcb_from_marker = |marker: BlockMarkerId| graph.bcb_from_bb(block_markers[marker]?);
-
-    let check_branch_bcb =
-        |raw_span: Span, true_marker: BlockMarkerId, false_marker: BlockMarkerId| {
-            // For now, ignore any branch span that was introduced by
-            // expansion. This makes things like assert macros less noisy.
-            if !raw_span.ctxt().outer_expn_data().is_root() {
-                return None;
-            }
-            let span = unexpand_into_body_span(raw_span, body_span)?;
-
-            let true_bcb = bcb_from_marker(true_marker)?;
-            let false_bcb = bcb_from_marker(false_marker)?;
-            Some((span, true_bcb, false_bcb))
-        };
-
-    let to_mcdc_branch = |&mir::coverage::MCDCBranchSpan {
-                              span: raw_span,
-                              condition_info,
-                              true_marker,
-                              false_marker,
-                          }| {
-        let (span, true_bcb, false_bcb) = check_branch_bcb(raw_span, true_marker, false_marker)?;
-        Some(MCDCBranch {
-            span,
-            true_bcb,
-            false_bcb,
-            condition_info,
-            true_index: usize::MAX,
-            false_index: usize::MAX,
-        })
-    };
-
-    let mut get_bitmap_idx = |num_test_vectors: usize| -> Option<usize> {
-        let bitmap_idx = *mcdc_bitmap_bits;
-        let next_bitmap_bits = bitmap_idx.saturating_add(num_test_vectors);
-        (next_bitmap_bits <= MCDC_MAX_BITMAP_SIZE).then(|| {
-            *mcdc_bitmap_bits = next_bitmap_bits;
-            bitmap_idx
-        })
-    };
-    mcdc_degraded_branches
-        .extend(coverage_info_hi.mcdc_degraded_branch_spans.iter().filter_map(to_mcdc_branch));
-
-    mcdc_mappings.extend(coverage_info_hi.mcdc_spans.iter().filter_map(|(decision, branches)| {
-        if branches.len() == 0 {
-            return None;
-        }
-        let decision_span = unexpand_into_body_span(decision.span, body_span)?;
-
-        let end_bcbs = decision
-            .end_markers
-            .iter()
-            .map(|&marker| bcb_from_marker(marker))
-            .collect::<Option<_>>()?;
-        let mut branch_mappings: Vec<_> = branches.into_iter().filter_map(to_mcdc_branch).collect();
-        if branch_mappings.len() != branches.len() {
-            mcdc_degraded_branches.extend(branch_mappings);
-            return None;
-        }
-        let num_test_vectors = calc_test_vectors_index(&mut branch_mappings);
-        let Some(bitmap_idx) = get_bitmap_idx(num_test_vectors) else {
-            tcx.dcx().emit_warn(MCDCExceedsTestVectorLimit {
-                span: decision_span,
-                max_num_test_vectors: MCDC_MAX_BITMAP_SIZE,
-            });
-            mcdc_degraded_branches.extend(branch_mappings);
-            return None;
-        };
-        // LLVM requires span of the decision contains all spans of its conditions.
-        // Usually the decision span meets the requirement well but in cases like macros it may not.
-        let span = branch_mappings
-            .iter()
-            .map(|branch| branch.span)
-            .reduce(|lhs, rhs| lhs.to(rhs))
-            .map(
-                |joint_span| {
-                    if decision_span.contains(joint_span) { decision_span } else { joint_span }
-                },
-            )
-            .expect("branch mappings are ensured to be non-empty as checked above");
-        Some((
-            MCDCDecision {
-                span,
-                end_bcbs,
-                bitmap_idx,
-                num_test_vectors,
-                decision_depth: decision.decision_depth,
-            },
-            branch_mappings,
-        ))
-    }));
-}
-
-// LLVM checks the executed test vector by accumulating indices of tested branches.
-// We calculate number of all possible test vectors of the decision and assign indices
-// to branches here.
-// See [the rfc](https://discourse.llvm.org/t/rfc-coverage-new-algorithm-and-file-format-for-mc-dc/76798/)
-// for more details about the algorithm.
-// This function is mostly like [`TVIdxBuilder::TvIdxBuilder`](https://github.com/llvm/llvm-project/blob/d594d9f7f4dc6eb748b3261917db689fdc348b96/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp#L226)
-fn calc_test_vectors_index(conditions: &mut Vec<MCDCBranch>) -> usize {
-    let mut indegree_stats = IndexVec::<ConditionId, usize>::from_elem_n(0, conditions.len());
-    // `num_paths` is `width` described at the llvm rfc, which indicates how many paths reaching the condition node.
-    let mut num_paths_stats = IndexVec::<ConditionId, usize>::from_elem_n(0, conditions.len());
-    let mut next_conditions = conditions
-        .iter_mut()
-        .map(|branch| {
-            let ConditionInfo { condition_id, true_next_id, false_next_id } = branch.condition_info;
-            [true_next_id, false_next_id]
-                .into_iter()
-                .flatten()
-                .for_each(|next_id| indegree_stats[next_id] += 1);
-            (condition_id, branch)
-        })
-        .collect::<FxIndexMap<_, _>>();
-
-    let mut queue =
-        std::collections::VecDeque::from_iter(next_conditions.swap_remove(&ConditionId::START));
-    num_paths_stats[ConditionId::START] = 1;
-    let mut decision_end_nodes = Vec::new();
-    while let Some(branch) = queue.pop_front() {
-        let ConditionInfo { condition_id, true_next_id, false_next_id } = branch.condition_info;
-        let (false_index, true_index) = (&mut branch.false_index, &mut branch.true_index);
-        let this_paths_count = num_paths_stats[condition_id];
-        // Note. First check the false next to ensure conditions are touched in same order with llvm-cov.
-        for (next, index) in [(false_next_id, false_index), (true_next_id, true_index)] {
-            if let Some(next_id) = next {
-                let next_paths_count = &mut num_paths_stats[next_id];
-                *index = *next_paths_count;
-                *next_paths_count = next_paths_count.saturating_add(this_paths_count);
-                let next_indegree = &mut indegree_stats[next_id];
-                *next_indegree -= 1;
-                if *next_indegree == 0 {
-                    queue.push_back(next_conditions.swap_remove(&next_id).expect(
-                        "conditions with non-zero indegree before must be in next_conditions",
-                    ));
-                }
-            } else {
-                decision_end_nodes.push((this_paths_count, condition_id, index));
-            }
-        }
-    }
-    assert!(next_conditions.is_empty(), "the decision tree has untouched nodes");
-    let mut cur_idx = 0;
-    // LLVM hopes the end nodes are sorted in descending order by `num_paths` so that it can
-    // optimize bitmap size for decisions in tree form such as `a && b && c && d && ...`.
-    decision_end_nodes.sort_by_key(|(num_paths, _, _)| usize::MAX - *num_paths);
-    for (num_paths, condition_id, index) in decision_end_nodes {
-        assert_eq!(
-            num_paths, num_paths_stats[condition_id],
-            "end nodes should not be updated since they were visited"
-        );
-        assert_eq!(*index, usize::MAX, "end nodes should not be assigned index before");
-        *index = cur_idx;
-        cur_idx += num_paths;
-    }
-    cur_idx
+            Mapping { span, kind: MappingKind::Branch { true_bcb, false_bcb } }
+        },
+    ));
 }
diff --git a/compiler/rustc_mir_transform/src/coverage/mod.rs b/compiler/rustc_mir_transform/src/coverage/mod.rs
index f253d1662ca..c5fef299244 100644
--- a/compiler/rustc_mir_transform/src/coverage/mod.rs
+++ b/compiler/rustc_mir_transform/src/coverage/mod.rs
@@ -1,5 +1,15 @@
+use rustc_middle::mir::coverage::{CoverageKind, FunctionCoverageInfo};
+use rustc_middle::mir::{self, BasicBlock, Statement, StatementKind, TerminatorKind};
+use rustc_middle::ty::TyCtxt;
+use tracing::{debug, debug_span, trace};
+
+use crate::coverage::counters::BcbCountersData;
+use crate::coverage::graph::CoverageGraph;
+use crate::coverage::mappings::ExtractedMappings;
+
 mod counters;
 mod graph;
+mod hir_info;
 mod mappings;
 pub(super) mod query;
 mod spans;
@@ -7,22 +17,6 @@ mod spans;
 mod tests;
 mod unexpand;
 
-use rustc_hir as hir;
-use rustc_hir::intravisit::{Visitor, walk_expr};
-use rustc_middle::hir::nested_filter;
-use rustc_middle::mir::coverage::{
-    CoverageKind, DecisionInfo, FunctionCoverageInfo, Mapping, MappingKind,
-};
-use rustc_middle::mir::{self, BasicBlock, Statement, StatementKind, TerminatorKind};
-use rustc_middle::ty::TyCtxt;
-use rustc_span::Span;
-use rustc_span::def_id::LocalDefId;
-use tracing::{debug, debug_span, trace};
-
-use crate::coverage::counters::BcbCountersData;
-use crate::coverage::graph::CoverageGraph;
-use crate::coverage::mappings::ExtractedMappings;
-
 /// Inserts `StatementKind::Coverage` statements that either instrument the binary with injected
 /// counters, via intrinsic `llvm.instrprof.increment`, and/or inject metadata used during codegen
 /// to construct the coverage map.
@@ -69,7 +63,7 @@ fn instrument_function_for_coverage<'tcx>(tcx: TyCtxt<'tcx>, mir_body: &mut mir:
     let def_id = mir_body.source.def_id();
     let _span = debug_span!("instrument_function_for_coverage", ?def_id).entered();
 
-    let hir_info = extract_hir_info(tcx, def_id.expect_local());
+    let hir_info = hir_info::extract_hir_info(tcx, def_id.expect_local());
 
     // Build the coverage graph, which is a simplified view of the MIR control-flow
     // graph that ignores some details not relevant to coverage instrumentation.
@@ -77,10 +71,8 @@ fn instrument_function_for_coverage<'tcx>(tcx: TyCtxt<'tcx>, mir_body: &mut mir:
 
     ////////////////////////////////////////////////////
     // Extract coverage spans and other mapping info from MIR.
-    let extracted_mappings =
-        mappings::extract_all_mapping_info_from_mir(tcx, mir_body, &hir_info, &graph);
-
-    let mappings = create_mappings(&extracted_mappings);
+    let ExtractedMappings { mappings } =
+        mappings::extract_mappings_from_mir(tcx, mir_body, &hir_info, &graph);
     if mappings.is_empty() {
         // No spans could be converted into valid mappings, so skip this function.
         debug!("no spans could be converted into valid mappings; skipping");
@@ -95,14 +87,6 @@ fn instrument_function_for_coverage<'tcx>(tcx: TyCtxt<'tcx>, mir_body: &mut mir:
 
     // Inject coverage statements into MIR.
     inject_coverage_statements(mir_body, &graph);
-    inject_mcdc_statements(mir_body, &graph, &extracted_mappings);
-
-    let mcdc_num_condition_bitmaps = extracted_mappings
-        .mcdc_mappings
-        .iter()
-        .map(|&(mappings::MCDCDecision { decision_depth, .. }, _)| decision_depth)
-        .max()
-        .map_or(0, |max| usize::from(max) + 1);
 
     mir_body.function_coverage_info = Some(Box::new(FunctionCoverageInfo {
         function_source_hash: hir_info.function_source_hash,
@@ -111,97 +95,9 @@ fn instrument_function_for_coverage<'tcx>(tcx: TyCtxt<'tcx>, mir_body: &mut mir:
         priority_list,
 
         mappings,
-
-        mcdc_bitmap_bits: extracted_mappings.mcdc_bitmap_bits,
-        mcdc_num_condition_bitmaps,
     }));
 }
 
-/// For each coverage span extracted from MIR, create a corresponding mapping.
-///
-/// FIXME(Zalathar): This used to be where BCBs in the extracted mappings were
-/// resolved to a `CovTerm`. But that is now handled elsewhere, so this
-/// function can potentially be simplified even further.
-fn create_mappings(extracted_mappings: &ExtractedMappings) -> Vec<Mapping> {
-    // Fully destructure the mappings struct to make sure we don't miss any kinds.
-    let ExtractedMappings {
-        code_mappings,
-        branch_pairs,
-        mcdc_bitmap_bits: _,
-        mcdc_degraded_branches,
-        mcdc_mappings,
-    } = extracted_mappings;
-    let mut mappings = Vec::new();
-
-    mappings.extend(code_mappings.iter().map(
-        // Ordinary code mappings are the simplest kind.
-        |&mappings::CodeMapping { span, bcb }| {
-            let kind = MappingKind::Code { bcb };
-            Mapping { kind, span }
-        },
-    ));
-
-    mappings.extend(branch_pairs.iter().map(
-        |&mappings::BranchPair { span, true_bcb, false_bcb }| {
-            let kind = MappingKind::Branch { true_bcb, false_bcb };
-            Mapping { kind, span }
-        },
-    ));
-
-    // MCDC branch mappings are appended with their decisions in case decisions were ignored.
-    mappings.extend(mcdc_degraded_branches.iter().map(
-        |&mappings::MCDCBranch {
-             span,
-             true_bcb,
-             false_bcb,
-             condition_info: _,
-             true_index: _,
-             false_index: _,
-         }| { Mapping { kind: MappingKind::Branch { true_bcb, false_bcb }, span } },
-    ));
-
-    for (decision, branches) in mcdc_mappings {
-        // FIXME(#134497): Previously it was possible for some of these branch
-        // conversions to fail, in which case the remaining branches in the
-        // decision would be degraded to plain `MappingKind::Branch`.
-        // The changes in #134497 made that failure impossible, because the
-        // fallible step was deferred to codegen. But the corresponding code
-        // in codegen wasn't updated to detect the need for a degrade step.
-        let conditions = branches
-            .into_iter()
-            .map(
-                |&mappings::MCDCBranch {
-                     span,
-                     true_bcb,
-                     false_bcb,
-                     condition_info,
-                     true_index: _,
-                     false_index: _,
-                 }| {
-                    Mapping {
-                        kind: MappingKind::MCDCBranch {
-                            true_bcb,
-                            false_bcb,
-                            mcdc_params: condition_info,
-                        },
-                        span,
-                    }
-                },
-            )
-            .collect::<Vec<_>>();
-
-        // LLVM requires end index for counter mapping regions.
-        let kind = MappingKind::MCDCDecision(DecisionInfo {
-            bitmap_idx: (decision.bitmap_idx + decision.num_test_vectors) as u32,
-            num_conditions: u16::try_from(conditions.len()).unwrap(),
-        });
-        let span = decision.span;
-        mappings.extend(std::iter::once(Mapping { kind, span }).chain(conditions.into_iter()));
-    }
-
-    mappings
-}
-
 /// Inject any necessary coverage statements into MIR, so that they influence codegen.
 fn inject_coverage_statements<'tcx>(mir_body: &mut mir::Body<'tcx>, graph: &CoverageGraph) {
     for (bcb, data) in graph.iter_enumerated() {
@@ -210,51 +106,6 @@ fn inject_coverage_statements<'tcx>(mir_body: &mut mir::Body<'tcx>, graph: &Cove
     }
 }
 
-/// For each conditions inject statements to update condition bitmap after it has been evaluated.
-/// For each decision inject statements to update test vector bitmap after it has been evaluated.
-fn inject_mcdc_statements<'tcx>(
-    mir_body: &mut mir::Body<'tcx>,
-    graph: &CoverageGraph,
-    extracted_mappings: &ExtractedMappings,
-) {
-    for (decision, conditions) in &extracted_mappings.mcdc_mappings {
-        // Inject test vector update first because `inject_statement` always insert new statement at head.
-        for &end in &decision.end_bcbs {
-            let end_bb = graph[end].leader_bb();
-            inject_statement(
-                mir_body,
-                CoverageKind::TestVectorBitmapUpdate {
-                    bitmap_idx: decision.bitmap_idx as u32,
-                    decision_depth: decision.decision_depth,
-                },
-                end_bb,
-            );
-        }
-
-        for &mappings::MCDCBranch {
-            span: _,
-            true_bcb,
-            false_bcb,
-            condition_info: _,
-            true_index,
-            false_index,
-        } in conditions
-        {
-            for (index, bcb) in [(false_index, false_bcb), (true_index, true_bcb)] {
-                let bb = graph[bcb].leader_bb();
-                inject_statement(
-                    mir_body,
-                    CoverageKind::CondBitmapUpdate {
-                        index: index as u32,
-                        decision_depth: decision.decision_depth,
-                    },
-                    bb,
-                );
-            }
-        }
-    }
-}
-
 fn inject_statement(mir_body: &mut mir::Body<'_>, counter_kind: CoverageKind, bb: BasicBlock) {
     debug!("  injecting statement {counter_kind:?} for {bb:?}");
     let data = &mut mir_body[bb];
@@ -262,122 +113,3 @@ fn inject_statement(mir_body: &mut mir::Body<'_>, counter_kind: CoverageKind, bb
     let statement = Statement::new(source_info, StatementKind::Coverage(counter_kind));
     data.statements.insert(0, statement);
 }
-
-/// Function information extracted from HIR by the coverage instrumentor.
-#[derive(Debug)]
-struct ExtractedHirInfo {
-    function_source_hash: u64,
-    is_async_fn: bool,
-    /// The span of the function's signature, if available.
-    /// Must have the same context and filename as the body span.
-    fn_sig_span: Option<Span>,
-    body_span: Span,
-    /// "Holes" are regions within the function body (or its expansions) that
-    /// should not be included in coverage spans for this function
-    /// (e.g. closures and nested items).
-    hole_spans: Vec<Span>,
-}
-
-fn extract_hir_info<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> ExtractedHirInfo {
-    // FIXME(#79625): Consider improving MIR to provide the information needed, to avoid going back
-    // to HIR for it.
-
-    // HACK: For synthetic MIR bodies (async closures), use the def id of the HIR body.
-    if tcx.is_synthetic_mir(def_id) {
-        return extract_hir_info(tcx, tcx.local_parent(def_id));
-    }
-
-    let hir_node = tcx.hir_node_by_def_id(def_id);
-    let fn_body_id = hir_node.body_id().expect("HIR node is a function with body");
-    let hir_body = tcx.hir_body(fn_body_id);
-
-    let maybe_fn_sig = hir_node.fn_sig();
-    let is_async_fn = maybe_fn_sig.is_some_and(|fn_sig| fn_sig.header.is_async());
-
-    let mut body_span = hir_body.value.span;
-
-    use hir::{Closure, Expr, ExprKind, Node};
-    // Unexpand a closure's body span back to the context of its declaration.
-    // This helps with closure bodies that consist of just a single bang-macro,
-    // and also with closure bodies produced by async desugaring.
-    if let Node::Expr(&Expr { kind: ExprKind::Closure(&Closure { fn_decl_span, .. }), .. }) =
-        hir_node
-    {
-        body_span = body_span.find_ancestor_in_same_ctxt(fn_decl_span).unwrap_or(body_span);
-    }
-
-    // The actual signature span is only used if it has the same context and
-    // filename as the body, and precedes the body.
-    let fn_sig_span = maybe_fn_sig.map(|fn_sig| fn_sig.span).filter(|&fn_sig_span| {
-        let source_map = tcx.sess.source_map();
-        let file_idx = |span: Span| source_map.lookup_source_file_idx(span.lo());
-
-        fn_sig_span.eq_ctxt(body_span)
-            && fn_sig_span.hi() <= body_span.lo()
-            && file_idx(fn_sig_span) == file_idx(body_span)
-    });
-
-    let function_source_hash = hash_mir_source(tcx, hir_body);
-
-    let hole_spans = extract_hole_spans_from_hir(tcx, hir_body);
-
-    ExtractedHirInfo { function_source_hash, is_async_fn, fn_sig_span, body_span, hole_spans }
-}
-
-fn hash_mir_source<'tcx>(tcx: TyCtxt<'tcx>, hir_body: &'tcx hir::Body<'tcx>) -> u64 {
-    // FIXME(cjgillot) Stop hashing HIR manually here.
-    let owner = hir_body.id().hir_id.owner;
-    tcx.hir_owner_nodes(owner).opt_hash_including_bodies.unwrap().to_smaller_hash().as_u64()
-}
-
-fn extract_hole_spans_from_hir<'tcx>(tcx: TyCtxt<'tcx>, hir_body: &hir::Body<'tcx>) -> Vec<Span> {
-    struct HolesVisitor<'tcx> {
-        tcx: TyCtxt<'tcx>,
-        hole_spans: Vec<Span>,
-    }
-
-    impl<'tcx> Visitor<'tcx> for HolesVisitor<'tcx> {
-        /// We have special handling for nested items, but we still want to
-        /// traverse into nested bodies of things that are not considered items,
-        /// such as "anon consts" (e.g. array lengths).
-        type NestedFilter = nested_filter::OnlyBodies;
-
-        fn maybe_tcx(&mut self) -> TyCtxt<'tcx> {
-            self.tcx
-        }
-
-        /// We override `visit_nested_item` instead of `visit_item` because we
-        /// only need the item's span, not the item itself.
-        fn visit_nested_item(&mut self, id: hir::ItemId) -> Self::Result {
-            let span = self.tcx.def_span(id.owner_id.def_id);
-            self.visit_hole_span(span);
-            // Having visited this item, we don't care about its children,
-            // so don't call `walk_item`.
-        }
-
-        // We override `visit_expr` instead of the more specific expression
-        // visitors, so that we have direct access to the expression span.
-        fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
-            match expr.kind {
-                hir::ExprKind::Closure(_) | hir::ExprKind::ConstBlock(_) => {
-                    self.visit_hole_span(expr.span);
-                    // Having visited this expression, we don't care about its
-                    // children, so don't call `walk_expr`.
-                }
-
-                // For other expressions, recursively visit as normal.
-                _ => walk_expr(self, expr),
-            }
-        }
-    }
-    impl HolesVisitor<'_> {
-        fn visit_hole_span(&mut self, hole_span: Span) {
-            self.hole_spans.push(hole_span);
-        }
-    }
-
-    let mut visitor = HolesVisitor { tcx, hole_spans: vec![] };
-
-    visitor.visit_body(hir_body);
-    visitor.hole_spans
-}
diff --git a/compiler/rustc_mir_transform/src/coverage/query.rs b/compiler/rustc_mir_transform/src/coverage/query.rs
index c195ca51540..63c550c27fe 100644
--- a/compiler/rustc_mir_transform/src/coverage/query.rs
+++ b/compiler/rustc_mir_transform/src/coverage/query.rs
@@ -111,11 +111,6 @@ fn coverage_ids_info<'tcx>(
                 bcb_needs_counter.insert(true_bcb);
                 bcb_needs_counter.insert(false_bcb);
             }
-            MappingKind::MCDCBranch { true_bcb, false_bcb, mcdc_params: _ } => {
-                bcb_needs_counter.insert(true_bcb);
-                bcb_needs_counter.insert(false_bcb);
-            }
-            MappingKind::MCDCDecision(_) => {}
         }
     }
 
diff --git a/compiler/rustc_mir_transform/src/coverage/spans.rs b/compiler/rustc_mir_transform/src/coverage/spans.rs
index 0ee42abb195..d1b04c8f587 100644
--- a/compiler/rustc_mir_transform/src/coverage/spans.rs
+++ b/compiler/rustc_mir_transform/src/coverage/spans.rs
@@ -1,14 +1,15 @@
 use rustc_data_structures::fx::FxHashSet;
 use rustc_middle::mir;
-use rustc_middle::mir::coverage::START_BCB;
+use rustc_middle::mir::coverage::{Mapping, MappingKind, START_BCB};
 use rustc_middle::ty::TyCtxt;
 use rustc_span::source_map::SourceMap;
 use rustc_span::{BytePos, DesugaringKind, ExpnKind, MacroKind, Span};
 use tracing::instrument;
 
 use crate::coverage::graph::{BasicCoverageBlock, CoverageGraph};
+use crate::coverage::hir_info::ExtractedHirInfo;
 use crate::coverage::spans::from_mir::{Hole, RawSpanFromMir, SpanFromMir};
-use crate::coverage::{ExtractedHirInfo, mappings, unexpand};
+use crate::coverage::unexpand;
 
 mod from_mir;
 
@@ -17,7 +18,7 @@ pub(super) fn extract_refined_covspans<'tcx>(
     mir_body: &mir::Body<'tcx>,
     hir_info: &ExtractedHirInfo,
     graph: &CoverageGraph,
-    code_mappings: &mut Vec<mappings::CodeMapping>,
+    mappings: &mut Vec<Mapping>,
 ) {
     if hir_info.is_async_fn {
         // An async function desugars into a function that returns a future,
@@ -25,7 +26,7 @@ pub(super) fn extract_refined_covspans<'tcx>(
         // outer function will be unhelpful, so just keep the signature span
         // and ignore all of the spans in the MIR body.
         if let Some(span) = hir_info.fn_sig_span {
-            code_mappings.push(mappings::CodeMapping { span, bcb: START_BCB });
+            mappings.push(Mapping { span, kind: MappingKind::Code { bcb: START_BCB } })
         }
         return;
     }
@@ -110,9 +111,9 @@ pub(super) fn extract_refined_covspans<'tcx>(
     // Merge covspans that can be merged.
     covspans.dedup_by(|b, a| a.merge_if_eligible(b));
 
-    code_mappings.extend(covspans.into_iter().map(|Covspan { span, bcb }| {
+    mappings.extend(covspans.into_iter().map(|Covspan { span, bcb }| {
         // Each span produced by the refiner represents an ordinary code region.
-        mappings::CodeMapping { span, bcb }
+        Mapping { span, kind: MappingKind::Code { bcb } }
     }));
 }
 
diff --git a/compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs b/compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs
index 804cd8ab3f7..7985e1c0798 100644
--- a/compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs
+++ b/compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs
@@ -101,11 +101,7 @@ fn filtered_statement_span(statement: &Statement<'_>) -> Option<Span> {
         StatementKind::Coverage(CoverageKind::BlockMarker { .. }) => None,
 
         // These coverage statements should not exist prior to coverage instrumentation.
-        StatementKind::Coverage(
-            CoverageKind::VirtualCounter { .. }
-            | CoverageKind::CondBitmapUpdate { .. }
-            | CoverageKind::TestVectorBitmapUpdate { .. },
-        ) => bug!(
+        StatementKind::Coverage(CoverageKind::VirtualCounter { .. }) => bug!(
             "Unexpected coverage statement found during coverage instrumentation: {statement:?}"
         ),
     }
diff --git a/compiler/rustc_mir_transform/src/cross_crate_inline.rs b/compiler/rustc_mir_transform/src/cross_crate_inline.rs
index b186c2bd775..03fdf9fbac5 100644
--- a/compiler/rustc_mir_transform/src/cross_crate_inline.rs
+++ b/compiler/rustc_mir_transform/src/cross_crate_inline.rs
@@ -18,7 +18,7 @@ fn cross_crate_inlinable(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
     let codegen_fn_attrs = tcx.codegen_fn_attrs(def_id);
     // If this has an extern indicator, then this function is globally shared and thus will not
     // generate cgu-internal copies which would make it cross-crate inlinable.
-    if codegen_fn_attrs.contains_extern_indicator() {
+    if codegen_fn_attrs.contains_extern_indicator(tcx, def_id.into()) {
         return false;
     }
 
diff --git a/compiler/rustc_mir_transform/src/errors.rs b/compiler/rustc_mir_transform/src/errors.rs
index cffa0183fa7..ad9635aae33 100644
--- a/compiler/rustc_mir_transform/src/errors.rs
+++ b/compiler/rustc_mir_transform/src/errors.rs
@@ -117,14 +117,6 @@ pub(crate) struct FnItemRef {
     pub ident: Ident,
 }
 
-#[derive(Diagnostic)]
-#[diag(mir_transform_exceeds_mcdc_test_vector_limit)]
-pub(crate) struct MCDCExceedsTestVectorLimit {
-    #[primary_span]
-    pub(crate) span: Span,
-    pub(crate) max_num_test_vectors: usize,
-}
-
 pub(crate) struct MustNotSupend<'a, 'tcx> {
     pub tcx: TyCtxt<'tcx>,
     pub yield_sp: Span,
diff --git a/compiler/rustc_mir_transform/src/gvn.rs b/compiler/rustc_mir_transform/src/gvn.rs
index dc99b67a1e8..952da2cdf72 100644
--- a/compiler/rustc_mir_transform/src/gvn.rs
+++ b/compiler/rustc_mir_transform/src/gvn.rs
@@ -756,7 +756,13 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                 && let Some(v) = self.simplify_place_value(&mut pointee, location)
             {
                 value = v;
-                place_ref = pointee.project_deeper(&place.projection[index..], self.tcx).as_ref();
+                // `pointee` holds a `Place`, so `ProjectionElem::Index` holds a `Local`.
+                // That local is SSA, but we otherwise have no guarantee on that local's value at
+                // the current location compared to its value where `pointee` was borrowed.
+                if pointee.projection.iter().all(|elem| !matches!(elem, ProjectionElem::Index(_))) {
+                    place_ref =
+                        pointee.project_deeper(&place.projection[index..], self.tcx).as_ref();
+                }
             }
             if let Some(local) = self.try_as_local(value, location) {
                 // Both `local` and `Place { local: place.local, projection: projection[..index] }`
@@ -774,7 +780,12 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             && let Some(v) = self.simplify_place_value(&mut pointee, location)
         {
             value = v;
-            place_ref = pointee.project_deeper(&[], self.tcx).as_ref();
+            // `pointee` holds a `Place`, so `ProjectionElem::Index` holds a `Local`.
+            // That local is SSA, but we otherwise have no guarantee on that local's value at
+            // the current location compared to its value where `pointee` was borrowed.
+            if pointee.projection.iter().all(|elem| !matches!(elem, ProjectionElem::Index(_))) {
+                place_ref = pointee.project_deeper(&[], self.tcx).as_ref();
+            }
         }
         if let Some(new_local) = self.try_as_local(value, location) {
             place_ref = PlaceRef { local: new_local, projection: &[] };
diff --git a/compiler/rustc_mir_transform/src/pass_manager.rs b/compiler/rustc_mir_transform/src/pass_manager.rs
index 7a8d3ba1ff1..5b3ddcc777b 100644
--- a/compiler/rustc_mir_transform/src/pass_manager.rs
+++ b/compiler/rustc_mir_transform/src/pass_manager.rs
@@ -41,19 +41,40 @@ fn to_profiler_name(type_name: &'static str) -> &'static str {
     })
 }
 
-// const wrapper for `if let Some((_, tail)) = name.rsplit_once(':') { tail } else { name }`
-const fn c_name(name: &'static str) -> &'static str {
+// A function that simplifies a pass's type_name. E.g. `Baz`, `Baz<'_>`,
+// `foo::bar::Baz`, and `foo::bar::Baz<'a, 'b>` all become `Baz`.
+//
+// It's `const` for perf reasons: it's called a lot, and doing the string
+// operations at runtime causes a non-trivial slowdown. If
+// `split_once`/`rsplit_once` become `const` its body could be simplified to
+// this:
+// ```ignore (fragment)
+// let name = if let Some((_, tail)) = name.rsplit_once(':') { tail } else { name };
+// let name = if let Some((head, _)) = name.split_once('<') { head } else { name };
+// name
+// ```
+const fn simplify_pass_type_name(name: &'static str) -> &'static str {
     // FIXME(const-hack) Simplify the implementation once more `str` methods get const-stable.
-    // and inline into call site
+
+    // Work backwards from the end. If a ':' is hit, strip it and everything before it.
     let bytes = name.as_bytes();
     let mut i = bytes.len();
     while i > 0 && bytes[i - 1] != b':' {
-        i = i - 1;
+        i -= 1;
     }
     let (_, bytes) = bytes.split_at(i);
+
+    // Work forwards from the start of what's left. If a '<' is hit, strip it and everything after
+    // it.
+    let mut i = 0;
+    while i < bytes.len() && bytes[i] != b'<' {
+        i += 1;
+    }
+    let (bytes, _) = bytes.split_at(i);
+
     match std::str::from_utf8(bytes) {
         Ok(name) => name,
-        Err(_) => name,
+        Err(_) => panic!(),
     }
 }
 
@@ -62,12 +83,7 @@ const fn c_name(name: &'static str) -> &'static str {
 /// loop that goes over each available MIR and applies `run_pass`.
 pub(super) trait MirPass<'tcx> {
     fn name(&self) -> &'static str {
-        // FIXME(const-hack) Simplify the implementation once more `str` methods get const-stable.
-        // See copypaste in `MirLint`
-        const {
-            let name = std::any::type_name::<Self>();
-            c_name(name)
-        }
+        const { simplify_pass_type_name(std::any::type_name::<Self>()) }
     }
 
     fn profiler_name(&self) -> &'static str {
@@ -101,12 +117,7 @@ pub(super) trait MirPass<'tcx> {
 /// disabled (via the `Lint` adapter).
 pub(super) trait MirLint<'tcx> {
     fn name(&self) -> &'static str {
-        // FIXME(const-hack) Simplify the implementation once more `str` methods get const-stable.
-        // See copypaste in `MirPass`
-        const {
-            let name = std::any::type_name::<Self>();
-            c_name(name)
-        }
+        const { simplify_pass_type_name(std::any::type_name::<Self>()) }
     }
 
     fn is_enabled(&self, _sess: &Session) -> bool {
diff --git a/compiler/rustc_mir_transform/src/remove_unneeded_drops.rs b/compiler/rustc_mir_transform/src/remove_unneeded_drops.rs
index 43f80508e4a..6c2dfc59da2 100644
--- a/compiler/rustc_mir_transform/src/remove_unneeded_drops.rs
+++ b/compiler/rustc_mir_transform/src/remove_unneeded_drops.rs
@@ -4,7 +4,13 @@
 //! useful because (unlike MIR building) it runs after type checking, so it can make use of
 //! `TypingMode::PostAnalysis` to provide more precise type information, especially about opaque
 //! types.
+//!
+//! When we're optimizing, we also remove calls to `drop_in_place<T>` when `T` isn't `needs_drop`,
+//! as those are essentially equivalent to `Drop` terminators. While the compiler doesn't insert
+//! them automatically, preferring the built-in instead, they're common in generic code (such as
+//! `Vec::truncate`) so removing them from things like inlined `Vec<u8>` is helpful.
 
+use rustc_hir::LangItem;
 use rustc_middle::mir::*;
 use rustc_middle::ty::TyCtxt;
 use tracing::{debug, trace};
@@ -21,15 +27,26 @@ impl<'tcx> crate::MirPass<'tcx> for RemoveUnneededDrops {
         let mut should_simplify = false;
         for block in body.basic_blocks.as_mut() {
             let terminator = block.terminator_mut();
-            if let TerminatorKind::Drop { place, target, .. } = terminator.kind {
-                let ty = place.ty(&body.local_decls, tcx);
-                if ty.ty.needs_drop(tcx, typing_env) {
-                    continue;
+            let (ty, target) = match terminator.kind {
+                TerminatorKind::Drop { place, target, .. } => {
+                    (place.ty(&body.local_decls, tcx).ty, target)
+                }
+                TerminatorKind::Call { ref func, target: Some(target), .. }
+                    if tcx.sess.mir_opt_level() > 0
+                        && let Some((def_id, generics)) = func.const_fn_def()
+                        && tcx.is_lang_item(def_id, LangItem::DropInPlace) =>
+                {
+                    (generics.type_at(0), target)
                 }
-                debug!("SUCCESS: replacing `drop` with goto({:?})", target);
-                terminator.kind = TerminatorKind::Goto { target };
-                should_simplify = true;
+                _ => continue,
+            };
+
+            if ty.needs_drop(tcx, typing_env) {
+                continue;
             }
+            debug!("SUCCESS: replacing `drop` with goto({:?})", target);
+            terminator.kind = TerminatorKind::Goto { target };
+            should_simplify = true;
         }
 
         // if we applied optimizations, we potentially have some cfg to cleanup to
diff --git a/compiler/rustc_mir_transform/src/shim.rs b/compiler/rustc_mir_transform/src/shim.rs
index c687036f544..c6760b3583f 100644
--- a/compiler/rustc_mir_transform/src/shim.rs
+++ b/compiler/rustc_mir_transform/src/shim.rs
@@ -75,7 +75,7 @@ fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceKind<'tcx>) -> Body<
             build_call_shim(tcx, instance, Some(adjustment), CallKind::Direct(def_id))
         }
         ty::InstanceKind::FnPtrShim(def_id, ty) => {
-            let trait_ = tcx.trait_of_assoc(def_id).unwrap();
+            let trait_ = tcx.parent(def_id);
             // Supports `Fn` or `async Fn` traits.
             let adjustment = match tcx
                 .fn_trait_kind_from_def_id(trait_)
diff --git a/compiler/rustc_monomorphize/Cargo.toml b/compiler/rustc_monomorphize/Cargo.toml
index 0ed5b4fc0d0..09a55f0b5f8 100644
--- a/compiler/rustc_monomorphize/Cargo.toml
+++ b/compiler/rustc_monomorphize/Cargo.toml
@@ -6,7 +6,6 @@ edition = "2024"
 [dependencies]
 # tidy-alphabetical-start
 rustc_abi = { path = "../rustc_abi" }
-rustc_ast = { path = "../rustc_ast" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
 rustc_fluent_macro = { path = "../rustc_fluent_macro" }
@@ -15,7 +14,6 @@ rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
-rustc_symbol_mangling = { path = "../rustc_symbol_mangling" }
 rustc_target = { path = "../rustc_target" }
 serde = "1"
 serde_json = "1"
diff --git a/compiler/rustc_monomorphize/messages.ftl b/compiler/rustc_monomorphize/messages.ftl
index 2bd19e81b01..9595a5b5ac7 100644
--- a/compiler/rustc_monomorphize/messages.ftl
+++ b/compiler/rustc_monomorphize/messages.ftl
@@ -40,7 +40,10 @@ monomorphize_couldnt_dump_mono_stats =
     unexpected error occurred while dumping monomorphization stats: {$error}
 
 monomorphize_encountered_error_while_instantiating =
-    the above error was encountered while instantiating `{$formatted_item}`
+    the above error was encountered while instantiating `{$kind} {$instance}`
+
+monomorphize_encountered_error_while_instantiating_global_asm =
+    the above error was encountered while instantiating `global_asm`
 
 monomorphize_large_assignments =
     moving {$size} bytes
@@ -52,12 +55,10 @@ monomorphize_no_optimized_mir =
     .note = missing optimized MIR for this item (was the crate `{$crate_name}` compiled with `--emit=metadata`?)
 
 monomorphize_recursion_limit =
-    reached the recursion limit while instantiating `{$shrunk}`
+    reached the recursion limit while instantiating `{$instance}`
     .note = `{$def_path_str}` defined here
 
 monomorphize_start_not_found = using `fn main` requires the standard library
     .help = use `#![no_main]` to bypass the Rust generated entrypoint and declare a platform specific entrypoint yourself, usually with `#[no_mangle]`
 
 monomorphize_symbol_already_defined = symbol `{$symbol}` is already defined
-
-monomorphize_written_to_path = the full type name has been written to '{$path}'
diff --git a/compiler/rustc_monomorphize/src/collector.rs b/compiler/rustc_monomorphize/src/collector.rs
index 35b80a9b96f..6a836442c32 100644
--- a/compiler/rustc_monomorphize/src/collector.rs
+++ b/compiler/rustc_monomorphize/src/collector.rs
@@ -205,8 +205,9 @@
 //! this is not implemented however: a mono item will be produced
 //! regardless of whether it is actually needed or not.
 
+mod autodiff;
+
 use std::cell::OnceCell;
-use std::path::PathBuf;
 
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::sync::{MTLock, par_for_each_in};
@@ -224,7 +225,6 @@ use rustc_middle::mir::{self, Location, MentionedItem, traversal};
 use rustc_middle::query::TyCtxtAt;
 use rustc_middle::ty::adjustment::{CustomCoerceUnsized, PointerCoercion};
 use rustc_middle::ty::layout::ValidityRequirement;
-use rustc_middle::ty::print::{shrunk_instance_name, with_no_trimmed_paths};
 use rustc_middle::ty::{
     self, GenericArgs, GenericParamDefKind, Instance, InstanceKind, Ty, TyCtxt, TypeFoldable,
     TypeVisitableExt, VtblEntry,
@@ -237,7 +237,11 @@ use rustc_span::source_map::{Spanned, dummy_spanned, respan};
 use rustc_span::{DUMMY_SP, Span};
 use tracing::{debug, instrument, trace};
 
-use crate::errors::{self, EncounteredErrorWhileInstantiating, NoOptimizedMir, RecursionLimit};
+use crate::collector::autodiff::collect_autodiff_fn;
+use crate::errors::{
+    self, EncounteredErrorWhileInstantiating, EncounteredErrorWhileInstantiatingGlobalAsm,
+    NoOptimizedMir, RecursionLimit,
+};
 
 #[derive(PartialEq)]
 pub(crate) enum MonoItemCollectionStrategy {
@@ -525,11 +529,23 @@ fn collect_items_rec<'tcx>(
         && starting_item.node.is_generic_fn()
         && starting_item.node.is_user_defined()
     {
-        let formatted_item = with_no_trimmed_paths!(starting_item.node.to_string());
-        tcx.dcx().emit_note(EncounteredErrorWhileInstantiating {
-            span: starting_item.span,
-            formatted_item,
-        });
+        match starting_item.node {
+            MonoItem::Fn(instance) => tcx.dcx().emit_note(EncounteredErrorWhileInstantiating {
+                span: starting_item.span,
+                kind: "fn",
+                instance,
+            }),
+            MonoItem::Static(def_id) => tcx.dcx().emit_note(EncounteredErrorWhileInstantiating {
+                span: starting_item.span,
+                kind: "static",
+                instance: Instance::new_raw(def_id, GenericArgs::empty()),
+            }),
+            MonoItem::GlobalAsm(_) => {
+                tcx.dcx().emit_note(EncounteredErrorWhileInstantiatingGlobalAsm {
+                    span: starting_item.span,
+                })
+            }
+        }
     }
     // Only updating `usage_map` for used items as otherwise we may be inserting the same item
     // multiple times (if it is first 'mentioned' and then later actually used), and the usage map
@@ -612,22 +628,7 @@ fn check_recursion_limit<'tcx>(
     if !recursion_limit.value_within_limit(adjusted_recursion_depth) {
         let def_span = tcx.def_span(def_id);
         let def_path_str = tcx.def_path_str(def_id);
-        let (shrunk, written_to_path) = shrunk_instance_name(tcx, instance);
-        let mut path = PathBuf::new();
-        let was_written = if let Some(written_to_path) = written_to_path {
-            path = written_to_path;
-            true
-        } else {
-            false
-        };
-        tcx.dcx().emit_fatal(RecursionLimit {
-            span,
-            shrunk,
-            def_span,
-            def_path_str,
-            was_written,
-            path,
-        });
+        tcx.dcx().emit_fatal(RecursionLimit { span, instance, def_span, def_path_str });
     }
 
     recursion_depths.insert(def_id, recursion_depth + 1);
@@ -788,7 +789,35 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirUsedCollector<'a, 'tcx> {
                 // *Before* monomorphizing, record that we already handled this mention.
                 self.used_mentioned_items.insert(MentionedItem::Fn(callee_ty));
                 let callee_ty = self.monomorphize(callee_ty);
-                visit_fn_use(self.tcx, callee_ty, true, source, &mut self.used_items)
+
+                // HACK(explicit_tail_calls): collect tail calls to `#[track_caller]` functions as indirect,
+                // because we later call them as such, to prevent issues with ABI incompatibility.
+                // Ideally we'd replace such tail calls with normal call + return, but this requires
+                // post-mono MIR optimizations, which we don't yet have.
+                let force_indirect_call =
+                    if matches!(terminator.kind, mir::TerminatorKind::TailCall { .. })
+                        && let &ty::FnDef(def_id, args) = callee_ty.kind()
+                        && let instance = ty::Instance::expect_resolve(
+                            self.tcx,
+                            ty::TypingEnv::fully_monomorphized(),
+                            def_id,
+                            args,
+                            source,
+                        )
+                        && instance.def.requires_caller_location(self.tcx)
+                    {
+                        true
+                    } else {
+                        false
+                    };
+
+                visit_fn_use(
+                    self.tcx,
+                    callee_ty,
+                    !force_indirect_call,
+                    source,
+                    &mut self.used_items,
+                )
             }
             mir::TerminatorKind::Drop { ref place, .. } => {
                 let ty = place.ty(self.body, self.tcx).ty;
@@ -913,6 +942,8 @@ fn visit_instance_use<'tcx>(
         return;
     }
     if let Some(intrinsic) = tcx.intrinsic(instance.def_id()) {
+        collect_autodiff_fn(tcx, instance, intrinsic, output);
+
         if let Some(_requirement) = ValidityRequirement::from_intrinsic(intrinsic.name) {
             // The intrinsics assert_inhabited, assert_zero_valid, and assert_mem_uninitialized_valid will
             // be lowered in codegen to nothing or a call to panic_nounwind. So if we encounter any
diff --git a/compiler/rustc_monomorphize/src/collector/autodiff.rs b/compiler/rustc_monomorphize/src/collector/autodiff.rs
new file mode 100644
index 00000000000..13868cca944
--- /dev/null
+++ b/compiler/rustc_monomorphize/src/collector/autodiff.rs
@@ -0,0 +1,48 @@
+use rustc_middle::bug;
+use rustc_middle::ty::{self, GenericArg, IntrinsicDef, TyCtxt};
+
+use crate::collector::{MonoItems, create_fn_mono_item};
+
+// Here, we force both primal and diff function to be collected in
+// mono so this does not interfere in `autodiff` intrinsics
+// codegen process. If they are unused, LLVM will remove them when
+// compiling with O3.
+pub(crate) fn collect_autodiff_fn<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    instance: ty::Instance<'tcx>,
+    intrinsic: IntrinsicDef,
+    output: &mut MonoItems<'tcx>,
+) {
+    if intrinsic.name != rustc_span::sym::autodiff {
+        return;
+    };
+
+    collect_autodiff_fn_from_arg(instance.args[0], tcx, output);
+}
+
+fn collect_autodiff_fn_from_arg<'tcx>(
+    arg: GenericArg<'tcx>,
+    tcx: TyCtxt<'tcx>,
+    output: &mut MonoItems<'tcx>,
+) {
+    let (instance, span) = match arg.kind() {
+        ty::GenericArgKind::Type(ty) => match ty.kind() {
+            ty::FnDef(def_id, substs) => {
+                let span = tcx.def_span(def_id);
+                let instance = ty::Instance::expect_resolve(
+                    tcx,
+                    ty::TypingEnv::non_body_analysis(tcx, def_id),
+                    *def_id,
+                    substs,
+                    span,
+                );
+
+                (instance, span)
+            }
+            _ => bug!("expected autodiff function"),
+        },
+        _ => bug!("expected type when matching autodiff arg"),
+    };
+
+    output.push(create_fn_mono_item(tcx, instance, span));
+}
diff --git a/compiler/rustc_monomorphize/src/errors.rs b/compiler/rustc_monomorphize/src/errors.rs
index 938c427b56c..89a78897dea 100644
--- a/compiler/rustc_monomorphize/src/errors.rs
+++ b/compiler/rustc_monomorphize/src/errors.rs
@@ -1,21 +1,16 @@
-use std::path::PathBuf;
-
 use rustc_macros::{Diagnostic, LintDiagnostic};
-use rustc_middle::ty::Ty;
+use rustc_middle::ty::{Instance, Ty};
 use rustc_span::{Span, Symbol};
 
 #[derive(Diagnostic)]
 #[diag(monomorphize_recursion_limit)]
-pub(crate) struct RecursionLimit {
+pub(crate) struct RecursionLimit<'tcx> {
     #[primary_span]
     pub span: Span,
-    pub shrunk: String,
+    pub instance: Instance<'tcx>,
     #[note]
     pub def_span: Span,
     pub def_path_str: String,
-    #[note(monomorphize_written_to_path)]
-    pub was_written: bool,
-    pub path: PathBuf,
 }
 
 #[derive(Diagnostic)]
@@ -53,10 +48,18 @@ pub(crate) struct CouldntDumpMonoStats {
 
 #[derive(Diagnostic)]
 #[diag(monomorphize_encountered_error_while_instantiating)]
-pub(crate) struct EncounteredErrorWhileInstantiating {
+pub(crate) struct EncounteredErrorWhileInstantiating<'tcx> {
+    #[primary_span]
+    pub span: Span,
+    pub kind: &'static str,
+    pub instance: Instance<'tcx>,
+}
+
+#[derive(Diagnostic)]
+#[diag(monomorphize_encountered_error_while_instantiating_global_asm)]
+pub(crate) struct EncounteredErrorWhileInstantiatingGlobalAsm {
     #[primary_span]
     pub span: Span,
-    pub formatted_item: String,
 }
 
 #[derive(Diagnostic)]
diff --git a/compiler/rustc_monomorphize/src/partitioning.rs b/compiler/rustc_monomorphize/src/partitioning.rs
index d76b27d9970..d784d3540c4 100644
--- a/compiler/rustc_monomorphize/src/partitioning.rs
+++ b/compiler/rustc_monomorphize/src/partitioning.rs
@@ -92,8 +92,6 @@
 //! source-level module, functions from the same module will be available for
 //! inlining, even when they are not marked `#[inline]`.
 
-mod autodiff;
-
 use std::cmp;
 use std::collections::hash_map::Entry;
 use std::fs::{self, File};
@@ -104,7 +102,7 @@ use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_data_structures::sync;
 use rustc_data_structures::unord::{UnordMap, UnordSet};
 use rustc_hir::LangItem;
-use rustc_hir::attrs::InlineAttr;
+use rustc_hir::attrs::{InlineAttr, Linkage};
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, DefIdSet, LOCAL_CRATE};
 use rustc_hir::definitions::DefPathDataName;
@@ -112,7 +110,7 @@ use rustc_middle::bug;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::middle::exported_symbols::{SymbolExportInfo, SymbolExportLevel};
 use rustc_middle::mir::mono::{
-    CodegenUnit, CodegenUnitNameBuilder, InstantiationMode, Linkage, MonoItem, MonoItemData,
+    CodegenUnit, CodegenUnitNameBuilder, InstantiationMode, MonoItem, MonoItemData,
     MonoItemPartitions, Visibility,
 };
 use rustc_middle::ty::print::{characteristic_def_id_of_type, with_no_trimmed_paths};
@@ -251,17 +249,7 @@ where
             always_export_generics,
         );
 
-        // We can't differentiate a function that got inlined.
-        let autodiff_active = cfg!(llvm_enzyme)
-            && matches!(mono_item, MonoItem::Fn(_))
-            && cx
-                .tcx
-                .codegen_fn_attrs(mono_item.def_id())
-                .autodiff_item
-                .as_ref()
-                .is_some_and(|ad| ad.is_active());
-
-        if !autodiff_active && visibility == Visibility::Hidden && can_be_internalized {
+        if visibility == Visibility::Hidden && can_be_internalized {
             internalization_candidates.insert(mono_item);
         }
         let size_estimate = mono_item.size_estimate(cx.tcx);
@@ -650,17 +638,18 @@ fn characteristic_def_id_of_mono_item<'tcx>(
             // its self-type. If the self-type does not provide a characteristic
             // DefId, we use the location of the impl after all.
 
-            if tcx.trait_of_assoc(def_id).is_some() {
+            let assoc_parent = tcx.assoc_parent(def_id);
+
+            if let Some((_, DefKind::Trait)) = assoc_parent {
                 let self_ty = instance.args.type_at(0);
                 // This is a default implementation of a trait method.
                 return characteristic_def_id_of_type(self_ty).or(Some(def_id));
             }
 
-            if let Some(impl_def_id) = tcx.impl_of_assoc(def_id) {
-                if tcx.sess.opts.incremental.is_some()
-                    && tcx
-                        .trait_id_of_impl(impl_def_id)
-                        .is_some_and(|def_id| tcx.is_lang_item(def_id, LangItem::Drop))
+            if let Some((impl_def_id, DefKind::Impl { of_trait })) = assoc_parent {
+                if of_trait
+                    && tcx.sess.opts.incremental.is_some()
+                    && tcx.is_lang_item(tcx.trait_id_of_impl(impl_def_id).unwrap(), LangItem::Drop)
                 {
                     // Put `Drop::drop` into the same cgu as `drop_in_place`
                     // since `drop_in_place` is the only thing that can
@@ -1156,27 +1145,15 @@ fn collect_and_partition_mono_items(tcx: TyCtxt<'_>, (): ()) -> MonoItemPartitio
         }
     }
 
-    #[cfg(not(llvm_enzyme))]
-    let autodiff_mono_items: Vec<_> = vec![];
-    #[cfg(llvm_enzyme)]
-    let mut autodiff_mono_items: Vec<_> = vec![];
     let mono_items: DefIdSet = items
         .iter()
         .filter_map(|mono_item| match *mono_item {
-            MonoItem::Fn(ref instance) => {
-                #[cfg(llvm_enzyme)]
-                autodiff_mono_items.push((mono_item, instance));
-                Some(instance.def_id())
-            }
+            MonoItem::Fn(ref instance) => Some(instance.def_id()),
             MonoItem::Static(def_id) => Some(def_id),
             _ => None,
         })
         .collect();
 
-    let autodiff_items =
-        autodiff::find_autodiff_source_functions(tcx, &usage_map, autodiff_mono_items);
-    let autodiff_items = tcx.arena.alloc_from_iter(autodiff_items);
-
     // Output monomorphization stats per def_id
     if let SwitchWithOptPath::Enabled(ref path) = tcx.sess.opts.unstable_opts.dump_mono_stats
         && let Err(err) =
@@ -1234,11 +1211,7 @@ fn collect_and_partition_mono_items(tcx: TyCtxt<'_>, (): ()) -> MonoItemPartitio
         }
     }
 
-    MonoItemPartitions {
-        all_mono_items: tcx.arena.alloc(mono_items),
-        codegen_units,
-        autodiff_items,
-    }
+    MonoItemPartitions { all_mono_items: tcx.arena.alloc(mono_items), codegen_units }
 }
 
 /// Outputs stats about instantiation counts and estimated size, per `MonoItem`'s
diff --git a/compiler/rustc_monomorphize/src/partitioning/autodiff.rs b/compiler/rustc_monomorphize/src/partitioning/autodiff.rs
deleted file mode 100644
index 22d593b80b8..00000000000
--- a/compiler/rustc_monomorphize/src/partitioning/autodiff.rs
+++ /dev/null
@@ -1,143 +0,0 @@
-use rustc_ast::expand::autodiff_attrs::{AutoDiffItem, DiffActivity};
-use rustc_hir::def_id::LOCAL_CRATE;
-use rustc_middle::bug;
-use rustc_middle::mir::mono::MonoItem;
-use rustc_middle::ty::{self, Instance, PseudoCanonicalInput, Ty, TyCtxt, TypingEnv};
-use rustc_symbol_mangling::symbol_name_for_instance_in_crate;
-use tracing::{debug, trace};
-
-use crate::partitioning::UsageMap;
-
-fn adjust_activity_to_abi<'tcx>(tcx: TyCtxt<'tcx>, fn_ty: Ty<'tcx>, da: &mut Vec<DiffActivity>) {
-    if !matches!(fn_ty.kind(), ty::FnDef(..)) {
-        bug!("expected fn def for autodiff, got {:?}", fn_ty);
-    }
-
-    // We don't actually pass the types back into the type system.
-    // All we do is decide how to handle the arguments.
-    let sig = fn_ty.fn_sig(tcx).skip_binder();
-
-    let mut new_activities = vec![];
-    let mut new_positions = vec![];
-    for (i, ty) in sig.inputs().iter().enumerate() {
-        if let Some(inner_ty) = ty.builtin_deref(true) {
-            if inner_ty.is_slice() {
-                // Now we need to figure out the size of each slice element in memory to allow
-                // safety checks and usability improvements in the backend.
-                let sty = match inner_ty.builtin_index() {
-                    Some(sty) => sty,
-                    None => {
-                        panic!("slice element type unknown");
-                    }
-                };
-                let pci = PseudoCanonicalInput {
-                    typing_env: TypingEnv::fully_monomorphized(),
-                    value: sty,
-                };
-
-                let layout = tcx.layout_of(pci);
-                let elem_size = match layout {
-                    Ok(layout) => layout.size,
-                    Err(_) => {
-                        bug!("autodiff failed to compute slice element size");
-                    }
-                };
-                let elem_size: u32 = elem_size.bytes() as u32;
-
-                // We know that the length will be passed as extra arg.
-                if !da.is_empty() {
-                    // We are looking at a slice. The length of that slice will become an
-                    // extra integer on llvm level. Integers are always const.
-                    // However, if the slice get's duplicated, we want to know to later check the
-                    // size. So we mark the new size argument as FakeActivitySize.
-                    // There is one FakeActivitySize per slice, so for convenience we store the
-                    // slice element size in bytes in it. We will use the size in the backend.
-                    let activity = match da[i] {
-                        DiffActivity::DualOnly
-                        | DiffActivity::Dual
-                        | DiffActivity::Dualv
-                        | DiffActivity::DuplicatedOnly
-                        | DiffActivity::Duplicated => {
-                            DiffActivity::FakeActivitySize(Some(elem_size))
-                        }
-                        DiffActivity::Const => DiffActivity::Const,
-                        _ => bug!("unexpected activity for ptr/ref"),
-                    };
-                    new_activities.push(activity);
-                    new_positions.push(i + 1);
-                }
-
-                continue;
-            }
-        }
-    }
-    // now add the extra activities coming from slices
-    // Reverse order to not invalidate the indices
-    for _ in 0..new_activities.len() {
-        let pos = new_positions.pop().unwrap();
-        let activity = new_activities.pop().unwrap();
-        da.insert(pos, activity);
-    }
-}
-
-pub(crate) fn find_autodiff_source_functions<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    usage_map: &UsageMap<'tcx>,
-    autodiff_mono_items: Vec<(&MonoItem<'tcx>, &Instance<'tcx>)>,
-) -> Vec<AutoDiffItem> {
-    let mut autodiff_items: Vec<AutoDiffItem> = vec![];
-    for (item, instance) in autodiff_mono_items {
-        let target_id = instance.def_id();
-        let cg_fn_attr = &tcx.codegen_fn_attrs(target_id).autodiff_item;
-        let Some(target_attrs) = cg_fn_attr else {
-            continue;
-        };
-        let mut input_activities: Vec<DiffActivity> = target_attrs.input_activity.clone();
-        if target_attrs.is_source() {
-            trace!("source found: {:?}", target_id);
-        }
-        if !target_attrs.apply_autodiff() {
-            continue;
-        }
-
-        let target_symbol = symbol_name_for_instance_in_crate(tcx, instance.clone(), LOCAL_CRATE);
-
-        let source =
-            usage_map.used_map.get(&item).unwrap().into_iter().find_map(|item| match *item {
-                MonoItem::Fn(ref instance_s) => {
-                    let source_id = instance_s.def_id();
-                    if let Some(ad) = &tcx.codegen_fn_attrs(source_id).autodiff_item
-                        && ad.is_active()
-                    {
-                        return Some(instance_s);
-                    }
-                    None
-                }
-                _ => None,
-            });
-        let inst = match source {
-            Some(source) => source,
-            None => continue,
-        };
-
-        debug!("source_id: {:?}", inst.def_id());
-        let fn_ty = inst.ty(tcx, ty::TypingEnv::fully_monomorphized());
-        assert!(fn_ty.is_fn());
-        adjust_activity_to_abi(tcx, fn_ty, &mut input_activities);
-        let symb = symbol_name_for_instance_in_crate(tcx, inst.clone(), LOCAL_CRATE);
-
-        let mut new_target_attrs = target_attrs.clone();
-        new_target_attrs.input_activity = input_activities;
-        let itm = new_target_attrs.into_item(symb, target_symbol);
-        autodiff_items.push(itm);
-    }
-
-    if !autodiff_items.is_empty() {
-        trace!("AUTODIFF ITEMS EXIST");
-        for item in &mut *autodiff_items {
-            trace!("{}", &item);
-        }
-    }
-
-    autodiff_items
-}
diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
index 5e08c3a03d8..a4a8317912a 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
@@ -8,6 +8,7 @@ use std::ops::ControlFlow;
 use derive_where::derive_where;
 use rustc_type_ir::inherent::*;
 use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::search_graph::CandidateHeadUsages;
 use rustc_type_ir::solve::SizedTraitKind;
 use rustc_type_ir::{
     self as ty, Interner, TypeFlags, TypeFoldable, TypeSuperVisitable, TypeVisitable,
@@ -33,10 +34,11 @@ enum AliasBoundKind {
 ///
 /// It consists of both the `source`, which describes how that goal would be proven,
 /// and the `result` when using the given `source`.
-#[derive_where(Clone, Debug; I: Interner)]
+#[derive_where(Debug; I: Interner)]
 pub(super) struct Candidate<I: Interner> {
     pub(super) source: CandidateSource<I>,
     pub(super) result: CanonicalResponse<I>,
+    pub(super) head_usages: CandidateHeadUsages,
 }
 
 /// Methods used to assemble candidates for either trait or projection goals.
@@ -116,8 +118,11 @@ where
         ecx: &mut EvalCtxt<'_, D>,
         goal: Goal<I, Self>,
         assumption: I::Clause,
-    ) -> Result<Candidate<I>, NoSolution> {
-        Self::fast_reject_assumption(ecx, goal, assumption)?;
+    ) -> Result<Candidate<I>, CandidateHeadUsages> {
+        match Self::fast_reject_assumption(ecx, goal, assumption) {
+            Ok(()) => {}
+            Err(NoSolution) => return Err(CandidateHeadUsages::default()),
+        }
 
         // Dealing with `ParamEnv` candidates is a bit of a mess as we need to lazily
         // check whether the candidate is global while considering normalization.
@@ -126,18 +131,23 @@ where
         // in `probe` even if the candidate does not apply before we get there. We handle this
         // by using a `Cell` here. We only ever write into it inside of `match_assumption`.
         let source = Cell::new(CandidateSource::ParamEnv(ParamEnvSource::Global));
-        ecx.probe(|result: &QueryResult<I>| inspect::ProbeKind::TraitCandidate {
-            source: source.get(),
-            result: *result,
-        })
-        .enter(|ecx| {
-            Self::match_assumption(ecx, goal, assumption, |ecx| {
-                ecx.try_evaluate_added_goals()?;
-                source.set(ecx.characterize_param_env_assumption(goal.param_env, assumption)?);
-                ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+        let (result, head_usages) = ecx
+            .probe(|result: &QueryResult<I>| inspect::ProbeKind::TraitCandidate {
+                source: source.get(),
+                result: *result,
             })
-        })
-        .map(|result| Candidate { source: source.get(), result })
+            .enter_single_candidate(|ecx| {
+                Self::match_assumption(ecx, goal, assumption, |ecx| {
+                    ecx.try_evaluate_added_goals()?;
+                    source.set(ecx.characterize_param_env_assumption(goal.param_env, assumption)?);
+                    ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+                })
+            });
+
+        match result {
+            Ok(result) => Ok(Candidate { source: source.get(), result, head_usages }),
+            Err(NoSolution) => Err(head_usages),
+        }
     }
 
     /// Try equating an assumption predicate against a goal's predicate. If it
@@ -355,6 +365,19 @@ pub(super) enum AssembleCandidatesFrom {
     EnvAndBounds,
 }
 
+/// This is currently used to track the [CandidateHeadUsages] of all failed `ParamEnv`
+/// candidates. This is then used to ignore their head usages in case there's another
+/// always applicable `ParamEnv` candidate. Look at how `param_env_head_usages` is
+/// used in the code for more details.
+///
+/// We could easily extend this to also ignore head usages of other ignored candidates.
+/// However, we currently don't have any tests where this matters and the complexity of
+/// doing so does not feel worth it for now.
+#[derive(Debug)]
+pub(super) struct FailedCandidateInfo {
+    pub param_env_head_usages: CandidateHeadUsages,
+}
+
 impl<D, I> EvalCtxt<'_, D>
 where
     D: SolverDelegate<Interner = I>,
@@ -364,16 +387,20 @@ where
         &mut self,
         goal: Goal<I, G>,
         assemble_from: AssembleCandidatesFrom,
-    ) -> Vec<Candidate<I>> {
+    ) -> (Vec<Candidate<I>>, FailedCandidateInfo) {
+        let mut candidates = vec![];
+        let mut failed_candidate_info =
+            FailedCandidateInfo { param_env_head_usages: CandidateHeadUsages::default() };
         let Ok(normalized_self_ty) =
             self.structurally_normalize_ty(goal.param_env, goal.predicate.self_ty())
         else {
-            return vec![];
+            return (candidates, failed_candidate_info);
         };
 
         if normalized_self_ty.is_ty_var() {
             debug!("self type has been normalized to infer");
-            return self.forced_ambiguity(MaybeCause::Ambiguity).into_iter().collect();
+            candidates.extend(self.forced_ambiguity(MaybeCause::Ambiguity));
+            return (candidates, failed_candidate_info);
         }
 
         let goal: Goal<I, G> = goal
@@ -382,16 +409,15 @@ where
         // normalizing the self type as well, since type variables are not uniquified.
         let goal = self.resolve_vars_if_possible(goal);
 
-        let mut candidates = vec![];
-
         if let TypingMode::Coherence = self.typing_mode()
             && let Ok(candidate) = self.consider_coherence_unknowable_candidate(goal)
         {
-            return vec![candidate];
+            candidates.push(candidate);
+            return (candidates, failed_candidate_info);
         }
 
         self.assemble_alias_bound_candidates(goal, &mut candidates);
-        self.assemble_param_env_candidates(goal, &mut candidates);
+        self.assemble_param_env_candidates(goal, &mut candidates, &mut failed_candidate_info);
 
         match assemble_from {
             AssembleCandidatesFrom::All => {
@@ -423,7 +449,7 @@ where
             AssembleCandidatesFrom::EnvAndBounds => {}
         }
 
-        candidates
+        (candidates, failed_candidate_info)
     }
 
     pub(super) fn forced_ambiguity(
@@ -584,9 +610,15 @@ where
         &mut self,
         goal: Goal<I, G>,
         candidates: &mut Vec<Candidate<I>>,
+        failed_candidate_info: &mut FailedCandidateInfo,
     ) {
         for assumption in goal.param_env.caller_bounds().iter() {
-            candidates.extend(G::probe_and_consider_param_env_candidate(self, goal, assumption));
+            match G::probe_and_consider_param_env_candidate(self, goal, assumption) {
+                Ok(candidate) => candidates.push(candidate),
+                Err(head_usages) => {
+                    failed_candidate_info.param_env_head_usages.merge_usages(head_usages)
+                }
+            }
         }
     }
 
@@ -661,7 +693,11 @@ where
                 if let Ok(result) =
                     self.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
                 {
-                    candidates.push(Candidate { source: CandidateSource::AliasBound, result });
+                    candidates.push(Candidate {
+                        source: CandidateSource::AliasBound,
+                        result,
+                        head_usages: CandidateHeadUsages::default(),
+                    });
                 }
                 return;
             }
@@ -959,7 +995,7 @@ where
                 // Even when a trait bound has been proven using a where-bound, we
                 // still need to consider alias-bounds for normalization, see
                 // `tests/ui/next-solver/alias-bound-shadowed-by-env.rs`.
-                let mut candidates: Vec<_> = self
+                let (mut candidates, _) = self
                     .assemble_and_evaluate_candidates(goal, AssembleCandidatesFrom::EnvAndBounds);
 
                 // We still need to prefer where-bounds over alias-bounds however.
@@ -972,23 +1008,20 @@ where
                     return inject_normalize_to_rigid_candidate(self);
                 }
 
-                if let Some(response) = self.try_merge_candidates(&candidates) {
+                if let Some((response, _)) = self.try_merge_candidates(&candidates) {
                     Ok(response)
                 } else {
                     self.flounder(&candidates)
                 }
             }
             TraitGoalProvenVia::Misc => {
-                let mut candidates =
+                let (mut candidates, _) =
                     self.assemble_and_evaluate_candidates(goal, AssembleCandidatesFrom::All);
 
                 // Prefer "orphaned" param-env normalization predicates, which are used
                 // (for example, and ideally only) when proving item bounds for an impl.
-                let candidates_from_env: Vec<_> = candidates
-                    .extract_if(.., |c| matches!(c.source, CandidateSource::ParamEnv(_)))
-                    .collect();
-                if let Some(response) = self.try_merge_candidates(&candidates_from_env) {
-                    return Ok(response);
+                if candidates.iter().any(|c| matches!(c.source, CandidateSource::ParamEnv(_))) {
+                    candidates.retain(|c| matches!(c.source, CandidateSource::ParamEnv(_)));
                 }
 
                 // We drop specialized impls to allow normalization via a final impl here. In case
@@ -997,7 +1030,7 @@ where
                 // means we can just ignore inference constraints and don't have to special-case
                 // constraining the normalized-to `term`.
                 self.filter_specialized_impls(AllowInferenceConstraints::Yes, &mut candidates);
-                if let Some(response) = self.try_merge_candidates(&candidates) {
+                if let Some((response, _)) = self.try_merge_candidates(&candidates) {
                     Ok(response)
                 } else {
                     self.flounder(&candidates)
diff --git a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
index 8671cc7c3d3..a4738306181 100644
--- a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
@@ -8,7 +8,7 @@ use rustc_type_ir::fast_reject::DeepRejectCtxt;
 use rustc_type_ir::inherent::*;
 use rustc_type_ir::relate::Relate;
 use rustc_type_ir::relate::solver_relating::RelateExt;
-use rustc_type_ir::search_graph::PathKind;
+use rustc_type_ir::search_graph::{CandidateHeadUsages, PathKind};
 use rustc_type_ir::{
     self as ty, CanonicalVarValues, InferCtxtLike, Interner, TypeFoldable, TypeFolder,
     TypeSuperFoldable, TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor,
@@ -399,6 +399,10 @@ where
         result
     }
 
+    pub(super) fn ignore_candidate_head_usages(&mut self, usages: CandidateHeadUsages) {
+        self.search_graph.ignore_candidate_head_usages(usages);
+    }
+
     /// Recursively evaluates `goal`, returning whether any inference vars have
     /// been constrained and the certainty of the result.
     fn evaluate_goal(
diff --git a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/probe.rs b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/probe.rs
index ed0cedc4077..e5658ba32ff 100644
--- a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/probe.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/probe.rs
@@ -1,5 +1,6 @@
 use std::marker::PhantomData;
 
+use rustc_type_ir::search_graph::CandidateHeadUsages;
 use rustc_type_ir::{InferCtxtLike, Interner};
 use tracing::instrument;
 
@@ -25,6 +26,20 @@ where
     D: SolverDelegate<Interner = I>,
     I: Interner,
 {
+    pub(in crate::solve) fn enter_single_candidate(
+        self,
+        f: impl FnOnce(&mut EvalCtxt<'_, D>) -> T,
+    ) -> (T, CandidateHeadUsages) {
+        self.ecx.search_graph.enter_single_candidate();
+        let mut candidate_usages = CandidateHeadUsages::default();
+        let result = self.enter(|ecx| {
+            let result = f(ecx);
+            candidate_usages = ecx.search_graph.finish_single_candidate();
+            result
+        });
+        (result, candidate_usages)
+    }
+
     pub(in crate::solve) fn enter(self, f: impl FnOnce(&mut EvalCtxt<'_, D>) -> T) -> T {
         let ProbeCtxt { ecx: outer, probe_kind, _result } = self;
 
@@ -78,7 +93,8 @@ where
         self,
         f: impl FnOnce(&mut EvalCtxt<'_, D>) -> QueryResult<I>,
     ) -> Result<Candidate<I>, NoSolution> {
-        self.cx.enter(|ecx| f(ecx)).map(|result| Candidate { source: self.source, result })
+        let (result, head_usages) = self.cx.enter_single_candidate(f);
+        result.map(|result| Candidate { source: self.source, result, head_usages })
     }
 }
 
diff --git a/compiler/rustc_next_trait_solver/src/solve/inspect/build.rs b/compiler/rustc_next_trait_solver/src/solve/inspect/build.rs
index c8521624ebb..fc56b006d94 100644
--- a/compiler/rustc_next_trait_solver/src/solve/inspect/build.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/inspect/build.rs
@@ -68,7 +68,7 @@ impl<I: Interner> From<WipCanonicalGoalEvaluationStep<I>> for DebugSolver<I> {
     }
 }
 
-#[derive_where(PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(PartialEq, Debug; I: Interner)]
 struct WipGoalEvaluation<I: Interner> {
     pub uncanonicalized_goal: Goal<I, I::Predicate>,
     pub orig_values: Vec<I::GenericArg>,
@@ -78,6 +78,8 @@ struct WipGoalEvaluation<I: Interner> {
     pub result: Option<QueryResult<I>>,
 }
 
+impl<I: Interner> Eq for WipGoalEvaluation<I> {}
+
 impl<I: Interner> WipGoalEvaluation<I> {
     fn finalize(self) -> inspect::GoalEvaluation<I> {
         inspect::GoalEvaluation {
@@ -98,7 +100,7 @@ impl<I: Interner> WipGoalEvaluation<I> {
 /// This only exists during proof tree building and does not have
 /// a corresponding struct in `inspect`. We need this to track a
 /// bunch of metadata about the current evaluation.
-#[derive_where(PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(PartialEq, Debug; I: Interner)]
 struct WipCanonicalGoalEvaluationStep<I: Interner> {
     /// Unlike `EvalCtxt::var_values`, we append a new
     /// generic arg here whenever we create a new inference
@@ -111,6 +113,8 @@ struct WipCanonicalGoalEvaluationStep<I: Interner> {
     evaluation: WipProbe<I>,
 }
 
+impl<I: Interner> Eq for WipCanonicalGoalEvaluationStep<I> {}
+
 impl<I: Interner> WipCanonicalGoalEvaluationStep<I> {
     fn current_evaluation_scope(&mut self) -> &mut WipProbe<I> {
         let mut current = &mut self.evaluation;
@@ -132,7 +136,7 @@ impl<I: Interner> WipCanonicalGoalEvaluationStep<I> {
     }
 }
 
-#[derive_where(PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(PartialEq, Debug; I: Interner)]
 struct WipProbe<I: Interner> {
     initial_num_var_values: usize,
     steps: Vec<WipProbeStep<I>>,
@@ -140,6 +144,8 @@ struct WipProbe<I: Interner> {
     final_state: Option<inspect::CanonicalState<I, ()>>,
 }
 
+impl<I: Interner> Eq for WipProbe<I> {}
+
 impl<I: Interner> WipProbe<I> {
     fn finalize(self) -> inspect::Probe<I> {
         inspect::Probe {
@@ -150,7 +156,7 @@ impl<I: Interner> WipProbe<I> {
     }
 }
 
-#[derive_where(PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(PartialEq, Debug; I: Interner)]
 enum WipProbeStep<I: Interner> {
     AddGoal(GoalSource, inspect::CanonicalState<I, Goal<I, I::Predicate>>),
     NestedProbe(WipProbe<I>),
@@ -158,6 +164,8 @@ enum WipProbeStep<I: Interner> {
     RecordImplArgs { impl_args: inspect::CanonicalState<I, I::GenericArgs> },
 }
 
+impl<I: Interner> Eq for WipProbeStep<I> {}
+
 impl<I: Interner> WipProbeStep<I> {
     fn finalize(self) -> inspect::ProbeStep<I> {
         match self {
diff --git a/compiler/rustc_next_trait_solver/src/solve/mod.rs b/compiler/rustc_next_trait_solver/src/solve/mod.rs
index 2feebe270a6..c2745c878dc 100644
--- a/compiler/rustc_next_trait_solver/src/solve/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/mod.rs
@@ -236,6 +236,12 @@ where
     }
 }
 
+#[derive(Debug)]
+enum MergeCandidateInfo {
+    AlwaysApplicable(usize),
+    EqualResponse,
+}
+
 impl<D, I> EvalCtxt<'_, D>
 where
     D: SolverDelegate<Interner = I>,
@@ -248,23 +254,25 @@ where
     fn try_merge_candidates(
         &mut self,
         candidates: &[Candidate<I>],
-    ) -> Option<CanonicalResponse<I>> {
+    ) -> Option<(CanonicalResponse<I>, MergeCandidateInfo)> {
         if candidates.is_empty() {
             return None;
         }
 
+        let always_applicable = candidates.iter().enumerate().find(|(_, candidate)| {
+            candidate.result.value.certainty == Certainty::Yes
+                && has_no_inference_or_external_constraints(candidate.result)
+        });
+        if let Some((i, c)) = always_applicable {
+            return Some((c.result, MergeCandidateInfo::AlwaysApplicable(i)));
+        }
+
         let one: CanonicalResponse<I> = candidates[0].result;
         if candidates[1..].iter().all(|candidate| candidate.result == one) {
-            return Some(one);
+            return Some((one, MergeCandidateInfo::EqualResponse));
         }
 
-        candidates
-            .iter()
-            .find(|candidate| {
-                candidate.result.value.certainty == Certainty::Yes
-                    && has_no_inference_or_external_constraints(candidate.result)
-            })
-            .map(|candidate| candidate.result)
+        None
     }
 
     fn bail_with_ambiguity(&mut self, candidates: &[Candidate<I>]) -> CanonicalResponse<I> {
diff --git a/compiler/rustc_next_trait_solver/src/solve/search_graph.rs b/compiler/rustc_next_trait_solver/src/solve/search_graph.rs
index 12cbc7e8f91..84f8eda4f8d 100644
--- a/compiler/rustc_next_trait_solver/src/solve/search_graph.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/search_graph.rs
@@ -48,7 +48,9 @@ where
     ) -> QueryResult<I> {
         match kind {
             PathKind::Coinductive => response_no_constraints(cx, input, Certainty::Yes),
-            PathKind::Unknown => response_no_constraints(cx, input, Certainty::overflow(false)),
+            PathKind::Unknown | PathKind::ForcedAmbiguity => {
+                response_no_constraints(cx, input, Certainty::overflow(false))
+            }
             // Even though we know these cycles to be unproductive, we still return
             // overflow during coherence. This is both as we are not 100% confident in
             // the implementation yet and any incorrect errors would be unsound there.
diff --git a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
index 60bae738e61..04ede365a21 100644
--- a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
@@ -13,11 +13,13 @@ use tracing::{debug, instrument, trace};
 
 use crate::delegate::SolverDelegate;
 use crate::solve::assembly::structural_traits::{self, AsyncCallableRelevantTypes};
-use crate::solve::assembly::{self, AllowInferenceConstraints, AssembleCandidatesFrom, Candidate};
+use crate::solve::assembly::{
+    self, AllowInferenceConstraints, AssembleCandidatesFrom, Candidate, FailedCandidateInfo,
+};
 use crate::solve::inspect::ProbeKind;
 use crate::solve::{
     BuiltinImplSource, CandidateSource, Certainty, EvalCtxt, Goal, GoalSource, MaybeCause,
-    NoSolution, ParamEnvSource, QueryResult, has_only_region_constraints,
+    MergeCandidateInfo, NoSolution, ParamEnvSource, QueryResult, has_only_region_constraints,
 };
 
 impl<D, I> assembly::GoalKind<D> for TraitPredicate<I>
@@ -1344,9 +1346,10 @@ where
     pub(super) fn merge_trait_candidates(
         &mut self,
         mut candidates: Vec<Candidate<I>>,
+        failed_candidate_info: FailedCandidateInfo,
     ) -> Result<(CanonicalResponse<I>, Option<TraitGoalProvenVia>), NoSolution> {
         if let TypingMode::Coherence = self.typing_mode() {
-            return if let Some(response) = self.try_merge_candidates(&candidates) {
+            return if let Some((response, _)) = self.try_merge_candidates(&candidates) {
                 Ok((response, Some(TraitGoalProvenVia::Misc)))
             } else {
                 self.flounder(&candidates).map(|r| (r, None))
@@ -1376,10 +1379,41 @@ where
             let where_bounds: Vec<_> = candidates
                 .extract_if(.., |c| matches!(c.source, CandidateSource::ParamEnv(_)))
                 .collect();
-            return if let Some(response) = self.try_merge_candidates(&where_bounds) {
-                Ok((response, Some(TraitGoalProvenVia::ParamEnv)))
+            if let Some((response, info)) = self.try_merge_candidates(&where_bounds) {
+                match info {
+                    // If there's an always applicable candidate, the result of all
+                    // other candidates does not matter. This means we can ignore
+                    // them when checking whether we've reached a fixpoint.
+                    //
+                    // We always prefer the first always applicable candidate, even if a
+                    // later candidate is also always applicable and would result in fewer
+                    // reruns. We could slightly improve this by e.g. searching for another
+                    // always applicable candidate which doesn't depend on any cycle heads.
+                    //
+                    // NOTE: This is optimization is observable in case there is an always
+                    // applicable global candidate and another non-global candidate which only
+                    // applies because of a provisional result. I can't even think of a test
+                    // case where this would occur and even then, this would not be unsound.
+                    // Supporting this makes the code more involved, so I am just going to
+                    // ignore this for now.
+                    MergeCandidateInfo::AlwaysApplicable(i) => {
+                        for (j, c) in where_bounds.into_iter().enumerate() {
+                            if i != j {
+                                self.ignore_candidate_head_usages(c.head_usages)
+                            }
+                        }
+                        // If a where-bound does not apply, we don't actually get a
+                        // candidate for it. We manually track the head usages
+                        // of all failed `ParamEnv` candidates instead.
+                        self.ignore_candidate_head_usages(
+                            failed_candidate_info.param_env_head_usages,
+                        );
+                    }
+                    MergeCandidateInfo::EqualResponse => {}
+                }
+                return Ok((response, Some(TraitGoalProvenVia::ParamEnv)));
             } else {
-                Ok((self.bail_with_ambiguity(&where_bounds), None))
+                return Ok((self.bail_with_ambiguity(&where_bounds), None));
             };
         }
 
@@ -1387,7 +1421,7 @@ where
             let alias_bounds: Vec<_> = candidates
                 .extract_if(.., |c| matches!(c.source, CandidateSource::AliasBound))
                 .collect();
-            return if let Some(response) = self.try_merge_candidates(&alias_bounds) {
+            return if let Some((response, _)) = self.try_merge_candidates(&alias_bounds) {
                 Ok((response, Some(TraitGoalProvenVia::AliasBound)))
             } else {
                 Ok((self.bail_with_ambiguity(&alias_bounds), None))
@@ -1412,7 +1446,7 @@ where
             TraitGoalProvenVia::Misc
         };
 
-        if let Some(response) = self.try_merge_candidates(&candidates) {
+        if let Some((response, _)) = self.try_merge_candidates(&candidates) {
             Ok((response, Some(proven_via)))
         } else {
             self.flounder(&candidates).map(|r| (r, None))
@@ -1424,8 +1458,9 @@ where
         &mut self,
         goal: Goal<I, TraitPredicate<I>>,
     ) -> Result<(CanonicalResponse<I>, Option<TraitGoalProvenVia>), NoSolution> {
-        let candidates = self.assemble_and_evaluate_candidates(goal, AssembleCandidatesFrom::All);
-        self.merge_trait_candidates(candidates)
+        let (candidates, failed_candidate_info) =
+            self.assemble_and_evaluate_candidates(goal, AssembleCandidatesFrom::All);
+        self.merge_trait_candidates(candidates, failed_candidate_info)
     }
 
     fn try_stall_coroutine(&mut self, self_ty: I::Ty) -> Option<Result<Candidate<I>, NoSolution>> {
diff --git a/compiler/rustc_parse/messages.ftl b/compiler/rustc_parse/messages.ftl
index 7059ffbf375..9e0075c21b9 100644
--- a/compiler/rustc_parse/messages.ftl
+++ b/compiler/rustc_parse/messages.ftl
@@ -642,7 +642,7 @@ parse_missing_for_in_trait_impl = missing `for` in a trait impl
     .suggestion = add `for` here
 
 parse_missing_in_in_for_loop = missing `in` in `for` loop
-    .use_in_not_of = try using `in` here instead
+    .use_in = try using `in` here instead
     .add_in = try adding `in` here
 
 parse_missing_let_before_mut = missing keyword
@@ -862,13 +862,18 @@ parse_too_many_hashes = too many `#` symbols: raw strings may be delimited by up
 
 parse_too_short_hex_escape = numeric character escape is too short
 
-parse_trailing_vert_not_allowed = a trailing `|` is not allowed in an or-pattern
-    .suggestion = remove the `{$token}`
+parse_trailing_vert_not_allowed = a trailing `{$token}` is not allowed in an or-pattern
+parse_trailing_vert_not_allowed_suggestion = remove the `{$token}`
 
 parse_trait_alias_cannot_be_auto = trait aliases cannot be `auto`
 parse_trait_alias_cannot_be_const = trait aliases cannot be `const`
 parse_trait_alias_cannot_be_unsafe = trait aliases cannot be `unsafe`
 
+parse_trait_impl_modifier_in_inherent_impl = inherent impls cannot be {$modifier_name}
+    .because = {$modifier_name} because of this
+    .type = inherent impl for this type
+    .note = only trait implementations may be annotated with `{$modifier}`
+
 parse_transpose_dyn_or_impl = `for<...>` expected after `{$kw}`, not before
     .suggestion = move `{$kw}` before the `for<...>`
 
diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index 48ff0394d46..a105dd1909e 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/compiler/rustc_parse/src/errors.rs
@@ -71,6 +71,20 @@ pub(crate) struct BadQPathStage2 {
     pub wrap: WrapType,
 }
 
+#[derive(Diagnostic)]
+#[diag(parse_trait_impl_modifier_in_inherent_impl)]
+#[note]
+pub(crate) struct TraitImplModifierInInherentImpl {
+    #[primary_span]
+    pub span: Span,
+    pub modifier: &'static str,
+    pub modifier_name: &'static str,
+    #[label(parse_because)]
+    pub modifier_span: Span,
+    #[label(parse_type)]
+    pub self_ty: Span,
+}
+
 #[derive(Subdiagnostic)]
 #[multipart_suggestion(parse_suggestion, applicability = "machine-applicable")]
 pub(crate) struct WrapType {
@@ -585,14 +599,13 @@ pub(crate) struct MissingInInForLoop {
 
 #[derive(Subdiagnostic)]
 pub(crate) enum MissingInInForLoopSub {
+    // User wrote `for pat of expr {}`
     // Has been misleading, at least in the past (closed Issue #48492), thus maybe-incorrect
-    #[suggestion(
-        parse_use_in_not_of,
-        style = "verbose",
-        applicability = "maybe-incorrect",
-        code = "in"
-    )]
+    #[suggestion(parse_use_in, style = "verbose", applicability = "maybe-incorrect", code = "in")]
     InNotOf(#[primary_span] Span),
+    // User wrote `for pat = expr {}`
+    #[suggestion(parse_use_in, style = "verbose", applicability = "maybe-incorrect", code = "in")]
+    InNotEq(#[primary_span] Span),
     #[suggestion(parse_add_in, style = "verbose", applicability = "maybe-incorrect", code = " in ")]
     AddIn(#[primary_span] Span),
 }
@@ -2648,7 +2661,7 @@ pub(crate) enum TopLevelOrPatternNotAllowedSugg {
         parse_sugg_remove_leading_vert_in_pattern,
         code = "",
         applicability = "machine-applicable",
-        style = "verbose"
+        style = "tool-only"
     )]
     RemoveLeadingVert {
         #[primary_span]
@@ -2681,12 +2694,25 @@ pub(crate) struct UnexpectedVertVertInPattern {
     pub start: Option<Span>,
 }
 
+#[derive(Subdiagnostic)]
+#[suggestion(
+    parse_trailing_vert_not_allowed,
+    code = "",
+    applicability = "machine-applicable",
+    style = "tool-only"
+)]
+pub(crate) struct TrailingVertSuggestion {
+    #[primary_span]
+    pub span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(parse_trailing_vert_not_allowed)]
 pub(crate) struct TrailingVertNotAllowed {
     #[primary_span]
-    #[suggestion(code = "", applicability = "machine-applicable", style = "verbose")]
     pub span: Span,
+    #[subdiagnostic]
+    pub suggestion: TrailingVertSuggestion,
     #[label(parse_label_while_parsing_or_pattern_here)]
     pub start: Option<Span>,
     pub token: Token,
diff --git a/compiler/rustc_parse/src/parser/asm.rs b/compiler/rustc_parse/src/parser/asm.rs
index d4d0612a317..41c3b0f0b67 100644
--- a/compiler/rustc_parse/src/parser/asm.rs
+++ b/compiler/rustc_parse/src/parser/asm.rs
@@ -1,4 +1,3 @@
-use rustc_ast::ptr::P;
 use rustc_ast::{self as ast, AsmMacro};
 use rustc_span::{Span, Symbol, kw};
 
