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-rw-r--r--compiler/rustc_ast/Cargo.toml2
-rw-r--r--compiler/rustc_ast/src/ast.rs56
-rw-r--r--compiler/rustc_ast/src/util/literal.rs6
-rw-r--r--compiler/rustc_ast/src/visit.rs3
-rw-r--r--compiler/rustc_ast_lowering/src/item.rs13
-rw-r--r--compiler/rustc_ast_passes/messages.ftl4
-rw-r--r--compiler/rustc_ast_passes/src/ast_validation.rs38
-rw-r--r--compiler/rustc_ast_passes/src/errors.rs2
-rw-r--r--compiler/rustc_ast_pretty/src/pprust/state/item.rs2
-rw-r--r--compiler/rustc_attr_data_structures/src/attributes.rs22
-rw-r--r--compiler/rustc_attr_data_structures/src/encode_cross_crate.rs2
-rw-r--r--compiler/rustc_attr_parsing/messages.ftl3
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/allow_unstable.rs20
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/cfg.rs53
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs41
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/stability.rs10
-rw-r--r--compiler/rustc_attr_parsing/src/attributes/traits.rs1
-rw-r--r--compiler/rustc_attr_parsing/src/context.rs58
-rw-r--r--compiler/rustc_attr_parsing/src/lib.rs2
-rw-r--r--compiler/rustc_attr_parsing/src/session_diagnostics.rs57
-rw-r--r--compiler/rustc_borrowck/src/type_check/constraint_conversion.rs33
-rw-r--r--compiler/rustc_borrowck/src/type_check/mod.rs5
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/bounds.rs4
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/clone.rs1
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs1
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs1
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs2
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs1
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/debug.rs1
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/default.rs1
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/generic/mod.rs47
-rw-r--r--compiler/rustc_builtin_macros/src/deriving/hash.rs1
-rw-r--r--compiler/rustc_builtin_macros/src/source_util.rs4
-rw-r--r--compiler/rustc_builtin_macros/src/test.rs9
-rw-r--r--compiler/rustc_codegen_cranelift/src/driver/aot.rs4
-rw-r--r--compiler/rustc_codegen_cranelift/src/driver/jit.rs2
-rw-r--r--compiler/rustc_codegen_cranelift/src/driver/mod.rs2
-rw-r--r--compiler/rustc_codegen_gcc/src/attributes.rs2
-rw-r--r--compiler/rustc_codegen_gcc/src/back/lto.rs15
-rw-r--r--compiler/rustc_codegen_gcc/src/back/write.rs4
-rw-r--r--compiler/rustc_codegen_gcc/src/callee.rs2
-rw-r--r--compiler/rustc_codegen_gcc/src/lib.rs33
-rw-r--r--compiler/rustc_codegen_gcc/src/mono_item.rs2
-rw-r--r--compiler/rustc_codegen_llvm/messages.ftl1
-rw-r--r--compiler/rustc_codegen_llvm/src/attributes.rs2
-rw-r--r--compiler/rustc_codegen_llvm/src/back/lto.rs17
-rw-r--r--compiler/rustc_codegen_llvm/src/back/write.rs81
-rw-r--r--compiler/rustc_codegen_llvm/src/builder.rs20
-rw-r--r--compiler/rustc_codegen_llvm/src/builder/autodiff.rs18
-rw-r--r--compiler/rustc_codegen_llvm/src/callee.rs2
-rw-r--r--compiler/rustc_codegen_llvm/src/common.rs8
-rw-r--r--compiler/rustc_codegen_llvm/src/consts.rs261
-rw-r--r--compiler/rustc_codegen_llvm/src/context.rs21
-rw-r--r--compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs2
-rw-r--r--compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs10
-rw-r--r--compiler/rustc_codegen_llvm/src/declare.rs6
-rw-r--r--compiler/rustc_codegen_llvm/src/errors.rs4
-rw-r--r--compiler/rustc_codegen_llvm/src/lib.rs49
-rw-r--r--compiler/rustc_codegen_llvm/src/llvm/ffi.rs14
-rw-r--r--compiler/rustc_codegen_llvm/src/llvm/mod.rs10
-rw-r--r--compiler/rustc_codegen_llvm/src/mono_item.rs8
-rw-r--r--compiler/rustc_codegen_llvm/src/type_.rs16
-rw-r--r--compiler/rustc_codegen_ssa/src/back/link.rs7
-rw-r--r--compiler/rustc_codegen_ssa/src/back/linker.rs33
-rw-r--r--compiler/rustc_codegen_ssa/src/back/lto.rs60
-rw-r--r--compiler/rustc_codegen_ssa/src/back/write.rs174
-rw-r--r--compiler/rustc_codegen_ssa/src/base.rs9
-rw-r--r--compiler/rustc_codegen_ssa/src/meth.rs3
-rw-r--r--compiler/rustc_codegen_ssa/src/mir/debuginfo.rs2
-rw-r--r--compiler/rustc_codegen_ssa/src/mir/mod.rs5
-rw-r--r--compiler/rustc_codegen_ssa/src/mir/naked_asm.rs2
-rw-r--r--compiler/rustc_codegen_ssa/src/mir/rvalue.rs12
-rw-r--r--compiler/rustc_codegen_ssa/src/mono_item.rs10
-rw-r--r--compiler/rustc_codegen_ssa/src/traits/type_.rs6
-rw-r--r--compiler/rustc_codegen_ssa/src/traits/write.rs24
-rw-r--r--compiler/rustc_const_eval/messages.ftl38
-rw-r--r--compiler/rustc_const_eval/src/check_consts/mod.rs2
-rw-r--r--compiler/rustc_const_eval/src/const_eval/dummy_machine.rs1
-rw-r--r--compiler/rustc_const_eval/src/const_eval/error.rs36
-rw-r--r--compiler/rustc_const_eval/src/const_eval/eval_queries.rs13
-rw-r--r--compiler/rustc_const_eval/src/const_eval/machine.rs29
-rw-r--r--compiler/rustc_const_eval/src/errors.rs8
-rw-r--r--compiler/rustc_const_eval/src/interpret/call.rs2
-rw-r--r--compiler/rustc_const_eval/src/interpret/eval_context.rs55
-rw-r--r--compiler/rustc_const_eval/src/interpret/intern.rs92
-rw-r--r--compiler/rustc_const_eval/src/interpret/intrinsics.rs99
-rw-r--r--compiler/rustc_const_eval/src/interpret/machine.rs1
-rw-r--r--compiler/rustc_const_eval/src/interpret/memory.rs54
-rw-r--r--compiler/rustc_const_eval/src/interpret/mod.rs2
-rw-r--r--compiler/rustc_const_eval/src/interpret/stack.rs7
-rw-r--r--compiler/rustc_const_eval/src/interpret/step.rs1
-rw-r--r--compiler/rustc_const_eval/src/interpret/validity.rs10
-rw-r--r--compiler/rustc_const_eval/src/util/check_validity_requirement.rs13
-rw-r--r--compiler/rustc_driver_impl/src/lib.rs46
-rw-r--r--compiler/rustc_expand/src/base.rs2
-rw-r--r--compiler/rustc_expand/src/build.rs10
-rw-r--r--compiler/rustc_expand/src/config.rs22
-rw-r--r--compiler/rustc_expand/src/expand.rs4
-rw-r--r--compiler/rustc_feature/src/builtin_attrs.rs5
-rw-r--r--compiler/rustc_hir/src/def.rs15
-rw-r--r--compiler/rustc_hir/src/definitions.rs36
-rw-r--r--compiler/rustc_hir/src/hir.rs23
-rw-r--r--compiler/rustc_hir/src/intravisit.rs10
-rw-r--r--compiler/rustc_hir/src/tests.rs3
-rw-r--r--compiler/rustc_hir_analysis/messages.ftl14
-rw-r--r--compiler/rustc_hir_analysis/src/check/check.rs10
-rw-r--r--compiler/rustc_hir_analysis/src/check/intrinsic.rs3
-rw-r--r--compiler/rustc_hir_analysis/src/check/wfcheck.rs14
-rw-r--r--compiler/rustc_hir_analysis/src/coherence/builtin.rs6
-rw-r--r--compiler/rustc_hir_analysis/src/collect.rs13
-rw-r--r--compiler/rustc_hir_analysis/src/collect/item_bounds.rs57
-rw-r--r--compiler/rustc_hir_analysis/src/collect/predicates_of.rs20
-rw-r--r--compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs2
-rw-r--r--compiler/rustc_hir_analysis/src/errors.rs3
-rw-r--r--compiler/rustc_hir_analysis/src/errors/wrong_number_of_generic_args.rs2
-rw-r--r--compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs2
-rw-r--r--compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs1
-rw-r--r--compiler/rustc_hir_analysis/src/outlives/explicit.rs1
-rw-r--r--compiler/rustc_hir_analysis/src/outlives/utils.rs3
-rw-r--r--compiler/rustc_hir_pretty/src/lib.rs11
-rw-r--r--compiler/rustc_hir_typeck/src/closure.rs11
-rw-r--r--compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs51
-rw-r--r--compiler/rustc_hir_typeck/src/fn_ctxt/inspect_obligations.rs1
-rw-r--r--compiler/rustc_hir_typeck/src/method/prelude_edition_lints.rs11
-rw-r--r--compiler/rustc_hir_typeck/src/method/probe.rs1
-rw-r--r--compiler/rustc_hir_typeck/src/method/suggest.rs6
-rw-r--r--compiler/rustc_hir_typeck/src/typeck_root_ctxt.rs3
-rw-r--r--compiler/rustc_infer/src/infer/canonical/query_response.rs28
-rw-r--r--compiler/rustc_infer/src/infer/mod.rs15
-rw-r--r--compiler/rustc_infer/src/infer/outlives/env.rs11
-rw-r--r--compiler/rustc_infer/src/infer/outlives/mod.rs21
-rw-r--r--compiler/rustc_infer/src/infer/outlives/obligations.rs20
-rw-r--r--compiler/rustc_infer/src/infer/snapshot/undo_log.rs4
-rw-r--r--compiler/rustc_lint/messages.ftl63
-rw-r--r--compiler/rustc_lint/src/builtin.rs5
-rw-r--r--compiler/rustc_lint/src/early/diagnostics.rs3
-rw-r--r--compiler/rustc_lint/src/lib.rs2
-rw-r--r--compiler/rustc_lint/src/lifetime_syntax.rs149
-rw-r--r--compiler/rustc_lint/src/lints.rs94
-rw-r--r--compiler/rustc_lint/src/multiple_supertrait_upcastable.rs2
-rw-r--r--compiler/rustc_lint/src/types/literal.rs42
-rw-r--r--compiler/rustc_lint_defs/src/lib.rs5
-rw-r--r--compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs7
-rw-r--r--compiler/rustc_metadata/src/rmeta/encoder.rs2
-rw-r--r--compiler/rustc_middle/src/hir/map.rs2
-rw-r--r--compiler/rustc_middle/src/infer/canonical.rs14
-rw-r--r--compiler/rustc_middle/src/middle/codegen_fn_attrs.rs22
-rw-r--r--compiler/rustc_middle/src/mir/interpret/error.rs2
-rw-r--r--compiler/rustc_middle/src/mir/mono.rs13
-rw-r--r--compiler/rustc_middle/src/query/mod.rs11
-rw-r--r--compiler/rustc_middle/src/ty/context.rs42
-rw-r--r--compiler/rustc_middle/src/ty/mod.rs2
-rw-r--r--compiler/rustc_middle/src/ty/predicate.rs4
-rw-r--r--compiler/rustc_middle/src/ty/print/pretty.rs7
-rw-r--r--compiler/rustc_middle/src/ty/structural_impls.rs1
-rw-r--r--compiler/rustc_middle/src/ty/trait_def.rs2
-rw-r--r--compiler/rustc_mir_transform/src/coverage/query.rs32
-rw-r--r--compiler/rustc_mir_transform/src/gvn.rs553
-rw-r--r--compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs12
-rw-r--r--compiler/rustc_next_trait_solver/src/solve/mod.rs14
-rw-r--r--compiler/rustc_parse/Cargo.toml2
-rw-r--r--compiler/rustc_parse/messages.ftl1
-rw-r--r--compiler/rustc_parse/src/errors.rs8
-rw-r--r--compiler/rustc_parse/src/parser/item.rs28
-rw-r--r--compiler/rustc_parse/src/validate_attr.rs1
-rw-r--r--compiler/rustc_parse_format/Cargo.toml2
-rw-r--r--compiler/rustc_passes/messages.ftl6
-rw-r--r--compiler/rustc_passes/src/check_attr.rs60
-rw-r--r--compiler/rustc_passes/src/errors.rs9
-rw-r--r--compiler/rustc_passes/src/stability.rs32
-rw-r--r--compiler/rustc_privacy/src/lib.rs1
-rw-r--r--compiler/rustc_proc_macro/Cargo.toml2
-rw-r--r--compiler/rustc_public/src/unstable/convert/stable/ty.rs3
-rw-r--r--compiler/rustc_resolve/src/build_reduced_graph.rs232
-rw-r--r--compiler/rustc_resolve/src/def_collector.rs4
-rw-r--r--compiler/rustc_resolve/src/diagnostics.rs115
-rw-r--r--compiler/rustc_resolve/src/effective_visibilities.rs9
-rw-r--r--compiler/rustc_resolve/src/ident.rs25
-rw-r--r--compiler/rustc_resolve/src/imports.rs46
-rw-r--r--compiler/rustc_resolve/src/late.rs24
-rw-r--r--compiler/rustc_resolve/src/late/diagnostics.rs50
-rw-r--r--compiler/rustc_resolve/src/lib.rs194
-rw-r--r--compiler/rustc_resolve/src/macros.rs11
-rw-r--r--compiler/rustc_resolve/src/rustdoc.rs10
-rw-r--r--compiler/rustc_session/src/config.rs5
-rw-r--r--compiler/rustc_session/src/options.rs2
-rw-r--r--compiler/rustc_session/src/parse.rs40
-rw-r--r--compiler/rustc_span/src/def_id.rs18
-rw-r--r--compiler/rustc_span/src/symbol.rs3
-rw-r--r--compiler/rustc_symbol_mangling/src/lib.rs2
-rw-r--r--compiler/rustc_target/src/spec/targets/mips64_unknown_linux_muslabi64.rs2
-rw-r--r--compiler/rustc_target/src/spec/targets/mips64el_unknown_linux_muslabi64.rs2
-rw-r--r--compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs11
-rw-r--r--compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs25
-rw-r--r--compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs2
-rw-r--r--compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs2
-rw-r--r--compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs30
-rw-r--r--compiler/rustc_trait_selection/src/errors.rs2
-rw-r--r--compiler/rustc_trait_selection/src/infer.rs4
-rw-r--r--compiler/rustc_trait_selection/src/regions.rs8
-rw-r--r--compiler/rustc_trait_selection/src/solve.rs2
-rw-r--r--compiler/rustc_trait_selection/src/solve/delegate.rs12
-rw-r--r--compiler/rustc_trait_selection/src/solve/fulfill.rs27
-rw-r--r--compiler/rustc_trait_selection/src/traits/auto_trait.rs1
-rw-r--r--compiler/rustc_trait_selection/src/traits/coherence.rs1
-rw-r--r--compiler/rustc_trait_selection/src/traits/dyn_compatibility.rs2
-rw-r--r--compiler/rustc_trait_selection/src/traits/fulfill.rs52
-rw-r--r--compiler/rustc_trait_selection/src/traits/outlives_bounds.rs5
-rw-r--r--compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs7
-rw-r--r--compiler/rustc_trait_selection/src/traits/query/type_op/implied_outlives_bounds.rs1
-rw-r--r--compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs3
-rw-r--r--compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs33
-rw-r--r--compiler/rustc_trait_selection/src/traits/select/confirmation.rs25
-rw-r--r--compiler/rustc_trait_selection/src/traits/select/mod.rs98
-rw-r--r--compiler/rustc_trait_selection/src/traits/util.rs8
-rw-r--r--compiler/rustc_trait_selection/src/traits/wf.rs2
-rw-r--r--compiler/rustc_traits/src/coroutine_witnesses.rs58
-rw-r--r--compiler/rustc_traits/src/normalize_erasing_regions.rs1
-rw-r--r--compiler/rustc_ty_utils/src/opaque_types.rs11
-rw-r--r--compiler/rustc_type_ir/src/elaborate.rs54
-rw-r--r--compiler/rustc_type_ir/src/flags.rs19
-rw-r--r--compiler/rustc_type_ir/src/infer_ctxt.rs37
-rw-r--r--compiler/rustc_type_ir/src/inherent.rs2
-rw-r--r--compiler/rustc_type_ir/src/interner.rs8
-rw-r--r--compiler/rustc_type_ir/src/predicate_kind.rs10
-rw-r--r--compiler/rustc_type_ir/src/ty_kind.rs1
-rw-r--r--compiler/rustc_type_ir/src/visit.rs4
227 files changed, 3222 insertions, 1855 deletions
diff --git a/compiler/rustc_ast/Cargo.toml b/compiler/rustc_ast/Cargo.toml
index 5de2e69072f..155e14a3796 100644
--- a/compiler/rustc_ast/Cargo.toml
+++ b/compiler/rustc_ast/Cargo.toml
@@ -7,7 +7,7 @@ edition = "2024"
 # tidy-alphabetical-start
 bitflags = "2.4.1"
 memchr = "2.7.4"
-rustc-literal-escaper = "0.0.4"
+rustc-literal-escaper = "0.0.5"
 rustc_ast_ir = { path = "../rustc_ast_ir" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_index = { path = "../rustc_index" }
diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index 3c576316f62..8c2b521c560 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -18,7 +18,7 @@
 //! - [`Attribute`]: Metadata associated with item.
 //! - [`UnOp`], [`BinOp`], and [`BinOpKind`]: Unary and binary operators.
 
-use std::borrow::Cow;
+use std::borrow::{Borrow, Cow};
 use std::{cmp, fmt};
 
 pub use GenericArgs::*;
@@ -155,6 +155,59 @@ impl Path {
     }
 }
 
+/// Joins multiple symbols with "::" into a path, e.g. "a::b::c". If the first
+/// segment is `kw::PathRoot` it will be printed as empty, e.g. "::b::c".
+///
+/// The generics on the `path` argument mean it can accept many forms, such as:
+/// - `&[Symbol]`
+/// - `Vec<Symbol>`
+/// - `Vec<&Symbol>`
+/// - `impl Iterator<Item = Symbol>`
+/// - `impl Iterator<Item = &Symbol>`
+///
+/// Panics if `path` is empty or a segment after the first is `kw::PathRoot`.
+pub fn join_path_syms(path: impl IntoIterator<Item = impl Borrow<Symbol>>) -> String {
+    // This is a guess at the needed capacity that works well in practice. It is slightly faster
+    // than (a) starting with an empty string, or (b) computing the exact capacity required.
+    // `8` works well because it's about the right size and jemalloc's size classes are all
+    // multiples of 8.
+    let mut iter = path.into_iter();
+    let len_hint = iter.size_hint().1.unwrap_or(1);
+    let mut s = String::with_capacity(len_hint * 8);
+
+    let first_sym = *iter.next().unwrap().borrow();
+    if first_sym != kw::PathRoot {
+        s.push_str(first_sym.as_str());
+    }
+    for sym in iter {
+        let sym = *sym.borrow();
+        debug_assert_ne!(sym, kw::PathRoot);
+        s.push_str("::");
+        s.push_str(sym.as_str());
+    }
+    s
+}
+
+/// Like `join_path_syms`, but for `Ident`s. This function is necessary because
+/// `Ident::to_string` does more than just print the symbol in the `name` field.
+pub fn join_path_idents(path: impl IntoIterator<Item = impl Borrow<Ident>>) -> String {
+    let mut iter = path.into_iter();
+    let len_hint = iter.size_hint().1.unwrap_or(1);
+    let mut s = String::with_capacity(len_hint * 8);
+
+    let first_ident = *iter.next().unwrap().borrow();
+    if first_ident.name != kw::PathRoot {
+        s.push_str(&first_ident.to_string());
+    }
+    for ident in iter {
+        let ident = *ident.borrow();
+        debug_assert_ne!(ident.name, kw::PathRoot);
+        s.push_str("::");
+        s.push_str(&ident.to_string());
+    }
+    s
+}
+
 /// A segment of a path: an identifier, an optional lifetime, and a set of types.
 ///
 /// E.g., `std`, `String` or `Box<T>`.
@@ -3637,6 +3690,7 @@ impl Default for FnHeader {
 