@@ -14,7 +13,7 @@ pub struct AsmArg {
 }
 
 pub enum AsmArgKind {
-    Template(P<ast::Expr>),
+    Template(Box<ast::Expr>),
     Operand(Option<Symbol>, ast::InlineAsmOperand),
     Options(Vec<AsmOption>),
     ClobberAbi(Vec<(Symbol, Span)>),
diff --git a/compiler/rustc_parse/src/parser/attr.rs b/compiler/rustc_parse/src/parser/attr.rs
index 41d3889c448..7f6afeba28c 100644
--- a/compiler/rustc_parse/src/parser/attr.rs
+++ b/compiler/rustc_parse/src/parser/attr.rs
@@ -11,6 +11,7 @@ use tracing::debug;
 use super::{
     AttrWrapper, Capturing, FnParseMode, ForceCollect, Parser, PathStyle, Trailing, UsePreAttrPos,
 };
+use crate::parser::FnContext;
 use crate::{errors, exp, fluent_generated as fluent};
 
 // Public for rustfmt usage
@@ -200,7 +201,7 @@ impl<'a> Parser<'a> {
             AttrWrapper::empty(),
             true,
             false,
-            FnParseMode { req_name: |_| true, req_body: true },
+            FnParseMode { req_name: |_| true, context: FnContext::Free, req_body: true },
             ForceCollect::No,
         ) {
             Ok(Some(item)) => {
diff --git a/compiler/rustc_parse/src/parser/cfg_select.rs b/compiler/rustc_parse/src/parser/cfg_select.rs
index 2c6fb224d70..08a71db4de8 100644
--- a/compiler/rustc_parse/src/parser/cfg_select.rs
+++ b/compiler/rustc_parse/src/parser/cfg_select.rs
@@ -1,11 +1,12 @@
 use rustc_ast::token::Token;
 use rustc_ast::tokenstream::{TokenStream, TokenTree};
+use rustc_ast::util::classify;
 use rustc_ast::{MetaItemInner, token};
 use rustc_errors::PResult;
 use rustc_span::Span;
 
 use crate::exp;
-use crate::parser::Parser;
+use crate::parser::{AttrWrapper, ForceCollect, Parser, Restrictions, Trailing, UsePreAttrPos};
 
 pub enum CfgSelectPredicate {
     Cfg(MetaItemInner),
@@ -23,19 +24,26 @@ pub struct CfgSelectBranches {
     pub unreachable: Vec<(CfgSelectPredicate, TokenStream, Span)>,
 }
 
-/// Parses a `TokenTree` that must be of the form `{ /* ... */ }`, and returns a `TokenStream` where
-/// the surrounding braces are stripped.
+/// Parses a `TokenTree` consisting either of `{ /* ... */ }` (and strip the braces) or an
+/// expression followed by a comma (and strip the comma).
 fn parse_token_tree<'a>(p: &mut Parser<'a>) -> PResult<'a, TokenStream> {
-    // Generate an error if the `=>` is not followed by `{`.
-    if p.token != token::OpenBrace {
-        p.expect(exp!(OpenBrace))?;
+    if p.token == token::OpenBrace {
+        // Strip the outer '{' and '}'.
+        match p.parse_token_tree() {
+            TokenTree::Token(..) => unreachable!("because of the expect above"),
+            TokenTree::Delimited(.., tts) => return Ok(tts),
+        }
     }
-
-    // Strip the outer '{' and '}'.
-    match p.parse_token_tree() {
-        TokenTree::Token(..) => unreachable!("because of the expect above"),
-        TokenTree::Delimited(.., tts) => Ok(tts),
+    let expr = p.collect_tokens(None, AttrWrapper::empty(), ForceCollect::Yes, |p, _| {
+        p.parse_expr_res(Restrictions::STMT_EXPR, AttrWrapper::empty())
+            .map(|(expr, _)| (expr, Trailing::No, UsePreAttrPos::No))
+    })?;
+    if !classify::expr_is_complete(&expr) && p.token != token::CloseBrace && p.token != token::Eof {
+        p.expect(exp!(Comma))?;
+    } else {
+        let _ = p.eat(exp!(Comma));
     }
+    Ok(TokenStream::from_ast(&expr))
 }
 
 pub fn parse_cfg_select<'a>(p: &mut Parser<'a>) -> PResult<'a, CfgSelectBranches> {
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index e0f810d8c1e..220e4ac18fc 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -3,7 +3,6 @@ use std::ops::{Deref, DerefMut};
 
 use ast::token::IdentIsRaw;
 use rustc_ast as ast;
-use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Lit, LitKind, Token, TokenKind};
 use rustc_ast::util::parser::AssocOp;
 use rustc_ast::{
@@ -45,12 +44,13 @@ use crate::errors::{
     UnexpectedConstParamDeclaration, UnexpectedConstParamDeclarationSugg, UnmatchedAngleBrackets,
     UseEqInstead, WrapType,
 };
+use crate::parser::FnContext;
 use crate::parser::attr::InnerAttrPolicy;
 use crate::{exp, fluent_generated as fluent};
 
 /// Creates a placeholder argument.
 pub(super) fn dummy_arg(ident: Ident, guar: ErrorGuaranteed) -> Param {
-    let pat = P(Pat {
+    let pat = Box::new(Pat {
         id: ast::DUMMY_NODE_ID,
         kind: PatKind::Ident(BindingMode::NONE, ident, None),
         span: ident.span,
@@ -62,23 +62,23 @@ pub(super) fn dummy_arg(ident: Ident, guar: ErrorGuaranteed) -> Param {
         id: ast::DUMMY_NODE_ID,
         pat,
         span: ident.span,
-        ty: P(ty),
+        ty: Box::new(ty),
         is_placeholder: false,
     }
 }
 
 pub(super) trait RecoverQPath: Sized + 'static {
     const PATH_STYLE: PathStyle = PathStyle::Expr;
-    fn to_ty(&self) -> Option<P<Ty>>;
-    fn recovered(qself: Option<P<QSelf>>, path: ast::Path) -> Self;
+    fn to_ty(&self) -> Option<Box<Ty>>;
+    fn recovered(qself: Option<Box<QSelf>>, path: ast::Path) -> Self;
 }
 
 impl RecoverQPath for Ty {
     const PATH_STYLE: PathStyle = PathStyle::Type;
-    fn to_ty(&self) -> Option<P<Ty>> {
-        Some(P(self.clone()))
+    fn to_ty(&self) -> Option<Box<Ty>> {
+        Some(Box::new(self.clone()))
     }
-    fn recovered(qself: Option<P<QSelf>>, path: ast::Path) -> Self {
+    fn recovered(qself: Option<Box<QSelf>>, path: ast::Path) -> Self {
         Self {
             span: path.span,
             kind: TyKind::Path(qself, path),
@@ -90,10 +90,10 @@ impl RecoverQPath for Ty {
 
 impl RecoverQPath for Pat {
     const PATH_STYLE: PathStyle = PathStyle::Pat;
-    fn to_ty(&self) -> Option<P<Ty>> {
+    fn to_ty(&self) -> Option<Box<Ty>> {
         self.to_ty()
     }
-    fn recovered(qself: Option<P<QSelf>>, path: ast::Path) -> Self {
+    fn recovered(qself: Option<Box<QSelf>>, path: ast::Path) -> Self {
         Self {
             span: path.span,
             kind: PatKind::Path(qself, path),
@@ -104,10 +104,10 @@ impl RecoverQPath for Pat {
 }
 
 impl RecoverQPath for Expr {
-    fn to_ty(&self) -> Option<P<Ty>> {
+    fn to_ty(&self) -> Option<Box<Ty>> {
         self.to_ty()
     }
-    fn recovered(qself: Option<P<QSelf>>, path: ast::Path) -> Self {
+    fn recovered(qself: Option<Box<QSelf>>, path: ast::Path) -> Self {
         Self {
             span: path.span,
             kind: ExprKind::Path(qself, path),
@@ -977,7 +977,7 @@ impl<'a> Parser<'a> {
         lo: Span,
         s: BlockCheckMode,
         maybe_struct_name: token::Token,
-    ) -> Option<PResult<'a, P<Block>>> {
+    ) -> Option<PResult<'a, Box<Block>>> {
         if self.token.is_ident() && self.look_ahead(1, |t| t == &token::Colon) {
             // We might be having a struct literal where people forgot to include the path:
             // fn foo() -> Foo {
@@ -1042,7 +1042,7 @@ impl<'a> Parser<'a> {
         token: token::Token,
         lo: Span,
         decl_hi: Span,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, Box<Expr>> {
         err.span_label(lo.to(decl_hi), "while parsing the body of this closure");
         let guar = match before.kind {
             token::OpenBrace if token.kind != token::OpenBrace => {
@@ -1260,7 +1260,7 @@ impl<'a> Parser<'a> {
     pub(super) fn check_mistyped_turbofish_with_multiple_type_params(
         &mut self,
         mut e: Diag<'a>,
-        expr: &mut P<Expr>,
+        expr: &mut Box<Expr>,
     ) -> PResult<'a, ErrorGuaranteed> {
         if let ExprKind::Binary(binop, _, _) = &expr.kind
             && let ast::BinOpKind::Lt = binop.node
@@ -1443,7 +1443,7 @@ impl<'a> Parser<'a> {
         &mut self,
         inner_op: &Expr,
         outer_op: &Spanned<AssocOp>,
-    ) -> PResult<'a, Option<P<Expr>>> {
+    ) -> PResult<'a, Option<Box<Expr>>> {
         debug_assert!(
             outer_op.node.is_comparison(),
             "check_no_chained_comparison: {:?} is not comparison",
@@ -1595,7 +1595,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Swift lets users write `Ty?` to mean `Option<Ty>`. Parse the construct and recover from it.
-    pub(super) fn maybe_recover_from_question_mark(&mut self, ty: P<Ty>) -> P<Ty> {
+    pub(super) fn maybe_recover_from_question_mark(&mut self, ty: Box<Ty>) -> Box<Ty> {
         if self.token == token::Question {
             self.bump();
             let guar = self.dcx().emit_err(QuestionMarkInType {
@@ -1690,10 +1690,10 @@ impl<'a> Parser<'a> {
 
     pub(super) fn recover_from_prefix_increment(
         &mut self,
-        operand_expr: P<Expr>,
+        operand_expr: Box<Expr>,
         op_span: Span,
         start_stmt: bool,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, Box<Expr>> {
         let standalone = if start_stmt { IsStandalone::Standalone } else { IsStandalone::Subexpr };
         let kind = IncDecRecovery { standalone, op: IncOrDec::Inc, fixity: UnaryFixity::Pre };
         self.recover_from_inc_dec(operand_expr, kind, op_span)
@@ -1701,10 +1701,10 @@ impl<'a> Parser<'a> {
 
     pub(super) fn recover_from_postfix_increment(
         &mut self,
-        operand_expr: P<Expr>,
+        operand_expr: Box<Expr>,
         op_span: Span,
         start_stmt: bool,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, Box<Expr>> {
         let kind = IncDecRecovery {
             standalone: if start_stmt { IsStandalone::Standalone } else { IsStandalone::Subexpr },
             op: IncOrDec::Inc,
@@ -1715,10 +1715,10 @@ impl<'a> Parser<'a> {
 
     pub(super) fn recover_from_postfix_decrement(
         &mut self,
-        operand_expr: P<Expr>,
+        operand_expr: Box<Expr>,
         op_span: Span,
         start_stmt: bool,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, Box<Expr>> {
         let kind = IncDecRecovery {
             standalone: if start_stmt { IsStandalone::Standalone } else { IsStandalone::Subexpr },
             op: IncOrDec::Dec,
@@ -1729,10 +1729,10 @@ impl<'a> Parser<'a> {
 
     fn recover_from_inc_dec(
         &mut self,
-        base: P<Expr>,
+        base: Box<Expr>,
         kind: IncDecRecovery,
         op_span: Span,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, Box<Expr>> {
         let mut err = self.dcx().struct_span_err(
             op_span,
             format!("Rust has no {} {} operator", kind.fixity, kind.op.name()),
@@ -1833,8 +1833,8 @@ impl<'a> Parser<'a> {
     /// tail, and combines them into a `<Ty>::AssocItem` expression/pattern/type.
     pub(super) fn maybe_recover_from_bad_qpath<T: RecoverQPath>(
         &mut self,
-        base: P<T>,
-    ) -> PResult<'a, P<T>> {
+        base: Box<T>,
+    ) -> PResult<'a, Box<T>> {
         if !self.may_recover() {
             return Ok(base);
         }
@@ -1853,8 +1853,8 @@ impl<'a> Parser<'a> {
     pub(super) fn maybe_recover_from_bad_qpath_stage_2<T: RecoverQPath>(
         &mut self,
         ty_span: Span,
-        ty: P<Ty>,
-    ) -> PResult<'a, P<T>> {
+        ty: Box<Ty>,
+    ) -> PResult<'a, Box<T>> {
         self.expect(exp!(PathSep))?;
 
         let mut path = ast::Path { segments: ThinVec::new(), span: DUMMY_SP, tokens: None };
@@ -1867,7 +1867,7 @@ impl<'a> Parser<'a> {
         });
 
         let path_span = ty_span.shrink_to_hi(); // Use an empty path since `position == 0`.
-        Ok(P(T::recovered(Some(P(QSelf { ty, path_span, position: 0 })), path)))
+        Ok(Box::new(T::recovered(Some(Box::new(QSelf { ty, path_span, position: 0 })), path)))
     }
 
     /// This function gets called in places where a semicolon is NOT expected and if there's a
@@ -1970,7 +1970,7 @@ impl<'a> Parser<'a> {
     pub(super) fn recover_incorrect_await_syntax(
         &mut self,
         await_sp: Span,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, Box<Expr>> {
         let (hi, expr, is_question) = if self.token == token::Bang {
             // Handle `await!(<expr>)`.
             self.recover_await_macro()?
@@ -1982,7 +1982,7 @@ impl<'a> Parser<'a> {
         self.maybe_recover_from_bad_qpath(expr)
     }
 
-    fn recover_await_macro(&mut self) -> PResult<'a, (Span, P<Expr>, bool)> {
+    fn recover_await_macro(&mut self) -> PResult<'a, (Span, Box<Expr>, bool)> {
         self.expect(exp!(Bang))?;
         self.expect(exp!(OpenParen))?;
         let expr = self.parse_expr()?;
@@ -1990,7 +1990,7 @@ impl<'a> Parser<'a> {
         Ok((self.prev_token.span, expr, false))
     }
 
-    fn recover_await_prefix(&mut self, await_sp: Span) -> PResult<'a, (Span, P<Expr>, bool)> {
+    fn recover_await_prefix(&mut self, await_sp: Span) -> PResult<'a, (Span, Box<Expr>, bool)> {
         let is_question = self.eat(exp!(Question)); // Handle `await? <expr>`.
         let expr = if self.token == token::OpenBrace {
             // Handle `await { <expr> }`.
@@ -2052,7 +2052,7 @@ impl<'a> Parser<'a> {
         }
     }
 
-    pub(super) fn try_macro_suggestion(&mut self) -> PResult<'a, P<Expr>> {
+    pub(super) fn try_macro_suggestion(&mut self) -> PResult<'a, Box<Expr>> {
         let is_try = self.token.is_keyword(kw::Try);
         let is_questionmark = self.look_ahead(1, |t| t == &token::Bang); //check for !
         let is_open = self.look_ahead(2, |t| t == &token::OpenParen); //check for (
@@ -2124,7 +2124,7 @@ impl<'a> Parser<'a> {
         close: ExpTokenPair<'_>,
         lo: Span,
         err: Diag<'a>,
-    ) -> P<Expr> {
+    ) -> Box<Expr> {
         let guar = err.emit();
         // Recover from parse error, callers expect the closing delim to be consumed.
         self.consume_block(open, close, ConsumeClosingDelim::Yes);
@@ -2244,9 +2244,10 @@ impl<'a> Parser<'a> {
     pub(super) fn parameter_without_type(
         &mut self,
         err: &mut Diag<'_>,
-        pat: P<ast::Pat>,
+        pat: Box<ast::Pat>,
         require_name: bool,
         first_param: bool,
+        fn_parse_mode: &crate::parser::item::FnParseMode,
     ) -> Option<Ident> {
         // If we find a pattern followed by an identifier, it could be an (incorrect)
         // C-style parameter declaration.
@@ -2269,7 +2270,14 @@ impl<'a> Parser<'a> {
                 || self.token == token::Lt
                 || self.token == token::CloseParen)
         {
-            let rfc_note = "anonymous parameters are removed in the 2018 edition (see RFC 1685)";
+            let maybe_emit_anon_params_note = |this: &mut Self, err: &mut Diag<'_>| {
+                let ed = this.token.span.with_neighbor(this.prev_token.span).edition();
+                if matches!(fn_parse_mode.context, crate::parser::item::FnContext::Trait)
+                    && (fn_parse_mode.req_name)(ed)
+                {
+                    err.note("anonymous parameters are removed in the 2018 edition (see RFC 1685)");
+                }
+            };
 
             let (ident, self_sugg, param_sugg, type_sugg, self_span, param_span, type_span) =
                 match pat.kind {
@@ -2306,7 +2314,7 @@ impl<'a> Parser<'a> {
                                 "_: ".to_string(),
                                 Applicability::MachineApplicable,
                             );
-                            err.note(rfc_note);
+                            maybe_emit_anon_params_note(self, err);
                         }
 
                         return None;
@@ -2314,7 +2322,13 @@ impl<'a> Parser<'a> {
                 };
 
             // `fn foo(a, b) {}`, `fn foo(a<x>, b<y>) {}` or `fn foo(usize, usize) {}`
-            if first_param {
+            if first_param
+                // Only when the fn is a method, we emit this suggestion.
+                && matches!(
+                    fn_parse_mode.context,
+                    FnContext::Trait | FnContext::Impl
+                )
+            {
                 err.span_suggestion_verbose(
                     self_span,
                     "if this is a `self` type, give it a parameter name",
@@ -2338,7 +2352,7 @@ impl<'a> Parser<'a> {
                 type_sugg,
                 Applicability::MachineApplicable,
             );
-            err.note(rfc_note);
+            maybe_emit_anon_params_note(self, err);
 
             // Don't attempt to recover by using the `X` in `X<Y>` as the parameter name.
             return if self.token == token::Lt { None } else { Some(ident) };
@@ -2346,7 +2360,7 @@ impl<'a> Parser<'a> {
         None
     }
 
-    pub(super) fn recover_arg_parse(&mut self) -> PResult<'a, (P<ast::Pat>, P<ast::Ty>)> {
+    pub(super) fn recover_arg_parse(&mut self) -> PResult<'a, (Box<ast::Pat>, Box<ast::Ty>)> {
         let pat = self.parse_pat_no_top_alt(Some(Expected::ArgumentName), None)?;
         self.expect(exp!(Colon))?;
         let ty = self.parse_ty()?;
@@ -2354,8 +2368,12 @@ impl<'a> Parser<'a> {
         self.dcx().emit_err(PatternMethodParamWithoutBody { span: pat.span });
 
         // Pretend the pattern is `_`, to avoid duplicate errors from AST validation.
-        let pat =
-            P(Pat { kind: PatKind::Wild, span: pat.span, id: ast::DUMMY_NODE_ID, tokens: None });
+        let pat = Box::new(Pat {
+            kind: PatKind::Wild,
+            span: pat.span,
+            id: ast::DUMMY_NODE_ID,
+            tokens: None,
+        });
         Ok((pat, ty))
     }
 
@@ -2506,7 +2524,7 @@ impl<'a> Parser<'a> {
     /// - Single-segment paths (i.e. standalone generic const parameters).
     /// All other expressions that can be parsed will emit an error suggesting the expression be
     /// wrapped in braces.
-    pub(super) fn handle_unambiguous_unbraced_const_arg(&mut self) -> PResult<'a, P<Expr>> {
+    pub(super) fn handle_unambiguous_unbraced_const_arg(&mut self) -> PResult<'a, Box<Expr>> {
         let start = self.token.span;
         let attrs = self.parse_outer_attributes()?;
         let (expr, _) =
@@ -2688,7 +2706,7 @@ impl<'a> Parser<'a> {
     pub(crate) fn recover_unbraced_const_arg_that_can_begin_ty(
         &mut self,
         mut snapshot: SnapshotParser<'a>,
-    ) -> Option<P<ast::Expr>> {
+    ) -> Option<Box<ast::Expr>> {
         match (|| {
             let attrs = self.parse_outer_attributes()?;
             snapshot.parse_expr_res(Restrictions::CONST_EXPR, attrs)
@@ -2724,9 +2742,9 @@ impl<'a> Parser<'a> {
     /// `for` loop, `let`, &c. (in contrast to subpatterns within such).
     pub(crate) fn maybe_recover_colon_colon_in_pat_typo(
         &mut self,
-        mut first_pat: P<Pat>,
+        mut first_pat: Box<Pat>,
         expected: Option<Expected>,
-    ) -> P<Pat> {
+    ) -> Box<Pat> {
         if token::Colon != self.token.kind {
             return first_pat;
         }
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 35b987cf50f..d0604f76317 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -6,7 +6,6 @@ use core::ops::{Bound, ControlFlow};
 use ast::mut_visit::{self, MutVisitor};
 use ast::token::IdentIsRaw;
 use ast::{CoroutineKind, ForLoopKind, GenBlockKind, MatchKind, Pat, Path, PathSegment, Recovered};
-use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Delimiter, InvisibleOrigin, MetaVarKind, Token, TokenKind};
 use rustc_ast::tokenstream::TokenTree;
 use rustc_ast::util::case::Case;
@@ -56,7 +55,7 @@ pub(super) enum DestructuredFloat {
 impl<'a> Parser<'a> {
     /// Parses an expression.
     #[inline]
-    pub fn parse_expr(&mut self) -> PResult<'a, P<Expr>> {
+    pub fn parse_expr(&mut self) -> PResult<'a, Box<Expr>> {
         self.current_closure.take();
 
         let attrs = self.parse_outer_attributes()?;
@@ -64,7 +63,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses an expression, forcing tokens to be collected.
-    pub fn parse_expr_force_collect(&mut self) -> PResult<'a, P<Expr>> {
+    pub fn parse_expr_force_collect(&mut self) -> PResult<'a, Box<Expr>> {
         self.current_closure.take();
 
         // If the expression is associative (e.g. `1 + 2`), then any preceding
@@ -90,7 +89,10 @@ impl<'a> Parser<'a> {
         self.parse_expr().map(|value| AnonConst { id: DUMMY_NODE_ID, value })
     }
 
-    fn parse_expr_catch_underscore(&mut self, restrictions: Restrictions) -> PResult<'a, P<Expr>> {
+    fn parse_expr_catch_underscore(
+        &mut self,
+        restrictions: Restrictions,
+    ) -> PResult<'a, Box<Expr>> {
         let attrs = self.parse_outer_attributes()?;
         match self.parse_expr_res(restrictions, attrs) {
             Ok((expr, _)) => Ok(expr),
@@ -109,7 +111,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses a sequence of expressions delimited by parentheses.
-    fn parse_expr_paren_seq(&mut self) -> PResult<'a, ThinVec<P<Expr>>> {
+    fn parse_expr_paren_seq(&mut self) -> PResult<'a, ThinVec<Box<Expr>>> {
         self.parse_paren_comma_seq(|p| p.parse_expr_catch_underscore(Restrictions::empty()))
             .map(|(r, _)| r)
     }
@@ -120,7 +122,7 @@ impl<'a> Parser<'a> {
         &mut self,
         r: Restrictions,
         attrs: AttrWrapper,
-    ) -> PResult<'a, (P<Expr>, bool)> {
+    ) -> PResult<'a, (Box<Expr>, bool)> {
         self.with_res(r, |this| this.parse_expr_assoc_with(Bound::Unbounded, attrs))
     }
 
@@ -131,7 +133,7 @@ impl<'a> Parser<'a> {
         &mut self,
         min_prec: Bound<ExprPrecedence>,
         attrs: AttrWrapper,
-    ) -> PResult<'a, (P<Expr>, bool)> {
+    ) -> PResult<'a, (Box<Expr>, bool)> {
         let lhs = if self.token.is_range_separator() {
             return self.parse_expr_prefix_range(attrs).map(|res| (res, false));
         } else {
@@ -147,8 +149,8 @@ impl<'a> Parser<'a> {
         &mut self,
         min_prec: Bound<ExprPrecedence>,
         starts_stmt: bool,
-        mut lhs: P<Expr>,
-    ) -> PResult<'a, (P<Expr>, bool)> {
+        mut lhs: Box<Expr>,
+    ) -> PResult<'a, (Box<Expr>, bool)> {
         let mut parsed_something = false;
         if !self.should_continue_as_assoc_expr(&lhs) {
             return Ok((lhs, parsed_something));
@@ -414,10 +416,10 @@ impl<'a> Parser<'a> {
     fn parse_expr_range(
         &mut self,
         prec: ExprPrecedence,
-        lhs: P<Expr>,
+        lhs: Box<Expr>,
         limits: RangeLimits,
         cur_op_span: Span,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, Box<Expr>> {
         let rhs = if self.is_at_start_of_range_notation_rhs() {
             let maybe_lt = self.token;
             let attrs = self.parse_outer_attributes()?;
@@ -448,7 +450,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses prefix-forms of range notation: `..expr`, `..`, `..=expr`.
-    fn parse_expr_prefix_range(&mut self, attrs: AttrWrapper) -> PResult<'a, P<Expr>> {
+    fn parse_expr_prefix_range(&mut self, attrs: AttrWrapper) -> PResult<'a, Box<Expr>> {
         if !attrs.is_empty() {
             let err = errors::DotDotRangeAttribute { span: self.token.span };
             self.dcx().emit_err(err);
@@ -490,7 +492,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses a prefix-unary-operator expr.
-    fn parse_expr_prefix(&mut self, attrs: AttrWrapper) -> PResult<'a, P<Expr>> {
+    fn parse_expr_prefix(&mut self, attrs: AttrWrapper) -> PResult<'a, Box<Expr>> {
         let lo = self.token.span;
 
         macro_rules! make_it {
@@ -564,7 +566,7 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn parse_expr_prefix_common(&mut self, lo: Span) -> PResult<'a, (Span, P<Expr>)> {
+    fn parse_expr_prefix_common(&mut self, lo: Span) -> PResult<'a, (Span, Box<Expr>)> {
         self.bump();
         let attrs = self.parse_outer_attributes()?;
         let expr = if self.token.is_range_separator() {
@@ -653,12 +655,12 @@ impl<'a> Parser<'a> {
 
     fn parse_assoc_op_cast(
         &mut self,
-        lhs: P<Expr>,
+        lhs: Box<Expr>,
         lhs_span: Span,
         op_span: Span,
-        expr_kind: fn(P<Expr>, P<Ty>) -> ExprKind,
-    ) -> PResult<'a, P<Expr>> {
-        let mk_expr = |this: &mut Self, lhs: P<Expr>, rhs: P<Ty>| {
+        expr_kind: fn(Box<Expr>, Box<Ty>) -> ExprKind,
+    ) -> PResult<'a, Box<Expr>> {
+        let mk_expr = |this: &mut Self, lhs: Box<Expr>, rhs: Box<Ty>| {
             this.mk_expr(this.mk_expr_sp(&lhs, lhs_span, op_span, rhs.span), expr_kind(lhs, rhs))
         };
 
@@ -873,7 +875,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses `a.b` or `a(13)` or `a[4]` or just `a`.
-    fn parse_expr_dot_or_call(&mut self, attrs: AttrWrapper) -> PResult<'a, P<Expr>> {
+    fn parse_expr_dot_or_call(&mut self, attrs: AttrWrapper) -> PResult<'a, Box<Expr>> {
         self.collect_tokens_for_expr(attrs, |this, attrs| {
             let base = this.parse_expr_bottom()?;
             let span = this.interpolated_or_expr_span(&base);
@@ -884,9 +886,9 @@ impl<'a> Parser<'a> {
     pub(super) fn parse_expr_dot_or_call_with(
         &mut self,
         mut attrs: ast::AttrVec,
-        mut e: P<Expr>,
+        mut e: Box<Expr>,
         lo: Span,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, Box<Expr>> {
         let mut res = ensure_sufficient_stack(|| {
             loop {
                 let has_question =
@@ -945,8 +947,8 @@ impl<'a> Parser<'a> {
     pub(super) fn parse_dot_suffix_expr(
         &mut self,
         lo: Span,
-        base: P<Expr>,
-    ) -> PResult<'a, P<Expr>> {
+        base: Box<Expr>,
+    ) -> PResult<'a, Box<Expr>> {
         // At this point we've consumed something like `expr.` and `self.token` holds the token
         // after the dot.
         match self.token.uninterpolate().kind {
@@ -1232,10 +1234,10 @@ impl<'a> Parser<'a> {
         &self,
         lo: Span,
         ident_span: Span,
-        base: P<Expr>,
+        base: Box<Expr>,
         field: Symbol,
         suffix: Option<Symbol>,
-    ) -> P<Expr> {
+    ) -> Box<Expr> {
         if let Some(suffix) = suffix {
             self.expect_no_tuple_index_suffix(ident_span, suffix);
         }
@@ -1243,7 +1245,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parse a function call expression, `expr(...)`.
-    fn parse_expr_fn_call(&mut self, lo: Span, fun: P<Expr>) -> P<Expr> {
+    fn parse_expr_fn_call(&mut self, lo: Span, fun: Box<Expr>) -> Box<Expr> {
         let snapshot = if self.token == token::OpenParen {
             Some((self.create_snapshot_for_diagnostic(), fun.kind.clone()))
         } else {
@@ -1267,9 +1269,9 @@ impl<'a> Parser<'a> {
         &mut self,
         lo: Span,
         open_paren: Span,
-        seq: PResult<'a, P<Expr>>,
+        seq: PResult<'a, Box<Expr>>,
         snapshot: Option<(SnapshotParser<'a>, ExprKind)>,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, Box<Expr>> {
         match (self.may_recover(), seq, snapshot) {
             (true, Err(err), Some((mut snapshot, ExprKind::Path(None, path)))) => {
                 snapshot.bump(); // `(`
@@ -1325,7 +1327,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parse an indexing expression `expr[...]`.
-    fn parse_expr_index(&mut self, lo: Span, base: P<Expr>) -> PResult<'a, P<Expr>> {
+    fn parse_expr_index(&mut self, lo: Span, base: Box<Expr>) -> PResult<'a, Box<Expr>> {
         let prev_span = self.prev_token.span;
         let open_delim_span = self.token.span;
         self.bump(); // `[`
@@ -1339,7 +1341,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Assuming we have just parsed `.`, continue parsing into an expression.
-    fn parse_dot_suffix(&mut self, self_arg: P<Expr>, lo: Span) -> PResult<'a, P<Expr>> {
+    fn parse_dot_suffix(&mut self, self_arg: Box<Expr>, lo: Span) -> PResult<'a, Box<Expr>> {
         if self.token_uninterpolated_span().at_least_rust_2018() && self.eat_keyword(exp!(Await)) {
             return Ok(self.mk_await_expr(self_arg, lo));
         }
@@ -1404,7 +1406,7 @@ impl<'a> Parser<'a> {
     ///
     /// N.B., this does not parse outer attributes, and is private because it only works
     /// correctly if called from `parse_expr_dot_or_call`.
-    fn parse_expr_bottom(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_expr_bottom(&mut self) -> PResult<'a, Box<Expr>> {
         maybe_recover_from_interpolated_ty_qpath!(self, true);
 
         let span = self.token.span;
@@ -1556,7 +1558,7 @@ impl<'a> Parser<'a> {
         })
     }
 
-    fn parse_expr_lit(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_expr_lit(&mut self) -> PResult<'a, Box<Expr>> {
         let lo = self.token.span;
         match self.parse_opt_token_lit() {
             Some((token_lit, _)) => {
@@ -1567,7 +1569,7 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn parse_expr_tuple_parens(&mut self, restrictions: Restrictions) -> PResult<'a, P<Expr>> {
+    fn parse_expr_tuple_parens(&mut self, restrictions: Restrictions) -> PResult<'a, Box<Expr>> {
         let lo = self.token.span;
         self.expect(exp!(OpenParen))?;
         let (es, trailing_comma) = match self.parse_seq_to_end(
@@ -1596,7 +1598,7 @@ impl<'a> Parser<'a> {
         self.maybe_recover_from_bad_qpath(expr)
     }
 
-    fn parse_expr_array_or_repeat(&mut self, close: ExpTokenPair<'_>) -> PResult<'a, P<Expr>> {
+    fn parse_expr_array_or_repeat(&mut self, close: ExpTokenPair<'_>) -> PResult<'a, Box<Expr>> {
         let lo = self.token.span;
         self.bump(); // `[` or other open delim
 
@@ -1627,7 +1629,7 @@ impl<'a> Parser<'a> {
         self.maybe_recover_from_bad_qpath(expr)
     }
 
-    fn parse_expr_path_start(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_expr_path_start(&mut self) -> PResult<'a, Box<Expr>> {
         let maybe_eq_tok = self.prev_token;
         let (qself, path) = if self.eat_lt() {
             let lt_span = self.prev_token.span;
@@ -1653,7 +1655,7 @@ impl<'a> Parser<'a> {
                 self.dcx().emit_err(errors::MacroInvocationWithQualifiedPath(path.span));
             }
             let lo = path.span;
-            let mac = P(MacCall { path, args: self.parse_delim_args()? });
+            let mac = Box::new(MacCall { path, args: self.parse_delim_args()? });
             (lo.to(self.prev_token.span), ExprKind::MacCall(mac))
         } else if self.check(exp!(OpenBrace))
             && let Some(expr) = self.maybe_parse_struct_expr(&qself, &path)
@@ -1675,7 +1677,7 @@ impl<'a> Parser<'a> {
         &mut self,
         label_: Label,
         mut consume_colon: bool,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, Box<Expr>> {
         let lo = label_.ident.span;
         let label = Some(label_);
         let ate_colon = self.eat(exp!(Colon));
@@ -1810,7 +1812,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Recover on the syntax `do catch { ... }` suggesting `try { ... }` instead.
-    fn recover_do_catch(&mut self) -> PResult<'a, P<Expr>> {
+    fn recover_do_catch(&mut self) -> PResult<'a, Box<Expr>> {
         let lo = self.token.span;
 
         self.bump(); // `do`
@@ -1823,12 +1825,12 @@ impl<'a> Parser<'a> {
     }
 
     /// Parse an expression if the token can begin one.
-    fn parse_expr_opt(&mut self) -> PResult<'a, Option<P<Expr>>> {
+    fn parse_expr_opt(&mut self) -> PResult<'a, Option<Box<Expr>>> {
         Ok(if self.token.can_begin_expr() { Some(self.parse_expr()?) } else { None })
     }
 
     /// Parse `"return" expr?`.
-    fn parse_expr_return(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_expr_return(&mut self) -> PResult<'a, Box<Expr>> {
         let lo = self.prev_token.span;
         let kind = ExprKind::Ret(self.parse_expr_opt()?);
         let expr = self.mk_expr(lo.to(self.prev_token.span), kind);
@@ -1836,7 +1838,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parse `"do" "yeet" expr?`.
-    fn parse_expr_yeet(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_expr_yeet(&mut self) -> PResult<'a, Box<Expr>> {
         let lo = self.token.span;
 
         self.bump(); // `do`
@@ -1851,7 +1853,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parse `"become" expr`, with `"become"` token already eaten.
-    fn parse_expr_become(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_expr_become(&mut self) -> PResult<'a, Box<Expr>> {
         let lo = self.prev_token.span;
         let kind = ExprKind::Become(self.parse_expr()?);
         let span = lo.to(self.prev_token.span);
@@ -1868,7 +1870,7 @@ impl<'a> Parser<'a> {
     /// `break 'lbl: loop {}`); a labeled break with an unlabeled loop as its value
     /// expression only gets a warning for compatibility reasons; and a labeled break
     /// with a labeled loop does not even get a warning because there is no ambiguity.
-    fn parse_expr_break(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_expr_break(&mut self) -> PResult<'a, Box<Expr>> {
         let lo = self.prev_token.span;
         let mut label = self.eat_label();
         let kind = if self.token == token::Colon
@@ -1930,7 +1932,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parse `"continue" label?`.
-    fn parse_expr_continue(&mut self, lo: Span) -> PResult<'a, P<Expr>> {
+    fn parse_expr_continue(&mut self, lo: Span) -> PResult<'a, Box<Expr>> {
         let mut label = self.eat_label();
 
         // Recover `continue label` -> `continue 'label`
@@ -1947,7 +1949,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parse `"yield" expr?`.
-    fn parse_expr_yield(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_expr_yield(&mut self) -> PResult<'a, Box<Expr>> {
         let lo = self.prev_token.span;
         let kind = ExprKind::Yield(YieldKind::Prefix(self.parse_expr_opt()?));
         let span = lo.to(self.prev_token.span);
@@ -1957,7 +1959,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parse `builtin # ident(args,*)`.
-    fn parse_expr_builtin(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_expr_builtin(&mut self) -> PResult<'a, Box<Expr>> {
         self.parse_builtin(|this, lo, ident| {
             Ok(match ident.name {
                 sym::offset_of => Some(this.parse_expr_offset_of(lo)?),
@@ -2005,7 +2007,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Built-in macro for `offset_of!` expressions.
-    pub(crate) fn parse_expr_offset_of(&mut self, lo: Span) -> PResult<'a, P<Expr>> {
+    pub(crate) fn parse_expr_offset_of(&mut self, lo: Span) -> PResult<'a, Box<Expr>> {
         let container = self.parse_ty()?;
         self.expect(exp!(Comma))?;
 
@@ -2033,7 +2035,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Built-in macro for type ascription expressions.
-    pub(crate) fn parse_expr_type_ascribe(&mut self, lo: Span) -> PResult<'a, P<Expr>> {
+    pub(crate) fn parse_expr_type_ascribe(&mut self, lo: Span) -> PResult<'a, Box<Expr>> {
         let expr = self.parse_expr()?;
         self.expect(exp!(Comma))?;
         let ty = self.parse_ty()?;
@@ -2045,7 +2047,7 @@ impl<'a> Parser<'a> {
         &mut self,
         lo: Span,
         kind: UnsafeBinderCastKind,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, Box<Expr>> {
         let expr = self.parse_expr()?;
         let ty = if self.eat(exp!(Comma)) { Some(self.parse_ty()?) } else { None };
         let span = lo.to(self.token.span);
@@ -2155,7 +2157,7 @@ impl<'a> Parser<'a> {
     /// Keep this in sync with `Token::can_begin_literal_maybe_minus` and
     /// `Lit::from_token` (excluding unary negation).
     fn eat_token_lit(&mut self) -> Option<token::Lit> {
-        let check_expr = |expr: P<Expr>| {
+        let check_expr = |expr: Box<Expr>| {
             if let ast::ExprKind::Lit(token_lit) = expr.kind {
                 Some(token_lit)
             } else if let ast::ExprKind::Unary(UnOp::Neg, inner) = &expr.kind
@@ -2243,7 +2245,7 @@ impl<'a> Parser<'a> {
 
     /// Matches `'-' lit | lit` (cf. `ast_validation::AstValidator::check_expr_within_pat`).
     /// Keep this in sync with `Token::can_begin_literal_maybe_minus`.
-    pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, P<Expr>> {
+    pub fn parse_literal_maybe_minus(&mut self) -> PResult<'a, Box<Expr>> {
         if let Some(expr) = self.eat_metavar_seq_with_matcher(
             |mv_kind| matches!(mv_kind, MetaVarKind::Expr { .. }),
             |this| {
@@ -2290,7 +2292,7 @@ impl<'a> Parser<'a> {
     /// Emits a suggestion if it looks like the user meant an array but
     /// accidentally used braces, causing the code to be interpreted as a block
     /// expression.
-    fn maybe_suggest_brackets_instead_of_braces(&mut self, lo: Span) -> Option<P<Expr>> {
+    fn maybe_suggest_brackets_instead_of_braces(&mut self, lo: Span) -> Option<Box<Expr>> {
         let mut snapshot = self.create_snapshot_for_diagnostic();
         match snapshot.parse_expr_array_or_repeat(exp!(CloseBrace)) {
             Ok(arr) => {
@@ -2360,7 +2362,7 @@ impl<'a> Parser<'a> {
         opt_label: Option<Label>,
         lo: Span,
         blk_mode: BlockCheckMode,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, Box<Expr>> {
         if self.may_recover() && self.is_array_like_block() {
             if let Some(arr) = self.maybe_suggest_brackets_instead_of_braces(lo) {
                 return Ok(arr);
@@ -2383,13 +2385,13 @@ impl<'a> Parser<'a> {
     }
 
     /// Parse a block which takes no attributes and has no label
-    fn parse_simple_block(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_simple_block(&mut self) -> PResult<'a, Box<Expr>> {
         let blk = self.parse_block()?;
         Ok(self.mk_expr(blk.span, ExprKind::Block(blk, None)))
     }
 
     /// Parses a closure expression (e.g., `move |args| expr`).
-    fn parse_expr_closure(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_expr_closure(&mut self) -> PResult<'a, Box<Expr>> {
         let lo = self.token.span;
 
         let before = self.prev_token;
@@ -2494,7 +2496,7 @@ impl<'a> Parser<'a> {
     }
 
     /// If an explicit return type is given, require a block to appear (RFC 968).
-    fn parse_closure_block_body(&mut self, ret_span: Span) -> PResult<'a, P<Expr>> {
+    fn parse_closure_block_body(&mut self, ret_span: Span) -> PResult<'a, Box<Expr>> {
         if self.may_recover()
             && self.token.can_begin_expr()
             && self.token.kind != TokenKind::OpenBrace
@@ -2565,7 +2567,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses the `|arg, arg|` header of a closure.
-    fn parse_fn_block_decl(&mut self) -> PResult<'a, (P<FnDecl>, Span)> {
+    fn parse_fn_block_decl(&mut self) -> PResult<'a, (Box<FnDecl>, Span)> {
         let arg_start = self.token.span.lo();
 
         let inputs = if self.eat(exp!(OrOr)) {
@@ -2587,7 +2589,7 @@ impl<'a> Parser<'a> {
         let output =
             self.parse_ret_ty(AllowPlus::Yes, RecoverQPath::Yes, RecoverReturnSign::Yes)?;
 
-        Ok((P(FnDecl { inputs, output }), arg_span))
+        Ok((Box::new(FnDecl { inputs, output }), arg_span))
     }
 
     /// Parses a parameter in a closure header (e.g., `|arg, arg|`).
@@ -2618,7 +2620,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses an `if` expression (`if` token already eaten).
-    fn parse_expr_if(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_expr_if(&mut self) -> PResult<'a, Box<Expr>> {
         let lo = self.prev_token.span;
         // Scoping code checks the top level edition of the `if`; let's match it here.
         // The `CondChecker` also checks the edition of the `let` itself, just to make sure.
@@ -2627,7 +2629,7 @@ impl<'a> Parser<'a> {
         self.parse_if_after_cond(lo, cond)
     }
 
-    fn parse_if_after_cond(&mut self, lo: Span, mut cond: P<Expr>) -> PResult<'a, P<Expr>> {
+    fn parse_if_after_cond(&mut self, lo: Span, mut cond: Box<Expr>) -> PResult<'a, Box<Expr>> {
         let cond_span = cond.span;
         // Tries to interpret `cond` as either a missing expression if it's a block,
         // or as an unfinished expression if it's a binop and the RHS is a block.
@@ -2737,7 +2739,10 @@ impl<'a> Parser<'a> {
     /// i.e. the same span we use to later decide whether the drop behaviour should be that of
     /// edition `..=2021` or that of `2024..`.
     // Public because it is used in rustfmt forks such as https://github.com/tucant/rustfmt/blob/30c83df9e1db10007bdd16dafce8a86b404329b2/src/parse/macros/html.rs#L57 for custom if expressions.
-    pub fn parse_expr_cond(&mut self, let_chains_policy: LetChainsPolicy) -> PResult<'a, P<Expr>> {
+    pub fn parse_expr_cond(
+        &mut self,
+        let_chains_policy: LetChainsPolicy,
+    ) -> PResult<'a, Box<Expr>> {
         let attrs = self.parse_outer_attributes()?;
         let (mut cond, _) =
             self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL | Restrictions::ALLOW_LET, attrs)?;
@@ -2748,7 +2753,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses a `let $pat = $expr` pseudo-expression.
-    fn parse_expr_let(&mut self, restrictions: Restrictions) -> PResult<'a, P<Expr>> {
+    fn parse_expr_let(&mut self, restrictions: Restrictions) -> PResult<'a, Box<Expr>> {
         let recovered = if !restrictions.contains(Restrictions::ALLOW_LET) {
             let err = errors::ExpectedExpressionFoundLet {
                 span: self.token.span,
@@ -2790,7 +2795,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses an `else { ... }` expression (`else` token already eaten).
-    fn parse_expr_else(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_expr_else(&mut self) -> PResult<'a, Box<Expr>> {
         let else_span = self.prev_token.span; // `else`
         let attrs = self.parse_outer_attributes()?; // For recovery.
         let expr = if self.eat_keyword(exp!(If)) {
@@ -2888,7 +2893,7 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn error_on_extra_if(&mut self, cond: &P<Expr>) -> PResult<'a, ()> {
+    fn error_on_extra_if(&mut self, cond: &Box<Expr>) -> PResult<'a, ()> {
         if let ExprKind::Binary(Spanned { span: binop_span, node: binop }, _, right) = &cond.kind
             && let BinOpKind::And = binop
             && let ExprKind::If(cond, ..) = &right.kind
@@ -2901,7 +2906,7 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn parse_for_head(&mut self) -> PResult<'a, (P<Pat>, P<Expr>)> {
+    fn parse_for_head(&mut self) -> PResult<'a, (Box<Pat>, Box<Expr>)> {
         let begin_paren = if self.token == token::OpenParen {
             // Record whether we are about to parse `for (`.
             // This is used below for recovery in case of `for ( $stuff ) $block`
@@ -2967,7 +2972,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses `for await? <src_pat> in <src_expr> <src_loop_block>` (`for` token already eaten).
-    fn parse_expr_for(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
+    fn parse_expr_for(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, Box<Expr>> {
         let is_await =
             self.token_uninterpolated_span().at_least_rust_2018() && self.eat_keyword(exp!(Await));
 
@@ -3028,6 +3033,8 @@ impl<'a> Parser<'a> {
             let span = self.token.span;
             self.bump();
             (span, errors::MissingInInForLoopSub::InNotOf)
+        } else if self.eat(exp!(Eq)) {
+            (self.prev_token.span, errors::MissingInInForLoopSub::InNotEq)
         } else {
             (self.prev_token.span.between(self.token.span), errors::MissingInInForLoopSub::AddIn)
         };
@@ -3036,7 +3043,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses a `while` or `while let` expression (`while` token already eaten).
-    fn parse_expr_while(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
+    fn parse_expr_while(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, Box<Expr>> {
         let policy = LetChainsPolicy::EditionDependent { current_edition: lo.edition() };
         let cond = self.parse_expr_cond(policy).map_err(|mut err| {
             err.span_label(lo, "while parsing the condition of this `while` expression");
@@ -3064,7 +3071,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses `loop { ... }` (`loop` token already eaten).
-    fn parse_expr_loop(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
+    fn parse_expr_loop(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, Box<Expr>> {
         let loop_span = self.prev_token.span;
         let (attrs, body) = self.parse_inner_attrs_and_block(
             // Only suggest moving erroneous block label to the loop header
@@ -3094,7 +3101,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses a `match ... { ... }` expression (`match` token already eaten).
-    fn parse_expr_match(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_expr_match(&mut self) -> PResult<'a, Box<Expr>> {
         let match_span = self.prev_token.span;
         let attrs = self.parse_outer_attributes()?;
         let (scrutinee, _) = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, attrs)?;
@@ -3108,9 +3115,9 @@ impl<'a> Parser<'a> {
         &mut self,
         lo: Span,
         match_span: Span,
-        scrutinee: P<Expr>,
+        scrutinee: Box<Expr>,
         match_kind: MatchKind,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, Box<Expr>> {
         if let Err(mut e) = self.expect(exp!(OpenBrace)) {
             if self.token == token::Semi {
                 e.span_suggestion_short(
@@ -3167,7 +3174,7 @@ impl<'a> Parser<'a> {
     /// Attempt to recover from match arm body with statements and no surrounding braces.
     fn parse_arm_body_missing_braces(
         &mut self,
-        first_expr: &P<Expr>,
+        first_expr: &Box<Expr>,
         arrow_span: Span,
     ) -> Option<(Span, ErrorGuaranteed)> {
         if self.token != token::Semi {
@@ -3439,7 +3446,7 @@ impl<'a> Parser<'a> {
         })
     }
 
-    fn parse_match_arm_guard(&mut self) -> PResult<'a, Option<P<Expr>>> {
+    fn parse_match_arm_guard(&mut self) -> PResult<'a, Option<Box<Expr>>> {
         // Used to check the `if_let_guard` feature mostly by scanning
         // `&&` tokens.
         fn has_let_expr(expr: &Expr) -> bool {
@@ -3470,7 +3477,7 @@ impl<'a> Parser<'a> {
         Ok(Some(cond))
     }
 
-    fn parse_match_arm_pat_and_guard(&mut self) -> PResult<'a, (P<Pat>, Option<P<Expr>>)> {
+    fn parse_match_arm_pat_and_guard(&mut self) -> PResult<'a, (Box<Pat>, Option<Box<Expr>>)> {
         if self.token == token::OpenParen {
             let left = self.token.span;
             let pat = self.parse_pat_no_top_guard(
@@ -3510,7 +3517,7 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn parse_match_guard_condition(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_match_guard_condition(&mut self) -> PResult<'a, Box<Expr>> {
         let attrs = self.parse_outer_attributes()?;
         match self.parse_expr_res(Restrictions::ALLOW_LET | Restrictions::IN_IF_GUARD, attrs) {
             Ok((expr, _)) => Ok(expr),
@@ -3544,7 +3551,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses a `try {...}` expression (`try` token already eaten).
-    fn parse_try_block(&mut self, span_lo: Span) -> PResult<'a, P<Expr>> {
+    fn parse_try_block(&mut self, span_lo: Span) -> PResult<'a, Box<Expr>> {
         let (attrs, body) = self.parse_inner_attrs_and_block(None)?;
         if self.eat_keyword(exp!(Catch)) {
             Err(self.dcx().create_err(errors::CatchAfterTry { span: self.prev_token.span }))
@@ -3573,7 +3580,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses an `async move? {...}` or `gen move? {...}` expression.
-    fn parse_gen_block(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_gen_block(&mut self) -> PResult<'a, Box<Expr>> {
         let lo = self.token.span;
         let kind = if self.eat_keyword(exp!(Async)) {
             if self.eat_keyword(exp!(Gen)) { GenBlockKind::AsyncGen } else { GenBlockKind::Async }
@@ -3622,9 +3629,9 @@ impl<'a> Parser<'a> {
 
     fn maybe_parse_struct_expr(
         &mut self,
-        qself: &Option<P<ast::QSelf>>,
+        qself: &Option<Box<ast::QSelf>>,
         path: &ast::Path,
-    ) -> Option<PResult<'a, P<Expr>>> {
+    ) -> Option<PResult<'a, Box<Expr>>> {
         let struct_allowed = !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL);
         if struct_allowed || self.is_certainly_not_a_block() {
             if let Err(err) = self.expect(exp!(OpenBrace)) {
@@ -3818,10 +3825,10 @@ impl<'a> Parser<'a> {
     /// Precondition: already parsed the '{'.
     pub(super) fn parse_expr_struct(
         &mut self,
-        qself: Option<P<ast::QSelf>>,
+        qself: Option<Box<ast::QSelf>>,
         pth: ast::Path,
         recover: bool,
-    ) -> PResult<'a, P<Expr>> {
+    ) -> PResult<'a, Box<Expr>> {
         let lo = pth.span;
         let (fields, base, recovered_async) =
             self.parse_struct_fields(pth.clone(), recover, exp!(CloseBrace))?;
@@ -3830,7 +3837,7 @@ impl<'a> Parser<'a> {
         let expr = if let Some(guar) = recovered_async {
             ExprKind::Err(guar)
         } else {
-            ExprKind::Struct(P(ast::StructExpr { qself, path: pth, fields, rest: base }))
+            ExprKind::Struct(Box::new(ast::StructExpr { qself, path: pth, fields, rest: base }))
         };
         Ok(self.mk_expr(span, expr))
     }
@@ -3945,14 +3952,14 @@ impl<'a> Parser<'a> {
         self.dcx().emit_err(errors::LeftArrowOperator { span });
     }
 
-    fn mk_assign_op(&self, assign_op: AssignOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
+    fn mk_assign_op(&self, assign_op: AssignOp, lhs: Box<Expr>, rhs: Box<Expr>) -> ExprKind {
         ExprKind::AssignOp(assign_op, lhs, rhs)
     }
 
     fn mk_range(
         &mut self,
-        start: Option<P<Expr>>,
-        end: Option<P<Expr>>,
+        start: Option<Box<Expr>>,
+        end: Option<Box<Expr>>,
         limits: RangeLimits,
     ) -> ExprKind {
         if end.is_none() && limits == RangeLimits::Closed {
@@ -3963,51 +3970,56 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn mk_unary(&self, unop: UnOp, expr: P<Expr>) -> ExprKind {
+    fn mk_unary(&self, unop: UnOp, expr: Box<Expr>) -> ExprKind {
         ExprKind::Unary(unop, expr)
     }
 
-    fn mk_binary(&self, binop: BinOp, lhs: P<Expr>, rhs: P<Expr>) -> ExprKind {
+    fn mk_binary(&self, binop: BinOp, lhs: Box<Expr>, rhs: Box<Expr>) -> ExprKind {
         ExprKind::Binary(binop, lhs, rhs)
     }
 
-    fn mk_index(&self, expr: P<Expr>, idx: P<Expr>, brackets_span: Span) -> ExprKind {
+    fn mk_index(&self, expr: Box<Expr>, idx: Box<Expr>, brackets_span: Span) -> ExprKind {
         ExprKind::Index(expr, idx, brackets_span)
     }
 
-    fn mk_call(&self, f: P<Expr>, args: ThinVec<P<Expr>>) -> ExprKind {
+    fn mk_call(&self, f: Box<Expr>, args: ThinVec<Box<Expr>>) -> ExprKind {
         ExprKind::Call(f, args)
     }
 
-    fn mk_await_expr(&mut self, self_arg: P<Expr>, lo: Span) -> P<Expr> {
+    fn mk_await_expr(&mut self, self_arg: Box<Expr>, lo: Span) -> Box<Expr> {
         let span = lo.to(self.prev_token.span);
         let await_expr = self.mk_expr(span, ExprKind::Await(self_arg, self.prev_token.span));
         self.recover_from_await_method_call();
         await_expr
     }
 
-    fn mk_use_expr(&mut self, self_arg: P<Expr>, lo: Span) -> P<Expr> {
+    fn mk_use_expr(&mut self, self_arg: Box<Expr>, lo: Span) -> Box<Expr> {
         let span = lo.to(self.prev_token.span);
         let use_expr = self.mk_expr(span, ExprKind::Use(self_arg, self.prev_token.span));
         self.recover_from_use();
         use_expr
     }
 
-    pub(crate) fn mk_expr_with_attrs(&self, span: Span, kind: ExprKind, attrs: AttrVec) -> P<Expr> {
-        P(Expr { kind, span, attrs, id: DUMMY_NODE_ID, tokens: None })
+    pub(crate) fn mk_expr_with_attrs(
+        &self,
+        span: Span,
+        kind: ExprKind,
+        attrs: AttrVec,
+    ) -> Box<Expr> {
+        Box::new(Expr { kind, span, attrs, id: DUMMY_NODE_ID, tokens: None })
     }
 
-    pub(crate) fn mk_expr(&self, span: Span, kind: ExprKind) -> P<Expr> {
+    pub(crate) fn mk_expr(&self, span: Span, kind: ExprKind) -> Box<Expr> {
         self.mk_expr_with_attrs(span, kind, AttrVec::new())
     }
 
-    pub(super) fn mk_expr_err(&self, span: Span, guar: ErrorGuaranteed) -> P<Expr> {
+    pub(super) fn mk_expr_err(&self, span: Span, guar: ErrorGuaranteed) -> Box<Expr> {
         self.mk_expr(span, ExprKind::Err(guar))
     }
 
     /// Create expression span ensuring the span of the parent node
     /// is larger than the span of lhs and rhs, including the attributes.
-    fn mk_expr_sp(&self, lhs: &P<Expr>, lhs_span: Span, op_span: Span, rhs_span: Span) -> Span {
+    fn mk_expr_sp(&self, lhs: &Box<Expr>, lhs_span: Span, op_span: Span, rhs_span: Span) -> Span {
         lhs.attrs
             .iter()
             .find(|a| a.style == AttrStyle::Outer)
@@ -4019,8 +4031,8 @@ impl<'a> Parser<'a> {
     fn collect_tokens_for_expr(
         &mut self,
         attrs: AttrWrapper,
-        f: impl FnOnce(&mut Self, ast::AttrVec) -> PResult<'a, P<Expr>>,
-    ) -> PResult<'a, P<Expr>> {
+        f: impl FnOnce(&mut Self, ast::AttrVec) -> PResult<'a, Box<Expr>>,
+    ) -> PResult<'a, Box<Expr>> {
         self.collect_tokens(None, attrs, ForceCollect::No, |this, attrs| {
             let res = f(this, attrs)?;
             let trailing = Trailing::from(
diff --git a/compiler/rustc_parse/src/parser/generics.rs b/compiler/rustc_parse/src/parser/generics.rs
index 86326341a75..4a8530a2b38 100644
--- a/compiler/rustc_parse/src/parser/generics.rs
+++ b/compiler/rustc_parse/src/parser/generics.rs
@@ -308,9 +308,7 @@ impl<'a> Parser<'a> {
 
     /// Parses an experimental fn contract
     /// (`contract_requires(WWW) contract_ensures(ZZZ)`)
-    pub(super) fn parse_contract(
-        &mut self,
-    ) -> PResult<'a, Option<rustc_ast::ptr::P<ast::FnContract>>> {
+    pub(super) fn parse_contract(&mut self) -> PResult<'a, Option<Box<ast::FnContract>>> {
         let requires = if self.eat_keyword_noexpect(exp!(ContractRequires).kw) {
             self.psess.gated_spans.gate(sym::contracts_internals, self.prev_token.span);
             let precond = self.parse_expr()?;
@@ -328,7 +326,7 @@ impl<'a> Parser<'a> {
         if requires.is_none() && ensures.is_none() {
             Ok(None)
         } else {
-            Ok(Some(rustc_ast::ptr::P(ast::FnContract { requires, ensures })))
+            Ok(Some(Box::new(ast::FnContract { requires, ensures })))
         }
     }
 
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index cb7c5649433..ca89eb1e2cf 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -3,7 +3,6 @@ use std::mem;
 
 use ast::token::IdentIsRaw;
 use rustc_ast::ast::*;
-use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Delimiter, InvisibleOrigin, MetaVarKind, TokenKind};
 use rustc_ast::tokenstream::{DelimSpan, TokenStream, TokenTree};
 use rustc_ast::util::case::Case;
@@ -56,12 +55,12 @@ impl<'a> Parser<'a> {
     pub fn parse_mod(
         &mut self,
         term: ExpTokenPair<'_>,
-    ) -> PResult<'a, (AttrVec, ThinVec<P<Item>>, ModSpans)> {
+    ) -> PResult<'a, (AttrVec, ThinVec<Box<Item>>, ModSpans)> {
         let lo = self.token.span;
         let attrs = self.parse_inner_attributes()?;
 
         let post_attr_lo = self.token.span;
-        let mut items: ThinVec<P<_>> = ThinVec::new();
+        let mut items: ThinVec<Box<_>> = ThinVec::new();
 
         // There shouldn't be any stray semicolons before or after items.
         // `parse_item` consumes the appropriate semicolons so any leftover is an error.
@@ -116,9 +115,10 @@ impl<'a> Parser<'a> {
 }
 
 impl<'a> Parser<'a> {
-    pub fn parse_item(&mut self, force_collect: ForceCollect) -> PResult<'a, Option<P<Item>>> {
-        let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: true };
-        self.parse_item_(fn_parse_mode, force_collect).map(|i| i.map(P))
+    pub fn parse_item(&mut self, force_collect: ForceCollect) -> PResult<'a, Option<Box<Item>>> {
+        let fn_parse_mode =
+            FnParseMode { req_name: |_| true, context: FnContext::Free, req_body: true };
+        self.parse_item_(fn_parse_mode, force_collect).map(|i| i.map(Box::new))
     }
 
     fn parse_item_(
@@ -327,7 +327,7 @@ impl<'a> Parser<'a> {
                 self.recover_missing_kw_before_item()?;
             }
             // MACRO INVOCATION ITEM
-            ItemKind::MacCall(P(self.parse_item_macro(vis)?))
+            ItemKind::MacCall(Box::new(self.parse_item_macro(vis)?))
         } else {
             return Ok(None);
         };
@@ -664,20 +664,44 @@ impl<'a> Parser<'a> {
                 };
                 let trait_ref = TraitRef { path, ref_id: ty_first.id };
 
-                (Some(trait_ref), ty_second)
+                let of_trait = Some(Box::new(TraitImplHeader {
+                    defaultness,
+                    safety,
+                    constness,
+                    polarity,
+                    trait_ref,
+                }));
+                (of_trait, ty_second)
+            }
+            None => {
+                let self_ty = ty_first;
+                let error = |modifier, modifier_name, modifier_span| {
+                    self.dcx().create_err(errors::TraitImplModifierInInherentImpl {
+                        span: self_ty.span,
+                        modifier,
+                        modifier_name,
+                        modifier_span,
+                        self_ty: self_ty.span,
+                    })
+                };
+
+                if let Safety::Unsafe(span) = safety {
+                    error("unsafe", "unsafe", span).with_code(E0197).emit();
+                }
+                if let ImplPolarity::Negative(span) = polarity {
+                    error("!", "negative", span).emit();
+                }
+                if let Defaultness::Default(def_span) = defaultness {
+                    error("default", "default", def_span).emit();
+                }
+                if let Const::Yes(span) = constness {
+                    error("const", "const", span).emit();
+                }
+                (None, self_ty)
             }
-            None => (None, ty_first), // impl Type
         };
-        Ok(ItemKind::Impl(Box::new(Impl {
-            safety,
-            polarity,
-            defaultness,
-            constness,
-            generics,
-            of_trait,
-            self_ty,
-            items: impl_items,
-        })))
+
+        Ok(ItemKind::Impl(Impl { generics, of_trait, self_ty, items: impl_items }))
     }
 
     fn parse_item_delegation(&mut self) -> PResult<'a, ItemKind> {
@@ -951,17 +975,21 @@ impl<'a> Parser<'a> {
     pub fn parse_impl_item(
         &mut self,
         force_collect: ForceCollect,
-    ) -> PResult<'a, Option<Option<P<AssocItem>>>> {
-        let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: true };
+    ) -> PResult<'a, Option<Option<Box<AssocItem>>>> {
+        let fn_parse_mode =
+            FnParseMode { req_name: |_| true, context: FnContext::Impl, req_body: true };
         self.parse_assoc_item(fn_parse_mode, force_collect)
     }
 
     pub fn parse_trait_item(
         &mut self,
         force_collect: ForceCollect,
-    ) -> PResult<'a, Option<Option<P<AssocItem>>>> {
-        let fn_parse_mode =
-            FnParseMode { req_name: |edition| edition >= Edition::Edition2018, req_body: false };
+    ) -> PResult<'a, Option<Option<Box<AssocItem>>>> {
+        let fn_parse_mode = FnParseMode {
+            req_name: |edition| edition >= Edition::Edition2018,
+            context: FnContext::Trait,
+            req_body: false,
+        };
         self.parse_assoc_item(fn_parse_mode, force_collect)
     }
 
@@ -970,7 +998,7 @@ impl<'a> Parser<'a> {
         &mut self,
         fn_parse_mode: FnParseMode,
         force_collect: ForceCollect,
-    ) -> PResult<'a, Option<Option<P<AssocItem>>>> {
+    ) -> PResult<'a, Option<Option<Box<AssocItem>>>> {
         Ok(self.parse_item_(fn_parse_mode, force_collect)?.map(
             |Item { attrs, id, span, vis, kind, tokens }| {
                 let kind = match AssocItemKind::try_from(kind) {
@@ -997,7 +1025,7 @@ impl<'a> Parser<'a> {
                         _ => return self.error_bad_item_kind(span, &kind, "`trait`s or `impl`s"),
                     },
                 };
-                Some(P(Item { attrs, id, span, vis, kind, tokens }))
+                Some(Box::new(Item { attrs, id, span, vis, kind, tokens }))
             },
         ))
     }
@@ -1237,8 +1265,9 @@ impl<'a> Parser<'a> {
     pub fn parse_foreign_item(
         &mut self,
         force_collect: ForceCollect,
-    ) -> PResult<'a, Option<Option<P<ForeignItem>>>> {
-        let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: false };
+    ) -> PResult<'a, Option<Option<Box<ForeignItem>>>> {
+        let fn_parse_mode =
+            FnParseMode { req_name: |_| true, context: FnContext::Free, req_body: false };
         Ok(self.parse_item_(fn_parse_mode, force_collect)?.map(
             |Item { attrs, id, span, vis, kind, tokens }| {
                 let kind = match ForeignItemKind::try_from(kind) {
@@ -1263,7 +1292,7 @@ impl<'a> Parser<'a> {
                         _ => return self.error_bad_item_kind(span, &kind, "`extern` blocks"),
                     },
                 };
-                Some(P(Item { attrs, id, span, vis, kind, tokens }))
+                Some(Box::new(Item { attrs, id, span, vis, kind, tokens }))
             },
         ))
     }
@@ -1365,10 +1394,10 @@ impl<'a> Parser<'a> {
         };
 
         match &mut item_kind {
-            ItemKind::Impl(box Impl { of_trait: Some(trai), constness, .. }) => {
-                *constness = Const::Yes(const_span);
+            ItemKind::Impl(Impl { of_trait: Some(of_trait), .. }) => {
+                of_trait.constness = Const::Yes(const_span);
 
-                let before_trait = trai.path.span.shrink_to_lo();
+                let before_trait = of_trait.trait_ref.path.span.shrink_to_lo();
                 let const_up_to_impl = const_span.with_hi(impl_span.lo());
                 err.with_multipart_suggestion(
                     "you might have meant to write a const trait impl",
@@ -1424,7 +1453,9 @@ impl<'a> Parser<'a> {
     /// ```ebnf
     /// Const = "const" ($ident | "_") Generics ":" $ty (= $expr)? WhereClause ";" ;
     /// ```
-    fn parse_const_item(&mut self) -> PResult<'a, (Ident, Generics, P<Ty>, Option<P<ast::Expr>>)> {
+    fn parse_const_item(
+        &mut self,
+    ) -> PResult<'a, (Ident, Generics, Box<Ty>, Option<Box<ast::Expr>>)> {
         let ident = self.parse_ident_or_underscore()?;
 
         let mut generics = self.parse_generics()?;
@@ -1517,7 +1548,7 @@ impl<'a> Parser<'a> {
         &mut self,
         colon_present: bool,
         m: Option<Mutability>,
-    ) -> P<Ty> {
+    ) -> Box<Ty> {
         // Construct the error and stash it away with the hope
         // that typeck will later enrich the error with a type.
         let kind = match m {
@@ -1537,7 +1568,7 @@ impl<'a> Parser<'a> {
 
         // The user intended that the type be inferred,
         // so treat this as if the user wrote e.g. `const A: _ = expr;`.
-        P(Ty { kind: TyKind::Infer, span, id: ast::DUMMY_NODE_ID, tokens: None })
+        Box::new(Ty { kind: TyKind::Infer, span, id: ast::DUMMY_NODE_ID, tokens: None })
     }
 
     /// Parses an enum declaration.
@@ -2110,7 +2141,8 @@ impl<'a> Parser<'a> {
                 let inherited_vis =
                     Visibility { span: DUMMY_SP, kind: VisibilityKind::Inherited, tokens: None };
                 // We use `parse_fn` to get a span for the function
-                let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: true };
+                let fn_parse_mode =
+                    FnParseMode { req_name: |_| true, context: FnContext::Free, req_body: true };
                 match self.parse_fn(
                     &mut AttrVec::new(),
                     fn_parse_mode,
@@ -2207,7 +2239,7 @@ impl<'a> Parser<'a> {
             let arrow = TokenTree::token_alone(token::FatArrow, pspan.between(bspan)); // `=>`
             let tokens = TokenStream::new(vec![params, arrow, body]);
             let dspan = DelimSpan::from_pair(pspan.shrink_to_lo(), bspan.shrink_to_hi());
-            P(DelimArgs { dspan, delim: Delimiter::Brace, tokens })
+            Box::new(DelimArgs { dspan, delim: Delimiter::Brace, tokens })
         } else {
             self.unexpected_any()?
         };
@@ -2378,6 +2410,9 @@ pub(crate) struct FnParseMode {
     ///   * The span is from Edition 2015. In particular, you can get a
     ///     2015 span inside a 2021 crate using macros.
     pub(super) req_name: ReqName,
+    /// The context in which this function is parsed, used for diagnostics.
+    /// This indicates the fn is a free function or method and so on.
+    pub(super) context: FnContext,
     /// If this flag is set to `true`, then plain, semicolon-terminated function
     /// prototypes are not allowed here.
     ///
@@ -2399,6 +2434,18 @@ pub(crate) struct FnParseMode {
     pub(super) req_body: bool,
 }
 
+/// The context in which a function is parsed.
+/// FIXME(estebank, xizheyin): Use more variants.
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub(crate) enum FnContext {
+    /// Free context.
+    Free,
+    /// A Trait context.
+    Trait,
+    /// An Impl block.
+    Impl,
+}
+
 /// Parsing of functions and methods.
 impl<'a> Parser<'a> {
     /// Parse a function starting from the front matter (`const ...`) to the body `{ ... }` or `;`.
@@ -2409,16 +2456,13 @@ impl<'a> Parser<'a> {
         sig_lo: Span,
         vis: &Visibility,
         case: Case,
-    ) -> PResult<'a, (Ident, FnSig, Generics, Option<P<FnContract>>, Option<P<Block>>)> {
+    ) -> PResult<'a, (Ident, FnSig, Generics, Option<Box<FnContract>>, Option<Box<Block>>)> {
         let fn_span = self.token.span;
         let header = self.parse_fn_front_matter(vis, case, FrontMatterParsingMode::Function)?; // `const ... fn`
         let ident = self.parse_ident()?; // `foo`
         let mut generics = self.parse_generics()?; // `<'a, T, ...>`
-        let decl = match self.parse_fn_decl(
-            fn_parse_mode.req_name,
-            AllowPlus::Yes,
-            RecoverReturnSign::Yes,
-        ) {
+        let decl = match self.parse_fn_decl(&fn_parse_mode, AllowPlus::Yes, RecoverReturnSign::Yes)
+        {
             Ok(decl) => decl,
             Err(old_err) => {
                 // If we see `for Ty ...` then user probably meant `impl` item.
@@ -2539,7 +2583,7 @@ impl<'a> Parser<'a> {
         sig_hi: &mut Span,
         req_body: bool,
         fn_params_end: Option<Span>,
-    ) -> PResult<'a, Option<P<Block>>> {
+    ) -> PResult<'a, Option<Box<Block>>> {
         let has_semi = if req_body {
             self.token == TokenKind::Semi
         } else {
@@ -2936,18 +2980,21 @@ impl<'a> Parser<'a> {
     /// Parses the parameter list and result type of a function declaration.
     pub(super) fn parse_fn_decl(
         &mut self,
-        req_name: ReqName,
+        fn_parse_mode: &FnParseMode,
         ret_allow_plus: AllowPlus,
         recover_return_sign: RecoverReturnSign,
-    ) -> PResult<'a, P<FnDecl>> {
-        Ok(P(FnDecl {
-            inputs: self.parse_fn_params(req_name)?,
+    ) -> PResult<'a, Box<FnDecl>> {
+        Ok(Box::new(FnDecl {
+            inputs: self.parse_fn_params(fn_parse_mode)?,
             output: self.parse_ret_ty(ret_allow_plus, RecoverQPath::Yes, recover_return_sign)?,
         }))
     }
 
     /// Parses the parameter list of a function, including the `(` and `)` delimiters.
-    pub(super) fn parse_fn_params(&mut self, req_name: ReqName) -> PResult<'a, ThinVec<Param>> {
+    pub(super) fn parse_fn_params(
+        &mut self,
+        fn_parse_mode: &FnParseMode,
+    ) -> PResult<'a, ThinVec<Param>> {
         let mut first_param = true;
         // Parse the arguments, starting out with `self` being allowed...
         if self.token != TokenKind::OpenParen
@@ -2963,7 +3010,7 @@ impl<'a> Parser<'a> {
         let (mut params, _) = self.parse_paren_comma_seq(|p| {
             p.recover_vcs_conflict_marker();
             let snapshot = p.create_snapshot_for_diagnostic();
-            let param = p.parse_param_general(req_name, first_param, true).or_else(|e| {
+            let param = p.parse_param_general(fn_parse_mode, first_param, true).or_else(|e| {
                 let guar = e.emit();
                 // When parsing a param failed, we should check to make the span of the param
                 // not contain '(' before it.
@@ -2994,7 +3041,7 @@ impl<'a> Parser<'a> {
     /// - `recover_arg_parse` is used to recover from a failed argument parse.
     pub(super) fn parse_param_general(
         &mut self,
-        req_name: ReqName,
+        fn_parse_mode: &FnParseMode,
         first_param: bool,
         recover_arg_parse: bool,
     ) -> PResult<'a, Param> {
@@ -3010,16 +3057,22 @@ impl<'a> Parser<'a> {
 
             let is_name_required = match this.token.kind {
                 token::DotDotDot => false,
-                _ => req_name(this.token.span.with_neighbor(this.prev_token.span).edition()),
+                _ => (fn_parse_mode.req_name)(
+                    this.token.span.with_neighbor(this.prev_token.span).edition(),
+                ),
             };
             let (pat, ty) = if is_name_required || this.is_named_param() {
                 debug!("parse_param_general parse_pat (is_name_required:{})", is_name_required);
                 let (pat, colon) = this.parse_fn_param_pat_colon()?;
                 if !colon {
                     let mut err = this.unexpected().unwrap_err();
-                    return if let Some(ident) =
-                        this.parameter_without_type(&mut err, pat, is_name_required, first_param)
-                    {
+                    return if let Some(ident) = this.parameter_without_type(
+                        &mut err,
+                        pat,
+                        is_name_required,
+                        first_param,
+                        fn_parse_mode,
+                    ) {
                         let guar = err.emit();
                         Ok((dummy_arg(ident, guar), Trailing::No, UsePreAttrPos::No))
                     } else {
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index 90491e53249..41ed1f95a01 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -22,10 +22,9 @@ use std::{fmt, mem, slice};
 use attr_wrapper::{AttrWrapper, UsePreAttrPos};
 pub use diagnostics::AttemptLocalParseRecovery;
 pub(crate) use expr::ForbiddenLetReason;
-pub(crate) use item::FnParseMode;
+pub(crate) use item::{FnContext, FnParseMode};
 pub use pat::{CommaRecoveryMode, RecoverColon, RecoverComma};
 use path::PathStyle;
-use rustc_ast::ptr::P;
 use rustc_ast::token::{
     self, IdentIsRaw, InvisibleOrigin, MetaVarKind, NtExprKind, NtPatKind, Token, TokenKind,
 };
@@ -1286,7 +1285,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses inline const expressions.
-    fn parse_const_block(&mut self, span: Span, pat: bool) -> PResult<'a, P<Expr>> {
+    fn parse_const_block(&mut self, span: Span, pat: bool) -> PResult<'a, Box<Expr>> {
         self.expect_keyword(exp!(Const))?;
         let (attrs, blk) = self.parse_inner_attrs_and_block(None)?;
         let anon_const = AnonConst {
@@ -1343,9 +1342,9 @@ impl<'a> Parser<'a> {
         }
     }
 
-    fn parse_delim_args(&mut self) -> PResult<'a, P<DelimArgs>> {
+    fn parse_delim_args(&mut self) -> PResult<'a, Box<DelimArgs>> {
         if let Some(args) = self.parse_delim_args_inner() {
-            Ok(P(args))
+            Ok(Box::new(args))
         } else {
             self.unexpected_any()
         }
@@ -1470,7 +1469,7 @@ impl<'a> Parser<'a> {
                 let path = self.parse_path(PathStyle::Mod)?; // `path`
                 self.expect(exp!(CloseParen))?; // `)`
                 let vis = VisibilityKind::Restricted {
-                    path: P(path),
+                    path: Box::new(path),
                     id: ast::DUMMY_NODE_ID,
                     shorthand: false,
                 };
@@ -1487,7 +1486,7 @@ impl<'a> Parser<'a> {
                 let path = self.parse_path(PathStyle::Mod)?; // `crate`/`super`/`self`
                 self.expect(exp!(CloseParen))?; // `)`
                 let vis = VisibilityKind::Restricted {
-                    path: P(path),
+                    path: Box::new(path),
                     id: ast::DUMMY_NODE_ID,
                     shorthand: true,
                 };
@@ -1652,14 +1651,14 @@ pub enum ParseNtResult {
     Tt(TokenTree),
     Ident(Ident, IdentIsRaw),
     Lifetime(Ident, IdentIsRaw),
-    Item(P<ast::Item>),
-    Block(P<ast::Block>),
-    Stmt(P<ast::Stmt>),
-    Pat(P<ast::Pat>, NtPatKind),
-    Expr(P<ast::Expr>, NtExprKind),
-    Literal(P<ast::Expr>),
-    Ty(P<ast::Ty>),
-    Meta(P<ast::AttrItem>),
-    Path(P<ast::Path>),
-    Vis(P<ast::Visibility>),
+    Item(Box<ast::Item>),
+    Block(Box<ast::Block>),
+    Stmt(Box<ast::Stmt>),
+    Pat(Box<ast::Pat>, NtPatKind),
+    Expr(Box<ast::Expr>, NtExprKind),
+    Literal(Box<ast::Expr>),
+    Ty(Box<ast::Ty>),
+    Meta(Box<ast::AttrItem>),
+    Path(Box<ast::Path>),
+    Vis(Box<ast::Visibility>),
 }
diff --git a/compiler/rustc_parse/src/parser/nonterminal.rs b/compiler/rustc_parse/src/parser/nonterminal.rs
index 7c83e96c160..42eb07858c2 100644
--- a/compiler/rustc_parse/src/parser/nonterminal.rs
+++ b/compiler/rustc_parse/src/parser/nonterminal.rs
@@ -1,4 +1,3 @@
-use rustc_ast::ptr::P;
 use rustc_ast::token::NtExprKind::*;
 use rustc_ast::token::NtPatKind::*;
 use rustc_ast::token::{self, InvisibleOrigin, MetaVarKind, NonterminalKind, Token};
@@ -129,7 +128,7 @@ impl<'a> Parser<'a> {
                 Ok(ParseNtResult::Block(self.collect_tokens_no_attrs(|this| this.parse_block())?))
             }
             NonterminalKind::Stmt => match self.parse_stmt(ForceCollect::Yes)? {
-                Some(stmt) => Ok(ParseNtResult::Stmt(P(stmt))),
+                Some(stmt) => Ok(ParseNtResult::Stmt(Box::new(stmt))),
                 None => {
                     Err(self.dcx().create_err(UnexpectedNonterminal::Statement(self.token.span)))
                 }
@@ -170,16 +169,15 @@ impl<'a> Parser<'a> {
                     }))
                 }
             }
-            NonterminalKind::Path => Ok(ParseNtResult::Path(P(
-                self.collect_tokens_no_attrs(|this| this.parse_path(PathStyle::Type))?
+            NonterminalKind::Path => Ok(ParseNtResult::Path(Box::new(
+                self.collect_tokens_no_attrs(|this| this.parse_path(PathStyle::Type))?,
             ))),
             NonterminalKind::Meta => {
-                Ok(ParseNtResult::Meta(P(self.parse_attr_item(ForceCollect::Yes)?)))
-            }
-            NonterminalKind::Vis => {
-                Ok(ParseNtResult::Vis(P(self
-                    .collect_tokens_no_attrs(|this| this.parse_visibility(FollowedByType::Yes))?)))
+                Ok(ParseNtResult::Meta(Box::new(self.parse_attr_item(ForceCollect::Yes)?)))
             }
+            NonterminalKind::Vis => Ok(ParseNtResult::Vis(Box::new(
+                self.collect_tokens_no_attrs(|this| this.parse_visibility(FollowedByType::Yes))?,
+            ))),
             NonterminalKind::Lifetime => {
                 // We want to keep `'keyword` parsing, just like `keyword` is still
                 // an ident for nonterminal purposes.
diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs
index 64653ee2a04..9754691a0b9 100644
--- a/compiler/rustc_parse/src/parser/pat.rs
+++ b/compiler/rustc_parse/src/parser/pat.rs
@@ -1,7 +1,6 @@
 use std::ops::Bound;
 
 use rustc_ast::mut_visit::{self, MutVisitor};
-use rustc_ast::ptr::P;
 use rustc_ast::token::NtPatKind::*;
 use rustc_ast::token::{self, IdentIsRaw, MetaVarKind, Token};
 use rustc_ast::util::parser::ExprPrecedence;
@@ -25,10 +24,10 @@ use crate::errors::{
     GenericArgsInPatRequireTurbofishSyntax, InclusiveRangeExtraEquals, InclusiveRangeMatchArrow,
     InclusiveRangeNoEnd, InvalidMutInPattern, ParenRangeSuggestion, PatternOnWrongSideOfAt,
     RemoveLet, RepeatedMutInPattern, SwitchRefBoxOrder, TopLevelOrPatternNotAllowed,
-    TopLevelOrPatternNotAllowedSugg, TrailingVertNotAllowed, UnexpectedExpressionInPattern,
-    UnexpectedExpressionInPatternSugg, UnexpectedLifetimeInPattern, UnexpectedParenInRangePat,
-    UnexpectedParenInRangePatSugg, UnexpectedVertVertBeforeFunctionParam,
-    UnexpectedVertVertInPattern, WrapInParens,
+    TopLevelOrPatternNotAllowedSugg, TrailingVertNotAllowed, TrailingVertSuggestion,
+    UnexpectedExpressionInPattern, UnexpectedExpressionInPatternSugg, UnexpectedLifetimeInPattern,
+    UnexpectedParenInRangePat, UnexpectedParenInRangePatSugg,
+    UnexpectedVertVertBeforeFunctionParam, UnexpectedVertVertInPattern, WrapInParens,
 };
 use crate::parser::expr::{DestructuredFloat, could_be_unclosed_char_literal};
 use crate::{exp, maybe_recover_from_interpolated_ty_qpath};
@@ -108,7 +107,7 @@ impl<'a> Parser<'a> {
         rc: RecoverComma,
         ra: RecoverColon,
         rt: CommaRecoveryMode,
-    ) -> PResult<'a, P<Pat>> {
+    ) -> PResult<'a, Box<Pat>> {
         let pat = self.parse_pat_no_top_guard(expected, rc, ra, rt)?;
 
         if self.eat_keyword(exp!(If)) {
@@ -131,7 +130,7 @@ impl<'a> Parser<'a> {
         &mut self,
         expected: Option<Expected>,
         syntax_loc: Option<PatternLocation>,
-    ) -> PResult<'a, P<Pat>> {
+    ) -> PResult<'a, Box<Pat>> {
         self.parse_pat_with_range_pat(true, expected, syntax_loc)
     }
 
@@ -150,7 +149,7 @@ impl<'a> Parser<'a> {
         rc: RecoverComma,
         ra: RecoverColon,
         rt: CommaRecoveryMode,
-    ) -> PResult<'a, P<Pat>> {
+    ) -> PResult<'a, Box<Pat>> {
         self.parse_pat_no_top_guard_inner(expected, rc, ra, rt, None).map(|(pat, _)| pat)
     }
 
@@ -163,7 +162,7 @@ impl<'a> Parser<'a> {
         ra: RecoverColon,
         rt: CommaRecoveryMode,
         syntax_loc: Option<PatternLocation>,
-    ) -> PResult<'a, (P<Pat>, bool)> {
+    ) -> PResult<'a, (Box<Pat>, bool)> {
         // Keep track of whether we recovered from a trailing vert so that we can avoid duplicated
         // suggestions (which bothers rustfix).
         //
@@ -253,7 +252,7 @@ impl<'a> Parser<'a> {
         expected: Option<Expected>,
         rc: RecoverComma,
         syntax_loc: PatternLocation,
-    ) -> PResult<'a, (P<Pat>, bool)> {
+    ) -> PResult<'a, (Box<Pat>, bool)> {
         // We use `parse_pat_allow_top_alt` regardless of whether we actually want top-level
         // or-patterns so that we can detect when a user tries to use it. This allows us to print a
         // better error message.
@@ -268,10 +267,9 @@ impl<'a> Parser<'a> {
 
         if let PatKind::Or(pats) = &pat.kind {
             let span = pat.span;
-            let sub = if pats.len() == 1 {
-                Some(TopLevelOrPatternNotAllowedSugg::RemoveLeadingVert {
-                    span: span.with_hi(span.lo() + BytePos(1)),
-                })
+            let sub = if let [_] = &pats[..] {
+                let span = span.with_hi(span.lo() + BytePos(1));
+                Some(TopLevelOrPatternNotAllowedSugg::RemoveLeadingVert { span })
             } else {
                 Some(TopLevelOrPatternNotAllowedSugg::WrapInParens {
                     span,
@@ -301,7 +299,7 @@ impl<'a> Parser<'a> {
     ///
     /// The return value represents the parsed pattern and `true` if a `Colon` was parsed (`false`
     /// otherwise).
-    pub(super) fn parse_fn_param_pat_colon(&mut self) -> PResult<'a, (P<Pat>, bool)> {
+    pub(super) fn parse_fn_param_pat_colon(&mut self) -> PResult<'a, (Box<Pat>, bool)> {
         // In order to get good UX, we first recover in the case of a leading vert for an illegal
         // top-level or-pat. Normally, this means recovering both `|` and `||`, but in this case,
         // a leading `||` probably doesn't indicate an or-pattern attempt, so we handle that
@@ -363,6 +361,9 @@ impl<'a> Parser<'a> {
                 self.dcx().emit_err(TrailingVertNotAllowed {
                     span: self.token.span,
                     start: lo,
+                    suggestion: TrailingVertSuggestion {
+                        span: self.prev_token.span.shrink_to_hi().with_hi(self.token.span.hi()),
+                    },
                     token: self.token,
                     note_double_vert: self.token.kind == token::OrOr,
                 });
@@ -685,7 +686,7 @@ impl<'a> Parser<'a> {
         PatVisitor { parser: self, stmt, arm: None, field: None }.visit_stmt(stmt);
     }
 
-    fn eat_metavar_pat(&mut self) -> Option<P<Pat>> {
+    fn eat_metavar_pat(&mut self) -> Option<Box<Pat>> {
         // Must try both kinds of pattern nonterminals.
         if let Some(pat) = self.eat_metavar_seq_with_matcher(
             |mv_kind| matches!(mv_kind, MetaVarKind::Pat(PatParam { .. })),
@@ -713,7 +714,7 @@ impl<'a> Parser<'a> {
         allow_range_pat: bool,
         expected: Option<Expected>,
         syntax_loc: Option<PatternLocation>,
-    ) -> PResult<'a, P<Pat>> {
+    ) -> PResult<'a, Box<Pat>> {
         maybe_recover_from_interpolated_ty_qpath!(self, true);
 
         if let Some(pat) = self.eat_metavar_pat() {
@@ -909,7 +910,7 @@ impl<'a> Parser<'a> {
     /// e.g. [F#][and] where they are called AND-patterns.
     ///
     /// [and]: https://docs.microsoft.com/en-us/dotnet/fsharp/language-reference/pattern-matching
-    fn recover_intersection_pat(&mut self, lhs: P<Pat>) -> PResult<'a, P<Pat>> {
+    fn recover_intersection_pat(&mut self, lhs: Box<Pat>) -> PResult<'a, Box<Pat>> {
         if self.token != token::At {
             // Next token is not `@` so it's not going to be an intersection pattern.
             return Ok(lhs);
@@ -1091,7 +1092,7 @@ impl<'a> Parser<'a> {
 
     /// Turn all by-value immutable bindings in a pattern into mutable bindings.
     /// Returns `true` if any change was made.
-    fn make_all_value_bindings_mutable(pat: &mut P<Pat>) -> bool {
+    fn make_all_value_bindings_mutable(pat: &mut Box<Pat>) -> bool {
         struct AddMut(bool);
         impl MutVisitor for AddMut {
             fn visit_pat(&mut self, pat: &mut Pat) {
@@ -1139,7 +1140,7 @@ impl<'a> Parser<'a> {
     fn parse_pat_mac_invoc(&mut self, path: Path) -> PResult<'a, PatKind> {
         self.bump();
         let args = self.parse_delim_args()?;
-        let mac = P(MacCall { path, args });
+        let mac = Box::new(MacCall { path, args });
         Ok(PatKind::MacCall(mac))
     }
 
@@ -1147,7 +1148,7 @@ impl<'a> Parser<'a> {
         &mut self,
         err: Diag<'a>,
         expected: Option<Expected>,
-    ) -> PResult<'a, P<Pat>> {
+    ) -> PResult<'a, Box<Pat>> {
         err.cancel();
 
         let expected = Expected::to_string_or_fallback(expected);
@@ -1182,7 +1183,7 @@ impl<'a> Parser<'a> {
     /// `$begin $form` has already been parsed.
     fn parse_pat_range_begin_with(
         &mut self,
-        begin: P<Expr>,
+        begin: Box<Expr>,
         re: Spanned<RangeEnd>,
     ) -> PResult<'a, PatKind> {
         let end = if self.is_pat_range_end_start(0) {
@@ -1262,7 +1263,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parse a range pattern end bound
-    fn parse_pat_range_end(&mut self) -> PResult<'a, P<Expr>> {
+    fn parse_pat_range_end(&mut self) -> PResult<'a, Box<Expr>> {
         // recover leading `(`
         let open_paren = (self.may_recover() && self.eat_noexpect(&token::OpenParen))
             .then_some(self.prev_token.span);
@@ -1380,7 +1381,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parse a struct ("record") pattern (e.g. `Foo { ... }` or `Foo::Bar { ... }`).
-    fn parse_pat_struct(&mut self, qself: Option<P<QSelf>>, path: Path) -> PResult<'a, PatKind> {
+    fn parse_pat_struct(&mut self, qself: Option<Box<QSelf>>, path: Path) -> PResult<'a, PatKind> {
         if qself.is_some() {
             // Feature gate the use of qualified paths in patterns
             self.psess.gated_spans.gate(sym::more_qualified_paths, path.span);
@@ -1400,7 +1401,7 @@ impl<'a> Parser<'a> {
     /// Parse tuple struct or tuple variant pattern (e.g. `Foo(...)` or `Foo::Bar(...)`).
     fn parse_pat_tuple_struct(
         &mut self,
-        qself: Option<P<QSelf>>,
+        qself: Option<Box<QSelf>>,
         path: Path,
     ) -> PResult<'a, PatKind> {
         let (fields, _) = self.parse_paren_comma_seq(|p| {
@@ -1749,11 +1750,11 @@ impl<'a> Parser<'a> {
         })
     }
 
-    pub(super) fn mk_pat_ident(&self, span: Span, ann: BindingMode, ident: Ident) -> P<Pat> {
+    pub(super) fn mk_pat_ident(&self, span: Span, ann: BindingMode, ident: Ident) -> Box<Pat> {
         self.mk_pat(span, PatKind::Ident(ann, ident, None))
     }
 
-    pub(super) fn mk_pat(&self, span: Span, kind: PatKind) -> P<Pat> {
-        P(Pat { kind, span, id: ast::DUMMY_NODE_ID, tokens: None })
+    pub(super) fn mk_pat(&self, span: Span, kind: PatKind) -> Box<Pat> {
+        Box::new(Pat { kind, span, id: ast::DUMMY_NODE_ID, tokens: None })
     }
 }
diff --git a/compiler/rustc_parse/src/parser/path.rs b/compiler/rustc_parse/src/parser/path.rs
index 8e65ab99c5e..37fc723cd89 100644
--- a/compiler/rustc_parse/src/parser/path.rs
+++ b/compiler/rustc_parse/src/parser/path.rs
@@ -1,7 +1,6 @@
 use std::mem;
 
 use ast::token::IdentIsRaw;
-use rustc_ast::ptr::P;
 use rustc_ast::token::{self, MetaVarKind, Token, TokenKind};
 use rustc_ast::{
     self as ast, AngleBracketedArg, AngleBracketedArgs, AnonConst, AssocItemConstraint,
@@ -21,7 +20,9 @@ use crate::errors::{
     PathFoundAttributeInParams, PathFoundCVariadicParams, PathSingleColon, PathTripleColon,
 };
 use crate::exp;
-use crate::parser::{CommaRecoveryMode, ExprKind, RecoverColon, RecoverComma};
+use crate::parser::{
+    CommaRecoveryMode, ExprKind, FnContext, FnParseMode, RecoverColon, RecoverComma,
+};
 
 /// Specifies how to parse a path.
 #[derive(Copy, Clone, PartialEq)]
@@ -75,7 +76,7 @@ impl<'a> Parser<'a> {
     /// `<T as U>::a`
     /// `<T as U>::F::a<S>` (without disambiguator)
     /// `<T as U>::F::a::<S>` (with disambiguator)
-    pub(super) fn parse_qpath(&mut self, style: PathStyle) -> PResult<'a, (P<QSelf>, Path)> {
+    pub(super) fn parse_qpath(&mut self, style: PathStyle) -> PResult<'a, (Box<QSelf>, Path)> {
         let lo = self.prev_token.span;
         let ty = self.parse_ty()?;
 
@@ -105,7 +106,7 @@ impl<'a> Parser<'a> {
             self.expect(exp!(PathSep))?;
         }
 
-        let qself = P(QSelf { ty, path_span, position: path.segments.len() });
+        let qself = Box::new(QSelf { ty, path_span, position: path.segments.len() });
         if !is_import_coupler {
             self.parse_path_segments(&mut path.segments, style, None)?;
         }
@@ -380,7 +381,7 @@ impl<'a> Parser<'a> {
                             .emit_err(errors::BadReturnTypeNotationOutput { span, suggestion });
                     }
 
-                    P(ast::GenericArgs::ParenthesizedElided(span))
+                    Box::new(ast::GenericArgs::ParenthesizedElided(span))
                 } else {
                     // `(T, U) -> R`
 
@@ -400,7 +401,13 @@ impl<'a> Parser<'a> {
 
                     let dcx = self.dcx();
                     let parse_params_result = self.parse_paren_comma_seq(|p| {
-                        let param = p.parse_param_general(|_| false, false, false);
+                        // Inside parenthesized type arguments, we want types only, not names.
+                        let mode = FnParseMode {
+                            context: FnContext::Free,
+                            req_name: |_| false,
+                            req_body: false,
+                        };
+                        let param = p.parse_param_general(&mode, false, false);
                         param.map(move |param| {
                             if !matches!(param.pat.kind, PatKind::Missing) {
                                 dcx.emit_err(FnPathFoundNamedParams {
@@ -842,7 +849,7 @@ impl<'a> Parser<'a> {
     /// - A literal.
     /// - A numeric literal prefixed by `-`.
     /// - A single-segment path.
-    pub(super) fn expr_is_valid_const_arg(&self, expr: &P<rustc_ast::Expr>) -> bool {
+    pub(super) fn expr_is_valid_const_arg(&self, expr: &Box<rustc_ast::Expr>) -> bool {
         match &expr.kind {
             ast::ExprKind::Block(_, _)
             | ast::ExprKind::Lit(_)
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index 2fa6520f2a4..b4943ff7de6 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -4,7 +4,6 @@ use std::ops::Bound;
 
 use ast::Label;
 use rustc_ast as ast;
-use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Delimiter, InvisibleOrigin, MetaVarKind, TokenKind};
 use rustc_ast::util::classify::{self, TrailingBrace};
 use rustc_ast::{
@@ -20,8 +19,8 @@ use super::diagnostics::AttemptLocalParseRecovery;
 use super::pat::{PatternLocation, RecoverComma};
 use super::path::PathStyle;
 use super::{
-    AttrWrapper, BlockMode, FnParseMode, ForceCollect, Parser, Restrictions, SemiColonMode,
-    Trailing, UsePreAttrPos,
+    AttrWrapper, BlockMode, FnContext, FnParseMode, ForceCollect, Parser, Restrictions,
+    SemiColonMode, Trailing, UsePreAttrPos,
 };
 use crate::errors::{self, MalformedLoopLabel};
 use crate::exp;
@@ -154,10 +153,10 @@ impl<'a> Parser<'a> {
             attrs.clone(), // FIXME: unwanted clone of attrs
             false,
             true,
-            FnParseMode { req_name: |_| true, req_body: true },
+            FnParseMode { req_name: |_| true, context: FnContext::Free, req_body: true },
             force_collect,
         )? {
-            self.mk_stmt(lo.to(item.span), StmtKind::Item(P(item)))
+            self.mk_stmt(lo.to(item.span), StmtKind::Item(Box::new(item)))
         } else if self.eat(exp!(Semi)) {
             // Do not attempt to parse an expression if we're done here.
             self.error_outer_attrs(attrs);
@@ -246,7 +245,7 @@ impl<'a> Parser<'a> {
             _ => MacStmtStyle::NoBraces,
         };
 
-        let mac = P(MacCall { path, args });
+        let mac = Box::new(MacCall { path, args });
 
         let kind = if (style == MacStmtStyle::Braces
             && !matches!(self.token.kind, token::Dot | token::Question))
@@ -256,7 +255,7 @@ impl<'a> Parser<'a> {
                     | token::Eof
                     | token::CloseInvisible(InvisibleOrigin::MetaVar(MetaVarKind::Stmt))
             ) {
-            StmtKind::MacCall(P(MacCallStmt { mac, style, attrs, tokens: None }))
+            StmtKind::MacCall(Box::new(MacCallStmt { mac, style, attrs, tokens: None }))
         } else {
             // Since none of the above applied, this is an expression statement macro.
             let e = self.mk_expr(lo.to(hi), ExprKind::MacCall(mac));
@@ -307,7 +306,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses a local variable declaration.
-    fn parse_local(&mut self, super_: Option<Span>, attrs: AttrVec) -> PResult<'a, P<Local>> {
+    fn parse_local(&mut self, super_: Option<Span>, attrs: AttrVec) -> PResult<'a, Box<Local>> {
         let lo = super_.unwrap_or(self.prev_token.span);
 
         if self.token.is_keyword(kw::Const) && self.look_ahead(1, |t| t.is_ident()) {
@@ -409,7 +408,7 @@ impl<'a> Parser<'a> {
             }
         };
         let hi = if self.token == token::Semi { self.token.span } else { self.prev_token.span };
-        Ok(P(ast::Local {
+        Ok(Box::new(ast::Local {
             super_,
             ty,
             pat,
@@ -463,7 +462,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses the RHS of a local variable declaration (e.g., `= 14;`).
-    fn parse_initializer(&mut self, eq_optional: bool) -> PResult<'a, Option<P<Expr>>> {
+    fn parse_initializer(&mut self, eq_optional: bool) -> PResult<'a, Option<Box<Expr>>> {
         let eq_consumed = match self.token.kind {
             token::PlusEq
             | token::MinusEq
@@ -494,7 +493,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses a block. No inner attributes are allowed.
-    pub fn parse_block(&mut self) -> PResult<'a, P<Block>> {
+    pub fn parse_block(&mut self) -> PResult<'a, Box<Block>> {
         let (attrs, block) = self.parse_inner_attrs_and_block(None)?;
         if let [.., last] = &*attrs {
             let suggest_to_outer = match &last.kind {
@@ -679,7 +678,7 @@ impl<'a> Parser<'a> {
     pub(super) fn parse_inner_attrs_and_block(
         &mut self,
         loop_header: Option<Span>,
-    ) -> PResult<'a, (AttrVec, P<Block>)> {
+    ) -> PResult<'a, (AttrVec, Box<Block>)> {
         self.parse_block_common(self.token.span, BlockCheckMode::Default, loop_header)
     }
 
@@ -692,7 +691,7 @@ impl<'a> Parser<'a> {
         lo: Span,
         blk_mode: BlockCheckMode,
         loop_header: Option<Span>,
-    ) -> PResult<'a, (AttrVec, P<Block>)> {
+    ) -> PResult<'a, (AttrVec, Box<Block>)> {
         if let Some(block) = self.eat_metavar_seq(MetaVarKind::Block, |this| this.parse_block()) {
             return Ok((AttrVec::new(), block));
         }
@@ -718,7 +717,7 @@ impl<'a> Parser<'a> {
         lo: Span,
         s: BlockCheckMode,
         recover: AttemptLocalParseRecovery,
-    ) -> PResult<'a, P<Block>> {
+    ) -> PResult<'a, Box<Block>> {
         let mut stmts = ThinVec::new();
         let mut snapshot = None;
         while !self.eat(exp!(CloseBrace)) {
@@ -1050,8 +1049,8 @@ impl<'a> Parser<'a> {
         stmts: ThinVec<Stmt>,
         rules: BlockCheckMode,
         span: Span,
-    ) -> P<Block> {
-        P(Block { stmts, id: DUMMY_NODE_ID, rules, span, tokens: None })
+    ) -> Box<Block> {
+        Box::new(Block { stmts, id: DUMMY_NODE_ID, rules, span, tokens: None })
     }
 
     pub(super) fn mk_stmt(&self, span: Span, kind: StmtKind) -> Stmt {
@@ -1062,7 +1061,7 @@ impl<'a> Parser<'a> {
         self.mk_stmt(span, StmtKind::Expr(self.mk_expr_err(span, guar)))
     }
 
-    pub(super) fn mk_block_err(&self, span: Span, guar: ErrorGuaranteed) -> P<Block> {
+    pub(super) fn mk_block_err(&self, span: Span, guar: ErrorGuaranteed) -> Box<Block> {
         self.mk_block(thin_vec![self.mk_stmt_err(span, guar)], BlockCheckMode::Default, span)
     }
 }
diff --git a/compiler/rustc_parse/src/parser/tests.rs b/compiler/rustc_parse/src/parser/tests.rs
index 43a1d779a75..a6e7266e71b 100644
--- a/compiler/rustc_parse/src/parser/tests.rs
+++ b/compiler/rustc_parse/src/parser/tests.rs
@@ -8,7 +8,6 @@ use std::sync::{Arc, Mutex};
 use std::{io, str};
 
 use ast::token::IdentIsRaw;
-use rustc_ast::ptr::P;
 use rustc_ast::token::{self, Delimiter, Token};
 use rustc_ast::tokenstream::{DelimSpacing, DelimSpan, Spacing, TokenStream, TokenTree};
 use rustc_ast::{self as ast, PatKind, visit};
@@ -2240,7 +2239,7 @@ fn parse_item_from_source_str(
     name: FileName,
     source: String,
     psess: &ParseSess,
-) -> PResult<'_, Option<P<ast::Item>>> {
+) -> PResult<'_, Option<Box<ast::Item>>> {
     unwrap_or_emit_fatal(new_parser_from_source_str(psess, name, source))
         .parse_item(ForceCollect::No)
 }
@@ -2251,12 +2250,12 @@ fn sp(a: u32, b: u32) -> Span {
 }
 
 /// Parses a string, return an expression.
-fn string_to_expr(source_str: String) -> P<ast::Expr> {
+fn string_to_expr(source_str: String) -> Box<ast::Expr> {
     with_error_checking_parse(source_str, &psess(), |p| p.parse_expr())
 }
 
 /// Parses a string, returns an item.
-fn string_to_item(source_str: String) -> Option<P<ast::Item>> {
+fn string_to_item(source_str: String) -> Option<Box<ast::Item>> {
     with_error_checking_parse(source_str, &psess(), |p| p.parse_item(ForceCollect::No))
 }
 
@@ -2520,7 +2519,7 @@ fn ttdelim_span() {
         name: FileName,
         source: String,
         psess: &ParseSess,
-    ) -> PResult<'_, P<ast::Expr>> {
+    ) -> PResult<'_, Box<ast::Expr>> {
         unwrap_or_emit_fatal(new_parser_from_source_str(psess, name, source)).parse_expr()
     }
 
diff --git a/compiler/rustc_parse/src/parser/ty.rs b/compiler/rustc_parse/src/parser/ty.rs
index 59048e42e6f..290f0a440af 100644
--- a/compiler/rustc_parse/src/parser/ty.rs
+++ b/compiler/rustc_parse/src/parser/ty.rs
@@ -1,4 +1,3 @@
-use rustc_ast::ptr::P;
 use rustc_ast::token::{self, IdentIsRaw, MetaVarKind, Token, TokenKind};
 use rustc_ast::util::case::Case;
 use rustc_ast::{
@@ -20,6 +19,7 @@ use crate::errors::{
     NestedCVariadicType, ReturnTypesUseThinArrow,
 };
 use crate::parser::item::FrontMatterParsingMode;
+use crate::parser::{FnContext, FnParseMode};
 use crate::{exp, maybe_recover_from_interpolated_ty_qpath};
 
 /// Signals whether parsing a type should allow `+`.
@@ -105,7 +105,7 @@ fn can_begin_dyn_bound_in_edition_2015(t: &Token) -> bool {
 
 impl<'a> Parser<'a> {
     /// Parses a type.
-    pub fn parse_ty(&mut self) -> PResult<'a, P<Ty>> {
+    pub fn parse_ty(&mut self) -> PResult<'a, Box<Ty>> {
         // Make sure deeply nested types don't overflow the stack.
         ensure_sufficient_stack(|| {
             self.parse_ty_common(
@@ -122,7 +122,7 @@ impl<'a> Parser<'a> {
     pub(super) fn parse_ty_with_generics_recovery(
         &mut self,
         ty_params: &Generics,
-    ) -> PResult<'a, P<Ty>> {
+    ) -> PResult<'a, Box<Ty>> {
         self.parse_ty_common(
             AllowPlus::Yes,
             AllowCVariadic::No,
@@ -136,7 +136,7 @@ impl<'a> Parser<'a> {
     /// Parse a type suitable for a function or function pointer parameter.
     /// The difference from `parse_ty` is that this version allows `...`
     /// (`CVarArgs`) at the top level of the type.
-    pub(super) fn parse_ty_for_param(&mut self) -> PResult<'a, P<Ty>> {
+    pub(super) fn parse_ty_for_param(&mut self) -> PResult<'a, Box<Ty>> {
         self.parse_ty_common(
             AllowPlus::Yes,
             AllowCVariadic::Yes,
@@ -153,7 +153,7 @@ impl<'a> Parser<'a> {
     ///     `+` is prohibited to maintain operator priority (P(+) < P(&)).
     /// Example 2: `value1 as TYPE + value2`
     ///     `+` is prohibited to avoid interactions with expression grammar.
-    pub(super) fn parse_ty_no_plus(&mut self) -> PResult<'a, P<Ty>> {
+    pub(super) fn parse_ty_no_plus(&mut self) -> PResult<'a, Box<Ty>> {
         self.parse_ty_common(
             AllowPlus::No,
             AllowCVariadic::No,
@@ -166,7 +166,7 @@ impl<'a> Parser<'a> {
 
     /// Parses a type following an `as` cast. Similar to `parse_ty_no_plus`, but signaling origin
     /// for better diagnostics involving `?`.
-    pub(super) fn parse_as_cast_ty(&mut self) -> PResult<'a, P<Ty>> {
+    pub(super) fn parse_as_cast_ty(&mut self) -> PResult<'a, Box<Ty>> {
         self.parse_ty_common(
             AllowPlus::No,
             AllowCVariadic::No,
@@ -177,7 +177,7 @@ impl<'a> Parser<'a> {
         )
     }
 
-    pub(super) fn parse_ty_no_question_mark_recover(&mut self) -> PResult<'a, P<Ty>> {
+    pub(super) fn parse_ty_no_question_mark_recover(&mut self) -> PResult<'a, Box<Ty>> {
         self.parse_ty_common(
             AllowPlus::Yes,
             AllowCVariadic::No,
@@ -190,7 +190,7 @@ impl<'a> Parser<'a> {
 
     /// Parse a type without recovering `:` as `->` to avoid breaking code such
     /// as `where fn() : for<'a>`.
-    pub(super) fn parse_ty_for_where_clause(&mut self) -> PResult<'a, P<Ty>> {
+    pub(super) fn parse_ty_for_where_clause(&mut self) -> PResult<'a, Box<Ty>> {
         self.parse_ty_common(
             AllowPlus::Yes,
             AllowCVariadic::No,
@@ -250,7 +250,7 @@ impl<'a> Parser<'a> {
         recover_return_sign: RecoverReturnSign,
         ty_generics: Option<&Generics>,
         recover_question_mark: RecoverQuestionMark,
-    ) -> PResult<'a, P<Ty>> {
+    ) -> PResult<'a, Box<Ty>> {
         let allow_qpath_recovery = recover_qpath == RecoverQPath::Yes;
         maybe_recover_from_interpolated_ty_qpath!(self, allow_qpath_recovery);
         if self.token == token::Pound && self.look_ahead(1, |t| *t == token::OpenBracket) {
@@ -425,7 +425,7 @@ impl<'a> Parser<'a> {
         let span = lo.to(self.prev_token.span);
         self.psess.gated_spans.gate(sym::unsafe_binders, span);
 
-        Ok(TyKind::UnsafeBinder(P(UnsafeBinderTy { generic_params, inner_ty })))
+        Ok(TyKind::UnsafeBinder(Box::new(UnsafeBinderTy { generic_params, inner_ty })))
     }
 
     /// Parses either:
@@ -610,7 +610,7 @@ impl<'a> Parser<'a> {
     /// - `[u8, 5]` → suggests using `;`, return a Array type
     /// - `[u8 5]` → suggests using `;`, return a Array type
     /// Consider to add more cases in the future.
-    fn maybe_recover_array_ty_without_semi(&mut self, elt_ty: P<Ty>) -> PResult<'a, TyKind> {
+    fn maybe_recover_array_ty_without_semi(&mut self, elt_ty: Box<Ty>) -> PResult<'a, TyKind> {
         let span = self.token.span;
         let token_descr = super::token_descr(&self.token);
         let mut err =
@@ -770,10 +770,21 @@ impl<'a> Parser<'a> {
         if self.may_recover() && self.token == TokenKind::Lt {
             self.recover_fn_ptr_with_generics(lo, &mut params, param_insertion_point)?;
         }
-        let decl = self.parse_fn_decl(|_| false, AllowPlus::No, recover_return_sign)?;
+        let mode = crate::parser::item::FnParseMode {
+            req_name: |_| false,
+            context: FnContext::Free,
+            req_body: false,
+        };
+        let decl = self.parse_fn_decl(&mode, AllowPlus::No, recover_return_sign)?;
 
         let decl_span = span_start.to(self.prev_token.span);
-        Ok(TyKind::FnPtr(P(FnPtrTy { ext, safety, generic_params: params, decl, decl_span })))
+        Ok(TyKind::FnPtr(Box::new(FnPtrTy {
+            ext,
+            safety,
+            generic_params: params,
+            decl,
+            decl_span,
+        })))
     }
 
     /// Recover from function pointer types with a generic parameter list (e.g. `fn<'a>(&'a str)`).
@@ -915,7 +926,7 @@ impl<'a> Parser<'a> {
         let path = self.parse_path_inner(PathStyle::Type, ty_generics)?;
         if self.eat(exp!(Bang)) {
             // Macro invocation in type position
-            Ok(TyKind::MacCall(P(MacCall { path, args: self.parse_delim_args()? })))
+            Ok(TyKind::MacCall(Box::new(MacCall { path, args: self.parse_delim_args()? })))
         } else if allow_plus == AllowPlus::Yes && self.check_plus() {
             // `Trait1 + Trait2 + 'a`
             self.parse_remaining_bounds_path(ThinVec::new(), path, lo, true, ast::Parens::No)
@@ -1015,7 +1026,7 @@ impl<'a> Parser<'a> {
         let bound = GenericBound::Outlives(lt);
         if let ast::Parens::Yes = parens {
             // FIXME(Centril): Consider not erroring here and accepting `('lt)` instead,
-            // possibly introducing `GenericBound::Paren(P<GenericBound>)`?
+            // possibly introducing `GenericBound::Paren(Box<GenericBound>)`?
             self.recover_paren_lifetime(lo)?;
         }
         Ok(bound)
@@ -1309,7 +1320,8 @@ impl<'a> Parser<'a> {
         self.bump();
         let args_lo = self.token.span;
         let snapshot = self.create_snapshot_for_diagnostic();
-        match self.parse_fn_decl(|_| false, AllowPlus::No, RecoverReturnSign::OnlyFatArrow) {
+        let mode = FnParseMode { req_name: |_| false, context: FnContext::Free, req_body: false };
+        match self.parse_fn_decl(&mode, AllowPlus::No, RecoverReturnSign::OnlyFatArrow) {
             Ok(decl) => {
                 self.dcx().emit_err(ExpectedFnPathFoundFnKeyword { fn_token_span });
                 Some(ast::Path {
@@ -1317,12 +1329,14 @@ impl<'a> Parser<'a> {
                     segments: thin_vec![ast::PathSegment {
                         ident: Ident::new(sym::Fn, fn_token_span),
                         id: DUMMY_NODE_ID,
-                        args: Some(P(ast::GenericArgs::Parenthesized(ast::ParenthesizedArgs {
-                            span: args_lo.to(self.prev_token.span),
-                            inputs: decl.inputs.iter().map(|a| a.ty.clone()).collect(),
-                            inputs_span: args_lo.until(decl.output.span()),
-                            output: decl.output.clone(),
-                        }))),
+                        args: Some(Box::new(ast::GenericArgs::Parenthesized(
+                            ast::ParenthesizedArgs {
+                                span: args_lo.to(self.prev_token.span),
+                                inputs: decl.inputs.iter().map(|a| a.ty.clone()).collect(),
+                                inputs_span: args_lo.until(decl.output.span()),
+                                output: decl.output.clone(),
+                            }
+                        ))),
                     }],
                     tokens: None,
                 })
@@ -1393,8 +1407,9 @@ impl<'a> Parser<'a> {
 
         // Parse `(T, U) -> R`.
         let inputs_lo = self.token.span;
+        let mode = FnParseMode { req_name: |_| false, context: FnContext::Free, req_body: false };
         let inputs: ThinVec<_> =
-            self.parse_fn_params(|_| false)?.into_iter().map(|input| input.ty).collect();
+            self.parse_fn_params(&mode)?.into_iter().map(|input| input.ty).collect();
         let inputs_span = inputs_lo.to(self.prev_token.span);
         let output = self.parse_ret_ty(AllowPlus::No, RecoverQPath::No, RecoverReturnSign::No)?;
         let args = ast::ParenthesizedArgs {
@@ -1464,7 +1479,7 @@ impl<'a> Parser<'a> {
         }
     }
 
-    pub(super) fn mk_ty(&self, span: Span, kind: TyKind) -> P<Ty> {
-        P(Ty { kind, span, id: ast::DUMMY_NODE_ID, tokens: None })
+    pub(super) fn mk_ty(&self, span: Span, kind: TyKind) -> Box<Ty> {
+        Box::new(Ty { kind, span, id: ast::DUMMY_NODE_ID, tokens: None })
     }
 }
diff --git a/compiler/rustc_parse/src/validate_attr.rs b/compiler/rustc_parse/src/validate_attr.rs
index a7f8d3b9139..68ef6d6f32c 100644
--- a/compiler/rustc_parse/src/validate_attr.rs
+++ b/compiler/rustc_parse/src/validate_attr.rs
@@ -298,35 +298,42 @@ fn emit_malformed_attribute(
         suggestions.push(format!("#{inner}[{name}]"));
     }
     if let Some(descr) = template.list {
-        suggestions.push(format!("#{inner}[{name}({descr})]"));
+        for descr in descr {
+            suggestions.push(format!("#{inner}[{name}({descr})]"));
+        }
     }
     suggestions.extend(template.one_of.iter().map(|&word| format!("#{inner}[{name}({word})]")));
     if let Some(descr) = template.name_value_str {
-        suggestions.push(format!("#{inner}[{name} = \"{descr}\"]"));
+        for descr in descr {
+            suggestions.push(format!("#{inner}[{name} = \"{descr}\"]"));
+        }
     }
     if should_warn(name) {
         psess.buffer_lint(
             ILL_FORMED_ATTRIBUTE_INPUT,
             span,
             ast::CRATE_NODE_ID,
-            BuiltinLintDiag::IllFormedAttributeInput { suggestions: suggestions.clone() },
+            BuiltinLintDiag::IllFormedAttributeInput {
+                suggestions: suggestions.clone(),
+                docs: template.docs,
+            },
         );
     } else {
         suggestions.sort();
-        psess
-            .dcx()
-            .struct_span_err(span, error_msg)
-            .with_span_suggestions(
-                span,
-                if suggestions.len() == 1 {
-                    "must be of the form"
-                } else {
-                    "the following are the possible correct uses"
-                },
-                suggestions,
-                Applicability::HasPlaceholders,
-            )
-            .emit();
+        let mut err = psess.dcx().struct_span_err(span, error_msg).with_span_suggestions(
+            span,
+            if suggestions.len() == 1 {
+                "must be of the form"
+            } else {
+                "the following are the possible correct uses"
+            },
+            suggestions,
+            Applicability::HasPlaceholders,
+        );
+        if let Some(link) = template.docs {
+            err.note(format!("for more information, visit <{link}>"));
+        }
+        err.emit();
     }
 }
 
diff --git a/compiler/rustc_passes/messages.ftl b/compiler/rustc_passes/messages.ftl
index 6a28fe2617e..7481b0ea960 100644
--- a/compiler/rustc_passes/messages.ftl
+++ b/compiler/rustc_passes/messages.ftl
@@ -13,23 +13,7 @@ passes_abi_ne =
 passes_abi_of =
     fn_abi_of({$fn_name}) = {$fn_abi}
 
-passes_align_attr_application =
-    `#[rustc_align(...)]` should be applied to a function item
-    .label = not a function item
-
-passes_align_on_fields =
-    attribute should be applied to a function or method
-    .warn = {-passes_previously_accepted}
-
-passes_align_should_be_repr_align =
-    `#[rustc_align(...)]` is not supported on {$item} items
-    .suggestion = use `#[repr(align(...))]` instead
-
-passes_allow_incoherent_impl =
-    `rustc_allow_incoherent_impl` attribute should be applied to impl items
-    .label = the only currently supported targets are inherent methods
-
-passes_allow_internal_unstable =
+passes_macro_only_attribute =
     attribute should be applied to a macro
     .label = not a macro
 
@@ -78,18 +62,10 @@ passes_change_fields_to_be_of_unit_type =
      *[other] fields
     }
 
-passes_cold =
-    {passes_should_be_applied_to_fn}
-    .warn = {-passes_previously_accepted}
-    .label = {passes_should_be_applied_to_fn.label}
-
 passes_collapse_debuginfo =
     `collapse_debuginfo` attribute should be applied to macro definitions
     .label = not a macro definition
 
-passes_confusables = attribute should be applied to an inherent method
-    .label = not an inherent method
-
 passes_const_continue_attr =
     `#[const_continue]` should be applied to a break expression
     .label = not a break expression
@@ -98,16 +74,6 @@ passes_const_stable_not_stable =
     attribute `#[rustc_const_stable]` can only be applied to functions that are declared `#[stable]`
     .label = attribute specified here
 
-passes_coroutine_on_non_closure =
-    attribute should be applied to closures
-    .label = not a closure
-
-passes_coverage_attribute_not_allowed =
-    coverage attribute not allowed here
-    .not_fn_impl_mod = not a function, impl block, or module
-    .no_body = function has no body
-    .help = coverage attribute can be applied to a function (with body), impl block, or module
-
 passes_dead_codes =
     { $multiple ->
       *[true] multiple {$descr}s are
@@ -129,9 +95,6 @@ passes_debug_visualizer_placement =
 passes_debug_visualizer_unreadable =
     couldn't read {$file}: {$error}
 
-passes_deprecated =
-    attribute is ignored here
-
 passes_deprecated_annotation_has_no_effect =
     this `#[deprecated]` annotation has no effect
     .suggestion = remove the unnecessary deprecation attribute
@@ -304,10 +267,6 @@ passes_duplicate_lang_item_crate_depends =
 passes_enum_variant_same_name =
     it is impossible to refer to the {$dead_descr} `{$dead_name}` because it is shadowed by this enum variant with the same name
 
-passes_export_name =
-    attribute should be applied to a free function, impl method or static
-    .label = not a free function, impl method or static
-
 passes_extern_main =
     the `main` function cannot be declared in an `extern` block
 
@@ -317,21 +276,10 @@ passes_feature_previously_declared =
 passes_feature_stable_twice =
     feature `{$feature}` is declared stable since {$since}, but was previously declared stable since {$prev_since}
 
-passes_ffi_const_invalid_target =
-    `#[ffi_const]` may only be used on foreign functions
-
-passes_ffi_pure_invalid_target =
-    `#[ffi_pure]` may only be used on foreign functions
-
 passes_has_incoherent_inherent_impl =
     `rustc_has_incoherent_inherent_impls` attribute should be applied to types or traits
     .label = only adts, extern types and traits are supported
 
-passes_ignored_attr =
-    `#[{$sym}]` is ignored on struct fields and match arms
-    .warn = {-passes_previously_accepted}
-    .note = {-passes_see_issue(issue: "80564")}
-
 passes_ignored_attr_with_macro =
     `#[{$sym}]` is ignored on struct fields, match arms and macro defs
     .warn = {-passes_previously_accepted}
@@ -373,22 +321,10 @@ passes_incorrect_target =
 passes_ineffective_unstable_impl = an `#[unstable]` annotation here has no effect
     .note = see issue #55436 <https://github.com/rust-lang/rust/issues/55436> for more information
 
-passes_inline_ignored_constants =
-    `#[inline]` is ignored on constants
-    .warn = {-passes_previously_accepted}
-    .note = {-passes_see_issue(issue: "65833")}
-
 passes_inline_ignored_for_exported =
     `#[inline]` is ignored on externally exported functions
     .help = externally exported functions are functions with `#[no_mangle]`, `#[export_name]`, or `#[linkage]`
 
-passes_inline_ignored_function_prototype =
-    `#[inline]` is ignored on function prototypes
-
-passes_inline_not_fn_or_closure =
-    attribute should be applied to function or closure
-    .label = not a function or closure
-
 passes_inner_crate_level_attr =
     crate-level attribute should be in the root module
 
@@ -438,25 +374,6 @@ passes_link =
     .warn = {-passes_previously_accepted}
     .label = not an `extern` block
 
-passes_link_name =
-    attribute should be applied to a foreign function or static
-    .warn = {-passes_previously_accepted}
-    .label = not a foreign function or static
-    .help = try `#[link(name = "{$value}")]` instead
-
-passes_link_ordinal =
-    attribute should be applied to a foreign function or static
-    .label = not a foreign function or static
-
-passes_link_section =
-    attribute should be applied to a function or static
-    .warn = {-passes_previously_accepted}
-    .label = not a function or static
-
-passes_linkage =
-    attribute should be applied to a function or static
-    .label = not a function definition or static
-
 passes_loop_match_attr =
     `#[loop_match]` should be applied to a loop
     .label = not a loop
@@ -468,9 +385,6 @@ passes_macro_export_on_decl_macro =
     `#[macro_export]` has no effect on declarative macro definitions
     .note = declarative macros follow the same exporting rules as regular items
 
-passes_macro_use =
-    `#[{$name}]` only has an effect on `extern crate` and modules
-
 passes_may_dangle =
     `#[may_dangle]` must be applied to a lifetime or type generic parameter in `Drop` impl
 
@@ -509,7 +423,8 @@ passes_must_not_suspend =
     .label = is not a struct, enum, union, or trait
 
 passes_must_use_no_effect =
-    `#[must_use]` has no effect when applied to {$article} {$target}
+    `#[must_use]` has no effect when applied to {$target}
+    .suggestion = remove the attribute
 
 passes_no_link =
     attribute should be applied to an `extern crate` item
@@ -529,18 +444,6 @@ passes_no_main_function =
     .teach_note = If you don't know the basics of Rust, you can go look to the Rust Book to get started: https://doc.rust-lang.org/book/
     .non_function_main = non-function item at `crate::main` is found
 
-passes_no_mangle =
-    attribute should be applied to a free function, impl method or static
-    .warn = {-passes_previously_accepted}
-    .label = not a free function, impl method or static
-
-passes_no_mangle_foreign =
-    `#[no_mangle]` has no effect on a foreign {$foreign_item_kind}
-    .warn = {-passes_previously_accepted}
-    .label = foreign {$foreign_item_kind}
-    .note = symbol names in extern blocks are not mangled
-    .suggestion = remove this attribute
-
 passes_no_sanitize =
     `#[no_sanitize({$attr_str})]` should be applied to {$accepted_kind}
     .label = not {$accepted_kind}
@@ -556,19 +459,6 @@ passes_non_exported_macro_invalid_attrs =
 passes_object_lifetime_err =
     {$repr}
 
-passes_only_has_effect_on =
-    `#[{$attr_name}]` only has an effect on {$target_name ->
-        [function] functions
-        [module] modules
-        [trait_implementation_block] trait implementation blocks
-        [inherent_implementation_block] inherent implementation blocks
-        *[unspecified] (unspecified--this is a compiler bug)
-    }
-
-passes_optimize_invalid_target =
-    attribute applied to an invalid target
-    .label = invalid target
-
 passes_outer_crate_level_attr =
     crate-level attribute should be an inner attribute: add an exclamation mark: `#![foo]`
 
@@ -584,10 +474,6 @@ passes_parent_info =
      *[other] {$descr}s
     } in this {$parent_descr}
 
-passes_pass_by_value =
-    `pass_by_value` attribute should be applied to a struct, enum or type alias
-    .label = is not a struct, enum or type alias
-
 passes_proc_macro_bad_sig = {$kind} has incorrect signature
 
 passes_remove_fields =
@@ -604,7 +490,7 @@ passes_repr_align_greater_than_target_max =
     .note = `isize::MAX` is {$size} for the current target
 
 passes_repr_align_should_be_align =
-    `#[repr(align(...))]` is not supported on {$item} items
+    `#[repr(align(...))]` is not supported on {$item}
     .help = use `#[rustc_align(...)]` instead
 
 passes_repr_conflicting =
@@ -619,18 +505,10 @@ passes_rustc_const_stable_indirect_pairing =
 passes_rustc_dirty_clean =
     attribute requires -Z query-dep-graph to be enabled
 
-passes_rustc_force_inline =
-    attribute should be applied to a function
-    .label = not a function definition
-
 passes_rustc_force_inline_coro =
     attribute cannot be applied to a `async`, `gen` or `async gen` function
     .label = `async`, `gen` or `async gen` function
 
-passes_rustc_layout_scalar_valid_range_not_struct =
-    attribute should be applied to a struct
-    .label = not a struct
-
 passes_rustc_legacy_const_generics_index =
     #[rustc_legacy_const_generics] must have one index for each generic parameter
     .label = generic parameters
@@ -664,14 +542,6 @@ passes_rustc_pub_transparent =
     attribute should be applied to `#[repr(transparent)]` types
     .label = not a `#[repr(transparent)]` type
 
-passes_rustc_std_internal_symbol =
-    attribute should be applied to functions or statics
-    .label = not a function or static
-
-passes_rustc_unstable_feature_bound =
-    attribute should be applied to `impl` or free function outside of any `impl` or trait
-    .label = not an `impl` or free function
-
 passes_should_be_applied_to_fn =
     attribute should be applied to a function definition
     .label = {$on_crate ->
@@ -683,24 +553,12 @@ passes_should_be_applied_to_static =
     attribute should be applied to a static
     .label = not a static
 
-passes_should_be_applied_to_struct_enum =
-    attribute should be applied to a struct or enum
-    .label = not a struct or enum
-
 passes_should_be_applied_to_trait =
     attribute should be applied to a trait
     .label = not a trait
 
-passes_stability_promotable =
-    attribute cannot be applied to an expression
-
 passes_string_interpolation_only_works = string interpolation only works in `format!` invocations
 
-passes_target_feature_on_statement =
-    {passes_should_be_applied_to_fn}
-    .warn = {-passes_previously_accepted}
-    .label = {passes_should_be_applied_to_fn.label}
-
 passes_trait_impl_const_stability_mismatch = const stability on the impl does not match the const stability on the trait
 passes_trait_impl_const_stability_mismatch_impl_stable = this impl is (implicitly) stable...
 passes_trait_impl_const_stability_mismatch_impl_unstable = this impl is unstable...
@@ -825,11 +683,6 @@ passes_unused_variable_try_prefix = unused variable: `{$name}`
     .label = unused variable
     .suggestion = if this is intentional, prefix it with an underscore
 
-
-passes_used_static =
-    attribute must be applied to a `static` variable
-    .label = but this is a {$target}
-
 passes_useless_assignment =
     useless assignment of {$is_field_assign ->
         [true] field
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index 890028d977d..0e28c51e981 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -10,7 +10,7 @@ use std::collections::hash_map::Entry;
 use std::slice;
 
 use rustc_abi::{Align, ExternAbi, Size};
-use rustc_ast::{AttrStyle, LitKind, MetaItemInner, MetaItemKind, ast, join_path_syms};
+use rustc_ast::{AttrStyle, LitKind, MetaItemInner, MetaItemKind, ast};
 use rustc_attr_parsing::{AttributeParser, Late};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::{Applicability, DiagCtxtHandle, IntoDiagArg, MultiSpan, StashKey};
@@ -40,7 +40,6 @@ use rustc_session::lint;
 use rustc_session::lint::builtin::{
     CONFLICTING_REPR_HINTS, INVALID_DOC_ATTRIBUTES, INVALID_MACRO_EXPORT_ARGUMENTS,
     MALFORMED_DIAGNOSTIC_ATTRIBUTES, MISPLACED_DIAGNOSTIC_ATTRIBUTES, UNUSED_ATTRIBUTES,
-    USELESS_DEPRECATED,
 };
 use rustc_session::parse::feature_err;
 use rustc_span::edition::Edition;
@@ -50,7 +49,6 @@ use rustc_trait_selection::infer::{TyCtxtInferExt, ValuePairs};
 use rustc_trait_selection::traits::ObligationCtxt;
 use tracing::debug;
 
-use crate::errors::AlignOnFields;
 use crate::{errors, fluent_generated as fluent};
 
 #[derive(LintDiagnostic)]
@@ -134,56 +132,12 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 Attribute::Parsed(AttributeKind::ProcMacroAttribute(_)) => {
                     self.check_proc_macro(hir_id, target, ProcMacroKind::Attribute);
                 }
-                Attribute::Parsed(AttributeKind::ProcMacroDerive { span: attr_span, .. }) => {
-                    self.check_generic_attr(
-                        hir_id,
-                        sym::proc_macro_derive,
-                        *attr_span,
-                        target,
-                        Target::Fn,
-                    );
+                Attribute::Parsed(AttributeKind::ProcMacroDerive { .. }) => {
                     self.check_proc_macro(hir_id, target, ProcMacroKind::Derive)
                 }
-                Attribute::Parsed(
-                    AttributeKind::SkipDuringMethodDispatch { span: attr_span, .. }
-                    | AttributeKind::Coinductive(attr_span)
-                    | AttributeKind::ConstTrait(attr_span)
-                    | AttributeKind::DenyExplicitImpl(attr_span)
-                    | AttributeKind::DoNotImplementViaObject(attr_span),
-                ) => {
-                    self.check_must_be_applied_to_trait(*attr_span, span, target);
-                }
-                &Attribute::Parsed(
-                    AttributeKind::SpecializationTrait(attr_span)
-                    | AttributeKind::UnsafeSpecializationMarker(attr_span)
-                    | AttributeKind::ParenSugar(attr_span),
-                ) => {
-                    // FIXME: more validation is needed
-                    self.check_must_be_applied_to_trait(attr_span, span, target);
-                }
                 &Attribute::Parsed(AttributeKind::TypeConst(attr_span)) => {
                     self.check_type_const(hir_id, attr_span, target)
                 }
-                &Attribute::Parsed(AttributeKind::Marker(attr_span)) => {
-                    self.check_marker(hir_id, attr_span, span, target)
-                }
-                Attribute::Parsed(AttributeKind::Fundamental | AttributeKind::CoherenceIsCore) => {
-                    // FIXME: add validation
-                }
-                &Attribute::Parsed(AttributeKind::AllowIncoherentImpl(attr_span)) => {
-                    self.check_allow_incoherent_impl(attr_span, span, target)
-                }
-                Attribute::Parsed(AttributeKind::Confusables { first_span, .. }) => {
-                    self.check_confusables(*first_span, target);
-                }
-                Attribute::Parsed(AttributeKind::AutomaticallyDerived(attr_span)) => self
-                    .check_generic_attr(
-                        hir_id,
-                        sym::automatically_derived,
-                        *attr_span,
-                        target,
-                        Target::Impl { of_trait: true },
-                    ),
                 Attribute::Parsed(
                     AttributeKind::Stability {
                         span: attr_span,
@@ -193,13 +147,10 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                         span: attr_span,
                         stability: PartialConstStability { level, feature, .. },
                     },
-                ) => self.check_stability(*attr_span, span, level, *feature, target),
+                ) => self.check_stability(*attr_span, span, level, *feature),
                 Attribute::Parsed(AttributeKind::Inline(InlineAttr::Force { .. }, ..)) => {} // handled separately below
                 Attribute::Parsed(AttributeKind::Inline(kind, attr_span)) => {
-                    self.check_inline(hir_id, *attr_span, span, kind, target)
-                }
-                Attribute::Parsed(AttributeKind::Optimize(_, attr_span)) => {
-                    self.check_optimize(hir_id, *attr_span, span, target)
+                    self.check_inline(hir_id, *attr_span, kind, target)
                 }
                 Attribute::Parsed(AttributeKind::LoopMatch(attr_span)) => {
                     self.check_loop_match(hir_id, *attr_span, target)
@@ -207,8 +158,8 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 Attribute::Parsed(AttributeKind::ConstContinue(attr_span)) => {
                     self.check_const_continue(hir_id, *attr_span, target)
                 }
-                Attribute::Parsed(AttributeKind::AllowInternalUnstable(_, first_span)) => {
-                    self.check_allow_internal_unstable(hir_id, *first_span, span, target, attrs)
+                Attribute::Parsed(AttributeKind::AllowInternalUnsafe(attr_span) | AttributeKind::AllowInternalUnstable(.., attr_span)) => {
+                    self.check_macro_only_attr(*attr_span, span, target, attrs)
                 }
                 Attribute::Parsed(AttributeKind::AllowConstFnUnstable(_, first_span)) => {
                     self.check_rustc_allow_const_fn_unstable(hir_id, *first_span, span, target)
@@ -217,11 +168,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     self.check_deprecated(hir_id, attr, span, target)
                 }
                 Attribute::Parsed(AttributeKind::TargetFeature(_, attr_span)) => {
-                    self.check_target_feature(hir_id, *attr_span, span, target, attrs)
-                }
-                Attribute::Parsed(AttributeKind::DocComment { .. }) => { /* `#[doc]` is actually a lot more than just doc comments, so is checked below*/
-                }
-                Attribute::Parsed(AttributeKind::Repr { .. }) => { /* handled below this loop and elsewhere */
+                    self.check_target_feature(hir_id, *attr_span, target, attrs)
                 }
                 Attribute::Parsed(AttributeKind::RustcObjectLifetimeDefault) => {
                     self.check_object_lifetime_default(hir_id);
@@ -229,59 +176,26 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 &Attribute::Parsed(AttributeKind::PubTransparent(attr_span)) => {
                     self.check_rustc_pub_transparent(attr_span, span, attrs)
                 }
-                Attribute::Parsed(AttributeKind::Cold(attr_span)) => {
-                    self.check_cold(hir_id, *attr_span, span, target)
-                }
-                Attribute::Parsed(AttributeKind::ExportName { span: attr_span, .. }) => {
-                    self.check_export_name(hir_id, *attr_span, span, target)
-                }
                 Attribute::Parsed(AttributeKind::Align { align, span: attr_span }) => {
-                    self.check_align(span, hir_id, target, *align, *attr_span)
-                }
-                Attribute::Parsed(AttributeKind::LinkSection { span: attr_span, .. }) => {
-                    self.check_link_section(hir_id, *attr_span, span, target)
-                }
-                Attribute::Parsed(AttributeKind::MacroUse { span, .. }) => {
-                    self.check_macro_use(hir_id, sym::macro_use, *span, target)
-                }
-                Attribute::Parsed(AttributeKind::MacroEscape(span)) => {
-                    self.check_macro_use(hir_id, sym::macro_escape, *span, target)
+                    self.check_align(*align, *attr_span)
                 }
-                Attribute::Parsed(AttributeKind::Naked(attr_span)) => {
-                    self.check_naked(hir_id, *attr_span, span, target)
-                }
-                Attribute::Parsed(AttributeKind::NoImplicitPrelude(attr_span)) => self
-                    .check_generic_attr(
-                        hir_id,
-                        sym::no_implicit_prelude,
-                        *attr_span,
-                        target,
-                        Target::Mod,
-                    ),
-                Attribute::Parsed(AttributeKind::Path(_, attr_span)) => {
-                    self.check_generic_attr(hir_id, sym::path, *attr_span, target, Target::Mod)
+                Attribute::Parsed(AttributeKind::Naked(..)) => {
+                    self.check_naked(hir_id, target)
                 }
                 Attribute::Parsed(AttributeKind::TrackCaller(attr_span)) => {
-                    self.check_track_caller(hir_id, *attr_span, attrs, span, target)
+                    self.check_track_caller(hir_id, *attr_span, attrs, target)
                 }
                 Attribute::Parsed(AttributeKind::NonExhaustive(attr_span)) => {
-                    self.check_non_exhaustive(hir_id, *attr_span, span, target, item)
-                }
-                Attribute::Parsed(
-                    AttributeKind::RustcLayoutScalarValidRangeStart(_num, attr_span)
-                    | AttributeKind::RustcLayoutScalarValidRangeEnd(_num, attr_span),
-                ) => self.check_rustc_layout_scalar_valid_range(*attr_span, span, target),
-                Attribute::Parsed(AttributeKind::ExportStable) => {
-                    // handled in `check_export`
-                }
-                &Attribute::Parsed(AttributeKind::FfiConst(attr_span)) => {
-                    self.check_ffi_const(attr_span, target)
+                    self.check_non_exhaustive(*attr_span, span, target, item)
                 }
                 &Attribute::Parsed(AttributeKind::FfiPure(attr_span)) => {
-                    self.check_ffi_pure(attr_span, attrs, target)
+                    self.check_ffi_pure(attr_span, attrs)
                 }
-                Attribute::Parsed(AttributeKind::UnstableFeatureBound(syms)) => {
-                    self.check_unstable_feature_bound(syms.first().unwrap().1, span, target)
+                Attribute::Parsed(AttributeKind::MayDangle(attr_span)) => {
+                    self.check_may_dangle(hir_id, *attr_span)
+                }
+                Attribute::Parsed(AttributeKind::MustUse { span, .. }) => {
+                    self.check_must_use(hir_id, *span, target)
                 }
                 Attribute::Parsed(
                     AttributeKind::BodyStability { .. }
@@ -289,44 +203,52 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     | AttributeKind::MacroTransparency(_)
                     | AttributeKind::Pointee(..)
                     | AttributeKind::Dummy
-                    | AttributeKind::RustcBuiltinMacro { .. },
+                    | AttributeKind::RustcBuiltinMacro { .. }
+                    | AttributeKind::Ignore { .. }
+                    | AttributeKind::Path(..)
+                    | AttributeKind::NoImplicitPrelude(..)
+                    | AttributeKind::AutomaticallyDerived(..)
+                    | AttributeKind::Marker(..)
+                    | AttributeKind::SkipDuringMethodDispatch { .. }
+                    | AttributeKind::Coinductive(..)
+                    | AttributeKind::ConstTrait(..)
+                    | AttributeKind::DenyExplicitImpl(..)
+                    | AttributeKind::DoNotImplementViaObject(..)
+                    | AttributeKind::SpecializationTrait(..)
+                    | AttributeKind::UnsafeSpecializationMarker(..)
+                    | AttributeKind::ParenSugar(..)
+                    | AttributeKind::AllowIncoherentImpl(..)
+                    | AttributeKind::Confusables { .. }
+                    // `#[doc]` is actually a lot more than just doc comments, so is checked below
+                    | AttributeKind::DocComment {..}
+                    // handled below this loop and elsewhere
+                    | AttributeKind::Repr { .. }
+                    | AttributeKind::Cold(..)
+                    | AttributeKind::ExportName { .. }
+                    | AttributeKind::CoherenceIsCore
+                    | AttributeKind::Fundamental
+                    | AttributeKind::Optimize(..)
+                    | AttributeKind::LinkSection { .. }
+                    | AttributeKind::MacroUse { .. }
+                    | AttributeKind::MacroEscape( .. )
+                    | AttributeKind::RustcLayoutScalarValidRangeStart(..)
+                    | AttributeKind::RustcLayoutScalarValidRangeEnd(..)
+                    | AttributeKind::ExportStable
+                    | AttributeKind::FfiConst(..)
+                    | AttributeKind::UnstableFeatureBound(..)
+                    | AttributeKind::AsPtr(..)
+                    | AttributeKind::LinkName { .. }
+                    | AttributeKind::LinkOrdinal { .. }
+                    | AttributeKind::NoMangle(..)
+                    | AttributeKind::Used { .. }
+                    | AttributeKind::PassByValue (..)
+                    | AttributeKind::StdInternalSymbol (..)
+                    | AttributeKind::Coverage (..)
+                    | AttributeKind::ShouldPanic { .. }
+                    | AttributeKind::Coroutine(..)
+                    | AttributeKind::Linkage(..),
                 ) => { /* do nothing  */ }
-                Attribute::Parsed(AttributeKind::AsPtr(attr_span)) => {
-                    self.check_applied_to_fn_or_method(hir_id, *attr_span, span, target)
-                }
-                Attribute::Parsed(AttributeKind::LinkName { span: attr_span, name }) => {
-                    self.check_link_name(hir_id, *attr_span, *name, span, target)
-                }
-                Attribute::Parsed(AttributeKind::LinkOrdinal { span: attr_span, .. }) => {
-                    self.check_link_ordinal(*attr_span, span, target)
-                }
-                Attribute::Parsed(AttributeKind::MayDangle(attr_span)) => {
-                    self.check_may_dangle(hir_id, *attr_span)
-                }
-                Attribute::Parsed(AttributeKind::Ignore { span, .. }) => {
-                    self.check_generic_attr(hir_id, sym::ignore, *span, target, Target::Fn)
-                }
-                Attribute::Parsed(AttributeKind::MustUse { span, .. }) => {
-                    self.check_must_use(hir_id, *span, target)
-                }
-                Attribute::Parsed(AttributeKind::NoMangle(attr_span)) => {
-                    self.check_no_mangle(hir_id, *attr_span, span, target)
-                }
-                Attribute::Parsed(AttributeKind::Used { span: attr_span, .. }) => {
-                    self.check_used(*attr_span, target, span);
-                }
-                &Attribute::Parsed(AttributeKind::PassByValue(attr_span)) => {
-                    self.check_pass_by_value(attr_span, span, target)
-                }
-                &Attribute::Parsed(AttributeKind::StdInternalSymbol(attr_span)) => {
-                    self.check_rustc_std_internal_symbol(attr_span, span, target)
-                }
-                &Attribute::Parsed(AttributeKind::Coverage(attr_span, _)) => {
-                    self.check_coverage(attr_span, span, target)
-                }
-                &Attribute::Parsed(AttributeKind::Coroutine(attr_span)) => {
-                    self.check_coroutine(attr_span, target)
-                }
+
                 Attribute::Unparsed(attr_item) => {
                     style = Some(attr_item.style);
                     match attr.path().as_slice() {
@@ -382,18 +304,11 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                         [sym::rustc_has_incoherent_inherent_impls, ..] => {
                             self.check_has_incoherent_inherent_impls(attr, span, target)
                         }
-                        [sym::ffi_pure, ..] => self.check_ffi_pure(attr.span(), attrs, target),
-                        [sym::ffi_const, ..] => self.check_ffi_const(attr.span(), target),
                         [sym::link, ..] => self.check_link(hir_id, attr, span, target),
-                        [sym::path, ..] => self.check_generic_attr_unparsed(hir_id, attr, target, Target::Mod),
                         [sym::macro_export, ..] => self.check_macro_export(hir_id, attr, target),
-                        [sym::should_panic, ..] => {
-                            self.check_generic_attr_unparsed(hir_id, attr, target, Target::Fn)
-                        }
                         [sym::autodiff_forward, ..] | [sym::autodiff_reverse, ..] => {
                             self.check_autodiff(hir_id, attr, span, target)
                         }
-                        [sym::linkage, ..] => self.check_linkage(attr, span, target),
                         [
                             // ok
                             sym::allow
@@ -414,7 +329,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                             // internal
                             | sym::prelude_import
                             | sym::panic_handler
-                            | sym::allow_internal_unsafe
                             | sym::lang
                             | sym::needs_allocator
                             | sym::default_lib_allocator
@@ -482,7 +396,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
 
         self.check_repr(attrs, span, target, item, hir_id);
-        self.check_rustc_force_inline(hir_id, attrs, span, target);
+        self.check_rustc_force_inline(hir_id, attrs, target);
         self.check_mix_no_mangle_export(hir_id, attrs);
     }
 
@@ -495,15 +409,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         );
     }
 
-    fn inline_attr_str_error_without_macro_def(&self, hir_id: HirId, attr_span: Span, sym: &str) {
-        self.tcx.emit_node_span_lint(
-            UNUSED_ATTRIBUTES,
-            hir_id,
-            attr_span,
-            errors::IgnoredAttr { sym },
-        );
-    }
-
     /// Checks if `#[diagnostic::do_not_recommend]` is applied on a trait impl and that it has no
     /// arguments.
     fn check_do_not_recommend(
@@ -551,110 +456,29 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
     }
 
     /// Checks if an `#[inline]` is applied to a function or a closure.
-    fn check_inline(
-        &self,
-        hir_id: HirId,
-        attr_span: Span,
-        defn_span: Span,
-        kind: &InlineAttr,
-        target: Target,
-    ) {
+    fn check_inline(&self, hir_id: HirId, attr_span: Span, kind: &InlineAttr, target: Target) {
         match target {
             Target::Fn
             | Target::Closure
-            | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => {}
-            Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
-                self.tcx.emit_node_span_lint(
-                    UNUSED_ATTRIBUTES,
-                    hir_id,
-                    attr_span,
-                    errors::IgnoredInlineAttrFnProto,
-                )
-            }
-            // FIXME(#65833): We permit associated consts to have an `#[inline]` attribute with
-            // just a lint, because we previously erroneously allowed it and some crates used it
-            // accidentally, to be compatible with crates depending on them, we can't throw an
-            // error here.
-            Target::AssocConst => self.tcx.emit_node_span_lint(
-                UNUSED_ATTRIBUTES,
-                hir_id,
-                attr_span,
-                errors::IgnoredInlineAttrConstants,
-            ),
-            // FIXME(#80564): Same for fields, arms, and macro defs
-            Target::Field | Target::Arm | Target::MacroDef => {
-                self.inline_attr_str_error_with_macro_def(hir_id, attr_span, "inline")
-            }
-            _ => {
-                self.dcx().emit_err(errors::InlineNotFnOrClosure { attr_span, defn_span });
-            }
-        }
-
-        // `#[inline]` is ignored if the symbol must be codegened upstream because it's exported.
-        if let Some(did) = hir_id.as_owner()
-            && self.tcx.def_kind(did).has_codegen_attrs()
-            && kind != &InlineAttr::Never
-        {
-            let attrs = self.tcx.codegen_fn_attrs(did);
-            // Not checking naked as `#[inline]` is forbidden for naked functions anyways.
-            if attrs.contains_extern_indicator() {
-                self.tcx.emit_node_span_lint(
-                    UNUSED_ATTRIBUTES,
-                    hir_id,
-                    attr_span,
-                    errors::InlineIgnoredForExported {},
-                );
-            }
-        }
-    }
-
-    /// Checks that `#[coverage(..)]` is applied to a function/closure/method,
-    /// or to an impl block or module.
-    fn check_coverage(&self, attr_span: Span, target_span: Span, target: Target) {
-        let mut not_fn_impl_mod = None;
-        let mut no_body = None;
-
-        match target {
-            Target::Fn
-            | Target::Closure
-            | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent)
-            | Target::Impl { .. }
-            | Target::Mod => return,
-
-            // These are "functions", but they aren't allowed because they don't
-            // have a body, so the usual explanation would be confusing.
-            Target::Method(MethodKind::Trait { body: false }) | Target::ForeignFn => {
-                no_body = Some(target_span);
-            }
-
-            _ => {
-                not_fn_impl_mod = Some(target_span);
+            | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => {
+                // `#[inline]` is ignored if the symbol must be codegened upstream because it's exported.
+                if let Some(did) = hir_id.as_owner()
+                    && self.tcx.def_kind(did).has_codegen_attrs()
+                    && kind != &InlineAttr::Never
+                {
+                    let attrs = self.tcx.codegen_fn_attrs(did);
+                    // Not checking naked as `#[inline]` is forbidden for naked functions anyways.
+                    if attrs.contains_extern_indicator(self.tcx, did.into()) {
+                        self.tcx.emit_node_span_lint(
+                            UNUSED_ATTRIBUTES,
+                            hir_id,
+                            attr_span,
+                            errors::InlineIgnoredForExported {},
+                        );
+                    }
+                }
             }
-        }
-
-        self.dcx().emit_err(errors::CoverageAttributeNotAllowed {
-            attr_span,
-            not_fn_impl_mod,
-            no_body,
-            help: (),
-        });
-    }
-
-    /// Checks that `#[optimize(..)]` is applied to a function/closure/method,
-    /// or to an impl block or module.
-    fn check_optimize(&self, hir_id: HirId, attr_span: Span, span: Span, target: Target) {
-        let is_valid = matches!(
-            target,
-            Target::Fn
-                | Target::Closure
-                | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent)
-        );
-        if !is_valid {
-            self.dcx().emit_err(errors::OptimizeInvalidTarget {
-                attr_span,
-                defn_span: span,
-                on_crate: hir_id == CRATE_HIR_ID,
-            });
+            _ => {}
         }
     }
 
@@ -694,51 +518,8 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    /// FIXME: Remove when all attributes are ported to the new parser
-    fn check_generic_attr_unparsed(
-        &self,
-        hir_id: HirId,
-        attr: &Attribute,
-        target: Target,
-        allowed_target: Target,
-    ) {
-        if target != allowed_target {
-            let attr_name = join_path_syms(attr.path());
-            self.tcx.emit_node_span_lint(
-                UNUSED_ATTRIBUTES,
-                hir_id,
-                attr.span(),
-                errors::OnlyHasEffectOn {
-                    attr_name,
-                    target_name: allowed_target.name().replace(' ', "_"),
-                },
-            );
-        }
-    }
-
-    fn check_generic_attr(
-        &self,
-        hir_id: HirId,
-        attr_name: Symbol,
-        attr_span: Span,
-        target: Target,
-        allowed_target: Target,
-    ) {
-        if target != allowed_target {
-            self.tcx.emit_node_span_lint(
-                UNUSED_ATTRIBUTES,
-                hir_id,
-                attr_span,
-                errors::OnlyHasEffectOn {
-                    attr_name: attr_name.to_string(),
-                    target_name: allowed_target.name().replace(' ', "_"),
-                },
-            );
-        }
-    }
-
     /// Checks if `#[naked]` is applied to a function definition.
-    fn check_naked(&self, hir_id: HirId, attr_span: Span, span: Span, target: Target) {
+    fn check_naked(&self, hir_id: HirId, target: Target) {
         match target {
             Target::Fn
             | Target::Method(MethodKind::Trait { body: true } | MethodKind::Inherent) => {
@@ -757,13 +538,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     .emit();
                 }
             }
-            _ => {
-                self.dcx().emit_err(errors::AttrShouldBeAppliedToFn {
-                    attr_span,
-                    defn_span: span,
-                    on_crate: hir_id == CRATE_HIR_ID,
-                });
-            }
+            _ => {}
         }
     }
 
@@ -806,7 +581,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         hir_id: HirId,
         attr_span: Span,
         attrs: &[Attribute],
-        span: Span,
         target: Target,
     ) {
         match target {
@@ -826,28 +600,13 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     });
                 }
             }
-            Target::Method(..) | Target::ForeignFn | Target::Closure => {}
-            // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
-            // `#[track_caller]` attribute with just a lint, because we previously
-            // erroneously allowed it and some crates used it accidentally, to be compatible
-            // with crates depending on them, we can't throw an error here.
-            Target::Field | Target::Arm | Target::MacroDef => {
-                self.inline_attr_str_error_with_macro_def(hir_id, attr_span, "track_caller");
-            }
-            _ => {
-                self.dcx().emit_err(errors::TrackedCallerWrongLocation {
-                    attr_span,
-                    defn_span: span,
-                    on_crate: hir_id == CRATE_HIR_ID,
-                });
-            }
+            _ => {}
         }
     }
 
     /// Checks if the `#[non_exhaustive]` attribute on an `item` is valid.
     fn check_non_exhaustive(
         &self,
-        hir_id: HirId,
         attr_span: Span,
         span: Span,
         target: Target,
@@ -868,36 +627,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     });
                 }
             }
-            Target::Enum | Target::Variant => {}
-            // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
-            // `#[non_exhaustive]` attribute with just a lint, because we previously
-            // erroneously allowed it and some crates used it accidentally, to be compatible
-            // with crates depending on them, we can't throw an error here.
-            Target::Field | Target::Arm | Target::MacroDef => {
-                self.inline_attr_str_error_with_macro_def(hir_id, attr_span, "non_exhaustive");
-            }
-            _ => {
-                self.dcx()
-                    .emit_err(errors::NonExhaustiveWrongLocation { attr_span, defn_span: span });
-            }
-        }
-    }
-
-    /// Checks if the `#[marker]` attribute on an `item` is valid.
-    fn check_marker(&self, hir_id: HirId, attr_span: Span, span: Span, target: Target) {
-        match target {
-            Target::Trait => {}
-            // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
-            // `#[marker]` attribute with just a lint, because we previously
-            // erroneously allowed it and some crates used it accidentally, to be compatible
-            // with crates depending on them, we can't throw an error here.
-            Target::Field | Target::Arm | Target::MacroDef => {
-                self.inline_attr_str_error_with_macro_def(hir_id, attr_span, "marker");
-            }
-            _ => {
-                self.dcx()
-                    .emit_err(errors::AttrShouldBeAppliedToTrait { attr_span, defn_span: span });
-            }
+            _ => {}
         }
     }
 
@@ -906,7 +636,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         &self,
         hir_id: HirId,
         attr_span: Span,
-        span: Span,
         target: Target,
         attrs: &[Attribute],
     ) {
@@ -929,30 +658,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     });
                 }
             }
-            // FIXME: #[target_feature] was previously erroneously allowed on statements and some
-            // crates used this, so only emit a warning.
-            Target::Statement => {
-                self.tcx.emit_node_span_lint(
-                    UNUSED_ATTRIBUTES,
-                    hir_id,
-                    attr_span,
-                    errors::TargetFeatureOnStatement,
-                );
-            }
-            // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
-            // `#[target_feature]` attribute with just a lint, because we previously
-            // erroneously allowed it and some crates used it accidentally, to be compatible
-            // with crates depending on them, we can't throw an error here.
-            Target::Field | Target::Arm | Target::MacroDef => {
-                self.inline_attr_str_error_with_macro_def(hir_id, attr_span, "target_feature");
-            }
-            _ => {
-                self.dcx().emit_err(errors::AttrShouldBeAppliedToFn {
-                    attr_span,
-                    defn_span: span,
-                    on_crate: hir_id == CRATE_HIR_ID,
-                });
-            }
+            _ => {}
         }
     }
 
@@ -1056,7 +762,10 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             | Target::GenericParam { .. }
             | Target::MacroDef
             | Target::PatField
-            | Target::ExprField => None,
+            | Target::ExprField
+            | Target::Crate
+            | Target::MacroCall
+            | Target::Delegation { .. } => None,
         } {
             tcx.dcx().emit_err(errors::DocAliasBadLocation { span, attr_str, location });
             return;
@@ -1156,8 +865,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 let is_valid = doc_fake_variadic_is_allowed_self_ty(i.self_ty)
                     || if let Some(&[hir::GenericArg::Type(ty)]) = i
                         .of_trait
-                        .as_ref()
-                        .and_then(|trait_ref| trait_ref.path.segments.last())
+                        .and_then(|of_trait| of_trait.trait_ref.path.segments.last())
                         .map(|last_segment| last_segment.args().args)
                     {
                         matches!(&ty.kind, hir::TyKind::Tup([_]))
@@ -1533,25 +1241,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    /// Warns against some misuses of `#[pass_by_value]`
-    fn check_pass_by_value(&self, attr_span: Span, span: Span, target: Target) {
-        match target {
-            Target::Struct | Target::Enum | Target::TyAlias => {}
-            _ => {
-                self.dcx().emit_err(errors::PassByValue { attr_span, span });
-            }
-        }
-    }
-
-    fn check_allow_incoherent_impl(&self, attr_span: Span, span: Span, target: Target) {
-        match target {
-            Target::Method(MethodKind::Inherent) => {}
-            _ => {
-                self.dcx().emit_err(errors::AllowIncoherentImpl { attr_span, span });
-            }
-        }
-    }
-
     fn check_has_incoherent_inherent_impls(&self, attr: &Attribute, span: Span, target: Target) {
         match target {
             Target::Trait | Target::Struct | Target::Enum | Target::Union | Target::ForeignTy => {}
@@ -1563,23 +1252,13 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    fn check_ffi_pure(&self, attr_span: Span, attrs: &[Attribute], target: Target) {
-        if target != Target::ForeignFn {
-            self.dcx().emit_err(errors::FfiPureInvalidTarget { attr_span });
-            return;
-        }
+    fn check_ffi_pure(&self, attr_span: Span, attrs: &[Attribute]) {
         if find_attr!(attrs, AttributeKind::FfiConst(_)) {
             // `#[ffi_const]` functions cannot be `#[ffi_pure]`
             self.dcx().emit_err(errors::BothFfiConstAndPure { attr_span });
         }
     }
 
-    fn check_ffi_const(&self, attr_span: Span, target: Target) {
-        if target != Target::ForeignFn {
-            self.dcx().emit_err(errors::FfiConstInvalidTarget { attr_span });
-        }
-    }
-
     /// Warns against some misuses of `#[must_use]`
     fn check_must_use(&self, hir_id: HirId, attr_span: Span, target: Target) {
         if matches!(
@@ -1607,22 +1286,11 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             return;
         }
 
-        let article = match target {
-            Target::ExternCrate
-            | Target::Enum
-            | Target::Impl { .. }
-            | Target::Expression
-            | Target::Arm
-            | Target::AssocConst
-            | Target::AssocTy => "an",
-            _ => "a",
-        };
-
         self.tcx.emit_node_span_lint(
             UNUSED_ATTRIBUTES,
             hir_id,
             attr_span,
-            errors::MustUseNoEffect { article, target },
+            errors::MustUseNoEffect { target: target.plural_name(), attr_span },
         );
     }
 
@@ -1647,8 +1315,8 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             && let parent_hir_id = self.tcx.parent_hir_id(hir_id)
             && let hir::Node::Item(item) = self.tcx.hir_node(parent_hir_id)
             && let hir::ItemKind::Impl(impl_) = item.kind
-            && let Some(trait_) = impl_.of_trait
-            && let Some(def_id) = trait_.trait_def_id()
+            && let Some(of_trait) = impl_.of_trait
+            && let Some(def_id) = of_trait.trait_ref.trait_def_id()
             && self.tcx.is_lang_item(def_id, hir::LangItem::Drop)
         {
             return;
@@ -1657,30 +1325,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         self.dcx().emit_err(errors::InvalidMayDangle { attr_span });
     }
 
-    /// Checks if `#[cold]` is applied to a non-function.
-    fn check_cold(&self, hir_id: HirId, attr_span: Span, span: Span, target: Target) {
-        match target {
-            Target::Fn | Target::Method(..) | Target::ForeignFn | Target::Closure => {}
-            // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
-            // `#[cold]` attribute with just a lint, because we previously
-            // erroneously allowed it and some crates used it accidentally, to be compatible
-            // with crates depending on them, we can't throw an error here.
-            Target::Field | Target::Arm | Target::MacroDef => {
-                self.inline_attr_str_error_with_macro_def(hir_id, attr_span, "cold");
-            }
-            _ => {
-                // FIXME: #[cold] was previously allowed on non-functions and some crates used
-                // this, so only emit a warning.
-                self.tcx.emit_node_span_lint(
-                    UNUSED_ATTRIBUTES,
-                    hir_id,
-                    attr_span,
-                    errors::Cold { span, on_crate: hir_id == CRATE_HIR_ID },
-                );
-            }
-        }
-    }
-
     /// Checks if `#[link]` is applied to an item other than a foreign module.
     fn check_link(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) {
         if target == Target::ForeignMod
@@ -1699,38 +1343,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         );
     }
 
-    /// Checks if `#[link_name]` is applied to an item other than a foreign function or static.
-    fn check_link_name(
-        &self,
-        hir_id: HirId,
-        attr_span: Span,
-        name: Symbol,
-        span: Span,
-        target: Target,
-    ) {
-        match target {
-            Target::ForeignFn | Target::ForeignStatic => {}
-            // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
-            // `#[link_name]` attribute with just a lint, because we previously
-            // erroneously allowed it and some crates used it accidentally, to be compatible
-            // with crates depending on them, we can't throw an error here.
-            Target::Field | Target::Arm | Target::MacroDef => {
-                self.inline_attr_str_error_with_macro_def(hir_id, attr_span, "link_name");
-            }
-            _ => {
-                // FIXME: #[link_name] was previously allowed on non-functions/statics and some crates
-                // used this, so only emit a warning.
-                let help_span = matches!(target, Target::ForeignMod).then_some(attr_span);
-                self.tcx.emit_node_span_lint(
-                    UNUSED_ATTRIBUTES,
-                    hir_id,
-                    attr_span,
-                    errors::LinkName { span, help_span, value: name.as_str() },
-                );
-            }
-        }
-    }
-
     /// Checks if `#[no_link]` is applied to an `extern crate`.
     fn check_no_link(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) {
         match target {
@@ -1748,35 +1360,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    fn is_impl_item(&self, hir_id: HirId) -> bool {
-        matches!(self.tcx.hir_node(hir_id), hir::Node::ImplItem(..))
-    }
-
-    /// Checks if `#[export_name]` is applied to a function or static.
-    fn check_export_name(&self, hir_id: HirId, attr_span: Span, span: Span, target: Target) {
-        match target {
-            Target::Static | Target::Fn => {}
-            Target::Method(..) if self.is_impl_item(hir_id) => {}
-            // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
-            // `#[export_name]` attribute with just a lint, because we previously
-            // erroneously allowed it and some crates used it accidentally, to be compatible
-            // with crates depending on them, we can't throw an error here.
-            Target::Field | Target::Arm | Target::MacroDef => {
-                self.inline_attr_str_error_with_macro_def(hir_id, attr_span, "export_name");
-            }
-            _ => {
-                self.dcx().emit_err(errors::ExportName { attr_span, span });
-            }
-        }
-    }
-
-    fn check_rustc_layout_scalar_valid_range(&self, attr_span: Span, span: Span, target: Target) {
-        if target != Target::Struct {
-            self.dcx().emit_err(errors::RustcLayoutScalarValidRangeNotStruct { attr_span, span });
-            return;
-        }
-    }
-
     /// Checks if `#[rustc_legacy_const_generics]` is applied to a function and has a valid argument.
     fn check_rustc_legacy_const_generics(
         &self,
@@ -1911,106 +1494,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    /// Checks if `#[link_section]` is applied to a function or static.
-    fn check_link_section(&self, hir_id: HirId, attr_span: Span, span: Span, target: Target) {
-        match target {
-            Target::Static | Target::Fn | Target::Method(..) => {}
-            // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
-            // `#[link_section]` attribute with just a lint, because we previously
-            // erroneously allowed it and some crates used it accidentally, to be compatible
-            // with crates depending on them, we can't throw an error here.
-            Target::Field | Target::Arm | Target::MacroDef => {
-                self.inline_attr_str_error_with_macro_def(hir_id, attr_span, "link_section");
-            }
-            _ => {
-                // FIXME: #[link_section] was previously allowed on non-functions/statics and some
-                // crates used this, so only emit a warning.
-                self.tcx.emit_node_span_lint(
-                    UNUSED_ATTRIBUTES,
-                    hir_id,
-                    attr_span,
-                    errors::LinkSection { span },
-                );
-            }
-        }
-    }
-
-    /// Checks if `#[no_mangle]` is applied to a function or static.
-    fn check_no_mangle(&self, hir_id: HirId, attr_span: Span, span: Span, target: Target) {
-        match target {
-            Target::Static | Target::Fn => {}
-            Target::Method(..) if self.is_impl_item(hir_id) => {}
-            // FIXME(#80564): We permit struct fields, match arms and macro defs to have an
-            // `#[no_mangle]` attribute with just a lint, because we previously
-            // erroneously allowed it and some crates used it accidentally, to be compatible
-            // with crates depending on them, we can't throw an error here.
-            Target::Field | Target::Arm | Target::MacroDef => {
-                self.inline_attr_str_error_with_macro_def(hir_id, attr_span, "no_mangle");
-            }
-            // FIXME: #[no_mangle] was previously allowed on non-functions/statics, this should be an error
-            // The error should specify that the item that is wrong is specifically a *foreign* fn/static
-            // otherwise the error seems odd
-            Target::ForeignFn | Target::ForeignStatic => {
-                let foreign_item_kind = match target {
-                    Target::ForeignFn => "function",
-                    Target::ForeignStatic => "static",
-                    _ => unreachable!(),
-                };
-                self.tcx.emit_node_span_lint(
-                    UNUSED_ATTRIBUTES,
-                    hir_id,
-                    attr_span,
-                    errors::NoMangleForeign { span, attr_span, foreign_item_kind },
-                );
-            }
-            _ => {
-                // FIXME: #[no_mangle] was previously allowed on non-functions/statics and some
-                // crates used this, so only emit a warning.
-                self.tcx.emit_node_span_lint(
-                    UNUSED_ATTRIBUTES,
-                    hir_id,
-                    attr_span,
-                    errors::NoMangle { span },
-                );
-            }
-        }
-    }
-
-    /// Checks if the `#[align]` attributes on `item` are valid.
-    // FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
-    fn check_align(
-        &self,
-        span: Span,
-        hir_id: HirId,
-        target: Target,
-        align: Align,
-        attr_span: Span,
-    ) {
-        match target {
-            Target::Fn | Target::Method(_) | Target::ForeignFn => {}
-            Target::Field => {
-                self.tcx.emit_node_span_lint(
-                    UNUSED_ATTRIBUTES,
-                    hir_id,
-                    attr_span,
-                    AlignOnFields { span },
-                );
-            }
-            Target::Struct | Target::Union | Target::Enum => {
-                self.dcx().emit_err(errors::AlignShouldBeReprAlign {
-                    span: attr_span,
-                    item: target.name(),
-                    align_bytes: align.bytes(),
-                });
-            }
-            _ => {
-                self.dcx().emit_err(errors::AlignAttrApplication { hint_span: attr_span, span });
-            }
-        }
-
-        self.check_align_value(align, attr_span);
-    }
-
     /// Checks if the `#[repr]` attributes on `item` are valid.
     fn check_repr(
         &self,
@@ -2065,7 +1548,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                         Target::Fn | Target::Method(_) => {
                             self.dcx().emit_err(errors::ReprAlignShouldBeAlign {
                                 span: *repr_span,
-                                item: target.name(),
+                                item: target.plural_name(),
                             });
                         }
                         _ => {
@@ -2076,7 +1559,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                         }
                     }
 
-                    self.check_align_value(*align, *repr_span);
+                    self.check_align(*align, *repr_span);
                 }
                 ReprAttr::ReprPacked(_) => {
                     if target != Target::Struct && target != Target::Union {
@@ -2135,7 +1618,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 Target::Fn | Target::Method(_) => {
                     self.dcx().emit_err(errors::ReprAlignShouldBeAlign {
                         span: first_attr_span,
-                        item: target.name(),
+                        item: target.plural_name(),
                     });
                 }
                 _ => {
@@ -2182,7 +1665,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    fn check_align_value(&self, align: Align, span: Span) {
+    fn check_align(&self, align: Align, span: Span) {
         if align.bytes() > 2_u64.pow(29) {
             // for values greater than 2^29, a different error will be emitted, make sure that happens
             self.dcx().span_delayed_bug(
@@ -2201,22 +1684,12 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    fn check_used(&self, attr_span: Span, target: Target, target_span: Span) {
-        if target != Target::Static {
-            self.dcx().emit_err(errors::UsedStatic {
-                attr_span,
-                span: target_span,
-                target: target.name(),
-            });
-        }
-    }
-
-    /// Outputs an error for `#[allow_internal_unstable]` which can only be applied to macros.
+    /// Outputs an error for attributes that can only be applied to macros, such as
+    /// `#[allow_internal_unsafe]` and `#[allow_internal_unstable]`.
     /// (Allows proc_macro functions)
     // FIXME(jdonszelmann): if possible, move to attr parsing
-    fn check_allow_internal_unstable(
+    fn check_macro_only_attr(
         &self,
-        hir_id: HirId,
         attr_span: Span,
         span: Span,
         target: Target,
@@ -2230,27 +1703,10 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                         return;
                     }
                 }
-                // continue out of the match
-            }
-            // return on decl macros
-            Target::MacroDef => return,
-            // FIXME(#80564): We permit struct fields and match arms to have an
-            // `#[allow_internal_unstable]` attribute with just a lint, because we previously
-            // erroneously allowed it and some crates used it accidentally, to be compatible
-            // with crates depending on them, we can't throw an error here.
-            Target::Field | Target::Arm => {
-                self.inline_attr_str_error_without_macro_def(
-                    hir_id,
-                    attr_span,
-                    "allow_internal_unstable",
-                );
-                return;
+                self.tcx.dcx().emit_err(errors::MacroOnlyAttribute { attr_span, span });
             }
-            // otherwise continue out of the match
             _ => {}
         }
-
-        self.tcx.dcx().emit_err(errors::AllowInternalUnstable { attr_span, span });
     }
 
     /// Checks if the items on the `#[debugger_visualizer]` attribute are valid.
@@ -2277,67 +1733,12 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         target: Target,
     ) {
         match target {
-            Target::Fn | Target::Method(_)
-                if self.tcx.is_const_fn(hir_id.expect_owner().to_def_id()) => {}
-            // FIXME(#80564): We permit struct fields and match arms to have an
-            // `#[allow_internal_unstable]` attribute with just a lint, because we previously
-            // erroneously allowed it and some crates used it accidentally, to be compatible
-            // with crates depending on them, we can't throw an error here.
-            Target::Field | Target::Arm | Target::MacroDef => self
-                .inline_attr_str_error_with_macro_def(hir_id, attr_span, "allow_internal_unstable"),
-            _ => {
-                self.tcx.dcx().emit_err(errors::RustcAllowConstFnUnstable { attr_span, span });
-            }
-        }
-    }
-
-    fn check_unstable_feature_bound(&self, attr_span: Span, span: Span, target: Target) {
-        match target {
-            // FIXME(staged_api): There's no reason we can't support more targets here. We're just
-            // being conservative to begin with.
-            Target::Fn | Target::Impl { .. } => {}
-            Target::ExternCrate
-            | Target::Use
-            | Target::Static
-            | Target::Const
-            | Target::Closure
-            | Target::Mod
-            | Target::ForeignMod
-            | Target::GlobalAsm
-            | Target::TyAlias
-            | Target::Enum
-            | Target::Variant
-            | Target::Struct
-            | Target::Field
-            | Target::Union
-            | Target::Trait
-            | Target::TraitAlias
-            | Target::Expression
-            | Target::Statement
-            | Target::Arm
-            | Target::AssocConst
-            | Target::Method(_)
-            | Target::AssocTy
-            | Target::ForeignFn
-            | Target::ForeignStatic
-            | Target::ForeignTy
-            | Target::GenericParam { .. }
-            | Target::MacroDef
-            | Target::Param
-            | Target::PatField
-            | Target::ExprField
-            | Target::WherePredicate => {
-                self.tcx.dcx().emit_err(errors::RustcUnstableFeatureBound { attr_span, span });
-            }
-        }
-    }
-
-    fn check_rustc_std_internal_symbol(&self, attr_span: Span, span: Span, target: Target) {
-        match target {
-            Target::Fn | Target::Static | Target::ForeignFn | Target::ForeignStatic => {}
-            _ => {
-                self.tcx.dcx().emit_err(errors::RustcStdInternalSymbol { attr_span, span });
+            Target::Fn | Target::Method(_) => {
+                if !self.tcx.is_const_fn(hir_id.expect_owner().to_def_id()) {
+                    self.tcx.dcx().emit_err(errors::RustcAllowConstFnUnstable { attr_span, span });
+                }
             }
+            _ => {}
         }
     }
 