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct Trait {
+    pub constness: Const,
     pub safety: Safety,
     pub is_auto: IsAuto,
     pub ident: Ident,
diff --git a/compiler/rustc_ast/src/util/literal.rs b/compiler/rustc_ast/src/util/literal.rs
index fa7878873e5..2dfd695d880 100644
--- a/compiler/rustc_ast/src/util/literal.rs
+++ b/compiler/rustc_ast/src/util/literal.rs
@@ -126,11 +126,11 @@ impl LitKind {
             token::CStr => {
                 let s = symbol.as_str();
                 let mut buf = Vec::with_capacity(s.len());
-                unescape_c_str(s, |_span, c| match c {
+                unescape_c_str(s, |_span, res| match res {
                     Ok(MixedUnit::Char(c)) => {
-                        buf.extend_from_slice(c.encode_utf8(&mut [0; 4]).as_bytes())
+                        buf.extend_from_slice(c.get().encode_utf8(&mut [0; 4]).as_bytes())
                     }
-                    Ok(MixedUnit::HighByte(b)) => buf.push(b),
+                    Ok(MixedUnit::HighByte(b)) => buf.push(b.get()),
                     Err(err) => {
                         assert!(!err.is_fatal(), "failed to unescape C string literal")
                     }
diff --git a/compiler/rustc_ast/src/visit.rs b/compiler/rustc_ast/src/visit.rs
index 37fcc0d2167..a344f23c345 100644
--- a/compiler/rustc_ast/src/visit.rs
+++ b/compiler/rustc_ast/src/visit.rs
@@ -738,7 +738,8 @@ macro_rules! common_visitor_and_walkers {
                         try_visit!(vis.visit_ty(self_ty));
                         visit_assoc_items(vis, items, AssocCtxt::Impl { of_trait: of_trait.is_some() })
                     }
-                    ItemKind::Trait(box Trait { safety, is_auto: _, ident, generics, bounds, items }) => {
+                    ItemKind::Trait(box Trait { constness, safety, is_auto: _, ident, generics, bounds, items }) => {
+                        try_visit!(visit_constness(vis, constness));
                         try_visit!(visit_safety(vis, safety));
                         try_visit!(vis.visit_ident(ident));
                         try_visit!(vis.visit_generics(generics));
diff --git a/compiler/rustc_ast_lowering/src/item.rs b/compiler/rustc_ast_lowering/src/item.rs
index 9d40a7386f6..abd70c7517c 100644
--- a/compiler/rustc_ast_lowering/src/item.rs
+++ b/compiler/rustc_ast_lowering/src/item.rs
@@ -417,7 +417,16 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     items: new_impl_items,
                 }))
             }
-            ItemKind::Trait(box Trait { is_auto, safety, ident, generics, bounds, items }) => {
+            ItemKind::Trait(box Trait {
+                constness,
+                is_auto,
+                safety,
+                ident,
+                generics,
+                bounds,
+                items,
+            }) => {
+                let constness = self.lower_constness(*constness);
                 let ident = self.lower_ident(*ident);
                 let (generics, (safety, items, bounds)) = self.lower_generics(
                     generics,
@@ -435,7 +444,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         (safety, items, bounds)
                     },
                 );
-                hir::ItemKind::Trait(*is_auto, safety, ident, generics, bounds, items)
+                hir::ItemKind::Trait(constness, *is_auto, safety, ident, generics, bounds, items)
             }
             ItemKind::TraitAlias(ident, generics, bounds) => {
                 let ident = self.lower_ident(*ident);
diff --git a/compiler/rustc_ast_passes/messages.ftl b/compiler/rustc_ast_passes/messages.ftl
index c5780c957c9..e419154d65d 100644
--- a/compiler/rustc_ast_passes/messages.ftl
+++ b/compiler/rustc_ast_passes/messages.ftl
@@ -240,10 +240,10 @@ ast_passes_static_without_body =
 ast_passes_tilde_const_disallowed = `[const]` is not allowed here
     .closure = closures cannot have `[const]` trait bounds
     .function = this function is not `const`, so it cannot have `[const]` trait bounds
-    .trait = this trait is not a `#[const_trait]`, so it cannot have `[const]` trait bounds
+    .trait = this trait is not `const`, so it cannot have `[const]` trait bounds
     .trait_impl = this impl is not `const`, so it cannot have `[const]` trait bounds
     .impl = inherent impls cannot have `[const]` trait bounds
-    .trait_assoc_ty = associated types in non-`#[const_trait]` traits cannot have `[const]` trait bounds
+    .trait_assoc_ty = associated types in non-`const` traits cannot have `[const]` trait bounds
     .trait_impl_assoc_ty = associated types in non-const impls cannot have `[const]` trait bounds
     .inherent_assoc_ty = inherent associated types cannot have `[const]` trait bounds
     .object = trait objects cannot have `[const]` trait bounds
diff --git a/compiler/rustc_ast_passes/src/ast_validation.rs b/compiler/rustc_ast_passes/src/ast_validation.rs
index 38889d28151..c69250c0305 100644
--- a/compiler/rustc_ast_passes/src/ast_validation.rs
+++ b/compiler/rustc_ast_passes/src/ast_validation.rs
@@ -49,14 +49,14 @@ enum SelfSemantic {
 }
 
 enum TraitOrTraitImpl {
-    Trait { span: Span, constness_span: Option<Span> },
+    Trait { span: Span, constness: Const },
     TraitImpl { constness: Const, polarity: ImplPolarity, trait_ref_span: Span },
 }
 
 impl TraitOrTraitImpl {
     fn constness(&self) -> Option<Span> {
         match self {
-            Self::Trait { constness_span: Some(span), .. }
+            Self::Trait { constness: Const::Yes(span), .. }
             | Self::TraitImpl { constness: Const::Yes(span), .. } => Some(*span),
             _ => None,
         }
@@ -110,15 +110,10 @@ impl<'a> AstValidator<'a> {
         self.outer_trait_or_trait_impl = old;
     }
 
-    fn with_in_trait(
-        &mut self,
-        span: Span,
-        constness_span: Option<Span>,
-        f: impl FnOnce(&mut Self),
-    ) {
+    fn with_in_trait(&mut self, span: Span, constness: Const, f: impl FnOnce(&mut Self)) {
         let old = mem::replace(
             &mut self.outer_trait_or_trait_impl,
-            Some(TraitOrTraitImpl::Trait { span, constness_span }),
+            Some(TraitOrTraitImpl::Trait { span, constness }),
         );
         f(self);
         self.outer_trait_or_trait_impl = old;
@@ -273,7 +268,7 @@ impl<'a> AstValidator<'a> {
         };
 
         let make_trait_const_sugg = if const_trait_impl
-            && let TraitOrTraitImpl::Trait { span, constness_span: None } = parent
+            && let TraitOrTraitImpl::Trait { span, constness: ast::Const::No } = parent
         {
             Some(span.shrink_to_lo())
         } else {
@@ -1131,10 +1126,23 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                 }
                 visit::walk_item(self, item)
             }
-            ItemKind::Trait(box Trait { is_auto, generics, ident, bounds, items, .. }) => {
+            ItemKind::Trait(box Trait {
+                constness,
+                is_auto,
+                generics,
+                ident,
+                bounds,
+                items,
+                ..
+            }) => {
                 self.visit_attrs_vis_ident(&item.attrs, &item.vis, ident);
-                let is_const_trait =
+                // FIXME(const_trait_impl) remove this
+                let alt_const_trait_span =
                     attr::find_by_name(&item.attrs, sym::const_trait).map(|attr| attr.span);
+                let constness = match (*constness, alt_const_trait_span) {
+                    (Const::Yes(span), _) | (Const::No, Some(span)) => Const::Yes(span),
+                    (Const::No, None) => Const::No,
+                };
                 if *is_auto == IsAuto::Yes {
                     // Auto traits cannot have generics, super traits nor contain items.
                     self.deny_generic_params(generics, ident.span);
@@ -1145,13 +1153,13 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
 
                 // Equivalent of `visit::walk_item` for `ItemKind::Trait` that inserts a bound
                 // context for the supertraits.
-                let disallowed =
-                    is_const_trait.is_none().then(|| TildeConstReason::Trait { span: item.span });
+                let disallowed = matches!(constness, ast::Const::No)
+                    .then(|| TildeConstReason::Trait { span: item.span });
                 self.with_tilde_const(disallowed, |this| {
                     this.visit_generics(generics);
                     walk_list!(this, visit_param_bound, bounds, BoundKind::SuperTraits)
                 });
-                self.with_in_trait(item.span, is_const_trait, |this| {
+                self.with_in_trait(item.span, constness, |this| {
                     walk_list!(this, visit_assoc_item, items, AssocCtxt::Trait);
                 });
             }
diff --git a/compiler/rustc_ast_passes/src/errors.rs b/compiler/rustc_ast_passes/src/errors.rs
index 3b2730d4ff9..c1ebd025c7a 100644
--- a/compiler/rustc_ast_passes/src/errors.rs
+++ b/compiler/rustc_ast_passes/src/errors.rs
@@ -590,7 +590,7 @@ pub(crate) struct ConstBoundTraitObject {
 }
 
 // FIXME(const_trait_impl): Consider making the note/reason the message of the diagnostic.
-// FIXME(const_trait_impl): Provide structured suggestions (e.g., add `const` / `#[const_trait]` here).
+// FIXME(const_trait_impl): Provide structured suggestions (e.g., add `const` here).
 #[derive(Diagnostic)]
 #[diag(ast_passes_tilde_const_disallowed)]
 pub(crate) struct TildeConstDisallowed {
diff --git a/compiler/rustc_ast_pretty/src/pprust/state/item.rs b/compiler/rustc_ast_pretty/src/pprust/state/item.rs
index 6c442553976..11c97a552c6 100644
--- a/compiler/rustc_ast_pretty/src/pprust/state/item.rs
+++ b/compiler/rustc_ast_pretty/src/pprust/state/item.rs
@@ -357,6 +357,7 @@ impl<'a> State<'a> {
                 self.bclose(item.span, empty, cb);
             }
             ast::ItemKind::Trait(box ast::Trait {
+                constness,
                 safety,
                 is_auto,
                 ident,
@@ -366,6 +367,7 @@ impl<'a> State<'a> {
             }) => {
                 let (cb, ib) = self.head("");
                 self.print_visibility(&item.vis);
+                self.print_constness(*constness);
                 self.print_safety(*safety);
                 self.print_is_auto(*is_auto);
                 self.word_nbsp("trait");
diff --git a/compiler/rustc_attr_data_structures/src/attributes.rs b/compiler/rustc_attr_data_structures/src/attributes.rs
index 3dedeb1b372..3157b18b635 100644
--- a/compiler/rustc_attr_data_structures/src/attributes.rs
+++ b/compiler/rustc_attr_data_structures/src/attributes.rs
@@ -110,6 +110,22 @@ pub enum DeprecatedSince {
     Err,
 }
 
+#[derive(
+    Copy,
+    Debug,
+    Eq,
+    PartialEq,
+    Encodable,
+    Decodable,
+    Clone,
+    HashStable_Generic,
+    PrintAttribute
+)]
+pub enum CoverageStatus {
+    On,
+    Off,
+}
+
 impl Deprecation {
     /// Whether an item marked with #[deprecated(since = "X")] is currently
     /// deprecated (i.e., whether X is not greater than the current rustc
@@ -274,6 +290,9 @@ pub enum AttributeKind {
     /// Represents `#[const_trait]`.
     ConstTrait(Span),
 
+    /// Represents `#[coverage]`.
+    Coverage(Span, CoverageStatus),
+
     ///Represents `#[rustc_deny_explicit_impl]`.
     DenyExplicitImpl(Span),
 
@@ -420,6 +439,9 @@ pub enum AttributeKind {
     /// Represents `#[rustc_unsafe_specialization_marker]`.
     UnsafeSpecializationMarker(Span),
 
+    /// Represents `#[unstable_feature_bound]`.
+    UnstableFeatureBound(ThinVec<(Symbol, Span)>),
+
     /// Represents `#[used]`
     Used { used_by: UsedBy, span: Span },
     // tidy-alphabetical-end
diff --git a/compiler/rustc_attr_data_structures/src/encode_cross_crate.rs b/compiler/rustc_attr_data_structures/src/encode_cross_crate.rs
index 3e2dc0a15b2..8a3eb2ac845 100644
--- a/compiler/rustc_attr_data_structures/src/encode_cross_crate.rs
+++ b/compiler/rustc_attr_data_structures/src/encode_cross_crate.rs
@@ -28,6 +28,7 @@ impl AttributeKind {
             ConstStability { .. } => Yes,
             ConstStabilityIndirect => No,
             ConstTrait(..) => No,
+            Coverage(..) => No,
             DenyExplicitImpl(..) => No,
             Deprecation { .. } => Yes,
             DoNotImplementViaObject(..) => No,
@@ -71,6 +72,7 @@ impl AttributeKind {
             TrackCaller(..) => Yes,
             TypeConst(..) => Yes,
             UnsafeSpecializationMarker(..) => No,
+            UnstableFeatureBound(..) => No,
             Used { .. } => No,
             // tidy-alphabetical-end
         }
diff --git a/compiler/rustc_attr_parsing/messages.ftl b/compiler/rustc_attr_parsing/messages.ftl
index 8d0ead63a8d..35ff48cb5f2 100644
--- a/compiler/rustc_attr_parsing/messages.ftl
+++ b/compiler/rustc_attr_parsing/messages.ftl
@@ -136,6 +136,9 @@ attr_parsing_unrecognized_repr_hint =
 attr_parsing_unstable_cfg_target_compact =
     compact `cfg(target(..))` is experimental and subject to change
 
+attr_parsing_unstable_feature_bound_incompatible_stability = Item annotated with `#[unstable_feature_bound]` should not be stable
+    .help = If this item is meant to be stable, do not use any functions annotated with `#[unstable_feature_bound]`. Otherwise, mark this item as unstable with `#[unstable]`
+
 attr_parsing_unsupported_literal_cfg_boolean =
     literal in `cfg` predicate value must be a boolean
 attr_parsing_unsupported_literal_cfg_string =
diff --git a/compiler/rustc_attr_parsing/src/attributes/allow_unstable.rs b/compiler/rustc_attr_parsing/src/attributes/allow_unstable.rs
index 1c51c3eee4e..a6bd2306ec5 100644
--- a/compiler/rustc_attr_parsing/src/attributes/allow_unstable.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/allow_unstable.rs
@@ -27,6 +27,26 @@ impl<S: Stage> CombineAttributeParser<S> for AllowInternalUnstableParser {
     }
 }
 
+pub(crate) struct UnstableFeatureBoundParser;
+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, ...");
+
+    fn extend<'c>(
+        cx: &'c mut AcceptContext<'_, '_, S>,
+        args: &'c ArgParser<'_>,
+    ) -> impl IntoIterator<Item = Self::Item> {
+        if !cx.features().staged_api() {
+            cx.emit_err(session_diagnostics::StabilityOutsideStd { span: cx.attr_span });
+        }
+        parse_unstable(cx, args, <Self as CombineAttributeParser<S>>::PATH[0])
+            .into_iter()
+            .zip(iter::repeat(cx.attr_span))
+    }
+}
+
 pub(crate) struct AllowConstFnUnstableParser;
 impl<S: Stage> CombineAttributeParser<S> for AllowConstFnUnstableParser {
     const PATH: &[Symbol] = &[sym::rustc_allow_const_fn_unstable];
diff --git a/compiler/rustc_attr_parsing/src/attributes/cfg.rs b/compiler/rustc_attr_parsing/src/attributes/cfg.rs
index a56855b3bd3..6373cf6e08a 100644
--- a/compiler/rustc_attr_parsing/src/attributes/cfg.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/cfg.rs
@@ -9,7 +9,7 @@ use rustc_session::parse::feature_err;
 use rustc_span::{Span, Symbol, sym};
 use thin_vec::ThinVec;
 
-use crate::context::{AcceptContext, Stage};
+use crate::context::{AcceptContext, ShouldEmit, Stage};
 use crate::parser::{ArgParser, MetaItemListParser, MetaItemOrLitParser, NameValueParser};
 use crate::{
     CfgMatchesLintEmitter, fluent_generated, parse_version, session_diagnostics, try_gate_cfg,
@@ -90,7 +90,7 @@ fn parse_cfg_entry_version<S: Stage>(
     list: &MetaItemListParser<'_>,
     meta_span: Span,
 ) -> Option<CfgEntry> {
-    try_gate_cfg(sym::version, meta_span, cx.sess(), Some(cx.features()));
+    try_gate_cfg(sym::version, meta_span, cx.sess(), cx.features_option());
     let Some(version) = list.single() else {
         cx.emit_err(session_diagnostics::ExpectedSingleVersionLiteral { span: list.span });
         return None;
@@ -119,7 +119,9 @@ fn parse_cfg_entry_target<S: Stage>(
     list: &MetaItemListParser<'_>,
     meta_span: Span,
 ) -> Option<CfgEntry> {
-    if !cx.features().cfg_target_compact() {
+    if let Some(features) = cx.features_option()
+        && !features.cfg_target_compact()
+    {
         feature_err(
             cx.sess(),
             sym::cfg_target_compact,
@@ -186,12 +188,13 @@ pub fn eval_config_entry(
     cfg_entry: &CfgEntry,
     id: NodeId,
     features: Option<&Features>,
+    emit_lints: ShouldEmit,
 ) -> EvalConfigResult {
     match cfg_entry {
         CfgEntry::All(subs, ..) => {
             let mut all = None;
             for sub in subs {
-                let res = eval_config_entry(sess, sub, id, features);
+                let res = eval_config_entry(sess, sub, id, features, emit_lints);
                 // We cannot short-circuit because `eval_config_entry` emits some lints
                 if !res.as_bool() {
                     all.get_or_insert(res);
@@ -202,7 +205,7 @@ pub fn eval_config_entry(
         CfgEntry::Any(subs, span) => {
             let mut any = None;
             for sub in subs {
-                let res = eval_config_entry(sess, sub, id, features);
+                let res = eval_config_entry(sess, sub, id, features, emit_lints);
                 // We cannot short-circuit because `eval_config_entry` emits some lints
                 if res.as_bool() {
                     any.get_or_insert(res);
@@ -214,7 +217,7 @@ pub fn eval_config_entry(
             })
         }
         CfgEntry::Not(sub, span) => {
-            if eval_config_entry(sess, sub, id, features).as_bool() {
+            if eval_config_entry(sess, sub, id, features, emit_lints).as_bool() {
                 EvalConfigResult::False { reason: cfg_entry.clone(), reason_span: *span }
             } else {
                 EvalConfigResult::True
@@ -228,24 +231,28 @@ pub fn eval_config_entry(
             }
         }
         CfgEntry::NameValue { name, name_span, value, span } => {
-            match sess.psess.check_config.expecteds.get(name) {
-                Some(ExpectedValues::Some(values)) if !values.contains(&value.map(|(v, _)| v)) => {
-                    id.emit_span_lint(
-                        sess,
-                        UNEXPECTED_CFGS,
-                        *span,
-                        BuiltinLintDiag::UnexpectedCfgValue((*name, *name_span), *value),
-                    );
+            if let ShouldEmit::ErrorsAndLints = emit_lints {
+                match sess.psess.check_config.expecteds.get(name) {
+                    Some(ExpectedValues::Some(values))
+                        if !values.contains(&value.map(|(v, _)| v)) =>
+                    {
+                        id.emit_span_lint(
+                            sess,
+                            UNEXPECTED_CFGS,
+                            *span,
+                            BuiltinLintDiag::UnexpectedCfgValue((*name, *name_span), *value),
+                        );
+                    }
+                    None if sess.psess.check_config.exhaustive_names => {
+                        id.emit_span_lint(
+                            sess,
+                            UNEXPECTED_CFGS,
+                            *span,
+                            BuiltinLintDiag::UnexpectedCfgName((*name, *name_span), *value),
+                        );
+                    }
+                    _ => { /* not unexpected */ }
                 }
-                None if sess.psess.check_config.exhaustive_names => {
-                    id.emit_span_lint(
-                        sess,
-                        UNEXPECTED_CFGS,
-                        *span,
-                        BuiltinLintDiag::UnexpectedCfgName((*name, *name_span), *value),
-                    );
-                }
-                _ => { /* not unexpected */ }
             }
 
             if sess.psess.config.contains(&(*name, value.map(|(v, _)| v))) {
diff --git a/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs b/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
index 34d9b048348..3e542771d58 100644
--- a/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/codegen_attrs.rs
@@ -1,4 +1,4 @@
-use rustc_attr_data_structures::{AttributeKind, OptimizeAttr, UsedBy};
+use rustc_attr_data_structures::{AttributeKind, CoverageStatus, OptimizeAttr, UsedBy};
 use rustc_feature::{AttributeTemplate, template};
 use rustc_session::parse::feature_err;
 use rustc_span::{Span, Symbol, sym};
@@ -52,6 +52,45 @@ impl<S: Stage> NoArgsAttributeParser<S> for ColdParser {
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::Cold;
 }
 
+pub(crate) struct CoverageParser;
+
+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 TEMPLATE: AttributeTemplate = template!(OneOf: &[sym::off, sym::on]);
+
+    fn convert(cx: &mut AcceptContext<'_, '_, S>, args: &ArgParser<'_>) -> Option<AttributeKind> {
+        let Some(args) = args.list() else {
+            cx.expected_specific_argument_and_list(cx.attr_span, vec!["on", "off"]);
+            return None;
+        };
+
+        let Some(arg) = args.single() else {
+            cx.expected_single_argument(args.span);
+            return None;
+        };
+
+        let fail_incorrect_argument = |span| cx.expected_specific_argument(span, vec!["on", "off"]);
+
+        let Some(arg) = arg.meta_item() else {
+            fail_incorrect_argument(args.span);
+            return None;
+        };
+
+        let status = match arg.path().word_sym() {
+            Some(sym::off) => CoverageStatus::Off,
+            Some(sym::on) => CoverageStatus::On,
+            None | Some(_) => {
+                fail_incorrect_argument(arg.span());
+                return None;
+            }
+        };
+
+        Some(AttributeKind::Coverage(cx.attr_span, status))
+    }
+}
+
 pub(crate) struct ExportNameParser;
 
 impl<S: Stage> SingleAttributeParser<S> for ExportNameParser {
diff --git a/compiler/rustc_attr_parsing/src/attributes/stability.rs b/compiler/rustc_attr_parsing/src/attributes/stability.rs
index 6bccd0042a8..8f405e5aad9 100644
--- a/compiler/rustc_attr_parsing/src/attributes/stability.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/stability.rs
@@ -98,6 +98,16 @@ impl<S: Stage> AttributeParser<S> for StabilityParser {
             }
         }
 
+        if let Some((Stability { level: StabilityLevel::Stable { .. }, .. }, _)) = self.stability {
+            for other_attr in cx.all_attrs {
+                if other_attr.word_is(sym::unstable_feature_bound) {
+                    cx.emit_err(session_diagnostics::UnstableFeatureBoundIncompatibleStability {
+                        span: cx.target_span,
+                    });
+                }
+            }
+        }
+
         let (stability, span) = self.stability?;
 
         Some(AttributeKind::Stability { stability, span })
diff --git a/compiler/rustc_attr_parsing/src/attributes/traits.rs b/compiler/rustc_attr_parsing/src/attributes/traits.rs
index d5e088effd5..e69a533699b 100644
--- a/compiler/rustc_attr_parsing/src/attributes/traits.rs
+++ b/compiler/rustc_attr_parsing/src/attributes/traits.rs
@@ -91,6 +91,7 @@ impl<S: Stage> NoArgsAttributeParser<S> for DoNotImplementViaObjectParser {
     const CREATE: fn(Span) -> AttributeKind = AttributeKind::DoNotImplementViaObject;
 }
 
+// FIXME(const_trait_impl): remove this
 // Const traits
 
 pub(crate) struct ConstTraitParser;
diff --git a/compiler/rustc_attr_parsing/src/context.rs b/compiler/rustc_attr_parsing/src/context.rs
index 567341d1517..4d692d9562c 100644
--- a/compiler/rustc_attr_parsing/src/context.rs
+++ b/compiler/rustc_attr_parsing/src/context.rs
@@ -13,10 +13,13 @@ use rustc_hir::{AttrArgs, AttrItem, AttrPath, Attribute, HashIgnoredAttrId, HirI
 use rustc_session::Session;
 use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span, Symbol, sym};
 
-use crate::attributes::allow_unstable::{AllowConstFnUnstableParser, AllowInternalUnstableParser};
+use crate::attributes::allow_unstable::{
+    AllowConstFnUnstableParser, AllowInternalUnstableParser, UnstableFeatureBoundParser,
+};
 use crate::attributes::codegen_attrs::{
-    ColdParser, ExportNameParser, NakedParser, NoMangleParser, OmitGdbPrettyPrinterSectionParser,
-    OptimizeParser, TargetFeatureParser, TrackCallerParser, UsedParser,
+    ColdParser, CoverageParser, ExportNameParser, NakedParser, NoMangleParser,
+    OmitGdbPrettyPrinterSectionParser, OptimizeParser, TargetFeatureParser, TrackCallerParser,
+    UsedParser,
 };
 use crate::attributes::confusables::ConfusablesParser;
 use crate::attributes::deprecation::DeprecationParser;
@@ -133,9 +136,11 @@ attribute_parsers!(
         Combine<AllowInternalUnstableParser>,
         Combine<ReprParser>,
         Combine<TargetFeatureParser>,
+        Combine<UnstableFeatureBoundParser>,
         // tidy-alphabetical-end
 
         // tidy-alphabetical-start
+        Single<CoverageParser>,
         Single<DeprecationParser>,
         Single<DummyParser>,
         Single<ExportNameParser>,
@@ -223,7 +228,7 @@ impl Stage for Early {
         sess: &'sess Session,
         diag: impl for<'x> Diagnostic<'x>,
     ) -> ErrorGuaranteed {
-        if self.emit_errors {
+        if self.emit_errors.should_emit() {
             sess.dcx().emit_err(diag)
         } else {
             sess.dcx().create_err(diag).delay_as_bug()
@@ -254,7 +259,7 @@ pub struct Early {
     /// Whether to emit errors or delay them as a bug
     /// For most attributes, the attribute will be parsed again in the `Late` stage and in this case the errors should be delayed
     /// But for some, such as `cfg`, the attribute will be removed before the `Late` stage so errors must be emitted
-    pub emit_errors: bool,
+    pub emit_errors: ShouldEmit,
 }
 /// used when parsing attributes during ast lowering
 pub struct Late;
@@ -449,6 +454,25 @@ impl<'f, 'sess: 'f, S: Stage> AcceptContext<'f, 'sess, S> {
             reason: AttributeParseErrorReason::ExpectedSpecificArgument {
                 possibilities,
                 strings: false,
+                list: false,
+            },
+        })
+    }
+
+    pub(crate) fn expected_specific_argument_and_list(
+        &self,
+        span: Span,
+        possibilities: Vec<&'static str>,
+    ) -> ErrorGuaranteed {
+        self.emit_err(AttributeParseError {
+            span,
+            attr_span: self.attr_span,
+            template: self.template.clone(),
+            attribute: self.attr_path.clone(),
+            reason: AttributeParseErrorReason::ExpectedSpecificArgument {
+                possibilities,
+                strings: false,
+                list: true,
             },
         })
     }
@@ -466,6 +490,7 @@ impl<'f, 'sess: 'f, S: Stage> AcceptContext<'f, 'sess, S> {
             reason: AttributeParseErrorReason::ExpectedSpecificArgument {
                 possibilities,
                 strings: true,
+                list: false,
             },
         })
     }
@@ -555,6 +580,25 @@ pub enum OmitDoc {
     Skip,
 }
 
+#[derive(Copy, Clone)]
+pub enum ShouldEmit {
+    /// The operation will emit errors and lints.
+    /// This is usually what you need.
+    ErrorsAndLints,
+    /// The operation will emit *not* errors and lints.
+    /// Use this if you are *sure* that this operation will be called at a different time with `ShouldEmit::Emit`.
+    Nothing,
+}
+
+impl ShouldEmit {
+    pub fn should_emit(&self) -> bool {
+        match self {
+            ShouldEmit::ErrorsAndLints => true,
+            ShouldEmit::Nothing => false,
+        }
+    }
+}
+
 /// 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> {
@@ -597,7 +641,7 @@ impl<'sess> AttributeParser<'sess, Early> {
             tools: Vec::new(),
             parse_only: Some(sym),
             sess,
-            stage: Early { emit_errors: false },
+            stage: Early { emit_errors: ShouldEmit::Nothing },
         };
         let mut parsed = p.parse_attribute_list(
             attrs,
@@ -620,7 +664,7 @@ impl<'sess> AttributeParser<'sess, Early> {
         target_span: Span,
         target_node_id: NodeId,
         features: Option<&'sess Features>,
-        emit_errors: bool,
+        emit_errors: ShouldEmit,
         parse_fn: fn(cx: &mut AcceptContext<'_, '_, Early>, item: &ArgParser<'_>) -> T,
         template: &AttributeTemplate,
     ) -> T {
diff --git a/compiler/rustc_attr_parsing/src/lib.rs b/compiler/rustc_attr_parsing/src/lib.rs
index 2102a26108b..dc54cb6b840 100644
--- a/compiler/rustc_attr_parsing/src/lib.rs
+++ b/compiler/rustc_attr_parsing/src/lib.rs
@@ -95,7 +95,7 @@ pub use attributes::cfg_old::*;
 pub use attributes::util::{
     find_crate_name, is_builtin_attr, is_doc_alias_attrs_contain_symbol, parse_version,
 };
-pub use context::{AttributeParser, Early, Late, OmitDoc};
+pub use context::{AttributeParser, Early, Late, OmitDoc, ShouldEmit};
 pub use lints::emit_attribute_lint;
 
 rustc_fluent_macro::fluent_messages! { "../messages.ftl" }
diff --git a/compiler/rustc_attr_parsing/src/session_diagnostics.rs b/compiler/rustc_attr_parsing/src/session_diagnostics.rs
index 97bf3d1c549..9a400e0fe10 100644
--- a/compiler/rustc_attr_parsing/src/session_diagnostics.rs
+++ b/compiler/rustc_attr_parsing/src/session_diagnostics.rs
@@ -504,6 +504,14 @@ pub(crate) struct UnrecognizedReprHint {
 }
 
 #[derive(Diagnostic)]
+#[diag(attr_parsing_unstable_feature_bound_incompatible_stability)]
+#[help]
+pub(crate) struct UnstableFeatureBoundIncompatibleStability {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
 #[diag(attr_parsing_naked_functions_incompatible_attribute, code = E0736)]
 pub(crate) struct NakedFunctionIncompatibleAttribute {
     #[primary_span]
@@ -525,7 +533,9 @@ pub(crate) struct LinkOrdinalOutOfRange {
 
 pub(crate) enum AttributeParseErrorReason {
     ExpectedNoArgs,
-    ExpectedStringLiteral { byte_string: Option<Span> },
+    ExpectedStringLiteral {
+        byte_string: Option<Span>,
+    },
     ExpectedIntegerLiteral,
     ExpectedAtLeastOneArgument,
     ExpectedSingleArgument,
@@ -533,7 +543,12 @@ pub(crate) enum AttributeParseErrorReason {
     UnexpectedLiteral,
     ExpectedNameValue(Option<Symbol>),
     DuplicateKey(Symbol),
-    ExpectedSpecificArgument { possibilities: Vec<&'static str>, strings: bool },
+    ExpectedSpecificArgument {
+        possibilities: Vec<&'static str>,
+        strings: bool,
+        /// Should we tell the user to write a list when they didn't?
+        list: bool,
+    },
 }
 
 pub(crate) struct AttributeParseError {
@@ -607,7 +622,11 @@ impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for AttributeParseError {
                     format!("expected this to be of the form `{name} = \"...\"`"),
                 );
             }
-            AttributeParseErrorReason::ExpectedSpecificArgument { possibilities, strings } => {
+            AttributeParseErrorReason::ExpectedSpecificArgument {
+                possibilities,
+                strings,
+                list: false,
+            } => {
                 let quote = if strings { '"' } else { '`' };
                 match possibilities.as_slice() {
                     &[] => {}
@@ -633,6 +652,38 @@ impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for AttributeParseError {
                     }
                 }
             }
+            AttributeParseErrorReason::ExpectedSpecificArgument {
+                possibilities,
+                strings,
+                list: true,
+            } => {
+                let quote = if strings { '"' } else { '`' };
+                match possibilities.as_slice() {
+                    &[] => {}
+                    &[x] => {
+                        diag.span_label(
+                            self.span,
+                            format!(
+                                "this attribute is only valid with {quote}{x}{quote} as an argument"
+                            ),
+                        );
+                    }
+                    [first, second] => {
+                        diag.span_label(self.span, format!("this attribute is only valid with either {quote}{first}{quote} or {quote}{second}{quote} as an argument"));
+                    }
+                    [first @ .., second_to_last, last] => {
+                        let mut res = String::new();
+                        for i in first {
+                            res.push_str(&format!("{quote}{i}{quote}, "));
+                        }
+                        res.push_str(&format!(
+                            "{quote}{second_to_last}{quote} or {quote}{last}{quote}"
+                        ));
+
+                        diag.span_label(self.span, format!("this attribute is only valid with one of the following arguments: {res}"));
+                    }
+                }
+            }
         }
 
         let suggestions = self.template.suggestions(false, &name);
diff --git a/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs b/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs
index ca636a8c999..9bb96b94506 100644
--- a/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs
+++ b/compiler/rustc_borrowck/src/type_check/constraint_conversion.rs
@@ -1,3 +1,4 @@
+use rustc_data_structures::fx::FxHashSet;
 use rustc_hir::def_id::LocalDefId;
 use rustc_infer::infer::canonical::QueryRegionConstraints;
 use rustc_infer::infer::outlives::env::RegionBoundPairs;
@@ -7,7 +8,7 @@ use rustc_infer::infer::{InferCtxt, SubregionOrigin};
 use rustc_infer::traits::query::type_op::DeeplyNormalize;
 use rustc_middle::bug;
 use rustc_middle::ty::{
-    self, GenericArgKind, Ty, TyCtxt, TypeFoldable, TypeVisitableExt, fold_regions,
+    self, GenericArgKind, Ty, TyCtxt, TypeFoldable, TypeVisitableExt, elaborate, fold_regions,
 };
 use rustc_span::Span;
 use rustc_trait_selection::traits::query::type_op::{TypeOp, TypeOpOutput};
@@ -70,10 +71,12 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
 
     #[instrument(skip(self), level = "debug")]
     pub(super) fn convert_all(&mut self, query_constraints: &QueryRegionConstraints<'tcx>) {
-        let QueryRegionConstraints { outlives } = query_constraints;
+        let QueryRegionConstraints { outlives, assumptions } = query_constraints;
+        let assumptions =
+            elaborate::elaborate_outlives_assumptions(self.infcx.tcx, assumptions.iter().copied());
 
         for &(predicate, constraint_category) in outlives {
-            self.convert(predicate, constraint_category);
+            self.convert(predicate, constraint_category, &assumptions);
         }
     }
 
@@ -112,15 +115,20 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
 
             self.category = outlives_requirement.category;
             self.span = outlives_requirement.blame_span;
-            self.convert(ty::OutlivesPredicate(subject, outlived_region), self.category);
+            self.convert(
+                ty::OutlivesPredicate(subject, outlived_region),
+                self.category,
+                &Default::default(),
+            );
         }
         (self.category, self.span, self.from_closure) = backup;
     }
 
     fn convert(
         &mut self,
-        predicate: ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>,
+        predicate: ty::ArgOutlivesPredicate<'tcx>,
         constraint_category: ConstraintCategory<'tcx>,
+        higher_ranked_assumptions: &FxHashSet<ty::ArgOutlivesPredicate<'tcx>>,
     ) {
         let tcx = self.infcx.tcx;
         debug!("generate: constraints at: {:#?}", self.locations);
@@ -150,7 +158,15 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
             }
 
             let mut next_outlives_predicates = vec![];
-            for (ty::OutlivesPredicate(k1, r2), constraint_category) in outlives_predicates {
+            for (pred, constraint_category) in outlives_predicates {
+                // Constraint is implied by a coroutine's well-formedness.
+                if self.infcx.tcx.sess.opts.unstable_opts.higher_ranked_assumptions
+                    && higher_ranked_assumptions.contains(&pred)
+                {
+                    continue;
+                }
+
+                let ty::OutlivesPredicate(k1, r2) = pred;
                 match k1.kind() {
                     GenericArgKind::Lifetime(r1) => {
                         let r1_vid = self.to_region_vid(r1);
@@ -266,14 +282,15 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
         &self,
         ty: Ty<'tcx>,
         next_outlives_predicates: &mut Vec<(
-            ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>,
+            ty::ArgOutlivesPredicate<'tcx>,
             ConstraintCategory<'tcx>,
         )>,
     ) -> Ty<'tcx> {
         match self.param_env.and(DeeplyNormalize { value: ty }).fully_perform(self.infcx, self.span)
         {
             Ok(TypeOpOutput { output: ty, constraints, .. }) => {
-                if let Some(QueryRegionConstraints { outlives }) = constraints {
+                // FIXME(higher_ranked_auto): What should we do with the assumptions here?
+                if let Some(QueryRegionConstraints { outlives, assumptions: _ }) = constraints {
                     next_outlives_predicates.extend(outlives.iter().copied());
                 }
                 ty
diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index f877e5eaadb..d500088c259 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -131,6 +131,11 @@ pub(crate) fn type_check<'tcx>(
         pre_obligations.is_empty(),
         "there should be no incoming region obligations = {pre_obligations:#?}",
     );
+    let pre_assumptions = infcx.take_registered_region_assumptions();
+    assert!(
+        pre_assumptions.is_empty(),
+        "there should be no incoming region assumptions = {pre_assumptions:#?}",
+    );
 
     debug!(?normalized_inputs_and_output);
 
diff --git a/compiler/rustc_builtin_macros/src/deriving/bounds.rs b/compiler/rustc_builtin_macros/src/deriving/bounds.rs
index a98e9c6d1c7..dd8f0e46a0e 100644
--- a/compiler/rustc_builtin_macros/src/deriving/bounds.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/bounds.rs
@@ -23,6 +23,7 @@ pub(crate) fn expand_deriving_copy(
         methods: Vec::new(),
         associated_types: Vec::new(),
         is_const,
+        is_staged_api_crate: cx.ecfg.features.staged_api(),
     };
 
     trait_def.expand(cx, mitem, item, push);
@@ -46,6 +47,7 @@ pub(crate) fn expand_deriving_const_param_ty(
         methods: Vec::new(),
         associated_types: Vec::new(),
         is_const,
+        is_staged_api_crate: cx.ecfg.features.staged_api(),
     };
 
     trait_def.expand(cx, mitem, item, push);
@@ -60,6 +62,7 @@ pub(crate) fn expand_deriving_const_param_ty(
         methods: Vec::new(),
         associated_types: Vec::new(),
         is_const,
+        is_staged_api_crate: cx.ecfg.features.staged_api(),
     };
 
     trait_def.expand(cx, mitem, item, push);
@@ -83,6 +86,7 @@ pub(crate) fn expand_deriving_unsized_const_param_ty(
         methods: Vec::new(),
         associated_types: Vec::new(),
         is_const,
+        is_staged_api_crate: cx.ecfg.features.staged_api(),
     };
 
     trait_def.expand(cx, mitem, item, push);
diff --git a/compiler/rustc_builtin_macros/src/deriving/clone.rs b/compiler/rustc_builtin_macros/src/deriving/clone.rs
index 69f8c273797..3c78f53c5cb 100644
--- a/compiler/rustc_builtin_macros/src/deriving/clone.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/clone.rs
@@ -87,6 +87,7 @@ pub(crate) fn expand_deriving_clone(
         }],
         associated_types: Vec::new(),
         is_const,
+        is_staged_api_crate: cx.ecfg.features.staged_api(),
     };
 
     trait_def.expand_ext(cx, mitem, item, push, is_simple)
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs
index eca79e4dc48..29d531219a6 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs
@@ -43,6 +43,7 @@ pub(crate) fn expand_deriving_eq(
         }],
         associated_types: Vec::new(),
         is_const,
+        is_staged_api_crate: cx.ecfg.features.staged_api(),
     };
     trait_def.expand_ext(cx, mitem, item, push, true)
 }
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
index 1ed44c20bc6..0e1ecf3118a 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
@@ -34,6 +34,7 @@ pub(crate) fn expand_deriving_ord(
         }],
         associated_types: Vec::new(),
         is_const,
+        is_staged_api_crate: cx.ecfg.features.staged_api(),
     };
 
     trait_def.expand(cx, mitem, item, push)
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 b1d950b8d89..990835fa277 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
@@ -30,6 +30,7 @@ pub(crate) fn expand_deriving_partial_eq(
         methods: Vec::new(),
         associated_types: Vec::new(),
         is_const: false,
+        is_staged_api_crate: cx.ecfg.features.staged_api(),
     };
     structural_trait_def.expand(cx, mitem, item, push);
 
@@ -58,6 +59,7 @@ pub(crate) fn expand_deriving_partial_eq(
         methods,
         associated_types: Vec::new(),
         is_const,
+        is_staged_api_crate: cx.ecfg.features.staged_api(),
     };
     trait_def.expand(cx, mitem, item, push)
 }
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
index 0a076dd670b..f5d262ece36 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
@@ -64,6 +64,7 @@ pub(crate) fn expand_deriving_partial_ord(
         methods: vec![partial_cmp_def],
         associated_types: Vec::new(),
         is_const,
+        is_staged_api_crate: cx.ecfg.features.staged_api(),
     };
     trait_def.expand(cx, mitem, item, push)
 }
diff --git a/compiler/rustc_builtin_macros/src/deriving/debug.rs b/compiler/rustc_builtin_macros/src/deriving/debug.rs
index 8ab21986e68..1d63ce7d5fd 100644
--- a/compiler/rustc_builtin_macros/src/deriving/debug.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/debug.rs
@@ -41,6 +41,7 @@ pub(crate) fn expand_deriving_debug(
         }],
         associated_types: Vec::new(),
         is_const,
+        is_staged_api_crate: cx.ecfg.features.staged_api(),
     };
     trait_def.expand(cx, mitem, item, push)
 }
diff --git a/compiler/rustc_builtin_macros/src/deriving/default.rs b/compiler/rustc_builtin_macros/src/deriving/default.rs
index 1fe567e23f4..b4e2d27fed3 100644
--- a/compiler/rustc_builtin_macros/src/deriving/default.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/default.rs
@@ -51,6 +51,7 @@ pub(crate) fn expand_deriving_default(
         }],
         associated_types: Vec::new(),
         is_const,
+        is_staged_api_crate: cx.ecfg.features.staged_api(),
     };
     trait_def.expand(cx, mitem, item, push)
 }
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
index c55a9e73e38..b24e5563761 100644
--- a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@@ -181,9 +181,11 @@ 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::{
-    self as ast, AnonConst, BindingMode, ByRef, EnumDef, Expr, GenericArg, GenericParamKind,
-    Generics, Mutability, PatKind, VariantData,
+    self as ast, AnonConst, AttrArgs, BindingMode, ByRef, DelimArgs, EnumDef, Expr, GenericArg,
+    GenericParamKind, Generics, Mutability, PatKind, Safety, VariantData,
 };
 use rustc_attr_data_structures::{AttributeKind, ReprPacked};
 use rustc_attr_parsing::AttributeParser;
@@ -222,6 +224,8 @@ pub(crate) struct TraitDef<'a> {
     pub associated_types: Vec<(Ident, Ty)>,
 
     pub is_const: bool,
+
+    pub is_staged_api_crate: bool,
 }
 
 pub(crate) struct MethodDef<'a> {
@@ -784,8 +788,45 @@ impl<'a> TraitDef<'a> {
         // Create the type of `self`.
         let path = cx.path_all(self.span, false, vec![type_ident], self_params);
         let self_type = cx.ty_path(path);
+        let rustc_const_unstable =
+            cx.path_ident(self.span, Ident::new(sym::rustc_const_unstable, self.span));
+
+        let mut attrs = thin_vec![cx.attr_word(sym::automatically_derived, self.span),];
+
+        // Only add `rustc_const_unstable` attributes if `derive_const` is used within libcore/libstd,
+        // Other crates don't need stability attributes, so adding them is not useful, but libcore needs them
+        // on all const trait impls.
+        if self.is_const && self.is_staged_api_crate {
+            attrs.push(
+                cx.attr_nested(
+                    rustc_ast::AttrItem {
+                        unsafety: Safety::Default,
+                        path: rustc_const_unstable,
+                        args: AttrArgs::Delimited(DelimArgs {
+                            dspan: DelimSpan::from_single(self.span),
+                            delim: rustc_ast::token::Delimiter::Parenthesis,
+                            tokens: [
+                                TokenKind::Ident(sym::feature, IdentIsRaw::No),
+                                TokenKind::Eq,
+                                TokenKind::lit(LitKind::Str, sym::derive_const, None),
+                                TokenKind::Comma,
+                                TokenKind::Ident(sym::issue, IdentIsRaw::No),
+                                TokenKind::Eq,
+                                TokenKind::lit(LitKind::Str, sym::derive_const_issue, None),
+                            ]
+                            .into_iter()
+                            .map(|kind| {
+                                TokenTree::Token(Token { kind, span: self.span }, Spacing::Alone)
+                            })
+                            .collect(),
+                        }),
+                        tokens: None,
+                    },
+                    self.span,
+                ),
+            )
+        }
 