@@ -2347,15 +1748,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         item_span: Span,
         level: &StabilityLevel,
         feature: Symbol,
-        target: Target,
     ) {
-        match target {
-            Target::Expression => {
-                self.dcx().emit_err(errors::StabilityPromotable { attr_span });
-            }
-            _ => {}
-        }
-
         // Stable *language* features shouldn't be used as unstable library features.
         // (Not doing this for stable library features is checked by tidy.)
         if level.is_unstable()
@@ -2367,40 +1760,8 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    fn check_link_ordinal(&self, attr_span: Span, _span: Span, target: Target) {
-        match target {
-            Target::ForeignFn | Target::ForeignStatic => {}
-            _ => {
-                self.dcx().emit_err(errors::LinkOrdinal { attr_span });
-            }
-        }
-    }
-
-    fn check_confusables(&self, span: Span, target: Target) {
-        if !matches!(target, Target::Method(MethodKind::Inherent)) {
-            self.dcx().emit_err(errors::Confusables { attr_span: span });
-        }
-    }
-
     fn check_deprecated(&self, hir_id: HirId, attr: &Attribute, _span: Span, target: Target) {
         match target {
-            Target::Closure | Target::Expression | Target::Statement | Target::Arm => {
-                self.tcx.emit_node_span_lint(
-                    UNUSED_ATTRIBUTES,
-                    hir_id,
-                    attr.span(),
-                    errors::Deprecated,
-                );
-            }
-            Target::Impl { of_trait: true }
-            | Target::GenericParam { has_default: false, kind: _ } => {
-                self.tcx.emit_node_span_lint(
-                    USELESS_DEPRECATED,
-                    hir_id,
-                    attr.span(),
-                    errors::DeprecatedAnnotationHasNoEffect { span: attr.span() },
-                );
-            }
             Target::AssocConst | Target::Method(..) | Target::AssocTy
                 if matches!(
                     self.tcx.def_kind(self.tcx.local_parent(hir_id.owner.def_id)),
@@ -2408,7 +1769,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 ) =>
             {
                 self.tcx.emit_node_span_lint(
-                    USELESS_DEPRECATED,
+                    UNUSED_ATTRIBUTES,
                     hir_id,
                     attr.span(),
                     errors::DeprecatedAnnotationHasNoEffect { span: attr.span() },
@@ -2418,20 +1779,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    fn check_macro_use(&self, hir_id: HirId, name: Symbol, attr_span: Span, target: Target) {
-        match target {
-            Target::ExternCrate | Target::Mod => {}
-            _ => {
-                self.tcx.emit_node_span_lint(
-                    UNUSED_ATTRIBUTES,
-                    hir_id,
-                    attr_span,
-                    errors::MacroUse { name },
-                );
-            }
-        }
-    }
-
     fn check_macro_export(&self, hir_id: HirId, attr: &Attribute, target: Target) {
         if target != Target::MacroDef {
             self.tcx.emit_node_span_lint(
@@ -2651,15 +1998,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    fn check_coroutine(&self, attr_span: Span, target: Target) {
-        match target {
-            Target::Closure => return,
-            _ => {
-                self.dcx().emit_err(errors::CoroutineOnNonClosure { span: attr_span });
-            }
-        }
-    }
-
     fn check_type_const(&self, hir_id: HirId, attr_span: Span, target: Target) {
         let tcx = self.tcx;
         if target == Target::AssocConst
@@ -2677,19 +2015,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    fn check_linkage(&self, attr: &Attribute, span: Span, target: Target) {
-        match target {
-            Target::Fn
-            | Target::Method(..)
-            | Target::Static
-            | Target::ForeignStatic
-            | Target::ForeignFn => {}
-            _ => {
-                self.dcx().emit_err(errors::Linkage { attr_span: attr.span(), span });
-            }
-        }
-    }
-
     fn check_rustc_pub_transparent(&self, attr_span: Span, span: Span, attrs: &[Attribute]) {
         if !find_attr!(attrs, AttributeKind::Repr { reprs, .. } => reprs.iter().any(|(r, _)| r == &ReprAttr::ReprTransparent))
             .unwrap_or(false)
@@ -2698,43 +2023,28 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    fn check_rustc_force_inline(
-        &self,
-        hir_id: HirId,
-        attrs: &[Attribute],
-        span: Span,
-        target: Target,
-    ) {
-        match (
+    fn check_rustc_force_inline(&self, hir_id: HirId, attrs: &[Attribute], target: Target) {
+        if let (Target::Closure, None) = (
             target,
             find_attr!(attrs, AttributeKind::Inline(InlineAttr::Force { attr_span, .. }, _) => *attr_span),
         ) {
-            (Target::Closure, None) => {
-                let is_coro = matches!(
-                    self.tcx.hir_expect_expr(hir_id).kind,
-                    hir::ExprKind::Closure(hir::Closure {
-                        kind: hir::ClosureKind::Coroutine(..)
-                            | hir::ClosureKind::CoroutineClosure(..),
-                        ..
-                    })
-                );
-                let parent_did = self.tcx.hir_get_parent_item(hir_id).to_def_id();
-                let parent_span = self.tcx.def_span(parent_did);
+            let is_coro = matches!(
+                self.tcx.hir_expect_expr(hir_id).kind,
+                hir::ExprKind::Closure(hir::Closure {
+                    kind: hir::ClosureKind::Coroutine(..) | hir::ClosureKind::CoroutineClosure(..),
+                    ..
+                })
+            );
+            let parent_did = self.tcx.hir_get_parent_item(hir_id).to_def_id();
+            let parent_span = self.tcx.def_span(parent_did);
 
-                if let Some(attr_span) = find_attr!(
-                    self.tcx.get_all_attrs(parent_did),
-                    AttributeKind::Inline(InlineAttr::Force { attr_span, .. }, _) => *attr_span
-                ) && is_coro
-                {
-                    self.dcx()
-                        .emit_err(errors::RustcForceInlineCoro { attr_span, span: parent_span });
-                }
-            }
-            (Target::Fn, _) => (),
-            (_, Some(attr_span)) => {
-                self.dcx().emit_err(errors::RustcForceInline { attr_span, span });
+            if let Some(attr_span) = find_attr!(
+                self.tcx.get_all_attrs(parent_did),
+                AttributeKind::Inline(InlineAttr::Force { attr_span, .. }, _) => *attr_span
+            ) && is_coro
+            {
+                self.dcx().emit_err(errors::RustcForceInlineCoro { attr_span, span: parent_span });
             }
-            (_, None) => (),
         }
     }
 
@@ -2784,8 +2094,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         let node_span = self.tcx.hir_span(hir_id);
 
         if !matches!(target, Target::Expression) {
-            self.dcx().emit_err(errors::LoopMatchAttr { attr_span, node_span });
-            return;
+            return; // Handled in target checking during attr parse
         }
 
         if !matches!(self.tcx.hir_expect_expr(hir_id).kind, hir::ExprKind::Loop(..)) {
@@ -2797,8 +2106,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         let node_span = self.tcx.hir_span(hir_id);
 
         if !matches!(target, Target::Expression) {
-            self.dcx().emit_err(errors::ConstContinueAttr { attr_span, node_span });
-            return;
+            return; // Handled in target checking during attr parse
         }
 
         if !matches!(self.tcx.hir_expect_expr(hir_id).kind, hir::ExprKind::Break(..)) {
@@ -2841,6 +2149,7 @@ impl<'tcx> Visitor<'tcx> for CheckAttrVisitor<'tcx> {
             .hir_attrs(where_predicate.hir_id)
             .iter()
             .filter(|attr| !ATTRS_ALLOWED.iter().any(|&sym| attr.has_name(sym)))
+            .filter(|attr| !attr.is_parsed_attr())
             .map(|attr| attr.span())
             .collect::<Vec<_>>();
         if !spans.is_empty() {
@@ -2971,10 +2280,6 @@ fn check_invalid_crate_level_attr(tcx: TyCtxt<'_>, attrs: &[Attribute]) {
         }) = attr
         {
             (*first_attr_span, sym::repr)
-        } else if let Attribute::Parsed(AttributeKind::Path(.., span)) = attr {
-            (*span, sym::path)
-        } else if let Attribute::Parsed(AttributeKind::AutomaticallyDerived(span)) = attr {
-            (*span, sym::automatically_derived)
         } else {
             continue;
         };
diff --git a/compiler/rustc_passes/src/dead.rs b/compiler/rustc_passes/src/dead.rs
index fa9d0c7b1b7..08d06402000 100644
--- a/compiler/rustc_passes/src/dead.rs
+++ b/compiler/rustc_passes/src/dead.rs
@@ -172,7 +172,6 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
         }
     }
 
-    #[allow(dead_code)] // FIXME(81658): should be used + lint reinstated after #83171 relands.
     fn handle_assign(&mut self, expr: &'tcx hir::Expr<'tcx>) {
         if self
             .typeck_results()
@@ -189,7 +188,6 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
         }
     }
 
-    #[allow(dead_code)] // FIXME(81658): should be used + lint reinstated after #83171 relands.
     fn check_for_self_assign(&mut self, assign: &'tcx hir::Expr<'tcx>) {
         fn check_for_self_assign_helper<'tcx>(
             typeck_results: &'tcx ty::TypeckResults<'tcx>,
@@ -373,7 +371,7 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
     /// will be ignored for the purposes of dead code analysis (see PR #85200
     /// for discussion).
     fn should_ignore_item(&mut self, def_id: DefId) -> bool {
-        if let Some(impl_of) = self.tcx.impl_of_assoc(def_id) {
+        if let Some(impl_of) = self.tcx.trait_impl_of_assoc(def_id) {
             if !self.tcx.is_automatically_derived(impl_of) {
                 return false;
             }
@@ -576,6 +574,10 @@ impl<'tcx> Visitor<'tcx> for MarkSymbolVisitor<'tcx> {
             hir::ExprKind::OffsetOf(..) => {
                 self.handle_offset_of(expr);
             }
+            hir::ExprKind::Assign(ref lhs, ..) => {
+                self.handle_assign(lhs);
+                self.check_for_self_assign(expr);
+            }
             _ => (),
         }
 
@@ -701,7 +703,7 @@ fn has_allow_dead_code_or_lang_attr(
 
             // #[used], #[no_mangle], #[export_name], etc also keeps the item alive
             // forcefully, e.g., for placing it in a specific section.
-            cg_attrs.contains_extern_indicator()
+            cg_attrs.contains_extern_indicator(tcx, def_id.into())
                 || cg_attrs.flags.contains(CodegenFnAttrFlags::USED_COMPILER)
                 || cg_attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER)
         }
diff --git a/compiler/rustc_passes/src/errors.rs b/compiler/rustc_passes/src/errors.rs
index c6ab6b0d601..c5d5155d0e5 100644
--- a/compiler/rustc_passes/src/errors.rs
+++ b/compiler/rustc_passes/src/errors.rs
@@ -75,58 +75,6 @@ pub(crate) struct IgnoredAttrWithMacro<'a> {
     pub sym: &'a str,
 }
 
-#[derive(LintDiagnostic)]
-#[diag(passes_ignored_attr)]
-pub(crate) struct IgnoredAttr<'a> {
-    pub sym: &'a str,
-}
-
-#[derive(LintDiagnostic)]
-#[diag(passes_inline_ignored_function_prototype)]
-pub(crate) struct IgnoredInlineAttrFnProto;
-
-#[derive(LintDiagnostic)]
-#[diag(passes_inline_ignored_constants)]
-#[warning]
-#[note]
-pub(crate) struct IgnoredInlineAttrConstants;
-
-#[derive(Diagnostic)]
-#[diag(passes_inline_not_fn_or_closure, code = E0518)]
-pub(crate) struct InlineNotFnOrClosure {
-    #[primary_span]
-    pub attr_span: Span,
-    #[label]
-    pub defn_span: Span,
-}
-
-/// "coverage attribute not allowed here"
-#[derive(Diagnostic)]
-#[diag(passes_coverage_attribute_not_allowed, code = E0788)]
-pub(crate) struct CoverageAttributeNotAllowed {
-    #[primary_span]
-    pub attr_span: Span,
-    /// "not a function, impl block, or module"
-    #[label(passes_not_fn_impl_mod)]
-    pub not_fn_impl_mod: Option<Span>,
-    /// "function has no body"
-    #[label(passes_no_body)]
-    pub no_body: Option<Span>,
-    /// "coverage attribute can be applied to a function (with body), impl block, or module"
-    #[help]
-    pub help: (),
-}
-
-#[derive(Diagnostic)]
-#[diag(passes_optimize_invalid_target)]
-pub(crate) struct OptimizeInvalidTarget {
-    #[primary_span]
-    pub attr_span: Span,
-    #[label]
-    pub defn_span: Span,
-    pub on_crate: bool,
-}
-
 #[derive(Diagnostic)]
 #[diag(passes_should_be_applied_to_fn)]
 pub(crate) struct AttrShouldBeAppliedToFn {
@@ -138,25 +86,6 @@ pub(crate) struct AttrShouldBeAppliedToFn {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_should_be_applied_to_fn, code = E0739)]
-pub(crate) struct TrackedCallerWrongLocation {
-    #[primary_span]
-    pub attr_span: Span,
-    #[label]
-    pub defn_span: Span,
-    pub on_crate: bool,
-}
-
-#[derive(Diagnostic)]
-#[diag(passes_should_be_applied_to_struct_enum, code = E0701)]
-pub(crate) struct NonExhaustiveWrongLocation {
-    #[primary_span]
-    pub attr_span: Span,
-    #[label]
-    pub defn_span: Span,
-}
-
-#[derive(Diagnostic)]
 #[diag(passes_non_exhaustive_with_default_field_values)]
 pub(crate) struct NonExhaustiveWithDefaultFieldValues {
     #[primary_span]
@@ -174,10 +103,6 @@ pub(crate) struct AttrShouldBeAppliedToTrait {
     pub defn_span: Span,
 }
 
-#[derive(LintDiagnostic)]
-#[diag(passes_target_feature_on_statement)]
-pub(crate) struct TargetFeatureOnStatement;
-
 #[derive(Diagnostic)]
 #[diag(passes_should_be_applied_to_static)]
 pub(crate) struct AttrShouldBeAppliedToStatic {
@@ -417,24 +342,6 @@ pub(crate) struct DocTestUnknownInclude {
 pub(crate) struct DocInvalid;
 
 #[derive(Diagnostic)]
-#[diag(passes_pass_by_value)]
-pub(crate) struct PassByValue {
-    #[primary_span]
-    pub attr_span: Span,
-    #[label]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(passes_allow_incoherent_impl)]
-pub(crate) struct AllowIncoherentImpl {
-    #[primary_span]
-    pub attr_span: Span,
-    #[label]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
 #[diag(passes_has_incoherent_inherent_impl)]
 pub(crate) struct HasIncoherentInherentImpl {
     #[primary_span]
@@ -450,25 +357,12 @@ pub(crate) struct BothFfiConstAndPure {
     pub attr_span: Span,
 }
 
-#[derive(Diagnostic)]
-#[diag(passes_ffi_pure_invalid_target, code = E0755)]
-pub(crate) struct FfiPureInvalidTarget {
-    #[primary_span]
-    pub attr_span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(passes_ffi_const_invalid_target, code = E0756)]
-pub(crate) struct FfiConstInvalidTarget {
-    #[primary_span]
-    pub attr_span: Span,
-}
-
 #[derive(LintDiagnostic)]
 #[diag(passes_must_use_no_effect)]
 pub(crate) struct MustUseNoEffect {
-    pub article: &'static str,
-    pub target: rustc_hir::Target,
+    pub target: &'static str,
+    #[suggestion(code = "", applicability = "machine-applicable", style = "tool-only")]
+    pub attr_span: Span,
 }
 
 #[derive(Diagnostic)]
@@ -481,15 +375,6 @@ pub(crate) struct MustNotSuspend {
 }
 
 #[derive(LintDiagnostic)]
-#[diag(passes_cold)]
-#[warning]
-pub(crate) struct Cold {
-    #[label]
-    pub span: Span,
-    pub on_crate: bool,
-}
-
-#[derive(LintDiagnostic)]
 #[diag(passes_link)]
 #[warning]
 pub(crate) struct Link {
@@ -497,17 +382,6 @@ pub(crate) struct Link {
     pub span: Option<Span>,
 }
 
-#[derive(LintDiagnostic)]
-#[diag(passes_link_name)]
-#[warning]
-pub(crate) struct LinkName<'a> {
-    #[help]
-    pub help_span: Option<Span>,
-    #[label]
-    pub span: Span,
-    pub value: &'a str,
-}
-
 #[derive(Diagnostic)]
 #[diag(passes_no_link)]
 pub(crate) struct NoLink {
@@ -518,24 +392,6 @@ pub(crate) struct NoLink {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_export_name)]
-pub(crate) struct ExportName {
-    #[primary_span]
-    pub attr_span: Span,
-    #[label]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(passes_rustc_layout_scalar_valid_range_not_struct)]
-pub(crate) struct RustcLayoutScalarValidRangeNotStruct {
-    #[primary_span]
-    pub attr_span: Span,
-    #[label]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
 #[diag(passes_rustc_legacy_const_generics_only)]
 pub(crate) struct RustcLegacyConstGenericsOnly {
     #[primary_span]
@@ -576,42 +432,6 @@ pub(crate) struct RustcDirtyClean {
     pub span: Span,
 }
 
-#[derive(LintDiagnostic)]
-#[diag(passes_link_section)]
-#[warning]
-pub(crate) struct LinkSection {
-    #[label]
-    pub span: Span,
-}
-
-#[derive(LintDiagnostic)]
-#[diag(passes_no_mangle_foreign)]
-#[warning]
-#[note]
-pub(crate) struct NoMangleForeign {
-    #[label]
-    pub span: Span,
-    #[suggestion(code = "", applicability = "machine-applicable")]
-    pub attr_span: Span,
-    pub foreign_item_kind: &'static str,
-}
-
-#[derive(LintDiagnostic)]
-#[diag(passes_no_mangle)]
-#[warning]
-pub(crate) struct NoMangle {
-    #[label]
-    pub span: Span,
-}
-
-#[derive(LintDiagnostic)]
-#[diag(passes_align_on_fields)]
-#[warning]
-pub(crate) struct AlignOnFields {
-    #[label]
-    pub span: Span,
-}
-
 #[derive(Diagnostic)]
 #[diag(passes_repr_conflicting, code = E0566)]
 pub(crate) struct ReprConflicting {
@@ -633,18 +453,8 @@ pub(crate) struct InvalidReprAlignForTarget {
 pub(crate) struct ReprConflictingLint;
 
 #[derive(Diagnostic)]
-#[diag(passes_used_static)]
-pub(crate) struct UsedStatic {
-    #[primary_span]
-    pub attr_span: Span,
-    #[label]
-    pub span: Span,
-    pub target: &'static str,
-}
-
-#[derive(Diagnostic)]
-#[diag(passes_allow_internal_unstable)]
-pub(crate) struct AllowInternalUnstable {
+#[diag(passes_macro_only_attribute)]
+pub(crate) struct MacroOnlyAttribute {
     #[primary_span]
     pub attr_span: Span,
     #[label]
@@ -687,24 +497,6 @@ pub(crate) struct RustcAllowConstFnUnstable {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_rustc_unstable_feature_bound)]
-pub(crate) struct RustcUnstableFeatureBound {
-    #[primary_span]
-    pub attr_span: Span,
-    #[label]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(passes_rustc_std_internal_symbol)]
-pub(crate) struct RustcStdInternalSymbol {
-    #[primary_span]
-    pub attr_span: Span,
-    #[label]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
 #[diag(passes_rustc_pub_transparent)]
 pub(crate) struct RustcPubTransparent {
     #[primary_span]
@@ -714,15 +506,6 @@ pub(crate) struct RustcPubTransparent {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_rustc_force_inline)]
-pub(crate) struct RustcForceInline {
-    #[primary_span]
-    pub attr_span: Span,
-    #[label]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
 #[diag(passes_rustc_force_inline_coro)]
 pub(crate) struct RustcForceInlineCoro {
     #[primary_span]
@@ -731,53 +514,6 @@ pub(crate) struct RustcForceInlineCoro {
     pub span: Span,
 }
 
-#[derive(Diagnostic)]
-#[diag(passes_link_ordinal)]
-pub(crate) struct LinkOrdinal {
-    #[primary_span]
-    pub attr_span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(passes_confusables)]
-pub(crate) struct Confusables {
-    #[primary_span]
-    pub attr_span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(passes_coroutine_on_non_closure)]
-pub(crate) struct CoroutineOnNonClosure {
-    #[primary_span]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(passes_linkage)]
-pub(crate) struct Linkage {
-    #[primary_span]
-    pub attr_span: Span,
-    #[label]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(passes_stability_promotable)]
-pub(crate) struct StabilityPromotable {
-    #[primary_span]
-    pub attr_span: Span,
-}
-
-#[derive(LintDiagnostic)]
-#[diag(passes_deprecated)]
-pub(crate) struct Deprecated;
-
-#[derive(LintDiagnostic)]
-#[diag(passes_macro_use)]
-pub(crate) struct MacroUse {
-    pub name: Symbol,
-}
-
 #[derive(LintDiagnostic)]
 pub(crate) enum MacroExport {
     #[diag(passes_macro_export)]
@@ -1281,13 +1017,6 @@ pub(crate) struct UselessAssignment<'a> {
 }
 
 #[derive(LintDiagnostic)]
-#[diag(passes_only_has_effect_on)]
-pub(crate) struct OnlyHasEffectOn {
-    pub attr_name: String,
-    pub target_name: String,
-}
-
-#[derive(LintDiagnostic)]
 #[diag(passes_inline_ignored_for_exported)]
 #[help]
 pub(crate) struct InlineIgnoredForExported {}
@@ -1841,26 +1570,3 @@ pub(crate) struct ReprAlignShouldBeAlign {
     pub span: Span,
     pub item: &'static str,
 }
-
-#[derive(Diagnostic)]
-#[diag(passes_align_should_be_repr_align)]
-pub(crate) struct AlignShouldBeReprAlign {
-    #[primary_span]
-    #[suggestion(
-        style = "verbose",
-        applicability = "machine-applicable",
-        code = "#[repr(align({align_bytes}))]"
-    )]
-    pub span: Span,
-    pub item: &'static str,
-    pub align_bytes: u64,
-}
-
-#[derive(Diagnostic)]
-#[diag(passes_align_attr_application)]
-pub(crate) struct AlignAttrApplication {
-    #[primary_span]
-    pub hint_span: Span,
-    #[label]
-    pub span: Span,
-}
diff --git a/compiler/rustc_passes/src/input_stats.rs b/compiler/rustc_passes/src/input_stats.rs
index 6ee325dce03..c83610da1aa 100644
--- a/compiler/rustc_passes/src/input_stats.rs
+++ b/compiler/rustc_passes/src/input_stats.rs
@@ -44,11 +44,11 @@ impl Node {
 /// For example, `ast::Visitor` has `visit_ident`, but `Ident`s are always
 /// stored inline within other AST nodes, so we don't implement `visit_ident`
 /// here. In contrast, we do implement `visit_expr` because `ast::Expr` is
-/// always stored as `P<ast::Expr>`, and every such expression should be
+/// always stored as `Box<ast::Expr>`, and every such expression should be
 /// measured separately.
 ///
 /// In general, a `visit_foo` method should be implemented here if the
-/// corresponding `Foo` type is always stored on its own, e.g.: `P<Foo>`,
+/// corresponding `Foo` type is always stored on its own, e.g.: `Box<Foo>`,
 /// `Box<Foo>`, `Vec<Foo>`, `Box<[Foo]>`.
 ///
 /// There are some types in the AST and HIR tree that the visitors do not have
diff --git a/compiler/rustc_passes/src/lang_items.rs b/compiler/rustc_passes/src/lang_items.rs
index 6fac01827a4..141a60a8ec3 100644
--- a/compiler/rustc_passes/src/lang_items.rs
+++ b/compiler/rustc_passes/src/lang_items.rs
@@ -329,7 +329,7 @@ impl<'ast, 'tcx> visit::Visitor<'ast> for LanguageItemCollector<'ast, 'tcx> {
                     match &self.parent_item.unwrap().kind {
                         ast::ItemKind::Impl(i) => {
                             if i.of_trait.is_some() {
-                                Target::Method(MethodKind::Trait { body })
+                                Target::Method(MethodKind::TraitImpl)
                             } else {
                                 Target::Method(MethodKind::Inherent)
                             }
diff --git a/compiler/rustc_passes/src/reachable.rs b/compiler/rustc_passes/src/reachable.rs
index 2f78c22c748..6cd8a54ecf4 100644
--- a/compiler/rustc_passes/src/reachable.rs
+++ b/compiler/rustc_passes/src/reachable.rs
@@ -183,7 +183,7 @@ impl<'tcx> ReachableContext<'tcx> {
             } else {
                 CodegenFnAttrs::EMPTY
             };
-            let is_extern = codegen_attrs.contains_extern_indicator();
+            let is_extern = codegen_attrs.contains_extern_indicator(self.tcx, search_item.into());
             if is_extern {
                 self.reachable_symbols.insert(search_item);
             }
@@ -423,8 +423,9 @@ fn has_custom_linkage(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
     if !tcx.def_kind(def_id).has_codegen_attrs() {
         return false;
     }
+
     let codegen_attrs = tcx.codegen_fn_attrs(def_id);
-    codegen_attrs.contains_extern_indicator()
+    codegen_attrs.contains_extern_indicator(tcx, def_id.into())
         // FIXME(nbdd0121): `#[used]` are marked as reachable here so it's picked up by
         // `linked_symbols` in cg_ssa. They won't be exported in binary or cdylib due to their
         // `SymbolExportLevel::Rust` export level but may end up being exported in dylibs.
diff --git a/compiler/rustc_passes/src/stability.rs b/compiler/rustc_passes/src/stability.rs
index c5056b9df76..71650c6b9b9 100644
--- a/compiler/rustc_passes/src/stability.rs
+++ b/compiler/rustc_passes/src/stability.rs
@@ -268,93 +268,51 @@ fn lookup_const_stability(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<ConstSt
     None
 }
 
-/// A private tree-walker for producing an `Index`.
-struct Annotator<'tcx> {
-    tcx: TyCtxt<'tcx>,
-    implications: UnordMap<Symbol, Symbol>,
-}
-
-impl<'tcx> Annotator<'tcx> {
-    /// Determine the stability for a node based on its attributes and inherited stability. The
-    /// stability is recorded in the index and used as the parent. If the node is a function,
-    /// `fn_sig` is its signature.
-    #[instrument(level = "trace", skip(self))]
-    fn annotate(&mut self, def_id: LocalDefId) {
-        if !self.tcx.features().staged_api() {
-            return;
-        }
+fn stability_implications(tcx: TyCtxt<'_>, LocalCrate: LocalCrate) -> UnordMap<Symbol, Symbol> {
+    let mut implications = UnordMap::default();
 
-        if let Some(stability) = self.tcx.lookup_stability(def_id)
+    let mut register_implication = |def_id| {
+        if let Some(stability) = tcx.lookup_stability(def_id)
             && let StabilityLevel::Unstable { implied_by: Some(implied_by), .. } = stability.level
         {
-            self.implications.insert(implied_by, stability.feature);
+            implications.insert(implied_by, stability.feature);
         }
 
-        if let Some(stability) = self.tcx.lookup_const_stability(def_id)
+        if let Some(stability) = tcx.lookup_const_stability(def_id)
             && let StabilityLevel::Unstable { implied_by: Some(implied_by), .. } = stability.level
         {
-            self.implications.insert(implied_by, stability.feature);
+            implications.insert(implied_by, stability.feature);
         }
-    }
-}
-
-impl<'tcx> Visitor<'tcx> for Annotator<'tcx> {
-    /// Because stability levels are scoped lexically, we want to walk
-    /// nested items in the context of the outer item, so enable
-    /// deep-walking.
-    type NestedFilter = nested_filter::All;
-
-    fn maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
-        self.tcx
-    }
+    };
 
-    fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
-        match i.kind {
-            hir::ItemKind::Struct(_, _, ref sd) => {
-                if let Some(ctor_def_id) = sd.ctor_def_id() {
-                    self.annotate(ctor_def_id);
+    if tcx.features().staged_api() {
+        register_implication(CRATE_DEF_ID);
+        for def_id in tcx.hir_crate_items(()).definitions() {
+            register_implication(def_id);
+            let def_kind = tcx.def_kind(def_id);
+            if def_kind.is_adt() {
+                let adt = tcx.adt_def(def_id);
+                for variant in adt.variants() {
+                    if variant.def_id != def_id.to_def_id() {
+                        register_implication(variant.def_id.expect_local());
+                    }
+                    for field in &variant.fields {
+                        register_implication(field.did.expect_local());
+                    }
+                    if let Some(ctor_def_id) = variant.ctor_def_id() {
+                        register_implication(ctor_def_id.expect_local())
+                    }
+                }
+            }
+            if def_kind.has_generics() {
+                for param in tcx.generics_of(def_id).own_params.iter() {
+                    register_implication(param.def_id.expect_local())
                 }
             }
-            _ => {}
-        }
-
-        self.annotate(i.owner_id.def_id);
-        intravisit::walk_item(self, i)
-    }
-
-    fn visit_trait_item(&mut self, ti: &'tcx hir::TraitItem<'tcx>) {
-        self.annotate(ti.owner_id.def_id);
-        intravisit::walk_trait_item(self, ti);
-    }
-
-    fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
-        self.annotate(ii.owner_id.def_id);
-        intravisit::walk_impl_item(self, ii);
-    }
-
-    fn visit_variant(&mut self, var: &'tcx Variant<'tcx>) {
-        self.annotate(var.def_id);
-        if let Some(ctor_def_id) = var.data.ctor_def_id() {
-            self.annotate(ctor_def_id);
         }
-
-        intravisit::walk_variant(self, var)
     }
 
-    fn visit_field_def(&mut self, s: &'tcx FieldDef<'tcx>) {
-        self.annotate(s.def_id);
-        intravisit::walk_field_def(self, s);
-    }
-
-    fn visit_foreign_item(&mut self, i: &'tcx hir::ForeignItem<'tcx>) {
-        self.annotate(i.owner_id.def_id);
-        intravisit::walk_foreign_item(self, i);
-    }
-
-    fn visit_generic_param(&mut self, p: &'tcx hir::GenericParam<'tcx>) {
-        self.annotate(p.def_id);
-        intravisit::walk_generic_param(self, p);
-    }
+    implications
 }
 
 struct MissingStabilityAnnotations<'tcx> {
@@ -566,13 +524,6 @@ impl<'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'tcx> {
     }
 }
 
-fn stability_implications(tcx: TyCtxt<'_>, LocalCrate: LocalCrate) -> UnordMap<Symbol, Symbol> {
-    let mut annotator = Annotator { tcx, implications: Default::default() };
-    annotator.annotate(CRATE_DEF_ID);
-    tcx.hir_walk_toplevel_module(&mut annotator);
-    annotator.implications
-}
-
 /// Cross-references the feature names of unstable APIs with enabled
 /// features and possibly prints errors.
 fn check_mod_unstable_api_usage(tcx: TyCtxt<'_>, module_def_id: LocalModDefId) {
@@ -639,9 +590,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
             // For implementations of traits, check the stability of each item
             // individually as it's possible to have a stable trait with unstable
             // items.
-            hir::ItemKind::Impl(hir::Impl {
-                of_trait: Some(t), self_ty, items, constness, ..
-            }) => {
+            hir::ItemKind::Impl(hir::Impl { of_trait: Some(of_trait), self_ty, items, .. }) => {
                 let features = self.tcx.features();
                 if features.staged_api() {
                     let attrs = self.tcx.hir_attrs(item.hir_id());
@@ -677,7 +626,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
                     {
                         let mut c = CheckTraitImplStable { tcx: self.tcx, fully_stable: true };
                         c.visit_ty_unambig(self_ty);
-                        c.visit_trait_ref(t);
+                        c.visit_trait_ref(&of_trait.trait_ref);
 
                         // Skip the lint if the impl is marked as unstable using
                         // #[unstable_feature_bound(..)]
@@ -690,7 +639,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
 
                         // do not lint when the trait isn't resolved, since resolution error should
                         // be fixed first
-                        if t.path.res != Res::Err
+                        if of_trait.trait_ref.path.res != Res::Err
                             && c.fully_stable
                             && !unstable_feature_bound_in_effect
                         {
@@ -704,7 +653,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
                     }
 
                     if features.const_trait_impl()
-                        && let hir::Constness::Const = constness
+                        && let hir::Constness::Const = of_trait.constness
                     {
                         let stable_or_implied_stable = match const_stab {
                             None => true,
@@ -720,7 +669,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
                             Some(_) => false,
                         };
 
-                        if let Some(trait_id) = t.trait_def_id()
+                        if let Some(trait_id) = of_trait.trait_ref.trait_def_id()
                             && let Some(const_stab) = self.tcx.lookup_const_stability(trait_id)
                         {
                             // the const stability of a trait impl must match the const stability on the trait.
@@ -748,14 +697,18 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
                     }
                 }
 
-                if let hir::Constness::Const = constness
-                    && let Some(def_id) = t.trait_def_id()
+                if let hir::Constness::Const = of_trait.constness
+                    && let Some(def_id) = of_trait.trait_ref.trait_def_id()
                 {
                     // FIXME(const_trait_impl): Improve the span here.
-                    self.tcx.check_const_stability(def_id, t.path.span, t.path.span);
+                    self.tcx.check_const_stability(
+                        def_id,
+                        of_trait.trait_ref.path.span,
+                        of_trait.trait_ref.path.span,
+                    );
                 }
 
-                for impl_item_ref in *items {
+                for impl_item_ref in items {
                     let impl_item = self.tcx.associated_item(impl_item_ref.owner_id);
 
                     if let Some(def_id) = impl_item.trait_item_def_id {
diff --git a/compiler/rustc_pattern_analysis/src/constructor.rs b/compiler/rustc_pattern_analysis/src/constructor.rs
index 9a9e0db964c..12f653a1337 100644
--- a/compiler/rustc_pattern_analysis/src/constructor.rs
+++ b/compiler/rustc_pattern_analysis/src/constructor.rs
@@ -1130,16 +1130,16 @@ impl<Cx: PatCx> ConstructorSet<Cx> {
                         seen_false = true;
                     }
                 }
-                if seen_false {
-                    present.push(Bool(false));
-                } else {
-                    missing.push(Bool(false));
-                }
                 if seen_true {
                     present.push(Bool(true));
                 } else {
                     missing.push(Bool(true));
                 }
+                if seen_false {
+                    present.push(Bool(false));
+                } else {
+                    missing.push(Bool(false));
+                }
             }
             ConstructorSet::Integers { range_1, range_2 } => {
                 let seen_ranges: Vec<_> =
diff --git a/compiler/rustc_pattern_analysis/src/rustc.rs b/compiler/rustc_pattern_analysis/src/rustc.rs
index 0c1b0d622f2..c9bf4fe4449 100644
--- a/compiler/rustc_pattern_analysis/src/rustc.rs
+++ b/compiler/rustc_pattern_analysis/src/rustc.rs
@@ -8,7 +8,6 @@ use rustc_hir::HirId;
 use rustc_hir::def_id::DefId;
 use rustc_index::{Idx, IndexVec};
 use rustc_middle::middle::stability::EvalResult;
-use rustc_middle::mir::{self, Const};
 use rustc_middle::thir::{self, Pat, PatKind, PatRange, PatRangeBoundary};
 use rustc_middle::ty::layout::IntegerExt;
 use rustc_middle::ty::{
@@ -430,7 +429,7 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
         match bdy {
             PatRangeBoundary::NegInfinity => MaybeInfiniteInt::NegInfinity,
             PatRangeBoundary::Finite(value) => {
-                let bits = value.eval_bits(self.tcx, self.typing_env);
+                let bits = value.try_to_scalar_int().unwrap().to_bits_unchecked();
                 match *ty.kind() {
                     ty::Int(ity) => {
                         let size = Integer::from_int_ty(&self.tcx, ity).size().bits();
@@ -520,75 +519,54 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
             PatKind::Constant { value } => {
                 match ty.kind() {
                     ty::Bool => {
-                        ctor = match value.try_eval_bool(cx.tcx, cx.typing_env) {
-                            Some(b) => Bool(b),
-                            None => Opaque(OpaqueId::new()),
-                        };
+                        ctor = Bool(value.try_to_bool().unwrap());
                         fields = vec![];
                         arity = 0;
                     }
                     ty::Char | ty::Int(_) | ty::Uint(_) => {
-                        ctor = match value.try_eval_bits(cx.tcx, cx.typing_env) {
-                            Some(bits) => {
-                                let x = match *ty.kind() {
-                                    ty::Int(ity) => {
-                                        let size = Integer::from_int_ty(&cx.tcx, ity).size().bits();
-                                        MaybeInfiniteInt::new_finite_int(bits, size)
-                                    }
-                                    _ => MaybeInfiniteInt::new_finite_uint(bits),
-                                };
-                                IntRange(IntRange::from_singleton(x))
-                            }
-                            None => Opaque(OpaqueId::new()),
+                        ctor = {
+                            let bits = value.valtree.unwrap_leaf().to_bits_unchecked();
+                            let x = match *ty.kind() {
+                                ty::Int(ity) => {
+                                    let size = Integer::from_int_ty(&cx.tcx, ity).size().bits();
+                                    MaybeInfiniteInt::new_finite_int(bits, size)
+                                }
+                                _ => MaybeInfiniteInt::new_finite_uint(bits),
+                            };
+                            IntRange(IntRange::from_singleton(x))
                         };
                         fields = vec![];
                         arity = 0;
                     }
                     ty::Float(ty::FloatTy::F16) => {
-                        ctor = match value.try_eval_bits(cx.tcx, cx.typing_env) {
-                            Some(bits) => {
-                                use rustc_apfloat::Float;
-                                let value = rustc_apfloat::ieee::Half::from_bits(bits);
-                                F16Range(value, value, RangeEnd::Included)
-                            }
-                            None => Opaque(OpaqueId::new()),
-                        };
+                        use rustc_apfloat::Float;
+                        let bits = value.valtree.unwrap_leaf().to_u16();
+                        let value = rustc_apfloat::ieee::Half::from_bits(bits.into());
+                        ctor = F16Range(value, value, RangeEnd::Included);
                         fields = vec![];
                         arity = 0;
                     }
                     ty::Float(ty::FloatTy::F32) => {
-                        ctor = match value.try_eval_bits(cx.tcx, cx.typing_env) {
-                            Some(bits) => {
-                                use rustc_apfloat::Float;
-                                let value = rustc_apfloat::ieee::Single::from_bits(bits);
-                                F32Range(value, value, RangeEnd::Included)
-                            }
-                            None => Opaque(OpaqueId::new()),
-                        };
+                        use rustc_apfloat::Float;
+                        let bits = value.valtree.unwrap_leaf().to_u32();
+                        let value = rustc_apfloat::ieee::Single::from_bits(bits.into());
+                        ctor = F32Range(value, value, RangeEnd::Included);
                         fields = vec![];
                         arity = 0;
                     }
                     ty::Float(ty::FloatTy::F64) => {
-                        ctor = match value.try_eval_bits(cx.tcx, cx.typing_env) {
-                            Some(bits) => {
-                                use rustc_apfloat::Float;
-                                let value = rustc_apfloat::ieee::Double::from_bits(bits);
-                                F64Range(value, value, RangeEnd::Included)
-                            }
-                            None => Opaque(OpaqueId::new()),
-                        };
+                        use rustc_apfloat::Float;
+                        let bits = value.valtree.unwrap_leaf().to_u64();
+                        let value = rustc_apfloat::ieee::Double::from_bits(bits.into());
+                        ctor = F64Range(value, value, RangeEnd::Included);
                         fields = vec![];
                         arity = 0;
                     }
                     ty::Float(ty::FloatTy::F128) => {
-                        ctor = match value.try_eval_bits(cx.tcx, cx.typing_env) {
-                            Some(bits) => {
-                                use rustc_apfloat::Float;
-                                let value = rustc_apfloat::ieee::Quad::from_bits(bits);
-                                F128Range(value, value, RangeEnd::Included)
-                            }
-                            None => Opaque(OpaqueId::new()),
-                        };
+                        use rustc_apfloat::Float;
+                        let bits = value.valtree.unwrap_leaf().to_u128();
+                        let value = rustc_apfloat::ieee::Quad::from_bits(bits);
+                        ctor = F128Range(value, value, RangeEnd::Included);
                         fields = vec![];
                         arity = 0;
                     }
@@ -630,8 +608,12 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
                     }
                     ty::Float(fty) => {
                         use rustc_apfloat::Float;
-                        let lo = lo.as_finite().map(|c| c.eval_bits(cx.tcx, cx.typing_env));
-                        let hi = hi.as_finite().map(|c| c.eval_bits(cx.tcx, cx.typing_env));
+                        let lo = lo
+                            .as_finite()
+                            .map(|c| c.try_to_scalar_int().unwrap().to_bits_unchecked());
+                        let hi = hi
+                            .as_finite()
+                            .map(|c| c.try_to_scalar_int().unwrap().to_bits_unchecked());
                         match fty {
                             ty::FloatTy::F16 => {
                                 use rustc_apfloat::ieee::Half;
@@ -739,8 +721,8 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
                 };
                 match ScalarInt::try_from_uint(bits, size) {
                     Some(scalar) => {
-                        let value = mir::Const::from_scalar(tcx, scalar.into(), ty.inner());
-                        PatRangeBoundary::Finite(value)
+                        let valtree = ty::ValTree::from_scalar_int(tcx, scalar);
+                        PatRangeBoundary::Finite(valtree)
                     }
                     // The value doesn't fit. Since `x >= 0` and 0 always encodes the minimum value
                     // for a type, the problem isn't that the value is too small. So it must be too
@@ -760,7 +742,7 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
             "_".to_string()
         } else if range.is_singleton() {
             let lo = cx.hoist_pat_range_bdy(range.lo, ty);
-            let value = lo.as_finite().unwrap();
+            let value = ty::Value { ty: ty.inner(), valtree: lo.as_finite().unwrap() };
             value.to_string()
         } else {
             // We convert to an inclusive range for diagnostics.
@@ -772,7 +754,9 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
                 // fictitious values after `{u,i}size::MAX` (see [`IntRange::split`] for why we do
                 // this). We show this to the user as `usize::MAX..` which is slightly incorrect but
                 // probably clear enough.
-                lo = PatRangeBoundary::Finite(ty.numeric_max_val(cx.tcx).unwrap());
+                let max = ty.numeric_max_val(cx.tcx).unwrap();
+                let max = ty::ValTree::from_scalar_int(cx.tcx, max.try_to_scalar_int().unwrap());
+                lo = PatRangeBoundary::Finite(max);
             }
             let hi = if let Some(hi) = range.hi.minus_one() {
                 hi
@@ -907,7 +891,7 @@ impl<'p, 'tcx: 'p> PatCx for RustcPatCtxt<'p, 'tcx> {
     type Ty = RevealedTy<'tcx>;
     type Error = ErrorGuaranteed;
     type VariantIdx = VariantIdx;
-    type StrLit = Const<'tcx>;
+    type StrLit = ty::Value<'tcx>;
     type ArmData = HirId;
     type PatData = &'p Pat<'tcx>;
 
diff --git a/compiler/rustc_pattern_analysis/tests/exhaustiveness.rs b/compiler/rustc_pattern_analysis/tests/exhaustiveness.rs
index 14ca0d057f0..4ad64f81560 100644
--- a/compiler/rustc_pattern_analysis/tests/exhaustiveness.rs
+++ b/compiler/rustc_pattern_analysis/tests/exhaustiveness.rs
@@ -176,6 +176,9 @@ fn test_witnesses() {
         ),
         vec!["Enum::Variant1(_)", "Enum::Variant2(_)", "_"],
     );
+
+    // Assert we put `true` before `false`.
+    assert_witnesses(AllOfThem, Ty::Bool, Vec::new(), vec!["true", "false"]);
 }
 
 #[test]
diff --git a/compiler/rustc_privacy/src/lib.rs b/compiler/rustc_privacy/src/lib.rs
index 5d02c02b23c..1bddbd03cc3 100644
--- a/compiler/rustc_privacy/src/lib.rs
+++ b/compiler/rustc_privacy/src/lib.rs
@@ -1779,7 +1779,8 @@ fn check_mod_privacy(tcx: TyCtxt<'_>, module_def_id: LocalModDefId) {
         if let DefKind::Impl { of_trait: true } = tcx.def_kind(def_id) {
             let trait_ref = tcx.impl_trait_ref(def_id).unwrap();
             let trait_ref = trait_ref.instantiate_identity();
-            visitor.span = tcx.hir_expect_item(def_id).expect_impl().of_trait.unwrap().path.span;
+            visitor.span =
+                tcx.hir_expect_item(def_id).expect_impl().of_trait.unwrap().trait_ref.path.span;
             let _ =
                 visitor.visit_def_id(trait_ref.def_id, "trait", &trait_ref.print_only_trait_path());
         }
diff --git a/compiler/rustc_public/src/mir/body.rs b/compiler/rustc_public/src/mir/body.rs
index 3d595286041..276adacd99e 100644
--- a/compiler/rustc_public/src/mir/body.rs
+++ b/compiler/rustc_public/src/mir/body.rs
@@ -349,7 +349,7 @@ impl AssertMessage {
     }
 }
 
-#[derive(Copy, Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum BinOp {
     Add,
     AddUnchecked,
@@ -384,7 +384,7 @@ impl BinOp {
     }
 }
 
-#[derive(Copy, Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum UnOp {
     Not,
     Neg,
@@ -490,7 +490,7 @@ pub enum StatementKind {
     Nop,
 }
 
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum Rvalue {
     /// Creates a pointer with the indicated mutability to the place.
     ///
@@ -666,7 +666,7 @@ impl Rvalue {
     }
 }
 
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum AggregateKind {
     Array(Ty),
     Tuple,
@@ -677,14 +677,14 @@ pub enum AggregateKind {
     RawPtr(Ty, Mutability),
 }
 
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum Operand {
     Copy(Place),
     Move(Place),
     Constant(ConstOperand),
 }
 
-#[derive(Clone, Eq, PartialEq, Serialize)]
+#[derive(Clone, Eq, PartialEq, Hash, Serialize)]
 pub struct Place {
     pub local: Local,
     /// projection out of a place (access a field, deref a pointer, etc)
@@ -697,7 +697,7 @@ impl From<Local> for Place {
     }
 }
 
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub struct ConstOperand {
     pub span: Span,
     pub user_ty: Option<UserTypeAnnotationIndex>,
@@ -770,7 +770,7 @@ pub enum VarDebugInfoContents {
 // ProjectionElem<Local, Ty>) and user-provided type annotations (for which the projection elements
 // are of type ProjectionElem<(), ()>).
 // In rustc_public's IR we don't need this generality, so we just use ProjectionElem for Places.
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum ProjectionElem {
     /// Dereference projections (e.g. `*_1`) project to the address referenced by the base place.
     Deref,
@@ -913,7 +913,7 @@ impl SwitchTargets {
     }
 }
 
-#[derive(Copy, Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum BorrowKind {
     /// Data must be immutable and is aliasable.
     Shared,
@@ -940,7 +940,7 @@ impl BorrowKind {
     }
 }
 
-#[derive(Copy, Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum RawPtrKind {
     Mut,
     Const,
@@ -958,14 +958,14 @@ impl RawPtrKind {
     }
 }
 
-#[derive(Copy, Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum MutBorrowKind {
     Default,
     TwoPhaseBorrow,
     ClosureCapture,
 }
 
-#[derive(Copy, Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum FakeBorrowKind {
     /// A shared (deep) borrow. Data must be immutable and is aliasable.
     Deep,
@@ -982,13 +982,13 @@ pub enum Mutability {
     Mut,
 }
 
-#[derive(Copy, Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum Safety {
     Safe,
     Unsafe,
 }
 
-#[derive(Copy, Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum PointerCoercion {
     /// Go from a fn-item type to a fn-pointer type.
     ReifyFnPointer,
@@ -1015,7 +1015,7 @@ pub enum PointerCoercion {
     Unsize,
 }
 
-#[derive(Copy, Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum CastKind {
     // FIXME(smir-rename): rename this to PointerExposeProvenance
     PointerExposeAddress,
@@ -1030,7 +1030,7 @@ pub enum CastKind {
     Transmute,
 }
 
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum NullOp {
     /// Returns the size of a value of that type.
     SizeOf,
diff --git a/compiler/rustc_public/src/mir/pretty.rs b/compiler/rustc_public/src/mir/pretty.rs
index 3183c020772..9dd1ce4de0e 100644
--- a/compiler/rustc_public/src/mir/pretty.rs
+++ b/compiler/rustc_public/src/mir/pretty.rs
@@ -100,7 +100,7 @@ fn pretty_statement<W: Write>(writer: &mut W, statement: &StatementKind) -> io::
             writeln!(writer, "{INDENT}FakeRead({cause:?}, {place:?});")
         }
         StatementKind::SetDiscriminant { place, variant_index } => {
-            writeln!(writer, "{INDENT}discriminant({place:?} = {};", variant_index.to_index())
+            writeln!(writer, "{INDENT}discriminant({place:?}) = {};", variant_index.to_index())
         }
         StatementKind::Deinit(place) => writeln!(writer, "Deinit({place:?};"),
         StatementKind::StorageLive(local) => {
diff --git a/compiler/rustc_public/src/ty.rs b/compiler/rustc_public/src/ty.rs
index de4b21b1764..1b5f0ed1429 100644
--- a/compiler/rustc_public/src/ty.rs
+++ b/compiler/rustc_public/src/ty.rs
@@ -113,7 +113,7 @@ pub enum Pattern {
 }
 
 /// Represents a constant in the type system
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub struct TyConst {
     pub(crate) kind: TyConstKind,
     pub id: TyConstId,
@@ -140,7 +140,7 @@ impl TyConst {
     }
 }
 
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum TyConstKind {
     Param(ParamConst),
     Bound(DebruijnIndex, BoundVar),
@@ -151,11 +151,11 @@ pub enum TyConstKind {
     ZSTValue(Ty),
 }
 
-#[derive(Copy, Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub struct TyConstId(usize);
 
 /// Represents a constant in MIR
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub struct MirConst {
     /// The constant kind.
     pub(crate) kind: ConstantKind,
@@ -212,17 +212,17 @@ impl MirConst {
     }
 }
 
-#[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Serialize)]
 pub struct MirConstId(usize);
 
 type Ident = Opaque;
 
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub struct Region {
     pub kind: RegionKind,
 }
 
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum RegionKind {
     ReEarlyParam(EarlyParamRegion),
     ReBound(DebruijnIndex, BoundRegion),
@@ -233,7 +233,7 @@ pub enum RegionKind {
 
 pub(crate) type DebruijnIndex = u32;
 
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub struct EarlyParamRegion {
     pub index: u32,
     pub name: Symbol,
@@ -241,7 +241,7 @@ pub struct EarlyParamRegion {
 
 pub(crate) type BoundVar = u32;
 
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub struct BoundRegion {
     pub var: BoundVar,
     pub kind: BoundRegionKind,
@@ -249,13 +249,13 @@ pub struct BoundRegion {
 
 pub(crate) type UniverseIndex = u32;
 
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub struct Placeholder<T> {
     pub universe: UniverseIndex,
     pub bound: T,
 }
 
-#[derive(Clone, Copy, PartialEq, Eq, Serialize)]
+#[derive(Clone, Copy, PartialEq, Eq, Hash, Serialize)]
 pub struct Span(usize);
 
 impl Debug for Span {
@@ -997,7 +997,7 @@ crate_def! {
 }
 
 /// A list of generic arguments.
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub struct GenericArgs(pub Vec<GenericArgKind>);
 
 impl std::ops::Index<ParamTy> for GenericArgs {
@@ -1016,7 +1016,7 @@ impl std::ops::Index<ParamConst> for GenericArgs {
     }
 }
 
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum GenericArgKind {
     Lifetime(Region),
     Type(Ty),
@@ -1199,7 +1199,7 @@ pub enum BoundTyKind {
     Param(ParamDef, String),
 }
 
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum BoundRegionKind {
     BrAnon,
     BrNamed(BrNamedDef, String),
@@ -1354,7 +1354,7 @@ impl Allocation {
     }
 }
 
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub enum ConstantKind {
     Ty(TyConst),
     Allocated(Allocation),
@@ -1365,13 +1365,13 @@ pub enum ConstantKind {
     ZeroSized,
 }
 
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub struct ParamConst {
     pub index: u32,
     pub name: String,
 }
 
-#[derive(Clone, Debug, Eq, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash, Serialize)]
 pub struct UnevaluatedConst {
     pub def: ConstDef,
     pub args: GenericArgs,
diff --git a/compiler/rustc_resolve/messages.ftl b/compiler/rustc_resolve/messages.ftl
index 39e9a9cc58a..d5ff8a4b609 100644
--- a/compiler/rustc_resolve/messages.ftl
+++ b/compiler/rustc_resolve/messages.ftl
@@ -242,8 +242,11 @@ resolve_lowercase_self =
     attempt to use a non-constant value in a constant
     .suggestion = try using `Self`
 
+resolve_macro_cannot_use_as_fn_like =
+    `{$ident}` exists, but has no rules for function-like invocation
+
 resolve_macro_cannot_use_as_attr =
-    `{$ident}` exists, but a declarative macro cannot be used as an attribute macro
+    `{$ident}` exists, but has no `attr` rules
 
 resolve_macro_cannot_use_as_derive =
      `{$ident}` exists, but a declarative macro cannot be used as a derive macro
diff --git a/compiler/rustc_resolve/src/build_reduced_graph.rs b/compiler/rustc_resolve/src/build_reduced_graph.rs
index d9671c43b3d..1eb4e1199e6 100644
--- a/compiler/rustc_resolve/src/build_reduced_graph.rs
+++ b/compiler/rustc_resolve/src/build_reduced_graph.rs
@@ -11,7 +11,7 @@ use std::sync::Arc;
 use rustc_ast::visit::{self, AssocCtxt, Visitor, WalkItemKind};
 use rustc_ast::{
     self as ast, AssocItem, AssocItemKind, Block, ConstItem, Delegation, Fn, ForeignItem,
-    ForeignItemKind, Impl, Item, ItemKind, NodeId, StaticItem, StmtKind, TyAlias,
+    ForeignItemKind, Item, ItemKind, NodeId, StaticItem, StmtKind, TyAlias,
 };
 use rustc_attr_parsing as attr;
 use rustc_attr_parsing::AttributeParser;
@@ -27,7 +27,7 @@ use rustc_middle::metadata::ModChild;
 use rustc_middle::ty::{Feed, Visibility};
 use rustc_middle::{bug, span_bug};
 use rustc_span::hygiene::{ExpnId, LocalExpnId, MacroKind};
-use rustc_span::{Ident, Span, Symbol, kw, sym};
+use rustc_span::{Ident, Macros20NormalizedIdent, Span, Symbol, kw, sym};
 use thin_vec::ThinVec;
 use tracing::debug;
 
@@ -223,7 +223,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
     pub(crate) fn build_reduced_graph_external(&self, module: Module<'ra>) {
         for child in self.tcx.module_children(module.def_id()) {
-            let parent_scope = ParentScope::module(module, self);
+            let parent_scope = ParentScope::module(module, self.arenas);
             self.build_reduced_graph_for_external_crate_res(child, parent_scope)
         }
     }
@@ -373,7 +373,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                         res,
                     ))
                 };
-                match self.r.resolve_path(
+                match self.r.cm().resolve_path(
                     &segments,
                     None,
                     parent_scope,
@@ -420,14 +420,18 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
             // The fields are not expanded yet.
             return;
         }
-        let fields = fields
+        let field_name = |i, field: &ast::FieldDef| {
+            field.ident.unwrap_or_else(|| Ident::from_str_and_span(&format!("{i}"), field.span))
+        };
+        let field_names: Vec<_> =
+            fields.iter().enumerate().map(|(i, field)| field_name(i, field)).collect();
+        let defaults = fields
             .iter()
             .enumerate()
-            .map(|(i, field)| {
-                field.ident.unwrap_or_else(|| Ident::from_str_and_span(&format!("{i}"), field.span))
-            })
+            .filter_map(|(i, field)| field.default.as_ref().map(|_| field_name(i, field).name))
             .collect();
-        self.r.field_names.insert(def_id, fields);
+        self.r.field_names.insert(def_id, field_names);
+        self.r.field_defaults.insert(def_id, defaults);
     }
 
     fn insert_field_visibilities_local(&mut self, def_id: DefId, fields: &[ast::FieldDef]) {
@@ -489,9 +493,6 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                     });
                 }
             }
-            // We don't add prelude imports to the globs since they only affect lexical scopes,
-            // which are not relevant to import resolution.
-            ImportKind::Glob { is_prelude: true, .. } => {}
             ImportKind::Glob { .. } => current_module.globs.borrow_mut().push(import),
             _ => unreachable!(),
         }
@@ -654,13 +655,19 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                 self.add_import(module_path, kind, use_tree.span, item, root_span, item.id, vis);
             }
             ast::UseTreeKind::Glob => {
-                let kind = ImportKind::Glob {
-                    is_prelude: ast::attr::contains_name(&item.attrs, sym::prelude_import),
-                    max_vis: Cell::new(None),
-                    id,
-                };
-
-                self.add_import(prefix, kind, use_tree.span, item, root_span, item.id, vis);
+                if !ast::attr::contains_name(&item.attrs, sym::prelude_import) {
+                    let kind = ImportKind::Glob { max_vis: Cell::new(None), id };
+                    self.add_import(prefix, kind, use_tree.span, item, root_span, item.id, vis);
+                } else {
+                    // Resolve the prelude import early.
+                    let path_res =
+                        self.r.cm().maybe_resolve_path(&prefix, None, &self.parent_scope, None);
+                    if let PathResult::Module(ModuleOrUniformRoot::Module(module)) = path_res {
+                        self.r.prelude = Some(module);
+                    } else {
+                        self.r.dcx().span_err(use_tree.span, "cannot resolve a prelude import");
+                    }
+                }
             }
             ast::UseTreeKind::Nested { ref items, .. } => {
                 // Ensure there is at most one `self` in the list
@@ -902,10 +909,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
             }
 
             // These items do not add names to modules.
-            ItemKind::Impl(box Impl { of_trait: Some(..), .. })
-            | ItemKind::Impl { .. }
-            | ItemKind::ForeignMod(..)
-            | ItemKind::GlobalAsm(..) => {}
+            ItemKind::Impl { .. } | ItemKind::ForeignMod(..) | ItemKind::GlobalAsm(..) => {}
 
             ItemKind::MacroDef(..) | ItemKind::MacCall(_) | ItemKind::DelegationMac(..) => {
                 unreachable!()
@@ -969,41 +973,36 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
         self.r.potentially_unused_imports.push(import);
         let imported_binding = self.r.import(binding, import);
         if ident.name != kw::Underscore && parent == self.r.graph_root {
-            let ident = ident.normalize_to_macros_2_0();
-            if let Some(entry) = self.r.extern_prelude.get(&ident)
+            let norm_ident = Macros20NormalizedIdent::new(ident);
+            // FIXME: this error is technically unnecessary now when extern prelude is split into
+            // two scopes, remove it with lang team approval.
+            if let Some(entry) = self.r.extern_prelude.get(&norm_ident)
                 && expansion != LocalExpnId::ROOT
                 && orig_name.is_some()
-                && !entry.is_import()
+                && entry.item_binding.is_none()
             {
                 self.r.dcx().emit_err(
                     errors::MacroExpandedExternCrateCannotShadowExternArguments { span: item.span },
                 );
-                // `return` is intended to discard this binding because it's an
-                // unregistered ambiguity error which would result in a panic
-                // caused by inconsistency `path_res`
-                // more details: https://github.com/rust-lang/rust/pull/111761
-                return;
             }
 
             use indexmap::map::Entry;
-            match self.r.extern_prelude.entry(ident) {
+            match self.r.extern_prelude.entry(norm_ident) {
                 Entry::Occupied(mut occupied) => {
                     let entry = occupied.get_mut();
-                    if let Some(old_binding) = entry.binding.get()
-                        && old_binding.is_import()
-                    {
+                    if entry.item_binding.is_some() {
                         let msg = format!("extern crate `{ident}` already in extern prelude");
                         self.r.tcx.dcx().span_delayed_bug(item.span, msg);
                     } else {
-                        // Binding from `extern crate` item in source code can replace
-                        // a binding from `--extern` on command line here.
-                        entry.binding.set(Some(imported_binding));
+                        entry.item_binding = Some(imported_binding);
                         entry.introduced_by_item = orig_name.is_some();
                     }
                     entry
                 }
                 Entry::Vacant(vacant) => vacant.insert(ExternPreludeEntry {
-                    binding: Cell::new(Some(imported_binding)),
+                    item_binding: Some(imported_binding),
+                    flag_binding: Cell::new(None),
+                    only_item: true,
                     introduced_by_item: true,
                 }),
             };
@@ -1128,7 +1127,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
             });
         } else {
             for ident in single_imports.iter().cloned() {
-                let result = self.r.maybe_resolve_ident_in_module(
+                let result = self.r.cm().maybe_resolve_ident_in_module(
                     ModuleOrUniformRoot::Module(module),
                     ident,
                     MacroNS,
@@ -1231,7 +1230,8 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
             ItemKind::Fn(box ast::Fn { ident: fn_ident, .. }) => {
                 match self.proc_macro_stub(item, *fn_ident) {
                     Some((macro_kind, ident, span)) => {
-                        let res = Res::Def(DefKind::Macro(macro_kind), def_id.to_def_id());
+                        let macro_kinds = macro_kind.into();
+                        let res = Res::Def(DefKind::Macro(macro_kinds), def_id.to_def_id());
                         let macro_data = MacroData::new(self.r.dummy_ext(macro_kind));
                         self.r.new_local_macro(def_id, macro_data);
                         self.r.proc_macro_stubs.insert(def_id);
diff --git a/compiler/rustc_resolve/src/check_unused.rs b/compiler/rustc_resolve/src/check_unused.rs
index b85a814776a..11d93a58ae2 100644
--- a/compiler/rustc_resolve/src/check_unused.rs
+++ b/compiler/rustc_resolve/src/check_unused.rs
@@ -33,7 +33,7 @@ use rustc_session::lint::BuiltinLintDiag;
 use rustc_session::lint::builtin::{
     MACRO_USE_EXTERN_CRATE, UNUSED_EXTERN_CRATES, UNUSED_IMPORTS, UNUSED_QUALIFICATIONS,
 };
-use rustc_span::{DUMMY_SP, Ident, Span, kw};
+use rustc_span::{DUMMY_SP, Ident, Macros20NormalizedIdent, Span, kw};
 
 use crate::imports::{Import, ImportKind};
 use crate::{LexicalScopeBinding, NameBindingKind, Resolver, module_to_string};
@@ -203,7 +203,7 @@ impl<'a, 'ra, 'tcx> UnusedImportCheckVisitor<'a, 'ra, 'tcx> {
             if self
                 .r
                 .extern_prelude
-                .get(&extern_crate.ident)
+                .get(&Macros20NormalizedIdent::new(extern_crate.ident))
                 .is_none_or(|entry| entry.introduced_by_item)
             {
                 continue;
diff --git a/compiler/rustc_resolve/src/def_collector.rs b/compiler/rustc_resolve/src/def_collector.rs
index 7d51fef28d3..14538df8187 100644
--- a/compiler/rustc_resolve/src/def_collector.rs
+++ b/compiler/rustc_resolve/src/def_collector.rs
@@ -5,6 +5,7 @@ use rustc_ast::*;
 use rustc_attr_parsing::{AttributeParser, Early, OmitDoc, ShouldEmit};
 use rustc_expand::expand::AstFragment;
 use rustc_hir as hir;
+use rustc_hir::Target;
 use rustc_hir::def::{CtorKind, CtorOf, DefKind};
 use rustc_hir::def_id::LocalDefId;
 use rustc_middle::span_bug;
@@ -138,6 +139,7 @@ impl<'a, 'ra, 'tcx> visit::Visitor<'a> for DefCollector<'a, 'ra, 'tcx> {
                     &i.attrs,
                     i.span,
                     i.id,
+                    Target::MacroDef,
                     OmitDoc::Skip,
                     std::convert::identity,
                     |_l| {
@@ -149,9 +151,9 @@ impl<'a, 'ra, 'tcx> visit::Visitor<'a> for DefCollector<'a, 'ra, 'tcx> {
 
                 let macro_data =
                     self.resolver.compile_macro(def, *ident, &attrs, i.span, i.id, edition);
-                let macro_kind = macro_data.ext.macro_kind();
+                let macro_kinds = macro_data.ext.macro_kinds();
                 opt_macro_data = Some(macro_data);
-                DefKind::Macro(macro_kind)
+                DefKind::Macro(macro_kinds)
             }
             ItemKind::GlobalAsm(..) => DefKind::GlobalAsm,
             ItemKind::Use(use_tree) => {
diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index d18554bba1b..a437f86e377 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -1,4 +1,3 @@
-use rustc_ast::ptr::P;
 use rustc_ast::visit::{self, Visitor};
 use rustc_ast::{
     self as ast, CRATE_NODE_ID, Crate, ItemKind, ModKind, NodeId, Path, join_path_idents,
@@ -14,7 +13,7 @@ use rustc_errors::{
 use rustc_feature::BUILTIN_ATTRIBUTES;
 use rustc_hir::attrs::{AttributeKind, CfgEntry, StrippedCfgItem};
 use rustc_hir::def::Namespace::{self, *};
-use rustc_hir::def::{self, CtorKind, CtorOf, DefKind, NonMacroAttrKind, PerNS};
+use rustc_hir::def::{self, CtorKind, CtorOf, DefKind, MacroKinds, NonMacroAttrKind, PerNS};
 use rustc_hir::def_id::{CRATE_DEF_ID, DefId};
 use rustc_hir::{PrimTy, Stability, StabilityLevel, find_attr};
 use rustc_middle::bug;
@@ -30,7 +29,7 @@ use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::edition::Edition;
 use rustc_span::hygiene::MacroKind;
 use rustc_span::source_map::SourceMap;
-use rustc_span::{BytePos, Ident, Span, Symbol, SyntaxContext, kw, sym};
+use rustc_span::{BytePos, Ident, Macros20NormalizedIdent, Span, Symbol, SyntaxContext, kw, sym};
 use thin_vec::{ThinVec, thin_vec};
 use tracing::{debug, instrument};
 
@@ -320,8 +319,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         // Check if the target of the use for both bindings is the same.
         let duplicate = new_binding.res().opt_def_id() == old_binding.res().opt_def_id();
         let has_dummy_span = new_binding.span.is_dummy() || old_binding.span.is_dummy();
-        let from_item =
-            self.extern_prelude.get(&ident).is_none_or(|entry| entry.introduced_by_item);
+        let from_item = self
+            .extern_prelude
+            .get(&Macros20NormalizedIdent::new(ident))
+            .is_none_or(|entry| entry.introduced_by_item);
         // Only suggest removing an import if both bindings are to the same def, if both spans
         // aren't dummy spans. Further, if both bindings are imports, then the ident must have
         // been introduced by an item.
@@ -467,13 +468,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
     pub(crate) fn lint_if_path_starts_with_module(
         &mut self,
-        finalize: Option<Finalize>,
+        finalize: Finalize,
         path: &[Segment],
         second_binding: Option<NameBinding<'_>>,
     ) {
-        let Some(Finalize { node_id, root_span, .. }) = finalize else {
-            return;
-        };
+        let Finalize { node_id, root_span, .. } = finalize;
 
         let first_name = match path.get(0) {
             // In the 2018 edition this lint is a hard error, so nothing to do
@@ -530,7 +529,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         module.for_each_child(self, |_this, ident, _ns, binding| {
             let res = binding.res();
             if filter_fn(res) && ctxt.is_none_or(|ctxt| ctxt == ident.span.ctxt()) {
-                names.push(TypoSuggestion::typo_from_ident(ident, res));
+                names.push(TypoSuggestion::typo_from_ident(ident.0, res));
             }
         });
     }
@@ -1017,17 +1016,15 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         .emit()
     }
 
-    /// Lookup typo candidate in scope for a macro or import.
-    fn early_lookup_typo_candidate(
+    pub(crate) fn add_scope_set_candidates(
         &mut self,
+        suggestions: &mut Vec<TypoSuggestion>,
         scope_set: ScopeSet<'ra>,
         parent_scope: &ParentScope<'ra>,
-        ident: Ident,
+        ctxt: SyntaxContext,
         filter_fn: &impl Fn(Res) -> bool,
-    ) -> Option<TypoSuggestion> {
-        let mut suggestions = Vec::new();
-        let ctxt = ident.span.ctxt();
-        self.visit_scopes(scope_set, parent_scope, ctxt, |this, scope, use_prelude, _| {
+    ) {
+        self.cm().visit_scopes(scope_set, parent_scope, ctxt, |this, scope, use_prelude, _| {
             match scope {
                 Scope::DeriveHelpers(expn_id) => {
                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
@@ -1042,28 +1039,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     }
                 }
                 Scope::DeriveHelpersCompat => {
-                    let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelperCompat);
-                    if filter_fn(res) {
-                        for derive in parent_scope.derives {
-                            let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
-                            let Ok((Some(ext), _)) = this.resolve_macro_path(
-                                derive,
-                                Some(MacroKind::Derive),
-                                parent_scope,
-                                false,
-                                false,
-                                None,
-                                None,
-                            ) else {
-                                continue;
-                            };
-                            suggestions.extend(
-                                ext.helper_attrs
-                                    .iter()
-                                    .map(|name| TypoSuggestion::typo_from_name(*name, res)),
-                            );
-                        }
-                    }
+                    // Never recommend deprecated helper attributes.
                 }
                 Scope::MacroRules(macro_rules_scope) => {
                     if let MacroRulesScope::Binding(macro_rules_binding) = macro_rules_scope.get() {
@@ -1077,7 +1053,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     }
                 }
                 Scope::Module(module, _) => {
-                    this.add_module_candidates(module, &mut suggestions, filter_fn, None);
+                    this.add_module_candidates(module, suggestions, filter_fn, None);
                 }
                 Scope::MacroUsePrelude => {
                     suggestions.extend(this.macro_use_prelude.iter().filter_map(
@@ -1097,12 +1073,14 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         );
                     }
                 }
-                Scope::ExternPrelude => {
+                Scope::ExternPreludeItems => {
+                    // Add idents from both item and flag scopes.
                     suggestions.extend(this.extern_prelude.keys().filter_map(|ident| {
                         let res = Res::Def(DefKind::Mod, CRATE_DEF_ID.to_def_id());
-                        filter_fn(res).then_some(TypoSuggestion::typo_from_ident(*ident, res))
+                        filter_fn(res).then_some(TypoSuggestion::typo_from_ident(ident.0, res))
                     }));
                 }
+                Scope::ExternPreludeFlags => {}
                 Scope::ToolPrelude => {
                     let res = Res::NonMacroAttr(NonMacroAttrKind::Tool);
                     suggestions.extend(
@@ -1133,6 +1111,19 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
             None::<()>
         });
+    }
+
+    /// Lookup typo candidate in scope for a macro or import.
+    fn early_lookup_typo_candidate(
+        &mut self,
+        scope_set: ScopeSet<'ra>,
+        parent_scope: &ParentScope<'ra>,
+        ident: Ident,
+        filter_fn: &impl Fn(Res) -> bool,
+    ) -> Option<TypoSuggestion> {
+        let mut suggestions = Vec::new();
+        let ctxt = ident.span.ctxt();
+        self.add_scope_set_candidates(&mut suggestions, scope_set, parent_scope, ctxt, filter_fn);
 
         // Make sure error reporting is deterministic.
         suggestions.sort_by(|a, b| a.candidate.as_str().cmp(b.candidate.as_str()));
@@ -1246,7 +1237,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     };
                     segms.append(&mut path_segments.clone());
 
-                    segms.push(ast::PathSegment::from_ident(ident));
+                    segms.push(ast::PathSegment::from_ident(ident.0));
                     let path = Path { span: name_binding.span, segments: segms, tokens: None };
 
                     if child_accessible
@@ -1319,7 +1310,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 if let Some(def_id) = name_binding.res().module_like_def_id() {
                     // form the path
                     let mut path_segments = path_segments.clone();
-                    path_segments.push(ast::PathSegment::from_ident(ident));
+                    path_segments.push(ast::PathSegment::from_ident(ident.0));
 
                     let alias_import = if let NameBindingKind::Import { import, .. } =
                         name_binding.kind
@@ -1453,7 +1444,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 if needs_disambiguation {
                     crate_path.push(ast::PathSegment::path_root(rustc_span::DUMMY_SP));
                 }
-                crate_path.push(ast::PathSegment::from_ident(ident));
+                crate_path.push(ast::PathSegment::from_ident(ident.0));
 
                 suggestions.extend(self.lookup_import_candidates_from_module(
                     lookup_ident,
@@ -1480,7 +1471,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     ) {
         // Bring imported but unused `derive` macros into `macro_map` so we ensure they can be used
         // for suggestions.
-        self.visit_scopes(
+        self.cm().visit_scopes(
             ScopeSet::Macro(MacroKind::Derive),
             &parent_scope,
             ident.span.ctxt(),
@@ -1492,11 +1483,12 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     let Some(binding) = resolution.borrow().best_binding() else {
                         continue;
                     };
-                    let Res::Def(DefKind::Macro(MacroKind::Derive | MacroKind::Attr), def_id) =
-                        binding.res()
-                    else {
+                    let Res::Def(DefKind::Macro(kinds), def_id) = binding.res() else {
                         continue;
                     };
+                    if !kinds.intersects(MacroKinds::ATTR | MacroKinds::DERIVE) {
+                        continue;
+                    }
                     // By doing this all *imported* macros get added to the `macro_map` even if they
                     // are *unused*, which makes the later suggestions find them and work.
                     let _ = this.get_macro_by_def_id(def_id);
@@ -1505,7 +1497,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             },
         );
 
-        let is_expected = &|res: Res| res.macro_kind() == Some(macro_kind);
+        let is_expected =
+            &|res: Res| res.macro_kinds().is_some_and(|k| k.contains(macro_kind.into()));
         let suggestion = self.early_lookup_typo_candidate(
             ScopeSet::Macro(macro_kind),
             parent_scope,
@@ -1554,11 +1547,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         if let Some((def_id, unused_ident)) = unused_macro {
             let scope = self.local_macro_def_scopes[&def_id];
             let parent_nearest = parent_scope.module.nearest_parent_mod();
-            if Some(parent_nearest) == scope.opt_def_id() {
+            let unused_macro_kinds = self.local_macro_map[def_id].ext.macro_kinds();
+            if !unused_macro_kinds.contains(macro_kind.into()) {
                 match macro_kind {
                     MacroKind::Bang => {
-                        err.subdiagnostic(MacroDefinedLater { span: unused_ident.span });
-                        err.subdiagnostic(MacroSuggMovePosition { span: ident.span, ident });
+                        err.subdiagnostic(MacroRulesNot::Func { span: unused_ident.span, ident });
                     }
                     MacroKind::Attr => {
                         err.subdiagnostic(MacroRulesNot::Attr { span: unused_ident.span, ident });
@@ -1567,14 +1560,13 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         err.subdiagnostic(MacroRulesNot::Derive { span: unused_ident.span, ident });
                     }
                 }
-
                 return;
             }
-        }
-
-        if self.macro_names.contains(&ident.normalize_to_macros_2_0()) {
-            err.subdiagnostic(AddedMacroUse);
-            return;
+            if Some(parent_nearest) == scope.opt_def_id() {
+                err.subdiagnostic(MacroDefinedLater { span: unused_ident.span });
+                err.subdiagnostic(MacroSuggMovePosition { span: ident.span, ident });
+                return;
+            }
         }
 
         if ident.name == kw::Default
@@ -1589,7 +1581,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             });
         }
         for ns in [Namespace::MacroNS, Namespace::TypeNS, Namespace::ValueNS] {
-            let Ok(binding) = self.early_resolve_ident_in_lexical_scope(
+            let Ok(binding) = self.cm().early_resolve_ident_in_lexical_scope(
                 ident,
                 ScopeSet::All(ns),
                 parent_scope,
@@ -1602,13 +1594,18 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             };
 
             let desc = match binding.res() {
-                Res::Def(DefKind::Macro(MacroKind::Bang), _) => "a function-like macro".to_string(),
-                Res::Def(DefKind::Macro(MacroKind::Attr), _) | Res::NonMacroAttr(..) => {
+                Res::Def(DefKind::Macro(MacroKinds::BANG), _) => {
+                    "a function-like macro".to_string()
+                }
+                Res::Def(DefKind::Macro(MacroKinds::ATTR), _) | Res::NonMacroAttr(..) => {
                     format!("an attribute: `#[{ident}]`")
                 }
-                Res::Def(DefKind::Macro(MacroKind::Derive), _) => {
+                Res::Def(DefKind::Macro(MacroKinds::DERIVE), _) => {
                     format!("a derive macro: `#[derive({ident})]`")
                 }
+                Res::Def(DefKind::Macro(kinds), _) => {
+                    format!("{} {}", kinds.article(), kinds.descr())
+                }
                 Res::ToolMod => {
                     // Don't confuse the user with tool modules.
                     continue;
@@ -1645,6 +1642,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             err.subdiagnostic(note);
             return;
         }
+
+        if self.macro_names.contains(&ident.normalize_to_macros_2_0()) {
+            err.subdiagnostic(AddedMacroUse);
+            return;
+        }
     }
 
     /// Given an attribute macro that failed to be resolved, look for `derive` macros that could
@@ -1863,14 +1865,20 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         }
     }
 
-    fn ambiguity_diagnostics(&self, ambiguity_error: &AmbiguityError<'_>) -> AmbiguityErrorDiag {
+    fn ambiguity_diagnostics(&self, ambiguity_error: &AmbiguityError<'ra>) -> AmbiguityErrorDiag {
         let AmbiguityError { kind, ident, b1, b2, misc1, misc2, .. } = *ambiguity_error;
+        let extern_prelude_ambiguity = || {
+            self.extern_prelude.get(&Macros20NormalizedIdent::new(ident)).is_some_and(|entry| {
+                entry.item_binding == Some(b1) && entry.flag_binding.get() == Some(b2)
+            })
+        };
         let (b1, b2, misc1, misc2, swapped) = if b2.span.is_dummy() && !b1.span.is_dummy() {
             // We have to print the span-less alternative first, otherwise formatting looks bad.
             (b2, b1, misc2, misc1, true)
         } else {
             (b1, b2, misc1, misc2, false)
         };
+
         let could_refer_to = |b: NameBinding<'_>, misc: AmbiguityErrorMisc, also: &str| {
             let what = self.binding_description(b, ident, misc == AmbiguityErrorMisc::FromPrelude);
             let note_msg = format!("`{ident}` could{also} refer to {what}");
@@ -1886,7 +1894,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     "consider adding an explicit import of `{ident}` to disambiguate"
                 ))
             }
-            if b.is_extern_crate() && ident.span.at_least_rust_2018() {
+            if b.is_extern_crate() && ident.span.at_least_rust_2018() && !extern_prelude_ambiguity()
+            {
                 help_msgs.push(format!("use `::{ident}` to refer to this {thing} unambiguously"))
             }
             match misc {
@@ -1944,8 +1953,15 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     }
 
     fn report_privacy_error(&mut self, privacy_error: &PrivacyError<'ra>) {
-        let PrivacyError { ident, binding, outermost_res, parent_scope, single_nested, dedup_span } =
-            *privacy_error;
+        let PrivacyError {
+            ident,
+            binding,
+            outermost_res,
+            parent_scope,
+            single_nested,
+            dedup_span,
+            ref source,
+        } = *privacy_error;
 
         let res = binding.res();
         let ctor_fields_span = self.ctor_fields_span(binding);
@@ -1961,6 +1977,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         let mut err =
             self.dcx().create_err(errors::IsPrivate { span: ident.span, ident_descr, ident });
 
+        self.mention_default_field_values(source, ident, &mut err);
+
         let mut not_publicly_reexported = false;
         if let Some((this_res, outer_ident)) = outermost_res {
             let import_suggestions = self.lookup_import_candidates(
@@ -2142,6 +2160,85 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         err.emit();
     }
 
+    /// When a private field is being set that has a default field value, we suggest using `..` and
+    /// setting the value of that field implicitly with its default.
+    ///
+    /// If we encounter code like
+    /// ```text
+    /// struct Priv;
+    /// pub struct S {
+    ///     pub field: Priv = Priv,
+    /// }
+    /// ```
+    /// which is used from a place where `Priv` isn't accessible
+    /// ```text
+    /// let _ = S { field: m::Priv1 {} };
+    /// //                    ^^^^^ private struct
+    /// ```
+    /// we will suggest instead using the `default_field_values` syntax instead:
+    /// ```text
+    /// let _ = S { .. };
+    /// ```
+    fn mention_default_field_values(
+        &self,
+        source: &Option<ast::Expr>,
+        ident: Ident,
+        err: &mut Diag<'_>,
+    ) {
+        let Some(expr) = source else { return };
+        let ast::ExprKind::Struct(struct_expr) = &expr.kind else { return };
+        // We don't have to handle type-relative paths because they're forbidden in ADT
+        // expressions, but that would change with `#[feature(more_qualified_paths)]`.
+        let Some(segment) = struct_expr.path.segments.last() else { return };
+        let Some(partial_res) = self.partial_res_map.get(&segment.id) else { return };
+        let Some(Res::Def(_, def_id)) = partial_res.full_res() else {
+            return;
+        };
+        let Some(default_fields) = self.field_defaults(def_id) else { return };
+        if struct_expr.fields.is_empty() {
+            return;
+        }
+        let last_span = struct_expr.fields.iter().last().unwrap().span;
+        let mut iter = struct_expr.fields.iter().peekable();
+        let mut prev: Option<Span> = None;
+        while let Some(field) = iter.next() {
+            if field.expr.span.overlaps(ident.span) {
+                err.span_label(field.ident.span, "while setting this field");
+                if default_fields.contains(&field.ident.name) {
+                    let sugg = if last_span == field.span {
+                        vec![(field.span, "..".to_string())]
+                    } else {
+                        vec![
+                            (
+                                // Account for trailing commas and ensure we remove them.
+                                match (prev, iter.peek()) {
+                                    (_, Some(next)) => field.span.with_hi(next.span.lo()),
+                                    (Some(prev), _) => field.span.with_lo(prev.hi()),
+                                    (None, None) => field.span,
+                                },
+                                String::new(),
+                            ),
+                            (last_span.shrink_to_hi(), ", ..".to_string()),
+                        ]
+                    };
+                    err.multipart_suggestion_verbose(
+                        format!(
+                            "the type `{ident}` of field `{}` is private, but you can construct \
+                             the default value defined for it in `{}` using `..` in the struct \
+                             initializer expression",
+                            field.ident,
+                            self.tcx.item_name(def_id),
+                        ),
+                        sugg,
+                        Applicability::MachineApplicable,
+                    );
+                    break;
+                }
+            }
+            prev = Some(field.span);
+        }
+    }
+
     pub(crate) fn find_similarly_named_module_or_crate(
         &self,
         ident: Symbol,
@@ -2269,16 +2366,17 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             if ns == TypeNS || ns == ValueNS {
                 let ns_to_try = if ns == TypeNS { ValueNS } else { TypeNS };
                 let binding = if let Some(module) = module {
-                    self.resolve_ident_in_module(
-                        module,
-                        ident,
-                        ns_to_try,
-                        parent_scope,
-                        None,
-                        ignore_binding,
-                        ignore_import,
-                    )
-                    .ok()
+                    self.cm()
+                        .resolve_ident_in_module(
+                            module,
+                            ident,
+                            ns_to_try,
+                            parent_scope,
+                            None,
+                            ignore_binding,
+                            ignore_import,
+                        )
+                        .ok()
                 } else if let Some(ribs) = ribs
                     && let Some(TypeNS | ValueNS) = opt_ns
                 {
@@ -2296,16 +2394,17 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         _ => None,
                     }
                 } else {
-                    self.early_resolve_ident_in_lexical_scope(
-                        ident,
-                        ScopeSet::All(ns_to_try),
-                        parent_scope,
-                        None,
-                        false,
-                        ignore_binding,
-                        ignore_import,
-                    )
-                    .ok()
+                    self.cm()
+                        .early_resolve_ident_in_lexical_scope(
+                            ident,
+                            ScopeSet::All(ns_to_try),
+                            parent_scope,
+                            None,
+                            false,
+                            ignore_binding,
+                            ignore_import,
+                        )
+                        .ok()
                 };
                 if let Some(binding) = binding {
                     msg = format!(
@@ -2399,7 +2498,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     },
                 )
             });
-            if let Ok(binding) = self.early_resolve_ident_in_lexical_scope(
+            if let Ok(binding) = self.cm().early_resolve_ident_in_lexical_scope(
                 ident,
                 ScopeSet::All(ValueNS),
                 parent_scope,
@@ -2529,7 +2628,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     ) -> Option<(Vec<Segment>, Option<String>)> {
         // Replace first ident with `self` and check if that is valid.
         path[0].ident.name = kw::SelfLower;
-        let result = self.maybe_resolve_path(&path, None, parent_scope, None);
+        let result = self.cm().maybe_resolve_path(&path, None, parent_scope, None);
         debug!(?path, ?result);
         if let PathResult::Module(..) = result { Some((path, None)) } else { None }
     }
@@ -2549,7 +2648,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     ) -> Option<(Vec<Segment>, Option<String>)> {
         // Replace first ident with `crate` and check if that is valid.
         path[0].ident.name = kw::Crate;
-        let result = self.maybe_resolve_path(&path, None, parent_scope, None);
+        let result = self.cm().maybe_resolve_path(&path, None, parent_scope, None);
         debug!(?path, ?result);
         if let PathResult::Module(..) = result {
             Some((
@@ -2581,7 +2680,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     ) -> Option<(Vec<Segment>, Option<String>)> {
         // Replace first ident with `crate` and check if that is valid.
         path[0].ident.name = kw::Super;
-        let result = self.maybe_resolve_path(&path, None, parent_scope, None);
+        let result = self.cm().maybe_resolve_path(&path, None, parent_scope, None);
         debug!(?path, ?result);
         if let PathResult::Module(..) = result { Some((path, None)) } else { None }
     }
@@ -2616,7 +2715,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         for name in extern_crate_names.into_iter() {
             // Replace first ident with a crate name and check if that is valid.
             path[0].ident.name = name;
-            let result = self.maybe_resolve_path(&path, None, parent_scope, None);
+            let result = self.cm().maybe_resolve_path(&path, None, parent_scope, None);
             debug!(?path, ?name, ?result);
             if let PathResult::Module(..) = result {
                 return Some((path, None));
@@ -2659,9 +2758,12 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
         let binding_key = BindingKey::new(ident, MacroNS);
         let binding = self.resolution(crate_module, binding_key)?.binding()?;
-        let Res::Def(DefKind::Macro(MacroKind::Bang), _) = binding.res() else {
+        let Res::Def(DefKind::Macro(kinds), _) = binding.res() else {
             return None;
         };
+        if !kinds.contains(MacroKinds::BANG) {
+            return None;
+        }
         let module_name = crate_module.kind.name().unwrap_or(kw::Crate);
         let import_snippet = match import.kind {
             ImportKind::Single { source, target, .. } if source != target => {
@@ -3345,7 +3447,7 @@ impl<'tcx> visit::Visitor<'tcx> for UsePlacementFinder {
     }
 }
 
-fn search_for_any_use_in_items(items: &[P<ast::Item>]) -> Option<Span> {
+fn search_for_any_use_in_items(items: &[Box<ast::Item>]) -> Option<Span> {
     for item in items {
         if let ItemKind::Use(..) = item.kind
             && is_span_suitable_for_use_injection(item.span)
diff --git a/compiler/rustc_resolve/src/errors.rs b/compiler/rustc_resolve/src/errors.rs
index 2747ba135ed..a1d62ba7a68 100644
--- a/compiler/rustc_resolve/src/errors.rs
+++ b/compiler/rustc_resolve/src/errors.rs
@@ -672,6 +672,12 @@ pub(crate) struct MacroSuggMovePosition {
 
 #[derive(Subdiagnostic)]
 pub(crate) enum MacroRulesNot {
+    #[label(resolve_macro_cannot_use_as_fn_like)]
+    Func {
+        #[primary_span]
+        span: Span,
+        ident: Ident,
+    },
     #[label(resolve_macro_cannot_use_as_attr)]
     Attr {
         #[primary_span]
diff --git a/compiler/rustc_resolve/src/ident.rs b/compiler/rustc_resolve/src/ident.rs
index f5bc46bf053..c1b3aff4e69 100644
--- a/compiler/rustc_resolve/src/ident.rs
+++ b/compiler/rustc_resolve/src/ident.rs
@@ -2,7 +2,7 @@ use Determinacy::*;
 use Namespace::*;
 use rustc_ast::{self as ast, NodeId};
 use rustc_errors::ErrorGuaranteed;
-use rustc_hir::def::{DefKind, Namespace, NonMacroAttrKind, PartialRes, PerNS};
+use rustc_hir::def::{DefKind, MacroKinds, Namespace, NonMacroAttrKind, PartialRes, PerNS};
 use rustc_middle::bug;
 use rustc_session::lint::BuiltinLintDiag;
 use rustc_session::lint::builtin::PROC_MACRO_DERIVE_RESOLUTION_FALLBACK;
@@ -16,10 +16,10 @@ use crate::imports::{Import, NameResolution};
 use crate::late::{ConstantHasGenerics, NoConstantGenericsReason, PathSource, Rib, RibKind};
 use crate::macros::{MacroRulesScope, sub_namespace_match};
 use crate::{
-    AmbiguityError, AmbiguityErrorMisc, AmbiguityKind, BindingKey, Determinacy, Finalize,
-    ImportKind, LexicalScopeBinding, Module, ModuleKind, ModuleOrUniformRoot, NameBinding,
-    NameBindingKind, ParentScope, PathResult, PrivacyError, Res, ResolutionError, Resolver, Scope,
-    ScopeSet, Segment, Used, Weak, errors,
+    AmbiguityError, AmbiguityErrorMisc, AmbiguityKind, BindingKey, CmResolver, Determinacy,
+    Finalize, ImportKind, LexicalScopeBinding, Module, ModuleKind, ModuleOrUniformRoot,
+    NameBinding, NameBindingKind, ParentScope, PathResult, PrivacyError, Res, ResolutionError,
+    Resolver, Scope, ScopeSet, Segment, Used, Weak, errors,
 };
 
 #[derive(Copy, Clone)]
@@ -44,12 +44,17 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     /// A generic scope visitor.
     /// Visits scopes in order to resolve some identifier in them or perform other actions.
     /// If the callback returns `Some` result, we stop visiting scopes and return it.
-    pub(crate) fn visit_scopes<T>(
-        &mut self,
+    pub(crate) fn visit_scopes<'r, T>(
+        mut self: CmResolver<'r, 'ra, 'tcx>,
         scope_set: ScopeSet<'ra>,
         parent_scope: &ParentScope<'ra>,
         ctxt: SyntaxContext,
-        mut visitor: impl FnMut(&mut Self, Scope<'ra>, UsePrelude, SyntaxContext) -> Option<T>,
+        mut visitor: impl FnMut(
+            &mut CmResolver<'r, 'ra, 'tcx>,
+            Scope<'ra>,
+            UsePrelude,
+            SyntaxContext,
+        ) -> Option<T>,
     ) -> Option<T> {
         // General principles:
         // 1. Not controlled (user-defined) names should have higher priority than controlled names
@@ -97,6 +102,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             ScopeSet::All(ns)
             | ScopeSet::ModuleAndExternPrelude(ns, _)
             | ScopeSet::Late(ns, ..) => (ns, None),
+            ScopeSet::ExternPrelude => (TypeNS, None),
             ScopeSet::Macro(macro_kind) => (MacroNS, Some(macro_kind)),
         };
         let module = match scope_set {
@@ -106,8 +112,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             _ => parent_scope.module.nearest_item_scope(),
         };
         let module_and_extern_prelude = matches!(scope_set, ScopeSet::ModuleAndExternPrelude(..));
+        let extern_prelude = matches!(scope_set, ScopeSet::ExternPrelude);
         let mut scope = match ns {
             _ if module_and_extern_prelude => Scope::Module(module, None),
+            _ if extern_prelude => Scope::ExternPreludeItems,
             TypeNS | ValueNS => Scope::Module(module, None),
             MacroNS => Scope::DeriveHelpers(parent_scope.expansion),
         };
@@ -138,7 +146,9 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 Scope::Module(..) => true,
                 Scope::MacroUsePrelude => use_prelude || rust_2015,
                 Scope::BuiltinAttrs => true,
-                Scope::ExternPrelude => use_prelude || module_and_extern_prelude,
+                Scope::ExternPreludeItems | Scope::ExternPreludeFlags => {
+                    use_prelude || module_and_extern_prelude || extern_prelude
+                }
                 Scope::ToolPrelude => use_prelude,
                 Scope::StdLibPrelude => use_prelude || ns == MacroNS,
                 Scope::BuiltinTypes => true,
@@ -146,7 +156,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
             if visit {
                 let use_prelude = if use_prelude { UsePrelude::Yes } else { UsePrelude::No };
-                if let break_result @ Some(..) = visitor(self, scope, use_prelude, ctxt) {
+                if let break_result @ Some(..) = visitor(&mut self, scope, use_prelude, ctxt) {
                     return break_result;
                 }
             }
@@ -177,7 +187,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 Scope::Module(..) if module_and_extern_prelude => match ns {
                     TypeNS => {
                         ctxt.adjust(ExpnId::root());
-                        Scope::ExternPrelude
+                        Scope::ExternPreludeItems
                     }
                     ValueNS | MacroNS => break,
                 },
@@ -194,7 +204,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         None => {
                             ctxt.adjust(ExpnId::root());
                             match ns {
-                                TypeNS => Scope::ExternPrelude,
+                                TypeNS => Scope::ExternPreludeItems,
                                 ValueNS => Scope::StdLibPrelude,
                                 MacroNS => Scope::MacroUsePrelude,
                             }
@@ -203,8 +213,9 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 }
                 Scope::MacroUsePrelude => Scope::StdLibPrelude,
                 Scope::BuiltinAttrs => break, // nowhere else to search
-                Scope::ExternPrelude if module_and_extern_prelude => break,
-                Scope::ExternPrelude => Scope::ToolPrelude,
+                Scope::ExternPreludeItems => Scope::ExternPreludeFlags,
+                Scope::ExternPreludeFlags if module_and_extern_prelude || extern_prelude => break,
+                Scope::ExternPreludeFlags => Scope::ToolPrelude,
                 Scope::ToolPrelude => Scope::StdLibPrelude,
                 Scope::StdLibPrelude => match ns {
                     TypeNS => Scope::BuiltinTypes,
@@ -254,7 +265,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         {
             let ext = &self.get_macro_by_def_id(def_id).ext;
             if ext.builtin_name.is_none()
-                && ext.macro_kind() == MacroKind::Derive
+                && ext.macro_kinds() == MacroKinds::DERIVE
                 && parent.expansion.outer_expn_is_descendant_of(*ctxt)
             {
                 return Some((parent, derive_fallback_lint_id));
@@ -307,7 +318,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         let normalized_ident = Ident { span: normalized_span, ..ident };
 
         // Walk backwards up the ribs in scope.
-        let mut module = self.graph_root;
         for (i, rib) in ribs.iter().enumerate().rev() {
             debug!("walk rib\n{:?}", rib.bindings);
             // Use the rib kind to determine whether we are resolving parameters
@@ -323,50 +333,47 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     *original_rib_ident_def,
                     ribs,
                 )));
+            } else if let RibKind::Block(Some(module)) = rib.kind
+                && let Ok(binding) = self.cm().resolve_ident_in_module_unadjusted(
+                    ModuleOrUniformRoot::Module(module),
+                    ident,
+                    ns,
+                    parent_scope,
+                    Shadowing::Unrestricted,
+                    finalize.map(|finalize| Finalize { used: Used::Scope, ..finalize }),
+                    ignore_binding,
+                    None,
+                )
+            {
+                // The ident resolves to an item in a block.
+                return Some(LexicalScopeBinding::Item(binding));
+            } else if let RibKind::Module(module) = rib.kind {
+                // Encountered a module item, abandon ribs and look into that module and preludes.
+                return self
+                    .cm()
+                    .early_resolve_ident_in_lexical_scope(
+                        orig_ident,
+                        ScopeSet::Late(ns, module, finalize.map(|finalize| finalize.node_id)),
+                        parent_scope,
+                        finalize,
+                        finalize.is_some(),
+                        ignore_binding,
+                        None,
+                    )
+                    .ok()
+                    .map(LexicalScopeBinding::Item);
             }
 
-            module = match rib.kind {
-                RibKind::Module(module) => module,
-                RibKind::MacroDefinition(def) if def == self.macro_def(ident.span.ctxt()) => {
-                    // If an invocation of this macro created `ident`, give up on `ident`
-                    // and switch to `ident`'s source from the macro definition.
-                    ident.span.remove_mark();
-                    continue;
-                }
-                _ => continue,
-            };
-
-            match module.kind {
-                ModuleKind::Block => {} // We can see through blocks
-                _ => break,
-            }
-
-            let item = self.resolve_ident_in_module_unadjusted(
-                ModuleOrUniformRoot::Module(module),
-                ident,
-                ns,
-                parent_scope,
-                Shadowing::Unrestricted,
-                finalize.map(|finalize| Finalize { used: Used::Scope, ..finalize }),
-                ignore_binding,
-                None,
-            );
-            if let Ok(binding) = item {
-                // The ident resolves to an item.
-                return Some(LexicalScopeBinding::Item(binding));
+            if let RibKind::MacroDefinition(def) = rib.kind
+                && def == self.macro_def(ident.span.ctxt())
+            {
+                // If an invocation of this macro created `ident`, give up on `ident`
+                // and switch to `ident`'s source from the macro definition.
+                ident.span.remove_mark();
             }
         }
-        self.early_resolve_ident_in_lexical_scope(
-            orig_ident,
-            ScopeSet::Late(ns, module, finalize.map(|finalize| finalize.node_id)),
-            parent_scope,
-            finalize,
-            finalize.is_some(),
-            ignore_binding,
-            None,
-        )
-        .ok()
-        .map(LexicalScopeBinding::Item)
+
+        unreachable!()
     }
 
     /// Resolve an identifier in lexical scope.
@@ -375,8 +382,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     /// The function is used for resolving initial segments of macro paths (e.g., `foo` in
     /// `foo::bar!();` or `foo!();`) and also for import paths on 2018 edition.
     #[instrument(level = "debug", skip(self))]
-    pub(crate) fn early_resolve_ident_in_lexical_scope(
-        &mut self,
+    pub(crate) fn early_resolve_ident_in_lexical_scope<'r>(
+        self: CmResolver<'r, 'ra, 'tcx>,
         orig_ident: Ident,
         scope_set: ScopeSet<'ra>,
         parent_scope: &ParentScope<'ra>,
@@ -407,6 +414,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             ScopeSet::All(ns)
             | ScopeSet::ModuleAndExternPrelude(ns, _)
             | ScopeSet::Late(ns, ..) => (ns, None),
+            ScopeSet::ExternPrelude => (TypeNS, None),
             ScopeSet::Macro(macro_kind) => (MacroNS, Some(macro_kind)),
         };
 
@@ -423,6 +431,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         // to detect potential ambiguities.
         let mut innermost_result: Option<(NameBinding<'_>, Flags)> = None;
         let mut determinacy = Determinacy::Determined;
+        // Shadowed bindings don't need to be marked as used or non-speculatively loaded.
+        macro finalize_scope() {
+            if innermost_result.is_none() { finalize } else { None }
+        }
 
         // Go through all the scopes and try to resolve the name.
         let break_result = self.visit_scopes(
@@ -442,17 +454,12 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         }
                     }
                     Scope::DeriveHelpersCompat => {
-                        // FIXME: Try running this logic earlier, to allocate name bindings for
-                        // legacy derive helpers when creating an attribute invocation with
-                        // following derives. Legacy derive helpers are not common, so it shouldn't
-                        // affect performance. It should also allow to remove the `derives`
-                        // component from `ParentScope`.
                         let mut result = Err(Determinacy::Determined);
                         for derive in parent_scope.derives {
                             let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
-                            match this.resolve_macro_path(
+                            match this.reborrow().resolve_macro_path(
                                 derive,
-                                Some(MacroKind::Derive),
+                                MacroKind::Derive,
                                 parent_scope,
                                 true,
                                 force,
@@ -488,7 +495,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         _ => Err(Determinacy::Determined),
                     },
                     Scope::Module(module, derive_fallback_lint_id) => {
-                        let (adjusted_parent_scope, finalize) =
+                        // FIXME: use `finalize_scope` here.
+                        let (adjusted_parent_scope, adjusted_finalize) =
                             if matches!(scope_set, ScopeSet::ModuleAndExternPrelude(..)) {
                                 (parent_scope, finalize)
                             } else {
@@ -497,7 +505,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                                     finalize.map(|f| Finalize { used: Used::Scope, ..f }),
                                 )
                             };
-                        let binding = this.resolve_ident_in_module_unadjusted(
+                        let binding = this.reborrow().resolve_ident_in_module_unadjusted(
                             ModuleOrUniformRoot::Module(module),
                             ident,
                             ns,
@@ -507,14 +515,14 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                             } else {
                                 Shadowing::Restricted
                             },
-                            finalize,
+                            adjusted_finalize,
                             ignore_binding,
                             ignore_import,
                         );
                         match binding {
                             Ok(binding) => {
                                 if let Some(lint_id) = derive_fallback_lint_id {
-                                    this.lint_buffer.buffer_lint(
+                                    this.get_mut().lint_buffer.buffer_lint(
                                         PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
                                         lint_id,
                                         orig_ident.span,
@@ -555,14 +563,21 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         Some(binding) => Ok((*binding, Flags::empty())),
                         None => Err(Determinacy::Determined),
                     },
-                    Scope::ExternPrelude => {
-                        match this.extern_prelude_get(ident, finalize.is_some()) {
+                    Scope::ExternPreludeItems => {
+                        // FIXME: use `finalize_scope` here.
+                        match this.reborrow().extern_prelude_get_item(ident, finalize.is_some()) {
                             Some(binding) => Ok((binding, Flags::empty())),
                             None => Err(Determinacy::determined(
                                 this.graph_root.unexpanded_invocations.borrow().is_empty(),
                             )),
                         }
                     }
+                    Scope::ExternPreludeFlags => {
+                        match this.extern_prelude_get_flag(ident, finalize_scope!().is_some()) {
+                            Some(binding) => Ok((binding, Flags::empty())),
+                            None => Err(Determinacy::Determined),
+                        }
+                    }
                     Scope::ToolPrelude => match this.registered_tool_bindings.get(&ident) {
                         Some(binding) => Ok((*binding, Flags::empty())),
                         None => Err(Determinacy::Determined),
@@ -570,7 +585,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     Scope::StdLibPrelude => {
                         let mut result = Err(Determinacy::Determined);
                         if let Some(prelude) = this.prelude
-                            && let Ok(binding) = this.resolve_ident_in_module_unadjusted(
+                            && let Ok(binding) = this.reborrow().resolve_ident_in_module_unadjusted(
                                 ModuleOrUniformRoot::Module(prelude),
                                 ident,
                                 ns,
@@ -593,8 +608,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                             if matches!(ident.name, sym::f16)
                                 && !this.tcx.features().f16()
                                 && !ident.span.allows_unstable(sym::f16)
-                                && finalize.is_some()
-                                && innermost_result.is_none()
+                                && finalize_scope!().is_some()
                             {
                                 feature_err(
                                     this.tcx.sess,
@@ -607,8 +621,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                             if matches!(ident.name, sym::f128)
                                 && !this.tcx.features().f128()
                                 && !ident.span.allows_unstable(sym::f128)
-                                && finalize.is_some()
-                                && innermost_result.is_none()
+                                && finalize_scope!().is_some()
                             {
                                 feature_err(
                                     this.tcx.sess,
@@ -625,9 +638,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 };
 
                 match result {
-                    Ok((binding, flags))
-                        if sub_namespace_match(binding.macro_kind(), macro_kind) =>
-                    {
+                    Ok((binding, flags)) => {
+                        if !sub_namespace_match(binding.macro_kinds(), macro_kind) {
+                            return None;
+                        }
+
                         if finalize.is_none() || matches!(scope_set, ScopeSet::Late(..)) {
                             return Some(Ok(binding));
                         }
@@ -687,7 +702,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                                             AmbiguityErrorMisc::None
                                         }
                                     };
-                                    this.ambiguity_errors.push(AmbiguityError {
+                                    this.get_mut().ambiguity_errors.push(AmbiguityError {
                                         kind,
                                         ident: orig_ident,
                                         b1: innermost_binding,
@@ -704,7 +719,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                             innermost_result = Some((binding, flags));
                         }
                     }
-                    Ok(..) | Err(Determinacy::Determined) => {}
+                    Err(Determinacy::Determined) => {}
                     Err(Determinacy::Undetermined) => determinacy = Determinacy::Undetermined,
                 }
 
@@ -725,8 +740,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     }
 
     #[instrument(level = "debug", skip(self))]
-    pub(crate) fn maybe_resolve_ident_in_module(
-        &mut self,
+    pub(crate) fn maybe_resolve_ident_in_module<'r>(
+        self: CmResolver<'r, 'ra, 'tcx>,
         module: ModuleOrUniformRoot<'ra>,
         ident: Ident,
         ns: Namespace,
@@ -738,8 +753,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     }
 
     #[instrument(level = "debug", skip(self))]
-    pub(crate) fn resolve_ident_in_module(
-        &mut self,
+    pub(crate) fn resolve_ident_in_module<'r>(
+        self: CmResolver<'r, 'ra, 'tcx>,
         module: ModuleOrUniformRoot<'ra>,
         mut ident: Ident,
         ns: Namespace,
@@ -776,12 +791,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             ignore_import,
         )
     }
-
     /// Attempts to resolve `ident` in namespaces `ns` of `module`.
     /// Invariant: if `finalize` is `Some`, expansion and import resolution must be complete.
     #[instrument(level = "debug", skip(self))]
-    fn resolve_ident_in_module_unadjusted(
-        &mut self,
+    fn resolve_ident_in_module_unadjusted<'r>(
+        mut self: CmResolver<'r, 'ra, 'tcx>,
         module: ModuleOrUniformRoot<'ra>,
         ident: Ident,
         ns: Namespace,
@@ -812,13 +826,17 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 assert_eq!(shadowing, Shadowing::Unrestricted);
                 return if ns != TypeNS {
                     Err((Determined, Weak::No))
-                } else if let Some(binding) = self.extern_prelude_get(ident, finalize.is_some()) {
-                    Ok(binding)
-                } else if !self.graph_root.unexpanded_invocations.borrow().is_empty() {
-                    // Macro-expanded `extern crate` items can add names to extern prelude.
-                    Err((Undetermined, Weak::No))
                 } else {
-                    Err((Determined, Weak::No))
+                    let binding = self.early_resolve_ident_in_lexical_scope(
+                        ident,
+                        ScopeSet::ExternPrelude,
+                        parent_scope,
+                        finalize,
+                        finalize.is_some(),
+                        ignore_binding,
+                        ignore_import,
+                    );
+                    return binding.map_err(|determinacy| (determinacy, Weak::No));
                 };
             }
             ModuleOrUniformRoot::CurrentScope => {
@@ -865,7 +883,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             .find_map(|binding| if binding == ignore_binding { None } else { binding });
 
         if let Some(finalize) = finalize {
-            return self.finalize_module_binding(
+            return self.get_mut().finalize_module_binding(
                 ident,
                 binding,
                 if resolution.non_glob_binding.is_some() { resolution.glob_binding } else { None },
@@ -875,7 +893,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             );
         }
 
-        let check_usable = |this: &Self, binding: NameBinding<'ra>| {
+        let check_usable = |this: CmResolver<'r, 'ra, 'tcx>, binding: NameBinding<'ra>| {
             let usable = this.is_accessible_from(binding.vis, parent_scope.module);
             if usable { Ok(binding) } else { Err((Determined, Weak::No)) }
         };
@@ -891,7 +909,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
         // Check if one of single imports can still define the name,
         // if it can then our result is not determined and can be invalidated.
-        if self.single_import_can_define_name(
+        if self.reborrow().single_import_can_define_name(
             &resolution,
             binding,
             ns,
@@ -962,7 +980,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 Some(None) => {}
                 None => continue,
             };
-            let result = self.resolve_ident_in_module_unadjusted(
+            let result = self.reborrow().resolve_ident_in_module_unadjusted(
                 ModuleOrUniformRoot::Module(module),
                 ident,
                 ns,
@@ -1010,6 +1028,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     binding,
                     dedup_span: path_span,
                     outermost_res: None,
+                    source: None,
                     parent_scope: *parent_scope,
                     single_nested: path_span != root_span,
                 });
@@ -1049,8 +1068,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
     // Checks if a single import can define the `Ident` corresponding to `binding`.
     // This is used to check whether we can definitively accept a glob as a resolution.
-    fn single_import_can_define_name(
-        &mut self,
+    fn single_import_can_define_name<'r>(
+        mut self: CmResolver<'r, 'ra, 'tcx>,
         resolution: &NameResolution<'ra>,
         binding: Option<NameBinding<'ra>>,
         ns: Namespace,
@@ -1086,7 +1105,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 }
             }
 
-            match self.resolve_ident_in_module(
+            match self.reborrow().resolve_ident_in_module(
                 module,
                 *source,
                 ns,
@@ -1147,6 +1166,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 for rib in ribs {
                     match rib.kind {
                         RibKind::Normal
+                        | RibKind::Block(..)
                         | RibKind::FnOrCoroutine
                         | RibKind::Module(..)
                         | RibKind::MacroDefinition(..)
@@ -1239,6 +1259,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 for rib in ribs {
                     let (has_generic_params, def_kind) = match rib.kind {
                         RibKind::Normal
+                        | RibKind::Block(..)
                         | RibKind::FnOrCoroutine
                         | RibKind::Module(..)
                         | RibKind::MacroDefinition(..)
@@ -1332,6 +1353,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 for rib in ribs {
                     let (has_generic_params, def_kind) = match rib.kind {
                         RibKind::Normal
+                        | RibKind::Block(..)
                         | RibKind::FnOrCoroutine
                         | RibKind::Module(..)
                         | RibKind::MacroDefinition(..)
@@ -1409,19 +1431,27 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     }
 
     #[instrument(level = "debug", skip(self))]
-    pub(crate) fn maybe_resolve_path(
-        &mut self,
+    pub(crate) fn maybe_resolve_path<'r>(
+        self: CmResolver<'r, 'ra, 'tcx>,
         path: &[Segment],
         opt_ns: Option<Namespace>, // `None` indicates a module path in import
         parent_scope: &ParentScope<'ra>,
         ignore_import: Option<Import<'ra>>,
     ) -> PathResult<'ra> {
-        self.resolve_path_with_ribs(path, opt_ns, parent_scope, None, None, None, ignore_import)
+        self.resolve_path_with_ribs(
+            path,
+            opt_ns,
+            parent_scope,
+            None,
+            None,
+            None,
+            None,
+            ignore_import,
+        )
     }
-
     #[instrument(level = "debug", skip(self))]
-    pub(crate) fn resolve_path(
-        &mut self,
+    pub(crate) fn resolve_path<'r>(
+        self: CmResolver<'r, 'ra, 'tcx>,
         path: &[Segment],
         opt_ns: Option<Namespace>, // `None` indicates a module path in import
         parent_scope: &ParentScope<'ra>,
@@ -1433,6 +1463,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             path,
             opt_ns,
             parent_scope,
+            None,
             finalize,
             None,
             ignore_binding,
@@ -1440,11 +1471,12 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         )
     }
 
-    pub(crate) fn resolve_path_with_ribs(
-        &mut self,
+    pub(crate) fn resolve_path_with_ribs<'r>(
+        mut self: CmResolver<'r, 'ra, 'tcx>,
         path: &[Segment],
         opt_ns: Option<Namespace>, // `None` indicates a module path in import
         parent_scope: &ParentScope<'ra>,
+        source: Option<PathSource<'_, '_, '_>>,
         finalize: Option<Finalize>,
         ribs: Option<&PerNS<Vec<Rib<'ra>>>>,
         ignore_binding: Option<NameBinding<'ra>>,
@@ -1457,18 +1489,23 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
         // We'll provide more context to the privacy errors later, up to `len`.
         let privacy_errors_len = self.privacy_errors.len();
+        fn record_segment_res<'r, 'ra, 'tcx>(
+            mut this: CmResolver<'r, 'ra, 'tcx>,
+            finalize: Option<Finalize>,
+            res: Res,
+            id: Option<NodeId>,
+        ) {
+            if finalize.is_some()
+                && let Some(id) = id
+                && !this.partial_res_map.contains_key(&id)
+            {
+                assert!(id != ast::DUMMY_NODE_ID, "Trying to resolve dummy id");
+                this.get_mut().record_partial_res(id, PartialRes::new(res));
+            }
+        }
 
         for (segment_idx, &Segment { ident, id, .. }) in path.iter().enumerate() {
             debug!("resolve_path ident {} {:?} {:?}", segment_idx, ident, id);
-            let record_segment_res = |this: &mut Self, res| {
-                if finalize.is_some()
-                    && let Some(id) = id
-                    && !this.partial_res_map.contains_key(&id)
-                {
-                    assert!(id != ast::DUMMY_NODE_ID, "Trying to resolve dummy id");
-                    this.record_partial_res(id, PartialRes::new(res));
-                }
-            };
 
             let is_last = segment_idx + 1 == path.len();
             let ns = if is_last { opt_ns.unwrap_or(TypeNS) } else { TypeNS };
@@ -1507,7 +1544,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         let mut ctxt = ident.span.ctxt().normalize_to_macros_2_0();
                         let self_mod = self.resolve_self(&mut ctxt, parent_scope.module);
                         if let Some(res) = self_mod.res() {
-                            record_segment_res(self, res);
+                            record_segment_res(self.reborrow(), finalize, res, id);
                         }
                         module = Some(ModuleOrUniformRoot::Module(self_mod));
                         continue;
@@ -1529,7 +1566,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         // `::a::b`, `crate::a::b` or `$crate::a::b`
                         let crate_root = self.resolve_crate_root(ident);
                         if let Some(res) = crate_root.res() {
-                            record_segment_res(self, res);
+                            record_segment_res(self.reborrow(), finalize, res, id);
                         }
                         module = Some(ModuleOrUniformRoot::Module(crate_root));
                         continue;
@@ -1562,21 +1599,22 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             }
 
             let binding = if let Some(module) = module {
-                self.resolve_ident_in_module(
-                    module,
-                    ident,
-                    ns,
-                    parent_scope,
-                    finalize,
-                    ignore_binding,
-                    ignore_import,
-                )
-                .map_err(|(determinacy, _)| determinacy)
+                self.reborrow()
+                    .resolve_ident_in_module(
+                        module,
+                        ident,
+                        ns,
+                        parent_scope,
+                        finalize,
+                        ignore_binding,
+                        ignore_import,
+                    )
+                    .map_err(|(determinacy, _)| determinacy)
             } else if let Some(ribs) = ribs
                 && let Some(TypeNS | ValueNS) = opt_ns
             {
                 assert!(ignore_import.is_none());
-                match self.resolve_ident_in_lexical_scope(
+                match self.get_mut().resolve_ident_in_lexical_scope(
                     ident,
                     ns,
                     parent_scope,
@@ -1588,7 +1626,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     Some(LexicalScopeBinding::Item(binding)) => Ok(binding),
                     // we found a local variable or type param
                     Some(LexicalScopeBinding::Res(res)) => {
-                        record_segment_res(self, res);
+                        record_segment_res(self.reborrow(), finalize, res, id);
                         return PathResult::NonModule(PartialRes::with_unresolved_segments(
                             res,
                             path.len() - 1,
@@ -1597,7 +1635,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     _ => Err(Determinacy::determined(finalize.is_some())),
                 }
             } else {
-                self.early_resolve_ident_in_lexical_scope(
+                self.reborrow().early_resolve_ident_in_lexical_scope(
                     ident,
                     ScopeSet::All(ns),
                     parent_scope,
@@ -1618,8 +1656,15 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     // Mark every privacy error in this path with the res to the last element. This allows us
                     // to detect the item the user cares about and either find an alternative import, or tell
                     // the user it is not accessible.
-                    for error in &mut self.privacy_errors[privacy_errors_len..] {
-                        error.outermost_res = Some((res, ident));
+                    if finalize.is_some() {
+                        for error in &mut self.get_mut().privacy_errors[privacy_errors_len..] {
+                            error.outermost_res = Some((res, ident));
+                            error.source = match source {
+                                Some(PathSource::Struct(Some(expr)))
+                                | Some(PathSource::Expr(Some(expr))) => Some(expr.clone()),
+                                _ => None,
+                            };
+                        }
                     }
 
                     let maybe_assoc = opt_ns != Some(MacroNS) && PathSource::Type.is_expected(res);
@@ -1628,7 +1673,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                             module_had_parse_errors = true;
                         }
                         module = Some(ModuleOrUniformRoot::Module(self.expect_module(def_id)));
-                        record_segment_res(self, res);
+                        record_segment_res(self.reborrow(), finalize, res, id);
                     } else if res == Res::ToolMod && !is_last && opt_ns.is_some() {
                         if binding.is_import() {
                             self.dcx().emit_err(errors::ToolModuleImported {
@@ -1641,8 +1686,14 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     } else if res == Res::Err {
                         return PathResult::NonModule(PartialRes::new(Res::Err));
                     } else if opt_ns.is_some() && (is_last || maybe_assoc) {
-                        self.lint_if_path_starts_with_module(finalize, path, second_binding);
-                        record_segment_res(self, res);
+                        if let Some(finalize) = finalize {
+                            self.get_mut().lint_if_path_starts_with_module(
+                                finalize,
+                                path,
+                                second_binding,
+                            );
+                        }
+                        record_segment_res(self.reborrow(), finalize, res, id);
                         return PathResult::NonModule(PartialRes::with_unresolved_segments(
                             res,
                             path.len() - segment_idx - 1,
@@ -1677,6 +1728,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         ));
                     }
 
+                    let mut this = self.reborrow();
                     return PathResult::failed(
                         ident,
                         is_last,
@@ -1684,7 +1736,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         module_had_parse_errors,
                         module,
                         || {
-                            self.report_path_resolution_error(
+                            this.get_mut().report_path_resolution_error(
                                 path,
                                 opt_ns,
                                 parent_scope,
@@ -1701,7 +1753,9 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             }
         }
 
-        self.lint_if_path_starts_with_module(finalize, path, second_binding);
+        if let Some(finalize) = finalize {
+            self.get_mut().lint_if_path_starts_with_module(finalize, path, second_binding);
+        }
 
         PathResult::Module(match module {
             Some(module) => module,
diff --git a/compiler/rustc_resolve/src/imports.rs b/compiler/rustc_resolve/src/imports.rs
index 156df45147f..7c93fdb88ee 100644
--- a/compiler/rustc_resolve/src/imports.rs
+++ b/compiler/rustc_resolve/src/imports.rs
@@ -33,9 +33,10 @@ use crate::errors::{
     ConsiderAddingMacroExport, ConsiderMarkingAsPub,
 };
 use crate::{
-    AmbiguityError, AmbiguityKind, BindingKey, Determinacy, Finalize, ImportSuggestion, Module,
-    ModuleOrUniformRoot, NameBinding, NameBindingData, NameBindingKind, ParentScope, PathResult,
-    PerNS, ResolutionError, Resolver, ScopeSet, Segment, Used, module_to_string, names_to_string,
+    AmbiguityError, AmbiguityKind, BindingKey, CmResolver, Determinacy, Finalize, ImportSuggestion,
+    Module, ModuleOrUniformRoot, NameBinding, NameBindingData, NameBindingKind, ParentScope,
+    PathResult, PerNS, ResolutionError, Resolver, ScopeSet, Segment, Used, module_to_string,
+    names_to_string,
 };
 
 type Res = def::Res<NodeId>;
@@ -86,7 +87,6 @@ pub(crate) enum ImportKind<'ra> {
         id: NodeId,
     },
     Glob {
-        is_prelude: bool,
         // The visibility of the greatest re-export.
         // n.b. `max_vis` is only used in `finalize_import` to check for re-export errors.
         max_vis: Cell<Option<Visibility>>,
@@ -124,12 +124,9 @@ impl<'ra> std::fmt::Debug for ImportKind<'ra> {
                 .field("nested", nested)
                 .field("id", id)
                 .finish(),
-            Glob { is_prelude, max_vis, id } => f
-                .debug_struct("Glob")
-                .field("is_prelude", is_prelude)
-                .field("max_vis", max_vis)
-                .field("id", id)
-                .finish(),
+            Glob { max_vis, id } => {
+                f.debug_struct("Glob").field("max_vis", max_vis).field("id", id).finish()
+            }
             ExternCrate { source, target, id } => f
                 .debug_struct("ExternCrate")
                 .field("source", source)
@@ -489,7 +486,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         // Define or update `binding` in `module`s glob importers.
         for import in glob_importers.iter() {
             let mut ident = key.ident;
-            let scope = match ident.span.reverse_glob_adjust(module.expansion, import.span) {
+            let scope = match ident.0.span.reverse_glob_adjust(module.expansion, import.span) {
                 Some(Some(def)) => self.expn_def_scope(def),
                 Some(None) => import.parent_scope.module,
                 None => continue,
@@ -498,7 +495,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 let imported_binding = self.import(binding, *import);
                 let _ = self.try_define_local(
                     import.parent_scope.module,
-                    ident,
+                    ident.0,
                     key.ns,
                     imported_binding,
                     warn_ambiguity,
@@ -551,13 +548,14 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     /// Resolves all imports for the crate. This method performs the fixed-
     /// point iteration.
     pub(crate) fn resolve_imports(&mut self) {
+        self.assert_speculative = true;
         let mut prev_indeterminate_count = usize::MAX;
         let mut indeterminate_count = self.indeterminate_imports.len() * 3;
         while indeterminate_count < prev_indeterminate_count {
             prev_indeterminate_count = indeterminate_count;
             indeterminate_count = 0;
             for import in mem::take(&mut self.indeterminate_imports) {
-                let import_indeterminate_count = self.resolve_import(import);
+                let import_indeterminate_count = self.cm().resolve_import(import);
                 indeterminate_count += import_indeterminate_count;
                 match import_indeterminate_count {
                     0 => self.determined_imports.push(import),
@@ -565,6 +563,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 }
             }
         }
+        self.assert_speculative = false;
     }
 
     pub(crate) fn finalize_imports(&mut self) {
@@ -837,7 +836,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     ///
     /// Meanwhile, if resolve successful, the resolved bindings are written
     /// into the module.
-    fn resolve_import(&mut self, import: Import<'ra>) -> usize {
+    fn resolve_import<'r>(mut self: CmResolver<'r, 'ra, 'tcx>, import: Import<'ra>) -> usize {
         debug!(
             "(resolving import for module) resolving import `{}::...` in `{}`",
             Segment::names_to_string(&import.module_path),
@@ -846,7 +845,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         let module = if let Some(module) = import.imported_module.get() {
             module
         } else {
-            let path_res = self.maybe_resolve_path(
+            let path_res = self.reborrow().maybe_resolve_path(
                 &import.module_path,
                 None,
                 &import.parent_scope,
@@ -866,19 +865,21 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 (source, target, bindings, type_ns_only)
             }
             ImportKind::Glob { .. } => {
-                self.resolve_glob_import(import);
+                // FIXME: Use mutable resolver directly as a hack, this should be an output of
+                // specualtive resolution.
+                self.get_mut_unchecked().resolve_glob_import(import);
                 return 0;
             }
             _ => unreachable!(),
         };
 
         let mut indeterminate_count = 0;
-        self.per_ns(|this, ns| {
+        self.per_ns_cm(|this, ns| {
             if !type_ns_only || ns == TypeNS {
                 if bindings[ns].get() != PendingBinding::Pending {
                     return;
                 };
-                let binding_result = this.maybe_resolve_ident_in_module(
+                let binding_result = this.reborrow().maybe_resolve_ident_in_module(
                     module,
                     source,
                     ns,
@@ -901,16 +902,30 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         }
                         // We need the `target`, `source` can be extracted.
                         let imported_binding = this.import(binding, import);
-                        this.define_binding_local(parent, target, ns, imported_binding);
+                        // FIXME: Use mutable resolver directly as a hack, this should be an output of
+                        // specualtive resolution.
+                        this.get_mut_unchecked().define_binding_local(
+                            parent,
+                            target,
+                            ns,
+                            imported_binding,
+                        );
                         PendingBinding::Ready(Some(imported_binding))
                     }
                     Err(Determinacy::Determined) => {
                         // Don't remove underscores from `single_imports`, they were never added.
                         if target.name != kw::Underscore {
                             let key = BindingKey::new(target, ns);
-                            this.update_local_resolution(parent, key, false, |_, resolution| {
-                                resolution.single_imports.swap_remove(&import);
-                            });
+                            // FIXME: Use mutable resolver directly as a hack, this should be an output of
+                            // specualtive resolution.
+                            this.get_mut_unchecked().update_local_resolution(
+                                parent,
+                                key,
+                                false,
+                                |_, resolution| {
+                                    resolution.single_imports.swap_remove(&import);
+                                },
+                            );
                         }
                         PendingBinding::Ready(None)
                     }
@@ -943,7 +958,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         // We'll provide more context to the privacy errors later, up to `len`.
         let privacy_errors_len = self.privacy_errors.len();
 
-        let path_res = self.resolve_path(
+        let path_res = self.cm().resolve_path(
             &import.module_path,
             None,
             &import.parent_scope,
@@ -1054,13 +1069,13 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             ImportKind::Single { source, target, ref bindings, type_ns_only, id, .. } => {
                 (source, target, bindings, type_ns_only, id)
             }
-            ImportKind::Glob { is_prelude, ref max_vis, id } => {
+            ImportKind::Glob { ref max_vis, id } => {
                 if import.module_path.len() <= 1 {
                     // HACK(eddyb) `lint_if_path_starts_with_module` needs at least
                     // 2 segments, so the `resolve_path` above won't trigger it.
                     let mut full_path = import.module_path.clone();
                     full_path.push(Segment::from_ident(Ident::dummy()));
-                    self.lint_if_path_starts_with_module(Some(finalize), &full_path, None);
+                    self.lint_if_path_starts_with_module(finalize, &full_path, None);
                 }
 
                 if let ModuleOrUniformRoot::Module(module) = module
@@ -1077,8 +1092,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         module: None,
                     });
                 }
-                if !is_prelude
-                    && let Some(max_vis) = max_vis.get()
+                if let Some(max_vis) = max_vis.get()
                     && !max_vis.is_at_least(import.vis, self.tcx)
                 {
                     let def_id = self.local_def_id(id);
@@ -1103,7 +1117,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             // importing it if available.
             let mut path = import.module_path.clone();
             path.push(Segment::from_ident(ident));
-            if let PathResult::Module(ModuleOrUniformRoot::Module(module)) = self.resolve_path(
+            if let PathResult::Module(ModuleOrUniformRoot::Module(module)) = self.cm().resolve_path(
                 &path,
                 None,
                 &import.parent_scope,
@@ -1121,7 +1135,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         let mut all_ns_err = true;
         self.per_ns(|this, ns| {
             if !type_ns_only || ns == TypeNS {
-                let binding = this.resolve_ident_in_module(
+                let binding = this.cm().resolve_ident_in_module(
                     module,
                     ident,
                     ns,
@@ -1184,7 +1198,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             let mut all_ns_failed = true;
             self.per_ns(|this, ns| {
                 if !type_ns_only || ns == TypeNS {
-                    let binding = this.resolve_ident_in_module(
+                    let binding = this.cm().resolve_ident_in_module(
                         module,
                         ident,
                         ns,
@@ -1373,7 +1387,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             full_path.push(Segment::from_ident(ident));
             self.per_ns(|this, ns| {
                 if let Some(binding) = bindings[ns].get().binding().map(|b| b.import_source()) {
-                    this.lint_if_path_starts_with_module(Some(finalize), &full_path, Some(binding));
+                    this.lint_if_path_starts_with_module(finalize, &full_path, Some(binding));
                 }
             });
         }
@@ -1426,7 +1440,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     return;
                 }
 
-                match this.early_resolve_ident_in_lexical_scope(
+                match this.cm().early_resolve_ident_in_lexical_scope(
                     target,
                     ScopeSet::All(ns),
                     &import.parent_scope,
@@ -1466,7 +1480,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
     fn resolve_glob_import(&mut self, import: Import<'ra>) {
         // This function is only called for glob imports.
-        let ImportKind::Glob { id, is_prelude, .. } = import.kind else { unreachable!() };
+        let ImportKind::Glob { id, .. } = import.kind else { unreachable!() };
 
         let ModuleOrUniformRoot::Module(module) = import.imported_module.get().unwrap() else {
             self.dcx().emit_err(CannotGlobImportAllCrates { span: import.span });
@@ -1485,9 +1499,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
         if module == import.parent_scope.module {
             return;
-        } else if is_prelude {
-            self.prelude = Some(module);
-            return;
         }
 
         // Add to module's glob_importers
@@ -1504,7 +1515,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             })
             .collect::<Vec<_>>();
         for (mut key, binding) in bindings {
-            let scope = match key.ident.span.reverse_glob_adjust(module.expansion, import.span) {
+            let scope = match key.ident.0.span.reverse_glob_adjust(module.expansion, import.span) {
                 Some(Some(def)) => self.expn_def_scope(def),
                 Some(None) => import.parent_scope.module,
                 None => continue,
@@ -1517,7 +1528,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     .is_some_and(|binding| binding.warn_ambiguity_recursive());
                 let _ = self.try_define_local(
                     import.parent_scope.module,
-                    key.ident,
+                    key.ident.0,
                     key.ns,
                     imported_binding,
                     warn_ambiguity,
@@ -1550,7 +1561,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     next_binding = binding;
                 }
 
-                children.push(ModChild { ident, res, vis: binding.vis, reexport_chain });
+                children.push(ModChild { ident: ident.0, res, vis: binding.vis, reexport_chain });
             }
         });
 
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index 163e4b5b7a9..5200f9340e1 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -12,7 +12,6 @@ use std::collections::BTreeSet;
 use std::collections::hash_map::Entry;
 use std::mem::{replace, swap, take};
 
-use rustc_ast::ptr::P;
 use rustc_ast::visit::{
     AssocCtxt, BoundKind, FnCtxt, FnKind, Visitor, try_visit, visit_opt, walk_list,
 };
@@ -193,6 +192,13 @@ pub(crate) enum RibKind<'ra> {
     /// No restriction needs to be applied.
     Normal,
 
+    /// We passed through an `ast::Block`.
+    /// Behaves like `Normal`, but also partially like `Module` if the block contains items.
+    /// `Block(None)` must be always processed in the same way as `Block(Some(module))`
+    /// with empty `module`. The module can be `None` only because creation of some definitely
+    /// empty modules is skipped as an optimization.
+    Block(Option<Module<'ra>>),
+
     /// We passed through an impl or trait and are now in one of its
     /// methods or associated types. Allow references to ty params that impl or trait
     /// binds. Disallow any other upvars (including other ty params that are
@@ -211,7 +217,7 @@ pub(crate) enum RibKind<'ra> {
     /// All other constants aren't allowed to use generic params at all.
     ConstantItem(ConstantHasGenerics, Option<(Ident, ConstantItemKind)>),
 
-    /// We passed through a module.
+    /// We passed through a module item.
     Module(Module<'ra>),
 
     /// We passed through a `macro_rules!` statement
@@ -243,6 +249,7 @@ impl RibKind<'_> {
     pub(crate) fn contains_params(&self) -> bool {
         match self {
             RibKind::Normal
+            | RibKind::Block(..)
             | RibKind::FnOrCoroutine
             | RibKind::ConstantItem(..)
             | RibKind::Module(_)
@@ -259,15 +266,8 @@ impl RibKind<'_> {
     fn is_label_barrier(self) -> bool {
         match self {
             RibKind::Normal | RibKind::MacroDefinition(..) => false,
-
-            RibKind::AssocItem
-            | RibKind::FnOrCoroutine
-            | RibKind::Item(..)
-            | RibKind::ConstantItem(..)
-            | RibKind::Module(..)
-            | RibKind::ForwardGenericParamBan(_)
-            | RibKind::ConstParamTy
-            | RibKind::InlineAsmSym => true,
+            RibKind::FnOrCoroutine | RibKind::ConstantItem(..) => true,
+            kind => bug!("unexpected rib kind: {kind:?}"),
         }
     }
 }
@@ -425,7 +425,7 @@ pub(crate) enum PathSource<'a, 'ast, 'ra> {
     /// Paths in path patterns `Path`.
     Pat,
     /// Paths in struct expressions and patterns `Path { .. }`.
-    Struct,
+    Struct(Option<&'a Expr>),
     /// Paths in tuple struct patterns `Path(..)`.
     TupleStruct(Span, &'ra [Span]),
     /// `m::A::B` in `<T as m::A>::B::C`.
@@ -448,7 +448,7 @@ impl PathSource<'_, '_, '_> {
         match self {
             PathSource::Type
             | PathSource::Trait(_)
-            | PathSource::Struct
+            | PathSource::Struct(_)
             | PathSource::DefineOpaques => TypeNS,
             PathSource::Expr(..)
             | PathSource::Pat
@@ -465,7 +465,7 @@ impl PathSource<'_, '_, '_> {
             PathSource::Type
             | PathSource::Expr(..)
             | PathSource::Pat
-            | PathSource::Struct
+            | PathSource::Struct(_)
             | PathSource::TupleStruct(..)
             | PathSource::ReturnTypeNotation => true,
             PathSource::Trait(_)
@@ -482,7 +482,7 @@ impl PathSource<'_, '_, '_> {
             PathSource::Type => "type",
             PathSource::Trait(_) => "trait",
             PathSource::Pat => "unit struct, unit variant or constant",
-            PathSource::Struct => "struct, variant or union type",
+            PathSource::Struct(_) => "struct, variant or union type",
             PathSource::TraitItem(ValueNS, PathSource::TupleStruct(..))
             | PathSource::TupleStruct(..) => "tuple struct or tuple variant",
             PathSource::TraitItem(ns, _) => match ns {
@@ -577,7 +577,7 @@ impl PathSource<'_, '_, '_> {
                     || matches!(res, Res::Def(DefKind::Const | DefKind::AssocConst, _))
             }
             PathSource::TupleStruct(..) => res.expected_in_tuple_struct_pat(),
-            PathSource::Struct => matches!(
+            PathSource::Struct(_) => matches!(
                 res,
                 Res::Def(
                     DefKind::Struct
@@ -617,8 +617,8 @@ impl PathSource<'_, '_, '_> {
             (PathSource::Trait(_), false) => E0405,
             (PathSource::Type | PathSource::DefineOpaques, true) => E0573,
             (PathSource::Type | PathSource::DefineOpaques, false) => E0412,
-            (PathSource::Struct, true) => E0574,
-            (PathSource::Struct, false) => E0422,
+            (PathSource::Struct(_), true) => E0574,
+            (PathSource::Struct(_), false) => E0422,
             (PathSource::Expr(..), true) | (PathSource::Delegation, true) => E0423,
             (PathSource::Expr(..), false) | (PathSource::Delegation, false) => E0425,
             (PathSource::Pat | PathSource::TupleStruct(..), true) => E0532,
@@ -670,7 +670,7 @@ pub(crate) struct UnnecessaryQualification<'ra> {
 #[derive(Default, Debug)]
 struct DiagMetadata<'ast> {
     /// The current trait's associated items' ident, used for diagnostic suggestions.
-    current_trait_assoc_items: Option<&'ast [P<AssocItem>]>,
+    current_trait_assoc_items: Option<&'ast [Box<AssocItem>]>,
 
     /// The current self type if inside an impl (used for better errors).
     current_self_type: Option<Ty>,
@@ -720,7 +720,7 @@ struct DiagMetadata<'ast> {
     current_type_path: Option<&'ast Ty>,
 
     /// The current impl items (used to suggest).
-    current_impl_items: Option<&'ast [P<AssocItem>]>,
+    current_impl_items: Option<&'ast [Box<AssocItem>]>,
 
     /// When processing impl trait
     currently_processing_impl_trait: Option<(TraitRef, Ty)>,
@@ -1424,7 +1424,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
         // During late resolution we only track the module component of the parent scope,
         // although it may be useful to track other components as well for diagnostics.
         let graph_root = resolver.graph_root;
-        let parent_scope = ParentScope::module(graph_root, resolver);
+        let parent_scope = ParentScope::module(graph_root, resolver.arenas);
         let start_rib_kind = RibKind::Module(graph_root);
         LateResolutionVisitor {
             r: resolver,
@@ -1483,11 +1483,13 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
         path: &[Segment],
         opt_ns: Option<Namespace>, // `None` indicates a module path in import
         finalize: Option<Finalize>,
+        source: PathSource<'_, 'ast, 'ra>,
     ) -> PathResult<'ra> {
-        self.r.resolve_path_with_ribs(
+        self.r.cm().resolve_path_with_ribs(
             path,
             opt_ns,
             &self.parent_scope,
+            Some(source),
             finalize,
             Some(&self.ribs),
             None,
@@ -1526,19 +1528,6 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
         ret
     }
 
-    fn with_mod_rib<T>(&mut self, id: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
-        let module = self.r.expect_module(self.r.local_def_id(id).to_def_id());
-        // Move down in the graph.
-        let orig_module = replace(&mut self.parent_scope.module, module);
-        self.with_rib(ValueNS, RibKind::Module(module), |this| {
-            this.with_rib(TypeNS, RibKind::Module(module), |this| {
-                let ret = f(this);
-                this.parent_scope.module = orig_module;
-                ret
-            })
-        })
-    }
-
     fn visit_generic_params(&mut self, params: &'ast [GenericParam], add_self_upper: bool) {
         // For type parameter defaults, we have to ban access
         // to following type parameters, as the GenericArgs can only
@@ -1967,7 +1956,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
         &mut self,
         partial_res: PartialRes,
         path: &[Segment],
-        source: PathSource<'_, '_, '_>,
+        source: PathSource<'_, 'ast, 'ra>,
         path_span: Span,
     ) {
         let proj_start = path.len() - partial_res.unresolved_segments();
@@ -2020,7 +2009,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
                 | PathSource::ReturnTypeNotation => false,
                 PathSource::Expr(..)
                 | PathSource::Pat
-                | PathSource::Struct
+                | PathSource::Struct(_)
                 | PathSource::TupleStruct(..)
                 | PathSource::DefineOpaques
                 | PathSource::Delegation => true,
@@ -2619,7 +2608,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
                 self.resolve_adt(item, generics);
             }
 
-            ItemKind::Impl(box Impl {
+            ItemKind::Impl(Impl {
                 ref generics,
                 ref of_trait,
                 ref self_ty,
@@ -2630,7 +2619,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
                 self.resolve_implementation(
                     &item.attrs,
                     generics,
-                    of_trait,
+                    of_trait.as_deref(),
                     self_ty,
                     item.id,
                     impl_items,
@@ -2676,20 +2665,25 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
             }
 
             ItemKind::Mod(..) => {
-                self.with_mod_rib(item.id, |this| {
-                    if mod_inner_docs {
-                        this.resolve_doc_links(&item.attrs, MaybeExported::Ok(item.id));
-                    }
-                    let old_macro_rules = this.parent_scope.macro_rules;
-                    visit::walk_item(this, item);
-                    // Maintain macro_rules scopes in the same way as during early resolution
-                    // for diagnostics and doc links.
-                    if item.attrs.iter().all(|attr| {
-                        !attr.has_name(sym::macro_use) && !attr.has_name(sym::macro_escape)
-                    }) {
-                        this.parent_scope.macro_rules = old_macro_rules;
-                    }
+                let module = self.r.expect_module(self.r.local_def_id(item.id).to_def_id());
+                let orig_module = replace(&mut self.parent_scope.module, module);
+                self.with_rib(ValueNS, RibKind::Module(module), |this| {
+                    this.with_rib(TypeNS, RibKind::Module(module), |this| {
+                        if mod_inner_docs {
+                            this.resolve_doc_links(&item.attrs, MaybeExported::Ok(item.id));
+                        }
+                        let old_macro_rules = this.parent_scope.macro_rules;
+                        visit::walk_item(this, item);
+                        // Maintain macro_rules scopes in the same way as during early resolution
+                        // for diagnostics and doc links.
+                        if item.attrs.iter().all(|attr| {
+                            !attr.has_name(sym::macro_use) && !attr.has_name(sym::macro_escape)
+                        }) {
+                            this.parent_scope.macro_rules = old_macro_rules;
+                        }
+                    })
                 });
+                self.parent_scope.module = orig_module;
             }
 
             ItemKind::Static(box ast::StaticItem {
@@ -2820,9 +2814,9 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
             // We also can't shadow bindings from associated parent items.
             for ns in [ValueNS, TypeNS] {
                 for parent_rib in self.ribs[ns].iter().rev() {
-                    // Break at mod level, to account for nested items which are
+                    // Break at module or block level, to account for nested items which are
                     // allowed to shadow generic param names.
-                    if matches!(parent_rib.kind, RibKind::Module(..)) {
+                    if matches!(parent_rib.kind, RibKind::Module(..) | RibKind::Block(..)) {
                         break;
                     }
 
@@ -3038,7 +3032,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
     }
 
     /// When evaluating a `trait` use its associated types' idents for suggestions in E0412.
-    fn resolve_trait_items(&mut self, trait_items: &'ast [P<AssocItem>]) {
+    fn resolve_trait_items(&mut self, trait_items: &'ast [Box<AssocItem>]) {
         let trait_assoc_items =
             replace(&mut self.diag_metadata.current_trait_assoc_items, Some(trait_items));
 
@@ -3176,10 +3170,10 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
         &mut self,
         attrs: &[ast::Attribute],
         generics: &'ast Generics,
-        opt_trait_reference: &'ast Option<TraitRef>,
+        of_trait: Option<&'ast ast::TraitImplHeader>,
         self_type: &'ast Ty,
         item_id: NodeId,
-        impl_items: &'ast [P<AssocItem>],
+        impl_items: &'ast [Box<AssocItem>],
     ) {
         debug!("resolve_implementation");
         // If applicable, create a rib for the type parameters.
@@ -3200,7 +3194,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
                         |this| {
                             // Resolve the trait reference, if necessary.
                             this.with_optional_trait_ref(
-                                opt_trait_reference.as_ref(),
+                                of_trait.map(|t| &t.trait_ref),
                                 self_type,
                                 |this, trait_id| {
                                     this.resolve_doc_links(attrs, MaybeExported::Impl(trait_id));
@@ -3223,9 +3217,9 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
                                         is_trait_impl: trait_id.is_some()
                                     };
                                     this.with_self_rib(res, |this| {
-                                        if let Some(trait_ref) = opt_trait_reference.as_ref() {
+                                        if let Some(of_trait) = of_trait {
                                             // Resolve type arguments in the trait path.
-                                            visit::walk_trait_ref(this, trait_ref);
+                                            visit::walk_trait_ref(this, &of_trait.trait_ref);
                                         }
                                         // Resolve the self type.
                                         this.visit_ty(self_type);
@@ -3671,7 +3665,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
     /// pattern as a whole counts as a never pattern (since it's definitionallly unreachable).
     fn compute_and_check_or_pat_binding_map(
         &mut self,
-        pats: &[P<Pat>],
+        pats: &[Box<Pat>],
     ) -> Result<FxIndexMap<Ident, BindingInfo>, IsNeverPattern> {
         let mut missing_vars = FxIndexMap::default();
         let mut inconsistent_vars = FxIndexMap::default();
@@ -3867,7 +3861,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
                     self.smart_resolve_path(pat.id, qself, path, PathSource::Pat);
                 }
                 PatKind::Struct(ref qself, ref path, ref _fields, ref rest) => {
-                    self.smart_resolve_path(pat.id, qself, path, PathSource::Struct);
+                    self.smart_resolve_path(pat.id, qself, path, PathSource::Struct(None));
                     self.record_patterns_with_skipped_bindings(pat, rest);
                 }
                 PatKind::Or(ref ps) => {
@@ -4109,9 +4103,9 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
     fn smart_resolve_path(
         &mut self,
         id: NodeId,
-        qself: &Option<P<QSelf>>,
+        qself: &Option<Box<QSelf>>,
         path: &Path,
-        source: PathSource<'_, 'ast, '_>,
+        source: PathSource<'_, 'ast, 'ra>,
     ) {
         self.smart_resolve_path_fragment(
             qself,
@@ -4126,9 +4120,9 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
     #[instrument(level = "debug", skip(self))]
     fn smart_resolve_path_fragment(
         &mut self,
-        qself: &Option<P<QSelf>>,
+        qself: &Option<Box<QSelf>>,
         path: &[Segment],
-        source: PathSource<'_, 'ast, '_>,
+        source: PathSource<'_, 'ast, 'ra>,
         finalize: Finalize,
         record_partial_res: RecordPartialRes,
         parent_qself: Option<&QSelf>,
@@ -4314,7 +4308,6 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
             qself,
             path,
             ns,
-            path_span,
             source.defer_to_typeck(),
             finalize,
             source,
@@ -4366,7 +4359,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
                     std_path.push(Segment::from_ident(Ident::with_dummy_span(sym::std)));
                     std_path.extend(path);
                     if let PathResult::Module(_) | PathResult::NonModule(_) =
-                        self.resolve_path(&std_path, Some(ns), None)
+                        self.resolve_path(&std_path, Some(ns), None, source)
                     {
                         // Check if we wrote `str::from_utf8` instead of `std::str::from_utf8`
                         let item_span =
@@ -4434,13 +4427,12 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
     // Resolve in alternative namespaces if resolution in the primary namespace fails.
     fn resolve_qpath_anywhere(
         &mut self,
-        qself: &Option<P<QSelf>>,
+        qself: &Option<Box<QSelf>>,
         path: &[Segment],
         primary_ns: Namespace,
-        span: Span,
         defer_to_typeck: bool,
         finalize: Finalize,
-        source: PathSource<'_, 'ast, '_>,
+        source: PathSource<'_, 'ast, 'ra>,
     ) -> Result<Option<PartialRes>, Spanned<ResolutionError<'ra>>> {
         let mut fin_res = None;
 
@@ -4462,15 +4454,11 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
         }
 
         assert!(primary_ns != MacroNS);
-
-        if qself.is_none() {
-            let path_seg = |seg: &Segment| PathSegment::from_ident(seg.ident);
-            let path = Path { segments: path.iter().map(path_seg).collect(), span, tokens: None };
-            if let Ok((_, res)) =
-                self.r.resolve_macro_path(&path, None, &self.parent_scope, false, false, None, None)
-            {
-                return Ok(Some(PartialRes::new(res)));
-            }
+        if qself.is_none()
+            && let PathResult::NonModule(res) =
+                self.r.cm().maybe_resolve_path(path, Some(MacroNS), &self.parent_scope, None)
+        {
+            return Ok(Some(res));
         }
 
         Ok(fin_res)
@@ -4479,11 +4467,11 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
     /// Handles paths that may refer to associated items.
     fn resolve_qpath(
         &mut self,
-        qself: &Option<P<QSelf>>,
+        qself: &Option<Box<QSelf>>,
         path: &[Segment],
         ns: Namespace,
         finalize: Finalize,
-        source: PathSource<'_, 'ast, '_>,
+        source: PathSource<'_, 'ast, 'ra>,
     ) -> Result<Option<PartialRes>, Spanned<ResolutionError<'ra>>> {
         debug!(
             "resolve_qpath(qself={:?}, path={:?}, ns={:?}, finalize={:?})",
@@ -4546,7 +4534,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
             )));
         }
 
-        let result = match self.resolve_path(path, Some(ns), Some(finalize)) {
+        let result = match self.resolve_path(path, Some(ns), Some(finalize), source) {
             PathResult::NonModule(path_res) => path_res,
             PathResult::Module(ModuleOrUniformRoot::Module(module)) if !module.is_normal() => {
                 PartialRes::new(module.res().unwrap())
@@ -4657,16 +4645,16 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
         debug!("(resolving block) entering block");
         // Move down in the graph, if there's an anonymous module rooted here.
         let orig_module = self.parent_scope.module;
-        let anonymous_module = self.r.block_map.get(&block.id).cloned(); // clones a reference
+        let anonymous_module = self.r.block_map.get(&block.id).copied();
 
         let mut num_macro_definition_ribs = 0;
         if let Some(anonymous_module) = anonymous_module {
             debug!("(resolving block) found anonymous module, moving down");
-            self.ribs[ValueNS].push(Rib::new(RibKind::Module(anonymous_module)));
-            self.ribs[TypeNS].push(Rib::new(RibKind::Module(anonymous_module)));
+            self.ribs[ValueNS].push(Rib::new(RibKind::Block(Some(anonymous_module))));
+            self.ribs[TypeNS].push(Rib::new(RibKind::Block(Some(anonymous_module))));
             self.parent_scope.module = anonymous_module;
         } else {
-            self.ribs[ValueNS].push(Rib::new(RibKind::Normal));
+            self.ribs[ValueNS].push(Rib::new(RibKind::Block(None)));
         }
 
         // Descend into the block.
@@ -4769,7 +4757,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
             }
 
             ExprKind::Struct(ref se) => {
-                self.smart_resolve_path(expr.id, &se.qself, &se.path, PathSource::Struct);
+                self.smart_resolve_path(expr.id, &se.qself, &se.path, PathSource::Struct(parent));
                 // This is the same as `visit::walk_expr(self, expr);`, but we want to pass the
                 // parent in for accurate suggestions when encountering `Foo { bar }` that should
                 // have been `Foo { bar: self.bar }`.
@@ -5176,7 +5164,7 @@ impl<'ast> Visitor<'ast> for ItemInfoCollector<'_, '_, '_> {
             | ItemKind::Enum(_, generics, _)
             | ItemKind::Struct(_, generics, _)
             | ItemKind::Union(_, generics, _)
-            | ItemKind::Impl(box Impl { generics, .. })
+            | ItemKind::Impl(Impl { generics, .. })
             | ItemKind::Trait(box Trait { generics, .. })
             | ItemKind::TraitAlias(_, generics, _) => {
                 if let ItemKind::Fn(box Fn { sig, .. }) = &item.kind {
diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
index c8ca57a380f..9b201e40d13 100644
--- a/compiler/rustc_resolve/src/late/diagnostics.rs
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -4,7 +4,6 @@ use std::borrow::Cow;
 use std::iter;
 use std::ops::Deref;
 
-use rustc_ast::ptr::P;
 use rustc_ast::visit::{FnCtxt, FnKind, LifetimeCtxt, Visitor, walk_ty};
 use rustc_ast::{
     self as ast, AssocItemKind, DUMMY_NODE_ID, Expr, ExprKind, GenericParam, GenericParamKind,
@@ -20,14 +19,13 @@ use rustc_errors::{
 };
 use rustc_hir as hir;
 use rustc_hir::def::Namespace::{self, *};
-use rustc_hir::def::{self, CtorKind, CtorOf, DefKind};
+use rustc_hir::def::{self, CtorKind, CtorOf, DefKind, MacroKinds};
 use rustc_hir::def_id::{CRATE_DEF_ID, DefId};
 use rustc_hir::{MissingLifetimeKind, PrimTy};
 use rustc_middle::ty;
 use rustc_session::{Session, lint};
 use rustc_span::edit_distance::{edit_distance, find_best_match_for_name};
 use rustc_span::edition::Edition;
-use rustc_span::hygiene::MacroKind;
 use rustc_span::{DUMMY_SP, Ident, Span, Symbol, kw, sym};
 use thin_vec::ThinVec;
 use tracing::debug;
@@ -40,8 +38,8 @@ use crate::late::{
 };
 use crate::ty::fast_reject::SimplifiedType;
 use crate::{
-    Module, ModuleKind, ModuleOrUniformRoot, PathResult, PathSource, Resolver, Segment, errors,
-    path_names_to_string,
+    Module, ModuleKind, ModuleOrUniformRoot, PathResult, PathSource, Resolver, ScopeSet, Segment,
+    errors, path_names_to_string,
 };
 
 type Res = def::Res<ast::NodeId>;
@@ -175,7 +173,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
         &mut self,
         path: &[Segment],
         span: Span,
-        source: PathSource<'_, '_, '_>,
+        source: PathSource<'_, 'ast, 'ra>,
         res: Option<Res>,
     ) -> BaseError {
         // Make the base error.
@@ -319,7 +317,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                 (String::new(), "the crate root".to_string(), Some(CRATE_DEF_ID.to_def_id()), None)
             } else {
                 let mod_path = &path[..path.len() - 1];
-                let mod_res = self.resolve_path(mod_path, Some(TypeNS), None);
+                let mod_res = self.resolve_path(mod_path, Some(TypeNS), None, source);
                 let mod_prefix = match mod_res {
                     PathResult::Module(ModuleOrUniformRoot::Module(module)) => module.res(),
                     _ => None,
@@ -420,7 +418,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
         path: &[Segment],
         following_seg: Option<&Segment>,
         span: Span,
-        source: PathSource<'_, '_, '_>,
+        source: PathSource<'_, 'ast, 'ra>,
         res: Option<Res>,
         qself: Option<&QSelf>,
     ) -> (Diag<'tcx>, Vec<ImportSuggestion>) {
@@ -851,9 +849,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
         }
 
         // Try to find in last block rib
-        if let Some(rib) = &self.last_block_rib
-            && let RibKind::Normal = rib.kind
-        {
+        if let Some(rib) = &self.last_block_rib {
             for (ident, &res) in &rib.bindings {
                 if let Res::Local(_) = res
                     && path.len() == 1
@@ -902,7 +898,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
         if path.len() == 1 {
             for rib in self.ribs[ns].iter().rev() {
                 let item = path[0].ident;
-                if let RibKind::Module(module) = rib.kind
+                if let RibKind::Module(module) | RibKind::Block(Some(module)) = rib.kind
                     && let Some(did) = find_doc_alias_name(self.r, module, item.name)
                 {
                     return Some((did, item));
@@ -1015,7 +1011,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
     fn suggest_typo(
         &mut self,
         err: &mut Diag<'_>,
-        source: PathSource<'_, '_, '_>,
+        source: PathSource<'_, 'ast, 'ra>,
         path: &[Segment],
         following_seg: Option<&Segment>,
         span: Span,
@@ -1334,7 +1330,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
     fn suggest_swapping_misplaced_self_ty_and_trait(
         &mut self,
         err: &mut Diag<'_>,
-        source: PathSource<'_, '_, '_>,
+        source: PathSource<'_, 'ast, 'ra>,
         res: Option<Res>,
         span: Span,
     ) {
@@ -1342,7 +1338,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
             self.diag_metadata.currently_processing_impl_trait.clone()
             && let TyKind::Path(_, self_ty_path) = &self_ty.kind
             && let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
-                self.resolve_path(&Segment::from_path(self_ty_path), Some(TypeNS), None)
+                self.resolve_path(&Segment::from_path(self_ty_path), Some(TypeNS), None, source)
             && let ModuleKind::Def(DefKind::Trait, ..) = module.kind
             && trait_ref.path.span == span
             && let PathSource::Trait(_) = source
@@ -1450,13 +1446,13 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
     fn get_single_associated_item(
         &mut self,
         path: &[Segment],
-        source: &PathSource<'_, '_, '_>,
+        source: &PathSource<'_, 'ast, 'ra>,
         filter_fn: &impl Fn(Res) -> bool,
     ) -> Option<TypoSuggestion> {
         if let crate::PathSource::TraitItem(_, _) = source {
             let mod_path = &path[..path.len() - 1];
             if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
-                self.resolve_path(mod_path, None, None)
+                self.resolve_path(mod_path, None, None, *source)
             {
                 let targets: Vec<_> = self
                     .r
@@ -1472,7 +1468,10 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                     })
                     .collect();
                 if let [target] = targets.as_slice() {
-                    return Some(TypoSuggestion::single_item_from_ident(target.0.ident, target.1));
+                    return Some(TypoSuggestion::single_item_from_ident(
+                        target.0.ident.0,
+                        target.1,
+                    ));
                 }
             }
         }
@@ -1848,12 +1847,12 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
 
         match (res, source) {
             (
-                Res::Def(DefKind::Macro(MacroKind::Bang), def_id),
+                Res::Def(DefKind::Macro(kinds), def_id),
                 PathSource::Expr(Some(Expr {
                     kind: ExprKind::Index(..) | ExprKind::Call(..), ..
                 }))
-                | PathSource::Struct,
-            ) => {
+                | PathSource::Struct(_),
+            ) if kinds.contains(MacroKinds::BANG) => {
                 // Don't suggest macro if it's unstable.
                 let suggestable = def_id.is_local()
                     || self.r.tcx.lookup_stability(def_id).is_none_or(|s| s.is_stable());
@@ -1878,7 +1877,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                     err.note("if you want the `try` keyword, you need Rust 2018 or later");
                 }
             }
-            (Res::Def(DefKind::Macro(MacroKind::Bang), _), _) => {
+            (Res::Def(DefKind::Macro(kinds), _), _) if kinds.contains(MacroKinds::BANG) => {
                 err.span_label(span, fallback_label.to_string());
             }
             (Res::Def(DefKind::TyAlias, def_id), PathSource::Trait(_)) => {
@@ -2147,7 +2146,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
         err: &mut Diag<'_>,
         path_span: Span,
         call_span: Span,
-        args: &[P<Expr>],
+        args: &[Box<Expr>],
     ) {
         if def_id.is_local() {
             // Doing analysis on local `DefId`s would cause infinite recursion.
@@ -2386,7 +2385,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
 
         // Look for associated items in the current trait.
         if let Some((module, _)) = self.current_trait_ref
-            && let Ok(binding) = self.r.maybe_resolve_ident_in_module(
+            && let Ok(binding) = self.r.cm().maybe_resolve_ident_in_module(
                 ModuleOrUniformRoot::Module(module),
                 ident,
                 ns,
@@ -2457,50 +2456,33 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                     }
                 }
 
+                if let RibKind::Block(Some(module)) = rib.kind {
+                    self.r.add_module_candidates(module, &mut names, &filter_fn, Some(ctxt));
+                } else if let RibKind::Module(module) = rib.kind {
+                    // Encountered a module item, abandon ribs and look into that module and preludes.
+                    self.r.add_scope_set_candidates(
+                        &mut names,
+                        ScopeSet::Late(ns, module, None),
+                        &self.parent_scope,
+                        ctxt,
+                        filter_fn,
+                    );
+                    break;
+                }
+
                 if let RibKind::MacroDefinition(def) = rib.kind
                     && def == self.r.macro_def(ctxt)
                 {
                     // If an invocation of this macro created `ident`, give up on `ident`
                     // and switch to `ident`'s source from the macro definition.
                     ctxt.remove_mark();
-                    continue;
                 }
-
-                // Items in scope
-                if let RibKind::Module(module) = rib.kind {
-                    // Items from this module
-                    self.r.add_module_candidates(module, &mut names, &filter_fn, Some(ctxt));
-
-                    if let ModuleKind::Block = module.kind {
-                        // We can see through blocks
-                    } else {
-                        // Items from the prelude
-                        if !module.no_implicit_prelude {
-                            names.extend(self.r.extern_prelude.keys().flat_map(|ident| {
-                                let res = Res::Def(DefKind::Mod, CRATE_DEF_ID.to_def_id());
-                                filter_fn(res)
-                                    .then_some(TypoSuggestion::typo_from_ident(*ident, res))
-                            }));
-
-                            if let Some(prelude) = self.r.prelude {
-                                self.r.add_module_candidates(prelude, &mut names, &filter_fn, None);
-                            }
-                        }
-                        break;
-                    }
-                }
-            }
-            // Add primitive types to the mix
-            if filter_fn(Res::PrimTy(PrimTy::Bool)) {
-                names.extend(PrimTy::ALL.iter().map(|prim_ty| {
-                    TypoSuggestion::typo_from_name(prim_ty.name(), Res::PrimTy(*prim_ty))
-                }))
             }
         } else {
             // Search in module.
             let mod_path = &path[..path.len() - 1];
             if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
-                self.resolve_path(mod_path, Some(TypeNS), None)
+                self.resolve_path(mod_path, Some(TypeNS), None, PathSource::Type)
             {
                 self.r.add_module_candidates(module, &mut names, &filter_fn, None);
             }
@@ -2639,7 +2621,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                 if let Some(module_def_id) = name_binding.res().module_like_def_id() {
                     // form the path
                     let mut path_segments = path_segments.clone();
-                    path_segments.push(ast::PathSegment::from_ident(ident));
+                    path_segments.push(ast::PathSegment::from_ident(ident.0));
                     let doc_visible = doc_visible
                         && (module_def_id.is_local() || !r.tcx.is_doc_hidden(module_def_id));
                     if module_def_id == def_id {
@@ -2678,7 +2660,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
             enum_module.for_each_child(self.r, |_, ident, _, name_binding| {
                 if let Res::Def(DefKind::Ctor(CtorOf::Variant, kind), def_id) = name_binding.res() {
                     let mut segms = enum_import_suggestion.path.segments.clone();
-                    segms.push(ast::PathSegment::from_ident(ident));
+                    segms.push(ast::PathSegment::from_ident(ident.0));
                     let path = Path { span: name_binding.span, segments: segms, tokens: None };
                     variants.push((path, def_id, kind));
                 }
@@ -3671,7 +3653,12 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                                 if let TyKind::Path(None, path) = &ty.kind {
                                     // Check if the path being borrowed is likely to be owned.
                                     let path: Vec<_> = Segment::from_path(path);
-                                    match self.resolve_path(&path, Some(TypeNS), None) {
+                                    match self.resolve_path(
+                                        &path,
+                                        Some(TypeNS),
+                                        None,
+                                        PathSource::Type,
+                                    ) {
                                         PathResult::Module(ModuleOrUniformRoot::Module(module)) => {
                                             match module.res() {
                                                 Some(Res::PrimTy(PrimTy::Str)) => {
@@ -3785,7 +3772,7 @@ fn mk_where_bound_predicate(
             ident: last.ident,
             gen_args: None,
             kind: ast::AssocItemConstraintKind::Equality {
-                term: ast::Term::Ty(ast::ptr::P(ast::Ty {
+                term: ast::Term::Ty(Box::new(ast::Ty {
                     kind: ast::TyKind::Path(None, poly_trait_ref.trait_ref.path.clone()),
                     id: DUMMY_NODE_ID,
                     span: DUMMY_SP,
@@ -3802,7 +3789,7 @@ fn mk_where_bound_predicate(
             Some(_) => return None,
             None => {
                 second_last.args =
-                    Some(ast::ptr::P(ast::GenericArgs::AngleBracketed(ast::AngleBracketedArgs {
+                    Some(Box::new(ast::GenericArgs::AngleBracketed(ast::AngleBracketedArgs {
                         args: ThinVec::from([added_constraint]),
                         span: DUMMY_SP,
                     })));
@@ -3815,7 +3802,7 @@ fn mk_where_bound_predicate(
 
     let new_where_bound_predicate = ast::WhereBoundPredicate {
         bound_generic_params: ThinVec::new(),
-        bounded_ty: ast::ptr::P(ty.clone()),
+        bounded_ty: Box::new(ty.clone()),
         bounds: vec![ast::GenericBound::Trait(ast::PolyTraitRef {
             bound_generic_params: ThinVec::new(),
             modifiers: ast::TraitBoundModifiers::NONE,
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index 6b034c5129f..ca9c124fca6 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -12,8 +12,11 @@
 #![allow(rustc::untranslatable_diagnostic)]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
+#![feature(arbitrary_self_types)]
 #![feature(assert_matches)]
 #![feature(box_patterns)]
+#![feature(decl_macro)]
+#![feature(default_field_values)]
 #![feature(if_let_guard)]
 #![feature(iter_intersperse)]
 #![feature(rustc_attrs)]
@@ -52,7 +55,8 @@ use rustc_feature::BUILTIN_ATTRIBUTES;
 use rustc_hir::attrs::StrippedCfgItem;
 use rustc_hir::def::Namespace::{self, *};
 use rustc_hir::def::{
-    self, CtorOf, DefKind, DocLinkResMap, LifetimeRes, NonMacroAttrKind, PartialRes, PerNS,
+    self, CtorOf, DefKind, DocLinkResMap, LifetimeRes, MacroKinds, NonMacroAttrKind, PartialRes,
+    PerNS,
 };
 use rustc_hir::def_id::{CRATE_DEF_ID, CrateNum, DefId, LOCAL_CRATE, LocalDefId, LocalDefIdMap};
 use rustc_hir::definitions::DisambiguatorState;
@@ -71,7 +75,7 @@ use rustc_query_system::ich::StableHashingContext;
 use rustc_session::lint::builtin::PRIVATE_MACRO_USE;
 use rustc_session::lint::{BuiltinLintDiag, LintBuffer};
 use rustc_span::hygiene::{ExpnId, LocalExpnId, MacroKind, SyntaxContext, Transparency};
-use rustc_span::{DUMMY_SP, Ident, Span, Symbol, kw, sym};
+use rustc_span::{DUMMY_SP, Ident, Macros20NormalizedIdent, Span, Symbol, kw, sym};
 use smallvec::{SmallVec, smallvec};
 use tracing::debug;
 
@@ -112,34 +116,46 @@ impl Determinacy {
 }
 
 /// A specific scope in which a name can be looked up.
-/// This enum is currently used only for early resolution (imports and macros),
-/// but not for late resolution yet.
 #[derive(Clone, Copy, Debug)]
 enum Scope<'ra> {
+    /// Inert attributes registered by derive macros.
     DeriveHelpers(LocalExpnId),
+    /// Inert attributes registered by derive macros, but used before they are actually declared.
+    /// This scope will exist until the compatibility lint `LEGACY_DERIVE_HELPERS`
+    /// is turned into a hard error.
     DeriveHelpersCompat,
+    /// Textual `let`-like scopes introduced by `macro_rules!` items.
     MacroRules(MacroRulesScopeRef<'ra>),
-    // The node ID is for reporting the `PROC_MACRO_DERIVE_RESOLUTION_FALLBACK`
-    // lint if it should be reported.
+    /// Names declared in the given module.
+    /// The node ID is for reporting the `PROC_MACRO_DERIVE_RESOLUTION_FALLBACK`
+    /// lint if it should be reported.
     Module(Module<'ra>, Option<NodeId>),
+    /// Names introduced by `#[macro_use]` attributes on `extern crate` items.
     MacroUsePrelude,
+    /// Built-in attributes.
     BuiltinAttrs,
-    ExternPrelude,
+    /// Extern prelude names introduced by `extern crate` items.
+    ExternPreludeItems,
+    /// Extern prelude names introduced by `--extern` flags.
+    ExternPreludeFlags,
+    /// Tool modules introduced with `#![register_tool]`.
     ToolPrelude,
+    /// Standard library prelude introduced with an internal `#[prelude_import]` import.
     StdLibPrelude,
+    /// Built-in types.
     BuiltinTypes,
 }
 
 /// Names from different contexts may want to visit different subsets of all specific scopes
 /// with different restrictions when looking up the resolution.
-/// This enum is currently used only for early resolution (imports and macros),
-/// but not for late resolution yet.
 #[derive(Clone, Copy, Debug)]
 enum ScopeSet<'ra> {
     /// All scopes with the given namespace.
     All(Namespace),
     /// A module, then extern prelude (used for mixed 2015-2018 mode in macros).
     ModuleAndExternPrelude(Namespace, Module<'ra>),
+    /// Just two extern prelude scopes.
+    ExternPrelude,
     /// All scopes with macro namespace and the given macro kind restriction.
     Macro(MacroKind),
     /// All scopes with the given namespace, used for partially performing late resolution.
@@ -162,11 +178,11 @@ struct ParentScope<'ra> {
 impl<'ra> ParentScope<'ra> {
     /// Creates a parent scope with the passed argument used as the module scope component,
     /// and other scope components set to default empty values.
-    fn module(module: Module<'ra>, resolver: &Resolver<'ra, '_>) -> ParentScope<'ra> {
+    fn module(module: Module<'ra>, arenas: &'ra ResolverArenas<'ra>) -> ParentScope<'ra> {
         ParentScope {
             module,
             expansion: LocalExpnId::ROOT,
-            macro_rules: resolver.arenas.alloc_macro_rules_scope(MacroRulesScope::Empty),
+            macro_rules: arenas.alloc_macro_rules_scope(MacroRulesScope::Empty),
             derives: &[],
         }
     }
@@ -531,7 +547,7 @@ impl ModuleKind {
 struct BindingKey {
     /// The identifier for the binding, always the `normalize_to_macros_2_0` version of the
     /// identifier.
-    ident: Ident,
+    ident: Macros20NormalizedIdent,
     ns: Namespace,
     /// When we add an underscore binding (with ident `_`) to some module, this field has
     /// a non-zero value that uniquely identifies this binding in that module.
@@ -543,7 +559,7 @@ struct BindingKey {
 
 impl BindingKey {
     fn new(ident: Ident, ns: Namespace) -> Self {
-        BindingKey { ident: ident.normalize_to_macros_2_0(), ns, disambiguator: 0 }
+        BindingKey { ident: Macros20NormalizedIdent::new(ident), ns, disambiguator: 0 }
     }
 
     fn new_disambiguated(
@@ -552,7 +568,7 @@ impl BindingKey {
         disambiguator: impl FnOnce() -> u32,
     ) -> BindingKey {
         let disambiguator = if ident.name == kw::Underscore { disambiguator() } else { 0 };
-        BindingKey { ident: ident.normalize_to_macros_2_0(), ns, disambiguator }
+        BindingKey { ident: Macros20NormalizedIdent::new(ident), ns, disambiguator }
     }
 }
 
@@ -593,7 +609,8 @@ struct ModuleData<'ra> {
     globs: RefCell<Vec<Import<'ra>>>,
 
     /// Used to memoize the traits in this module for faster searches through all traits in scope.
-    traits: RefCell<Option<Box<[(Ident, NameBinding<'ra>, Option<Module<'ra>>)]>>>,
+    traits:
+        RefCell<Option<Box<[(Macros20NormalizedIdent, NameBinding<'ra>, Option<Module<'ra>>)]>>>,
 
     /// Span of the module itself. Used for error reporting.
     span: Span,
@@ -659,7 +676,7 @@ impl<'ra> Module<'ra> {
     fn for_each_child<'tcx, R: AsRef<Resolver<'ra, 'tcx>>>(
         self,
         resolver: &R,
-        mut f: impl FnMut(&R, Ident, Namespace, NameBinding<'ra>),
+        mut f: impl FnMut(&R, Macros20NormalizedIdent, Namespace, NameBinding<'ra>),
     ) {
         for (key, name_resolution) in resolver.as_ref().resolutions(self).borrow().iter() {
             if let Some(binding) = name_resolution.borrow().best_binding() {
@@ -671,7 +688,7 @@ impl<'ra> Module<'ra> {
     fn for_each_child_mut<'tcx, R: AsMut<Resolver<'ra, 'tcx>>>(
         self,
         resolver: &mut R,
-        mut f: impl FnMut(&mut R, Ident, Namespace, NameBinding<'ra>),
+        mut f: impl FnMut(&mut R, Macros20NormalizedIdent, Namespace, NameBinding<'ra>),
     ) {
         for (key, name_resolution) in resolver.as_mut().resolutions(self).borrow().iter() {
             if let Some(binding) = name_resolution.borrow().best_binding() {
@@ -820,6 +837,7 @@ struct PrivacyError<'ra> {
     parent_scope: ParentScope<'ra>,
     /// Is the format `use a::{b,c}`?
     single_nested: bool,
+    source: Option<ast::Expr>,
 }
 
 #[derive(Debug)]
@@ -966,8 +984,8 @@ impl<'ra> NameBindingData<'ra> {
         matches!(self.res(), Res::Def(DefKind::AssocConst | DefKind::AssocFn | DefKind::AssocTy, _))
     }
 
-    fn macro_kind(&self) -> Option<MacroKind> {
-        self.res().macro_kind()
+    fn macro_kinds(&self) -> Option<MacroKinds> {
+        self.res().macro_kinds()
     }
 
     // Suppose that we resolved macro invocation with `invoc_parent_expansion` to binding `binding`
@@ -1009,16 +1027,18 @@ impl<'ra> NameBindingData<'ra> {
 
 #[derive(Default, Clone)]
 struct ExternPreludeEntry<'ra> {
-    binding: Cell<Option<NameBinding<'ra>>>,
+    /// Binding from an `extern crate` item.
+    item_binding: Option<NameBinding<'ra>>,
+    /// Binding from an `--extern` flag, lazily populated on first use.
+    flag_binding: Cell<Option<NameBinding<'ra>>>,
+    /// There was no `--extern` flag introducing this name,
+    /// `flag_binding` doesn't need to be populated.
+    only_item: bool,
+    /// `item_binding` is non-redundant, happens either when `only_item` is true,
+    /// or when `extern crate` introducing `item_binding` used renaming.
     introduced_by_item: bool,
 }
 
-impl ExternPreludeEntry<'_> {
-    fn is_import(&self) -> bool {
-        self.binding.get().is_some_and(|binding| binding.is_import())
-    }
-}
-
 struct DeriveData {
     resolutions: Vec<DeriveResolution>,
     helper_attrs: Vec<(usize, Ident)>,
@@ -1053,21 +1073,25 @@ pub struct Resolver<'ra, 'tcx> {
 
     graph_root: Module<'ra>,
 
-    prelude: Option<Module<'ra>>,
-    extern_prelude: FxIndexMap<Ident, ExternPreludeEntry<'ra>>,
+    /// Assert that we are in speculative resolution mode.
+    assert_speculative: bool,
+
+    prelude: Option<Module<'ra>> = None,
+    extern_prelude: FxIndexMap<Macros20NormalizedIdent, ExternPreludeEntry<'ra>>,
 
     /// N.B., this is used only for better diagnostics, not name resolution itself.
     field_names: LocalDefIdMap<Vec<Ident>>,
+    field_defaults: LocalDefIdMap<Vec<Symbol>>,
 
     /// Span of the privacy modifier in fields of an item `DefId` accessible with dot syntax.
     /// Used for hints during error reporting.
     field_visibility_spans: FxHashMap<DefId, Vec<Span>>,
 
     /// All imports known to succeed or fail.
-    determined_imports: Vec<Import<'ra>>,
+    determined_imports: Vec<Import<'ra>> = Vec::new(),
 
     /// All non-determined imports.
-    indeterminate_imports: Vec<Import<'ra>>,
+    indeterminate_imports: Vec<Import<'ra>> = Vec::new(),
 
     // Spans for local variables found during pattern resolution.
     // Used for suggestions during error reporting.
@@ -1118,19 +1142,19 @@ pub struct Resolver<'ra, 'tcx> {
 
     /// Maps glob imports to the names of items actually imported.
     glob_map: FxIndexMap<LocalDefId, FxIndexSet<Symbol>>,
-    glob_error: Option<ErrorGuaranteed>,
-    visibilities_for_hashing: Vec<(LocalDefId, Visibility)>,
+    glob_error: Option<ErrorGuaranteed> = None,
+    visibilities_for_hashing: Vec<(LocalDefId, Visibility)> = Vec::new(),
     used_imports: FxHashSet<NodeId>,
     maybe_unused_trait_imports: FxIndexSet<LocalDefId>,
 
     /// Privacy errors are delayed until the end in order to deduplicate them.
-    privacy_errors: Vec<PrivacyError<'ra>>,
+    privacy_errors: Vec<PrivacyError<'ra>> = Vec::new(),
     /// Ambiguity errors are delayed for deduplication.
-    ambiguity_errors: Vec<AmbiguityError<'ra>>,
+    ambiguity_errors: Vec<AmbiguityError<'ra>> = Vec::new(),
     /// `use` injections are delayed for better placement and deduplication.
-    use_injections: Vec<UseError<'tcx>>,
+    use_injections: Vec<UseError<'tcx>> = Vec::new(),
     /// Crate-local macro expanded `macro_export` referred to by a module-relative path.
-    macro_expanded_macro_export_errors: BTreeSet<(Span, Span)>,
+    macro_expanded_macro_export_errors: BTreeSet<(Span, Span)> = BTreeSet::new(),
 
     arenas: &'ra ResolverArenas<'ra>,
     dummy_binding: NameBinding<'ra>,
@@ -1155,10 +1179,11 @@ pub struct Resolver<'ra, 'tcx> {
     unused_macro_rules: FxIndexMap<NodeId, DenseBitSet<usize>>,
     proc_macro_stubs: FxHashSet<LocalDefId>,
     /// Traces collected during macro resolution and validated when it's complete.
+    // FIXME: Remove interior mutability when speculative resolution produces these as outputs.
     single_segment_macro_resolutions:
-        Vec<(Ident, MacroKind, ParentScope<'ra>, Option<NameBinding<'ra>>, Option<Span>)>,
+        RefCell<Vec<(Ident, MacroKind, ParentScope<'ra>, Option<NameBinding<'ra>>, Option<Span>)>>,
     multi_segment_macro_resolutions:
-        Vec<(Vec<Segment>, Span, MacroKind, ParentScope<'ra>, Option<Res>, Namespace)>,
+        RefCell<Vec<(Vec<Segment>, Span, MacroKind, ParentScope<'ra>, Option<Res>, Namespace)>>,
     builtin_attrs: Vec<(Ident, ParentScope<'ra>)>,
     /// `derive(Copy)` marks items they are applied to so they are treated specially later.
     /// Derive macros cannot modify the item themselves and have to store the markers in the global
@@ -1181,9 +1206,9 @@ pub struct Resolver<'ra, 'tcx> {
     /// Avoid duplicated errors for "name already defined".
     name_already_seen: FxHashMap<Symbol, Span>,
 
-    potentially_unused_imports: Vec<Import<'ra>>,
+    potentially_unused_imports: Vec<Import<'ra>> = Vec::new(),
 
-    potentially_unnecessary_qualifications: Vec<UnnecessaryQualification<'ra>>,
+    potentially_unnecessary_qualifications: Vec<UnnecessaryQualification<'ra>> = Vec::new(),
 
     /// Table for mapping struct IDs into struct constructor IDs,
     /// it's not used during normal resolution, only for better error reporting.
@@ -1192,7 +1217,7 @@ pub struct Resolver<'ra, 'tcx> {
 
     lint_buffer: LintBuffer,
 
-    next_node_id: NodeId,
+    next_node_id: NodeId = CRATE_NODE_ID,
 
     node_id_to_def_id: NodeMap<Feed<'tcx, LocalDefId>>,
 
@@ -1210,17 +1235,17 @@ pub struct Resolver<'ra, 'tcx> {
     item_generics_num_lifetimes: FxHashMap<LocalDefId, usize>,
     delegation_fn_sigs: LocalDefIdMap<DelegationFnSig>,
 