-        let attrs = thin_vec![cx.attr_word(sym::automatically_derived, self.span),];
         let opt_trait_ref = Some(trait_ref);
 
         cx.item(
diff --git a/compiler/rustc_builtin_macros/src/deriving/hash.rs b/compiler/rustc_builtin_macros/src/deriving/hash.rs
index 6e6dbe19e4d..78534449895 100644
--- a/compiler/rustc_builtin_macros/src/deriving/hash.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/hash.rs
@@ -41,6 +41,7 @@ pub(crate) fn expand_deriving_hash(
         }],
         associated_types: Vec::new(),
         is_const,
+        is_staged_api_crate: cx.ecfg.features.staged_api(),
     };
 
     hash_trait_def.expand(cx, mitem, item, push);
diff --git a/compiler/rustc_builtin_macros/src/source_util.rs b/compiler/rustc_builtin_macros/src/source_util.rs
index cebfffa1e16..ecfd46a84ec 100644
--- a/compiler/rustc_builtin_macros/src/source_util.rs
+++ b/compiler/rustc_builtin_macros/src/source_util.rs
@@ -4,8 +4,8 @@ use std::sync::Arc;
 
 use rustc_ast as ast;
 use rustc_ast::ptr::P;
-use rustc_ast::token;
 use rustc_ast::tokenstream::TokenStream;
+use rustc_ast::{join_path_idents, token};
 use rustc_ast_pretty::pprust;
 use rustc_expand::base::{
     DummyResult, ExpandResult, ExtCtxt, MacEager, MacResult, MacroExpanderResult, resolve_path,
@@ -100,7 +100,7 @@ pub(crate) fn expand_mod(
     let sp = cx.with_def_site_ctxt(sp);
     check_zero_tts(cx, sp, tts, "module_path!");
     let mod_path = &cx.current_expansion.module.mod_path;
-    let string = mod_path.iter().map(|x| x.to_string()).collect::<Vec<String>>().join("::");
+    let string = join_path_idents(mod_path);
 
     ExpandResult::Ready(MacEager::expr(cx.expr_str(sp, Symbol::intern(&string))))
 }
diff --git a/compiler/rustc_builtin_macros/src/test.rs b/compiler/rustc_builtin_macros/src/test.rs
index b067578794b..ba3d8368b2a 100644
--- a/compiler/rustc_builtin_macros/src/test.rs
+++ b/compiler/rustc_builtin_macros/src/test.rs
@@ -5,7 +5,7 @@ use std::assert_matches::assert_matches;
 use std::iter;
 
 use rustc_ast::ptr::P;
-use rustc_ast::{self as ast, GenericParamKind, attr};
+use rustc_ast::{self as ast, GenericParamKind, attr, join_path_idents};
 use rustc_ast_pretty::pprust;
 use rustc_errors::{Applicability, Diag, Level};
 use rustc_expand::base::*;
@@ -446,12 +446,7 @@ fn get_location_info(cx: &ExtCtxt<'_>, fn_: &ast::Fn) -> (Symbol, usize, usize,
 }
 
 fn item_path(mod_path: &[Ident], item_ident: &Ident) -> String {
-    mod_path
-        .iter()
-        .chain(iter::once(item_ident))
-        .map(|x| x.to_string())
-        .collect::<Vec<String>>()
-        .join("::")
+    join_path_idents(mod_path.iter().chain(iter::once(item_ident)))
 }
 
 enum ShouldPanic {
diff --git a/compiler/rustc_codegen_cranelift/src/driver/aot.rs b/compiler/rustc_codegen_cranelift/src/driver/aot.rs
index 442151fe32d..8ec3599b63d 100644
--- a/compiler/rustc_codegen_cranelift/src/driver/aot.rs
+++ b/compiler/rustc_codegen_cranelift/src/driver/aot.rs
@@ -530,8 +530,8 @@ fn codegen_cgu_content(
     for (mono_item, item_data) in mono_items {
         match mono_item {
             MonoItem::Fn(instance) => {
-                if tcx.codegen_fn_attrs(instance.def_id()).flags.contains(CodegenFnAttrFlags::NAKED)
-                {
+                let flags = tcx.codegen_instance_attrs(instance.def).flags;
+                if flags.contains(CodegenFnAttrFlags::NAKED) {
                     rustc_codegen_ssa::mir::naked_asm::codegen_naked_asm(
                         &mut GlobalAsmContext { tcx, global_asm: &mut cx.global_asm },
                         instance,
diff --git a/compiler/rustc_codegen_cranelift/src/driver/jit.rs b/compiler/rustc_codegen_cranelift/src/driver/jit.rs
index b1f185b551c..b3497503bf0 100644
--- a/compiler/rustc_codegen_cranelift/src/driver/jit.rs
+++ b/compiler/rustc_codegen_cranelift/src/driver/jit.rs
@@ -127,7 +127,7 @@ fn codegen_and_compile_fn<'tcx>(
     module: &mut dyn Module,
     instance: Instance<'tcx>,
 ) {
-    if tcx.codegen_fn_attrs(instance.def_id()).flags.contains(CodegenFnAttrFlags::NAKED) {
+    if tcx.codegen_instance_attrs(instance.def).flags.contains(CodegenFnAttrFlags::NAKED) {
         tcx.dcx()
             .span_fatal(tcx.def_span(instance.def_id()), "Naked asm is not supported in JIT mode");
     }
diff --git a/compiler/rustc_codegen_cranelift/src/driver/mod.rs b/compiler/rustc_codegen_cranelift/src/driver/mod.rs
index ffd47cace38..8f83c30b598 100644
--- a/compiler/rustc_codegen_cranelift/src/driver/mod.rs
+++ b/compiler/rustc_codegen_cranelift/src/driver/mod.rs
@@ -35,7 +35,7 @@ fn predefine_mono_items<'tcx>(
                         is_compiler_builtins,
                     );
                     let is_naked = tcx
-                        .codegen_fn_attrs(instance.def_id())
+                        .codegen_instance_attrs(instance.def)
                         .flags
                         .contains(CodegenFnAttrFlags::NAKED);
                     module
diff --git a/compiler/rustc_codegen_gcc/src/attributes.rs b/compiler/rustc_codegen_gcc/src/attributes.rs
index bf0927dc590..7a1ae6ca9c8 100644
--- a/compiler/rustc_codegen_gcc/src/attributes.rs
+++ b/compiler/rustc_codegen_gcc/src/attributes.rs
@@ -87,7 +87,7 @@ pub fn from_fn_attrs<'gcc, 'tcx>(
     #[cfg_attr(not(feature = "master"), allow(unused_variables))] func: Function<'gcc>,
     instance: ty::Instance<'tcx>,
 ) {
-    let codegen_fn_attrs = cx.tcx.codegen_fn_attrs(instance.def_id());
+    let codegen_fn_attrs = cx.tcx.codegen_instance_attrs(instance.def);
 
     #[cfg(feature = "master")]
     {
diff --git a/compiler/rustc_codegen_gcc/src/back/lto.rs b/compiler/rustc_codegen_gcc/src/back/lto.rs
index 10fce860b77..e554dd2500b 100644
--- a/compiler/rustc_codegen_gcc/src/back/lto.rs
+++ b/compiler/rustc_codegen_gcc/src/back/lto.rs
@@ -24,7 +24,7 @@ use std::sync::Arc;
 
 use gccjit::{Context, OutputKind};
 use object::read::archive::ArchiveFile;
-use rustc_codegen_ssa::back::lto::{LtoModuleCodegen, SerializedModule, ThinModule, ThinShared};
+use rustc_codegen_ssa::back::lto::{SerializedModule, ThinModule, ThinShared};
 use rustc_codegen_ssa::back::symbol_export;
 use rustc_codegen_ssa::back::write::{CodegenContext, FatLtoInput};
 use rustc_codegen_ssa::traits::*;
@@ -176,7 +176,7 @@ pub(crate) fn run_fat(
     cgcx: &CodegenContext<GccCodegenBackend>,
     modules: Vec<FatLtoInput<GccCodegenBackend>>,
     cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>,
-) -> Result<LtoModuleCodegen<GccCodegenBackend>, FatalError> {
+) -> Result<ModuleCodegen<GccContext>, FatalError> {
     let dcx = cgcx.create_dcx();
     let dcx = dcx.handle();
     let lto_data = prepare_lto(cgcx, dcx)?;
@@ -201,7 +201,7 @@ fn fat_lto(
     mut serialized_modules: Vec<(SerializedModule<ModuleBuffer>, CString)>,
     tmp_path: TempDir,
     //symbols_below_threshold: &[String],
-) -> Result<LtoModuleCodegen<GccCodegenBackend>, FatalError> {
+) -> Result<ModuleCodegen<GccContext>, FatalError> {
     let _timer = cgcx.prof.generic_activity("GCC_fat_lto_build_monolithic_module");
     info!("going for a fat lto");
 
@@ -334,7 +334,7 @@ fn fat_lto(
     // of now.
     module.module_llvm.temp_dir = Some(tmp_path);
 
-    Ok(LtoModuleCodegen::Fat(module))
+    Ok(module)
 }
 
 pub struct ModuleBuffer(PathBuf);
@@ -358,7 +358,7 @@ pub(crate) fn run_thin(
     cgcx: &CodegenContext<GccCodegenBackend>,
     modules: Vec<(String, ThinBuffer)>,
     cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>,
-) -> Result<(Vec<LtoModuleCodegen<GccCodegenBackend>>, Vec<WorkProduct>), FatalError> {
+) -> Result<(Vec<ThinModule<GccCodegenBackend>>, Vec<WorkProduct>), FatalError> {
     let dcx = cgcx.create_dcx();
     let dcx = dcx.handle();
     let lto_data = prepare_lto(cgcx, dcx)?;
@@ -427,7 +427,7 @@ fn thin_lto(
     tmp_path: TempDir,
     cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>,
     //_symbols_below_threshold: &[String],
-) -> Result<(Vec<LtoModuleCodegen<GccCodegenBackend>>, Vec<WorkProduct>), FatalError> {
+) -> Result<(Vec<ThinModule<GccCodegenBackend>>, Vec<WorkProduct>), FatalError> {
     let _timer = cgcx.prof.generic_activity("LLVM_thin_lto_global_analysis");
     info!("going for that thin, thin LTO");
 
@@ -573,8 +573,7 @@ fn thin_lto(
         }*/
 
         info!(" - {}: re-compiled", module_name);
-        opt_jobs
-            .push(LtoModuleCodegen::Thin(ThinModule { shared: shared.clone(), idx: module_index }));
+        opt_jobs.push(ThinModule { shared: shared.clone(), idx: module_index });
     }
 
     // Save the current ThinLTO import information for the next compilation
diff --git a/compiler/rustc_codegen_gcc/src/back/write.rs b/compiler/rustc_codegen_gcc/src/back/write.rs
index d03d063bdac..113abe70805 100644
--- a/compiler/rustc_codegen_gcc/src/back/write.rs
+++ b/compiler/rustc_codegen_gcc/src/back/write.rs
@@ -16,10 +16,12 @@ use crate::{GccCodegenBackend, GccContext};
 
 pub(crate) fn codegen(
     cgcx: &CodegenContext<GccCodegenBackend>,
-    dcx: DiagCtxtHandle<'_>,
     module: ModuleCodegen<GccContext>,
     config: &ModuleConfig,
 ) -> Result<CompiledModule, FatalError> {
+    let dcx = cgcx.create_dcx();
+    let dcx = dcx.handle();
+
     let _timer = cgcx.prof.generic_activity_with_arg("GCC_module_codegen", &*module.name);
     {
         let context = &module.module_llvm.context;
diff --git a/compiler/rustc_codegen_gcc/src/callee.rs b/compiler/rustc_codegen_gcc/src/callee.rs
index 189ac7cd779..e7ca95af594 100644
--- a/compiler/rustc_codegen_gcc/src/callee.rs
+++ b/compiler/rustc_codegen_gcc/src/callee.rs
@@ -105,7 +105,7 @@ pub fn get_fn<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, instance: Instance<'tcx>)
             let is_hidden = if is_generic {
                 // This is a monomorphization of a generic function.
                 if !(cx.tcx.sess.opts.share_generics()
-                    || tcx.codegen_fn_attrs(instance_def_id).inline
+                    || tcx.codegen_instance_attrs(instance.def).inline
                         == rustc_attr_data_structures::InlineAttr::Never)
                 {
                     // When not sharing generics, all instances are in the same
diff --git a/compiler/rustc_codegen_gcc/src/lib.rs b/compiler/rustc_codegen_gcc/src/lib.rs
index d8fae1ca47d..d81bcc59775 100644
--- a/compiler/rustc_codegen_gcc/src/lib.rs
+++ b/compiler/rustc_codegen_gcc/src/lib.rs
@@ -93,7 +93,7 @@ use gccjit::{CType, Context, OptimizationLevel};
 use gccjit::{TargetInfo, Version};
 use rustc_ast::expand::allocator::AllocatorKind;
 use rustc_ast::expand::autodiff_attrs::AutoDiffItem;
-use rustc_codegen_ssa::back::lto::{LtoModuleCodegen, SerializedModule, ThinModule};
+use rustc_codegen_ssa::back::lto::{SerializedModule, ThinModule};
 use rustc_codegen_ssa::back::write::{
     CodegenContext, FatLtoInput, ModuleConfig, TargetMachineFactoryFn,
 };
@@ -353,11 +353,16 @@ impl WriteBackendMethods for GccCodegenBackend {
     type ThinData = ThinData;
     type ThinBuffer = ThinBuffer;
 
-    fn run_fat_lto(
+    fn run_and_optimize_fat_lto(
         cgcx: &CodegenContext<Self>,
         modules: Vec<FatLtoInput<Self>>,
         cached_modules: Vec<(SerializedModule<Self::ModuleBuffer>, WorkProduct)>,
-    ) -> Result<LtoModuleCodegen<Self>, FatalError> {
+        diff_fncs: Vec<AutoDiffItem>,
+    ) -> Result<ModuleCodegen<Self::Module>, FatalError> {
+        if !diff_fncs.is_empty() {
+            unimplemented!();
+        }
+
         back::lto::run_fat(cgcx, modules, cached_modules)
     }
 
@@ -365,7 +370,7 @@ impl WriteBackendMethods for GccCodegenBackend {
         cgcx: &CodegenContext<Self>,
         modules: Vec<(String, Self::ThinBuffer)>,
         cached_modules: Vec<(SerializedModule<Self::ModuleBuffer>, WorkProduct)>,
-    ) -> Result<(Vec<LtoModuleCodegen<Self>>, Vec<WorkProduct>), FatalError> {
+    ) -> Result<(Vec<ThinModule<Self>>, Vec<WorkProduct>), FatalError> {
         back::lto::run_thin(cgcx, modules, cached_modules)
     }
 
@@ -387,14 +392,6 @@ impl WriteBackendMethods for GccCodegenBackend {
         Ok(())
     }
 
-    fn optimize_fat(
-        _cgcx: &CodegenContext<Self>,
-        _module: &mut ModuleCodegen<Self::Module>,
-    ) -> Result<(), FatalError> {
-        // TODO(antoyo)
-        Ok(())
-    }
-
     fn optimize_thin(
         cgcx: &CodegenContext<Self>,
         thin: ThinModule<Self>,
@@ -404,11 +401,10 @@ impl WriteBackendMethods for GccCodegenBackend {
 
     fn codegen(
         cgcx: &CodegenContext<Self>,
-        dcx: DiagCtxtHandle<'_>,
         module: ModuleCodegen<Self::Module>,
         config: &ModuleConfig,
     ) -> Result<CompiledModule, FatalError> {
-        back::write::codegen(cgcx, dcx, module, config)
+        back::write::codegen(cgcx, module, config)
     }
 
     fn prepare_thin(
@@ -429,15 +425,6 @@ impl WriteBackendMethods for GccCodegenBackend {
     ) -> Result<ModuleCodegen<Self::Module>, FatalError> {
         back::write::link(cgcx, dcx, modules)
     }
-
-    fn autodiff(
-        _cgcx: &CodegenContext<Self>,
-        _module: &ModuleCodegen<Self::Module>,
-        _diff_functions: Vec<AutoDiffItem>,
-        _config: &ModuleConfig,
-    ) -> Result<(), FatalError> {
-        unimplemented!()
-    }
 }
 
 /// This is the entrypoint for a hot plugged rustc_codegen_gccjit
diff --git a/compiler/rustc_codegen_gcc/src/mono_item.rs b/compiler/rustc_codegen_gcc/src/mono_item.rs
index 539e3ac8507..51f35cbdee4 100644
--- a/compiler/rustc_codegen_gcc/src/mono_item.rs
+++ b/compiler/rustc_codegen_gcc/src/mono_item.rs
@@ -53,7 +53,7 @@ impl<'gcc, 'tcx> PreDefineCodegenMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
         let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty());
         self.linkage.set(base::linkage_to_gcc(linkage));
         let decl = self.declare_fn(symbol_name, fn_abi);
-        //let attrs = self.tcx.codegen_fn_attrs(instance.def_id());
+        //let attrs = self.tcx.codegen_instance_attrs(instance.def);
 
         attributes::from_fn_attrs(self, decl, instance);
 
diff --git a/compiler/rustc_codegen_llvm/messages.ftl b/compiler/rustc_codegen_llvm/messages.ftl
index 3885f18271f..f197ea74473 100644
--- a/compiler/rustc_codegen_llvm/messages.ftl
+++ b/compiler/rustc_codegen_llvm/messages.ftl
@@ -1,5 +1,4 @@
 codegen_llvm_autodiff_without_enable = using the autodiff feature requires -Z autodiff=Enable
-codegen_llvm_autodiff_without_lto = using the autodiff feature requires using fat-lto
 
 codegen_llvm_copy_bitcode = failed to copy bitcode to object file: {$err}
 
diff --git a/compiler/rustc_codegen_llvm/src/attributes.rs b/compiler/rustc_codegen_llvm/src/attributes.rs
index 1ea5a062254..c32f11b27f3 100644
--- a/compiler/rustc_codegen_llvm/src/attributes.rs
+++ b/compiler/rustc_codegen_llvm/src/attributes.rs
@@ -344,7 +344,7 @@ pub(crate) fn llfn_attrs_from_instance<'ll, 'tcx>(
     llfn: &'ll Value,
     instance: ty::Instance<'tcx>,
 ) {
-    let codegen_fn_attrs = cx.tcx.codegen_fn_attrs(instance.def_id());
+    let codegen_fn_attrs = cx.tcx.codegen_instance_attrs(instance.def);
 
     let mut to_add = SmallVec::<[_; 16]>::new();
 
diff --git a/compiler/rustc_codegen_llvm/src/back/lto.rs b/compiler/rustc_codegen_llvm/src/back/lto.rs
index 74418adc43c..655e1c95373 100644
--- a/compiler/rustc_codegen_llvm/src/back/lto.rs
+++ b/compiler/rustc_codegen_llvm/src/back/lto.rs
@@ -7,7 +7,7 @@ use std::sync::Arc;
 use std::{io, iter, slice};
 
 use object::read::archive::ArchiveFile;
-use rustc_codegen_ssa::back::lto::{LtoModuleCodegen, SerializedModule, ThinModule, ThinShared};
+use rustc_codegen_ssa::back::lto::{SerializedModule, ThinModule, ThinShared};
 use rustc_codegen_ssa::back::symbol_export;
 use rustc_codegen_ssa::back::write::{CodegenContext, FatLtoInput};
 use rustc_codegen_ssa::traits::*;
@@ -201,7 +201,7 @@ pub(crate) fn run_fat(
     cgcx: &CodegenContext<LlvmCodegenBackend>,
     modules: Vec<FatLtoInput<LlvmCodegenBackend>>,
     cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>,
-) -> Result<LtoModuleCodegen<LlvmCodegenBackend>, FatalError> {
+) -> Result<ModuleCodegen<ModuleLlvm>, FatalError> {
     let dcx = cgcx.create_dcx();
     let dcx = dcx.handle();
     let (symbols_below_threshold, upstream_modules) = prepare_lto(cgcx, dcx)?;
@@ -217,7 +217,7 @@ pub(crate) fn run_thin(
     cgcx: &CodegenContext<LlvmCodegenBackend>,
     modules: Vec<(String, ThinBuffer)>,
     cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>,
-) -> Result<(Vec<LtoModuleCodegen<LlvmCodegenBackend>>, Vec<WorkProduct>), FatalError> {
+) -> Result<(Vec<ThinModule<LlvmCodegenBackend>>, Vec<WorkProduct>), FatalError> {
     let dcx = cgcx.create_dcx();
     let dcx = dcx.handle();
     let (symbols_below_threshold, upstream_modules) = prepare_lto(cgcx, dcx)?;
@@ -248,7 +248,7 @@ fn fat_lto(
     cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>,
     mut serialized_modules: Vec<(SerializedModule<ModuleBuffer>, CString)>,
     symbols_below_threshold: &[*const libc::c_char],
-) -> Result<LtoModuleCodegen<LlvmCodegenBackend>, FatalError> {
+) -> Result<ModuleCodegen<ModuleLlvm>, FatalError> {
     let _timer = cgcx.prof.generic_activity("LLVM_fat_lto_build_monolithic_module");
     info!("going for a fat lto");
 
@@ -366,7 +366,7 @@ fn fat_lto(
         save_temp_bitcode(cgcx, &module, "lto.after-restriction");
     }
 
-    Ok(LtoModuleCodegen::Fat(module))
+    Ok(module)
 }
 
 pub(crate) struct Linker<'a>(&'a mut llvm::Linker<'a>);
@@ -436,7 +436,7 @@ fn thin_lto(
     serialized_modules: Vec<(SerializedModule<ModuleBuffer>, CString)>,
     cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>,
     symbols_below_threshold: &[*const libc::c_char],
-) -> Result<(Vec<LtoModuleCodegen<LlvmCodegenBackend>>, Vec<WorkProduct>), FatalError> {
+) -> Result<(Vec<ThinModule<LlvmCodegenBackend>>, Vec<WorkProduct>), FatalError> {
     let _timer = cgcx.prof.generic_activity("LLVM_thin_lto_global_analysis");
     unsafe {
         info!("going for that thin, thin LTO");
@@ -568,10 +568,7 @@ fn thin_lto(
             }
 
             info!(" - {}: re-compiled", module_name);
-            opt_jobs.push(LtoModuleCodegen::Thin(ThinModule {
-                shared: Arc::clone(&shared),
-                idx: module_index,
-            }));
+            opt_jobs.push(ThinModule { shared: Arc::clone(&shared), idx: module_index });
         }
 