-    main_def: Option<MainDefinition>,
+    main_def: Option<MainDefinition> = None,
     trait_impls: FxIndexMap<DefId, Vec<LocalDefId>>,
     /// A list of proc macro LocalDefIds, written out in the order in which
     /// they are declared in the static array generated by proc_macro_harness.
-    proc_macros: Vec<LocalDefId>,
+    proc_macros: Vec<LocalDefId> = Vec::new(),
     confused_type_with_std_module: FxIndexMap<Span, Span>,
     /// Whether lifetime elision was successful.
     lifetime_elision_allowed: FxHashSet<NodeId>,
 
     /// Names of items that were stripped out via cfg with their corresponding cfg meta item.
-    stripped_cfg_items: Vec<StrippedCfgItem<NodeId>>,
+    stripped_cfg_items: Vec<StrippedCfgItem<NodeId>> = Vec::new(),
 
     effective_visibilities: EffectiveVisibilities,
     doc_link_resolutions: FxIndexMap<LocalDefId, DocLinkResMap>,
@@ -1499,7 +1524,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     && let name = Symbol::intern(name)
                     && name.can_be_raw()
                 {
-                    Some((Ident::with_dummy_span(name), Default::default()))
+                    Some((Macros20NormalizedIdent::with_dummy_span(name), Default::default()))
                 } else {
                     None
                 }
@@ -1507,9 +1532,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             .collect();
 
         if !attr::contains_name(attrs, sym::no_core) {
-            extern_prelude.insert(Ident::with_dummy_span(sym::core), Default::default());
+            extern_prelude
+                .insert(Macros20NormalizedIdent::with_dummy_span(sym::core), Default::default());
             if !attr::contains_name(attrs, sym::no_std) {
-                extern_prelude.insert(Ident::with_dummy_span(sym::std), Default::default());
+                extern_prelude
+                    .insert(Macros20NormalizedIdent::with_dummy_span(sym::std), Default::default());
             }
         }
 
@@ -1524,15 +1551,14 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             // The outermost module has def ID 0; this is not reflected in the
             // AST.
             graph_root,
+            assert_speculative: false, // Only set/cleared in Resolver::resolve_imports for now
             prelude: None,
             extern_prelude,
 
             field_names: Default::default(),
+            field_defaults: Default::default(),
             field_visibility_spans: FxHashMap::default(),
 
-            determined_imports: Vec::new(),
-            indeterminate_imports: Vec::new(),
-
             pat_span_map: Default::default(),
             partial_res_map: Default::default(),
             import_res_map: Default::default(),
@@ -1551,16 +1577,9 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             ast_transform_scopes: FxHashMap::default(),
 
             glob_map: Default::default(),
-            glob_error: None,
-            visibilities_for_hashing: Default::default(),
             used_imports: FxHashSet::default(),
             maybe_unused_trait_imports: Default::default(),
 
-            privacy_errors: Vec::new(),
-            ambiguity_errors: Vec::new(),
-            use_injections: Vec::new(),
-            macro_expanded_macro_export_errors: BTreeSet::new(),
-
             arenas,
             dummy_binding: arenas.new_pub_res_binding(Res::Err, DUMMY_SP, LocalExpnId::ROOT),
             builtin_types_bindings: PrimTy::ALL
@@ -1604,8 +1623,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             derive_data: Default::default(),
             local_macro_def_scopes: FxHashMap::default(),
             name_already_seen: FxHashMap::default(),
-            potentially_unused_imports: Vec::new(),
-            potentially_unnecessary_qualifications: Default::default(),
             struct_constructors: Default::default(),
             unused_macros: Default::default(),
             unused_macro_rules: Default::default(),
@@ -1615,16 +1632,13 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             builtin_attrs: Default::default(),
             containers_deriving_copy: Default::default(),
             lint_buffer: LintBuffer::default(),
-            next_node_id: CRATE_NODE_ID,
             node_id_to_def_id,
             disambiguator: DisambiguatorState::new(),
             placeholder_field_indices: Default::default(),
             invocation_parents,
             legacy_const_generic_args: Default::default(),
             item_generics_num_lifetimes: Default::default(),
-            main_def: Default::default(),
             trait_impls: Default::default(),
-            proc_macros: Default::default(),
             confused_type_with_std_module: Default::default(),
             lifetime_elision_allowed: Default::default(),
             stripped_cfg_items: Default::default(),
@@ -1639,9 +1653,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             current_crate_outer_attr_insert_span,
             mods_with_parse_errors: Default::default(),
             impl_trait_names: Default::default(),
+            ..
         };
 
-        let root_parent_scope = ParentScope::module(graph_root, &resolver);
+        let root_parent_scope = ParentScope::module(graph_root, resolver.arenas);
         resolver.invocation_parent_scopes.insert(LocalExpnId::ROOT, root_parent_scope);
         resolver.feed_visibility(crate_feed, Visibility::Public);
 
@@ -1789,6 +1804,14 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         }
     }
 
+    /// Returns a conditionally mutable resolver.
+    ///
+    /// Currently only dependent on `assert_speculative`, if `assert_speculative` is false,
+    /// the resolver will allow mutation; otherwise, it will be immutable.
+    fn cm(&mut self) -> CmResolver<'_, 'ra, 'tcx> {
+        CmResolver::new(self, !self.assert_speculative)
+    }
+
     /// Runs the function on each namespace.
     fn per_ns<F: FnMut(&mut Self, Namespace)>(&mut self, mut f: F) {
         f(self, TypeNS);
@@ -1796,6 +1819,15 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         f(self, MacroNS);
     }
 
+    fn per_ns_cm<'r, F: FnMut(&mut CmResolver<'r, 'ra, 'tcx>, Namespace)>(
+        mut self: CmResolver<'r, 'ra, 'tcx>,
+        mut f: F,
+    ) {
+        f(&mut self, TypeNS);
+        f(&mut self, ValueNS);
+        f(&mut self, MacroNS);
+    }
+
     fn is_builtin_macro(&self, res: Res) -> bool {
         self.get_macro(res).is_some_and(|macro_data| macro_data.ext.builtin_name.is_some())
     }
@@ -1849,17 +1881,20 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             }
         }
 
-        self.visit_scopes(ScopeSet::All(TypeNS), parent_scope, ctxt, |this, scope, _, _| {
+        self.cm().visit_scopes(ScopeSet::All(TypeNS), parent_scope, ctxt, |this, scope, _, _| {
             match scope {
                 Scope::Module(module, _) => {
-                    this.traits_in_module(module, assoc_item, &mut found_traits);
+                    this.get_mut().traits_in_module(module, assoc_item, &mut found_traits);
                 }
                 Scope::StdLibPrelude => {
                     if let Some(module) = this.prelude {
-                        this.traits_in_module(module, assoc_item, &mut found_traits);
+                        this.get_mut().traits_in_module(module, assoc_item, &mut found_traits);
                     }
                 }
-                Scope::ExternPrelude | Scope::ToolPrelude | Scope::BuiltinTypes => {}
+                Scope::ExternPreludeItems
+                | Scope::ExternPreludeFlags
+                | Scope::ToolPrelude
+                | Scope::BuiltinTypes => {}
                 _ => unreachable!(),
             }
             None::<()>
@@ -1879,7 +1914,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         for &(trait_name, trait_binding, trait_module) in traits.as_ref().unwrap().iter() {
             if self.trait_may_have_item(trait_module, assoc_item) {
                 let def_id = trait_binding.res().def_id();
-                let import_ids = self.find_transitive_imports(&trait_binding.kind, trait_name);
+                let import_ids = self.find_transitive_imports(&trait_binding.kind, trait_name.0);
                 found_traits.push(TraitCandidate { def_id, import_ids });
             }
         }
@@ -1999,14 +2034,17 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 // Do not report the lint if the macro name resolves in stdlib prelude
                 // even without the problematic `macro_use` import.
                 let found_in_stdlib_prelude = self.prelude.is_some_and(|prelude| {
-                    self.maybe_resolve_ident_in_module(
-                        ModuleOrUniformRoot::Module(prelude),
-                        ident,
-                        MacroNS,
-                        &ParentScope::module(self.empty_module, self),
-                        None,
-                    )
-                    .is_ok()
+                    let empty_module = self.empty_module;
+                    let arenas = self.arenas;
+                    self.cm()
+                        .maybe_resolve_ident_in_module(
+                            ModuleOrUniformRoot::Module(prelude),
+                            ident,
+                            MacroNS,
+                            &ParentScope::module(empty_module, arenas),
+                            None,
+                        )
+                        .is_ok()
                 });
                 if !found_in_stdlib_prelude {
                     self.lint_buffer().buffer_lint(
@@ -2020,8 +2058,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             // Avoid marking `extern crate` items that refer to a name from extern prelude,
             // but not introduce it, as used if they are accessed from lexical scope.
             if used == Used::Scope {
-                if let Some(entry) = self.extern_prelude.get(&ident.normalize_to_macros_2_0()) {
-                    if !entry.introduced_by_item && entry.binding.get() == Some(used_binding) {
+                if let Some(entry) = self.extern_prelude.get(&Macros20NormalizedIdent::new(ident)) {
+                    if !entry.introduced_by_item && entry.item_binding == Some(used_binding) {
                         return;
                     }
                 }
@@ -2177,22 +2215,30 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         }
     }
 
-    fn extern_prelude_get(&mut self, ident: Ident, finalize: bool) -> Option<NameBinding<'ra>> {
-        let mut record_use = None;
-        let entry = self.extern_prelude.get(&ident.normalize_to_macros_2_0());
-        let binding = entry.and_then(|entry| match entry.binding.get() {
-            Some(binding) if binding.is_import() => {
-                if finalize {
-                    record_use = Some(binding);
-                }
-                Some(binding)
+    fn extern_prelude_get_item<'r>(
+        mut self: CmResolver<'r, 'ra, 'tcx>,
+        ident: Ident,
+        finalize: bool,
+    ) -> Option<NameBinding<'ra>> {
+        let entry = self.extern_prelude.get(&Macros20NormalizedIdent::new(ident));
+        entry.and_then(|entry| entry.item_binding).map(|binding| {
+            if finalize {
+                self.get_mut().record_use(ident, binding, Used::Scope);
             }
+            binding
+        })
+    }
+
+    fn extern_prelude_get_flag(&self, ident: Ident, finalize: bool) -> Option<NameBinding<'ra>> {
+        let entry = self.extern_prelude.get(&Macros20NormalizedIdent::new(ident));
+        entry.and_then(|entry| match entry.flag_binding.get() {
             Some(binding) => {
                 if finalize {
                     self.cstore_mut().process_path_extern(self.tcx, ident.name, ident.span);
                 }
                 Some(binding)
             }
+            None if entry.only_item => None,
             None => {
                 let crate_id = if finalize {
                     self.cstore_mut().process_path_extern(self.tcx, ident.name, ident.span)
@@ -2204,19 +2250,13 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         let res = Res::Def(DefKind::Mod, crate_id.as_def_id());
                         let binding =
                             self.arenas.new_pub_res_binding(res, DUMMY_SP, LocalExpnId::ROOT);
-                        entry.binding.set(Some(binding));
+                        entry.flag_binding.set(Some(binding));
                         Some(binding)
                     }
                     None => finalize.then_some(self.dummy_binding),
                 }
             }
-        });
-
-        if let Some(binding) = record_use {
-            self.record_use(ident, binding, Used::Scope);
-        }
-
-        binding
+        })
     }
 
     /// Rustdoc uses this to resolve doc link paths in a recoverable way. `PathResult<'a>`
@@ -2248,7 +2288,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             .collect();
         let Ok(segments) = segments else { return None };
 
-        match self.maybe_resolve_path(&segments, Some(ns), &parent_scope, None) {
+        match self.cm().maybe_resolve_path(&segments, Some(ns), &parent_scope, None) {
             PathResult::Module(ModuleOrUniformRoot::Module(module)) => Some(module.res().unwrap()),
             PathResult::NonModule(path_res) => {
                 path_res.full_res().filter(|res| !matches!(res, Res::Def(DefKind::Ctor(..), _)))
@@ -2284,6 +2324,21 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         }
     }
 
+    fn field_defaults(&self, def_id: DefId) -> Option<Vec<Symbol>> {
+        match def_id.as_local() {
+            Some(def_id) => self.field_defaults.get(&def_id).cloned(),
+            None => Some(
+                self.tcx
+                    .associated_item_def_ids(def_id)
+                    .iter()
+                    .filter_map(|&def_id| {
+                        self.tcx.default_field(def_id).map(|_| self.tcx.item_name(def_id))
+                    })
+                    .collect(),
+            ),
+        }
+    }
+
     /// Checks if an expression refers to a function marked with
     /// `#[rustc_legacy_const_generics]` and returns the argument index list
     /// from the attribute.
@@ -2327,9 +2382,9 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     fn resolve_main(&mut self) {
         let module = self.graph_root;
         let ident = Ident::with_dummy_span(sym::main);
-        let parent_scope = &ParentScope::module(module, self);
+        let parent_scope = &ParentScope::module(module, self.arenas);
 
-        let Ok(name_binding) = self.maybe_resolve_ident_in_module(
+        let Ok(name_binding) = self.cm().maybe_resolve_ident_in_module(
             ModuleOrUniformRoot::Module(module),
             ident,
             ValueNS,
@@ -2423,3 +2478,63 @@ impl Finalize {
 pub fn provide(providers: &mut Providers) {
     providers.registered_tools = macros::registered_tools;
 }
+
+mod ref_mut {
+    use std::ops::Deref;
+
+    /// A wrapper around a mutable reference that conditionally allows mutable access.
+    pub(crate) struct RefOrMut<'a, T> {
+        p: &'a mut T,
+        mutable: bool,
+    }
+
+    impl<'a, T> Deref for RefOrMut<'a, T> {
+        type Target = T;
+
+        fn deref(&self) -> &Self::Target {
+            self.p
+        }
+    }
+
+    impl<'a, T> AsRef<T> for RefOrMut<'a, T> {
+        fn as_ref(&self) -> &T {
+            self.p
+        }
+    }
+
+    impl<'a, T> RefOrMut<'a, T> {
+        pub(crate) fn new(p: &'a mut T, mutable: bool) -> Self {
+            RefOrMut { p, mutable }
+        }
+
+        /// This is needed because this wraps a `&mut T` and is therefore not `Copy`.
+        pub(crate) fn reborrow(&mut self) -> RefOrMut<'_, T> {
+            RefOrMut { p: self.p, mutable: self.mutable }
+        }
+
+        /// Returns a mutable reference to the inner value if allowed.
+        ///
+        /// # Panics
+        /// Panics if the `mutable` flag is false.
+        #[track_caller]
+        pub(crate) fn get_mut(&mut self) -> &mut T {
+            match self.mutable {
+                false => panic!("Can't mutably borrow speculative resolver"),
+                true => self.p,
+            }
+        }
+
+        /// Returns a mutable reference to the inner value without checking if
+        /// it's in a mutable state.
+        pub(crate) fn get_mut_unchecked(&mut self) -> &mut T {
+            self.p
+        }
+    }
+}
+
+/// A wrapper around `&mut Resolver` that may be mutable or immutable, depending on a conditions.
+///
+/// `Cm` stands for "conditionally mutable".
+///
+/// Prefer constructing it through [`Resolver::cm`] to ensure correctness.
+type CmResolver<'r, 'ra, 'tcx> = ref_mut::RefOrMut<'r, Resolver<'ra, 'tcx>>;
diff --git a/compiler/rustc_resolve/src/macros.rs b/compiler/rustc_resolve/src/macros.rs
index 4e3c0cd5bc0..72ed8990241 100644
--- a/compiler/rustc_resolve/src/macros.rs
+++ b/compiler/rustc_resolve/src/macros.rs
@@ -1,7 +1,6 @@
 //! A bunch of methods and structures more or less related to resolving macros and
 //! interface provided by `Resolver` to macro expander.
 
-use std::any::Any;
 use std::cell::Cell;
 use std::mem;
 use std::sync::Arc;
@@ -13,13 +12,13 @@ use rustc_expand::base::{
     Annotatable, DeriveResolution, Indeterminate, ResolverExpand, SyntaxExtension,
     SyntaxExtensionKind,
 };
+use rustc_expand::compile_declarative_macro;
 use rustc_expand::expand::{
     AstFragment, AstFragmentKind, Invocation, InvocationKind, SupportsMacroExpansion,
 };
-use rustc_expand::{MacroRulesMacroExpander, compile_declarative_macro};
 use rustc_hir::StabilityLevel;
 use rustc_hir::attrs::{CfgEntry, StrippedCfgItem};
-use rustc_hir::def::{self, DefKind, Namespace, NonMacroAttrKind};
+use rustc_hir::def::{self, DefKind, MacroKinds, Namespace, NonMacroAttrKind};
 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId};
 use rustc_middle::middle::stability;
 use rustc_middle::ty::{RegisteredTools, TyCtxt};
@@ -41,9 +40,9 @@ use crate::errors::{
 };
 use crate::imports::Import;
 use crate::{
-    BindingKey, DeriveData, Determinacy, Finalize, InvocationParent, MacroData, ModuleKind,
-    ModuleOrUniformRoot, NameBinding, NameBindingKind, ParentScope, PathResult, ResolutionError,
-    Resolver, ScopeSet, Segment, Used,
+    BindingKey, CmResolver, DeriveData, Determinacy, Finalize, InvocationParent, MacroData,
+    ModuleKind, ModuleOrUniformRoot, NameBinding, NameBindingKind, ParentScope, PathResult,
+    ResolutionError, Resolver, ScopeSet, Segment, Used,
 };
 
 type Res = def::Res<NodeId>;
@@ -86,22 +85,19 @@ pub(crate) type MacroRulesScopeRef<'ra> = &'ra Cell<MacroRulesScope<'ra>>;
 /// one for attribute-like macros (attributes, derives).
 /// We ignore resolutions from one sub-namespace when searching names in scope for another.
 pub(crate) fn sub_namespace_match(
-    candidate: Option<MacroKind>,
+    candidate: Option<MacroKinds>,
     requirement: Option<MacroKind>,
 ) -> bool {
-    #[derive(PartialEq)]
-    enum SubNS {
-        Bang,
-        AttrLike,
-    }
-    let sub_ns = |kind| match kind {
-        MacroKind::Bang => SubNS::Bang,
-        MacroKind::Attr | MacroKind::Derive => SubNS::AttrLike,
-    };
-    let candidate = candidate.map(sub_ns);
-    let requirement = requirement.map(sub_ns);
     // "No specific sub-namespace" means "matches anything" for both requirements and candidates.
-    candidate.is_none() || requirement.is_none() || candidate == requirement
+    let (Some(candidate), Some(requirement)) = (candidate, requirement) else {
+        return true;
+    };
+    match requirement {
+        MacroKind::Bang => candidate.contains(MacroKinds::BANG),
+        MacroKind::Attr | MacroKind::Derive => {
+            candidate.intersects(MacroKinds::ATTR | MacroKinds::DERIVE)
+        }
+    }
 }
 
 // We don't want to format a path using pretty-printing,
@@ -323,6 +319,7 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
                 parent_scope.expansion,
                 span,
                 fast_print_path(path),
+                kind,
                 def_id,
                 def_id.map(|def_id| self.macro_def_scope(def_id).nearest_parent_mod()),
             ),
@@ -356,11 +353,7 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
             }
             let def_id = self.local_def_id(node_id);
             let m = &self.local_macro_map[&def_id];
-            let SyntaxExtensionKind::LegacyBang(ref ext) = m.ext.kind else {
-                continue;
-            };
-            let ext: &dyn Any = ext.as_ref();
-            let Some(m) = ext.downcast_ref::<MacroRulesMacroExpander>() else {
+            let SyntaxExtensionKind::MacroRules(ref m) = m.ext.kind else {
                 continue;
             };
             for arm_i in unused_arms.iter() {
@@ -403,9 +396,9 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
         for (i, resolution) in entry.resolutions.iter_mut().enumerate() {
             if resolution.exts.is_none() {
                 resolution.exts = Some(
-                    match self.resolve_macro_path(
+                    match self.cm().resolve_macro_path(
                         &resolution.path,
-                        Some(MacroKind::Derive),
+                        MacroKind::Derive,
                         &parent_scope,
                         true,
                         force,
@@ -536,11 +529,11 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
         target_trait.for_each_child(self, |this, ident, ns, _binding| {
             // FIXME: Adjust hygiene for idents from globs, like for glob imports.
             if let Some(overriding_keys) = this.impl_binding_keys.get(&impl_def_id)
-                && overriding_keys.contains(&BindingKey::new(ident, ns))
+                && overriding_keys.contains(&BindingKey::new(ident.0, ns))
             {
                 // The name is overridden, do not produce it from the glob delegation.
             } else {
-                idents.push((ident, None));
+                idents.push((ident.0, None));
             }
         });
         Ok(idents)
@@ -568,9 +561,9 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         invoc_in_mod_inert_attr: Option<LocalDefId>,
         suggestion_span: Option<Span>,
     ) -> Result<(Arc<SyntaxExtension>, Res), Indeterminate> {
-        let (ext, res) = match self.resolve_macro_or_delegation_path(
+        let (ext, res) = match self.cm().resolve_macro_or_delegation_path(
             path,
-            Some(kind),
+            kind,
             parent_scope,
             true,
             force,
@@ -633,7 +626,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
         self.check_stability_and_deprecation(&ext, path, node_id);
 
-        let unexpected_res = if ext.macro_kind() != kind {
+        let unexpected_res = if !ext.macro_kinds().contains(kind.into()) {
             Some((kind.article(), kind.descr_expected()))
         } else if matches!(res, Res::Def(..)) {
             match supports_macro_expansion {
@@ -665,7 +658,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             // Suggest moving the macro out of the derive() if the macro isn't Derive
             if !path.span.from_expansion()
                 && kind == MacroKind::Derive
-                && ext.macro_kind() != MacroKind::Derive
+                && !ext.macro_kinds().contains(MacroKinds::DERIVE)
+                && ext.macro_kinds().contains(MacroKinds::ATTR)
             {
                 err.remove_surrounding_derive = Some(RemoveSurroundingDerive { span: path.span });
                 err.add_as_non_derive = Some(AddAsNonDerive { macro_path: &path_str });
@@ -713,10 +707,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         Ok((ext, res))
     }
 
-    pub(crate) fn resolve_macro_path(
-        &mut self,
+    pub(crate) fn resolve_macro_path<'r>(
+        self: CmResolver<'r, 'ra, 'tcx>,
         path: &ast::Path,
-        kind: Option<MacroKind>,
+        kind: MacroKind,
         parent_scope: &ParentScope<'ra>,
         trace: bool,
         force: bool,
@@ -736,10 +730,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         )
     }
 
-    fn resolve_macro_or_delegation_path(
-        &mut self,
+    fn resolve_macro_or_delegation_path<'r>(
+        mut self: CmResolver<'r, 'ra, 'tcx>,
         ast_path: &ast::Path,
-        kind: Option<MacroKind>,
+        kind: MacroKind,
         parent_scope: &ParentScope<'ra>,
         trace: bool,
         force: bool,
@@ -753,7 +747,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
         // Possibly apply the macro helper hack
         if deleg_impl.is_none()
-            && kind == Some(MacroKind::Bang)
+            && kind == MacroKind::Bang
             && let [segment] = path.as_slice()
             && segment.ident.span.ctxt().outer_expn_data().local_inner_macros
         {
@@ -763,7 +757,12 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
         let res = if deleg_impl.is_some() || path.len() > 1 {
             let ns = if deleg_impl.is_some() { TypeNS } else { MacroNS };
-            let res = match self.maybe_resolve_path(&path, Some(ns), parent_scope, ignore_import) {
+            let res = match self.reborrow().maybe_resolve_path(
+                &path,
+                Some(ns),
+                parent_scope,
+                ignore_import,
+            ) {
                 PathResult::NonModule(path_res) if let Some(res) = path_res.full_res() => Ok(res),
                 PathResult::Indeterminate if !force => return Err(Determinacy::Undetermined),
                 PathResult::NonModule(..)
@@ -776,8 +775,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             };
 
             if trace {
-                let kind = kind.expect("macro kind must be specified if tracing is enabled");
-                self.multi_segment_macro_resolutions.push((
+                // FIXME: Should be an output of Speculative Resolution.
+                self.multi_segment_macro_resolutions.borrow_mut().push((
                     path,
                     path_span,
                     kind,
@@ -790,10 +789,9 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             self.prohibit_imported_non_macro_attrs(None, res.ok(), path_span);
             res
         } else {
-            let scope_set = kind.map_or(ScopeSet::All(MacroNS), ScopeSet::Macro);
-            let binding = self.early_resolve_ident_in_lexical_scope(
+            let binding = self.reborrow().early_resolve_ident_in_lexical_scope(
                 path[0].ident,
-                scope_set,
+                ScopeSet::Macro(kind),
                 parent_scope,
                 None,
                 force,
@@ -805,8 +803,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             }
 
             if trace {
-                let kind = kind.expect("macro kind must be specified if tracing is enabled");
-                self.single_segment_macro_resolutions.push((
+                // FIXME: Should be an output of Speculative Resolution.
+                self.single_segment_macro_resolutions.borrow_mut().push((
                     path[0].ident,
                     kind,
                     *parent_scope,
@@ -817,7 +815,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
             let res = binding.map(|binding| binding.res());
             self.prohibit_imported_non_macro_attrs(binding.ok(), res.ok(), path_span);
-            self.report_out_of_scope_macro_calls(
+            self.reborrow().report_out_of_scope_macro_calls(
                 ast_path,
                 parent_scope,
                 invoc_in_mod_inert_attr,
@@ -872,13 +870,14 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             }
         };
 
-        let macro_resolutions = mem::take(&mut self.multi_segment_macro_resolutions);
+        // FIXME: Should be an output of Speculative Resolution.
+        let macro_resolutions = self.multi_segment_macro_resolutions.take();
         for (mut path, path_span, kind, parent_scope, initial_res, ns) in macro_resolutions {
             // FIXME: Path resolution will ICE if segment IDs present.
             for seg in &mut path {
                 seg.id = None;
             }
-            match self.resolve_path(
+            match self.cm().resolve_path(
                 &path,
                 Some(ns),
                 &parent_scope,
@@ -905,8 +904,9 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                             path_res
                         {
                             // try to suggest if it's not a macro, maybe a function
-                            if let PathResult::NonModule(partial_res) =
-                                self.maybe_resolve_path(&path, Some(ValueNS), &parent_scope, None)
+                            if let PathResult::NonModule(partial_res) = self
+                                .cm()
+                                .maybe_resolve_path(&path, Some(ValueNS), &parent_scope, None)
                                 && partial_res.unresolved_segments() == 0
                             {
                                 let sm = self.tcx.sess.source_map();
@@ -948,9 +948,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             }
         }
 
-        let macro_resolutions = mem::take(&mut self.single_segment_macro_resolutions);
+        // FIXME: Should be an output of Speculative Resolution.
+        let macro_resolutions = self.single_segment_macro_resolutions.take();
         for (ident, kind, parent_scope, initial_binding, sugg_span) in macro_resolutions {
-            match self.early_resolve_ident_in_lexical_scope(
+            match self.cm().early_resolve_ident_in_lexical_scope(
                 ident,
                 ScopeSet::Macro(kind),
                 &parent_scope,
@@ -1005,7 +1006,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
         let builtin_attrs = mem::take(&mut self.builtin_attrs);
         for (ident, parent_scope) in builtin_attrs {
-            let _ = self.early_resolve_ident_in_lexical_scope(
+            let _ = self.cm().early_resolve_ident_in_lexical_scope(
                 ident,
                 ScopeSet::Macro(MacroKind::Attr),
                 &parent_scope,
@@ -1090,8 +1091,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         }
     }
 
-    fn report_out_of_scope_macro_calls(
-        &mut self,
+    fn report_out_of_scope_macro_calls<'r>(
+        mut self: CmResolver<'r, 'ra, 'tcx>,
         path: &ast::Path,
         parent_scope: &ParentScope<'ra>,
         invoc_in_mod_inert_attr: Option<(LocalDefId, NodeId)>,
@@ -1101,7 +1102,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             && let Some(binding) = binding
             // This is a `macro_rules` itself, not some import.
             && let NameBindingKind::Res(res) = binding.kind
-            && let Res::Def(DefKind::Macro(MacroKind::Bang), def_id) = res
+            && let Res::Def(DefKind::Macro(kinds), def_id) = res
+            && kinds.contains(MacroKinds::BANG)
             // And the `macro_rules` is defined inside the attribute's module,
             // so it cannot be in scope unless imported.
             && self.tcx.is_descendant_of(def_id, mod_def_id.to_def_id())
@@ -1110,7 +1112,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             // If such resolution is successful and gives the same result
             // (e.g. if the macro is re-imported), then silence the lint.
             let no_macro_rules = self.arenas.alloc_macro_rules_scope(MacroRulesScope::Empty);
-            let fallback_binding = self.early_resolve_ident_in_lexical_scope(
+            let fallback_binding = self.reborrow().early_resolve_ident_in_lexical_scope(
                 path.segments[0].ident,
                 ScopeSet::Macro(MacroKind::Bang),
                 &ParentScope { macro_rules: no_macro_rules, ..*parent_scope },
@@ -1148,8 +1150,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         // Reserve some names that are not quite covered by the general check
         // performed on `Resolver::builtin_attrs`.
         if ident.name == sym::cfg || ident.name == sym::cfg_attr {
-            let macro_kind = self.get_macro(res).map(|macro_data| macro_data.ext.macro_kind());
-            if macro_kind.is_some() && sub_namespace_match(macro_kind, Some(MacroKind::Attr)) {
+            let macro_kinds = self.get_macro(res).map(|macro_data| macro_data.ext.macro_kinds());
+            if macro_kinds.is_some() && sub_namespace_match(macro_kinds, Some(MacroKind::Attr)) {
                 self.dcx()
                     .emit_err(errors::NameReservedInAttributeNamespace { span: ident.span, ident });
             }
@@ -1206,7 +1208,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
         let mut indeterminate = false;
         for ns in namespaces {
-            match self.maybe_resolve_path(path, Some(*ns), &parent_scope, None) {
+            match self.cm().maybe_resolve_path(path, Some(*ns), &parent_scope, None) {
                 PathResult::Module(ModuleOrUniformRoot::Module(_)) => return Ok(true),
                 PathResult::NonModule(partial_res) if partial_res.unresolved_segments() == 0 => {
                     return Ok(true);
diff --git a/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/transform.rs b/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/transform.rs
index 52717d73b8a..d81fa062e01 100644
--- a/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/transform.rs
+++ b/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/transform.rs
@@ -342,7 +342,7 @@ pub(crate) fn transform_instance<'tcx>(
         let upcast_ty = match tcx.trait_of_assoc(def_id) {
             Some(trait_id) => trait_object_ty(
                 tcx,
-                ty::Binder::dummy(ty::TraitRef::from_method(tcx, trait_id, instance.args)),
+                ty::Binder::dummy(ty::TraitRef::from_assoc(tcx, trait_id, instance.args)),
             ),
             // drop_in_place won't have a defining trait, skip the upcast
             None => instance.args.type_at(0),
@@ -481,7 +481,7 @@ fn implemented_method<'tcx>(
         trait_method = trait_method_bound;
         method_id = instance.def_id();
         trait_id = tcx.trait_of_assoc(method_id)?;
-        trait_ref = ty::EarlyBinder::bind(TraitRef::from_method(tcx, trait_id, instance.args));
+        trait_ref = ty::EarlyBinder::bind(TraitRef::from_assoc(tcx, trait_id, instance.args));
         trait_id
     } else {
         return None;
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index cfeadf3c759..9793d8091e2 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -16,10 +16,11 @@ use std::{cmp, fmt, fs, iter};
 
 use externs::{ExternOpt, split_extern_opt};
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
-use rustc_data_structures::stable_hasher::{StableOrd, ToStableHashKey};
+use rustc_data_structures::stable_hasher::{StableHasher, StableOrd, ToStableHashKey};
 use rustc_errors::emitter::HumanReadableErrorType;
 use rustc_errors::{ColorConfig, DiagArgValue, DiagCtxtFlags, IntoDiagArg};
 use rustc_feature::UnstableFeatures;
+use rustc_hashes::Hash64;
 use rustc_macros::{Decodable, Encodable, HashStable_Generic};
 use rustc_span::edition::{DEFAULT_EDITION, EDITION_NAME_LIST, Edition, LATEST_STABLE_EDITION};
 use rustc_span::source_map::FilePathMapping;
@@ -190,7 +191,7 @@ pub struct CoverageOptions {
     pub discard_all_spans_in_codegen: bool,
 }
 
-/// Controls whether branch coverage or MC/DC coverage is enabled.
+/// Controls whether branch coverage is enabled.
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Default)]
 pub enum CoverageLevel {
     /// Instrument for coverage at the MIR block level.
@@ -214,9 +215,6 @@ pub enum CoverageLevel {
     /// instrumentation, so it might be removed in the future when MC/DC is
     /// sufficiently complete, or if it is making MC/DC changes difficult.
     Condition,
-    /// Instrument for MC/DC. Mostly a superset of condition coverage, but might
-    /// differ in some corner cases.
-    Mcdc,
 }
 
 // The different settings that the `-Z offload` flag can have.
@@ -1198,7 +1196,25 @@ pub struct OutputFilenames {
 pub const RLINK_EXT: &str = "rlink";
 pub const RUST_CGU_EXT: &str = "rcgu";
 pub const DWARF_OBJECT_EXT: &str = "dwo";
+pub const MAX_FILENAME_LENGTH: usize = 143; // ecryptfs limits filenames to 143 bytes see #49914
 
+/// Ensure the filename is not too long, as some filesystems have a limit.
+/// If the filename is too long, hash part of it and append the hash to the filename.
+/// This is a workaround for long crate names generating overly long filenames.
+fn maybe_strip_file_name(mut path: PathBuf) -> PathBuf {
+    if path.file_name().map_or(0, |name| name.len()) > MAX_FILENAME_LENGTH {
+        let filename = path.file_name().unwrap().to_string_lossy();
+        let hash_len = 64 / 4; // Hash64 is 64 bits encoded in hex
+        let stripped_len = filename.len() - MAX_FILENAME_LENGTH + hash_len;
+
+        let mut hasher = StableHasher::new();
+        filename[..stripped_len].hash(&mut hasher);
+        let hash = hasher.finish::<Hash64>();
+
+        path.set_file_name(format!("{:x}-{}", hash, &filename[stripped_len..]));
+    }
+    path
+}
 impl OutputFilenames {
     pub fn new(
         out_directory: PathBuf,
@@ -1291,7 +1307,7 @@ impl OutputFilenames {
         }
 
         let temps_directory = self.temps_directory.as_ref().unwrap_or(&self.out_directory);
-        self.with_directory_and_extension(temps_directory, &extension)
+        maybe_strip_file_name(self.with_directory_and_extension(temps_directory, &extension))
     }
 
     pub fn temp_path_for_diagnostic(&self, ext: &str) -> PathBuf {
@@ -2831,16 +2847,27 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
         // This is the location used by the `rustc-dev` `rustup` component.
         real_source_base_dir("lib/rustlib/rustc-src/rust", "compiler/rustc/src/main.rs");
 
-    let mut search_paths = vec![];
-    for s in &matches.opt_strs("L") {
-        search_paths.push(SearchPath::from_cli_opt(
-            sysroot.path(),
-            &target_triple,
-            early_dcx,
-            s,
-            unstable_opts.unstable_options,
-        ));
-    }
+    // We eagerly scan all files in each passed -L path. If the same directory is passed multiple
+    // times, and the directory contains a lot of files, this can take a lot of time.
+    // So we remove -L paths that were passed multiple times, and keep only the first occurrence.
+    // We still have to keep the original order of the -L arguments.
+    let search_paths: Vec<SearchPath> = {
+        let mut seen_search_paths = FxHashSet::default();
+        let search_path_matches: Vec<String> = matches.opt_strs("L");
+        search_path_matches
+            .iter()
+            .filter(|p| seen_search_paths.insert(*p))
+            .map(|path| {
+                SearchPath::from_cli_opt(
+                    sysroot.path(),
+                    &target_triple,
+                    early_dcx,
+                    &path,
+                    unstable_opts.unstable_options,
+                )
+            })
+            .collect()
+    };
 
     let working_dir = std::env::current_dir().unwrap_or_else(|e| {
         early_dcx.early_fatal(format!("Current directory is invalid: {e}"));
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 880b08d4444..0e112edc733 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -755,7 +755,7 @@ mod desc {
     pub(crate) const parse_linker_flavor: &str = ::rustc_target::spec::LinkerFlavorCli::one_of();
     pub(crate) const parse_dump_mono_stats: &str = "`markdown` (default) or `json`";
     pub(crate) const parse_instrument_coverage: &str = parse_bool;
-    pub(crate) const parse_coverage_options: &str = "`block` | `branch` | `condition` | `mcdc`";
+    pub(crate) const parse_coverage_options: &str = "`block` | `branch` | `condition`";
     pub(crate) const parse_instrument_xray: &str = "either a boolean (`yes`, `no`, `on`, `off`, etc), or a comma separated list of settings: `always` or `never` (mutually exclusive), `ignore-loops`, `instruction-threshold=N`, `skip-entry`, `skip-exit`";
     pub(crate) const parse_unpretty: &str = "`string` or `string=string`";
     pub(crate) const parse_treat_err_as_bug: &str = "either no value or a non-negative number";
@@ -1458,7 +1458,6 @@ pub mod parse {
                 "block" => slot.level = CoverageLevel::Block,
                 "branch" => slot.level = CoverageLevel::Branch,
                 "condition" => slot.level = CoverageLevel::Condition,
-                "mcdc" => slot.level = CoverageLevel::Mcdc,
                 "discard-all-spans-in-codegen" => slot.discard_all_spans_in_codegen = true,
                 _ => return false,
             }
@@ -2166,6 +2165,8 @@ options! {
         "hash algorithm of source files used to check freshness in cargo (`blake3` or `sha256`)"),
     codegen_backend: Option<String> = (None, parse_opt_string, [TRACKED],
         "the backend to use"),
+    codegen_source_order: bool = (false, parse_bool, [UNTRACKED],
+        "emit mono items in the order of spans in source files (default: no)"),
     contract_checks: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "emit runtime checks for contract pre- and post-conditions (default: no)"),
     coverage_options: CoverageOptions = (CoverageOptions::default(), parse_coverage_options, [TRACKED],
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index b94636fea94..c6956cf5f23 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -354,11 +354,6 @@ impl Session {
             && self.opts.unstable_opts.coverage_options.level >= CoverageLevel::Condition
     }
 
-    pub fn instrument_coverage_mcdc(&self) -> bool {
-        self.instrument_coverage()
-            && self.opts.unstable_opts.coverage_options.level >= CoverageLevel::Mcdc
-    }
-
     /// Provides direct access to the `CoverageOptions` struct, so that
     /// individual flags for debugging/testing coverage instrumetation don't
     /// need separate accessors.
diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index 3f72ccd9f89..d647ec28aae 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -66,7 +66,8 @@ pub use span_encoding::{DUMMY_SP, Span};
 
 pub mod symbol;
 pub use symbol::{
-    ByteSymbol, Ident, MacroRulesNormalizedIdent, STDLIB_STABLE_CRATES, Symbol, kw, sym,
+    ByteSymbol, Ident, MacroRulesNormalizedIdent, Macros20NormalizedIdent, STDLIB_STABLE_CRATES,
+    Symbol, kw, sym,
 };
 
 mod analyze_source_file;
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index d54175548e3..f4a6d0f5891 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -3,6 +3,7 @@
 //! type, and vice versa.
 
 use std::hash::{Hash, Hasher};
+use std::ops::Deref;
 use std::{fmt, str};
 
 use rustc_arena::DroplessArena;
@@ -279,6 +280,7 @@ symbols! {
         IterPeekable,
         Iterator,
         IteratorItem,
+        IteratorMap,
         Layout,
         Left,
         LinkedList,
@@ -390,6 +392,7 @@ symbols! {
         __D,
         __H,
         __S,
+        __T,
         __awaitee,
         __try_var,
         _t,
@@ -540,9 +543,11 @@ symbols! {
         audit_that,
         augmented_assignments,
         auto_traits,
+        autodiff,
         autodiff_forward,
         autodiff_reverse,
         automatically_derived,
+        available_externally,
         avx,
         avx10_target_feature,
         avx512_target_feature,
@@ -674,6 +679,7 @@ symbols! {
         cold_path,
         collapse_debuginfo,
         column,
+        common,
         compare_bytes,
         compare_exchange,
         compare_exchange_weak,
@@ -741,6 +747,7 @@ symbols! {
         contracts_ensures,
         contracts_internals,
         contracts_requires,
+        convert,
         convert_identity,
         copy,
         copy_closures,
@@ -842,6 +849,7 @@ symbols! {
         derive_const,
         derive_const_issue: "118304",
         derive_default_enum,
+        derive_from,
         derive_smart_pointer,
         destruct,
         destructuring_assignment,
@@ -954,6 +962,7 @@ symbols! {
         extern_prelude,
         extern_system_varargs,
         extern_types,
+        extern_weak,
         external,
         external_doc,
         f,
@@ -1211,6 +1220,7 @@ symbols! {
         instruction_set,
         integer_: "integer", // underscore to avoid clashing with the function `sym::integer` below
         integral,
+        internal,
         internal_features,
         into_async_iter_into_iter,
         into_future,
@@ -1285,6 +1295,8 @@ symbols! {
         linkage,
         linker,
         linker_messages,
+        linkonce,
+        linkonce_odr,
         lint_reasons,
         literal,
         load,
@@ -1310,6 +1322,7 @@ symbols! {
         lt,
         m68k_target_feature,
         macro_at_most_once_rep,
+        macro_attr,
         macro_attributes_in_derive_output,
         macro_concat,
         macro_escape,
@@ -1512,6 +1525,7 @@ symbols! {
         not,
         notable_trait,
         note,
+        nvptx_target_feature,
         object_safe_for_dispatch,
         of,
         off,
@@ -1579,6 +1593,7 @@ symbols! {
         panic_const_shl_overflow,
         panic_const_shr_overflow,
         panic_const_sub_overflow,
+        panic_display,
         panic_fmt,
         panic_handler,
         panic_impl,
@@ -1824,7 +1839,6 @@ symbols! {
         rustc_coherence_is_core,
         rustc_coinductive,
         rustc_confusables,
-        rustc_const_panic_str,
         rustc_const_stable,
         rustc_const_stable_indirect,
         rustc_const_unstable,
@@ -2320,6 +2334,7 @@ symbols! {
         va_start,
         val,
         validity,
+        value,
         values,
         var,
         variant_count,
@@ -2356,6 +2371,8 @@ symbols! {
         wasm_abi,
         wasm_import_module,
         wasm_target_feature,
+        weak,
+        weak_odr,
         where_clause_attrs,
         while_let,
         width,
@@ -2562,16 +2579,17 @@ impl fmt::Display for IdentPrinter {
 }
 
 /// An newtype around `Ident` that calls [Ident::normalize_to_macro_rules] on
-/// construction.
-// FIXME(matthewj, petrochenkov) Use this more often, add a similar
-// `ModernIdent` struct and use that as well.
+/// construction for "local variable hygiene" comparisons.
+///
+/// Use this type when you need to compare identifiers according to macro_rules hygiene.
+/// This ensures compile-time safety and avoids manual normalization calls.
 #[derive(Copy, Clone, Eq, PartialEq, Hash)]
 pub struct MacroRulesNormalizedIdent(Ident);
 
 impl MacroRulesNormalizedIdent {
     #[inline]
     pub fn new(ident: Ident) -> Self {
-        Self(ident.normalize_to_macro_rules())
+        MacroRulesNormalizedIdent(ident.normalize_to_macro_rules())
     }
 }
 
@@ -2587,6 +2605,48 @@ impl fmt::Display for MacroRulesNormalizedIdent {
     }
 }
 
+/// An newtype around `Ident` that calls [Ident::normalize_to_macros_2_0] on
+/// construction for "item hygiene" comparisons.
+///
+/// Identifiers with same string value become same if they came from the same macro 2.0 macro
+/// (e.g., `macro` item, but not `macro_rules` item) and stay different if they came from
+/// different macro 2.0 macros.
+#[derive(Copy, Clone, Eq, PartialEq, Hash)]
+pub struct Macros20NormalizedIdent(pub Ident);
+
+impl Macros20NormalizedIdent {
+    #[inline]
+    pub fn new(ident: Ident) -> Self {
+        Macros20NormalizedIdent(ident.normalize_to_macros_2_0())
+    }
+
+    // dummy_span does not need to be normalized, so we can use `Ident` directly
+    pub fn with_dummy_span(name: Symbol) -> Self {
+        Macros20NormalizedIdent(Ident::with_dummy_span(name))
+    }
+}
+
+impl fmt::Debug for Macros20NormalizedIdent {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&self.0, f)
+    }
+}
+
+impl fmt::Display for Macros20NormalizedIdent {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.0, f)
+    }
+}
+
+/// By impl Deref, we can access the wrapped Ident as if it were a normal Ident
+/// such as `norm_ident.name` instead of `norm_ident.0.name`.
+impl Deref for Macros20NormalizedIdent {
+    type Target = Ident;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
 /// An interned UTF-8 string.
 ///
 /// Internally, a `Symbol` is implemented as an index, and all operations
diff --git a/compiler/rustc_symbol_mangling/src/export.rs b/compiler/rustc_symbol_mangling/src/export.rs
index 956c996326b..76ac82cf95a 100644
--- a/compiler/rustc_symbol_mangling/src/export.rs
+++ b/compiler/rustc_symbol_mangling/src/export.rs
@@ -21,7 +21,7 @@ macro_rules! default_hash_impl {
     };
 }
 
-default_hash_impl! { i8, i16, i32, i64, i128, isize, u8, u16, u32, u64, u128, usize, }
+default_hash_impl! { u8, u64, usize, }
 
 impl<'tcx> AbiHashStable<'tcx> for bool {
     #[inline]
@@ -37,13 +37,6 @@ impl<'tcx> AbiHashStable<'tcx> for str {
     }
 }
 
-impl<'tcx> AbiHashStable<'tcx> for String {
-    #[inline]
-    fn abi_hash(&self, tcx: TyCtxt<'tcx>, hasher: &mut StableHasher) {
-        self[..].abi_hash(tcx, hasher);
-    }
-}
-
 impl<'tcx> AbiHashStable<'tcx> for Symbol {
     #[inline]
     fn abi_hash(&self, tcx: TyCtxt<'tcx>, hasher: &mut StableHasher) {
diff --git a/compiler/rustc_symbol_mangling/src/legacy.rs b/compiler/rustc_symbol_mangling/src/legacy.rs
index aa8292c0504..4d9741f1d11 100644
--- a/compiler/rustc_symbol_mangling/src/legacy.rs
+++ b/compiler/rustc_symbol_mangling/src/legacy.rs
@@ -58,7 +58,7 @@ pub(super) fn mangle<'tcx>(
 
     let hash = get_symbol_hash(tcx, instance, instance_ty, instantiating_crate);
 
-    let mut p = SymbolPrinter { tcx, path: SymbolPath::new(), keep_within_component: false };
+    let mut p = LegacySymbolMangler { tcx, path: SymbolPath::new(), keep_within_component: false };
     p.print_def_path(
         def_id,
         if let ty::InstanceKind::DropGlue(_, _)
@@ -213,13 +213,13 @@ impl SymbolPath {
     }
 }
 
-struct SymbolPrinter<'tcx> {
+struct LegacySymbolMangler<'tcx> {
     tcx: TyCtxt<'tcx>,
     path: SymbolPath,
 
     // When `true`, `finalize_pending_component` isn't used.
-    // This is needed when recursing into `path_qualified`,
-    // or `path_generic_args`, as any nested paths are
+    // This is needed when recursing into `print_path_with_qualified`,
+    // or `print_path_with_generic_args`, as any nested paths are
     // logically within one component.
     keep_within_component: bool,
 }
@@ -228,13 +228,16 @@ struct SymbolPrinter<'tcx> {
 // `PrettyPrinter` aka pretty printing of e.g. types in paths,
 // symbol names should have their own printing machinery.
 
-impl<'tcx> Printer<'tcx> for SymbolPrinter<'tcx> {
+impl<'tcx> Printer<'tcx> for LegacySymbolMangler<'tcx> {
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }
 
     fn print_region(&mut self, _region: ty::Region<'_>) -> Result<(), PrintError> {
-        unreachable!(); // because `<Self As PrettyPrinter>::should_print_region` returns false
+        // This might be reachable (via `pretty_print_dyn_existential`) even though
+        // `<Self As PrettyPrinter>::should_print_optional_region` returns false and
+        // `print_path_with_generic_args` filters out lifetimes. See #144994.
+        Ok(())
     }
 
     fn print_type(&mut self, ty: Ty<'tcx>) -> Result<(), PrintError> {
@@ -303,16 +306,17 @@ impl<'tcx> Printer<'tcx> for SymbolPrinter<'tcx> {
         Ok(())
     }
 
-    fn path_crate(&mut self, cnum: CrateNum) -> Result<(), PrintError> {
+    fn print_crate_name(&mut self, cnum: CrateNum) -> Result<(), PrintError> {
         self.write_str(self.tcx.crate_name(cnum).as_str())?;
         Ok(())
     }
-    fn path_qualified(
+
+    fn print_path_with_qualified(
         &mut self,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
     ) -> Result<(), PrintError> {
-        // Similar to `pretty_path_qualified`, but for the other
+        // Similar to `pretty_print_path_with_qualified`, but for the other
         // types that are printed as paths (see `print_type` above).
         match self_ty.kind() {
             ty::FnDef(..)
@@ -325,17 +329,17 @@ impl<'tcx> Printer<'tcx> for SymbolPrinter<'tcx> {
                 self.print_type(self_ty)
             }
 
-            _ => self.pretty_path_qualified(self_ty, trait_ref),
+            _ => self.pretty_print_path_with_qualified(self_ty, trait_ref),
         }
     }
 
-    fn path_append_impl(
+    fn print_path_with_impl(
         &mut self,
         print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
     ) -> Result<(), PrintError> {
-        self.pretty_path_append_impl(
+        self.pretty_print_path_with_impl(
             |cx| {
                 print_prefix(cx)?;
 
@@ -352,7 +356,8 @@ impl<'tcx> Printer<'tcx> for SymbolPrinter<'tcx> {
             trait_ref,
         )
     }
-    fn path_append(
+
+    fn print_path_with_simple(
         &mut self,
         print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
         disambiguated_data: &DisambiguatedDefPathData,
@@ -375,7 +380,8 @@ impl<'tcx> Printer<'tcx> for SymbolPrinter<'tcx> {
 
         Ok(())
     }
-    fn path_generic_args(
+
+    fn print_path_with_generic_args(
         &mut self,
         print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
         args: &[GenericArg<'tcx>],
@@ -384,7 +390,6 @@ impl<'tcx> Printer<'tcx> for SymbolPrinter<'tcx> {
 
         let args =
             args.iter().cloned().filter(|arg| !matches!(arg.kind(), GenericArgKind::Lifetime(_)));
-
         if args.clone().next().is_some() {
             self.generic_delimiters(|cx| cx.comma_sep(args))
         } else {
@@ -453,8 +458,8 @@ impl<'tcx> Printer<'tcx> for SymbolPrinter<'tcx> {
     }
 }
 
-impl<'tcx> PrettyPrinter<'tcx> for SymbolPrinter<'tcx> {
-    fn should_print_region(&self, _region: ty::Region<'_>) -> bool {
+impl<'tcx> PrettyPrinter<'tcx> for LegacySymbolMangler<'tcx> {
+    fn should_print_optional_region(&self, _region: ty::Region<'_>) -> bool {
         false
     }
 
@@ -489,7 +494,7 @@ impl<'tcx> PrettyPrinter<'tcx> for SymbolPrinter<'tcx> {
     }
 }
 
-impl fmt::Write for SymbolPrinter<'_> {
+impl fmt::Write for LegacySymbolMangler<'_> {
     fn write_str(&mut self, s: &str) -> fmt::Result {
         // Name sanitation. LLVM will happily accept identifiers with weird names, but
         // gas doesn't!
diff --git a/compiler/rustc_symbol_mangling/src/lib.rs b/compiler/rustc_symbol_mangling/src/lib.rs
index 6bcb7f6e093..f3c96f64190 100644
--- a/compiler/rustc_symbol_mangling/src/lib.rs
+++ b/compiler/rustc_symbol_mangling/src/lib.rs
@@ -218,32 +218,33 @@ fn compute_symbol_name<'tcx>(
         }
     }
 
-    // Foreign items by default use no mangling for their symbol name. There's a
-    // few exceptions to this rule though:
-    //
-    // * This can be overridden with the `#[link_name]` attribute
-    //
-    // * On the wasm32 targets there is a bug (or feature) in LLD [1] where the
-    //   same-named symbol when imported from different wasm modules will get
-    //   hooked up incorrectly. As a result foreign symbols, on the wasm target,
-    //   with a wasm import module, get mangled. Additionally our codegen will
-    //   deduplicate symbols based purely on the symbol name, but for wasm this
-    //   isn't quite right because the same-named symbol on wasm can come from
-    //   different modules. For these reasons if `#[link(wasm_import_module)]`
-    //   is present we mangle everything on wasm because the demangled form will
-    //   show up in the `wasm-import-name` custom attribute in LLVM IR.
-    //
-    // * `#[rustc_std_internal_symbol]` mangles the symbol name in a special way
-    //   both for exports and imports through foreign items. This is handled above.
-    // [1]: https://bugs.llvm.org/show_bug.cgi?id=44316
-    if tcx.is_foreign_item(def_id)
-        && (!tcx.sess.target.is_like_wasm
-            || !tcx.wasm_import_module_map(def_id.krate).contains_key(&def_id))
+    let wasm_import_module_exception_force_mangling = {
+        // * On the wasm32 targets there is a bug (or feature) in LLD [1] where the
+        //   same-named symbol when imported from different wasm modules will get
+        //   hooked up incorrectly. As a result foreign symbols, on the wasm target,
+        //   with a wasm import module, get mangled. Additionally our codegen will
+        //   deduplicate symbols based purely on the symbol name, but for wasm this
+        //   isn't quite right because the same-named symbol on wasm can come from
+        //   different modules. For these reasons if `#[link(wasm_import_module)]`
+        //   is present we mangle everything on wasm because the demangled form will
+        //   show up in the `wasm-import-name` custom attribute in LLVM IR.
+        //
+        // [1]: https://bugs.llvm.org/show_bug.cgi?id=44316
+        //
+        // So, on wasm if a foreign item loses its `#[no_mangle]`, it might *still*
+        // be mangled if we're forced to. Note: I don't like this.
+        // These kinds of exceptions should be added during the `codegen_attrs` query.
+        // However, we don't have the wasm import module map there yet.
+        tcx.is_foreign_item(def_id)
+            && tcx.sess.target.is_like_wasm
+            && tcx.wasm_import_module_map(LOCAL_CRATE).contains_key(&def_id.into())
+    };
+
+    if let Some(name) = attrs.link_name
+        && !wasm_import_module_exception_force_mangling
     {
-        if let Some(name) = attrs.link_name {
-            return name.to_string();
-        }
-        return tcx.item_name(def_id).to_string();
+        // Use provided name
+        return name.to_string();
     }
 
     if let Some(name) = attrs.export_name {
@@ -251,7 +252,9 @@ fn compute_symbol_name<'tcx>(
         return name.to_string();
     }
 
-    if attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE) {
+    if attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE)
+        && !wasm_import_module_exception_force_mangling
+    {
         // Don't mangle
         return tcx.item_name(def_id).to_string();
     }
diff --git a/compiler/rustc_symbol_mangling/src/v0.rs b/compiler/rustc_symbol_mangling/src/v0.rs
index c2458ae814b..0cbd48ba08c 100644
--- a/compiler/rustc_symbol_mangling/src/v0.rs
+++ b/compiler/rustc_symbol_mangling/src/v0.rs
@@ -33,7 +33,7 @@ pub(super) fn mangle<'tcx>(
     let args = tcx.normalize_erasing_regions(ty::TypingEnv::fully_monomorphized(), instance.args);
 
     let prefix = "_R";
-    let mut p: SymbolMangler<'_> = SymbolMangler {
+    let mut p: V0SymbolMangler<'_> = V0SymbolMangler {
         tcx,
         start_offset: prefix.len(),
         is_exportable,
@@ -88,7 +88,7 @@ pub fn mangle_internal_symbol<'tcx>(tcx: TyCtxt<'tcx>, item_name: &str) -> Strin
     }
 
     let prefix = "_R";
-    let mut p: SymbolMangler<'_> = SymbolMangler {
+    let mut p: V0SymbolMangler<'_> = V0SymbolMangler {
         tcx,
         start_offset: prefix.len(),
         is_exportable: false,
@@ -131,7 +131,7 @@ pub(super) fn mangle_typeid_for_trait_ref<'tcx>(
     trait_ref: ty::ExistentialTraitRef<'tcx>,
 ) -> String {
     // FIXME(flip1995): See comment in `mangle_typeid_for_fnabi`.
-    let mut p = SymbolMangler {
+    let mut p = V0SymbolMangler {
         tcx,
         start_offset: 0,
         is_exportable: false,
@@ -159,7 +159,7 @@ struct BinderLevel {
     lifetime_depths: Range<u32>,
 }
 
-struct SymbolMangler<'tcx> {
+struct V0SymbolMangler<'tcx> {
     tcx: TyCtxt<'tcx>,
     binders: Vec<BinderLevel>,
     out: String,
@@ -173,7 +173,7 @@ struct SymbolMangler<'tcx> {
     consts: FxHashMap<ty::Const<'tcx>, usize>,
 }
 
-impl<'tcx> SymbolMangler<'tcx> {
+impl<'tcx> V0SymbolMangler<'tcx> {
     fn push(&mut self, s: &str) {
         self.out.push_str(s);
     }
@@ -272,7 +272,7 @@ impl<'tcx> SymbolMangler<'tcx> {
     }
 }
 
-impl<'tcx> Printer<'tcx> for SymbolMangler<'tcx> {
+impl<'tcx> Printer<'tcx> for V0SymbolMangler<'tcx> {
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.tcx
     }
@@ -365,7 +365,7 @@ impl<'tcx> Printer<'tcx> for SymbolMangler<'tcx> {
         // Encode impl generic params if the generic parameters contain non-region parameters
         // and this isn't an inherent impl.
         if impl_trait_ref.is_some() && args.iter().any(|a| a.has_non_region_param()) {
-            self.path_generic_args(
+            self.print_path_with_generic_args(
                 |this| {
                     this.path_append_ns(
                         |p| p.print_def_path(parent_def_id, &[]),
@@ -786,7 +786,7 @@ impl<'tcx> Printer<'tcx> for SymbolMangler<'tcx> {
                             None => {
                                 self.push("S");
                                 for (field_def, field) in iter::zip(&variant_def.fields, fields) {
-                                    // HACK(eddyb) this mimics `path_append`,
+                                    // HACK(eddyb) this mimics `print_path_with_simple`,
                                     // instead of simply using `field_def.ident`,
                                     // just to be able to handle disambiguators.
                                     let disambiguated_field =
@@ -819,7 +819,7 @@ impl<'tcx> Printer<'tcx> for SymbolMangler<'tcx> {
         Ok(())
     }
 
-    fn path_crate(&mut self, cnum: CrateNum) -> Result<(), PrintError> {
+    fn print_crate_name(&mut self, cnum: CrateNum) -> Result<(), PrintError> {
         self.push("C");
         if !self.is_exportable {
             let stable_crate_id = self.tcx.def_path_hash(cnum.as_def_id()).stable_crate_id();
@@ -830,7 +830,7 @@ impl<'tcx> Printer<'tcx> for SymbolMangler<'tcx> {
         Ok(())
     }
 
-    fn path_qualified(
+    fn print_path_with_qualified(
         &mut self,
         self_ty: Ty<'tcx>,
         trait_ref: Option<ty::TraitRef<'tcx>>,
@@ -843,7 +843,7 @@ impl<'tcx> Printer<'tcx> for SymbolMangler<'tcx> {
         self.print_def_path(trait_ref.def_id, trait_ref.args)
     }
 
-    fn path_append_impl(
+    fn print_path_with_impl(
         &mut self,
         _: impl FnOnce(&mut Self) -> Result<(), PrintError>,
         _: Ty<'tcx>,
@@ -853,7 +853,7 @@ impl<'tcx> Printer<'tcx> for SymbolMangler<'tcx> {
         unreachable!()
     }
 
-    fn path_append(
+    fn print_path_with_simple(
         &mut self,
         print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
         disambiguated_data: &DisambiguatedDefPathData,
@@ -873,7 +873,7 @@ impl<'tcx> Printer<'tcx> for SymbolMangler<'tcx> {
             DefPathData::SyntheticCoroutineBody => 's',
             DefPathData::NestedStatic => 'n',
 
-            // These should never show up as `path_append` arguments.
+            // These should never show up as `print_path_with_simple` arguments.
             DefPathData::CrateRoot
             | DefPathData::Use
             | DefPathData::GlobalAsm
@@ -896,7 +896,7 @@ impl<'tcx> Printer<'tcx> for SymbolMangler<'tcx> {
         )
     }
 
-    fn path_generic_args(
+    fn print_path_with_generic_args(
         &mut self,
         print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
         args: &[GenericArg<'tcx>],
diff --git a/compiler/rustc_target/src/spec/abi_map.rs b/compiler/rustc_target/src/spec/abi_map.rs
index b13e2112478..23e74539ddc 100644
--- a/compiler/rustc_target/src/spec/abi_map.rs
+++ b/compiler/rustc_target/src/spec/abi_map.rs
@@ -60,7 +60,15 @@ impl AbiMap {
             "x86_64" => Arch::X86_64,
             _ => Arch::Other,
         };
-        let os = if target.is_like_windows { OsKind::Windows } else { OsKind::Other };
+
+        let os = if target.is_like_windows {
+            OsKind::Windows
+        } else if target.is_like_vexos {
+            OsKind::VEXos
+        } else {
+            OsKind::Other
+        };
+
         AbiMap { arch, os }
     }
 
@@ -82,6 +90,10 @@ impl AbiMap {
             (ExternAbi::System { .. }, Arch::X86) if os == OsKind::Windows && !has_c_varargs => {
                 CanonAbi::X86(X86Call::Stdcall)
             }
+            (ExternAbi::System { .. }, Arch::Arm(..)) if self.os == OsKind::VEXos => {
+                // Calls to VEXos APIs do not use VFP registers.
+                CanonAbi::Arm(ArmCall::Aapcs)
+            }
             (ExternAbi::System { .. }, _) => CanonAbi::C,
 
             // fallible lowerings
@@ -191,6 +203,7 @@ enum Arch {
 #[derive(Debug, PartialEq, Copy, Clone)]
 enum OsKind {
     Windows,
+    VEXos,
     Other,
 }
 
diff --git a/compiler/rustc_target/src/spec/base/apple/mod.rs b/compiler/rustc_target/src/spec/base/apple/mod.rs
index aa6d1ec7009..ecc74264160 100644
--- a/compiler/rustc_target/src/spec/base/apple/mod.rs
+++ b/compiler/rustc_target/src/spec/base/apple/mod.rs
@@ -1,5 +1,4 @@
 use std::borrow::Cow;
-use std::env;
 use std::fmt::{Display, from_fn};
 use std::num::ParseIntError;
 use std::str::FromStr;
@@ -51,14 +50,14 @@ impl Arch {
         })
     }
 
-    fn target_cpu(self, abi: TargetAbi) -> &'static str {
+    fn target_cpu(self, env: TargetEnv) -> &'static str {
         match self {
             Armv7k => "cortex-a8",
             Armv7s => "swift", // iOS 10 is only supported on iPhone 5 or higher.
-            Arm64 => match abi {
-                TargetAbi::Normal => "apple-a7",
-                TargetAbi::Simulator => "apple-a12",
-                TargetAbi::MacCatalyst => "apple-a12",
+            Arm64 => match env {
+                TargetEnv::Normal => "apple-a7",
+                TargetEnv::Simulator => "apple-a12",
+                TargetEnv::MacCatalyst => "apple-a12",
             },
             Arm64e => "apple-a12",
             Arm64_32 => "apple-s4",
@@ -83,14 +82,14 @@ impl Arch {
 }
 
 #[derive(Copy, Clone, PartialEq)]
-pub(crate) enum TargetAbi {
+pub(crate) enum TargetEnv {
     Normal,
     Simulator,
     MacCatalyst,
 }
 
-impl TargetAbi {
-    fn target_abi(self) -> &'static str {
+impl TargetEnv {
+    fn target_env(self) -> &'static str {
         match self {
             Self::Normal => "",
             Self::MacCatalyst => "macabi",
@@ -104,13 +103,20 @@ impl TargetAbi {
 pub(crate) fn base(
     os: &'static str,
     arch: Arch,
-    abi: TargetAbi,
+    env: TargetEnv,
 ) -> (TargetOptions, StaticCow<str>, StaticCow<str>) {
     let mut opts = TargetOptions {
-        abi: abi.target_abi().into(),
         llvm_floatabi: Some(FloatAbi::Hard),
         os: os.into(),
-        cpu: arch.target_cpu(abi).into(),
+        env: env.target_env().into(),
+        // NOTE: We originally set `cfg(target_abi = "macabi")` / `cfg(target_abi = "sim")`,
+        // before it was discovered that those are actually environments:
+        // https://github.com/rust-lang/rust/issues/133331
+        //
+        // But let's continue setting them for backwards compatibility.
+        // FIXME(madsmtm): Warn about using these in the future.
+        abi: env.target_env().into(),
+        cpu: arch.target_cpu(env).into(),
         link_env_remove: link_env_remove(os),
         vendor: "apple".into(),
         linker_flavor: LinkerFlavor::Darwin(Cc::Yes, Lld::No),
@@ -168,14 +174,14 @@ pub(crate) fn base(
         // All Apple x86-32 targets have SSE2.
         opts.rustc_abi = Some(RustcAbi::X86Sse2);
     }
-    (opts, unversioned_llvm_target(os, arch, abi), arch.target_arch())
+    (opts, unversioned_llvm_target(os, arch, env), arch.target_arch())
 }
 
 /// Generate part of the LLVM target triple.
 ///
 /// See `rustc_codegen_ssa::back::versioned_llvm_target` for the full triple passed to LLVM and
 /// Clang.
-fn unversioned_llvm_target(os: &str, arch: Arch, abi: TargetAbi) -> StaticCow<str> {
+fn unversioned_llvm_target(os: &str, arch: Arch, env: TargetEnv) -> StaticCow<str> {
     let arch = arch.target_name();
     // Convert to the "canonical" OS name used by LLVM:
     // https://github.com/llvm/llvm-project/blob/llvmorg-18.1.8/llvm/lib/TargetParser/Triple.cpp#L236-L282
@@ -187,10 +193,10 @@ fn unversioned_llvm_target(os: &str, arch: Arch, abi: TargetAbi) -> StaticCow<st
         "visionos" => "xros",
         _ => unreachable!("tried to get LLVM target OS for non-Apple platform"),
     };
-    let environment = match abi {
-        TargetAbi::Normal => "",
-        TargetAbi::MacCatalyst => "-macabi",
-        TargetAbi::Simulator => "-simulator",
+    let environment = match env {
+        TargetEnv::Normal => "",
+        TargetEnv::MacCatalyst => "-macabi",
+        TargetEnv::Simulator => "-simulator",
     };
     format!("{arch}-apple-{os}{environment}").into()
 }
@@ -202,29 +208,10 @@ fn link_env_remove(os: &'static str) -> StaticCow<[StaticCow<str>]> {
     // that's only applicable to cross-OS compilation. Always leave anything for the
     // host OS alone though.
     if os == "macos" {
-        let mut env_remove = Vec::with_capacity(2);
-        // Remove the `SDKROOT` environment variable if it's clearly set for the wrong platform, which
-        // may occur when we're linking a custom build script while targeting iOS for example.
-        if let Ok(sdkroot) = env::var("SDKROOT") {
-            if sdkroot.contains("iPhoneOS.platform")
-                || sdkroot.contains("iPhoneSimulator.platform")
-                || sdkroot.contains("AppleTVOS.platform")
-                || sdkroot.contains("AppleTVSimulator.platform")
-                || sdkroot.contains("WatchOS.platform")
-                || sdkroot.contains("WatchSimulator.platform")
-                || sdkroot.contains("XROS.platform")
-                || sdkroot.contains("XRSimulator.platform")
-            {
-                env_remove.push("SDKROOT".into())
-            }
-        }
-        // Additionally, `IPHONEOS_DEPLOYMENT_TARGET` must not be set when using the Xcode linker at
+        // `IPHONEOS_DEPLOYMENT_TARGET` must not be set when using the Xcode linker at
         // "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld",
         // although this is apparently ignored when using the linker at "/usr/bin/ld".
-        env_remove.push("IPHONEOS_DEPLOYMENT_TARGET".into());
-        env_remove.push("TVOS_DEPLOYMENT_TARGET".into());
-        env_remove.push("XROS_DEPLOYMENT_TARGET".into());
-        env_remove.into()
+        cvs!["IPHONEOS_DEPLOYMENT_TARGET", "TVOS_DEPLOYMENT_TARGET", "XROS_DEPLOYMENT_TARGET"]
     } else {
         // Otherwise if cross-compiling for a different OS/SDK (including Mac Catalyst), remove any part
         // of the linking environment that's wrong and reversed.
@@ -309,7 +296,7 @@ impl OSVersion {
     /// This matches what LLVM does, see in part:
     /// <https://github.com/llvm/llvm-project/blob/llvmorg-18.1.8/llvm/lib/TargetParser/Triple.cpp#L1900-L1932>
     pub fn minimum_deployment_target(target: &Target) -> Self {
-        let (major, minor, patch) = match (&*target.os, &*target.arch, &*target.abi) {
+        let (major, minor, patch) = match (&*target.os, &*target.arch, &*target.env) {
             ("macos", "aarch64", _) => (11, 0, 0),
             ("ios", "aarch64", "macabi") => (14, 0, 0),
             ("ios", "aarch64", "sim") => (14, 0, 0),
diff --git a/compiler/rustc_target/src/spec/base/apple/tests.rs b/compiler/rustc_target/src/spec/base/apple/tests.rs
index 391f3470104..bca86ce33c3 100644
--- a/compiler/rustc_target/src/spec/base/apple/tests.rs
+++ b/compiler/rustc_target/src/spec/base/apple/tests.rs
@@ -6,7 +6,7 @@ use crate::spec::targets::{
 };
 
 #[test]
-fn simulator_targets_set_abi() {
+fn simulator_targets_set_env() {
     let all_sim_targets = [
         x86_64_apple_ios::target(),
         x86_64_apple_tvos::target(),
@@ -18,7 +18,9 @@ fn simulator_targets_set_abi() {
     ];
 
     for target in &all_sim_targets {
-        assert_eq!(target.abi, "sim")
+        assert_eq!(target.env, "sim");
+        // Ensure backwards compat
+        assert_eq!(target.abi, "sim");
     }
 }
 
diff --git a/compiler/rustc_target/src/spec/json.rs b/compiler/rustc_target/src/spec/json.rs
index d27c1929aef..f56a65d9c0c 100644
--- a/compiler/rustc_target/src/spec/json.rs
+++ b/compiler/rustc_target/src/spec/json.rs
@@ -153,6 +153,7 @@ impl Target {
         forward!(is_like_msvc);
         forward!(is_like_wasm);
         forward!(is_like_android);
+        forward!(is_like_vexos);
         forward!(binary_format);
         forward!(default_dwarf_version);
         forward!(allows_weak_linkage);
@@ -167,7 +168,6 @@ impl Target {
         forward!(main_needs_argc_argv);
         forward!(has_thread_local);
         forward!(obj_is_bitcode);
-        forward!(bitcode_llvm_cmdline);
         forward_opt!(max_atomic_width);
         forward_opt!(min_atomic_width);
         forward!(atomic_cas);
@@ -345,6 +345,7 @@ impl ToJson for Target {
         target_option_val!(is_like_msvc);
         target_option_val!(is_like_wasm);
         target_option_val!(is_like_android);
+        target_option_val!(is_like_vexos);
         target_option_val!(binary_format);
         target_option_val!(default_dwarf_version);
         target_option_val!(allows_weak_linkage);
@@ -359,7 +360,6 @@ impl ToJson for Target {
         target_option_val!(main_needs_argc_argv);
         target_option_val!(has_thread_local);
         target_option_val!(obj_is_bitcode);
-        target_option_val!(bitcode_llvm_cmdline);
         target_option_val!(min_atomic_width);
         target_option_val!(max_atomic_width);
         target_option_val!(atomic_cas);
@@ -538,6 +538,7 @@ struct TargetSpecJson {
     is_like_msvc: Option<bool>,
     is_like_wasm: Option<bool>,
     is_like_android: Option<bool>,
+    is_like_vexos: Option<bool>,
     binary_format: Option<BinaryFormat>,
     default_dwarf_version: Option<u32>,
     allows_weak_linkage: Option<bool>,
@@ -552,7 +553,6 @@ struct TargetSpecJson {
     main_needs_argc_argv: Option<bool>,
     has_thread_local: Option<bool>,
     obj_is_bitcode: Option<bool>,
-    bitcode_llvm_cmdline: Option<StaticCow<str>>,
     max_atomic_width: Option<u64>,
     min_atomic_width: Option<u64>,
     atomic_cas: Option<bool>,
diff --git a/compiler/rustc_target/src/spec/mod.rs b/compiler/rustc_target/src/spec/mod.rs
index 033590e01a6..2aa8ab5d317 100644
--- a/compiler/rustc_target/src/spec/mod.rs
+++ b/compiler/rustc_target/src/spec/mod.rs
@@ -2101,6 +2101,7 @@ supported_targets! {
     ("armv7a-none-eabihf", armv7a_none_eabihf),
     ("armv7a-nuttx-eabi", armv7a_nuttx_eabi),
     ("armv7a-nuttx-eabihf", armv7a_nuttx_eabihf),
+    ("armv7a-vex-v5", armv7a_vex_v5),
 
     ("msp430-none-elf", msp430_none_elf),
 
@@ -2146,6 +2147,7 @@ supported_targets! {
 
     ("aarch64-unknown-none", aarch64_unknown_none),
     ("aarch64-unknown-none-softfloat", aarch64_unknown_none_softfloat),
+    ("aarch64_be-unknown-none-softfloat", aarch64_be_unknown_none_softfloat),
     ("aarch64-unknown-nuttx", aarch64_unknown_nuttx),
 
     ("x86_64-fortanix-unknown-sgx", x86_64_fortanix_unknown_sgx),
@@ -2571,6 +2573,8 @@ pub struct TargetOptions {
     pub is_like_wasm: bool,
     /// Whether a target toolchain is like Android, implying a Linux kernel and a Bionic libc
     pub is_like_android: bool,
+    /// Whether a target toolchain is like VEXos, the operating system used by the VEX Robotics V5 Brain.
+    pub is_like_vexos: bool,
     /// Target's binary file format. Defaults to BinaryFormat::Elf
     pub binary_format: BinaryFormat,
     /// Default supported version of DWARF on this platform.
@@ -2620,8 +2624,6 @@ pub struct TargetOptions {
     /// If we give emcc .o files that are actually .bc files it
     /// will 'just work'.
     pub obj_is_bitcode: bool,
-    /// Content of the LLVM cmdline section associated with embedded bitcode.
-    pub bitcode_llvm_cmdline: StaticCow<str>,
 
     /// Don't use this field; instead use the `.min_atomic_width()` method.
     pub min_atomic_width: Option<u64>,
@@ -2953,6 +2955,7 @@ impl Default for TargetOptions {
             is_like_msvc: false,
             is_like_wasm: false,
             is_like_android: false,
+            is_like_vexos: false,
             binary_format: BinaryFormat::Elf,
             default_dwarf_version: 4,
             allows_weak_linkage: true,
@@ -2984,7 +2987,6 @@ impl Default for TargetOptions {
             allow_asm: true,
             has_thread_local: false,
             obj_is_bitcode: false,
-            bitcode_llvm_cmdline: "".into(),
             min_atomic_width: None,
             max_atomic_width: None,
             atomic_cas: true,
diff --git a/compiler/rustc_target/src/spec/targets/aarch64_apple_darwin.rs b/compiler/rustc_target/src/spec/targets/aarch64_apple_darwin.rs
index 4dd39877715..e1960472555 100644
--- a/compiler/rustc_target/src/spec/targets/aarch64_apple_darwin.rs
+++ b/compiler/rustc_target/src/spec/targets/aarch64_apple_darwin.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{SanitizerSet, Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("macos", Arch::Arm64, TargetAbi::Normal);
+    let (opts, llvm_target, arch) = base("macos", Arch::Arm64, TargetEnv::Normal);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/aarch64_apple_ios.rs b/compiler/rustc_target/src/spec/targets/aarch64_apple_ios.rs
index 769a7b6c391..3b522c34522 100644
--- a/compiler/rustc_target/src/spec/targets/aarch64_apple_ios.rs
+++ b/compiler/rustc_target/src/spec/targets/aarch64_apple_ios.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{SanitizerSet, Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("ios", Arch::Arm64, TargetAbi::Normal);
+    let (opts, llvm_target, arch) = base("ios", Arch::Arm64, TargetEnv::Normal);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/aarch64_apple_ios_macabi.rs b/compiler/rustc_target/src/spec/targets/aarch64_apple_ios_macabi.rs
index 4bb2f73e4f9..4d6a3103ee3 100644
--- a/compiler/rustc_target/src/spec/targets/aarch64_apple_ios_macabi.rs
+++ b/compiler/rustc_target/src/spec/targets/aarch64_apple_ios_macabi.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{SanitizerSet, Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("ios", Arch::Arm64, TargetAbi::MacCatalyst);
+    let (opts, llvm_target, arch) = base("ios", Arch::Arm64, TargetEnv::MacCatalyst);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/aarch64_apple_ios_sim.rs b/compiler/rustc_target/src/spec/targets/aarch64_apple_ios_sim.rs
index 7d04034e759..d366ed26482 100644
--- a/compiler/rustc_target/src/spec/targets/aarch64_apple_ios_sim.rs
+++ b/compiler/rustc_target/src/spec/targets/aarch64_apple_ios_sim.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{SanitizerSet, Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("ios", Arch::Arm64, TargetAbi::Simulator);
+    let (opts, llvm_target, arch) = base("ios", Arch::Arm64, TargetEnv::Simulator);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/aarch64_apple_tvos.rs b/compiler/rustc_target/src/spec/targets/aarch64_apple_tvos.rs
index ec92a40e255..7aef6f96e1c 100644
--- a/compiler/rustc_target/src/spec/targets/aarch64_apple_tvos.rs
+++ b/compiler/rustc_target/src/spec/targets/aarch64_apple_tvos.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("tvos", Arch::Arm64, TargetAbi::Normal);
+    let (opts, llvm_target, arch) = base("tvos", Arch::Arm64, TargetEnv::Normal);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/aarch64_apple_tvos_sim.rs b/compiler/rustc_target/src/spec/targets/aarch64_apple_tvos_sim.rs
index 74fbe5a89ca..f0d17db873b 100644
--- a/compiler/rustc_target/src/spec/targets/aarch64_apple_tvos_sim.rs
+++ b/compiler/rustc_target/src/spec/targets/aarch64_apple_tvos_sim.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("tvos", Arch::Arm64, TargetAbi::Simulator);
+    let (opts, llvm_target, arch) = base("tvos", Arch::Arm64, TargetEnv::Simulator);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/aarch64_apple_visionos.rs b/compiler/rustc_target/src/spec/targets/aarch64_apple_visionos.rs
index dc595fbe7b6..22ce52e637f 100644
--- a/compiler/rustc_target/src/spec/targets/aarch64_apple_visionos.rs
+++ b/compiler/rustc_target/src/spec/targets/aarch64_apple_visionos.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{SanitizerSet, Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("visionos", Arch::Arm64, TargetAbi::Normal);
+    let (opts, llvm_target, arch) = base("visionos", Arch::Arm64, TargetEnv::Normal);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/aarch64_apple_visionos_sim.rs b/compiler/rustc_target/src/spec/targets/aarch64_apple_visionos_sim.rs
index 06ff1bfb2f0..21739ba9fdb 100644
--- a/compiler/rustc_target/src/spec/targets/aarch64_apple_visionos_sim.rs
+++ b/compiler/rustc_target/src/spec/targets/aarch64_apple_visionos_sim.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{SanitizerSet, Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("visionos", Arch::Arm64, TargetAbi::Simulator);
+    let (opts, llvm_target, arch) = base("visionos", Arch::Arm64, TargetEnv::Simulator);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/aarch64_apple_watchos.rs b/compiler/rustc_target/src/spec/targets/aarch64_apple_watchos.rs
index 23596271107..2e88f95f1dd 100644
--- a/compiler/rustc_target/src/spec/targets/aarch64_apple_watchos.rs
+++ b/compiler/rustc_target/src/spec/targets/aarch64_apple_watchos.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("watchos", Arch::Arm64, TargetAbi::Normal);
+    let (opts, llvm_target, arch) = base("watchos", Arch::Arm64, TargetEnv::Normal);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/aarch64_apple_watchos_sim.rs b/compiler/rustc_target/src/spec/targets/aarch64_apple_watchos_sim.rs
index bad9f6c1485..272dc682dc0 100644
--- a/compiler/rustc_target/src/spec/targets/aarch64_apple_watchos_sim.rs
+++ b/compiler/rustc_target/src/spec/targets/aarch64_apple_watchos_sim.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("watchos", Arch::Arm64, TargetAbi::Simulator);
+    let (opts, llvm_target, arch) = base("watchos", Arch::Arm64, TargetEnv::Simulator);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/aarch64_be_unknown_none_softfloat.rs b/compiler/rustc_target/src/spec/targets/aarch64_be_unknown_none_softfloat.rs
new file mode 100644
index 00000000000..7f918e85080
--- /dev/null
+++ b/compiler/rustc_target/src/spec/targets/aarch64_be_unknown_none_softfloat.rs
@@ -0,0 +1,43 @@
+// Generic big-endian AArch64 target for bare-metal code - Floating point disabled
+//
+// Can be used in conjunction with the `target-feature` and
+// `target-cpu` compiler flags to opt-in more hardware-specific
+// features.
+//
+// For example, `-C target-cpu=cortex-a53`.
+use rustc_abi::Endian;
+
+use crate::spec::{
+    Cc, LinkerFlavor, Lld, PanicStrategy, RelocModel, SanitizerSet, StackProbeType, Target,
+    TargetMetadata, TargetOptions,
+};
+
+pub(crate) fn target() -> Target {
+    let opts = TargetOptions {
+        abi: "softfloat".into(),
+        linker_flavor: LinkerFlavor::Gnu(Cc::No, Lld::Yes),
+        linker: Some("rust-lld".into()),
+        features: "+v8a,+strict-align,-neon,-fp-armv8".into(),
+        relocation_model: RelocModel::Static,
+        disable_redzone: true,
+        max_atomic_width: Some(128),
+        supported_sanitizers: SanitizerSet::KCFI | SanitizerSet::KERNELADDRESS,
+        stack_probes: StackProbeType::Inline,
+        panic_strategy: PanicStrategy::Abort,
+        endian: Endian::Big,
+        ..Default::default()
+    };
+    Target {
+        llvm_target: "aarch64_be-unknown-none".into(),
+        metadata: TargetMetadata {
+            description: Some("Bare ARM64 (big-endian), softfloat".into()),
+            tier: Some(3),
+            host_tools: Some(false),
+            std: Some(false),
+        },
+        pointer_width: 64,
+        data_layout: "E-m:e-p270:32:32-p271:32:32-p272:64:64-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-Fn32".into(),
+        arch: "aarch64".into(),
+        options: opts,
+    }
+}
diff --git a/compiler/rustc_target/src/spec/targets/arm64_32_apple_watchos.rs b/compiler/rustc_target/src/spec/targets/arm64_32_apple_watchos.rs
index 4c3a2f43743..564ac2cd708 100644
--- a/compiler/rustc_target/src/spec/targets/arm64_32_apple_watchos.rs
+++ b/compiler/rustc_target/src/spec/targets/arm64_32_apple_watchos.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("watchos", Arch::Arm64_32, TargetAbi::Normal);
+    let (opts, llvm_target, arch) = base("watchos", Arch::Arm64_32, TargetEnv::Normal);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/arm64e_apple_darwin.rs b/compiler/rustc_target/src/spec/targets/arm64e_apple_darwin.rs
index 326f2b16d59..86e178a9572 100644
--- a/compiler/rustc_target/src/spec/targets/arm64e_apple_darwin.rs
+++ b/compiler/rustc_target/src/spec/targets/arm64e_apple_darwin.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{SanitizerSet, Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("macos", Arch::Arm64e, TargetAbi::Normal);
+    let (opts, llvm_target, arch) = base("macos", Arch::Arm64e, TargetEnv::Normal);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/arm64e_apple_ios.rs b/compiler/rustc_target/src/spec/targets/arm64e_apple_ios.rs
index 01c6f0b888d..dae3f77d7ae 100644
--- a/compiler/rustc_target/src/spec/targets/arm64e_apple_ios.rs
+++ b/compiler/rustc_target/src/spec/targets/arm64e_apple_ios.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{SanitizerSet, Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("ios", Arch::Arm64e, TargetAbi::Normal);
+    let (opts, llvm_target, arch) = base("ios", Arch::Arm64e, TargetEnv::Normal);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/arm64e_apple_tvos.rs b/compiler/rustc_target/src/spec/targets/arm64e_apple_tvos.rs
index cad3650bda1..a99fc5dc68c 100644
--- a/compiler/rustc_target/src/spec/targets/arm64e_apple_tvos.rs
+++ b/compiler/rustc_target/src/spec/targets/arm64e_apple_tvos.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("tvos", Arch::Arm64e, TargetAbi::Normal);
+    let (opts, llvm_target, arch) = base("tvos", Arch::Arm64e, TargetEnv::Normal);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/armv7a_vex_v5.rs b/compiler/rustc_target/src/spec/targets/armv7a_vex_v5.rs
new file mode 100644
index 00000000000..e78f7839974
--- /dev/null
+++ b/compiler/rustc_target/src/spec/targets/armv7a_vex_v5.rs
@@ -0,0 +1,44 @@
+use crate::spec::{
+    Cc, FloatAbi, LinkerFlavor, Lld, PanicStrategy, RelocModel, Target, TargetMetadata,
+    TargetOptions,
+};
+
+const LINKER_SCRIPT: &str = include_str!("./armv7a_vex_v5_linker_script.ld");
+
+pub(crate) fn target() -> Target {
+    let opts = TargetOptions {
+        vendor: "vex".into(),
+        env: "v5".into(),
+        os: "vexos".into(),
+        cpu: "cortex-a9".into(),
+        abi: "eabihf".into(),
+        is_like_vexos: true,
+        llvm_floatabi: Some(FloatAbi::Hard),
+        linker_flavor: LinkerFlavor::Gnu(Cc::No, Lld::Yes),
+        linker: Some("rust-lld".into()),
+        features: "+v7,+neon,+vfp3d16,+thumb2".into(),
+        relocation_model: RelocModel::Static,
+        disable_redzone: true,
+        max_atomic_width: Some(64),
+        panic_strategy: PanicStrategy::Abort,
+        emit_debug_gdb_scripts: false,
+        c_enum_min_bits: Some(8),
+        default_uwtable: true,
+        has_thumb_interworking: true,
+        link_script: Some(LINKER_SCRIPT.into()),
+        ..Default::default()
+    };
+    Target {
+        llvm_target: "armv7a-none-eabihf".into(),
+        metadata: TargetMetadata {
+            description: Some("ARMv7-A Cortex-A9 VEX V5 Brain".into()),
+            tier: Some(3),
+            host_tools: Some(false),
+            std: Some(false),
+        },
+        pointer_width: 32,
+        data_layout: "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64".into(),
+        arch: "arm".into(),
+        options: opts,
+    }
+}
diff --git a/compiler/rustc_target/src/spec/targets/armv7a_vex_v5_linker_script.ld b/compiler/rustc_target/src/spec/targets/armv7a_vex_v5_linker_script.ld
new file mode 100644
index 00000000000..a4783de0183
--- /dev/null
+++ b/compiler/rustc_target/src/spec/targets/armv7a_vex_v5_linker_script.ld
@@ -0,0 +1,144 @@
+OUTPUT_FORMAT("elf32-littlearm")
+ENTRY(_boot)
+
+/*
+ * PROVIDE() is used here so that users can override default values.
+ * This is intended to give developers the option to use this Rust
+ * target even if the default values in this linker script aren't
+ * suitable for their needs.
+ *
+ * For example: `-C link-arg=--defsym=__stack_length=8M` could
+ * be used to increase the stack size above the value set in this
+ * file.
+ */
+
+PROVIDE(__vcodesig_magic = 0x35585658);     /* XVX5                 */
+PROVIDE(__vcodesig_type = 0);               /* V5_SIG_TYPE_USER     */
+PROVIDE(__vcodesig_owner = 2);              /* V5_SIG_OWNER_PARTNER */
+PROVIDE(__vcodesig_options = 0);            /* none (0)             */
+
+PROVIDE(__user_ram_start = 0x03800000);
+PROVIDE(__user_ram_length = 48M);
+PROVIDE(__user_ram_end = __user_ram_start + __user_ram_length); /* 0x8000000 */
+
+PROVIDE(__code_signature_length = 0x20);
+
+PROVIDE(__stack_length = 4M);
+PROVIDE(__heap_end = __user_ram_end - __stack_length);
+PROVIDE(__user_length = __heap_start - __user_ram_start);
+
+MEMORY {
+    USER_RAM (RWX) : ORIGIN = __user_ram_start, LENGTH = __user_ram_length
+}
+
+SECTIONS {
+    /*
+     * VEXos expects program binaries to have a 32-byte header called a "code signature"
+     * at their start which tells the OS that we are a valid program and configures some
+     * miscellaneous startup behavior.
+     */
+    .code_signature : {
+        LONG(__vcodesig_magic)
+        LONG(__vcodesig_type)
+        LONG(__vcodesig_owner)
+        LONG(__vcodesig_options)
+
+        FILL(0)
+        . = __user_ram_start + __code_signature_length;
+    } > USER_RAM
+
+    /*
+     * Executable program instructions.
+     */
+    .text : {
+        /* _boot routine (entry point from VEXos, must be at 0x03800020) */
+        *(.boot)
+
+        /* The rest of the program. */
+        *(.text .text.*)
+    } > USER_RAM
+
+    /*
+     * Global/uninitialized/static/constant data sections.
+     */
+    .rodata : {
+        *(.rodata .rodata1 .rodata.*)
+        *(.srodata .srodata.*)
+    } > USER_RAM
+
+    /*
+     * ARM Stack Unwinding Sections
+     *
+     * These sections are added by the compiler in some cases to facilitate stack unwinding.
+     * __eh_frame_start and similar symbols are used by libunwind.
+     */
+
+    .except_ordered : {
+        PROVIDE(__extab_start = .);
+        *(.gcc_except_table *.gcc_except_table.*)
+        *(.ARM.extab*)
+        PROVIDE(__extab_end = .);
+    } > USER_RAM
+
+    .eh_frame_hdr : {
+        /* see https://github.com/llvm/llvm-project/blob/main/libunwind/src/AddressSpace.hpp#L78 */
+        PROVIDE(__eh_frame_hdr_start = .);
+        KEEP(*(.eh_frame_hdr))
+        PROVIDE(__eh_frame_hdr_end = .);
+    } > USER_RAM
+
+    .eh_frame : {
+        PROVIDE(__eh_frame_start = .);
+        KEEP(*(.eh_frame))
+        PROVIDE(__eh_frame_end = .);
+    } > USER_RAM
+
+    .except_unordered : {
+        PROVIDE(__exidx_start = .);
+        *(.ARM.exidx*)
+        PROVIDE(__exidx_end = .);
+    } > USER_RAM
+
+    /* -- Data intended to be mutable at runtime begins here. -- */
+
+    .data : {
+        *(.data .data1 .data.*)
+        *(.sdata .sdata.* .sdata2.*)
+    } > USER_RAM
+
+    /* -- End of loadable sections - anything beyond this point shouldn't go in the binary uploaded to the device. -- */
+
+    .bss (NOLOAD) : {
+        __bss_start = .;
+        *(.sbss*)
+        *(.bss .bss.*)
+
+        /* Align the heap */
+        . = ALIGN(8);
+        __bss_end = .;
+    } > USER_RAM
+
+    /*
+     * Active memory sections for the stack/heap.
+     *
+     * Because these are (NOLOAD), they will not influence the final size of the binary.
+     */
+    .heap (NOLOAD) : {
+        __heap_start = .;
+        . = __heap_end;
+    } > USER_RAM
+
+    .stack (NOLOAD) : ALIGN(8) {
+        __stack_bottom = .;
+        . += __stack_length;
+        __stack_top = .;
+    } > USER_RAM
+
+    /*
+     * `.ARM.attributes` contains arch metadata for compatibility purposes, but we
+     * only target one hardware configuration, meaning it'd just take up space.
+     */
+    /DISCARD/ : {
+        *(.ARM.attributes*)
+    }
+}
diff --git a/compiler/rustc_target/src/spec/targets/armv7k_apple_watchos.rs b/compiler/rustc_target/src/spec/targets/armv7k_apple_watchos.rs
index 8103d132cea..df58559848a 100644
--- a/compiler/rustc_target/src/spec/targets/armv7k_apple_watchos.rs
+++ b/compiler/rustc_target/src/spec/targets/armv7k_apple_watchos.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("watchos", Arch::Armv7k, TargetAbi::Normal);
+    let (opts, llvm_target, arch) = base("watchos", Arch::Armv7k, TargetEnv::Normal);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/armv7s_apple_ios.rs b/compiler/rustc_target/src/spec/targets/armv7s_apple_ios.rs
index ba9edd71461..63259043b73 100644
--- a/compiler/rustc_target/src/spec/targets/armv7s_apple_ios.rs
+++ b/compiler/rustc_target/src/spec/targets/armv7s_apple_ios.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("ios", Arch::Armv7s, TargetAbi::Normal);
+    let (opts, llvm_target, arch) = base("ios", Arch::Armv7s, TargetEnv::Normal);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/avr_none.rs b/compiler/rustc_target/src/spec/targets/avr_none.rs
index 07ed2a37803..ad056d02326 100644
--- a/compiler/rustc_target/src/spec/targets/avr_none.rs
+++ b/compiler/rustc_target/src/spec/targets/avr_none.rs
@@ -9,7 +9,7 @@ pub(crate) fn target() -> Target {
             host_tools: None,
             std: None,
         },
-        data_layout: "e-P1-p:16:8-i8:8-i16:8-i32:8-i64:8-f32:8-f64:8-n8-a:8".into(),
+        data_layout: "e-P1-p:16:8-i8:8-i16:8-i32:8-i64:8-f32:8-f64:8-n8:16-a:8".into(),
         llvm_target: "avr-unknown-unknown".into(),
         pointer_width: 16,
         options: TargetOptions {
diff --git a/compiler/rustc_target/src/spec/targets/i386_apple_ios.rs b/compiler/rustc_target/src/spec/targets/i386_apple_ios.rs
index 29865fcd4c4..a919be765a2 100644
--- a/compiler/rustc_target/src/spec/targets/i386_apple_ios.rs
+++ b/compiler/rustc_target/src/spec/targets/i386_apple_ios.rs
@@ -1,10 +1,10 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
     // i386-apple-ios is a simulator target, even though it isn't declared
     // that way in the target name like the other ones...
-    let (opts, llvm_target, arch) = base("ios", Arch::I386, TargetAbi::Simulator);
+    let (opts, llvm_target, arch) = base("ios", Arch::I386, TargetEnv::Simulator);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/i686_apple_darwin.rs b/compiler/rustc_target/src/spec/targets/i686_apple_darwin.rs
index d1339c57b00..96c477d5236 100644
--- a/compiler/rustc_target/src/spec/targets/i686_apple_darwin.rs
+++ b/compiler/rustc_target/src/spec/targets/i686_apple_darwin.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("macos", Arch::I686, TargetAbi::Normal);
+    let (opts, llvm_target, arch) = base("macos", Arch::I686, TargetEnv::Normal);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/x86_64_apple_darwin.rs b/compiler/rustc_target/src/spec/targets/x86_64_apple_darwin.rs
index eba595ba7dd..53e2cb469ee 100644
--- a/compiler/rustc_target/src/spec/targets/x86_64_apple_darwin.rs
+++ b/compiler/rustc_target/src/spec/targets/x86_64_apple_darwin.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{SanitizerSet, Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("macos", Arch::X86_64, TargetAbi::Normal);
+    let (opts, llvm_target, arch) = base("macos", Arch::X86_64, TargetEnv::Normal);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/x86_64_apple_ios.rs b/compiler/rustc_target/src/spec/targets/x86_64_apple_ios.rs
index df45f430ecb..d74a688fa0f 100644
--- a/compiler/rustc_target/src/spec/targets/x86_64_apple_ios.rs
+++ b/compiler/rustc_target/src/spec/targets/x86_64_apple_ios.rs
@@ -1,10 +1,10 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{SanitizerSet, Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
     // x86_64-apple-ios is a simulator target, even though it isn't declared
     // that way in the target name like the other ones...
-    let (opts, llvm_target, arch) = base("ios", Arch::X86_64, TargetAbi::Simulator);
+    let (opts, llvm_target, arch) = base("ios", Arch::X86_64, TargetEnv::Simulator);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/x86_64_apple_ios_macabi.rs b/compiler/rustc_target/src/spec/targets/x86_64_apple_ios_macabi.rs
index ee0c2bf31cd..193e26f94c9 100644
--- a/compiler/rustc_target/src/spec/targets/x86_64_apple_ios_macabi.rs
+++ b/compiler/rustc_target/src/spec/targets/x86_64_apple_ios_macabi.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{SanitizerSet, Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("ios", Arch::X86_64, TargetAbi::MacCatalyst);
+    let (opts, llvm_target, arch) = base("ios", Arch::X86_64, TargetEnv::MacCatalyst);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/x86_64_apple_tvos.rs b/compiler/rustc_target/src/spec/targets/x86_64_apple_tvos.rs
index 80ca80013f0..e69bd17a049 100644
--- a/compiler/rustc_target/src/spec/targets/x86_64_apple_tvos.rs
+++ b/compiler/rustc_target/src/spec/targets/x86_64_apple_tvos.rs
@@ -1,10 +1,10 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
     // x86_64-apple-tvos is a simulator target, even though it isn't declared
     // that way in the target name like the other ones...
-    let (opts, llvm_target, arch) = base("tvos", Arch::X86_64, TargetAbi::Simulator);
+    let (opts, llvm_target, arch) = base("tvos", Arch::X86_64, TargetEnv::Simulator);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/x86_64_apple_watchos_sim.rs b/compiler/rustc_target/src/spec/targets/x86_64_apple_watchos_sim.rs
index c503baedb8b..9490ca6aa36 100644
--- a/compiler/rustc_target/src/spec/targets/x86_64_apple_watchos_sim.rs
+++ b/compiler/rustc_target/src/spec/targets/x86_64_apple_watchos_sim.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (opts, llvm_target, arch) = base("watchos", Arch::X86_64, TargetAbi::Simulator);
+    let (opts, llvm_target, arch) = base("watchos", Arch::X86_64, TargetEnv::Simulator);
     Target {
         llvm_target,
         metadata: TargetMetadata {
diff --git a/compiler/rustc_target/src/spec/targets/x86_64h_apple_darwin.rs b/compiler/rustc_target/src/spec/targets/x86_64h_apple_darwin.rs
index e64556c4132..67b5a160a89 100644
--- a/compiler/rustc_target/src/spec/targets/x86_64h_apple_darwin.rs
+++ b/compiler/rustc_target/src/spec/targets/x86_64h_apple_darwin.rs
@@ -1,8 +1,8 @@
-use crate::spec::base::apple::{Arch, TargetAbi, base};
+use crate::spec::base::apple::{Arch, TargetEnv, base};
 use crate::spec::{SanitizerSet, Target, TargetMetadata, TargetOptions};
 
 pub(crate) fn target() -> Target {
-    let (mut opts, llvm_target, arch) = base("macos", Arch::X86_64h, TargetAbi::Normal);
+    let (mut opts, llvm_target, arch) = base("macos", Arch::X86_64h, TargetEnv::Normal);
     opts.max_atomic_width = Some(128);
     opts.supported_sanitizers =
         SanitizerSet::ADDRESS | SanitizerSet::CFI | SanitizerSet::LEAK | SanitizerSet::THREAD;
diff --git a/compiler/rustc_target/src/target_features.rs b/compiler/rustc_target/src/target_features.rs
index b2af99228fe..507e938d5cc 100644
--- a/compiler/rustc_target/src/target_features.rs
+++ b/compiler/rustc_target/src/target_features.rs
@@ -248,6 +248,10 @@ static AARCH64_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     ("mte", Stable, &[]),
     // FEAT_AdvSimd & FEAT_FP
     ("neon", Stable, &[]),
+    // Backend option to turn atomic operations into an intrinsic call when `lse` is not known to be
+    // available, so the intrinsic can do runtime LSE feature detection rather than unconditionally
+    // using slower non-LSE operations. Unstable since it doesn't need to user-togglable.
+    ("outline-atomics", Unstable(sym::aarch64_unstable_target_feature), &[]),
     // FEAT_PAUTH (address authentication)
     ("paca", Stable, &[]),
     // FEAT_PAUTH (generic authentication)
@@ -471,9 +475,9 @@ static X86_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     ("sse3", Stable, &["sse2"]),
     ("sse4.1", Stable, &["ssse3"]),
     ("sse4.2", Stable, &["sse4.1"]),
-    ("sse4a", Unstable(sym::sse4a_target_feature), &["sse3"]),
+    ("sse4a", Stable, &["sse3"]),
     ("ssse3", Stable, &["sse3"]),
-    ("tbm", Unstable(sym::tbm_target_feature), &[]),
+    ("tbm", Stable, &[]),
     ("vaes", Stable, &["avx2", "aes"]),
     ("vpclmulqdq", Stable, &["avx", "pclmulqdq"]),
     ("widekl", Stable, &["kl"]),
@@ -517,6 +521,71 @@ const MIPS_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     // tidy-alphabetical-end
 ];
 
+const NVPTX_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
+    // tidy-alphabetical-start
+    ("sm_20", Unstable(sym::nvptx_target_feature), &[]),
+    ("sm_21", Unstable(sym::nvptx_target_feature), &["sm_20"]),
+    ("sm_30", Unstable(sym::nvptx_target_feature), &["sm_21"]),
+    ("sm_32", Unstable(sym::nvptx_target_feature), &["sm_30"]),
+    ("sm_35", Unstable(sym::nvptx_target_feature), &["sm_32"]),
+    ("sm_37", Unstable(sym::nvptx_target_feature), &["sm_35"]),
+    ("sm_50", Unstable(sym::nvptx_target_feature), &["sm_37"]),
+    ("sm_52", Unstable(sym::nvptx_target_feature), &["sm_50"]),
+    ("sm_53", Unstable(sym::nvptx_target_feature), &["sm_52"]),
+    ("sm_60", Unstable(sym::nvptx_target_feature), &["sm_53"]),
+    ("sm_61", Unstable(sym::nvptx_target_feature), &["sm_60"]),
+    ("sm_62", Unstable(sym::nvptx_target_feature), &["sm_61"]),
+    ("sm_70", Unstable(sym::nvptx_target_feature), &["sm_62"]),
+    ("sm_72", Unstable(sym::nvptx_target_feature), &["sm_70"]),
+    ("sm_75", Unstable(sym::nvptx_target_feature), &["sm_72"]),
+    ("sm_80", Unstable(sym::nvptx_target_feature), &["sm_75"]),
+    ("sm_86", Unstable(sym::nvptx_target_feature), &["sm_80"]),
+    ("sm_87", Unstable(sym::nvptx_target_feature), &["sm_86"]),
+    ("sm_89", Unstable(sym::nvptx_target_feature), &["sm_87"]),
+    ("sm_90", Unstable(sym::nvptx_target_feature), &["sm_89"]),
+    ("sm_90a", Unstable(sym::nvptx_target_feature), &["sm_90"]),
+    // tidy-alphabetical-end
+    // tidy-alphabetical-start
+    ("sm_100", Unstable(sym::nvptx_target_feature), &["sm_90"]),
+    ("sm_100a", Unstable(sym::nvptx_target_feature), &["sm_100"]),
+    ("sm_101", Unstable(sym::nvptx_target_feature), &["sm_100"]),
+    ("sm_101a", Unstable(sym::nvptx_target_feature), &["sm_101"]),
+    ("sm_120", Unstable(sym::nvptx_target_feature), &["sm_101"]),
+    ("sm_120a", Unstable(sym::nvptx_target_feature), &["sm_120"]),
+    // tidy-alphabetical-end
+    // tidy-alphabetical-start
+    ("ptx32", Unstable(sym::nvptx_target_feature), &[]),
+    ("ptx40", Unstable(sym::nvptx_target_feature), &["ptx32"]),
+    ("ptx41", Unstable(sym::nvptx_target_feature), &["ptx40"]),
+    ("ptx42", Unstable(sym::nvptx_target_feature), &["ptx41"]),
+    ("ptx43", Unstable(sym::nvptx_target_feature), &["ptx42"]),
+    ("ptx50", Unstable(sym::nvptx_target_feature), &["ptx43"]),
+    ("ptx60", Unstable(sym::nvptx_target_feature), &["ptx50"]),
+    ("ptx61", Unstable(sym::nvptx_target_feature), &["ptx60"]),
+    ("ptx62", Unstable(sym::nvptx_target_feature), &["ptx61"]),
+    ("ptx63", Unstable(sym::nvptx_target_feature), &["ptx62"]),
+    ("ptx64", Unstable(sym::nvptx_target_feature), &["ptx63"]),
+    ("ptx65", Unstable(sym::nvptx_target_feature), &["ptx64"]),
+    ("ptx70", Unstable(sym::nvptx_target_feature), &["ptx65"]),
+    ("ptx71", Unstable(sym::nvptx_target_feature), &["ptx70"]),
+    ("ptx72", Unstable(sym::nvptx_target_feature), &["ptx71"]),
+    ("ptx73", Unstable(sym::nvptx_target_feature), &["ptx72"]),
+    ("ptx74", Unstable(sym::nvptx_target_feature), &["ptx73"]),
+    ("ptx75", Unstable(sym::nvptx_target_feature), &["ptx74"]),
+    ("ptx76", Unstable(sym::nvptx_target_feature), &["ptx75"]),
+    ("ptx77", Unstable(sym::nvptx_target_feature), &["ptx76"]),
+    ("ptx78", Unstable(sym::nvptx_target_feature), &["ptx77"]),
+    ("ptx80", Unstable(sym::nvptx_target_feature), &["ptx78"]),
+    ("ptx81", Unstable(sym::nvptx_target_feature), &["ptx80"]),
+    ("ptx82", Unstable(sym::nvptx_target_feature), &["ptx81"]),
+    ("ptx83", Unstable(sym::nvptx_target_feature), &["ptx82"]),
+    ("ptx84", Unstable(sym::nvptx_target_feature), &["ptx83"]),
+    ("ptx85", Unstable(sym::nvptx_target_feature), &["ptx84"]),
+    ("ptx86", Unstable(sym::nvptx_target_feature), &["ptx85"]),
+    ("ptx87", Unstable(sym::nvptx_target_feature), &["ptx86"]),
+    // tidy-alphabetical-end
+];
+
 static RISCV_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     // tidy-alphabetical-start
     ("a", Stable, &["zaamo", "zalrsc"]),
@@ -782,6 +851,7 @@ pub fn all_rust_features() -> impl Iterator<Item = (&'static str, Stability)> {
         .chain(HEXAGON_FEATURES.iter())
         .chain(POWERPC_FEATURES.iter())
         .chain(MIPS_FEATURES.iter())
+        .chain(NVPTX_FEATURES.iter())
         .chain(RISCV_FEATURES.iter())
         .chain(WASM_FEATURES.iter())
         .chain(BPF_FEATURES.iter())
@@ -847,6 +917,7 @@ impl Target {
             "x86" | "x86_64" => X86_FEATURES,
             "hexagon" => HEXAGON_FEATURES,
             "mips" | "mips32r6" | "mips64" | "mips64r6" => MIPS_FEATURES,
+            "nvptx64" => NVPTX_FEATURES,
             "powerpc" | "powerpc64" => POWERPC_FEATURES,
             "riscv32" | "riscv64" => RISCV_FEATURES,
             "wasm32" | "wasm64" => WASM_FEATURES,
@@ -873,7 +944,7 @@ impl Target {
             "sparc" | "sparc64" => SPARC_FEATURES_FOR_CORRECT_VECTOR_ABI,
             "hexagon" => HEXAGON_FEATURES_FOR_CORRECT_VECTOR_ABI,
             "mips" | "mips32r6" | "mips64" | "mips64r6" => MIPS_FEATURES_FOR_CORRECT_VECTOR_ABI,
-            "bpf" | "m68k" => &[], // no vector ABI
+            "nvptx64" | "bpf" | "m68k" => &[], // no vector ABI
             "csky" => CSKY_FEATURES_FOR_CORRECT_VECTOR_ABI,
             // FIXME: for some tier3 targets, we are overly cautious and always give warnings
             // when passing args in vector registers.
diff --git a/compiler/rustc_trait_selection/messages.ftl b/compiler/rustc_trait_selection/messages.ftl
index 8232da4df43..fcb25025087 100644
--- a/compiler/rustc_trait_selection/messages.ftl
+++ b/compiler/rustc_trait_selection/messages.ftl
@@ -171,8 +171,6 @@ trait_selection_fps_remove_ref = consider removing the reference
 trait_selection_fps_use_ref = consider using a reference
 trait_selection_fulfill_req_lifetime = the type `{$ty}` does not fulfill the required lifetime
 
-trait_selection_full_type_written = the full type name has been written to '{$path}'
-
 trait_selection_ignored_diagnostic_option = `{$option_name}` is ignored due to previous definition of `{$option_name}`
     .other_label = `{$option_name}` is first declared here
     .label = `{$option_name}` is already declared here
diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs
index ed8229154a9..9447612d026 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs
@@ -224,41 +224,41 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         use ty::GenericArg;
         use ty::print::Printer;
 
-        struct AbsolutePathPrinter<'tcx> {
+        struct ConflictingPathPrinter<'tcx> {
             tcx: TyCtxt<'tcx>,
             segments: Vec<Symbol>,
         }
 
-        impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
+        impl<'tcx> Printer<'tcx> for ConflictingPathPrinter<'tcx> {
             fn tcx<'a>(&'a self) -> TyCtxt<'tcx> {
                 self.tcx
             }
 
             fn print_region(&mut self, _region: ty::Region<'_>) -> Result<(), PrintError> {
-                unreachable!(); // because `path_generic_args` ignores the `GenericArgs`
+                unreachable!(); // because `print_path_with_generic_args` ignores the `GenericArgs`
             }
 
             fn print_type(&mut self, _ty: Ty<'tcx>) -> Result<(), PrintError> {
-                unreachable!(); // because `path_generic_args` ignores the `GenericArgs`
+                unreachable!(); // because `print_path_with_generic_args` ignores the `GenericArgs`
             }
 
             fn print_dyn_existential(
                 &mut self,
                 _predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
             ) -> Result<(), PrintError> {
-                unreachable!(); // because `path_generic_args` ignores the `GenericArgs`
+                unreachable!(); // because `print_path_with_generic_args` ignores the `GenericArgs`
             }
 
             fn print_const(&mut self, _ct: ty::Const<'tcx>) -> Result<(), PrintError> {
-                unreachable!(); // because `path_generic_args` ignores the `GenericArgs`
+                unreachable!(); // because `print_path_with_generic_args` ignores the `GenericArgs`
             }
 
-            fn path_crate(&mut self, cnum: CrateNum) -> Result<(), PrintError> {
+            fn print_crate_name(&mut self, cnum: CrateNum) -> Result<(), PrintError> {
                 self.segments = vec![self.tcx.crate_name(cnum)];
                 Ok(())
             }
 
-            fn path_qualified(
+            fn print_path_with_qualified(
                 &mut self,
                 _self_ty: Ty<'tcx>,
                 _trait_ref: Option<ty::TraitRef<'tcx>>,
@@ -266,7 +266,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 Err(fmt::Error)
             }
 
-            fn path_append_impl(
+            fn print_path_with_impl(
                 &mut self,
                 _print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
                 _self_ty: Ty<'tcx>,
@@ -275,7 +275,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 Err(fmt::Error)
             }
 
-            fn path_append(
+            fn print_path_with_simple(
                 &mut self,
                 print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
                 disambiguated_data: &DisambiguatedDefPathData,
@@ -285,7 +285,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 Ok(())
             }
 
-            fn path_generic_args(
+            fn print_path_with_generic_args(
                 &mut self,
                 print_prefix: impl FnOnce(&mut Self) -> Result<(), PrintError>,
                 _args: &[GenericArg<'tcx>],
@@ -300,28 +300,27 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             // let _ = [{struct Foo; Foo}, {struct Foo; Foo}];
             if did1.krate != did2.krate {
                 let abs_path = |def_id| {
-                    let mut p = AbsolutePathPrinter { tcx: self.tcx, segments: vec![] };
+                    let mut p = ConflictingPathPrinter { tcx: self.tcx, segments: vec![] };
                     p.print_def_path(def_id, &[]).map(|_| p.segments)
                 };
 
-                // We compare strings because DefPath can be different
-                // for imported and non-imported crates
+                // We compare strings because DefPath can be different for imported and
+                // non-imported crates.
                 let expected_str = self.tcx.def_path_str(did1);
                 let found_str = self.tcx.def_path_str(did2);
                 let Ok(expected_abs) = abs_path(did1) else { return false };
                 let Ok(found_abs) = abs_path(did2) else { return false };
-                let same_path = || -> Result<_, PrintError> {
-                    Ok(expected_str == found_str || expected_abs == found_abs)
-                };
-                // We want to use as unique a type path as possible. If both types are "locally
-                // known" by the same name, we use the "absolute path" which uses the original
-                // crate name instead.
-                let (expected, found) = if expected_str == found_str {
-                    (join_path_syms(&expected_abs), join_path_syms(&found_abs))
-                } else {
-                    (expected_str.clone(), found_str.clone())
-                };
-                if same_path().unwrap_or(false) {
+                let same_path = expected_str == found_str || expected_abs == found_abs;
+                if same_path {
+                    // We want to use as unique a type path as possible. If both types are "locally
+                    // known" by the same name, we use the "absolute path" which uses the original
+                    // crate name instead.
+                    let (expected, found) = if expected_str == found_str {
+                        (join_path_syms(&expected_abs), join_path_syms(&found_abs))
+                    } else {
+                        (expected_str.clone(), found_str.clone())
+                    };
+
                     // We've displayed "expected `a::b`, found `a::b`". We add context to
                     // differentiate the different cases where that might happen.
                     let expected_crate_name = self.tcx.crate_name(did1.krate);
@@ -459,7 +458,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                             span,
                             format!("this is an iterator with items of type `{}`", args.type_at(0)),
                         );
-                    } else {
+                    } else if !span.overlaps(cause.span) {
                         let expected_ty = self.tcx.short_string(expected_ty, err.long_ty_path());
                         err.span_label(span, format!("this expression has type `{expected_ty}`"));
                     }
@@ -1620,8 +1619,18 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         {
             let e = self.tcx.erase_regions(e);
             let f = self.tcx.erase_regions(f);
-            let expected = with_forced_trimmed_paths!(e.sort_string(self.tcx));
-            let found = with_forced_trimmed_paths!(f.sort_string(self.tcx));
+            let mut expected = with_forced_trimmed_paths!(e.sort_string(self.tcx));
+            let mut found = with_forced_trimmed_paths!(f.sort_string(self.tcx));
+            if let ObligationCauseCode::Pattern { span, .. } = cause.code()
+                && let Some(span) = span
+                && !span.from_expansion()
+                && cause.span.from_expansion()
+            {
+                // When the type error comes from a macro like `assert!()`, and we are pointing at
+                // code the user wrote the cause and effect are reversed as the expected value is
+                // what the macro expanded to.
+                (found, expected) = (expected, found);
+            }
             if expected == found {
                 label_or_note(span, terr.to_string(self.tcx));
             } else {
@@ -1930,7 +1939,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         &self,
         trace: &TypeTrace<'tcx>,
         terr: TypeError<'tcx>,
-        path: &mut Option<PathBuf>,
+        long_ty_path: &mut Option<PathBuf>,
     ) -> Vec<TypeErrorAdditionalDiags> {
         let mut suggestions = Vec::new();
         let span = trace.cause.span;
@@ -2009,7 +2018,8 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         })
         | ObligationCauseCode::BlockTailExpression(.., source)) = code
             && let hir::MatchSource::TryDesugar(_) = source
-            && let Some((expected_ty, found_ty)) = self.values_str(trace.values, &trace.cause, path)
+            && let Some((expected_ty, found_ty)) =
+                self.values_str(trace.values, &trace.cause, long_ty_path)
         {
             suggestions.push(TypeErrorAdditionalDiags::TryCannotConvert {
                 found: found_ty.content(),
@@ -2139,11 +2149,13 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         &self,
         values: ValuePairs<'tcx>,
         cause: &ObligationCause<'tcx>,
-        file: &mut Option<PathBuf>,
+        long_ty_path: &mut Option<PathBuf>,
     ) -> Option<(DiagStyledString, DiagStyledString)> {
         match values {
             ValuePairs::Regions(exp_found) => self.expected_found_str(exp_found),
-            ValuePairs::Terms(exp_found) => self.expected_found_str_term(exp_found, file),
+            ValuePairs::Terms(exp_found) => {
+                self.expected_found_str_term(cause, exp_found, long_ty_path)
+            }
             ValuePairs::Aliases(exp_found) => self.expected_found_str(exp_found),
             ValuePairs::ExistentialTraitRef(exp_found) => self.expected_found_str(exp_found),
             ValuePairs::ExistentialProjection(exp_found) => self.expected_found_str(exp_found),
@@ -2182,15 +2194,35 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
 
     fn expected_found_str_term(
         &self,
+        cause: &ObligationCause<'tcx>,
         exp_found: ty::error::ExpectedFound<ty::Term<'tcx>>,
-        path: &mut Option<PathBuf>,
+        long_ty_path: &mut Option<PathBuf>,
     ) -> Option<(DiagStyledString, DiagStyledString)> {
         let exp_found = self.resolve_vars_if_possible(exp_found);
         if exp_found.references_error() {
             return None;
         }
+        let (mut expected, mut found) = (exp_found.expected, exp_found.found);
+
+        if let ObligationCauseCode::Pattern { span, .. } = cause.code()
+            && let Some(span) = span
+            && !span.from_expansion()
+            && cause.span.from_expansion()
+        {
+            // When the type error comes from a macro like `assert!()`, and we are pointing at
+            // code the user wrote, the cause and effect are reversed as the expected value is
+            // what the macro expanded to. So if the user provided a `Type` when the macro is
+            // written in such a way that a `bool` was expected, we want to print:
+            // = note: expected `bool`
+            //            found `Type`"
+            // but as far as the compiler is concerned, after expansion what was expected was `Type`
+            // = note: expected `Type`
+            //            found `bool`"
+            // so we reverse them here to match user expectation.
+            (expected, found) = (found, expected);
+        }
 
-        Some(match (exp_found.expected.kind(), exp_found.found.kind()) {
+        Some(match (expected.kind(), found.kind()) {
             (ty::TermKind::Ty(expected), ty::TermKind::Ty(found)) => {
                 let (mut exp, mut fnd) = self.cmp(expected, found);
                 // Use the terminal width as the basis to determine when to compress the printed
@@ -2200,11 +2232,11 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 let exp_s = exp.content();
                 let fnd_s = fnd.content();
                 if exp_s.len() > len {
-                    let exp_s = self.tcx.short_string(expected, path);
+                    let exp_s = self.tcx.short_string(expected, long_ty_path);
                     exp = DiagStyledString::highlighted(exp_s);
                 }
                 if fnd_s.len() > len {
-                    let fnd_s = self.tcx.short_string(found, path);
+                    let fnd_s = self.tcx.short_string(found, long_ty_path);
                     fnd = DiagStyledString::highlighted(fnd_s);
                 }
                 (exp, fnd)
diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/need_type_info.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/need_type_info.rs
index 966f117a1bf..ec2287ed516 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/need_type_info.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/need_type_info.rs
@@ -436,8 +436,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 infer_subdiags,
                 multi_suggestions,
                 bad_label,
-                was_written: false,
-                path: Default::default(),
             }),
             TypeAnnotationNeeded::E0283 => self.dcx().create_err(AmbiguousImpl {
                 span,
@@ -447,8 +445,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 infer_subdiags,
                 multi_suggestions,
                 bad_label,
-                was_written: false,
-                path: Default::default(),
             }),
             TypeAnnotationNeeded::E0284 => self.dcx().create_err(AmbiguousReturn {
                 span,
@@ -458,8 +454,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 infer_subdiags,
                 multi_suggestions,
                 bad_label,
-                was_written: false,
-                path: Default::default(),
             }),
         }
     }
@@ -496,7 +490,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             return self.bad_inference_failure_err(failure_span, arg_data, error_code);
         };
 
-        let (source_kind, name, path) = kind.ty_localized_msg(self);
+        let (source_kind, name, long_ty_path) = kind.ty_localized_msg(self);
         let failure_span = if should_label_span && !failure_span.overlaps(span) {
             Some(failure_span)
         } else {
@@ -628,7 +622,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 }
             }
         }
-        match error_code {
+        let mut err = match error_code {
             TypeAnnotationNeeded::E0282 => self.dcx().create_err(AnnotationRequired {
                 span,
                 source_kind,
@@ -637,8 +631,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 infer_subdiags,
                 multi_suggestions,
                 bad_label: None,
-                was_written: path.is_some(),
-                path: path.unwrap_or_default(),
             }),
             TypeAnnotationNeeded::E0283 => self.dcx().create_err(AmbiguousImpl {
                 span,
@@ -648,8 +640,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 infer_subdiags,
                 multi_suggestions,
                 bad_label: None,
-                was_written: path.is_some(),
-                path: path.unwrap_or_default(),
             }),
             TypeAnnotationNeeded::E0284 => self.dcx().create_err(AmbiguousReturn {
                 span,
@@ -659,10 +649,10 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 infer_subdiags,
                 multi_suggestions,
                 bad_label: None,
-                was_written: path.is_some(),
-                path: path.unwrap_or_default(),
             }),
-        }
+        };
+        *err.long_ty_path() = long_ty_path;
+        err
     }
 }
 
@@ -726,22 +716,24 @@ impl<'tcx> InferSource<'tcx> {
 
 impl<'tcx> InferSourceKind<'tcx> {
     fn ty_localized_msg(&self, infcx: &InferCtxt<'tcx>) -> (&'static str, String, Option<PathBuf>) {
-        let mut path = None;
+        let mut long_ty_path = None;
         match *self {
             InferSourceKind::LetBinding { ty, .. }
             | InferSourceKind::ClosureArg { ty, .. }
             | InferSourceKind::ClosureReturn { ty, .. } => {
                 if ty.is_closure() {
-                    ("closure", closure_as_fn_str(infcx, ty), path)
+                    ("closure", closure_as_fn_str(infcx, ty), long_ty_path)
                 } else if !ty.is_ty_or_numeric_infer() {
-                    ("normal", infcx.tcx.short_string(ty, &mut path), path)
+                    ("normal", infcx.tcx.short_string(ty, &mut long_ty_path), long_ty_path)
                 } else {
-                    ("other", String::new(), path)
+                    ("other", String::new(), long_ty_path)
                 }
             }
             // FIXME: We should be able to add some additional info here.
             InferSourceKind::GenericArg { .. }
-            | InferSourceKind::FullyQualifiedMethodCall { .. } => ("other", String::new(), path),
+            | InferSourceKind::FullyQualifiedMethodCall { .. } => {
+                ("other", String::new(), long_ty_path)
+            }
         }
     }
 }
diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs
index 129d0963a75..f31a85ec07a 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs
@@ -653,7 +653,6 @@ impl<T> Trait<T> for X {
             )
         );
         let impl_comparison = matches!(cause_code, ObligationCauseCode::CompareImplItem { .. });
-        let assoc = tcx.associated_item(proj_ty.def_id);
         if impl_comparison {
             // We do not want to suggest calling functions when the reason of the
             // type error is a comparison of an `impl` with its `trait`.
@@ -661,7 +660,7 @@ impl<T> Trait<T> for X {
             let point_at_assoc_fn = if callable_scope
                 && self.point_at_methods_that_satisfy_associated_type(
                     diag,
-                    assoc.container_id(tcx),
+                    tcx.parent(proj_ty.def_id),
                     current_method_ident,
                     proj_ty.def_id,
                     values.expected,
@@ -947,7 +946,7 @@ fn foo(&self) -> Self::T { String::new() }
 
     pub fn format_generic_args(&self, args: &[ty::GenericArg<'tcx>]) -> String {
         FmtPrinter::print_string(self.tcx, hir::def::Namespace::TypeNS, |p| {
-            p.path_generic_args(|_| Ok(()), args)
+            p.print_path_with_generic_args(|_| Ok(()), args)
         })
         .expect("could not write to `String`.")
     }
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs
index cdf1402252a..af912227ce4 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs
@@ -169,7 +169,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
 
         let predicate = self.resolve_vars_if_possible(obligation.predicate);
         let span = obligation.cause.span;
-        let mut file = None;
+        let mut long_ty_path = None;
 
         debug!(?predicate, obligation.cause.code = ?obligation.cause.code());
 
@@ -211,19 +211,18 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     self.tcx.as_lang_item(trait_pred.def_id()),
                     Some(LangItem::Sized | LangItem::MetaSized)
                 ) {
-                    match self.tainted_by_errors() {
-                        None => {
-                            let err = self.emit_inference_failure_err(
+                    return match self.tainted_by_errors() {
+                        None => self
+                            .emit_inference_failure_err(
                                 obligation.cause.body_id,
                                 span,
                                 trait_pred.self_ty().skip_binder().into(),
                                 TypeAnnotationNeeded::E0282,
                                 false,
-                            );
-                            return err.emit();
-                        }
-                        Some(e) => return e,
-                    }
+                            )
+                            .emit(),
+                        Some(e) => e,
+                    };
                 }
 
                 // Typically, this ambiguity should only happen if
@@ -260,8 +259,9 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         span,
                         E0283,
                         "type annotations needed: cannot satisfy `{}`",
-                        self.tcx.short_string(predicate, &mut file),
+                        self.tcx.short_string(predicate, &mut long_ty_path),
                     )
+                    .with_long_ty_path(long_ty_path)
                 };
 
                 let mut ambiguities = compute_applicable_impls_for_diagnostics(
@@ -307,7 +307,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         err.cancel();
                         return e;
                     }
-                    let pred = self.tcx.short_string(predicate, &mut file);
+                    let pred = self.tcx.short_string(predicate, &mut err.long_ty_path());
                     err.note(format!("cannot satisfy `{pred}`"));
                     let impl_candidates =
                         self.find_similar_impl_candidates(predicate.as_trait_clause().unwrap());
@@ -512,6 +512,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     true,
                 )
             }
+
             ty::PredicateKind::Clause(ty::ClauseKind::Projection(data)) => {
                 if let Err(e) = predicate.error_reported() {
                     return e;
@@ -536,7 +537,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     .filter_map(ty::GenericArg::as_term)
                     .chain([data.term])
                     .find(|g| g.has_non_region_infer());
-                let predicate = self.tcx.short_string(predicate, &mut file);
+                let predicate = self.tcx.short_string(predicate, &mut long_ty_path);
                 if let Some(term) = term {
                     self.emit_inference_failure_err(
                         obligation.cause.body_id,
@@ -546,6 +547,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         true,
                     )
                     .with_note(format!("cannot satisfy `{predicate}`"))
+                    .with_long_ty_path(long_ty_path)
                 } else {
                     // If we can't find a generic parameter, just print a generic error
                     struct_span_code_err!(
@@ -555,6 +557,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         "type annotations needed: cannot satisfy `{predicate}`",
                     )
                     .with_span_label(span, format!("cannot satisfy `{predicate}`"))
+                    .with_long_ty_path(long_ty_path)
                 }
             }
 
@@ -568,17 +571,16 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 let term =
                     data.walk().filter_map(ty::GenericArg::as_term).find(|term| term.is_infer());
                 if let Some(term) = term {
-                    let err = self.emit_inference_failure_err(
+                    self.emit_inference_failure_err(
                         obligation.cause.body_id,
                         span,
                         term,
                         TypeAnnotationNeeded::E0284,
                         true,
-                    );
-                    err
+                    )
                 } else {
                     // If we can't find a generic parameter, just print a generic error
-                    let predicate = self.tcx.short_string(predicate, &mut file);
+                    let predicate = self.tcx.short_string(predicate, &mut long_ty_path);
                     struct_span_code_err!(
                         self.dcx(),
                         span,
@@ -586,6 +588,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         "type annotations needed: cannot satisfy `{predicate}`",
                     )
                     .with_span_label(span, format!("cannot satisfy `{predicate}`"))
+                    .with_long_ty_path(long_ty_path)
                 }
             }
 
@@ -597,13 +600,14 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     TypeAnnotationNeeded::E0284,
                     true,
                 ),
+
             ty::PredicateKind::NormalizesTo(ty::NormalizesTo { alias, term })
                 if term.is_infer() =>
             {
                 if let Some(e) = self.tainted_by_errors() {
                     return e;
                 }
-                let alias = self.tcx.short_string(alias, &mut file);
+                let alias = self.tcx.short_string(alias, &mut long_ty_path);
                 struct_span_code_err!(
                     self.dcx(),
                     span,
@@ -611,37 +615,34 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     "type annotations needed: cannot normalize `{alias}`",
                 )
                 .with_span_label(span, format!("cannot normalize `{alias}`"))
+                .with_long_ty_path(long_ty_path)
             }
+
             ty::PredicateKind::Clause(ty::ClauseKind::UnstableFeature(sym)) => {
                 if let Some(e) = self.tainted_by_errors() {
                     return e;
                 }
 
-                let mut err;
-
                 if self.tcx.features().staged_api() {
-                    err = self.dcx().struct_span_err(
+                    self.dcx().struct_span_err(
                         span,
                         format!("unstable feature `{sym}` is used without being enabled."),
-                    );
-
-                    err.help(format!("The feature can be enabled by marking the current item with `#[unstable_feature_bound({sym})]`"));
+                    ).with_help(format!("The feature can be enabled by marking the current item with `#[unstable_feature_bound({sym})]`"))
                 } else {
-                    err = feature_err_unstable_feature_bound(
+                    feature_err_unstable_feature_bound(
                         &self.tcx.sess,
                         sym,
                         span,
                         format!("use of unstable library feature `{sym}`"),
-                    );
+                    )
                 }
-                err
             }
 
             _ => {
                 if let Some(e) = self.tainted_by_errors() {
                     return e;
                 }
-                let predicate = self.tcx.short_string(predicate, &mut file);
+                let predicate = self.tcx.short_string(predicate, &mut long_ty_path);
                 struct_span_code_err!(
                     self.dcx(),
                     span,
@@ -649,9 +650,9 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     "type annotations needed: cannot satisfy `{predicate}`",
                 )
                 .with_span_label(span, format!("cannot satisfy `{predicate}`"))
+                .with_long_ty_path(long_ty_path)
             }
         };
-        *err.long_ty_path() = file;
         self.note_obligation_cause(&mut err, obligation);
         err.emit()
     }
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
index a9e346a5cdb..214a6e86d39 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
@@ -37,7 +37,6 @@ use super::on_unimplemented::{AppendConstMessage, OnUnimplementedNote};
 use super::suggestions::get_explanation_based_on_obligation;
 use super::{
     ArgKind, CandidateSimilarity, FindExprBySpan, GetSafeTransmuteErrorAndReason, ImplCandidate,
-    UnsatisfiedConst,
 };
 use crate::error_reporting::TypeErrCtxt;
 use crate::error_reporting::infer::TyCategory;
@@ -208,16 +207,19 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                                                      performs a conversion on the error value \
                                                      using the `From` trait";
                         let (message, notes, append_const_msg) = if is_try_conversion {
+                            let ty = self.tcx.short_string(
+                                main_trait_predicate.skip_binder().self_ty(),
+                                &mut long_ty_file,
+                            );
                             // We have a `-> Result<_, E1>` and `gives_E2()?`.
                             (
-                                Some(format!(
-                                    "`?` couldn't convert the error to `{}`",
-                                    main_trait_predicate.skip_binder().self_ty(),
-                                )),
+                                Some(format!("`?` couldn't convert the error to `{ty}`")),
                                 vec![question_mark_message.to_owned()],
                                 Some(AppendConstMessage::Default),
                             )
                         } else if is_question_mark {
+                            let main_trait_predicate =
+                                self.tcx.short_string(main_trait_predicate, &mut long_ty_file);
                             // Similar to the case above, but in this case the conversion is for a
                             // trait object: `-> Result<_, Box<dyn Error>` and `gives_E()?` when
                             // `E: Error` isn't met.
@@ -233,7 +235,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                             (message, notes, append_const_msg)
                         };
 
-                        let err_msg = self.get_standard_error_message(
+                        let default_err_msg = || self.get_standard_error_message(
                             main_trait_predicate,
                             message,
                             None,
@@ -258,7 +260,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                                     );
                                 }
                                 GetSafeTransmuteErrorAndReason::Default => {
-                                    (err_msg, None)
+                                    (default_err_msg(), None)
                                 }
                                 GetSafeTransmuteErrorAndReason::Error {
                                     err_msg,
@@ -266,7 +268,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                                 } => (err_msg, safe_transmute_explanation),
                             }
                         } else {
-                            (err_msg, None)
+                            (default_err_msg(), None)
                         };
 
                         let mut err = struct_span_code_err!(self.dcx(), span, E0277, "{}", err_msg);
@@ -279,15 +281,21 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
 
                         if let Some(ret_span) = self.return_type_span(&obligation) {
                             if is_try_conversion {
+                                let ty = self.tcx.short_string(
+                                    main_trait_predicate.skip_binder().self_ty(),
+                                    err.long_ty_path(),
+                                );
                                 err.span_label(
                                     ret_span,
-                                    format!(
-                                        "expected `{}` because of this",
-                                        main_trait_predicate.skip_binder().self_ty()
-                                    ),
+                                    format!("expected `{ty}` because of this"),
                                 );
                             } else if is_question_mark {
-                                err.span_label(ret_span, format!("required `{main_trait_predicate}` because of this"));
+                                let main_trait_predicate =
+                                    self.tcx.short_string(main_trait_predicate, err.long_ty_path());
+                                err.span_label(
+                                    ret_span,
+                                    format!("required `{main_trait_predicate}` because of this"),
+                                );
                             }
                         }
 
@@ -303,6 +311,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                             &obligation,
                             leaf_trait_predicate,
                             pre_message,
+                            err.long_ty_path(),
                         );
 
                         self.check_for_binding_assigned_block_without_tail_expression(
@@ -364,13 +373,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                             }
                         }
 
-                        let UnsatisfiedConst(unsatisfied_const) = self
-                            .maybe_add_note_for_unsatisfied_const(
-                                leaf_trait_predicate,
-                                &mut err,
-                                span,
-                            );
-
                         if let Some((msg, span)) = type_def {
                             err.span_label(span, msg);
                         }
@@ -414,11 +416,12 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                                 } else {
                                     vec![(span.shrink_to_hi(), format!(" as {}", cand.self_ty()))]
                                 };
+                                let trait_ = self.tcx.short_string(cand.print_trait_sugared(), err.long_ty_path());
+                                let ty = self.tcx.short_string(cand.self_ty(), err.long_ty_path());
                                 err.multipart_suggestion(
                                     format!(
-                                        "the trait `{}` is implemented for fn pointer `{}`, try casting using `as`",
-                                        cand.print_trait_sugared(),
-                                        cand.self_ty(),
+                                        "the trait `{trait_}` is implemented for fn pointer \
+                                         `{ty}`, try casting using `as`",
                                     ),
                                     suggestion,
                                     Applicability::MaybeIncorrect,
@@ -495,7 +498,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                             span,
                             is_fn_trait,
                             suggested,
-                            unsatisfied_const,
                         );
 
                         // Changing mutability doesn't make a difference to whether we have
@@ -522,7 +524,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                                     <https://github.com/rust-lang/rust/issues/48950> \
                                     for more information)",
                                 );
-                                err.help("did you intend to use the type `()` here instead?");
+                                err.help("you might have intended to use the type `()` here instead");
                             }
                         }
 
@@ -722,10 +724,13 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             }
 
             SelectionError::ConstArgHasWrongType { ct, ct_ty, expected_ty } => {
+                let expected_ty_str = self.tcx.short_string(expected_ty, &mut long_ty_file);
+                let ct_str = self.tcx.short_string(ct, &mut long_ty_file);
                 let mut diag = self.dcx().struct_span_err(
                     span,
-                    format!("the constant `{ct}` is not of type `{expected_ty}`"),
+                    format!("the constant `{ct_str}` is not of type `{expected_ty_str}`"),
                 );
+                diag.long_ty_path = long_ty_file;
 
                 self.note_type_err(
                     &mut diag,
@@ -1118,9 +1123,11 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 .must_apply_modulo_regions()
             {
                 if !suggested {
+                    let err_ty = self.tcx.short_string(err_ty, err.long_ty_path());
                     err.span_label(span, format!("this has type `Result<_, {err_ty}>`"));
                 }
             } else {
+                let err_ty = self.tcx.short_string(err_ty, err.long_ty_path());
                 err.span_label(
                     span,
                     format!(
@@ -1156,12 +1163,13 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 );
             }
             (ty::Adt(def, _), None) if def.did().is_local() => {
+                let trait_path = self.tcx.short_string(
+                    trait_pred.skip_binder().trait_ref.print_only_trait_path(),
+                    err.long_ty_path(),
+                );
                 err.span_note(
                     self.tcx.def_span(def.did()),
-                    format!(
-                        "`{self_ty}` needs to implement `{}`",
-                        trait_pred.skip_binder().trait_ref.print_only_trait_path(),
-                    ),
+                    format!("`{self_ty}` needs to implement `{trait_path}`"),
                 );
             }
             (ty::Adt(def, _), Some(ty)) if def.did().is_local() => {
@@ -1195,13 +1203,15 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             bug!()
         };
 
+        let mut file = None;
+        let ty_str = self.tcx.short_string(ty, &mut file);
         let mut diag = match ty.kind() {
             ty::Float(_) => {
                 struct_span_code_err!(
                     self.dcx(),
                     span,
                     E0741,
-                    "`{ty}` is forbidden as the type of a const generic parameter",
+                    "`{ty_str}` is forbidden as the type of a const generic parameter",
                 )
             }
             ty::FnPtr(..) => {
@@ -1226,7 +1236,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     self.dcx(),
                     span,
                     E0741,
-                    "`{ty}` must implement `ConstParamTy` to be used as the type of a const generic parameter",
+                    "`{ty_str}` must implement `ConstParamTy` to be used as the type of a const generic parameter",
                 );
                 // Only suggest derive if this isn't a derived obligation,
                 // and the struct is local.
@@ -1258,21 +1268,22 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     self.dcx(),
                     span,
                     E0741,
-                    "`{ty}` can't be used as a const parameter type",
+                    "`{ty_str}` can't be used as a const parameter type",
                 )
             }
         };
+        diag.long_ty_path = file;
 
         let mut code = obligation.cause.code();
         let mut pred = obligation.predicate.as_trait_clause();
         while let Some((next_code, next_pred)) = code.parent_with_predicate() {
             if let Some(pred) = pred {
                 self.enter_forall(pred, |pred| {
-                    diag.note(format!(
-                        "`{}` must implement `{}`, but it does not",
-                        pred.self_ty(),
-                        pred.print_modifiers_and_trait_path()
-                    ));
+                    let ty = self.tcx.short_string(pred.self_ty(), diag.long_ty_path());
+                    let trait_path = self
+                        .tcx
+                        .short_string(pred.print_modifiers_and_trait_path(), diag.long_ty_path());
+                    diag.note(format!("`{ty}` must implement `{trait_path}`, but it does not"));
                 })
             }
             code = next_code;
@@ -1584,7 +1595,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         projection_term: ty::AliasTerm<'tcx>,
         normalized_ty: ty::Term<'tcx>,
         expected_ty: ty::Term<'tcx>,
-        file: &mut Option<PathBuf>,
+        long_ty_path: &mut Option<PathBuf>,
     ) -> Option<(String, Span, Option<Span>)> {
         let trait_def_id = projection_term.trait_def_id(self.tcx);
         let self_ty = projection_term.self_ty();
@@ -1624,17 +1635,25 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 };
                 let item = match self_ty.kind() {
                     ty::FnDef(def, _) => self.tcx.item_name(*def).to_string(),
-                    _ => self.tcx.short_string(self_ty, file),
+                    _ => self.tcx.short_string(self_ty, long_ty_path),
                 };
+                let expected_ty = self.tcx.short_string(expected_ty, long_ty_path);
+                let normalized_ty = self.tcx.short_string(normalized_ty, long_ty_path);
                 Some((format!(
                     "expected `{item}` to return `{expected_ty}`, but it returns `{normalized_ty}`",
                 ), span, closure_span))
             } else if self.tcx.is_lang_item(trait_def_id, LangItem::Future) {
+                let self_ty = self.tcx.short_string(self_ty, long_ty_path);
+                let expected_ty = self.tcx.short_string(expected_ty, long_ty_path);
+                let normalized_ty = self.tcx.short_string(normalized_ty, long_ty_path);
                 Some((format!(
                     "expected `{self_ty}` to be a future that resolves to `{expected_ty}`, but it \
                      resolves to `{normalized_ty}`"
                 ), span, None))
             } else if Some(trait_def_id) == self.tcx.get_diagnostic_item(sym::Iterator) {
+                let self_ty = self.tcx.short_string(self_ty, long_ty_path);
+                let expected_ty = self.tcx.short_string(expected_ty, long_ty_path);
+                let normalized_ty = self.tcx.short_string(normalized_ty, long_ty_path);
                 Some((format!(
                     "expected `{self_ty}` to be an iterator that yields `{expected_ty}`, but it \
                      yields `{normalized_ty}`"
@@ -2097,12 +2116,15 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
 
                     if let [TypeError::Sorts(exp_found)] = &terrs[..] {
                         let exp_found = self.resolve_vars_if_possible(*exp_found);
+                        let expected =
+                            self.tcx.short_string(exp_found.expected, err.long_ty_path());
+                        let found = self.tcx.short_string(exp_found.found, err.long_ty_path());
                         err.highlighted_help(vec![
                             StringPart::normal("for that trait implementation, "),
                             StringPart::normal("expected `"),
-                            StringPart::highlighted(exp_found.expected.to_string()),
+                            StringPart::highlighted(expected),
                             StringPart::normal("`, found `"),
-                            StringPart::highlighted(exp_found.found.to_string()),
+                            StringPart::highlighted(found),
                             StringPart::normal("`"),
                         ]);
                         self.suggest_function_pointers_impl(None, &exp_found, err);
@@ -2135,11 +2157,13 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         (ty::FnPtr(..), _) => (" implemented for fn pointer `", ""),
                         _ => (" implemented for `", ""),
                     };
+                let trait_ = self.tcx.short_string(cand.print_trait_sugared(), err.long_ty_path());
+                let self_ty = self.tcx.short_string(cand.self_ty(), err.long_ty_path());
                 err.highlighted_help(vec![
-                    StringPart::normal(format!("the trait `{}` ", cand.print_trait_sugared())),
+                    StringPart::normal(format!("the trait `{trait_}` ",)),
                     StringPart::highlighted("is"),
                     StringPart::normal(desc),
-                    StringPart::highlighted(cand.self_ty().to_string()),
+                    StringPart::highlighted(self_ty),
                     StringPart::normal("`"),
                     StringPart::normal(mention_castable),
                 ]);
@@ -2159,9 +2183,13 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 .into_iter()
                 .map(|c| {
                     if all_traits_equal {
-                        format!("\n  {}", c.self_ty())
+                        format!("\n  {}", self.tcx.short_string(c.self_ty(), err.long_ty_path()))
                     } else {
-                        format!("\n  `{}` implements `{}`", c.self_ty(), c.print_only_trait_path())
+                        format!(
+                            "\n  `{}` implements `{}`",
+                            self.tcx.short_string(c.self_ty(), err.long_ty_path()),
+                            self.tcx.short_string(c.print_only_trait_path(), err.long_ty_path()),
+                        )
                     }
                 })
                 .collect();
@@ -2477,7 +2505,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         predicate_constness: Option<ty::BoundConstness>,
         append_const_msg: Option<AppendConstMessage>,
         post_message: String,
-        long_ty_file: &mut Option<PathBuf>,
+        long_ty_path: &mut Option<PathBuf>,
     ) -> String {
         message
             .and_then(|cannot_do_this| {
@@ -2503,7 +2531,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     "the trait bound `{}` is not satisfied{post_message}",
                     self.tcx.short_string(
                         trait_predicate.print_with_bound_constness(predicate_constness),
-                        long_ty_file,
+                        long_ty_path,
                     ),
                 )
             })
@@ -2608,8 +2636,8 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                             dst_min_align,
                         } => {
                             format!(
-                                "the minimum alignment of `{src}` ({src_min_align}) should \
-                        be greater than that of `{dst}` ({dst_min_align})"
+                                "the minimum alignment of `{src}` ({src_min_align}) should be \
+                                 greater than that of `{dst}` ({dst_min_align})"
                             )
                         }
                         rustc_transmute::Reason::DstIsMoreUnique => {
@@ -2679,7 +2707,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         span: Span,
         is_fn_trait: bool,
         suggested: bool,
-        unsatisfied_const: bool,
     ) {
         let body_def_id = obligation.cause.body_id;
         let span = if let ObligationCauseCode::BinOp { rhs_span: Some(rhs_span), .. } =
@@ -2726,10 +2753,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 self.tcx.def_span(trait_def_id),
                 crate::fluent_generated::trait_selection_trait_has_no_impls,
             );
-        } else if !suggested
-            && !unsatisfied_const
-            && trait_predicate.polarity() == ty::PredicatePolarity::Positive
-        {
+        } else if !suggested && trait_predicate.polarity() == ty::PredicatePolarity::Positive {
             // Can't show anything else useful, try to find similar impls.
             let impl_candidates = self.find_similar_impl_candidates(trait_predicate);
             if !self.report_similar_impl_candidates(
@@ -2841,17 +2865,6 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         }
     }
 
-    fn maybe_add_note_for_unsatisfied_const(
-        &self,
-        _trait_predicate: ty::PolyTraitPredicate<'tcx>,
-        _err: &mut Diag<'_>,
-        _span: Span,
-    ) -> UnsatisfiedConst {
-        let unsatisfied_const = UnsatisfiedConst(false);
-        // FIXME(const_trait_impl)
-        unsatisfied_const
-    }
-
     fn report_closure_error(
         &self,
         obligation: &PredicateObligation<'tcx>,
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs
index 1d8b934cef3..c8500b2d9d4 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs
@@ -51,8 +51,6 @@ enum GetSafeTransmuteErrorAndReason {
     Error { err_msg: String, safe_transmute_explanation: Option<String> },
 }
 
-struct UnsatisfiedConst(pub bool);
-
 /// Crude way of getting back an `Expr` from a `Span`.
 pub struct FindExprBySpan<'hir> {
     pub span: Span,
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/on_unimplemented.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/on_unimplemented.rs
index 5765dfd891d..bb5c6469f34 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/on_unimplemented.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/on_unimplemented.rs
@@ -99,7 +99,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         &self,
         trait_pred: ty::PolyTraitPredicate<'tcx>,
         obligation: &PredicateObligation<'tcx>,
-        long_ty_file: &mut Option<PathBuf>,
+        long_ty_path: &mut Option<PathBuf>,
     ) -> OnUnimplementedNote {
         if trait_pred.polarity() != ty::PredicatePolarity::Positive {
             return OnUnimplementedNote::default();
@@ -281,7 +281,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
                         if let Some(ty) = trait_pred.trait_ref.args[param.index as usize].as_type()
                         {
-                            self.tcx.short_string(ty, long_ty_file)
+                            self.tcx.short_string(ty, long_ty_path)
                         } else {
                             trait_pred.trait_ref.args[param.index as usize].to_string()
                         }
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
index 718cff6d135..bc8c8a44405 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
@@ -3,6 +3,7 @@
 use std::assert_matches::debug_assert_matches;
 use std::borrow::Cow;
 use std::iter;
+use std::path::PathBuf;
 
 use itertools::{EitherOrBoth, Itertools};
 use rustc_abi::ExternAbi;
@@ -737,7 +738,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 get_name(err, &local.pat.kind)
             }
             // Different to previous arm because one is `&hir::Local` and the other
-            // is `P<hir::Local>`.
+            // is `Box<hir::Local>`.
             hir::Node::LetStmt(local) => get_name(err, &local.pat.kind),
             _ => None,
         }
@@ -1369,6 +1370,10 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 );
                 let self_ty_str =
                     self.tcx.short_string(old_pred.self_ty().skip_binder(), err.long_ty_path());
+                let trait_path = self
+                    .tcx
+                    .short_string(old_pred.print_modifiers_and_trait_path(), err.long_ty_path());
+
                 if has_custom_message {
                     err.note(msg);
                 } else {
@@ -1376,10 +1381,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 }
                 err.span_label(
                     span,
-                    format!(
-                        "the trait `{}` is not implemented for `{self_ty_str}`",
-                        old_pred.print_modifiers_and_trait_path()
-                    ),
+                    format!("the trait `{trait_path}` is not implemented for `{self_ty_str}`"),
                 );
             };
 
@@ -3333,17 +3335,22 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     tcx.async_fn_trait_kind_from_def_id(data.parent_trait_pred.def_id()).is_some();
 
                 if !is_upvar_tys_infer_tuple && !is_builtin_async_fn_trait {
-                    let ty_str = tcx.short_string(ty, err.long_ty_path());
-                    let msg = format!("required because it appears within the type `{ty_str}`");
+                    let mut msg = || {
+                        let ty_str = tcx.short_string(ty, err.long_ty_path());
+                        format!("required because it appears within the type `{ty_str}`")
+                    };
                     match ty.kind() {
-                        ty::Adt(def, _) => match tcx.opt_item_ident(def.did()) {
-                            Some(ident) => {
-                                err.span_note(ident.span, msg);
-                            }
-                            None => {
-                                err.note(msg);
+                        ty::Adt(def, _) => {
+                            let msg = msg();
+                            match tcx.opt_item_ident(def.did()) {
+                                Some(ident) => {
+                                    err.span_note(ident.span, msg);
+                                }
+                                None => {
+                                    err.note(msg);
+                                }
                             }
-                        },
+                        }
                         ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }) => {
                             // If the previous type is async fn, this is the future generated by the body of an async function.
                             // Avoid printing it twice (it was already printed in the `ty::Coroutine` arm below).
@@ -3363,6 +3370,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                             {
                                 // See comment above; skip printing twice.
                             } else {
+                                let msg = msg();
                                 err.span_note(tcx.def_span(def_id), msg);
                             }
                         }
@@ -3392,6 +3400,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                             err.note("`str` is considered to contain a `[u8]` slice for auto trait purposes");
                         }
                         _ => {
+                            let msg = msg();
                             err.note(msg);
                         }
                     };
@@ -3441,7 +3450,10 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 }
                 let self_ty_str =
                     tcx.short_string(parent_trait_pred.skip_binder().self_ty(), err.long_ty_path());
-                let trait_name = parent_trait_pred.print_modifiers_and_trait_path().to_string();
+                let trait_name = tcx.short_string(
+                    parent_trait_pred.print_modifiers_and_trait_path(),
+                    err.long_ty_path(),
+                );
                 let msg = format!("required for `{self_ty_str}` to implement `{trait_name}`");
                 let mut is_auto_trait = false;
                 match tcx.hir_get_if_local(data.impl_or_alias_def_id) {
@@ -3459,8 +3471,8 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         ..
                     })) => {
                         let mut spans = Vec::with_capacity(2);
-                        if let Some(trait_ref) = of_trait {
-                            spans.push(trait_ref.path.span);
+                        if let Some(of_trait) = of_trait {
+                            spans.push(of_trait.trait_ref.path.span);
                         }
                         spans.push(self_ty.span);
                         let mut spans: MultiSpan = spans.into();
@@ -3468,7 +3480,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                             self_ty.span.ctxt().outer_expn_data().kind,
                             ExpnKind::Macro(MacroKind::Derive, _)
                         ) || matches!(
-                            of_trait.as_ref().map(|t| t.path.span.ctxt().outer_expn_data().kind),
+                            of_trait.map(|t| t.trait_ref.path.span.ctxt().outer_expn_data().kind),
                             Some(ExpnKind::Macro(MacroKind::Derive, _))
                         ) {
                             spans.push_span_label(
@@ -3539,10 +3551,11 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         parent_trait_pred.skip_binder().self_ty(),
                         err.long_ty_path(),
                     );
-                    err.note(format!(
-                        "required for `{self_ty}` to implement `{}`",
-                        parent_trait_pred.print_modifiers_and_trait_path()
-                    ));
+                    let trait_path = tcx.short_string(
+                        parent_trait_pred.print_modifiers_and_trait_path(),
+                        err.long_ty_path(),
+                    );
+                    err.note(format!("required for `{self_ty}` to implement `{trait_path}`"));
                 }
                 // #74711: avoid a stack overflow
                 ensure_sufficient_stack(|| {
@@ -3558,15 +3571,20 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 });
             }
             ObligationCauseCode::ImplDerivedHost(ref data) => {
-                let self_ty =
-                    self.resolve_vars_if_possible(data.derived.parent_host_pred.self_ty());
-                let msg = format!(
-                    "required for `{self_ty}` to implement `{} {}`",
-                    data.derived.parent_host_pred.skip_binder().constness,
+                let self_ty = tcx.short_string(
+                    self.resolve_vars_if_possible(data.derived.parent_host_pred.self_ty()),
+                    err.long_ty_path(),
+                );
+                let trait_path = tcx.short_string(
                     data.derived
                         .parent_host_pred
                         .map_bound(|pred| pred.trait_ref)
                         .print_only_trait_path(),
+                    err.long_ty_path(),
+                );
+                let msg = format!(
+                    "required for `{self_ty}` to implement `{} {trait_path}`",
+                    data.derived.parent_host_pred.skip_binder().constness,
                 );
                 match tcx.hir_get_if_local(data.impl_def_id) {
                     Some(Node::Item(hir::Item {
@@ -3574,7 +3592,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         ..
                     })) => {
                         let mut spans = vec![self_ty.span];
-                        spans.extend(of_trait.as_ref().map(|t| t.path.span));
+                        spans.extend(of_trait.map(|t| t.trait_ref.path.span));
                         let mut spans: MultiSpan = spans.into();
                         spans.push_span_label(data.span, "unsatisfied trait bound introduced here");
                         err.span_note(spans, msg);
@@ -5351,6 +5369,7 @@ pub(super) fn get_explanation_based_on_obligation<'tcx>(
     obligation: &PredicateObligation<'tcx>,
     trait_predicate: ty::PolyTraitPredicate<'tcx>,
     pre_message: String,
+    long_ty_path: &mut Option<PathBuf>,
 ) -> String {
     if let ObligationCauseCode::MainFunctionType = obligation.cause.code() {
         "consider using `()`, or a `Result`".to_owned()
@@ -5369,7 +5388,7 @@ pub(super) fn get_explanation_based_on_obligation<'tcx>(
             format!(
                 "{pre_message}the trait `{}` is not implemented for{desc} `{}`",
                 trait_predicate.print_modifiers_and_trait_path(),
-                tcx.short_string(trait_predicate.self_ty().skip_binder(), &mut None),
+                tcx.short_string(trait_predicate.self_ty().skip_binder(), long_ty_path),
             )
         } else {
             // "the trait bound `T: !Send` is not satisfied" reads better than "`!Send` is
diff --git a/compiler/rustc_trait_selection/src/errors.rs b/compiler/rustc_trait_selection/src/errors.rs
index 7901d52dffb..af241099c01 100644
--- a/compiler/rustc_trait_selection/src/errors.rs
+++ b/compiler/rustc_trait_selection/src/errors.rs
@@ -1,5 +1,3 @@
-use std::path::PathBuf;
-
 use rustc_ast::Path;
 use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
 use rustc_errors::codes::*;
@@ -224,9 +222,6 @@ pub struct AnnotationRequired<'a> {
     pub infer_subdiags: Vec<SourceKindSubdiag<'a>>,
     #[subdiagnostic]
     pub multi_suggestions: Vec<SourceKindMultiSuggestion<'a>>,
-    #[note(trait_selection_full_type_written)]
-    pub was_written: bool,
-    pub path: PathBuf,
 }
 
 // Copy of `AnnotationRequired` for E0283
@@ -245,9 +240,6 @@ pub struct AmbiguousImpl<'a> {
     pub infer_subdiags: Vec<SourceKindSubdiag<'a>>,
     #[subdiagnostic]
     pub multi_suggestions: Vec<SourceKindMultiSuggestion<'a>>,
-    #[note(trait_selection_full_type_written)]
-    pub was_written: bool,
-    pub path: PathBuf,
 }
 
 // Copy of `AnnotationRequired` for E0284
@@ -266,9 +258,6 @@ pub struct AmbiguousReturn<'a> {
     pub infer_subdiags: Vec<SourceKindSubdiag<'a>>,
     #[subdiagnostic]
     pub multi_suggestions: Vec<SourceKindMultiSuggestion<'a>>,
-    #[note(trait_selection_full_type_written)]
-    pub was_written: bool,
-    pub path: PathBuf,
 }
 
 // Used when a better one isn't available
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs
index 08315dbd21f..a9fb16b8000 100644
--- a/compiler/rustc_trait_selection/src/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/mod.rs
@@ -763,7 +763,7 @@ fn instantiate_and_check_impossible_predicates<'tcx>(
     // Specifically check trait fulfillment to avoid an error when trying to resolve
     // associated items.
     if let Some(trait_def_id) = tcx.trait_of_assoc(key.0) {
-        let trait_ref = ty::TraitRef::from_method(tcx, trait_def_id, key.1);
+        let trait_ref = ty::TraitRef::from_assoc(tcx, trait_def_id, key.1);
         predicates.push(trait_ref.upcast(tcx));
     }
 
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index 581191b2036..884d53732fe 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -1507,7 +1507,7 @@ fn confirm_builtin_candidate<'cx, 'tcx>(
     let tcx = selcx.tcx();
     let self_ty = obligation.predicate.self_ty();
     let item_def_id = obligation.predicate.def_id;
-    let trait_def_id = tcx.trait_of_assoc(item_def_id).unwrap();
+    let trait_def_id = tcx.parent(item_def_id);
     let args = tcx.mk_args(&[self_ty.into()]);
     let (term, obligations) = if tcx.is_lang_item(trait_def_id, LangItem::DiscriminantKind) {
         let discriminant_def_id =
diff --git a/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs b/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs
index b1b331d1b61..de404532899 100644
--- a/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs
@@ -319,39 +319,65 @@ pub fn dtorck_constraint_for_ty_inner<'tcx>(
         }
 
         ty::Coroutine(def_id, args) => {
-            // rust-lang/rust#49918: types can be constructed, stored
-            // in the interior, and sit idle when coroutine yields
-            // (and is subsequently dropped).
+            // rust-lang/rust#49918: Locals can be stored across await points in the coroutine,
+            // called interior/witness types. Since we do not compute these witnesses until after
+            // building MIR, we consider all coroutines to unconditionally require a drop during
+            // MIR building. However, considering the coroutine to unconditionally require a drop
+            // here may unnecessarily require its upvars' regions to be live when they don't need
+            // to be, leading to borrowck errors: <https://github.com/rust-lang/rust/issues/116242>.
             //
-            // It would be nice to descend into interior of a
-            // coroutine to determine what effects dropping it might
-            // have (by looking at any drop effects associated with
-            // its interior).
+            // Here, we implement a more precise approximation for the coroutine's dtorck constraint
+            // by considering whether any of the interior types needs drop. Note that this is still
+            // an approximation because the coroutine interior has its regions erased, so we must add
+            // *all* of the upvars to live types set if we find that *any* interior type needs drop.
+            // This is because any of the regions captured in the upvars may be stored in the interior,
+            // which then has its regions replaced by a binder (conceptually erasing the regions),
+            // so there's no way to enforce that the precise region in the interior type is live
+            // since we've lost that information by this point.
             //
-            // However, the interior's representation uses things like
-            // CoroutineWitness that explicitly assume they are not
-            // traversed in such a manner. So instead, we will
-            // simplify things for now by treating all coroutines as
-            // if they were like trait objects, where its upvars must
-            // all be alive for the coroutine's (potential)
-            // destructor.
+            // Note also that this check requires that the coroutine's upvars are use-live, since
+            // a region from a type that does not have a destructor that was captured in an upvar
+            // may flow into an interior type with a destructor. This is stronger than requiring
+            // the upvars are drop-live.
             //
-            // In particular, skipping over `_interior` is safe
-            // because any side-effects from dropping `_interior` can
-            // only take place through references with lifetimes
-            // derived from lifetimes attached to the upvars and resume
-            // argument, and we *do* incorporate those here.
+            // For example, if we capture two upvar references `&'1 (), &'2 ()` and have some type
+            // in the interior, `for<'r> { NeedsDrop<'r> }`, we have no way to tell whether the
+            // region `'r` came from the `'1` or `'2` region, so we require both are live. This
+            // could even be unnecessary if `'r` was actually a `'static` region or some region
+            // local to the coroutine! That's why it's an approximation.
             let args = args.as_coroutine();
 
-            // While we conservatively assume that all coroutines require drop
-            // to avoid query cycles during MIR building, we can check the actual
-            // witness during borrowck to avoid unnecessary liveness constraints.
+            // Note that we don't care about whether the resume type has any drops since this is
+            // redundant; there is no storage for the resume type, so if it is actually stored
+            // in the interior, we'll already detect the need for a drop by checking the interior.
             let typing_env = tcx.erase_regions(typing_env);
-            if tcx.mir_coroutine_witnesses(def_id).is_some_and(|witness| {
+            let needs_drop = tcx.mir_coroutine_witnesses(def_id).is_some_and(|witness| {
                 witness.field_tys.iter().any(|field| field.ty.needs_drop(tcx, typing_env))
-            }) {
+            });
+            if needs_drop {
+                // Pushing types directly to `constraints.outlives` is equivalent
+                // to requiring them to be use-live, since if we were instead to
+                // recurse on them like we do below, we only end up collecting the
+                // types that are relevant for drop-liveness.
                 constraints.outlives.extend(args.upvar_tys().iter().map(ty::GenericArg::from));
                 constraints.outlives.push(args.resume_ty().into());
+            } else {
+                // Even if a witness type doesn't need a drop, we still require that
+                // the upvars are drop-live. This is only needed if we aren't already
+                // counting *all* of the upvars as use-live above, since use-liveness
+                // is a *stronger requirement* than drop-liveness. Recursing here
+                // unconditionally would just be collecting duplicated types for no
+                // reason.
+                for ty in args.upvar_tys() {
+                    dtorck_constraint_for_ty_inner(
+                        tcx,
+                        typing_env,
+                        span,
+                        depth + 1,
+                        ty,
+                        constraints,
+                    );
+                }
             }
         }
 
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 7ea1548f8f2..468c42abf48 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -2333,10 +2333,23 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
 
             ty::Coroutine(def_id, args) => {
                 let ty = self.infcx.shallow_resolve(args.as_coroutine().tupled_upvars_ty());
+                let tcx = self.tcx();
                 let witness = Ty::new_coroutine_witness(
-                    self.tcx(),
+                    tcx,
                     def_id,
-                    self.tcx().mk_args(args.as_coroutine().parent_args()),
+                    ty::GenericArgs::for_item(tcx, def_id, |def, _| match def.kind {
+                        // HACK: Coroutine witnesse types are lifetime erased, so they
+                        // never reference any lifetime args from the coroutine. We erase
+                        // the regions here since we may get into situations where a
+                        // coroutine is recursively contained within itself, leading to
+                        // witness types that differ by region args. This means that
+                        // cycle detection in fulfillment will not kick in, which leads
+                        // to unnecessary overflows in async code. See the issue:
+                        // <https://github.com/rust-lang/rust/issues/145151>.
+                        ty::GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
+                        ty::GenericParamDefKind::Type { .. }
+                        | ty::GenericParamDefKind::Const { .. } => args[def.index as usize],
+                    }),
                 );
                 ty::Binder::dummy(AutoImplConstituents {
                     types: [ty].into_iter().chain(iter::once(witness)).collect(),
diff --git a/compiler/rustc_ty_utils/src/abi.rs b/compiler/rustc_ty_utils/src/abi.rs
index af2e000e340..89d1dd8cf23 100644
--- a/compiler/rustc_ty_utils/src/abi.rs
+++ b/compiler/rustc_ty_utils/src/abi.rs
@@ -39,7 +39,7 @@ fn fn_sig_for_fn_abi<'tcx>(
             tcx.thread_local_ptr_ty(instance.def_id()),
             false,
             hir::Safety::Safe,
-            rustc_abi::ExternAbi::Unadjusted,
+            rustc_abi::ExternAbi::Rust,
         );
     }
 
@@ -268,20 +268,21 @@ fn fn_abi_of_instance<'tcx>(
 }
 
 // Handle safe Rust thin and wide pointers.
-fn adjust_for_rust_scalar<'tcx>(
+fn arg_attrs_for_rust_scalar<'tcx>(
     cx: LayoutCx<'tcx>,
-    attrs: &mut ArgAttributes,
     scalar: Scalar,
     layout: TyAndLayout<'tcx>,
     offset: Size,
     is_return: bool,
     drop_target_pointee: Option<Ty<'tcx>>,
-) {
+) -> ArgAttributes {
+    let mut attrs = ArgAttributes::new();
+
     // Booleans are always a noundef i1 that needs to be zero-extended.
     if scalar.is_bool() {
         attrs.ext(ArgExtension::Zext);
         attrs.set(ArgAttribute::NoUndef);
-        return;
+        return attrs;
     }
 
     if !scalar.is_uninit_valid() {
@@ -289,7 +290,7 @@ fn adjust_for_rust_scalar<'tcx>(
     }
 
     // Only pointer types handled below.
-    let Scalar::Initialized { value: Pointer(_), valid_range } = scalar else { return };
+    let Scalar::Initialized { value: Pointer(_), valid_range } = scalar else { return attrs };
 
     // Set `nonnull` if the validity range excludes zero, or for the argument to `drop_in_place`,
     // which must be nonnull per its documented safety requirements.
@@ -358,6 +359,8 @@ fn adjust_for_rust_scalar<'tcx>(
             }
         }
     }
+
+    attrs
 }
 
 /// Ensure that the ABI makes basic sense.
@@ -471,9 +474,10 @@ fn fn_abi_new_uncached<'tcx>(
     let (caller_location, determined_fn_def_id, is_virtual_call) = if let Some(instance) = instance
     {
         let is_virtual_call = matches!(instance.def, ty::InstanceKind::Virtual(..));
+        let is_tls_shim_call = matches!(instance.def, ty::InstanceKind::ThreadLocalShim(_));
         (
             instance.def.requires_caller_location(tcx).then(|| tcx.caller_location_ty()),
-            if is_virtual_call { None } else { Some(instance.def_id()) },
+            if is_virtual_call || is_tls_shim_call { None } else { Some(instance.def_id()) },
             is_virtual_call,
         )
     } else {
@@ -530,17 +534,7 @@ fn fn_abi_new_uncached<'tcx>(
         };
 
         let mut arg = ArgAbi::new(cx, layout, |layout, scalar, offset| {
-            let mut attrs = ArgAttributes::new();
-            adjust_for_rust_scalar(
-                *cx,
-                &mut attrs,
-                scalar,
-                *layout,
-                offset,
-                is_return,
-                drop_target_pointee,
-            );
-            attrs
+            arg_attrs_for_rust_scalar(*cx, scalar, *layout, offset, is_return, drop_target_pointee)
         });
 
         if arg.layout.is_zst() {
@@ -563,6 +557,7 @@ fn fn_abi_new_uncached<'tcx>(
         c_variadic: sig.c_variadic,
         fixed_count: inputs.len() as u32,
         conv,
+        // FIXME return false for tls shim
         can_unwind: fn_can_unwind(
             tcx,
             // Since `#[rustc_nounwind]` can change unwinding, we cannot infer unwinding by `fn_def_id` for a virtual call.
@@ -575,8 +570,9 @@ fn fn_abi_new_uncached<'tcx>(
         &mut fn_abi,
         sig.abi,
         // If this is a virtual call, we cannot pass the `fn_def_id`, as it might call other
-        // functions from vtable. Internally, `deduced_param_attrs` attempts to infer attributes by
-        // visit the function body.
+        // functions from vtable. And for a tls shim, passing the `fn_def_id` would refer to
+        // the underlying static. Internally, `deduced_param_attrs` attempts to infer attributes
+        // by visit the function body.
         determined_fn_def_id,
     );
     debug!("fn_abi_new_uncached = {:?}", fn_abi);
diff --git a/compiler/rustc_ty_utils/src/assoc.rs b/compiler/rustc_ty_utils/src/assoc.rs
index 37cb64511c7..e9629e31482 100644
--- a/compiler/rustc_ty_utils/src/assoc.rs
+++ b/compiler/rustc_ty_utils/src/assoc.rs
@@ -174,10 +174,10 @@ fn associated_types_for_impl_traits_in_trait_or_impl<'tcx>(
             })
             .collect(),
         ItemKind::Impl(impl_) => {
-            let Some(trait_ref) = impl_.of_trait else {
+            let Some(of_trait) = impl_.of_trait else {
                 return Default::default();
             };
-            let Some(trait_def_id) = trait_ref.trait_def_id() else {
+            let Some(trait_def_id) = of_trait.trait_ref.trait_def_id() else {
                 return Default::default();
             };
             let in_trait_def = tcx.associated_types_for_impl_traits_in_trait_or_impl(trait_def_id);
diff --git a/compiler/rustc_ty_utils/src/implied_bounds.rs b/compiler/rustc_ty_utils/src/implied_bounds.rs
index 6fa763f18ef..cdfb93c4e7d 100644
--- a/compiler/rustc_ty_utils/src/implied_bounds.rs
+++ b/compiler/rustc_ty_utils/src/implied_bounds.rs
@@ -172,10 +172,12 @@ fn impl_spans(tcx: TyCtxt<'_>, def_id: LocalDefId) -> impl Iterator<Item = Span>
         let trait_args = impl_
             .of_trait
             .into_iter()
-            .flat_map(|trait_ref| trait_ref.path.segments.last().unwrap().args().args)
+            .flat_map(|of_trait| of_trait.trait_ref.path.segments.last().unwrap().args().args)
             .map(|arg| arg.span());
-        let dummy_spans_for_default_args =
-            impl_.of_trait.into_iter().flat_map(|trait_ref| iter::repeat(trait_ref.path.span));
+        let dummy_spans_for_default_args = impl_
+            .of_trait
+            .into_iter()
+            .flat_map(|of_trait| iter::repeat(of_trait.trait_ref.path.span));
         iter::once(impl_.self_ty.span).chain(trait_args).chain(dummy_spans_for_default_args)
     } else {
         bug!("unexpected item for impl {def_id:?}: {item:?}")
diff --git a/compiler/rustc_ty_utils/src/instance.rs b/compiler/rustc_ty_utils/src/instance.rs
index e6c3568620b..5c3f7d491a5 100644
--- a/compiler/rustc_ty_utils/src/instance.rs
+++ b/compiler/rustc_ty_utils/src/instance.rs
@@ -109,7 +109,7 @@ fn resolve_associated_item<'tcx>(
 ) -> Result<Option<Instance<'tcx>>, ErrorGuaranteed> {
     debug!(?trait_item_id, ?typing_env, ?trait_id, ?rcvr_args, "resolve_associated_item");
 
-    let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_args);
+    let trait_ref = ty::TraitRef::from_assoc(tcx, trait_id, rcvr_args);
 
     let input = typing_env.as_query_input(trait_ref);
     let vtbl = match tcx.codegen_select_candidate(input) {
@@ -238,7 +238,7 @@ fn resolve_associated_item<'tcx>(
             Some(ty::Instance::new_raw(leaf_def.item.def_id, args))
         }
         traits::ImplSource::Builtin(BuiltinImplSource::Object(_), _) => {
-            let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_args);
+            let trait_ref = ty::TraitRef::from_assoc(tcx, trait_id, rcvr_args);
             if trait_ref.has_non_region_infer() || trait_ref.has_non_region_param() {
                 // We only resolve totally substituted vtable entries.
                 None
diff --git a/compiler/rustc_ty_utils/src/sig_types.rs b/compiler/rustc_ty_utils/src/sig_types.rs
index dc6009116ac..d95660810e5 100644
--- a/compiler/rustc_ty_utils/src/sig_types.rs
+++ b/compiler/rustc_ty_utils/src/sig_types.rs
@@ -87,7 +87,7 @@ pub fn walk_types<'tcx, V: SpannedTypeVisitor<'tcx>>(
         DefKind::InlineConst | DefKind::Closure | DefKind::SyntheticCoroutineBody => {}
         DefKind::Impl { of_trait } => {
             if of_trait {
-                let span = tcx.hir_node_by_def_id(item).expect_item().expect_impl().of_trait.unwrap().path.span;
+                let span = tcx.hir_node_by_def_id(item).expect_item().expect_impl().of_trait.unwrap().trait_ref.path.span;
                 let args = &tcx.impl_trait_ref(item).unwrap().instantiate_identity().args[1..];
                 try_visit!(visitor.visit(span, args));
             }
diff --git a/compiler/rustc_ty_utils/src/ty.rs b/compiler/rustc_ty_utils/src/ty.rs
index 2e0b16d9227..b22c326b9f2 100644
--- a/compiler/rustc_ty_utils/src/ty.rs
+++ b/compiler/rustc_ty_utils/src/ty.rs
@@ -81,7 +81,11 @@ fn sizedness_constraint_for_ty<'tcx>(
 fn defaultness(tcx: TyCtxt<'_>, def_id: LocalDefId) -> hir::Defaultness {
     match tcx.hir_node_by_def_id(def_id) {
         hir::Node::Item(hir::Item {
-            kind: hir::ItemKind::Impl(hir::Impl { defaultness, of_trait: Some(_), .. }),
+            kind:
+                hir::ItemKind::Impl(hir::Impl {
+                    of_trait: Some(hir::TraitImplHeader { defaultness, .. }),
+                    ..
+                }),
             ..
         })
         | hir::Node::ImplItem(hir::ImplItem { defaultness, .. })
diff --git a/compiler/rustc_type_ir/src/binder.rs b/compiler/rustc_type_ir/src/binder.rs
index 189afa32852..6591d3148cb 100644
--- a/compiler/rustc_type_ir/src/binder.rs
+++ b/compiler/rustc_type_ir/src/binder.rs
@@ -1,5 +1,3 @@
-use std::fmt::Debug;
-use std::hash::Hash;
 use std::marker::PhantomData;
 use std::ops::{ControlFlow, Deref};
 
@@ -15,27 +13,24 @@ use crate::lift::Lift;
 use crate::visit::{Flags, TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor};
 use crate::{self as ty, Interner};
 
-/// Binder is a binder for higher-ranked lifetimes or types. It is part of the
+/// `Binder` is a binder for higher-ranked lifetimes or types. It is part of the
 /// compiler's representation for things like `for<'a> Fn(&'a isize)`
-/// (which would be represented by the type `PolyTraitRef ==
-/// Binder<I, TraitRef>`). Note that when we instantiate,
-/// erase, or otherwise "discharge" these bound vars, we change the
-/// type from `Binder<I, T>` to just `T` (see
-/// e.g., `liberate_late_bound_regions`).
+/// (which would be represented by the type `PolyTraitRef == Binder<I, TraitRef>`).
+///
+/// See <https://rustc-dev-guide.rust-lang.org/ty_module/instantiating_binders.html>
+/// for more details.
 ///
 /// `Decodable` and `Encodable` are implemented for `Binder<T>` using the `impl_binder_encode_decode!` macro.
-#[derive_where(Clone; I: Interner, T: Clone)]
+#[derive_where(Clone, Hash, PartialEq, Debug; I: Interner, T)]
 #[derive_where(Copy; I: Interner, T: Copy)]
-#[derive_where(Hash; I: Interner, T: Hash)]
-#[derive_where(PartialEq; I: Interner, T: PartialEq)]
-#[derive_where(Eq; I: Interner, T: Eq)]
-#[derive_where(Debug; I: Interner, T: Debug)]
 #[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
 pub struct Binder<I: Interner, T> {
     value: T,
     bound_vars: I::BoundVarKinds,
 }
 