         // Save the current ThinLTO import information for the next compilation
diff --git a/compiler/rustc_codegen_llvm/src/back/write.rs b/compiler/rustc_codegen_llvm/src/back/write.rs
index 506286fc255..68279008c03 100644
--- a/compiler/rustc_codegen_llvm/src/back/write.rs
+++ b/compiler/rustc_codegen_llvm/src/back/write.rs
@@ -817,10 +817,12 @@ pub(crate) fn link(
 
 pub(crate) fn codegen(
     cgcx: &CodegenContext<LlvmCodegenBackend>,
-    dcx: DiagCtxtHandle<'_>,
     module: ModuleCodegen<ModuleLlvm>,
     config: &ModuleConfig,
 ) -> Result<CompiledModule, FatalError> {
+    let dcx = cgcx.create_dcx();
+    let dcx = dcx.handle();
+
     let _timer = cgcx.prof.generic_activity_with_arg("LLVM_module_codegen", &*module.name);
     {
         let llmod = module.module_llvm.llmod();
@@ -879,9 +881,7 @@ 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");
-                unsafe {
-                    embed_bitcode(cgcx, llcx, llmod, &config.bc_cmdline, &thin_bc);
-                }
+                embed_bitcode(cgcx, llcx, llmod, &config.bc_cmdline, &thin_bc);
             }
         }
 
@@ -945,7 +945,7 @@ pub(crate) fn codegen(
             // binaries. So we must clone the module to produce the asm output
             // if we are also producing object code.
             let llmod = if let EmitObj::ObjectCode(_) = config.emit_obj {
-                unsafe { llvm::LLVMCloneModule(llmod) }
+                llvm::LLVMCloneModule(llmod)
             } else {
                 llmod
             };
@@ -1073,7 +1073,7 @@ pub(crate) fn bitcode_section_name(cgcx: &CodegenContext<LlvmCodegenBackend>) ->
 }
 
 /// Embed the bitcode of an LLVM module for LTO in the LLVM module itself.
-unsafe fn embed_bitcode(
+fn embed_bitcode(
     cgcx: &CodegenContext<LlvmCodegenBackend>,
     llcx: &llvm::Context,
     llmod: &llvm::Module,
@@ -1115,43 +1115,40 @@ unsafe fn embed_bitcode(
     // Unfortunately, LLVM provides no way to set custom section flags. For ELF
     // and COFF we emit the sections using module level inline assembly for that
     // reason (see issue #90326 for historical background).
-    unsafe {
-        if cgcx.target_is_like_darwin
-            || cgcx.target_is_like_aix
-            || cgcx.target_arch == "wasm32"
-            || cgcx.target_arch == "wasm64"
-        {
-            // We don't need custom section flags, create LLVM globals.
-            let llconst = common::bytes_in_context(llcx, bitcode);
-            let llglobal =
-                llvm::add_global(llmod, common::val_ty(llconst), c"rustc.embedded.module");
-            llvm::set_initializer(llglobal, llconst);
-
-            llvm::set_section(llglobal, bitcode_section_name(cgcx));
-            llvm::set_linkage(llglobal, llvm::Linkage::PrivateLinkage);
-            llvm::LLVMSetGlobalConstant(llglobal, llvm::True);
-
-            let llconst = common::bytes_in_context(llcx, cmdline.as_bytes());
-            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 {
-                c"__LLVM,__cmdline"
-            } else if cgcx.target_is_like_aix {
-                c".info"
-            } else {
-                c".llvmcmd"
-            };
-            llvm::set_section(llglobal, section);
-            llvm::set_linkage(llglobal, llvm::Linkage::PrivateLinkage);
+
+    if cgcx.target_is_like_darwin
+        || cgcx.target_is_like_aix
+        || cgcx.target_arch == "wasm32"
+        || cgcx.target_arch == "wasm64"
+    {
+        // We don't need custom section flags, create LLVM globals.
+        let llconst = common::bytes_in_context(llcx, bitcode);
+        let llglobal = llvm::add_global(llmod, common::val_ty(llconst), c"rustc.embedded.module");
+        llvm::set_initializer(llglobal, llconst);
+
+        llvm::set_section(llglobal, bitcode_section_name(cgcx));
+        llvm::set_linkage(llglobal, llvm::Linkage::PrivateLinkage);
+        llvm::LLVMSetGlobalConstant(llglobal, llvm::True);
+
+        let llconst = common::bytes_in_context(llcx, cmdline.as_bytes());
+        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 {
+            c"__LLVM,__cmdline"
+        } else if cgcx.target_is_like_aix {
+            c".info"
         } else {
-            // We need custom section flags, so emit module-level inline assembly.
-            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());
-            llvm::append_module_inline_asm(llmod, &asm);
-        }
+            c".llvmcmd"
+        };
+        llvm::set_section(llglobal, section);
+        llvm::set_linkage(llglobal, llvm::Linkage::PrivateLinkage);
+    } else {
+        // We need custom section flags, so emit module-level inline assembly.
+        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());
+        llvm::append_module_inline_asm(llmod, &asm);
     }
 }
 
diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs
index 9c3b866aa3c..514923ad6f3 100644
--- a/compiler/rustc_codegen_llvm/src/builder.rs
+++ b/compiler/rustc_codegen_llvm/src/builder.rs
@@ -302,10 +302,7 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
             return;
         }
 
-        let id_str = "branch_weights";
-        let id = unsafe {
-            llvm::LLVMMDStringInContext2(self.cx.llcx, id_str.as_ptr().cast(), id_str.len())
-        };
+        let id = self.cx.create_metadata(b"branch_weights");
 
         // For switch instructions with 2 targets, the `llvm.expect` intrinsic is used.
         // This function handles switch instructions with more than 2 targets and it needs to
@@ -637,17 +634,16 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         } else if place.layout.is_llvm_immediate() {
             let mut const_llval = None;
             let llty = place.layout.llvm_type(self);
-            unsafe {
-                if let Some(global) = llvm::LLVMIsAGlobalVariable(place.val.llval) {
-                    if llvm::LLVMIsGlobalConstant(global) == llvm::True {
-                        if let Some(init) = llvm::LLVMGetInitializer(global) {
-                            if self.val_ty(init) == llty {
-                                const_llval = Some(init);
-                            }
+            if let Some(global) = llvm::LLVMIsAGlobalVariable(place.val.llval) {
+                if llvm::LLVMIsGlobalConstant(global) == llvm::True {
+                    if let Some(init) = llvm::LLVMGetInitializer(global) {
+                        if self.val_ty(init) == llty {
+                            const_llval = Some(init);
                         }
                     }
                 }
             }
+
             let llval = const_llval.unwrap_or_else(|| {
                 let load = self.load(llty, place.val.llval, place.val.align);
                 if let abi::BackendRepr::Scalar(scalar) = place.layout.backend_repr {
@@ -1721,7 +1717,7 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
             } else {
                 cfi::typeid_for_fnabi(self.tcx, fn_abi, options)
             };
-            let typeid_metadata = self.cx.typeid_metadata(typeid).unwrap();
+            let typeid_metadata = self.cx.create_metadata(typeid.as_bytes());
             let dbg_loc = self.get_dbg_loc();
 
             // Test whether the function pointer is associated with the type identifier using the
diff --git a/compiler/rustc_codegen_llvm/src/builder/autodiff.rs b/compiler/rustc_codegen_llvm/src/builder/autodiff.rs
index 5afb9a60d42..829b3c513c2 100644
--- a/compiler/rustc_codegen_llvm/src/builder/autodiff.rs
+++ b/compiler/rustc_codegen_llvm/src/builder/autodiff.rs
@@ -2,7 +2,6 @@ use std::ptr;
 
 use rustc_ast::expand::autodiff_attrs::{AutoDiffAttrs, AutoDiffItem, DiffActivity, DiffMode};
 use rustc_codegen_ssa::ModuleCodegen;
-use rustc_codegen_ssa::back::write::ModuleConfig;
 use rustc_codegen_ssa::common::TypeKind;
 use rustc_codegen_ssa::traits::BaseTypeCodegenMethods;
 use rustc_errors::FatalError;
@@ -76,12 +75,12 @@ fn match_args_from_caller_to_enzyme<'ll>(
         outer_pos = 1;
     }
 
-    let enzyme_const = cx.create_metadata("enzyme_const".to_string()).unwrap();
-    let enzyme_out = cx.create_metadata("enzyme_out".to_string()).unwrap();
-    let enzyme_dup = cx.create_metadata("enzyme_dup".to_string()).unwrap();
-    let enzyme_dupv = cx.create_metadata("enzyme_dupv".to_string()).unwrap();
-    let enzyme_dupnoneed = cx.create_metadata("enzyme_dupnoneed".to_string()).unwrap();
-    let enzyme_dupnoneedv = cx.create_metadata("enzyme_dupnoneedv".to_string()).unwrap();
+    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");
+    let enzyme_dupv = cx.create_metadata(b"enzyme_dupv");
+    let enzyme_dupnoneed = cx.create_metadata(b"enzyme_dupnoneed");
+    let enzyme_dupnoneedv = cx.create_metadata(b"enzyme_dupnoneedv");
 
     while activity_pos < inputs.len() {
         let diff_activity = inputs[activity_pos as usize];
@@ -378,12 +377,12 @@ fn generate_enzyme_call<'ll>(
         let mut args = Vec::with_capacity(num_args as usize + 1);
         args.push(fn_to_diff);
 
-        let enzyme_primal_ret = cx.create_metadata("enzyme_primal_return".to_string()).unwrap();
+        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("enzyme_width".to_string()).unwrap();
+            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));
         }
@@ -461,7 +460,6 @@ pub(crate) fn differentiate<'ll>(
     module: &'ll ModuleCodegen<ModuleLlvm>,
     cgcx: &CodegenContext<LlvmCodegenBackend>,
     diff_items: Vec<AutoDiffItem>,
-    _config: &ModuleConfig,
 ) -> Result<(), FatalError> {
     for item in &diff_items {
         trace!("{}", item);
diff --git a/compiler/rustc_codegen_llvm/src/callee.rs b/compiler/rustc_codegen_llvm/src/callee.rs
index 6d68eca60af..5a3dd90ab24 100644
--- a/compiler/rustc_codegen_llvm/src/callee.rs
+++ b/compiler/rustc_codegen_llvm/src/callee.rs
@@ -102,7 +102,7 @@ pub(crate) fn get_fn<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>, instance: Instance<'t
         let is_hidden = if is_generic {
             // This is a monomorphization of a generic function.
             if !(cx.tcx.sess.opts.share_generics()
-                || tcx.codegen_fn_attrs(instance_def_id).inline
+                || tcx.codegen_instance_attrs(instance.def).inline
                     == rustc_attr_data_structures::InlineAttr::Never)
             {
                 // When not sharing generics, all instances are in the same
diff --git a/compiler/rustc_codegen_llvm/src/common.rs b/compiler/rustc_codegen_llvm/src/common.rs
index b9b5c776d86..f9ab96b5789 100644
--- a/compiler/rustc_codegen_llvm/src/common.rs
+++ b/compiler/rustc_codegen_llvm/src/common.rs
@@ -215,10 +215,10 @@ impl<'ll, 'tcx> ConstCodegenMethods for CodegenCx<'ll, 'tcx> {
                 bug!("symbol `{}` is already defined", sym);
             });
             llvm::set_initializer(g, sc);
-            unsafe {
-                llvm::LLVMSetGlobalConstant(g, True);
-                llvm::LLVMSetUnnamedAddress(g, llvm::UnnamedAddr::Global);
-            }
+
+            llvm::set_global_constant(g, true);
+            llvm::set_unnamed_address(g, llvm::UnnamedAddr::Global);
+
             llvm::set_linkage(g, llvm::Linkage::InternalLinkage);
             // Cast to default address space if globals are in a different addrspace
             let g = self.const_pointercast(g, self.type_ptr());
diff --git a/compiler/rustc_codegen_llvm/src/consts.rs b/compiler/rustc_codegen_llvm/src/consts.rs
index 5deddb3ed98..0b96b63bc85 100644
--- a/compiler/rustc_codegen_llvm/src/consts.rs
+++ b/compiler/rustc_codegen_llvm/src/consts.rs
@@ -17,13 +17,12 @@ use rustc_middle::ty::{self, Instance};
 use rustc_middle::{bug, span_bug};
 use tracing::{debug, instrument, trace};
 
-use crate::common::{AsCCharPtr, CodegenCx};
+use crate::common::CodegenCx;
 use crate::errors::SymbolAlreadyDefined;
-use crate::llvm::{self, True};
 use crate::type_::Type;
 use crate::type_of::LayoutLlvmExt;
 use crate::value::Value;
-use crate::{base, debuginfo};
+use crate::{base, debuginfo, llvm};
 
 pub(crate) fn const_alloc_to_llvm<'ll>(
     cx: &CodegenCx<'ll, '_>,
@@ -247,7 +246,7 @@ impl<'ll> CodegenCx<'ll, '_> {
         };
         llvm::set_initializer(gv, cv);
         set_global_alignment(self, gv, align);
-        llvm::SetUnnamedAddress(gv, llvm::UnnamedAddr::Global);
+        llvm::set_unnamed_address(gv, llvm::UnnamedAddr::Global);
         gv
     }
 
@@ -272,9 +271,8 @@ impl<'ll> CodegenCx<'ll, '_> {
             return gv;
         }
         let gv = self.static_addr_of_mut(cv, align, kind);
-        unsafe {
-            llvm::LLVMSetGlobalConstant(gv, True);
-        }
+        llvm::set_global_constant(gv, true);
+
         self.const_globals.borrow_mut().insert(cv, gv);
         gv
     }
@@ -398,149 +396,140 @@ impl<'ll> CodegenCx<'ll, '_> {
     }
 
     fn codegen_static_item(&mut self, def_id: DefId) {
-        unsafe {
-            assert!(
-                llvm::LLVMGetInitializer(
-                    self.instances.borrow().get(&Instance::mono(self.tcx, def_id)).unwrap()
-                )
-                .is_none()
-            );
-            let attrs = self.tcx.codegen_fn_attrs(def_id);
+        assert!(
+            llvm::LLVMGetInitializer(
+                self.instances.borrow().get(&Instance::mono(self.tcx, def_id)).unwrap()
+            )
+            .is_none()
+        );
+        let attrs = self.tcx.codegen_fn_attrs(def_id);
 
-            let Ok((v, alloc)) = codegen_static_initializer(self, def_id) else {
-                // Error has already been reported
-                return;
-            };
-            let alloc = alloc.inner();
+        let Ok((v, alloc)) = codegen_static_initializer(self, def_id) else {
+            // Error has already been reported
+            return;
+        };
+        let alloc = alloc.inner();
 
-            let val_llty = self.val_ty(v);
+        let val_llty = self.val_ty(v);
 
-            let g = self.get_static_inner(def_id, val_llty);
-            let llty = self.get_type_of_global(g);
+        let g = self.get_static_inner(def_id, val_llty);
+        let llty = self.get_type_of_global(g);
 
-            let g = if val_llty == llty {
-                g
-            } else {
-                // codegen_static_initializer creates the global value just from the
-                // `Allocation` data by generating one big struct value that is just
-                // all the bytes and pointers after each other. This will almost never
-                // match the type that the static was declared with. Unfortunately
-                // we can't just LLVMConstBitCast our way out of it because that has very
-                // specific rules on what can be cast. So instead of adding a new way to
-                // generate static initializers that match the static's type, we picked
-                // the easier option and retroactively change the type of the static item itself.
-                let name = llvm::get_value_name(g);
-                llvm::set_value_name(g, b"");
-
-                let linkage = llvm::get_linkage(g);
-                let visibility = llvm::get_visibility(g);
-
-                let new_g = llvm::LLVMRustGetOrInsertGlobal(
-                    self.llmod,
-                    name.as_c_char_ptr(),
-                    name.len(),
-                    val_llty,
-                );
-
-                llvm::set_linkage(new_g, linkage);
-                llvm::set_visibility(new_g, visibility);
-
-                // The old global has had its name removed but is returned by
-                // get_static since it is in the instance cache. Provide an
-                // alternative lookup that points to the new global so that
-                // global_asm! can compute the correct mangled symbol name
-                // for the global.
-                self.renamed_statics.borrow_mut().insert(def_id, new_g);
-
-                // To avoid breaking any invariants, we leave around the old
-                // global for the moment; we'll replace all references to it
-                // with the new global later. (See base::codegen_backend.)
-                self.statics_to_rauw.borrow_mut().push((g, new_g));
-                new_g
-            };
-            set_global_alignment(self, g, alloc.align);
-            llvm::set_initializer(g, v);
-
-            self.assume_dso_local(g, true);
-
-            // Forward the allocation's mutability (picked by the const interner) to LLVM.
-            if alloc.mutability.is_not() {
-                llvm::LLVMSetGlobalConstant(g, llvm::True);
-            }
+        let g = if val_llty == llty {
+            g
+        } else {
+            // codegen_static_initializer creates the global value just from the
+            // `Allocation` data by generating one big struct value that is just
+            // all the bytes and pointers after each other. This will almost never
+            // match the type that the static was declared with. Unfortunately
+            // we can't just LLVMConstBitCast our way out of it because that has very
+            // specific rules on what can be cast. So instead of adding a new way to
+            // generate static initializers that match the static's type, we picked
+            // the easier option and retroactively change the type of the static item itself.
+            let name = String::from_utf8(llvm::get_value_name(g))
+                .expect("we declare our statics with a utf8-valid name");
+            llvm::set_value_name(g, b"");
+
+            let linkage = llvm::get_linkage(g);
+            let visibility = llvm::get_visibility(g);
+
+            let new_g = self.declare_global(&name, val_llty);
+
+            llvm::set_linkage(new_g, linkage);
+            llvm::set_visibility(new_g, visibility);
+
+            // The old global has had its name removed but is returned by
+            // get_static since it is in the instance cache. Provide an
+            // alternative lookup that points to the new global so that
+            // global_asm! can compute the correct mangled symbol name
+            // for the global.
+            self.renamed_statics.borrow_mut().insert(def_id, new_g);
+
+            // To avoid breaking any invariants, we leave around the old
+            // global for the moment; we'll replace all references to it
+            // with the new global later. (See base::codegen_backend.)
+            self.statics_to_rauw.borrow_mut().push((g, new_g));
+            new_g
+        };
+        set_global_alignment(self, g, alloc.align);
+        llvm::set_initializer(g, v);
 
-            debuginfo::build_global_var_di_node(self, def_id, g);
+        self.assume_dso_local(g, true);
 
-            if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
-                llvm::set_thread_local_mode(g, self.tls_model);
-            }
+        // Forward the allocation's mutability (picked by the const interner) to LLVM.
+        if alloc.mutability.is_not() {
+            llvm::set_global_constant(g, true);
+        }
 
-            // Wasm statics with custom link sections get special treatment as they
-            // go into custom sections of the wasm executable. The exception to this
-            // is the `.init_array` section which are treated specially by the wasm linker.
-            if self.tcx.sess.target.is_like_wasm
-                && attrs
-                    .link_section
-                    .map(|link_section| !link_section.as_str().starts_with(".init_array"))
-                    .unwrap_or(true)
-            {
-                if let Some(section) = attrs.link_section {
-                    let section = llvm::LLVMMDStringInContext2(
-                        self.llcx,
-                        section.as_str().as_c_char_ptr(),
-                        section.as_str().len(),
-                    );
-                    assert!(alloc.provenance().ptrs().is_empty());
-
-                    // The `inspect` method is okay here because we checked for provenance, and
-                    // because we are doing this access to inspect the final interpreter state (not
-                    // as part of the interpreter execution).
-                    let bytes =
-                        alloc.inspect_with_uninit_and_ptr_outside_interpreter(0..alloc.len());
-                    let alloc =
-                        llvm::LLVMMDStringInContext2(self.llcx, bytes.as_c_char_ptr(), bytes.len());
-                    let data = [section, alloc];
-                    let meta = llvm::LLVMMDNodeInContext2(self.llcx, data.as_ptr(), data.len());
-                    let val = self.get_metadata_value(meta);
+        debuginfo::build_global_var_di_node(self, def_id, g);
+
+        if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
+            llvm::set_thread_local_mode(g, self.tls_model);
+        }
+
+        // Wasm statics with custom link sections get special treatment as they
+        // go into custom sections of the wasm executable. The exception to this
+        // is the `.init_array` section which are treated specially by the wasm linker.
+        if self.tcx.sess.target.is_like_wasm
+            && attrs
+                .link_section
+                .map(|link_section| !link_section.as_str().starts_with(".init_array"))
+                .unwrap_or(true)
+        {
+            if let Some(section) = attrs.link_section {
+                let section = self.create_metadata(section.as_str().as_bytes());
+                assert!(alloc.provenance().ptrs().is_empty());
+
+                // The `inspect` method is okay here because we checked for provenance, and
+                // because we are doing this access to inspect the final interpreter state (not
+                // as part of the interpreter execution).
+                let bytes = alloc.inspect_with_uninit_and_ptr_outside_interpreter(0..alloc.len());
+                let alloc = self.create_metadata(bytes);
+                let data = [section, alloc];
+                let meta =
+                    unsafe { llvm::LLVMMDNodeInContext2(self.llcx, data.as_ptr(), data.len()) };
+                let val = self.get_metadata_value(meta);
+                unsafe {
                     llvm::LLVMAddNamedMetadataOperand(
                         self.llmod,
                         c"wasm.custom_sections".as_ptr(),
                         val,
-                    );
-                }
-            } else {
-                base::set_link_section(g, attrs);
+                    )
+                };
             }
+        } else {
+            base::set_link_section(g, attrs);
+        }
 
-            base::set_variable_sanitizer_attrs(g, attrs);
-
-            if attrs.flags.contains(CodegenFnAttrFlags::USED_COMPILER) {
-                // `USED` and `USED_LINKER` can't be used together.
-                assert!(!attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER));
-
-                // The semantics of #[used] in Rust only require the symbol to make it into the
-                // object file. It is explicitly allowed for the linker to strip the symbol if it
-                // is dead, which means we are allowed to use `llvm.compiler.used` instead of
-                // `llvm.used` here.
-                //
-                // Additionally, https://reviews.llvm.org/D97448 in LLVM 13 started emitting unique
-                // sections with SHF_GNU_RETAIN flag for llvm.used symbols, which may trigger bugs
-                // in the handling of `.init_array` (the static constructor list) in versions of
-                // the gold linker (prior to the one released with binutils 2.36).
-                //
-                // That said, we only ever emit these when `#[used(compiler)]` is explicitly
-                // requested. This is to avoid similar breakage on other targets, in particular
-                // MachO targets have *their* static constructor lists broken if `llvm.compiler.used`
-                // is emitted rather than `llvm.used`. However, that check happens when assigning
-                // the `CodegenFnAttrFlags` in the `codegen_fn_attrs` query, so we don't need to
-                // take care of it here.
-                self.add_compiler_used_global(g);
-            }
-            if attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER) {
-                // `USED` and `USED_LINKER` can't be used together.
-                assert!(!attrs.flags.contains(CodegenFnAttrFlags::USED_COMPILER));
+        base::set_variable_sanitizer_attrs(g, attrs);
+
+        if attrs.flags.contains(CodegenFnAttrFlags::USED_COMPILER) {
+            // `USED` and `USED_LINKER` can't be used together.
+            assert!(!attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER));
+
+            // The semantics of #[used] in Rust only require the symbol to make it into the
+            // object file. It is explicitly allowed for the linker to strip the symbol if it
+            // is dead, which means we are allowed to use `llvm.compiler.used` instead of
+            // `llvm.used` here.
+            //
+            // Additionally, https://reviews.llvm.org/D97448 in LLVM 13 started emitting unique
+            // sections with SHF_GNU_RETAIN flag for llvm.used symbols, which may trigger bugs
+            // in the handling of `.init_array` (the static constructor list) in versions of
+            // the gold linker (prior to the one released with binutils 2.36).
+            //
+            // That said, we only ever emit these when `#[used(compiler)]` is explicitly
+            // requested. This is to avoid similar breakage on other targets, in particular
+            // MachO targets have *their* static constructor lists broken if `llvm.compiler.used`
+            // is emitted rather than `llvm.used`. However, that check happens when assigning
+            // the `CodegenFnAttrFlags` in the `codegen_fn_attrs` query, so we don't need to
+            // take care of it here.
+            self.add_compiler_used_global(g);
+        }
+        if attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER) {
+            // `USED` and `USED_LINKER` can't be used together.
+            assert!(!attrs.flags.contains(CodegenFnAttrFlags::USED_COMPILER));
 
-                self.add_used_global(g);
-            }
+            self.add_used_global(g);
         }
     }
 
diff --git a/compiler/rustc_codegen_llvm/src/context.rs b/compiler/rustc_codegen_llvm/src/context.rs
index 90582e23b04..6a23becaa96 100644
--- a/compiler/rustc_codegen_llvm/src/context.rs
+++ b/compiler/rustc_codegen_llvm/src/context.rs
@@ -34,7 +34,6 @@ use smallvec::SmallVec;
 
 use crate::back::write::to_llvm_code_model;
 use crate::callee::get_fn;
-use crate::common::AsCCharPtr;
 use crate::debuginfo::metadata::apply_vcall_visibility_metadata;
 use crate::llvm::Metadata;
 use crate::type_::Type;
@@ -169,6 +168,8 @@ pub(crate) unsafe fn create_module<'ll>(
     let mod_name = SmallCStr::new(mod_name);
     let llmod = unsafe { llvm::LLVMModuleCreateWithNameInContext(mod_name.as_ptr(), llcx) };
 
+    let cx = SimpleCx::new(llmod, llcx, tcx.data_layout.pointer_size());
+
     let mut target_data_layout = sess.target.data_layout.to_string();
     let llvm_version = llvm_util::get_version();
 
@@ -473,18 +474,14 @@ pub(crate) unsafe fn create_module<'ll>(
     #[allow(clippy::option_env_unwrap)]
     let rustc_producer =
         format!("rustc version {}", option_env!("CFG_VERSION").expect("CFG_VERSION"));
-    let name_metadata = unsafe {
-        llvm::LLVMMDStringInContext2(
-            llcx,
-            rustc_producer.as_c_char_ptr(),
-            rustc_producer.as_bytes().len(),
-        )
-    };
+
+    let name_metadata = cx.create_metadata(rustc_producer.as_bytes());
+
     unsafe {
         llvm::LLVMAddNamedMetadataOperand(
             llmod,
             c"llvm.ident".as_ptr(),
-            &llvm::LLVMMetadataAsValue(llcx, llvm::LLVMMDNodeInContext2(llcx, &name_metadata, 1)),
+            &cx.get_metadata_value(llvm::LLVMMDNodeInContext2(llcx, &name_metadata, 1)),
         );
     }
 
@@ -698,10 +695,10 @@ impl<'ll, CX: Borrow<SCx<'ll>>> GenericCx<'ll, CX> {
         }
     }
 
-    pub(crate) fn create_metadata(&self, name: String) -> Option<&'ll Metadata> {
-        Some(unsafe {
+    pub(crate) fn create_metadata(&self, name: &[u8]) -> &'ll Metadata {
+        unsafe {
             llvm::LLVMMDStringInContext2(self.llcx(), name.as_ptr() as *const c_char, name.len())
-        })
+        }
     }
 
     pub(crate) fn get_functions(&self) -> Vec<&'ll Value> {
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs b/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs
index 49ee96a41d6..61555ac2f6f 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/gdb.rs
@@ -74,7 +74,7 @@ pub(crate) fn get_or_insert_gdb_debug_scripts_section_global<'ll>(
             llvm::set_section(section_var, c".debug_gdb_scripts");
             llvm::set_initializer(section_var, cx.const_bytes(section_contents));
             llvm::LLVMSetGlobalConstant(section_var, llvm::True);
-            llvm::LLVMSetUnnamedAddress(section_var, llvm::UnnamedAddr::Global);
+            llvm::set_unnamed_address(section_var, llvm::UnnamedAddr::Global);
             llvm::set_linkage(section_var, llvm::Linkage::LinkOnceODRLinkage);
             // This should make sure that the whole section is not larger than
             // the string it contains. Otherwise we get a warning from GDB.
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
index 9b4736e50e6..0e9dbfba658 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
@@ -5,7 +5,7 @@ use std::path::{Path, PathBuf};
 use std::sync::Arc;
 use std::{iter, ptr};
 
-use libc::{c_char, c_longlong, c_uint};
+use libc::{c_longlong, c_uint};
 use rustc_abi::{Align, Size};
 use rustc_codegen_ssa::debuginfo::type_names::{VTableNameKind, cpp_like_debuginfo};
 use rustc_codegen_ssa::traits::*;
@@ -1582,13 +1582,9 @@ pub(crate) fn apply_vcall_visibility_metadata<'ll, 'tcx>(
     };
 
     let trait_ref_typeid = typeid_for_trait_ref(cx.tcx, trait_ref);
+    let typeid = cx.create_metadata(trait_ref_typeid.as_bytes());
 
     unsafe {
-        let typeid = llvm::LLVMMDStringInContext2(
-            cx.llcx,
-            trait_ref_typeid.as_ptr() as *const c_char,
-            trait_ref_typeid.as_bytes().len(),
-        );
         let v = [llvm::LLVMValueAsMetadata(cx.const_usize(0)), typeid];
         llvm::LLVMRustGlobalAddMetadata(
             vtable,
@@ -1630,7 +1626,7 @@ pub(crate) fn create_vtable_di_node<'ll, 'tcx>(
     // When full debuginfo is enabled, we want to try and prevent vtables from being
     // merged. Otherwise debuggers will have a hard time mapping from dyn pointer
     // to concrete type.
-    llvm::SetUnnamedAddress(vtable, llvm::UnnamedAddr::No);
+    llvm::set_unnamed_address(vtable, llvm::UnnamedAddr::No);
 
     let vtable_name =
         compute_debuginfo_vtable_name(cx.tcx, ty, poly_trait_ref, VTableNameKind::GlobalVariable);
diff --git a/compiler/rustc_codegen_llvm/src/declare.rs b/compiler/rustc_codegen_llvm/src/declare.rs
index 2419ec1f888..eb75716d768 100644
--- a/compiler/rustc_codegen_llvm/src/declare.rs
+++ b/compiler/rustc_codegen_llvm/src/declare.rs
@@ -49,7 +49,7 @@ pub(crate) fn declare_simple_fn<'ll>(
     };
 
     llvm::SetFunctionCallConv(llfn, callconv);
-    llvm::SetUnnamedAddress(llfn, unnamed);
+    llvm::set_unnamed_address(llfn, unnamed);
     llvm::set_visibility(llfn, visibility);
 
     llfn
@@ -176,7 +176,7 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
                 {
                     let typeid = cfi::typeid_for_instance(self.tcx, instance, options);
                     if typeids.insert(typeid.clone()) {
-                        self.add_type_metadata(llfn, typeid);
+                        self.add_type_metadata(llfn, typeid.as_bytes());
                     }
                 }
             } else {
@@ -189,7 +189,7 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
                 .map(cfi::TypeIdOptions::from_iter)
                 {
                     let typeid = cfi::typeid_for_fnabi(self.tcx, fn_abi, options);
-                    self.add_type_metadata(llfn, typeid);
+                    self.add_type_metadata(llfn, typeid.as_bytes());
                 }
             }
         }
diff --git a/compiler/rustc_codegen_llvm/src/errors.rs b/compiler/rustc_codegen_llvm/src/errors.rs
index d50ad8a1a9c..31d49e86319 100644
--- a/compiler/rustc_codegen_llvm/src/errors.rs
+++ b/compiler/rustc_codegen_llvm/src/errors.rs
@@ -38,10 +38,6 @@ impl<G: EmissionGuarantee> Diagnostic<'_, G> for ParseTargetMachineConfig<'_> {
 }
 
 #[derive(Diagnostic)]
-#[diag(codegen_llvm_autodiff_without_lto)]
-pub(crate) struct AutoDiffWithoutLTO;
-
-#[derive(Diagnostic)]
 #[diag(codegen_llvm_autodiff_without_enable)]
 pub(crate) struct AutoDiffWithoutEnable;
 
diff --git a/compiler/rustc_codegen_llvm/src/lib.rs b/compiler/rustc_codegen_llvm/src/lib.rs
index 63ca51b006d..6db4e122ad6 100644
--- a/compiler/rustc_codegen_llvm/src/lib.rs
+++ b/compiler/rustc_codegen_llvm/src/lib.rs
@@ -26,11 +26,11 @@ use std::mem::ManuallyDrop;
 use back::owned_target_machine::OwnedTargetMachine;
 use back::write::{create_informational_target_machine, create_target_machine};
 use context::SimpleCx;
-use errors::{AutoDiffWithoutLTO, ParseTargetMachineConfig};
+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::{LtoModuleCodegen, SerializedModule, ThinModule};
+use rustc_codegen_ssa::back::lto::{SerializedModule, ThinModule};
 use rustc_codegen_ssa::back::write::{
     CodegenContext, FatLtoInput, ModuleConfig, TargetMachineFactoryConfig, TargetMachineFactoryFn,
 };
@@ -43,7 +43,7 @@ use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
 use rustc_middle::ty::TyCtxt;
 use rustc_middle::util::Providers;
 use rustc_session::Session;
-use rustc_session::config::{Lto, OptLevel, OutputFilenames, PrintKind, PrintRequest};
+use rustc_session::config::{OptLevel, OutputFilenames, PrintKind, PrintRequest};
 use rustc_span::Symbol;
 
 mod back {
@@ -174,18 +174,29 @@ impl WriteBackendMethods for LlvmCodegenBackend {
     ) -> Result<ModuleCodegen<Self::Module>, FatalError> {
         back::write::link(cgcx, dcx, modules)
     }
-    fn run_fat_lto(
+    fn run_and_optimize_fat_lto(
         cgcx: &CodegenContext<Self>,
         modules: Vec<FatLtoInput<Self>>,
         cached_modules: Vec<(SerializedModule<Self::ModuleBuffer>, WorkProduct)>,
-    ) -> Result<LtoModuleCodegen<Self>, FatalError> {
-        back::lto::run_fat(cgcx, modules, cached_modules)
+        diff_fncs: Vec<AutoDiffItem>,
+    ) -> Result<ModuleCodegen<Self::Module>, FatalError> {
+        let mut module = back::lto::run_fat(cgcx, modules, cached_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)?;
+
+        Ok(module)
     }
     fn run_thin_lto(
         cgcx: &CodegenContext<Self>,
         modules: Vec<(String, Self::ThinBuffer)>,
         cached_modules: Vec<(SerializedModule<Self::ModuleBuffer>, WorkProduct)>,
-    ) -> Result<(Vec<LtoModuleCodegen<Self>>, Vec<WorkProduct>), FatalError> {
+    ) -> Result<(Vec<ThinModule<Self>>, Vec<WorkProduct>), FatalError> {
         back::lto::run_thin(cgcx, modules, cached_modules)
     }
     fn optimize(
@@ -196,14 +207,6 @@ impl WriteBackendMethods for LlvmCodegenBackend {
     ) -> Result<(), FatalError> {
         back::write::optimize(cgcx, dcx, module, config)
     }
-    fn optimize_fat(
-        cgcx: &CodegenContext<Self>,
-        module: &mut ModuleCodegen<Self::Module>,
-    ) -> Result<(), FatalError> {
-        let dcx = cgcx.create_dcx();
-        let dcx = dcx.handle();
-        back::lto::run_pass_manager(cgcx, dcx, module, false)
-    }
     fn optimize_thin(
         cgcx: &CodegenContext<Self>,
         thin: ThinModule<Self>,
@@ -212,11 +215,10 @@ impl WriteBackendMethods for LlvmCodegenBackend {
     }
     fn codegen(
         cgcx: &CodegenContext<Self>,
-        dcx: DiagCtxtHandle<'_>,
         module: ModuleCodegen<Self::Module>,
         config: &ModuleConfig,
     ) -> Result<CompiledModule, FatalError> {
-        back::write::codegen(cgcx, dcx, module, config)
+        back::write::codegen(cgcx, module, config)
     }
     fn prepare_thin(
         module: ModuleCodegen<Self::Module>,
@@ -227,19 +229,6 @@ impl WriteBackendMethods for LlvmCodegenBackend {
     fn serialize_module(module: ModuleCodegen<Self::Module>) -> (String, Self::ModuleBuffer) {
         (module.name, back::lto::ModuleBuffer::new(module.module_llvm.llmod()))
     }
-    /// Generate autodiff rules
-    fn autodiff(
-        cgcx: &CodegenContext<Self>,
-        module: &ModuleCodegen<Self::Module>,
-        diff_fncs: Vec<AutoDiffItem>,
-        config: &ModuleConfig,
-    ) -> Result<(), FatalError> {
-        if cgcx.lto != Lto::Fat {
-            let dcx = cgcx.create_dcx();
-            return Err(dcx.handle().emit_almost_fatal(AutoDiffWithoutLTO));
-        }
-        builder::autodiff::differentiate(module, cgcx, diff_fncs, config)
-    }
 }
 
 impl LlvmCodegenBackend {
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 5c34ab2e304..0b1e632cbc4 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -1009,7 +1009,7 @@ unsafe extern "C" {
         ModuleID: *const c_char,
         C: &Context,
     ) -> &Module;
-    pub(crate) fn LLVMCloneModule(M: &Module) -> &Module;
+    pub(crate) safe fn LLVMCloneModule(M: &Module) -> &Module;
 
     /// Data layout. See Module::getDataLayout.
     pub(crate) fn LLVMGetDataLayoutStr(M: &Module) -> *const c_char;
@@ -1168,18 +1168,18 @@ unsafe extern "C" {
     pub(crate) fn LLVMGlobalGetValueType(Global: &Value) -> &Type;
 
     // Operations on global variables
-    pub(crate) fn LLVMIsAGlobalVariable(GlobalVar: &Value) -> Option<&Value>;
+    pub(crate) safe fn LLVMIsAGlobalVariable(GlobalVar: &Value) -> Option<&Value>;
     pub(crate) fn LLVMAddGlobal<'a>(M: &'a Module, Ty: &'a Type, Name: *const c_char) -> &'a Value;
     pub(crate) fn LLVMGetNamedGlobal(M: &Module, Name: *const c_char) -> Option<&Value>;
     pub(crate) fn LLVMGetFirstGlobal(M: &Module) -> Option<&Value>;
     pub(crate) fn LLVMGetNextGlobal(GlobalVar: &Value) -> Option<&Value>;
     pub(crate) fn LLVMDeleteGlobal(GlobalVar: &Value);
-    pub(crate) fn LLVMGetInitializer(GlobalVar: &Value) -> Option<&Value>;
+    pub(crate) safe fn LLVMGetInitializer(GlobalVar: &Value) -> Option<&Value>;
     pub(crate) fn LLVMSetInitializer<'a>(GlobalVar: &'a Value, ConstantVal: &'a Value);
-    pub(crate) fn LLVMIsThreadLocal(GlobalVar: &Value) -> Bool;
+    pub(crate) safe fn LLVMIsThreadLocal(GlobalVar: &Value) -> Bool;
     pub(crate) fn LLVMSetThreadLocalMode(GlobalVar: &Value, Mode: ThreadLocalMode);
-    pub(crate) fn LLVMIsGlobalConstant(GlobalVar: &Value) -> Bool;
-    pub(crate) fn LLVMSetGlobalConstant(GlobalVar: &Value, IsConstant: Bool);
+    pub(crate) safe fn LLVMIsGlobalConstant(GlobalVar: &Value) -> Bool;
+    pub(crate) safe fn LLVMSetGlobalConstant(GlobalVar: &Value, IsConstant: Bool);
     pub(crate) safe fn LLVMSetTailCall(CallInst: &Value, IsTailCall: Bool);
 
     // Operations on attributes
@@ -1718,7 +1718,7 @@ unsafe extern "C" {
 
     pub(crate) safe fn LLVMMetadataAsValue<'a>(C: &'a Context, MD: &'a Metadata) -> &'a Value;
 
-    pub(crate) fn LLVMSetUnnamedAddress(Global: &Value, UnnamedAddr: UnnamedAddr);
+    pub(crate) safe fn LLVMSetUnnamedAddress(Global: &Value, UnnamedAddr: UnnamedAddr);
 
     pub(crate) fn LLVMIsAConstantInt(value_ref: &Value) -> Option<&ConstantInt>;
 
diff --git a/compiler/rustc_codegen_llvm/src/llvm/mod.rs b/compiler/rustc_codegen_llvm/src/llvm/mod.rs
index 3fc83fca352..154ba4fd690 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/mod.rs
@@ -217,10 +217,8 @@ pub(crate) fn SetUniqueComdat(llmod: &Module, val: &Value) {
     set_comdat(llmod, val, &name);
 }
 
-pub(crate) fn SetUnnamedAddress(global: &Value, unnamed: UnnamedAddr) {
-    unsafe {
-        LLVMSetUnnamedAddress(global, unnamed);
-    }
+pub(crate) fn set_unnamed_address(global: &Value, unnamed: UnnamedAddr) {
+    LLVMSetUnnamedAddress(global, unnamed);
 }
 
 pub(crate) fn set_thread_local_mode(global: &Value, mode: ThreadLocalMode) {
@@ -260,9 +258,7 @@ pub(crate) fn set_initializer(llglobal: &Value, constant_val: &Value) {
 }
 
 pub(crate) fn set_global_constant(llglobal: &Value, is_constant: bool) {
-    unsafe {
-        LLVMSetGlobalConstant(llglobal, if is_constant { ffi::True } else { ffi::False });
-    }
+    LLVMSetGlobalConstant(llglobal, if is_constant { ffi::True } else { ffi::False });
 }
 
 pub(crate) fn get_linkage(llglobal: &Value) -> Linkage {
diff --git a/compiler/rustc_codegen_llvm/src/mono_item.rs b/compiler/rustc_codegen_llvm/src/mono_item.rs
index 3f38e1e191b..f9edaded60d 100644
--- a/compiler/rustc_codegen_llvm/src/mono_item.rs
+++ b/compiler/rustc_codegen_llvm/src/mono_item.rs
@@ -55,8 +55,8 @@ impl<'tcx> PreDefineCodegenMethods<'tcx> for CodegenCx<'_, 'tcx> {
         let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty());
         let lldecl = self.declare_fn(symbol_name, fn_abi, Some(instance));
         llvm::set_linkage(lldecl, base::linkage_to_llvm(linkage));
-        let attrs = self.tcx.codegen_fn_attrs(instance.def_id());
-        base::set_link_section(lldecl, attrs);
+        let attrs = self.tcx.codegen_instance_attrs(instance.def);
+        base::set_link_section(lldecl, &attrs);
         if (linkage == Linkage::LinkOnceODR || linkage == Linkage::WeakODR)
             && self.tcx.sess.target.supports_comdat()
         {
@@ -131,8 +131,8 @@ impl CodegenCx<'_, '_> {
         }
 
         // Thread-local variables generally don't support copy relocations.
-        let is_thread_local_var = unsafe { llvm::LLVMIsAGlobalVariable(llval) }
-            .is_some_and(|v| unsafe { llvm::LLVMIsThreadLocal(v) } == llvm::True);
+        let is_thread_local_var = llvm::LLVMIsAGlobalVariable(llval)
+            .is_some_and(|v| llvm::LLVMIsThreadLocal(v) == llvm::True);
         if is_thread_local_var {
             return false;
         }
diff --git a/compiler/rustc_codegen_llvm/src/type_.rs b/compiler/rustc_codegen_llvm/src/type_.rs
index ee472e75ed4..89365503138 100644
--- a/compiler/rustc_codegen_llvm/src/type_.rs
+++ b/compiler/rustc_codegen_llvm/src/type_.rs
@@ -2,7 +2,7 @@ use std::borrow::Borrow;
 use std::hash::{Hash, Hasher};
 use std::{fmt, ptr};
 