+impl<I: Interner, T: Eq> Eq for Binder<I, T> {}
+
 // FIXME: We manually derive `Lift` because the `derive(Lift_Generic)` doesn't
 // understand how to turn `T` to `T::Lifted` in the output `type Lifted`.
 impl<I: Interner, U: Interner, T> Lift<U> for Binder<I, T>
@@ -154,22 +149,19 @@ impl<I: Interner, T: TypeVisitable<I>> TypeSuperVisitable<I> for Binder<I, T> {
 }
 
 impl<I: Interner, T> Binder<I, T> {
-    /// Skips the binder and returns the "bound" value. This is a
-    /// risky thing to do because it's easy to get confused about
-    /// De Bruijn indices and the like. It is usually better to
-    /// discharge the binder using `no_bound_vars` or
-    /// `instantiate_bound_regions` or something like
-    /// that. `skip_binder` is only valid when you are either
-    /// extracting data that has nothing to do with bound vars, you
-    /// are doing some sort of test that does not involve bound
-    /// regions, or you are being very careful about your depth
-    /// accounting.
+    /// Returns the value contained inside of this `for<'a>`. Accessing generic args
+    /// in the returned value is generally incorrect.
     ///
-    /// Some examples where `skip_binder` is reasonable:
+    /// Please read <https://rustc-dev-guide.rust-lang.org/ty_module/instantiating_binders.html>
+    /// before using this function. It is usually better to discharge the binder using
+    /// `no_bound_vars` or `instantiate_bound_regions` or something like that.
     ///
-    /// - extracting the `DefId` from a PolyTraitRef;
-    /// - comparing the self type of a PolyTraitRef to see if it is equal to
-    ///   a type parameter `X`, since the type `X` does not reference any regions
+    /// `skip_binder` is only valid when you are either extracting data that does not reference
+    /// any generic arguments, e.g. a `DefId`, or when you're making sure you only pass the
+    /// value to things which can handle escaping bound vars.
+    ///
+    /// See existing uses of `.skip_binder()` in `rustc_trait_selection::traits::select`
+    /// or `rustc_next_trait_solver` for examples.
     pub fn skip_binder(self) -> T {
         self.value
     }
@@ -355,20 +347,14 @@ impl<I: Interner> TypeVisitor<I> for ValidateBoundVars<I> {
     }
 }
 
-/// Similar to [`super::Binder`] except that it tracks early bound generics, i.e. `struct Foo<T>(T)`
+/// Similar to [`Binder`] except that it tracks early bound generics, i.e. `struct Foo<T>(T)`
 /// needs `T` instantiated immediately. This type primarily exists to avoid forgetting to call
 /// `instantiate`.
 ///
-/// If you don't have anything to `instantiate`, you may be looking for
-/// [`instantiate_identity`](EarlyBinder::instantiate_identity) or [`skip_binder`](EarlyBinder::skip_binder).
-#[derive_where(Clone; I: Interner, T: Clone)]
-#[derive_where(Copy; I: Interner, T: Copy)]
-#[derive_where(PartialEq; I: Interner, T: PartialEq)]
-#[derive_where(Eq; I: Interner, T: Eq)]
-#[derive_where(Ord; I: Interner, T: Ord)]
+/// See <https://rustc-dev-guide.rust-lang.org/ty_module/early_binder.html> for more details.
+#[derive_where(Clone, PartialEq, Ord, Hash, Debug; I: Interner, T)]
 #[derive_where(PartialOrd; I: Interner, T: Ord)]
-#[derive_where(Hash; I: Interner, T: Hash)]
-#[derive_where(Debug; I: Interner, T: Debug)]
+#[derive_where(Copy; I: Interner, T: Copy)]
 #[cfg_attr(
     feature = "nightly",
     derive(Encodable_NoContext, Decodable_NoContext, HashStable_NoContext)
@@ -379,6 +365,8 @@ pub struct EarlyBinder<I: Interner, T> {
     _tcx: PhantomData<fn() -> I>,
 }
 
+impl<I: Interner, T: Eq> Eq for EarlyBinder<I, T> {}
+
 /// For early binders, you should first call `instantiate` before using any visitors.
 #[cfg(feature = "nightly")]
 impl<I: Interner, T> !TypeFoldable<I> for ty::EarlyBinder<I, T> {}
@@ -423,17 +411,22 @@ impl<I: Interner, T> EarlyBinder<I, T> {
         EarlyBinder { value, _tcx: PhantomData }
     }
 
-    /// Skips the binder and returns the "bound" value.
-    /// This can be used to extract data that does not depend on generic parameters
-    /// (e.g., getting the `DefId` of the inner value or getting the number of
-    /// arguments of an `FnSig`). Otherwise, consider using
-    /// [`instantiate_identity`](EarlyBinder::instantiate_identity).
+    /// Skips the binder and returns the "bound" value. Accessing generic args
+    /// in the returned value is generally incorrect.
+    ///
+    /// Please read <https://rustc-dev-guide.rust-lang.org/ty_module/early_binder.html>
+    /// before using this function.
+    ///
+    /// Only use this to extract data that does not depend on generic parameters, e.g.
+    /// to get the `DefId` of the inner value or the number of arguments ofan `FnSig`,
+    /// or while making sure to only pass the value to functions which are explicitly
+    /// set up to handle these uninstantiated generic parameters.
     ///
     /// To skip the binder on `x: &EarlyBinder<I, T>` to obtain `&T`, leverage
     /// [`EarlyBinder::as_ref`](EarlyBinder::as_ref): `x.as_ref().skip_binder()`.
     ///
-    /// See also [`Binder::skip_binder`](super::Binder::skip_binder), which is
-    /// the analogous operation on [`super::Binder`].
+    /// See also [`Binder::skip_binder`](Binder::skip_binder), which is
+    /// the analogous operation on [`Binder`].
     pub fn skip_binder(self) -> T {
         self.value
     }
diff --git a/compiler/rustc_type_ir/src/canonical.rs b/compiler/rustc_type_ir/src/canonical.rs
index c66a83662d7..de2a9186e7c 100644
--- a/compiler/rustc_type_ir/src/canonical.rs
+++ b/compiler/rustc_type_ir/src/canonical.rs
@@ -11,11 +11,7 @@ use crate::data_structures::HashMap;
 use crate::inherent::*;
 use crate::{self as ty, Interner, TypingMode, UniverseIndex};
 
-#[derive_where(Clone; I: Interner, V: Clone)]
-#[derive_where(Hash; I: Interner, V: Hash)]
-#[derive_where(PartialEq; I: Interner, V: PartialEq)]
-#[derive_where(Eq; I: Interner, V: Eq)]
-#[derive_where(Debug; I: Interner, V: fmt::Debug)]
+#[derive_where(Clone, Hash, PartialEq, Debug; I: Interner, V)]
 #[derive_where(Copy; I: Interner, V: Copy)]
 #[cfg_attr(
     feature = "nightly",
@@ -26,14 +22,12 @@ pub struct CanonicalQueryInput<I: Interner, V> {
     pub typing_mode: TypingMode<I>,
 }
 
+impl<I: Interner, V: Eq> Eq for CanonicalQueryInput<I, V> {}
+
 /// A "canonicalized" type `V` is one where all free inference
 /// variables have been rewritten to "canonical vars". These are
 /// numbered starting from 0 in order of first appearance.
-#[derive_where(Clone; I: Interner, V: Clone)]
-#[derive_where(Hash; I: Interner, V: Hash)]
-#[derive_where(PartialEq; I: Interner, V: PartialEq)]
-#[derive_where(Eq; I: Interner, V: Eq)]
-#[derive_where(Debug; I: Interner, V: fmt::Debug)]
+#[derive_where(Clone, Hash, PartialEq, Debug; I: Interner, V)]
 #[derive_where(Copy; I: Interner, V: Copy)]
 #[cfg_attr(
     feature = "nightly",
@@ -45,6 +39,8 @@ pub struct Canonical<I: Interner, V> {
     pub variables: I::CanonicalVarKinds,
 }
 
+impl<I: Interner, V: Eq> Eq for Canonical<I, V> {}
+
 impl<I: Interner, V> Canonical<I, V> {
     /// Allows you to map the `value` of a canonical while keeping the
     /// same set of bound variables.
@@ -89,7 +85,7 @@ impl<I: Interner, V: fmt::Display> fmt::Display for Canonical<I, V> {
 /// canonical value. This is sufficient information for code to create
 /// a copy of the canonical value in some other inference context,
 /// with fresh inference variables replacing the canonical values.
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq, Debug; I: Interner)]
 #[cfg_attr(
     feature = "nightly",
     derive(Decodable_NoContext, Encodable_NoContext, HashStable_NoContext)
@@ -116,6 +112,8 @@ pub enum CanonicalVarKind<I: Interner> {
     PlaceholderConst(I::PlaceholderConst),
 }
 
+impl<I: Interner> Eq for CanonicalVarKind<I> {}
+
 impl<I: Interner> CanonicalVarKind<I> {
     pub fn universe(self) -> UniverseIndex {
         match self {
@@ -199,7 +197,6 @@ impl<I: Interner> CanonicalVarKind<I> {
 /// usize or f32). In order to faithfully reproduce a type, we need to
 /// know what set of types a given type variable can be unified with.
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
-#[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
 #[cfg_attr(
     feature = "nightly",
     derive(Decodable_NoContext, Encodable_NoContext, HashStable_NoContext)
@@ -224,7 +221,7 @@ pub enum CanonicalTyVarKind {
 /// vectors with the original values that were replaced by canonical
 /// variables. You will need to supply it later to instantiate the
 /// canonicalized query response.
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq, Debug; I: Interner)]
 #[cfg_attr(
     feature = "nightly",
     derive(Encodable_NoContext, Decodable_NoContext, HashStable_NoContext)
@@ -234,6 +231,8 @@ pub struct CanonicalVarValues<I: Interner> {
     pub var_values: I::GenericArgs,
 }
 
+impl<I: Interner> Eq for CanonicalVarValues<I> {}
+
 impl<I: Interner> CanonicalVarValues<I> {
     pub fn is_identity(&self) -> bool {
         self.var_values.iter().enumerate().all(|(bv, arg)| match arg.kind() {
diff --git a/compiler/rustc_type_ir/src/const_kind.rs b/compiler/rustc_type_ir/src/const_kind.rs
index 70a8509b513..6de41b47bde 100644
--- a/compiler/rustc_type_ir/src/const_kind.rs
+++ b/compiler/rustc_type_ir/src/const_kind.rs
@@ -10,7 +10,7 @@ use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Gen
 use crate::{self as ty, DebruijnIndex, Interner};
 
 /// Represents a constant in Rust.
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq; I: Interner)]
 #[cfg_attr(
     feature = "nightly",
     derive(Encodable_NoContext, Decodable_NoContext, HashStable_NoContext)
@@ -45,6 +45,8 @@ pub enum ConstKind<I: Interner> {
     Expr(I::ExprConst),
 }
 
+impl<I: Interner> Eq for ConstKind<I> {}
+
 impl<I: Interner> fmt::Debug for ConstKind<I> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         use ConstKind::*;
@@ -63,7 +65,7 @@ impl<I: Interner> fmt::Debug for ConstKind<I> {
 }
 
 /// An unevaluated (potentially generic) constant used in the type-system.
-#[derive_where(Clone, Copy, Debug, Hash, PartialEq, Eq; I: Interner)]
+#[derive_where(Clone, Copy, Debug, Hash, PartialEq; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -74,6 +76,8 @@ pub struct UnevaluatedConst<I: Interner> {
     pub args: I::GenericArgs,
 }
 
+impl<I: Interner> Eq for UnevaluatedConst<I> {}
+
 impl<I: Interner> UnevaluatedConst<I> {
     #[inline]
     pub fn new(def: I::DefId, args: I::GenericArgs) -> UnevaluatedConst<I> {
diff --git a/compiler/rustc_type_ir/src/error.rs b/compiler/rustc_type_ir/src/error.rs
index 68b11489ae7..e8840bcfaca 100644
--- a/compiler/rustc_type_ir/src/error.rs
+++ b/compiler/rustc_type_ir/src/error.rs
@@ -18,7 +18,7 @@ impl<T> ExpectedFound<T> {
 }
 
 // Data structures used in type unification
-#[derive_where(Clone, Copy, PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(Clone, Copy, PartialEq, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic)]
 #[cfg_attr(feature = "nightly", rustc_pass_by_value)]
 pub enum TypeError<I: Interner> {
@@ -58,6 +58,8 @@ pub enum TypeError<I: Interner> {
     TargetFeatureCast(I::DefId),
 }
 
+impl<I: Interner> Eq for TypeError<I> {}
+
 impl<I: Interner> TypeError<I> {
     pub fn involves_regions(self) -> bool {
         match self {
diff --git a/compiler/rustc_type_ir/src/generic_arg.rs b/compiler/rustc_type_ir/src/generic_arg.rs
index c18cade0e39..d6e33f724d0 100644
--- a/compiler/rustc_type_ir/src/generic_arg.rs
+++ b/compiler/rustc_type_ir/src/generic_arg.rs
@@ -4,7 +4,7 @@ use rustc_macros::{Decodable_NoContext, Encodable_NoContext, HashStable_NoContex
 
 use crate::Interner;
 
-#[derive_where(Clone, Copy, PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(Clone, Copy, PartialEq, Debug; I: Interner)]
 #[cfg_attr(
     feature = "nightly",
     derive(Decodable_NoContext, Encodable_NoContext, HashStable_NoContext)
@@ -15,7 +15,9 @@ pub enum GenericArgKind<I: Interner> {
     Const(I::Const),
 }
 
-#[derive_where(Clone, Copy, PartialEq, Eq, Debug; I: Interner)]
+impl<I: Interner> Eq for GenericArgKind<I> {}
+
+#[derive_where(Clone, Copy, PartialEq, Debug; I: Interner)]
 #[cfg_attr(
     feature = "nightly",
     derive(Decodable_NoContext, Encodable_NoContext, HashStable_NoContext)
@@ -24,3 +26,5 @@ pub enum TermKind<I: Interner> {
     Ty(I::Ty),
     Const(I::Const),
 }
+
+impl<I: Interner> Eq for TermKind<I> {}
diff --git a/compiler/rustc_type_ir/src/infer_ctxt.rs b/compiler/rustc_type_ir/src/infer_ctxt.rs
index b4873c8c71c..e39b99e992b 100644
--- a/compiler/rustc_type_ir/src/infer_ctxt.rs
+++ b/compiler/rustc_type_ir/src/infer_ctxt.rs
@@ -1,7 +1,6 @@
 use derive_where::derive_where;
 #[cfg(feature = "nightly")]
 use rustc_macros::{Decodable_NoContext, Encodable_NoContext, HashStable_NoContext};
-use rustc_type_ir_macros::{TypeFoldable_Generic, TypeVisitable_Generic};
 
 use crate::fold::TypeFoldable;
 use crate::inherent::*;
@@ -19,8 +18,7 @@ use crate::{self as ty, Interner};
 ///
 /// If neither of these functions are available, feel free to reach out to
 /// t-types for help.
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq, Debug; I: Interner)]
-#[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
+#[derive_where(Clone, Copy, Hash, PartialEq, Debug; I: Interner)]
 #[cfg_attr(
     feature = "nightly",
     derive(Encodable_NoContext, Decodable_NoContext, HashStable_NoContext)
@@ -92,6 +90,8 @@ pub enum TypingMode<I: Interner> {
     PostAnalysis,
 }
 
+impl<I: Interner> Eq for TypingMode<I> {}
+
 impl<I: Interner> TypingMode<I> {
     /// Analysis outside of a body does not define any opaque types.
     pub fn non_body_analysis() -> TypingMode<I> {
diff --git a/compiler/rustc_type_ir/src/opaque_ty.rs b/compiler/rustc_type_ir/src/opaque_ty.rs
index 416d355fd03..b6fb9f28930 100644
--- a/compiler/rustc_type_ir/src/opaque_ty.rs
+++ b/compiler/rustc_type_ir/src/opaque_ty.rs
@@ -6,7 +6,7 @@ use rustc_type_ir_macros::{TypeFoldable_Generic, TypeVisitable_Generic};
 use crate::inherent::*;
 use crate::{self as ty, Interner};
 
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -17,6 +17,8 @@ pub struct OpaqueTypeKey<I: Interner> {
     pub args: I::GenericArgs,
 }
 
+impl<I: Interner> Eq for OpaqueTypeKey<I> {}
+
 impl<I: Interner> OpaqueTypeKey<I> {
     pub fn iter_captured_args(self, cx: I) -> impl Iterator<Item = (usize, I::GenericArg)> {
         let variances = cx.variances_of(self.def_id.into());
diff --git a/compiler/rustc_type_ir/src/pattern.rs b/compiler/rustc_type_ir/src/pattern.rs
index 7e56565917c..d757ac625f2 100644
--- a/compiler/rustc_type_ir/src/pattern.rs
+++ b/compiler/rustc_type_ir/src/pattern.rs
@@ -5,7 +5,7 @@ use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Gen
 
 use crate::Interner;
 
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -15,3 +15,5 @@ pub enum PatternKind<I: Interner> {
     Range { start: I::Const, end: I::Const },
     Or(I::PatList),
 }
+
+impl<I: Interner> Eq for PatternKind<I> {}
diff --git a/compiler/rustc_type_ir/src/predicate.rs b/compiler/rustc_type_ir/src/predicate.rs
index c9489c98cce..b53eb099c4b 100644
--- a/compiler/rustc_type_ir/src/predicate.rs
+++ b/compiler/rustc_type_ir/src/predicate.rs
@@ -15,12 +15,8 @@ use crate::visit::TypeVisitableExt as _;
 use crate::{self as ty, Interner};
 
 /// `A: 'region`
-#[derive_where(Clone; I: Interner, A: Clone)]
+#[derive_where(Clone, Hash, PartialEq, Debug; I: Interner, A)]
 #[derive_where(Copy; I: Interner, A: Copy)]
-#[derive_where(Hash; I: Interner, A: Hash)]
-#[derive_where(PartialEq; I: Interner, A: PartialEq)]
-#[derive_where(Eq; I: Interner, A: Eq)]
-#[derive_where(Debug; I: Interner, A: fmt::Debug)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -28,6 +24,8 @@ use crate::{self as ty, Interner};
 )]
 pub struct OutlivesPredicate<I: Interner, A>(pub A, pub I::Region);
 
+impl<I: Interner, A: Eq> Eq for OutlivesPredicate<I, A> {}
+
 // FIXME: We manually derive `Lift` because the `derive(Lift_Generic)` doesn't
 // understand how to turn `A` to `A::Lifted` in the output `type Lifted`.
 impl<I: Interner, U: Interner, A> Lift<U> for OutlivesPredicate<I, A>
@@ -53,7 +51,7 @@ where
 ///
 /// Trait references also appear in object types like `Foo<U>`, but in
 /// that case the `Self` parameter is absent from the generic parameters.
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -67,6 +65,8 @@ pub struct TraitRef<I: Interner> {
     _use_trait_ref_new_instead: (),
 }
 
+impl<I: Interner> Eq for TraitRef<I> {}
+
 impl<I: Interner> TraitRef<I> {
     pub fn new_from_args(interner: I, trait_def_id: I::DefId, args: I::GenericArgs) -> Self {
         interner.debug_assert_args_compatible(trait_def_id, args);
@@ -82,7 +82,7 @@ impl<I: Interner> TraitRef<I> {
         Self::new_from_args(interner, trait_def_id, args)
     }
 
-    pub fn from_method(interner: I, trait_id: I::DefId, args: I::GenericArgs) -> TraitRef<I> {
+    pub fn from_assoc(interner: I, trait_id: I::DefId, args: I::GenericArgs) -> TraitRef<I> {
         let generics = interner.generics_of(trait_id);
         TraitRef::new(interner, trait_id, args.iter().take(generics.count()))
     }
@@ -128,7 +128,7 @@ impl<I: Interner> ty::Binder<I, TraitRef<I>> {
     }
 }
 
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -145,6 +145,8 @@ pub struct TraitPredicate<I: Interner> {
     pub polarity: PredicatePolarity,
 }
 
+impl<I: Interner> Eq for TraitPredicate<I> {}
+
 impl<I: Interner> TraitPredicate<I> {
     pub fn with_replaced_self_ty(self, interner: I, self_ty: I::Ty) -> Self {
         Self {
@@ -184,6 +186,15 @@ impl<I: Interner> UpcastFrom<I, TraitRef<I>> for TraitPredicate<I> {
     }
 }
 
+impl<I: Interner> UpcastFrom<I, ty::Binder<I, TraitRef<I>>> for ty::Binder<I, TraitPredicate<I>> {
+    fn upcast_from(from: ty::Binder<I, TraitRef<I>>, _tcx: I) -> Self {
+        from.map_bound(|trait_ref| TraitPredicate {
+            trait_ref,
+            polarity: PredicatePolarity::Positive,
+        })
+    }
+}
+
 impl<I: Interner> fmt::Debug for TraitPredicate<I> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "TraitPredicate({:?}, polarity:{:?})", self.trait_ref, self.polarity)
@@ -262,7 +273,7 @@ impl fmt::Display for PredicatePolarity {
     }
 }
 
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -277,6 +288,8 @@ pub enum ExistentialPredicate<I: Interner> {
     AutoTrait(I::DefId),
 }
 
+impl<I: Interner> Eq for ExistentialPredicate<I> {}
+
 impl<I: Interner> ty::Binder<I, ExistentialPredicate<I>> {
     /// Given an existential predicate like `?Self: PartialEq<u32>` (e.g., derived from `dyn PartialEq<u32>`),
     /// and a concrete type `self_ty`, returns a full predicate where the existentially quantified variable `?Self`
@@ -310,7 +323,7 @@ impl<I: Interner> ty::Binder<I, ExistentialPredicate<I>> {
 /// ```
 /// The generic parameters don't include the erased `Self`, only trait
 /// type and lifetime parameters (`[X, Y]` and `['a, 'b]` above).
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -324,6 +337,8 @@ pub struct ExistentialTraitRef<I: Interner> {
     _use_existential_trait_ref_new_instead: (),
 }
 
+impl<I: Interner> Eq for ExistentialTraitRef<I> {}
+
 impl<I: Interner> ExistentialTraitRef<I> {
     pub fn new_from_args(interner: I, trait_def_id: I::DefId, args: I::GenericArgs) -> Self {
         interner.debug_assert_existential_args_compatible(trait_def_id, args);
@@ -377,7 +392,7 @@ impl<I: Interner> ty::Binder<I, ExistentialTraitRef<I>> {
 }
 
 /// A `ProjectionPredicate` for an `ExistentialTraitRef`.
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -393,6 +408,8 @@ pub struct ExistentialProjection<I: Interner> {
     use_existential_projection_new_instead: (),
 }
 
+impl<I: Interner> Eq for ExistentialProjection<I> {}
+
 impl<I: Interner> ExistentialProjection<I> {
     pub fn new_from_args(
         interner: I,
@@ -533,7 +550,7 @@ impl From<ty::AliasTyKind> for AliasTermKind {
 /// * For a projection, this would be `<Ty as Trait<...>>::N<...>`.
 /// * For an inherent projection, this would be `Ty::N<...>`.
 /// * For an opaque type, there is no explicit syntax.
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -569,6 +586,8 @@ pub struct AliasTerm<I: Interner> {
     _use_alias_term_new_instead: (),
 }
 
+impl<I: Interner> Eq for AliasTerm<I> {}
+
 impl<I: Interner> AliasTerm<I> {
     pub fn new_from_args(interner: I, def_id: I::DefId, args: I::GenericArgs) -> AliasTerm<I> {
         interner.debug_assert_args_compatible(def_id, args);
@@ -743,7 +762,7 @@ impl<I: Interner> From<ty::UnevaluatedConst<I>> for AliasTerm<I> {
 /// equality between arbitrary types. Processing an instance of
 /// Form #2 eventually yields one of these `ProjectionPredicate`
 /// instances to normalize the LHS.
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -754,6 +773,8 @@ pub struct ProjectionPredicate<I: Interner> {
     pub term: I::Term,
 }
 
+impl<I: Interner> Eq for ProjectionPredicate<I> {}
+
 impl<I: Interner> ProjectionPredicate<I> {
     pub fn self_ty(self) -> I::Ty {
         self.projection_term.self_ty()
@@ -804,7 +825,7 @@ impl<I: Interner> fmt::Debug for ProjectionPredicate<I> {
 
 /// Used by the new solver to normalize an alias. This always expects the `term` to
 /// be an unconstrained inference variable which is used as the output.
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -815,6 +836,8 @@ pub struct NormalizesTo<I: Interner> {
     pub term: I::Term,
 }
 
+impl<I: Interner> Eq for NormalizesTo<I> {}
+
 impl<I: Interner> NormalizesTo<I> {
     pub fn self_ty(self) -> I::Ty {
         self.alias.self_ty()
@@ -839,7 +862,7 @@ impl<I: Interner> fmt::Debug for NormalizesTo<I> {
     }
 }
 
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -850,6 +873,8 @@ pub struct HostEffectPredicate<I: Interner> {
     pub constness: BoundConstness,
 }
 
+impl<I: Interner> Eq for HostEffectPredicate<I> {}
+
 impl<I: Interner> HostEffectPredicate<I> {
     pub fn self_ty(self) -> I::Ty {
         self.trait_ref.self_ty()
@@ -883,7 +908,7 @@ impl<I: Interner> ty::Binder<I, HostEffectPredicate<I>> {
 /// Encodes that `a` must be a subtype of `b`. The `a_is_expected` flag indicates
 /// whether the `a` type is the type that we should label as "expected" when
 /// presenting user diagnostics.
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -895,8 +920,10 @@ pub struct SubtypePredicate<I: Interner> {
     pub b: I::Ty,
 }
 
+impl<I: Interner> Eq for SubtypePredicate<I> {}
+
 /// Encodes that we have to coerce *from* the `a` type to the `b` type.
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -907,6 +934,8 @@ pub struct CoercePredicate<I: Interner> {
     pub b: I::Ty,
 }
 
+impl<I: Interner> Eq for CoercePredicate<I> {}
+
 #[derive(Clone, Copy, Hash, PartialEq, Eq, Debug)]
 #[cfg_attr(
     feature = "nightly",
diff --git a/compiler/rustc_type_ir/src/predicate_kind.rs b/compiler/rustc_type_ir/src/predicate_kind.rs
index 8bc15ec4ff5..ff92a0070cc 100644
--- a/compiler/rustc_type_ir/src/predicate_kind.rs
+++ b/compiler/rustc_type_ir/src/predicate_kind.rs
@@ -9,7 +9,7 @@ use crate::{self as ty, Interner};
 
 /// A clause is something that can appear in where bounds or be inferred
 /// by implied bounds.
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -55,7 +55,9 @@ pub enum ClauseKind<I: Interner> {
     ),
 }
 
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq; I: Interner)]
+impl<I: Interner> Eq for ClauseKind<I> {}
+
+#[derive_where(Clone, Copy, Hash, PartialEq; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -109,6 +111,8 @@ pub enum PredicateKind<I: Interner> {
     AliasRelate(I::Term, I::Term, AliasRelationDirection),
 }
 
+impl<I: Interner> Eq for PredicateKind<I> {}
+
 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Copy)]
 #[cfg_attr(
     feature = "nightly",
diff --git a/compiler/rustc_type_ir/src/region_kind.rs b/compiler/rustc_type_ir/src/region_kind.rs
index 1b5d04e6025..cca81dcb4a0 100644
--- a/compiler/rustc_type_ir/src/region_kind.rs
+++ b/compiler/rustc_type_ir/src/region_kind.rs
@@ -125,7 +125,7 @@ rustc_index::newtype_index! {
 /// [1]: https://smallcultfollowing.com/babysteps/blog/2013/10/29/intermingled-parameter-lists/
 /// [2]: https://smallcultfollowing.com/babysteps/blog/2013/11/04/intermingled-parameter-lists/
 /// [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/hrtb.html
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq; I: Interner)]
 #[cfg_attr(feature = "nightly", derive(Encodable_NoContext, Decodable_NoContext))]
 pub enum RegionKind<I: Interner> {
     /// A region parameter; for example `'a` in `impl<'a> Trait for &'a ()`.
@@ -177,6 +177,8 @@ pub enum RegionKind<I: Interner> {
     ReError(I::ErrorGuaranteed),
 }
 
+impl<I: Interner> Eq for RegionKind<I> {}
+
 impl<I: Interner> fmt::Debug for RegionKind<I> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
diff --git a/compiler/rustc_type_ir/src/relate.rs b/compiler/rustc_type_ir/src/relate.rs
index 3a00fe89360..223230fde9e 100644
--- a/compiler/rustc_type_ir/src/relate.rs
+++ b/compiler/rustc_type_ir/src/relate.rs
@@ -33,7 +33,7 @@ pub enum StructurallyRelateAliases {
 /// a miscompilation or unsoundness.
 ///
 /// When in doubt, use `VarianceDiagInfo::default()`
-#[derive_where(Clone, Copy, PartialEq, Eq, Debug, Default; I: Interner)]
+#[derive_where(Clone, Copy, PartialEq, Debug, Default; I: Interner)]
 pub enum VarianceDiagInfo<I: Interner> {
     /// No additional information - this is the default.
     /// We will not add any additional information to error messages.
@@ -51,6 +51,8 @@ pub enum VarianceDiagInfo<I: Interner> {
     },
 }
 
+impl<I: Interner> Eq for VarianceDiagInfo<I> {}
+
 impl<I: Interner> VarianceDiagInfo<I> {
     /// Mirrors `Variance::xform` - used to 'combine' the existing
     /// and new `VarianceDiagInfo`s when our variance changes.
diff --git a/compiler/rustc_type_ir/src/search_graph/mod.rs b/compiler/rustc_type_ir/src/search_graph/mod.rs
index 7433c215e6f..348178a527f 100644
--- a/compiler/rustc_type_ir/src/search_graph/mod.rs
+++ b/compiler/rustc_type_ir/src/search_graph/mod.rs
@@ -12,19 +12,19 @@
 //! The global cache has to be completely unobservable, while the per-cycle cache may impact
 //! behavior as long as the resulting behavior is still correct.
 use std::cmp::Ordering;
-use std::collections::BTreeMap;
 use std::collections::hash_map::Entry;
+use std::collections::{BTreeMap, btree_map};
 use std::fmt::Debug;
 use std::hash::Hash;
+use std::iter;
 use std::marker::PhantomData;
 
 use derive_where::derive_where;
 #[cfg(feature = "nightly")]
 use rustc_macros::{Decodable_NoContext, Encodable_NoContext, HashStable_NoContext};
+use rustc_type_ir::data_structures::HashMap;
 use tracing::{debug, instrument};
 
-use crate::data_structures::HashMap;
-
 mod stack;
 use stack::{Stack, StackDepth, StackEntry};
 mod global_cache;
@@ -137,6 +137,12 @@ pub enum PathKind {
     Unknown,
     /// A path with at least one coinductive step. Such cycles hold.
     Coinductive,
+    /// A path which is treated as ambiguous. Once a path has this path kind
+    /// any other segment does not change its kind.
+    ///
+    /// This is currently only used when fuzzing to support negative reasoning.
+    /// For more details, see #143054.
+    ForcedAmbiguity,
 }
 
 impl PathKind {
@@ -149,6 +155,9 @@ impl PathKind {
     /// to `max(self, rest)`.
     fn extend(self, rest: PathKind) -> PathKind {
         match (self, rest) {
+            (PathKind::ForcedAmbiguity, _) | (_, PathKind::ForcedAmbiguity) => {
+                PathKind::ForcedAmbiguity
+            }
             (PathKind::Coinductive, _) | (_, PathKind::Coinductive) => PathKind::Coinductive,
             (PathKind::Unknown, _) | (_, PathKind::Unknown) => PathKind::Unknown,
             (PathKind::Inductive, PathKind::Inductive) => PathKind::Inductive,
@@ -161,65 +170,79 @@ impl PathKind {
 /// This is used to avoid rerunning a cycle if there's
 /// just a single usage kind and the final result matches
 /// its provisional result.
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub enum UsageKind {
-    Single(PathKind),
-    Mixed,
-}
-impl From<PathKind> for UsageKind {
-    fn from(path: PathKind) -> UsageKind {
-        UsageKind::Single(path)
-    }
-}
-impl UsageKind {
-    #[must_use]
-    fn merge(self, other: impl Into<Self>) -> Self {
-        match (self, other.into()) {
-            (UsageKind::Mixed, _) | (_, UsageKind::Mixed) => UsageKind::Mixed,
-            (UsageKind::Single(lhs), UsageKind::Single(rhs)) => {
-                if lhs == rhs {
-                    UsageKind::Single(lhs)
-                } else {
-                    UsageKind::Mixed
-                }
-            }
-        }
-    }
-}
-
-/// For each goal we track whether the paths from this goal
-/// to its cycle heads are coinductive.
 ///
-/// This is a necessary condition to rebase provisional cache
-/// entries.
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub enum AllPathsToHeadCoinductive {
-    Yes,
-    No,
+/// While it tracks the amount of usages using `u32`, we only ever
+/// care whether there are any. We only count them to be able to ignore
+/// usages from irrelevant candidates while evaluating a goal.
+///
+/// This cares about how nested goals relied on a cycle head. It does
+/// not care about how frequently the nested goal relied on it.
+#[derive(Default, Debug, Clone, Copy, PartialEq, Eq)]
+struct HeadUsages {
+    inductive: u32,
+    unknown: u32,
+    coinductive: u32,
+    forced_ambiguity: u32,
 }
-impl From<PathKind> for AllPathsToHeadCoinductive {
-    fn from(path: PathKind) -> AllPathsToHeadCoinductive {
+
+impl HeadUsages {
+    fn add_usage(&mut self, path: PathKind) {
         match path {
-            PathKind::Coinductive => AllPathsToHeadCoinductive::Yes,
-            _ => AllPathsToHeadCoinductive::No,
+            PathKind::Inductive => self.inductive += 1,
+            PathKind::Unknown => self.unknown += 1,
+            PathKind::Coinductive => self.coinductive += 1,
+            PathKind::ForcedAmbiguity => self.forced_ambiguity += 1,
         }
     }
+
+    /// This adds the usages which occurred while computing a nested goal.
+    ///
+    /// We don't actually care about how frequently the nested goal relied
+    /// on its cycle heads, only whether it did.
+    fn add_usages_from_nested(&mut self, usages: HeadUsages) {
+        let HeadUsages { inductive, unknown, coinductive, forced_ambiguity } = usages;
+        self.inductive += if inductive == 0 { 0 } else { 1 };
+        self.unknown += if unknown == 0 { 0 } else { 1 };
+        self.coinductive += if coinductive == 0 { 0 } else { 1 };
+        self.forced_ambiguity += if forced_ambiguity == 0 { 0 } else { 1 };
+    }
+
+    fn ignore_usages(&mut self, usages: HeadUsages) {
+        let HeadUsages { inductive, unknown, coinductive, forced_ambiguity } = usages;
+        self.inductive = self.inductive.checked_sub(inductive).unwrap();
+        self.unknown = self.unknown.checked_sub(unknown).unwrap();
+        self.coinductive = self.coinductive.checked_sub(coinductive).unwrap();
+        self.forced_ambiguity = self.forced_ambiguity.checked_sub(forced_ambiguity).unwrap();
+    }
+
+    fn is_empty(self) -> bool {
+        let HeadUsages { inductive, unknown, coinductive, forced_ambiguity } = self;
+        inductive == 0 && unknown == 0 && coinductive == 0 && forced_ambiguity == 0
+    }
 }
-impl AllPathsToHeadCoinductive {
-    #[must_use]
-    fn merge(self, other: impl Into<Self>) -> Self {
-        match (self, other.into()) {
-            (AllPathsToHeadCoinductive::Yes, AllPathsToHeadCoinductive::Yes) => {
-                AllPathsToHeadCoinductive::Yes
-            }
-            (AllPathsToHeadCoinductive::No, _) | (_, AllPathsToHeadCoinductive::No) => {
-                AllPathsToHeadCoinductive::No
+
+#[derive(Debug, Default)]
+pub struct CandidateHeadUsages {
+    usages: Option<Box<HashMap<StackDepth, HeadUsages>>>,
+}
+impl CandidateHeadUsages {
+    pub fn merge_usages(&mut self, other: CandidateHeadUsages) {
+        if let Some(other_usages) = other.usages {
+            if let Some(ref mut self_usages) = self.usages {
+                #[allow(rustc::potential_query_instability)]
+                for (head_index, head) in other_usages.into_iter() {
+                    let HeadUsages { inductive, unknown, coinductive, forced_ambiguity } = head;
+                    let self_usages = self_usages.entry(head_index).or_default();
+                    self_usages.inductive += inductive;
+                    self_usages.unknown += unknown;
+                    self_usages.coinductive += coinductive;
+                    self_usages.forced_ambiguity += forced_ambiguity;
+                }
+            } else {
+                self.usages = Some(other_usages);
             }
         }
     }
-    fn and_merge(&mut self, other: impl Into<Self>) {
-        *self = self.merge(other);
-    }
 }
 
 #[derive(Debug, Clone, Copy)]
@@ -257,13 +280,24 @@ impl AvailableDepth {
     }
 }
 
+#[derive(Clone, Copy, Debug)]
+struct CycleHead {
+    paths_to_head: PathsToNested,
+    /// If the `usages` are empty, the result of that head does not matter
+    /// for the current goal. However, we still don't completely drop this
+    /// cycle head as whether or not it exists impacts which queries we
+    /// access, so ignoring it would cause incremental compilation verification
+    /// failures or hide query cycles.
+    usages: HeadUsages,
+}
+
 /// All cycle heads a given goal depends on, ordered by their stack depth.
 ///
 /// We also track all paths from this goal to that head. This is necessary
 /// when rebasing provisional cache results.
-#[derive(Clone, Debug, PartialEq, Eq, Default)]
+#[derive(Clone, Debug, Default)]
 struct CycleHeads {
-    heads: BTreeMap<StackDepth, AllPathsToHeadCoinductive>,
+    heads: BTreeMap<StackDepth, CycleHead>,
 }
 
 impl CycleHeads {
@@ -271,60 +305,51 @@ impl CycleHeads {
         self.heads.is_empty()
     }
 
-    fn highest_cycle_head(&self) -> StackDepth {
-        self.opt_highest_cycle_head().unwrap()
+    fn highest_cycle_head(&self) -> (StackDepth, CycleHead) {
+        self.heads.last_key_value().map(|(k, v)| (*k, *v)).unwrap()
     }
 
-    fn opt_highest_cycle_head(&self) -> Option<StackDepth> {
+    fn highest_cycle_head_index(&self) -> StackDepth {
+        self.opt_highest_cycle_head_index().unwrap()
+    }
+
+    fn opt_highest_cycle_head_index(&self) -> Option<StackDepth> {
         self.heads.last_key_value().map(|(k, _)| *k)
     }
 
-    fn opt_lowest_cycle_head(&self) -> Option<StackDepth> {
+    fn opt_lowest_cycle_head_index(&self) -> Option<StackDepth> {
         self.heads.first_key_value().map(|(k, _)| *k)
     }
 
-    fn remove_highest_cycle_head(&mut self) {
+    fn remove_highest_cycle_head(&mut self) -> CycleHead {
         let last = self.heads.pop_last();
-        debug_assert_ne!(last, None);
+        last.unwrap().1
     }
 
     fn insert(
         &mut self,
-        head: StackDepth,
-        path_from_entry: impl Into<AllPathsToHeadCoinductive> + Copy,
+        head_index: StackDepth,
+        path_from_entry: impl Into<PathsToNested> + Copy,
+        usages: HeadUsages,
     ) {
-        self.heads.entry(head).or_insert(path_from_entry.into()).and_merge(path_from_entry);
-    }
-
-    fn merge(&mut self, heads: &CycleHeads) {
-        for (&head, &path_from_entry) in heads.heads.iter() {
-            self.insert(head, path_from_entry);
-            debug_assert!(matches!(self.heads[&head], AllPathsToHeadCoinductive::Yes));
+        match self.heads.entry(head_index) {
+            btree_map::Entry::Vacant(entry) => {
+                entry.insert(CycleHead { paths_to_head: path_from_entry.into(), usages });
+            }
+            btree_map::Entry::Occupied(entry) => {
+                let head = entry.into_mut();
+                head.paths_to_head |= path_from_entry.into();
+                head.usages.add_usages_from_nested(usages);
+            }
         }
     }
 
-    fn iter(&self) -> impl Iterator<Item = (StackDepth, AllPathsToHeadCoinductive)> + '_ {
-        self.heads.iter().map(|(k, v)| (*k, *v))
+    fn ignore_usages(&mut self, head_index: StackDepth, usages: HeadUsages) {
+        self.heads.get_mut(&head_index).unwrap().usages.ignore_usages(usages)
     }
 
-    /// Update the cycle heads of a goal at depth `this` given the cycle heads
-    /// of a nested goal. This merges the heads after filtering the parent goal
-    /// itself.
-    fn extend_from_child(&mut self, this: StackDepth, step_kind: PathKind, child: &CycleHeads) {
-        for (&head, &path_from_entry) in child.heads.iter() {
-            match head.cmp(&this) {
-                Ordering::Less => {}
-                Ordering::Equal => continue,
-                Ordering::Greater => unreachable!(),
-            }
-
-            let path_from_entry = match step_kind {
-                PathKind::Coinductive => AllPathsToHeadCoinductive::Yes,
-                PathKind::Unknown | PathKind::Inductive => path_from_entry,
-            };
-
-            self.insert(head, path_from_entry);
-        }
+    fn iter(&self) -> impl Iterator<Item = (StackDepth, CycleHead)> + '_ {
+        self.heads.iter().map(|(k, v)| (*k, *v))
     }
 }
 
@@ -332,13 +357,14 @@ bitflags::bitflags! {
     /// Tracks how nested goals have been accessed. This is necessary to disable
     /// global cache entries if computing them would otherwise result in a cycle or
     /// access a provisional cache entry.
-    #[derive(Debug, Clone, Copy)]
+    #[derive(Debug, Clone, Copy, PartialEq, Eq)]
     pub struct PathsToNested: u8 {
         /// The initial value when adding a goal to its own nested goals.
         const EMPTY                      = 1 << 0;
         const INDUCTIVE                  = 1 << 1;
         const UNKNOWN                    = 1 << 2;
         const COINDUCTIVE                = 1 << 3;
+        const FORCED_AMBIGUITY           = 1 << 4;
     }
 }
 impl From<PathKind> for PathsToNested {
@@ -347,6 +373,7 @@ impl From<PathKind> for PathsToNested {
             PathKind::Inductive => PathsToNested::INDUCTIVE,
             PathKind::Unknown => PathsToNested::UNKNOWN,
             PathKind::Coinductive => PathsToNested::COINDUCTIVE,
+            PathKind::ForcedAmbiguity => PathsToNested::FORCED_AMBIGUITY,
         }
     }
 }
@@ -379,10 +406,45 @@ impl PathsToNested {
                     self.insert(PathsToNested::COINDUCTIVE);
                 }
             }
+            PathKind::ForcedAmbiguity => {
+                if self.intersects(
+                    PathsToNested::EMPTY
+                        | PathsToNested::INDUCTIVE
+                        | PathsToNested::UNKNOWN
+                        | PathsToNested::COINDUCTIVE,
+                ) {
+                    self.remove(
+                        PathsToNested::EMPTY
+                            | PathsToNested::INDUCTIVE
+                            | PathsToNested::UNKNOWN
+                            | PathsToNested::COINDUCTIVE,
+                    );
+                    self.insert(PathsToNested::FORCED_AMBIGUITY);
+                }
+            }
         }
 
         self
     }
+
+    #[must_use]
+    fn extend_with_paths(self, path: PathsToNested) -> Self {
+        let mut new = PathsToNested::empty();
+        for p in path.iter_paths() {
+            new |= self.extend_with(p);
+        }
+        new
+    }
+
+    fn iter_paths(self) -> impl Iterator<Item = PathKind> {
+        let (PathKind::Inductive
+        | PathKind::Unknown
+        | PathKind::Coinductive
+        | PathKind::ForcedAmbiguity);
+        [PathKind::Inductive, PathKind::Unknown, PathKind::Coinductive, PathKind::ForcedAmbiguity]
+            .into_iter()
+            .filter(move |&p| self.contains(p.into()))
+    }
 }
 
 /// The nested goals of each stack entry and the path from the
@@ -494,9 +556,6 @@ impl<X: Cx> EvaluationResult<X> {
 
 pub struct SearchGraph<D: Delegate<Cx = X>, X: Cx = <D as Delegate>::Cx> {
     root_depth: AvailableDepth,
-    /// The stack of goals currently being computed.
-    ///
-    /// An element is *deeper* in the stack if its index is *lower*.
     stack: Stack<X>,
     /// The provisional cache contains entries for already computed goals which
     /// still depend on goals higher-up in the stack. We don't move them to the
@@ -518,6 +577,7 @@ pub struct SearchGraph<D: Delegate<Cx = X>, X: Cx = <D as Delegate>::Cx> {
 /// cache entry.
 enum UpdateParentGoalCtxt<'a, X: Cx> {
     Ordinary(&'a NestedGoals<X>),
+    CycleOnStack(X::Input),
     ProvisionalCacheHit,
 }
 
@@ -539,21 +599,47 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
         stack: &mut Stack<X>,
         step_kind_from_parent: PathKind,
         required_depth_for_nested: usize,
-        heads: &CycleHeads,
+        heads: impl Iterator<Item = (StackDepth, CycleHead)>,
         encountered_overflow: bool,
         context: UpdateParentGoalCtxt<'_, X>,
     ) {
-        if let Some(parent_index) = stack.last_index() {
-            let parent = &mut stack[parent_index];
+        if let Some((parent_index, parent)) = stack.last_mut_with_index() {
             parent.required_depth = parent.required_depth.max(required_depth_for_nested + 1);
             parent.encountered_overflow |= encountered_overflow;
 
-            parent.heads.extend_from_child(parent_index, step_kind_from_parent, heads);
+            for (head_index, head) in heads {
+                if let Some(candidate_usages) = &mut parent.candidate_usages {
+                    candidate_usages
+                        .usages
+                        .get_or_insert_default()
+                        .entry(head_index)
+                        .or_default()
+                        .add_usages_from_nested(head.usages);
+                }
+                match head_index.cmp(&parent_index) {
+                    Ordering::Less => parent.heads.insert(
+                        head_index,
+                        head.paths_to_head.extend_with(step_kind_from_parent),
+                        head.usages,
+                    ),
+                    Ordering::Equal => {
+                        parent.usages.get_or_insert_default().add_usages_from_nested(head.usages);
+                    }
+                    Ordering::Greater => unreachable!(),
+                }
+            }
             let parent_depends_on_cycle = match context {
                 UpdateParentGoalCtxt::Ordinary(nested_goals) => {
                     parent.nested_goals.extend_from_child(step_kind_from_parent, nested_goals);
                     !nested_goals.is_empty()
                 }
+                UpdateParentGoalCtxt::CycleOnStack(head) => {
+                    // We lookup provisional cache entries before detecting cycles.
+                    // We therefore can't use a global cache entry if it contains a cycle
+                    // whose head is in the provisional cache.
+                    parent.nested_goals.insert(head, step_kind_from_parent.into());
+                    true
+                }
                 UpdateParentGoalCtxt::ProvisionalCacheHit => true,
             };
             // Once we've got goals which encountered overflow or a cycle,
@@ -594,6 +680,29 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
         stack.cycle_step_kinds(head).fold(step_kind_to_head, |curr, step| curr.extend(step))
     }
 
+    pub fn enter_single_candidate(&mut self) {
+        let prev = self.stack.last_mut().unwrap().candidate_usages.replace(Default::default());
+        debug_assert!(prev.is_none(), "existing candidate_usages: {prev:?}");
+    }
+
+    pub fn finish_single_candidate(&mut self) -> CandidateHeadUsages {
+        self.stack.last_mut().unwrap().candidate_usages.take().unwrap()
+    }
+
+    pub fn ignore_candidate_head_usages(&mut self, usages: CandidateHeadUsages) {
+        if let Some(usages) = usages.usages {
+            let (entry_index, entry) = self.stack.last_mut_with_index().unwrap();
+            #[allow(rustc::potential_query_instability)]
+            for (head_index, usages) in usages.into_iter() {
+                if head_index == entry_index {
+                    entry.usages.unwrap().ignore_usages(usages);
+                } else {
+                    entry.heads.ignore_usages(head_index, usages);
+                }
+            }
+        }
+    }
+
     /// Probably the most involved method of the whole solver.
     ///
     /// While goals get computed via `D::compute_goal`, this function handles
@@ -662,7 +771,8 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
             required_depth: 0,
             heads: Default::default(),
             encountered_overflow: false,
-            has_been_used: None,
+            usages: None,
+            candidate_usages: None,
             nested_goals: Default::default(),
         });
 
@@ -681,7 +791,7 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
             &mut self.stack,
             step_kind_from_parent,
             evaluation_result.required_depth,
-            &evaluation_result.heads,
+            evaluation_result.heads.iter(),
             evaluation_result.encountered_overflow,
             UpdateParentGoalCtxt::Ordinary(&evaluation_result.nested_goals),
         );
@@ -693,7 +803,7 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
             if let Some((_scope, expected)) = validate_cache {
                 // Do not try to move a goal into the cache again if we're testing
                 // the global cache.
-                assert_eq!(evaluation_result.result, expected, "input={input:?}");
+                assert_eq!(expected, evaluation_result.result, "input={input:?}");
             } else if D::inspect_is_noop(inspect) {
                 self.insert_global_cache(cx, input, evaluation_result, dep_node)
             }
@@ -710,7 +820,7 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
             let path_from_head = Self::cycle_path_kind(
                 &self.stack,
                 step_kind_from_parent,
-                heads.highest_cycle_head(),
+                heads.highest_cycle_head_index(),
             );
             let provisional_cache_entry =
                 ProvisionalCacheEntry { encountered_overflow, heads, path_from_head, result };
@@ -748,11 +858,17 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
 
     /// When reevaluating a goal with a changed provisional result, all provisional cache entry
     /// which depend on this goal get invalidated.
-    fn clear_dependent_provisional_results(&mut self) {
-        let head = self.stack.next_index();
+    ///
+    /// Note that we keep provisional cache entries which accessed this goal as a cycle head, but
+    /// don't depend on its value.
+    fn clear_dependent_provisional_results_for_rerun(&mut self) {
+        let rerun_index = self.stack.next_index();
         #[allow(rustc::potential_query_instability)]
         self.provisional_cache.retain(|_, entries| {
-            entries.retain(|entry| entry.heads.highest_cycle_head() != head);
+            entries.retain(|entry| {
+                let (head_index, head) = entry.heads.highest_cycle_head();
+                head_index != rerun_index || head.usages.is_empty()
+            });
             !entries.is_empty()
         });
     }
@@ -763,14 +879,11 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
     /// provisional cache entry is still applicable. We need to keep the cache entries to
     /// prevent hangs.
     ///
-    /// What we therefore do is check whether the cycle kind of all cycles the goal of a
-    /// provisional cache entry is involved in would stay the same when computing the
-    /// goal without its cycle head on the stack. For more details, see the relevant
+    /// This can be thought of as pretending to reevaluate the popped head as nested goals
+    /// of this provisional result. For this to be correct, all cycles encountered while
+    /// we'd reevaluate the cycle head as a nested goal must keep the same cycle kind.
     /// [rustc-dev-guide chapter](https://rustc-dev-guide.rust-lang.org/solve/caching.html).
     ///
-    /// This can be thought of rotating the sub-tree of this provisional result and changing
-    /// its entry point while making sure that all paths through this sub-tree stay the same.
-    ///
     /// In case the popped cycle head failed to reach a fixpoint anything which depends on
     /// its provisional result is invalid. Actually discarding provisional cache entries in
     /// this case would cause hangs, so we instead change the result of dependant provisional
@@ -782,7 +895,7 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
         stack_entry: &StackEntry<X>,
         mut mutate_result: impl FnMut(X::Input, X::Result) -> X::Result,
     ) {
-        let head = self.stack.next_index();
+        let popped_head_index = self.stack.next_index();
         #[allow(rustc::potential_query_instability)]
         self.provisional_cache.retain(|&input, entries| {
             entries.retain_mut(|entry| {
@@ -792,31 +905,65 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
                     path_from_head,
                     result,
                 } = entry;
-                if heads.highest_cycle_head() == head {
+                let popped_head = if heads.highest_cycle_head_index() == popped_head_index {
                     heads.remove_highest_cycle_head()
                 } else {
                     return true;
-                }
-
-                // We only try to rebase if all paths from the cache entry
-                // to its heads are coinductive. In this case these cycle
-                // kinds won't change, no matter the goals between these
-                // heads and the provisional cache entry.
-                if heads.iter().any(|(_, p)| matches!(p, AllPathsToHeadCoinductive::No)) {
-                    return false;
-                }
+                };
 
-                // The same for nested goals of the cycle head.
-                if stack_entry.heads.iter().any(|(_, p)| matches!(p, AllPathsToHeadCoinductive::No))
-                {
-                    return false;
+                // We're rebasing an entry `e` over a head `p`. This head
+                // has a number of own heads `h` it depends on.
+                //
+                // This causes our provisional result to depend on the heads
+                // of `p` to avoid moving any goal which uses this cache entry to
+                // the global cache.
+                if popped_head.usages.is_empty() {
+                    // The result of `e` does not depend on the value of `p`. This we can
+                    // keep using the result of this provisional cache entry even if evaluating
+                    // `p` as a nested goal of `e` would have a different result.
+                    for (head_index, _) in stack_entry.heads.iter() {
+                        heads.insert(head_index, PathsToNested::EMPTY, HeadUsages::default());
+                    }
+                } else {
+                    // The entry `e` actually depends on the value of `p`. We need
+                    // to make sure that the value of `p` wouldn't change even if we
+                    // were to reevaluate it as a nested goal of `e` instead. For this
+                    // we check that the path kind of all paths `hph` remain the
+                    // same after rebasing.
+                    //
+                    // After rebasing the cycles `hph` will go through `e`. We need to make
+                    // sure that forall possible paths `hep`, `heph` is equal to `hph.`
+                    let ep = popped_head.paths_to_head;
+                    for (head_index, head) in stack_entry.heads.iter() {
+                        let ph = head.paths_to_head;
+                        let hp = Self::cycle_path_kind(
+                            &self.stack,
+                            stack_entry.step_kind_from_parent,
+                            head_index,
+                        );
+                        // We first validate that all cycles while computing `p` would stay
+                        // the same if we were to recompute it as a nested goal of `e`.
+                        let he = hp.extend(*path_from_head);
+                        for ph in ph.iter_paths() {
+                            let hph = hp.extend(ph);
+                            for ep in ep.iter_paths() {
+                                let hep = ep.extend(he);
+                                let heph = hep.extend(ph);
+                                if hph != heph {
+                                    return false;
+                                }
+                            }
+                        }
+
+                        // If so, all paths reached while computing `p` have to get added
+                        // the heads of `e` to make sure that rebasing `e` again also considers
+                        // them.
+                        let eph = ep.extend_with_paths(ph);
+                        heads.insert(head_index, eph, head.usages);
+                    }
                 }
 
-                // Merge the cycle heads of the provisional cache entry and the
-                // popped head. If the popped cycle head was a root, discard all
-                // provisional cache entries which depend on it.
-                heads.merge(&stack_entry.heads);
-                let Some(head) = heads.opt_highest_cycle_head() else {
+                let Some(head_index) = heads.opt_highest_cycle_head_index() else {
                     return false;
                 };
 
@@ -825,7 +972,7 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
                 *path_from_head = path_from_head.extend(Self::cycle_path_kind(
                     &self.stack,
                     stack_entry.step_kind_from_parent,
-                    head,
+                    head_index,
                 ));
                 // Mutate the result of the provisional cache entry in case we did
                 // not reach a fixpoint.
@@ -849,7 +996,7 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
         for &ProvisionalCacheEntry { encountered_overflow, ref heads, path_from_head, result } in
             entries
         {
-            let head = heads.highest_cycle_head();
+            let head_index = heads.highest_cycle_head_index();
             if encountered_overflow {
                 // This check is overly strict and very subtle. We need to make sure that if
                 // a global cache entry depends on some goal without adding it to its
@@ -861,24 +1008,26 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
                 // current goal is already part of the same cycle. This check could be
                 // improved but seems to be good enough for now.
                 let last = self.stack.last().unwrap();
-                if last.heads.opt_lowest_cycle_head().is_none_or(|lowest| lowest > head) {
+                if last.heads.opt_lowest_cycle_head_index().is_none_or(|lowest| lowest > head_index)
+                {
                     continue;
                 }
             }
 
             // A provisional cache entry is only valid if the current path from its
             // highest cycle head to the goal is the same.
-            if path_from_head == Self::cycle_path_kind(&self.stack, step_kind_from_parent, head) {
+            if path_from_head
+                == Self::cycle_path_kind(&self.stack, step_kind_from_parent, head_index)
+            {
                 Self::update_parent_goal(
                     &mut self.stack,
                     step_kind_from_parent,
                     0,
-                    heads,
+                    heads.iter(),
                     encountered_overflow,
                     UpdateParentGoalCtxt::ProvisionalCacheHit,
                 );
-                debug_assert!(self.stack[head].has_been_used.is_some());
-                debug!(?head, ?path_from_head, "provisional cache hit");
+                debug!(?head_index, ?path_from_head, "provisional cache hit");
                 return Some(result);
             }
         }
@@ -936,8 +1085,9 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
                 //
                 // We check if any of the paths taken while computing the global goal
                 // would end up with an applicable provisional cache entry.
-                let head = heads.highest_cycle_head();
-                let head_to_curr = Self::cycle_path_kind(&self.stack, step_kind_from_parent, head);
+                let head_index = heads.highest_cycle_head_index();
+                let head_to_curr =
+                    Self::cycle_path_kind(&self.stack, step_kind_from_parent, head_index);
                 let full_paths = path_from_global_entry.extend_with(head_to_curr);
                 if full_paths.contains(head_to_provisional.into()) {
                     debug!(
@@ -989,12 +1139,12 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
 
             // We don't move cycle participants to the global cache, so the
             // cycle heads are always empty.
-            let heads = Default::default();
+            let heads = iter::empty();
             Self::update_parent_goal(
                 &mut self.stack,
                 step_kind_from_parent,
                 required_depth,
-                &heads,
+                heads,
                 encountered_overflow,
                 UpdateParentGoalCtxt::Ordinary(nested_goals),
             );
@@ -1010,34 +1160,30 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
         input: X::Input,
         step_kind_from_parent: PathKind,
     ) -> Option<X::Result> {
-        let head = self.stack.find(input)?;
+        let head_index = self.stack.find(input)?;
         // We have a nested goal which directly relies on a goal deeper in the stack.
         //
         // We start by tagging all cycle participants, as that's necessary for caching.
         //
         // Finally we can return either the provisional response or the initial response
         // in case we're in the first fixpoint iteration for this goal.
-        let path_kind = Self::cycle_path_kind(&self.stack, step_kind_from_parent, head);
-        debug!(?path_kind, "encountered cycle with depth {head:?}");
-        let usage_kind = UsageKind::Single(path_kind);
-        self.stack[head].has_been_used =
-            Some(self.stack[head].has_been_used.map_or(usage_kind, |prev| prev.merge(usage_kind)));
-
-        // Subtle: when encountering a cyclic goal, we still first checked for overflow,
-        // so we have to update the reached depth.
-        let last_index = self.stack.last_index().unwrap();
-        let last = &mut self.stack[last_index];
-        last.required_depth = last.required_depth.max(1);
-
-        last.nested_goals.insert(input, step_kind_from_parent.into());
-        last.nested_goals.insert(last.input, PathsToNested::EMPTY);
-        if last_index != head {
-            last.heads.insert(head, step_kind_from_parent);
-        }
+        let path_kind = Self::cycle_path_kind(&self.stack, step_kind_from_parent, head_index);
+        debug!(?path_kind, "encountered cycle with depth {head_index:?}");
+        let mut usages = HeadUsages::default();
+        usages.add_usage(path_kind);
+        let head = CycleHead { paths_to_head: step_kind_from_parent.into(), usages };
+        Self::update_parent_goal(
+            &mut self.stack,
+            step_kind_from_parent,
+            0,
+            iter::once((head_index, head)),
+            false,
+            UpdateParentGoalCtxt::CycleOnStack(input),
+        );
 
         // Return the provisional result or, if we're in the first iteration,
         // start with no constraints.
-        if let Some(result) = self.stack[head].provisional_result {
+        if let Some(result) = self.stack[head_index].provisional_result {
             Some(result)
         } else {
             Some(D::initial_provisional_result(cx, path_kind, input))
@@ -1049,15 +1195,31 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
         &mut self,
         cx: X,
         stack_entry: &StackEntry<X>,
-        usage_kind: UsageKind,
+        usages: HeadUsages,
         result: X::Result,
     ) -> bool {
-        if let Some(prev) = stack_entry.provisional_result {
-            prev == result
-        } else if let UsageKind::Single(kind) = usage_kind {
-            D::is_initial_provisional_result(cx, kind, stack_entry.input, result)
+        let provisional_result = stack_entry.provisional_result;
+        if usages.is_empty() {
+            true
+        } else if let Some(provisional_result) = provisional_result {
+            provisional_result == result
         } else {
-            false
+            let check = |k| D::is_initial_provisional_result(cx, k, stack_entry.input, result);
+            match usages {
+                HeadUsages { inductive: _, unknown: 0, coinductive: 0, forced_ambiguity: 0 } => {
+                    check(PathKind::Inductive)
+                }
+                HeadUsages { inductive: 0, unknown: _, coinductive: 0, forced_ambiguity: 0 } => {
+                    check(PathKind::Unknown)
+                }
+                HeadUsages { inductive: 0, unknown: 0, coinductive: _, forced_ambiguity: 0 } => {
+                    check(PathKind::Coinductive)
+                }
+                HeadUsages { inductive: 0, unknown: 0, coinductive: 0, forced_ambiguity: _ } => {
+                    check(PathKind::ForcedAmbiguity)
+                }
+                _ => false,
+            }
         }
     }
 
@@ -1087,7 +1249,7 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
             // If the current goal is not the root of a cycle, we are done.
             //
             // There are no provisional cache entries which depend on this goal.
-            let Some(usage_kind) = stack_entry.has_been_used else {
+            let Some(usages) = stack_entry.usages else {
                 return EvaluationResult::finalize(stack_entry, encountered_overflow, result);
             };
 
@@ -1102,7 +1264,7 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
             // is equal to the provisional result of the previous iteration, or because
             // this was only the root of either coinductive or inductive cycles, and the
             // final result is equal to the initial response for that case.
-            if self.reached_fixpoint(cx, &stack_entry, usage_kind, result) {
+            if self.reached_fixpoint(cx, &stack_entry, usages, result) {
                 self.rebase_provisional_cache_entries(&stack_entry, |_, result| result);
                 return EvaluationResult::finalize(stack_entry, encountered_overflow, result);
             }
@@ -1140,7 +1302,7 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
 
             // Clear all provisional cache entries which depend on a previous provisional
             // result of this goal and rerun.
-            self.clear_dependent_provisional_results();
+            self.clear_dependent_provisional_results_for_rerun();
 
             debug!(?result, "fixpoint changed provisional results");
             self.stack.push(StackEntry {
@@ -1159,7 +1321,8 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
                 // similar to the previous iterations when reevaluating, it's better
                 // for caching if the reevaluation also starts out with `false`.
                 encountered_overflow: false,
-                has_been_used: None,
+                usages: None,
+                candidate_usages: None,
             });
         }
     }
diff --git a/compiler/rustc_type_ir/src/search_graph/stack.rs b/compiler/rustc_type_ir/src/search_graph/stack.rs
index e0fd934df69..3fd8e2bd16e 100644
--- a/compiler/rustc_type_ir/src/search_graph/stack.rs
+++ b/compiler/rustc_type_ir/src/search_graph/stack.rs
@@ -1,9 +1,11 @@
-use std::ops::{Index, IndexMut};
+use std::ops::Index;
 
 use derive_where::derive_where;
 use rustc_index::IndexVec;
 
-use super::{AvailableDepth, Cx, CycleHeads, NestedGoals, PathKind, UsageKind};
+use crate::search_graph::{
+    AvailableDepth, CandidateHeadUsages, Cx, CycleHeads, HeadUsages, NestedGoals, PathKind,
+};
 
 rustc_index::newtype_index! {
     #[orderable]
@@ -26,13 +28,13 @@ pub(super) struct StackEntry<X: Cx> {
     /// The available depth of a given goal, immutable.
     pub available_depth: AvailableDepth,
 
+    /// The maximum depth required while evaluating this goal.
+    pub required_depth: usize,
+
     /// Starts out as `None` and gets set when rerunning this
     /// goal in case we encounter a cycle.
     pub provisional_result: Option<X::Result>,
 
-    /// The maximum depth required while evaluating this goal.
-    pub required_depth: usize,
-
     /// All cycle heads this goal depends on. Lazily updated and only
     /// up-to date for the top of the stack.
     pub heads: CycleHeads,
@@ -40,14 +42,27 @@ pub(super) struct StackEntry<X: Cx> {
     /// Whether evaluating this goal encountered overflow. Lazily updated.
     pub encountered_overflow: bool,
 
-    /// Whether this goal has been used as the root of a cycle. This gets
-    /// eagerly updated when encountering a cycle.
-    pub has_been_used: Option<UsageKind>,
+    /// Whether and how this goal has been used as the root of a cycle. Lazily updated.
+    pub usages: Option<HeadUsages>,
+
+    /// We want to be able to ignore head usages if they happen inside of candidates
+    /// which don't impact the result of a goal. This enables us to avoid rerunning goals
+    /// and is also used when rebasing provisional cache entries.
+    ///
+    /// To implement this, we track all usages while evaluating a candidate. If this candidate
+    /// then ends up ignored, we manually remove its usages from `usages` and `heads`.
+    pub candidate_usages: Option<CandidateHeadUsages>,
 
     /// The nested goals of this goal, see the doc comment of the type.
     pub nested_goals: NestedGoals<X>,
 }
 
+/// The stack of goals currently being computed.
+///
+/// An element is *deeper* in the stack if its index is *lower*.
+///
+/// Only the last entry of the stack is mutable. All other entries get
+/// lazily updated in `update_parent_goal`.
 #[derive_where(Default; X: Cx)]
 pub(super) struct Stack<X: Cx> {
     entries: IndexVec<StackDepth, StackEntry<X>>,
@@ -62,10 +77,6 @@ impl<X: Cx> Stack<X> {
         self.entries.len()
     }
 
-    pub(super) fn last_index(&self) -> Option<StackDepth> {
-        self.entries.last_index()
-    }
-
     pub(super) fn last(&self) -> Option<&StackEntry<X>> {
         self.entries.raw.last()
     }
@@ -74,11 +85,18 @@ impl<X: Cx> Stack<X> {
         self.entries.raw.last_mut()
     }
 
+    pub(super) fn last_mut_with_index(&mut self) -> Option<(StackDepth, &mut StackEntry<X>)> {
+        self.entries.last_index().map(|idx| (idx, &mut self.entries[idx]))
+    }
+
     pub(super) fn next_index(&self) -> StackDepth {
         self.entries.next_index()
     }
 
     pub(super) fn push(&mut self, entry: StackEntry<X>) -> StackDepth {
+        if cfg!(debug_assertions) && self.entries.iter().any(|e| e.input == entry.input) {
+            panic!("pushing duplicate entry on stack: {entry:?} {:?}", self.entries);
+        }
         self.entries.push(entry)
     }
 
@@ -105,9 +123,3 @@ impl<X: Cx> Index<StackDepth> for Stack<X> {
         &self.entries[index]
     }
 }
-
-impl<X: Cx> IndexMut<StackDepth> for Stack<X> {
-    fn index_mut(&mut self, index: StackDepth) -> &mut Self::Output {
-        &mut self.entries[index]
-    }
-}
diff --git a/compiler/rustc_type_ir/src/solve/inspect.rs b/compiler/rustc_type_ir/src/solve/inspect.rs
index 089695d0475..afb4043648f 100644
--- a/compiler/rustc_type_ir/src/solve/inspect.rs
+++ b/compiler/rustc_type_ir/src/solve/inspect.rs
@@ -17,9 +17,6 @@
 //!
 //! [canonicalized]: https://rustc-dev-guide.rust-lang.org/solve/canonicalization.html
 
-use std::fmt::Debug;
-use std::hash::Hash;
-
 use derive_where::derive_where;
 use rustc_type_ir_macros::{TypeFoldable_Generic, TypeVisitable_Generic};
 
@@ -32,25 +29,23 @@ use crate::{Canonical, CanonicalVarValues, Interner};
 /// This is only ever used as [CanonicalState]. Any type information in proof
 /// trees used mechanically has to be canonicalized as we otherwise leak
 /// inference variables from a nested `InferCtxt`.
-#[derive_where(Clone; I: Interner, T: Clone)]
+#[derive_where(Clone, PartialEq, Hash, Debug; I: Interner, T)]
 #[derive_where(Copy; I: Interner, T: Copy)]
-#[derive_where(PartialEq; I: Interner, T: PartialEq)]
-#[derive_where(Eq; I: Interner, T: Eq)]
-#[derive_where(Hash; I: Interner, T: Hash)]
-#[derive_where(Debug; I: Interner, T: Debug)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
 pub struct State<I: Interner, T> {
     pub var_values: CanonicalVarValues<I>,
     pub data: T,
 }
 
+impl<I: Interner, T: Eq> Eq for State<I, T> {}
+
 pub type CanonicalState<I, T> = Canonical<I, State<I, T>>;
 
 /// When evaluating a goal we also store the original values
 /// for the `CanonicalVarValues` of the canonicalized goal.
 /// We use this to map any [CanonicalState] from the local `InferCtxt`
 /// of the solver query to the `InferCtxt` of the caller.
-#[derive_where(PartialEq, Eq, Hash; I: Interner)]
+#[derive_where(PartialEq, Hash; I: Interner)]
 pub struct GoalEvaluation<I: Interner> {
     pub uncanonicalized_goal: Goal<I, I::Predicate>,
     pub orig_values: Vec<I::GenericArg>,
@@ -58,7 +53,9 @@ pub struct GoalEvaluation<I: Interner> {
     pub result: QueryResult<I>,
 }
 
-#[derive_where(PartialEq, Eq, Hash, Debug; I: Interner)]
+impl<I: Interner> Eq for GoalEvaluation<I> {}
+
+#[derive_where(PartialEq, Hash, Debug; I: Interner)]
 pub enum GoalEvaluationKind<I: Interner> {
     Overflow,
     Evaluation {
@@ -67,10 +64,12 @@ pub enum GoalEvaluationKind<I: Interner> {
     },
 }
 
+impl<I: Interner> Eq for GoalEvaluationKind<I> {}
+
 /// A self-contained computation during trait solving. This either
 /// corresponds to a `EvalCtxt::probe(_X)` call or the root evaluation
 /// of a goal.
-#[derive_where(PartialEq, Eq, Hash, Debug; I: Interner)]
+#[derive_where(PartialEq, Hash, Debug; I: Interner)]
 pub struct Probe<I: Interner> {
     /// What happened inside of this probe in chronological order.
     pub steps: Vec<ProbeStep<I>>,
@@ -78,7 +77,9 @@ pub struct Probe<I: Interner> {
     pub final_state: CanonicalState<I, ()>,
 }
 
-#[derive_where(PartialEq, Eq, Hash, Debug; I: Interner)]
+impl<I: Interner> Eq for Probe<I> {}
+
+#[derive_where(PartialEq, Hash, Debug; I: Interner)]
 pub enum ProbeStep<I: Interner> {
     /// We added a goal to the `EvalCtxt` which will get proven
     /// the next time `EvalCtxt::try_evaluate_added_goals` is called.
@@ -97,10 +98,12 @@ pub enum ProbeStep<I: Interner> {
     MakeCanonicalResponse { shallow_certainty: Certainty },
 }
 
+impl<I: Interner> Eq for ProbeStep<I> {}
+
 /// What kind of probe we're in. In case the probe represents a candidate, or
 /// the final result of the current goal - via [ProbeKind::Root] - we also
 /// store the [QueryResult].
-#[derive_where(Clone, Copy, PartialEq, Eq, Hash, Debug; I: Interner)]
+#[derive_where(Clone, Copy, PartialEq, Hash, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
 pub enum ProbeKind<I: Interner> {
     /// The root inference context while proving a goal.
@@ -125,3 +128,5 @@ pub enum ProbeKind<I: Interner> {
     /// Checking that a rigid alias is well-formed.
     RigidAlias { result: QueryResult<I> },
 }
+
+impl<I: Interner> Eq for ProbeKind<I> {}
diff --git a/compiler/rustc_type_ir/src/solve/mod.rs b/compiler/rustc_type_ir/src/solve/mod.rs
index a6571ef261a..1497236039f 100644
--- a/compiler/rustc_type_ir/src/solve/mod.rs
+++ b/compiler/rustc_type_ir/src/solve/mod.rs
@@ -1,6 +1,5 @@
 pub mod inspect;
 
-use std::fmt;
 use std::hash::Hash;
 
 use derive_where::derive_where;
@@ -32,12 +31,8 @@ pub struct NoSolution;
 ///
 /// Most of the time the `param_env` contains the `where`-bounds of the function
 /// we're currently typechecking while the `predicate` is some trait bound.
-#[derive_where(Clone; I: Interner, P: Clone)]
+#[derive_where(Clone, Hash, PartialEq, Debug; I: Interner, P)]
 #[derive_where(Copy; I: Interner, P: Copy)]
-#[derive_where(Hash; I: Interner, P: Hash)]
-#[derive_where(PartialEq; I: Interner, P: PartialEq)]
-#[derive_where(Eq; I: Interner, P: Eq)]
-#[derive_where(Debug; I: Interner, P: fmt::Debug)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -48,6 +43,8 @@ pub struct Goal<I: Interner, P> {
     pub predicate: P,
 }
 
+impl<I: Interner, P: Eq> Eq for Goal<I, P> {}
+
 impl<I: Interner, P> Goal<I, P> {
     pub fn new(cx: I, param_env: I::ParamEnv, predicate: impl Upcast<I, P>) -> Goal<I, P> {
         Goal { param_env, predicate: predicate.upcast(cx) }
@@ -98,12 +95,8 @@ pub enum GoalSource {
     NormalizeGoal(PathKind),
 }
 
-#[derive_where(Clone; I: Interner, Goal<I, P>: Clone)]
+#[derive_where(Clone, Hash, PartialEq, Debug; I: Interner, Goal<I, P>)]
 #[derive_where(Copy; I: Interner, Goal<I, P>: Copy)]
-#[derive_where(Hash; I: Interner, Goal<I, P>: Hash)]
-#[derive_where(PartialEq; I: Interner, Goal<I, P>: PartialEq)]
-#[derive_where(Eq; I: Interner, Goal<I, P>: Eq)]
-#[derive_where(Debug; I: Interner, Goal<I, P>: fmt::Debug)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -114,8 +107,10 @@ pub struct QueryInput<I: Interner, P> {
     pub predefined_opaques_in_body: I::PredefinedOpaques,
 }
 
+impl<I: Interner, P: Eq> Eq for QueryInput<I, P> {}
+
 /// Opaques that are defined in the inference context before a query is called.
-#[derive_where(Clone, Hash, PartialEq, Eq, Debug, Default; I: Interner)]
+#[derive_where(Clone, Hash, PartialEq, Debug, Default; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -125,8 +120,10 @@ pub struct PredefinedOpaquesData<I: Interner> {
     pub opaque_types: Vec<(ty::OpaqueTypeKey<I>, I::Ty)>,
 }
 
+impl<I: Interner> Eq for PredefinedOpaquesData<I> {}
+
 /// Possible ways the given goal can be proven.
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq, Debug; I: Interner)]
 pub enum CandidateSource<I: Interner> {
     /// A user written impl.
     ///
@@ -189,6 +186,8 @@ pub enum CandidateSource<I: Interner> {
     CoherenceUnknowable,
 }
 
+impl<I: Interner> Eq for CandidateSource<I> {}
+
 #[derive(Clone, Copy, Hash, PartialEq, Eq, Debug)]
 pub enum ParamEnvSource {
     /// Preferred eagerly.
@@ -217,7 +216,7 @@ pub enum BuiltinImplSource {
     TraitUpcasting(usize),
 }
 
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
 #[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
 pub struct Response<I: Interner> {
@@ -227,8 +226,10 @@ pub struct Response<I: Interner> {
     pub external_constraints: I::ExternalConstraints,
 }
 
+impl<I: Interner> Eq for Response<I> {}
+
 /// Additional constraints returned on success.
-#[derive_where(Clone, Hash, PartialEq, Eq, Debug, Default; I: Interner)]
+#[derive_where(Clone, Hash, PartialEq, Debug, Default; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
 #[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
 pub struct ExternalConstraintsData<I: Interner> {
@@ -237,6 +238,8 @@ pub struct ExternalConstraintsData<I: Interner> {
     pub normalization_nested_goals: NestedNormalizationGoals<I>,
 }
 
+impl<I: Interner> Eq for ExternalConstraintsData<I> {}
+
 impl<I: Interner> ExternalConstraintsData<I> {
     pub fn is_empty(&self) -> bool {
         self.region_constraints.is_empty()
@@ -245,11 +248,13 @@ impl<I: Interner> ExternalConstraintsData<I> {
     }
 }
 
-#[derive_where(Clone, Hash, PartialEq, Eq, Debug, Default; I: Interner)]
+#[derive_where(Clone, Hash, PartialEq, Debug, Default; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
 #[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
 pub struct NestedNormalizationGoals<I: Interner>(pub Vec<(GoalSource, Goal<I, I::Predicate>)>);
 
+impl<I: Interner> Eq for NestedNormalizationGoals<I> {}
+
 impl<I: Interner> NestedNormalizationGoals<I> {
     pub fn empty() -> Self {
         NestedNormalizationGoals(vec![])
diff --git a/compiler/rustc_type_ir/src/ty_kind.rs b/compiler/rustc_type_ir/src/ty_kind.rs
index 73aeab5092d..bde506ffd93 100644
--- a/compiler/rustc_type_ir/src/ty_kind.rs
+++ b/compiler/rustc_type_ir/src/ty_kind.rs
@@ -69,7 +69,7 @@ impl AliasTyKind {
 /// Types written by the user start out as `hir::TyKind` and get
 /// converted to this representation using `<dyn HirTyLowerer>::lower_ty`.
 #[cfg_attr(feature = "nightly", rustc_diagnostic_item = "IrTyKind")]
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq; I: Interner)]
 #[cfg_attr(
     feature = "nightly",
     derive(Encodable_NoContext, Decodable_NoContext, HashStable_NoContext)
@@ -268,6 +268,8 @@ pub enum TyKind<I: Interner> {
     Error(I::ErrorGuaranteed),
 }
 
+impl<I: Interner> Eq for TyKind<I> {}
+
 impl<I: Interner> TyKind<I> {
     pub fn fn_sig(self, interner: I) -> ty::Binder<I, ty::FnSig<I>> {
         match self {
@@ -404,7 +406,7 @@ impl<I: Interner> fmt::Debug for TyKind<I> {
 /// * For a projection, this would be `<Ty as Trait<...>>::N<...>`.
 /// * For an inherent projection, this would be `Ty::N<...>`.
 /// * For an opaque type, there is no explicit syntax.
-#[derive_where(Clone, Copy, Hash, PartialEq, Eq, Debug; I: Interner)]
+#[derive_where(Clone, Copy, Hash, PartialEq, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 #[cfg_attr(
     feature = "nightly",
@@ -440,6 +442,8 @@ pub struct AliasTy<I: Interner> {
     pub(crate) _use_alias_ty_new_instead: (),
 }
 
+impl<I: Interner> Eq for AliasTy<I> {}
+
 impl<I: Interner> AliasTy<I> {
     pub fn new_from_args(interner: I, def_id: I::DefId, args: I::GenericArgs) -> AliasTy<I> {
         interner.debug_assert_args_compatible(def_id, args);
@@ -720,7 +724,7 @@ impl fmt::Debug for InferTy {
     }
 }
 
-#[derive_where(Clone, Copy, PartialEq, Eq, Hash, Debug; I: Interner)]
+#[derive_where(Clone, Copy, PartialEq, Hash, Debug; I: Interner)]
 #[cfg_attr(
     feature = "nightly",
     derive(Encodable_NoContext, Decodable_NoContext, HashStable_NoContext)
@@ -731,7 +735,9 @@ pub struct TypeAndMut<I: Interner> {
     pub mutbl: Mutability,
 }
 
-#[derive_where(Clone, Copy, PartialEq, Eq, Hash; I: Interner)]
+impl<I: Interner> Eq for TypeAndMut<I> {}
+
+#[derive_where(Clone, Copy, PartialEq, Hash; I: Interner)]
 #[cfg_attr(
     feature = "nightly",
     derive(Encodable_NoContext, Decodable_NoContext, HashStable_NoContext)
@@ -748,6 +754,8 @@ pub struct FnSig<I: Interner> {
     pub abi: I::Abi,
 }
 
+impl<I: Interner> Eq for FnSig<I> {}
+
 impl<I: Interner> FnSig<I> {
     pub fn inputs(self) -> I::FnInputTys {
         self.inputs_and_output.inputs()
@@ -845,11 +853,13 @@ impl<I: Interner> fmt::Debug for FnSig<I> {
 
 // FIXME: this is a distinct type because we need to define `Encode`/`Decode`
 // impls in this crate for `Binder<I, I::Ty>`.
-#[derive_where(Clone, Copy, PartialEq, Eq, Hash; I: Interner)]
+#[derive_where(Clone, Copy, PartialEq, Hash; I: Interner)]
 #[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 pub struct UnsafeBinderInner<I: Interner>(ty::Binder<I, I::Ty>);
 
+impl<I: Interner> Eq for UnsafeBinderInner<I> {}
+
 impl<I: Interner> From<ty::Binder<I, I::Ty>> for UnsafeBinderInner<I> {
     fn from(value: ty::Binder<I, I::Ty>) -> Self {
         UnsafeBinderInner(value)
@@ -906,7 +916,7 @@ where
 }
 
 // This is just a `FnSig` without the `FnHeader` fields.
-#[derive_where(Clone, Copy, Debug, PartialEq, Eq, Hash; I: Interner)]
+#[derive_where(Clone, Copy, Debug, PartialEq, Hash; I: Interner)]
 #[cfg_attr(
     feature = "nightly",
     derive(Encodable_NoContext, Decodable_NoContext, HashStable_NoContext)
@@ -916,6 +926,8 @@ pub struct FnSigTys<I: Interner> {
     pub inputs_and_output: I::Tys,
 }
 
+impl<I: Interner> Eq for FnSigTys<I> {}
+
 impl<I: Interner> FnSigTys<I> {
     pub fn inputs(self) -> I::FnInputTys {
         self.inputs_and_output.inputs()
@@ -958,7 +970,7 @@ impl<I: Interner> ty::Binder<I, FnSigTys<I>> {
     }
 }
 
-#[derive_where(Clone, Copy, Debug, PartialEq, Eq, Hash; I: Interner)]
+#[derive_where(Clone, Copy, Debug, PartialEq, Hash; I: Interner)]
 #[cfg_attr(
     feature = "nightly",
     derive(Encodable_NoContext, Decodable_NoContext, HashStable_NoContext)
@@ -970,7 +982,9 @@ pub struct FnHeader<I: Interner> {
     pub abi: I::Abi,
 }
 
-#[derive_where(Clone, Copy, Debug, PartialEq, Eq, Hash; I: Interner)]
+impl<I: Interner> Eq for FnHeader<I> {}
+
+#[derive_where(Clone, Copy, Debug, PartialEq, Hash; I: Interner)]
 #[cfg_attr(
     feature = "nightly",
     derive(Encodable_NoContext, Decodable_NoContext, HashStable_NoContext)
@@ -980,3 +994,5 @@ pub struct CoroutineWitnessTypes<I: Interner> {
     pub types: I::Tys,
     pub assumptions: I::RegionAssumptions,
 }
+
+impl<I: Interner> Eq for CoroutineWitnessTypes<I> {}
diff --git a/compiler/rustc_type_ir/src/ty_kind/closure.rs b/compiler/rustc_type_ir/src/ty_kind/closure.rs
index c32f8339d0b..a2e16d917a9 100644
--- a/compiler/rustc_type_ir/src/ty_kind/closure.rs
+++ b/compiler/rustc_type_ir/src/ty_kind/closure.rs
@@ -101,7 +101,7 @@ use crate::{self as ty, Interner};
 ///   `yield` inside the coroutine.
 /// * `GR`: The "return type", which is the type of value returned upon
 ///   completion of the coroutine.
-#[derive_where(Clone, Copy, PartialEq, Eq, Hash, Debug; I: Interner)]
+#[derive_where(Clone, Copy, PartialEq, Hash, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 pub struct ClosureArgs<I: Interner> {
     /// Lifetime and type parameters from the enclosing function,
@@ -112,6 +112,8 @@ pub struct ClosureArgs<I: Interner> {
     pub args: I::GenericArgs,
 }
 
+impl<I: Interner> Eq for ClosureArgs<I> {}
+
 /// Struct returned by `split()`.
 pub struct ClosureArgsParts<I: Interner> {
     /// This is the args of the typeck root.
@@ -203,12 +205,14 @@ impl<I: Interner> ClosureArgs<I> {
     }
 }
 
-#[derive_where(Clone, Copy, PartialEq, Eq, Hash, Debug; I: Interner)]
+#[derive_where(Clone, Copy, PartialEq, Hash, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 pub struct CoroutineClosureArgs<I: Interner> {
     pub args: I::GenericArgs,
 }
 
+impl<I: Interner> Eq for CoroutineClosureArgs<I> {}
+
 /// See docs for explanation of how each argument is used.
 ///
 /// See [`CoroutineClosureSignature`] for how these arguments are put together
@@ -348,7 +352,7 @@ impl<I: Interner> TypeVisitor<I> for HasRegionsBoundAt {
     }
 }
 
-#[derive_where(Clone, Copy, PartialEq, Eq, Hash, Debug; I: Interner)]
+#[derive_where(Clone, Copy, PartialEq, Hash, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
 pub struct CoroutineClosureSignature<I: Interner> {
     pub tupled_inputs_ty: I::Ty,
@@ -371,6 +375,8 @@ pub struct CoroutineClosureSignature<I: Interner> {
     pub abi: I::Abi,
 }
 
+impl<I: Interner> Eq for CoroutineClosureSignature<I> {}
+
 impl<I: Interner> CoroutineClosureSignature<I> {
     /// Construct a coroutine from the closure signature. Since a coroutine signature
     /// is agnostic to the type of generator that is returned (by-ref/by-move),
@@ -541,7 +547,7 @@ impl<I: Interner> TypeFolder<I> for FoldEscapingRegions<I> {
     }
 }
 
-#[derive_where(Clone, Copy, PartialEq, Eq, Hash, Debug; I: Interner)]
+#[derive_where(Clone, Copy, PartialEq, Hash, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic)]
 pub struct GenSig<I: Interner> {
     pub resume_ty: I::Ty,
@@ -549,13 +555,16 @@ pub struct GenSig<I: Interner> {
     pub return_ty: I::Ty,
 }
 
+impl<I: Interner> Eq for GenSig<I> {}
 /// Similar to `ClosureArgs`; see the above documentation for more.
-#[derive_where(Clone, Copy, PartialEq, Eq, Hash, Debug; I: Interner)]
+#[derive_where(Clone, Copy, PartialEq, Hash, Debug; I: Interner)]
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 pub struct CoroutineArgs<I: Interner> {
     pub args: I::GenericArgs,
 }
 
+impl<I: Interner> Eq for CoroutineArgs<I> {}
+
 pub struct CoroutineArgsParts<I: Interner> {
     /// This is the args of the typeck root.
     pub parent_args: I::GenericArgsSlice,