-use libc::{c_char, c_uint};
+use libc::c_uint;
 use rustc_abi::{AddressSpace, Align, Integer, Reg, Size};
 use rustc_codegen_ssa::common::TypeKind;
 use rustc_codegen_ssa::traits::*;
@@ -298,8 +298,8 @@ impl<'ll, 'tcx> LayoutTypeCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
 }
 
 impl<'ll, 'tcx> TypeMembershipCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
-    fn add_type_metadata(&self, function: &'ll Value, typeid: String) {
-        let typeid_metadata = self.typeid_metadata(typeid).unwrap();
+    fn add_type_metadata(&self, function: &'ll Value, typeid: &[u8]) {
+        let typeid_metadata = self.create_metadata(typeid);
         unsafe {
             let v = [llvm::LLVMValueAsMetadata(self.const_usize(0)), typeid_metadata];
             llvm::LLVMRustGlobalAddMetadata(
@@ -310,8 +310,8 @@ impl<'ll, 'tcx> TypeMembershipCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         }
     }
 
-    fn set_type_metadata(&self, function: &'ll Value, typeid: String) {
-        let typeid_metadata = self.typeid_metadata(typeid).unwrap();
+    fn set_type_metadata(&self, function: &'ll Value, typeid: &[u8]) {
+        let typeid_metadata = self.create_metadata(typeid);
         unsafe {
             let v = [llvm::LLVMValueAsMetadata(self.const_usize(0)), typeid_metadata];
             llvm::LLVMGlobalSetMetadata(
@@ -322,10 +322,8 @@ impl<'ll, 'tcx> TypeMembershipCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         }
     }
 
-    fn typeid_metadata(&self, typeid: String) -> Option<&'ll Metadata> {
-        Some(unsafe {
-            llvm::LLVMMDStringInContext2(self.llcx, typeid.as_ptr() as *const c_char, typeid.len())
-        })
+    fn typeid_metadata(&self, typeid: &[u8]) -> Option<&'ll Metadata> {
+        Some(self.create_metadata(typeid))
     }
 
     fn add_kcfi_type_metadata(&self, function: &'ll Value, kcfi_typeid: u32) {
diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index b46773396fc..5ce301c0eb9 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -2542,12 +2542,7 @@ fn add_order_independent_options(
         // sections to ensure we have all the data for PGO.
         let keep_metadata =
             crate_type == CrateType::Dylib || sess.opts.cg.profile_generate.enabled();
-        if crate_type != CrateType::Executable || !sess.opts.unstable_opts.export_executable_symbols
-        {
-            cmd.gc_sections(keep_metadata);
-        } else {
-            cmd.no_gc_sections();
-        }
+        cmd.gc_sections(keep_metadata);
     }
 
     cmd.set_output_kind(link_output_kind, crate_type, out_filename);
diff --git a/compiler/rustc_codegen_ssa/src/back/linker.rs b/compiler/rustc_codegen_ssa/src/back/linker.rs
index e0a3ad55be0..050797354b4 100644
--- a/compiler/rustc_codegen_ssa/src/back/linker.rs
+++ b/compiler/rustc_codegen_ssa/src/back/linker.rs
@@ -326,7 +326,6 @@ pub(crate) trait Linker {
         link_or_cc_args(self, &[path]);
     }
     fn gc_sections(&mut self, keep_metadata: bool);
-    fn no_gc_sections(&mut self);
     fn full_relro(&mut self);
     fn partial_relro(&mut self);
     fn no_relro(&mut self);
@@ -688,12 +687,6 @@ impl<'a> Linker for GccLinker<'a> {
         }
     }
 
-    fn no_gc_sections(&mut self) {
-        if self.is_gnu || self.sess.target.is_like_wasm {
-            self.link_arg("--no-gc-sections");
-        }
-    }
-
     fn optimize(&mut self) {
         if !self.is_gnu && !self.sess.target.is_like_wasm {
             return;
@@ -1010,10 +1003,6 @@ impl<'a> Linker for MsvcLinker<'a> {
         }
     }
 
-    fn no_gc_sections(&mut self) {
-        self.link_arg("/OPT:NOREF,NOICF");
-    }
-
     fn full_relro(&mut self) {
         // noop
     }
@@ -1243,10 +1232,6 @@ impl<'a> Linker for EmLinker<'a> {
         // noop
     }
 
-    fn no_gc_sections(&mut self) {
-        // noop
-    }
-
     fn optimize(&mut self) {
         // Emscripten performs own optimizations
         self.cc_arg(match self.sess.opts.optimize {
@@ -1418,10 +1403,6 @@ impl<'a> Linker for WasmLd<'a> {
         self.link_arg("--gc-sections");
     }
 
-    fn no_gc_sections(&mut self) {
-        self.link_arg("--no-gc-sections");
-    }
-
     fn optimize(&mut self) {
         // The -O flag is, as of late 2023, only used for merging of strings and debuginfo, and
         // only differentiates -O0 and -O1. It does not apply to LTO.
@@ -1567,10 +1548,6 @@ impl<'a> Linker for L4Bender<'a> {
         }
     }
 
-    fn no_gc_sections(&mut self) {
-        self.link_arg("--no-gc-sections");
-    }
-
     fn optimize(&mut self) {
         // GNU-style linkers support optimization with -O. GNU ld doesn't
         // need a numeric argument, but other linkers do.
@@ -1734,10 +1711,6 @@ impl<'a> Linker for AixLinker<'a> {
         self.link_arg("-bgc");
     }
 
-    fn no_gc_sections(&mut self) {
-        self.link_arg("-bnogc");
-    }
-
     fn optimize(&mut self) {}
 
     fn pgo_gen(&mut self) {
@@ -1982,8 +1955,6 @@ impl<'a> Linker for PtxLinker<'a> {
 
     fn gc_sections(&mut self, _keep_metadata: bool) {}
 
-    fn no_gc_sections(&mut self) {}
-
     fn pgo_gen(&mut self) {}
 
     fn no_crt_objects(&mut self) {}
@@ -2057,8 +2028,6 @@ impl<'a> Linker for LlbcLinker<'a> {
 
     fn gc_sections(&mut self, _keep_metadata: bool) {}
 
-    fn no_gc_sections(&mut self) {}
-
     fn pgo_gen(&mut self) {}
 
     fn no_crt_objects(&mut self) {}
@@ -2139,8 +2108,6 @@ impl<'a> Linker for BpfLinker<'a> {
 
     fn gc_sections(&mut self, _keep_metadata: bool) {}
 
-    fn no_gc_sections(&mut self) {}
-
     fn pgo_gen(&mut self) {}
 
     fn no_crt_objects(&mut self) {}
diff --git a/compiler/rustc_codegen_ssa/src/back/lto.rs b/compiler/rustc_codegen_ssa/src/back/lto.rs
index ce6fe8a191b..b49b6783bbd 100644
--- a/compiler/rustc_codegen_ssa/src/back/lto.rs
+++ b/compiler/rustc_codegen_ssa/src/back/lto.rs
@@ -1,13 +1,8 @@
 use std::ffi::CString;
 use std::sync::Arc;
 
-use rustc_ast::expand::autodiff_attrs::AutoDiffItem;
 use rustc_data_structures::memmap::Mmap;
-use rustc_errors::FatalError;
 
-use super::write::CodegenContext;
-use crate::ModuleCodegen;
-use crate::back::write::ModuleConfig;
 use crate::traits::*;
 
 pub struct ThinModule<B: WriteBackendMethods> {
@@ -42,61 +37,6 @@ pub struct ThinShared<B: WriteBackendMethods> {
     pub module_names: Vec<CString>,
 }
 
-pub enum LtoModuleCodegen<B: WriteBackendMethods> {
-    Fat(ModuleCodegen<B::Module>),
-    Thin(ThinModule<B>),
-}
-
-impl<B: WriteBackendMethods> LtoModuleCodegen<B> {
-    pub fn name(&self) -> &str {
-        match *self {
-            LtoModuleCodegen::Fat(_) => "everything",
-            LtoModuleCodegen::Thin(ref m) => m.name(),
-        }
-    }
-
-    /// Optimize this module within the given codegen context.
-    pub fn optimize(
-        self,
-        cgcx: &CodegenContext<B>,
-    ) -> Result<ModuleCodegen<B::Module>, FatalError> {
-        match self {
-            LtoModuleCodegen::Fat(mut module) => {
-                B::optimize_fat(cgcx, &mut module)?;
-                Ok(module)
-            }
-            LtoModuleCodegen::Thin(thin) => B::optimize_thin(cgcx, thin),
-        }
-    }
-
-    /// A "gauge" of how costly it is to optimize this module, used to sort
-    /// biggest modules first.
-    pub fn cost(&self) -> u64 {
-        match *self {
-            // Only one module with fat LTO, so the cost doesn't matter.
-            LtoModuleCodegen::Fat(_) => 0,
-            LtoModuleCodegen::Thin(ref m) => m.cost(),
-        }
-    }
-
-    /// Run autodiff on Fat LTO module
-    pub fn autodiff(
-        self,
-        cgcx: &CodegenContext<B>,
-        diff_fncs: Vec<AutoDiffItem>,
-        config: &ModuleConfig,
-    ) -> Result<LtoModuleCodegen<B>, FatalError> {
-        match &self {
-            LtoModuleCodegen::Fat(module) => {
-                B::autodiff(cgcx, &module, diff_fncs, config)?;
-            }
-            _ => panic!("autodiff called with non-fat LTO module"),
-        }
-
-        Ok(self)
-    }
-}
-
 pub enum SerializedModule<M: ModuleBufferMethods> {
     Local(M),
     FromRlib(Vec<u8>),
diff --git a/compiler/rustc_codegen_ssa/src/back/write.rs b/compiler/rustc_codegen_ssa/src/back/write.rs
index d2a64ec2993..50a7cba300b 100644
--- a/compiler/rustc_codegen_ssa/src/back/write.rs
+++ b/compiler/rustc_codegen_ssa/src/back/write.rs
@@ -397,50 +397,31 @@ impl<B: WriteBackendMethods> CodegenContext<B> {
     }
 }
 
-fn generate_lto_work<B: ExtraBackendMethods>(
+fn generate_thin_lto_work<B: ExtraBackendMethods>(
     cgcx: &CodegenContext<B>,
-    autodiff: Vec<AutoDiffItem>,
-    needs_fat_lto: Vec<FatLtoInput<B>>,
     needs_thin_lto: Vec<(String, B::ThinBuffer)>,
     import_only_modules: Vec<(SerializedModule<B::ModuleBuffer>, WorkProduct)>,
 ) -> Vec<(WorkItem<B>, u64)> {
-    let _prof_timer = cgcx.prof.generic_activity("codegen_generate_lto_work");
-
-    if !needs_fat_lto.is_empty() {
-        assert!(needs_thin_lto.is_empty());
-        let mut module =
-            B::run_fat_lto(cgcx, needs_fat_lto, import_only_modules).unwrap_or_else(|e| e.raise());
-        if cgcx.lto == Lto::Fat && !autodiff.is_empty() {
-            let config = cgcx.config(ModuleKind::Regular);
-            module = module.autodiff(cgcx, autodiff, config).unwrap_or_else(|e| e.raise());
-        }
-        // We are adding a single work item, so the cost doesn't matter.
-        vec![(WorkItem::LTO(module), 0)]
-    } else {
-        if !autodiff.is_empty() {
-            let dcx = cgcx.create_dcx();
-            dcx.handle().emit_fatal(AutodiffWithoutLto {});
-        }
-        assert!(needs_fat_lto.is_empty());
-        let (lto_modules, copy_jobs) = B::run_thin_lto(cgcx, needs_thin_lto, import_only_modules)
-            .unwrap_or_else(|e| e.raise());
-        lto_modules
-            .into_iter()
-            .map(|module| {
-                let cost = module.cost();
-                (WorkItem::LTO(module), cost)
-            })
-            .chain(copy_jobs.into_iter().map(|wp| {
-                (
-                    WorkItem::CopyPostLtoArtifacts(CachedModuleCodegen {
-                        name: wp.cgu_name.clone(),
-                        source: wp,
-                    }),
-                    0, // copying is very cheap
-                )
-            }))
-            .collect()
-    }
+    let _prof_timer = cgcx.prof.generic_activity("codegen_thin_generate_lto_work");
+
+    let (lto_modules, copy_jobs) =
+        B::run_thin_lto(cgcx, needs_thin_lto, import_only_modules).unwrap_or_else(|e| e.raise());
+    lto_modules
+        .into_iter()
+        .map(|module| {
+            let cost = module.cost();
+            (WorkItem::ThinLto(module), cost)
+        })
+        .chain(copy_jobs.into_iter().map(|wp| {
+            (
+                WorkItem::CopyPostLtoArtifacts(CachedModuleCodegen {
+                    name: wp.cgu_name.clone(),
+                    source: wp,
+                }),
+                0, // copying is very cheap
+            )
+        }))
+        .collect()
 }
 
 struct CompiledModules {
@@ -470,6 +451,7 @@ 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();
 
@@ -488,6 +470,7 @@ pub(crate) fn start_async_codegen<B: ExtraBackendMethods>(
         backend.clone(),
         tcx,
         &crate_info,
+        autodiff_items,
         shared_emitter,
         codegen_worker_send,
         coordinator_receive,
@@ -736,15 +719,23 @@ pub(crate) enum WorkItem<B: WriteBackendMethods> {
     /// Copy the post-LTO artifacts from the incremental cache to the output
     /// directory.
     CopyPostLtoArtifacts(CachedModuleCodegen),
-    /// Performs (Thin)LTO on the given module.
-    LTO(lto::LtoModuleCodegen<B>),
+    /// Performs fat LTO on the given module.
+    FatLto {
+        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>),
 }
 
 impl<B: WriteBackendMethods> WorkItem<B> {
     fn module_kind(&self) -> ModuleKind {
         match *self {
             WorkItem::Optimize(ref m) => m.kind,
-            WorkItem::CopyPostLtoArtifacts(_) | WorkItem::LTO(_) => ModuleKind::Regular,
+            WorkItem::CopyPostLtoArtifacts(_) | WorkItem::FatLto { .. } | WorkItem::ThinLto(_) => {
+                ModuleKind::Regular
+            }
         }
     }
 
@@ -792,7 +783,8 @@ impl<B: WriteBackendMethods> WorkItem<B> {
         match self {
             WorkItem::Optimize(m) => desc("opt", "optimize module", &m.name),
             WorkItem::CopyPostLtoArtifacts(m) => desc("cpy", "copy LTO artifacts for", &m.name),
-            WorkItem::LTO(m) => desc("lto", "LTO module", m.name()),
+            WorkItem::FatLto { .. } => desc("lto", "fat LTO module", "everything"),
+            WorkItem::ThinLto(m) => desc("lto", "thin-LTO module", m.name()),
         }
     }
 }
@@ -996,12 +988,24 @@ fn execute_copy_from_cache_work_item<B: ExtraBackendMethods>(
     })
 }
 
-fn execute_lto_work_item<B: ExtraBackendMethods>(
+fn execute_fat_lto_work_item<B: ExtraBackendMethods>(
+    cgcx: &CodegenContext<B>,
+    needs_fat_lto: Vec<FatLtoInput<B>>,
+    import_only_modules: Vec<(SerializedModule<B::ModuleBuffer>, WorkProduct)>,
+    autodiff: Vec<AutoDiffItem>,
+    module_config: &ModuleConfig,
+) -> Result<WorkItemResult<B>, FatalError> {
+    let module = B::run_and_optimize_fat_lto(cgcx, needs_fat_lto, import_only_modules, autodiff)?;
+    let module = B::codegen(cgcx, module, module_config)?;
+    Ok(WorkItemResult::Finished(module))
+}
+
+fn execute_thin_lto_work_item<B: ExtraBackendMethods>(
     cgcx: &CodegenContext<B>,
-    module: lto::LtoModuleCodegen<B>,
+    module: lto::ThinModule<B>,
     module_config: &ModuleConfig,
 ) -> Result<WorkItemResult<B>, FatalError> {
-    let module = module.optimize(cgcx)?;
+    let module = B::optimize_thin(cgcx, module)?;
     finish_intra_module_work(cgcx, module, module_config)
 }
 
@@ -1010,11 +1014,8 @@ fn finish_intra_module_work<B: ExtraBackendMethods>(
     module: ModuleCodegen<B::Module>,
     module_config: &ModuleConfig,
 ) -> Result<WorkItemResult<B>, FatalError> {
-    let dcx = cgcx.create_dcx();
-    let dcx = dcx.handle();
-
     if !cgcx.opts.unstable_opts.combine_cgu || module.kind == ModuleKind::Allocator {
-        let module = B::codegen(cgcx, dcx, module, module_config)?;
+        let module = B::codegen(cgcx, module, module_config)?;
         Ok(WorkItemResult::Finished(module))
     } else {
         Ok(WorkItemResult::NeedsLink(module))
@@ -1031,9 +1032,6 @@ pub(crate) enum Message<B: WriteBackendMethods> {
     /// Sent from a backend worker thread.
     WorkItem { result: Result<WorkItemResult<B>, Option<WorkerFatalError>>, worker_id: usize },
 
-    /// A vector containing all the AutoDiff tasks that we have to pass to Enzyme.
-    AddAutoDiffItems(Vec<AutoDiffItem>),
-
     /// The frontend has finished generating something (backend IR or a
     /// post-LTO artifact) for a codegen unit, and it should be passed to the
     /// backend. Sent from the main thread.
@@ -1100,6 +1098,7 @@ 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<Box<dyn Any + Send>>,
@@ -1109,6 +1108,7 @@ 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();
     drop(link::each_linked_rlib(crate_info, None, &mut |cnum, path| {
@@ -1362,7 +1362,6 @@ fn start_executing_work<B: ExtraBackendMethods>(
 
         // This is where we collect codegen units that have gone all the way
         // through codegen and LLVM.
-        let mut autodiff_items = Vec::new();
         let mut compiled_modules = vec![];
         let mut compiled_allocator_module = None;
         let mut needs_link = Vec::new();
@@ -1474,20 +1473,37 @@ fn start_executing_work<B: ExtraBackendMethods>(
                     let needs_thin_lto = mem::take(&mut needs_thin_lto);
                     let import_only_modules = mem::take(&mut lto_import_only_modules);
 
-                    for (work, cost) in generate_lto_work(
-                        &cgcx,
-                        autodiff_items.clone(),
-                        needs_fat_lto,
-                        needs_thin_lto,
-                        import_only_modules,
-                    ) {
-                        let insertion_index = work_items
-                            .binary_search_by_key(&cost, |&(_, cost)| cost)
-                            .unwrap_or_else(|e| e);
-                        work_items.insert(insertion_index, (work, cost));
+                    if !needs_fat_lto.is_empty() {
+                        assert!(needs_thin_lto.is_empty());
+
+                        work_items.push((
+                            WorkItem::FatLto {
+                                needs_fat_lto,
+                                import_only_modules,
+                                autodiff: autodiff_items.clone(),
+                            },
+                            0,
+                        ));
                         if cgcx.parallel {
                             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, needs_thin_lto, import_only_modules)
+                        {
+                            let insertion_index = work_items
+                                .binary_search_by_key(&cost, |&(_, cost)| cost)
+                                .unwrap_or_else(|e| e);
+                            work_items.insert(insertion_index, (work, cost));
+                            if cgcx.parallel {
+                                helper.request_token();
+                            }
+                        }
                     }
                 }
 
@@ -1616,10 +1632,6 @@ fn start_executing_work<B: ExtraBackendMethods>(
                     main_thread_state = MainThreadState::Idle;
                 }
 
-                Message::AddAutoDiffItems(mut items) => {
-                    autodiff_items.append(&mut items);
-                }
-
                 Message::CodegenComplete => {
                     if codegen_state != Aborted {
                         codegen_state = Completed;
@@ -1702,7 +1714,7 @@ fn start_executing_work<B: ExtraBackendMethods>(
             let dcx = dcx.handle();
             let module = B::run_link(&cgcx, dcx, needs_link).map_err(|_| ())?;
             let module =
-                B::codegen(&cgcx, dcx, module, cgcx.config(ModuleKind::Regular)).map_err(|_| ())?;
+                B::codegen(&cgcx, module, cgcx.config(ModuleKind::Regular)).map_err(|_| ())?;
             compiled_modules.push(module);
         }
 
@@ -1842,10 +1854,22 @@ fn spawn_work<'a, B: ExtraBackendMethods>(
                     );
                     Ok(execute_copy_from_cache_work_item(&cgcx, m, module_config))
                 }
-                WorkItem::LTO(m) => {
+                WorkItem::FatLto { needs_fat_lto, import_only_modules, autodiff } => {
+                    let _timer = cgcx
+                        .prof
+                        .generic_activity_with_arg("codegen_module_perform_lto", "everything");
+                    execute_fat_lto_work_item(
+                        &cgcx,
+                        needs_fat_lto,
+                        import_only_modules,
+                        autodiff,
+                        module_config,
+                    )
+                }
+                WorkItem::ThinLto(m) => {
                     let _timer =
                         cgcx.prof.generic_activity_with_arg("codegen_module_perform_lto", m.name());
-                    execute_lto_work_item(&cgcx, m, module_config)
+                    execute_thin_lto_work_item(&cgcx, m, module_config)
                 }
             })
         };
@@ -2082,10 +2106,6 @@ impl<B: ExtraBackendMethods> OngoingCodegen<B> {
         drop(self.coordinator.sender.send(Box::new(Message::CodegenComplete::<B>)));
     }
 
-    pub(crate) fn submit_autodiff_items(&self, items: Vec<AutoDiffItem>) {
-        drop(self.coordinator.sender.send(Box::new(Message::<B>::AddAutoDiffItems(items))));
-    }
-
     pub(crate) fn check_for_errors(&self, sess: &Session) {
         self.shared_emitter_main.check(sess, false);
     }
diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs
index 18581f854b6..833456abb8a 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);
 
@@ -667,7 +667,6 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
     // codegen units.
     let MonoItemPartitions { codegen_units, autodiff_items, .. } =
         tcx.collect_and_partition_mono_items(());
-    let autodiff_fncs = autodiff_items.to_vec();
 
     // 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
@@ -680,7 +679,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
         }
     }
 
-    let ongoing_codegen = start_async_codegen(backend.clone(), tcx, target_cpu);
+    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) {
@@ -710,10 +709,6 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
         );
     }
 
-    if !autodiff_fncs.is_empty() {
-        ongoing_codegen.submit_autodiff_items(autodiff_fncs);
-    }
-
     // For better throughput during parallel processing by LLVM, we used to sort
     // CGUs largest to smallest. This would lead to better thread utilization
     // by, for example, preventing a large CGU from being processed last and
diff --git a/compiler/rustc_codegen_ssa/src/meth.rs b/compiler/rustc_codegen_ssa/src/meth.rs
index 2aa5c3c27ea..34ad35a729b 100644
--- a/compiler/rustc_codegen_ssa/src/meth.rs
+++ b/compiler/rustc_codegen_ssa/src/meth.rs
@@ -139,7 +139,8 @@ pub(crate) fn load_vtable<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         && bx.cx().sess().lto() == Lto::Fat
     {
         if let Some(trait_ref) = dyn_trait_in_self(bx.tcx(), ty) {
-            let typeid = bx.typeid_metadata(typeid_for_trait_ref(bx.tcx(), trait_ref)).unwrap();
+            let typeid =
+                bx.typeid_metadata(typeid_for_trait_ref(bx.tcx(), trait_ref).as_bytes()).unwrap();
             let func = bx.type_checked_load(llvtable, vtable_byte_offset, typeid);
             return func;
         } else if nonnull {
diff --git a/compiler/rustc_codegen_ssa/src/mir/debuginfo.rs b/compiler/rustc_codegen_ssa/src/mir/debuginfo.rs
index 025f5fb54f4..b8f635ab781 100644
--- a/compiler/rustc_codegen_ssa/src/mir/debuginfo.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/debuginfo.rs
@@ -356,7 +356,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             LocalRef::Operand(operand) => {
                 // Don't spill operands onto the stack in naked functions.
                 // See: https://github.com/rust-lang/rust/issues/42779
-                let attrs = bx.tcx().codegen_fn_attrs(self.instance.def_id());
+                let attrs = bx.tcx().codegen_instance_attrs(self.instance.def);
                 if attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
                     return;
                 }
diff --git a/compiler/rustc_codegen_ssa/src/mir/mod.rs b/compiler/rustc_codegen_ssa/src/mir/mod.rs
index fa69820d5d2..50d0f910744 100644
--- a/compiler/rustc_codegen_ssa/src/mir/mod.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/mod.rs
@@ -390,9 +390,8 @@ fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 
     let mut num_untupled = None;
 
-    let codegen_fn_attrs = bx.tcx().codegen_fn_attrs(fx.instance.def_id());
-    let naked = codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED);
-    if naked {
+    let codegen_fn_attrs = bx.tcx().codegen_instance_attrs(fx.instance.def);
+    if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
         return vec![];
     }
 
diff --git a/compiler/rustc_codegen_ssa/src/mir/naked_asm.rs b/compiler/rustc_codegen_ssa/src/mir/naked_asm.rs
index beaf8950978..42e435cf0a3 100644
--- a/compiler/rustc_codegen_ssa/src/mir/naked_asm.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/naked_asm.rs
@@ -128,7 +128,7 @@ fn prefix_and_suffix<'tcx>(
     let is_arm = tcx.sess.target.arch == "arm";
     let is_thumb = tcx.sess.unstable_target_features.contains(&sym::thumb_mode);
 
-    let attrs = tcx.codegen_fn_attrs(instance.def_id());
+    let attrs = tcx.codegen_instance_attrs(instance.def);
     let link_section = attrs.link_section.map(|symbol| symbol.as_str().to_string());
 
     // If no alignment is specified, an alignment of 4 bytes is used.
diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
index e90463aacc8..2587e89417a 100644
--- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
@@ -611,11 +611,19 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     let fn_abi = bx.fn_abi_of_instance(instance, ty::List::empty());
                     let fn_ty = bx.fn_decl_backend_type(fn_abi);
                     let fn_attrs = if bx.tcx().def_kind(instance.def_id()).has_codegen_attrs() {
-                        Some(bx.tcx().codegen_fn_attrs(instance.def_id()))
+                        Some(bx.tcx().codegen_instance_attrs(instance.def))
                     } else {
                         None
                     };
-                    bx.call(fn_ty, fn_attrs, Some(fn_abi), fn_ptr, &[], None, Some(instance))
+                    bx.call(
+                        fn_ty,
+                        fn_attrs.as_deref(),
+                        Some(fn_abi),
+                        fn_ptr,
+                        &[],
+                        None,
+                        Some(instance),
+                    )
                 } else {
                     bx.get_static(def_id)
                 };
diff --git a/compiler/rustc_codegen_ssa/src/mono_item.rs b/compiler/rustc_codegen_ssa/src/mono_item.rs
index 7b4268abe4b..b9040c330fb 100644
--- a/compiler/rustc_codegen_ssa/src/mono_item.rs
+++ b/compiler/rustc_codegen_ssa/src/mono_item.rs
@@ -41,12 +41,8 @@ impl<'a, 'tcx: 'a> MonoItemExt<'a, 'tcx> for MonoItem<'tcx> {
                 base::codegen_global_asm(cx, item_id);
             }
             MonoItem::Fn(instance) => {
-                if cx
-                    .tcx()
-                    .codegen_fn_attrs(instance.def_id())
-                    .flags
-                    .contains(CodegenFnAttrFlags::NAKED)
-                {
+                let flags = cx.tcx().codegen_instance_attrs(instance.def).flags;
+                if flags.contains(CodegenFnAttrFlags::NAKED) {
                     naked_asm::codegen_naked_asm::<Bx::CodegenCx>(cx, instance, item_data);
                 } else {
                     base::codegen_instance::<Bx>(cx, instance);
@@ -75,7 +71,7 @@ impl<'a, 'tcx: 'a> MonoItemExt<'a, 'tcx> for MonoItem<'tcx> {
                 cx.predefine_static(def_id, linkage, visibility, symbol_name);
             }
             MonoItem::Fn(instance) => {
-                let attrs = cx.tcx().codegen_fn_attrs(instance.def_id());
+                let attrs = cx.tcx().codegen_instance_attrs(instance.def);
 
                 if attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
                     // do not define this function; it will become a global assembly block
diff --git a/compiler/rustc_codegen_ssa/src/traits/type_.rs b/compiler/rustc_codegen_ssa/src/traits/type_.rs
index dcd9e25b2c9..32c24965e1b 100644
--- a/compiler/rustc_codegen_ssa/src/traits/type_.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/type_.rs
@@ -154,9 +154,9 @@ pub trait LayoutTypeCodegenMethods<'tcx>: BackendTypes {
 // For backends that support CFI using type membership (i.e., testing whether a given pointer is
 // associated with a type identifier).
 pub trait TypeMembershipCodegenMethods<'tcx>: BackendTypes {
-    fn add_type_metadata(&self, _function: Self::Function, _typeid: String) {}
-    fn set_type_metadata(&self, _function: Self::Function, _typeid: String) {}
-    fn typeid_metadata(&self, _typeid: String) -> Option<Self::Metadata> {
+    fn add_type_metadata(&self, _function: Self::Function, _typeid: &[u8]) {}
+    fn set_type_metadata(&self, _function: Self::Function, _typeid: &[u8]) {}
+    fn typeid_metadata(&self, _typeid: &[u8]) -> Option<Self::Metadata> {
         None
     }
     fn add_kcfi_type_metadata(&self, _function: Self::Function, _typeid: u32) {}
diff --git a/compiler/rustc_codegen_ssa/src/traits/write.rs b/compiler/rustc_codegen_ssa/src/traits/write.rs
index 07a0609fda1..5e993640472 100644
--- a/compiler/rustc_codegen_ssa/src/traits/write.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/write.rs
@@ -2,7 +2,7 @@ use rustc_ast::expand::autodiff_attrs::AutoDiffItem;
 use rustc_errors::{DiagCtxtHandle, FatalError};
 use rustc_middle::dep_graph::WorkProduct;
 
-use crate::back::lto::{LtoModuleCodegen, SerializedModule, ThinModule};
+use crate::back::lto::{SerializedModule, ThinModule};
 use crate::back::write::{CodegenContext, FatLtoInput, ModuleConfig};
 use crate::{CompiledModule, ModuleCodegen};
 
@@ -20,13 +20,14 @@ pub trait WriteBackendMethods: Clone + 'static {
         dcx: DiagCtxtHandle<'_>,
         modules: Vec<ModuleCodegen<Self::Module>>,
     ) -> Result<ModuleCodegen<Self::Module>, FatalError>;
-    /// Performs fat LTO by merging all modules into a single one and returning it
-    /// for further optimization.
-    fn run_fat_lto(
+    /// Performs fat LTO by merging all modules into a single one, running autodiff
+    /// if necessary and running any further optimizations
+    fn run_and_optimize_fat_lto(
         cgcx: &CodegenContext<Self>,
         modules: Vec<FatLtoInput<Self>>,
         cached_modules: Vec<(SerializedModule<Self::ModuleBuffer>, WorkProduct)>,
-    ) -> Result<LtoModuleCodegen<Self>, FatalError>;
+        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
     /// can simply be copied over from the incr. comp. cache.
@@ -34,7 +35,7 @@ pub trait WriteBackendMethods: Clone + 'static {
         cgcx: &CodegenContext<Self>,
         modules: Vec<(String, Self::ThinBuffer)>,
         cached_modules: Vec<(SerializedModule<Self::ModuleBuffer>, WorkProduct)>,
-    ) -> Result<(Vec<LtoModuleCodegen<Self>>, Vec<WorkProduct>), FatalError>;
+    ) -> Result<(Vec<ThinModule<Self>>, Vec<WorkProduct>), FatalError>;
     fn print_pass_timings(&self);
     fn print_statistics(&self);
     fn optimize(
@@ -43,17 +44,12 @@ pub trait WriteBackendMethods: Clone + 'static {
         module: &mut ModuleCodegen<Self::Module>,
         config: &ModuleConfig,
     ) -> Result<(), FatalError>;
-    fn optimize_fat(
-        cgcx: &CodegenContext<Self>,
-        llmod: &mut ModuleCodegen<Self::Module>,
-    ) -> Result<(), FatalError>;
     fn optimize_thin(
         cgcx: &CodegenContext<Self>,
         thin: ThinModule<Self>,
     ) -> Result<ModuleCodegen<Self::Module>, FatalError>;
     fn codegen(
         cgcx: &CodegenContext<Self>,
-        dcx: DiagCtxtHandle<'_>,
         module: ModuleCodegen<Self::Module>,
         config: &ModuleConfig,
     ) -> Result<CompiledModule, FatalError>;
@@ -62,12 +58,6 @@ pub trait WriteBackendMethods: Clone + 'static {
         want_summary: bool,
     ) -> (String, Self::ThinBuffer);
     fn serialize_module(module: ModuleCodegen<Self::Module>) -> (String, Self::ModuleBuffer);
-    fn autodiff(
-        cgcx: &CodegenContext<Self>,
-        module: &ModuleCodegen<Self::Module>,
-        diff_fncs: Vec<AutoDiffItem>,
-        config: &ModuleConfig,
-    ) -> Result<(), FatalError>;
 }
 
 pub trait ThinBufferMethods: Send + Sync {
diff --git a/compiler/rustc_const_eval/messages.ftl b/compiler/rustc_const_eval/messages.ftl
index b767ca9a3c2..aa0bc42d448 100644
--- a/compiler/rustc_const_eval/messages.ftl
+++ b/compiler/rustc_const_eval/messages.ftl
@@ -56,6 +56,17 @@ const_eval_const_context = {$kind ->
     *[other] {""}
 }
 
+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
+
+const_eval_const_make_global_ptr_already_made_global = attempting to call `const_make_global` twice on the same allocation {$alloc}
+
+const_eval_const_make_global_ptr_is_non_heap = pointer passed to `const_make_global` does not point to a heap allocation: {$ptr}
+
+const_eval_const_make_global_with_dangling_ptr = pointer passed to `const_make_global` is dangling: {$ptr}
+
+const_eval_const_make_global_with_offset = making {$ptr} global which does not point to the beginning of an object
+
 const_eval_copy_nonoverlapping_overlapping =
     `copy_nonoverlapping` called on overlapping ranges
 
@@ -296,19 +307,22 @@ const_eval_pointer_arithmetic_overflow =
     overflowing pointer arithmetic: the total offset in bytes does not fit in an `isize`
 
 const_eval_pointer_out_of_bounds =
-    {const_eval_bad_pointer_op_attempting}, but got {$pointer} which {$inbounds_size_is_neg ->
-        [false] {$alloc_size_minus_ptr_offset ->
-                [0] is at or beyond the end of the allocation of size {$alloc_size ->
-                    [1] 1 byte
-                    *[x] {$alloc_size} bytes
+    {const_eval_bad_pointer_op_attempting}, but got {$pointer} which {$ptr_offset_is_neg ->
+        [true] points to before the beginning of the allocation
+        *[false] {$inbounds_size_is_neg ->
+            [false] {$alloc_size_minus_ptr_offset ->
+                        [0] is at or beyond the end of the allocation of size {$alloc_size ->
+                            [1] 1 byte
+                            *[x] {$alloc_size} bytes
+                        }
+                        [1] is only 1 byte from the end of the allocation
+                        *[x] is only {$alloc_size_minus_ptr_offset} bytes from the end of the allocation
+                    }
+            *[true] {$ptr_offset_abs ->
+                    [0] is at the beginning of the allocation
+                    *[other] is only {$ptr_offset_abs} bytes from the beginning of the allocation
                 }
-                [1] is only 1 byte from the end of the allocation
-                *[x] is only {$alloc_size_minus_ptr_offset} bytes from the end of the allocation
-            }
-        *[true] {$ptr_offset_abs ->
-                [0] is at the beginning of the allocation
-                *[other] is only {$ptr_offset_abs} bytes from the beginning of the allocation
-            }
+        }
     }
 
 const_eval_pointer_use_after_free =
diff --git a/compiler/rustc_const_eval/src/check_consts/mod.rs b/compiler/rustc_const_eval/src/check_consts/mod.rs
index 9ab8e0692e1..ebf18c6f2ac 100644
--- a/compiler/rustc_const_eval/src/check_consts/mod.rs
+++ b/compiler/rustc_const_eval/src/check_consts/mod.rs
@@ -93,7 +93,7 @@ pub fn rustc_allow_const_fn_unstable(
 /// world into two functions: those that are safe to expose on stable (and hence may not use
 /// unstable features, not even recursively), and those that are not.
 pub fn is_fn_or_trait_safe_to_expose_on_stable(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
-    // A default body in a `#[const_trait]` is const-stable when the trait is const-stable.
+    // A default body in a `const trait` is const-stable when the trait is const-stable.
     if tcx.is_const_default_method(def_id) {
         return is_fn_or_trait_safe_to_expose_on_stable(tcx, tcx.parent(def_id));
     }
diff --git a/compiler/rustc_const_eval/src/const_eval/dummy_machine.rs b/compiler/rustc_const_eval/src/const_eval/dummy_machine.rs
index b6e2682af36..438aed41b8b 100644
--- a/compiler/rustc_const_eval/src/const_eval/dummy_machine.rs
+++ b/compiler/rustc_const_eval/src/const_eval/dummy_machine.rs
@@ -49,7 +49,6 @@ impl HasStaticRootDefId for DummyMachine {
 
 impl<'tcx> interpret::Machine<'tcx> for DummyMachine {
     interpret::compile_time_machine!(<'tcx>);
-    type MemoryKind = !;
     const PANIC_ON_ALLOC_FAIL: bool = true;
 
     // We want to just eval random consts in the program, so `eval_mir_const` can fail.
diff --git a/compiler/rustc_const_eval/src/const_eval/error.rs b/compiler/rustc_const_eval/src/const_eval/error.rs
index 08fc03d9c46..3e880d02001 100644
--- a/compiler/rustc_const_eval/src/const_eval/error.rs
+++ b/compiler/rustc_const_eval/src/const_eval/error.rs
@@ -2,7 +2,7 @@ use std::mem;
 
 use rustc_errors::{Diag, DiagArgName, DiagArgValue, DiagMessage, IntoDiagArg};
 use rustc_middle::mir::AssertKind;
-use rustc_middle::mir::interpret::{Provenance, ReportedErrorInfo};
+use rustc_middle::mir::interpret::{AllocId, Provenance, ReportedErrorInfo};
 use rustc_middle::query::TyCtxtAt;
 use rustc_middle::ty::layout::LayoutError;
 use rustc_middle::ty::{ConstInt, TyCtxt};
@@ -11,8 +11,8 @@ use rustc_span::{Span, Symbol};
 use super::CompileTimeMachine;
 use crate::errors::{self, FrameNote, ReportErrorExt};
 use crate::interpret::{
-    ErrorHandled, Frame, InterpErrorInfo, InterpErrorKind, MachineStopType, err_inval,
-    err_machine_stop,
+    CtfeProvenance, ErrorHandled, Frame, InterpErrorInfo, InterpErrorKind, MachineStopType,
+    Pointer, err_inval, err_machine_stop,
 };
 
 /// The CTFE machine has some custom error kinds.
@@ -22,8 +22,22 @@ pub enum ConstEvalErrKind {
     ModifiedGlobal,
     RecursiveStatic,
     AssertFailure(AssertKind<ConstInt>),
-    Panic { msg: Symbol, line: u32, col: u32, file: Symbol },
+    Panic {
+        msg: Symbol,
+        line: u32,
+        col: u32,
+        file: Symbol,
+    },
     WriteThroughImmutablePointer,
+    /// Called `const_make_global` twice.
+    ConstMakeGlobalPtrAlreadyMadeGlobal(AllocId),
+    /// Called `const_make_global` on a non-heap pointer.
+    ConstMakeGlobalPtrIsNonHeap(Pointer<Option<CtfeProvenance>>),
+    /// Called `const_make_global` on a dangling pointer.
+    ConstMakeGlobalWithDanglingPtr(Pointer<Option<CtfeProvenance>>),
+    /// Called `const_make_global` on a pointer that does not start at the
+    /// beginning of an object.
+    ConstMakeGlobalWithOffset(Pointer<Option<CtfeProvenance>>),
 }
 
 impl MachineStopType for ConstEvalErrKind {
@@ -38,6 +52,12 @@ impl MachineStopType for ConstEvalErrKind {
             RecursiveStatic => const_eval_recursive_static,
             AssertFailure(x) => x.diagnostic_message(),
             WriteThroughImmutablePointer => const_eval_write_through_immutable_pointer,
+            ConstMakeGlobalPtrAlreadyMadeGlobal { .. } => {
+                const_eval_const_make_global_ptr_already_made_global
+            }
+            ConstMakeGlobalPtrIsNonHeap(_) => const_eval_const_make_global_ptr_is_non_heap,
+            ConstMakeGlobalWithDanglingPtr(_) => const_eval_const_make_global_with_dangling_ptr,
+            ConstMakeGlobalWithOffset(_) => const_eval_const_make_global_with_offset,
         }
     }
     fn add_args(self: Box<Self>, adder: &mut dyn FnMut(DiagArgName, DiagArgValue)) {
@@ -51,6 +71,14 @@ impl MachineStopType for ConstEvalErrKind {
             Panic { msg, .. } => {
                 adder("msg".into(), msg.into_diag_arg(&mut None));
             }
+            ConstMakeGlobalPtrIsNonHeap(ptr)
+            | ConstMakeGlobalWithOffset(ptr)
+            | ConstMakeGlobalWithDanglingPtr(ptr) => {
+                adder("ptr".into(), format!("{ptr:?}").into_diag_arg(&mut None));
+            }
+            ConstMakeGlobalPtrAlreadyMadeGlobal(alloc) => {
+                adder("alloc".into(), alloc.into_diag_arg(&mut None));
+            }
         }
     }
 }
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 4bd4b493009..ce72d59b8b0 100644
--- a/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
+++ b/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
@@ -18,7 +18,7 @@ use tracing::{debug, instrument, trace};
 use super::{CanAccessMutGlobal, CompileTimeInterpCx, CompileTimeMachine};
 use crate::const_eval::CheckAlignment;
 use crate::interpret::{
-    CtfeValidationMode, GlobalId, Immediate, InternKind, InternResult, InterpCx, InterpErrorKind,
+    CtfeValidationMode, GlobalId, Immediate, InternError, InternKind, InterpCx, InterpErrorKind,
     InterpResult, MPlaceTy, MemoryKind, OpTy, RefTracking, ReturnContinuation, create_static_alloc,
     intern_const_alloc_recursive, interp_ok, throw_exhaust,
 };
@@ -93,25 +93,30 @@ fn eval_body_using_ecx<'tcx, R: InterpretationResult<'tcx>>(
     // Since evaluation had no errors, validate the resulting constant.
     const_validate_mplace(ecx, &ret, cid)?;
 
-    // Only report this after validation, as validaiton produces much better diagnostics.
+    // Only report this after validation, as validation produces much better diagnostics.
     // FIXME: ensure validation always reports this and stop making interning care about it.
 
     match intern_result {
         Ok(()) => {}
-        Err(InternResult::FoundDanglingPointer) => {
+        Err(InternError::DanglingPointer) => {
             throw_inval!(AlreadyReported(ReportedErrorInfo::non_const_eval_error(
                 ecx.tcx
                     .dcx()
                     .emit_err(errors::DanglingPtrInFinal { span: ecx.tcx.span, kind: intern_kind }),
             )));
         }
-        Err(InternResult::FoundBadMutablePointer) => {
+        Err(InternError::BadMutablePointer) => {
             throw_inval!(AlreadyReported(ReportedErrorInfo::non_const_eval_error(
                 ecx.tcx
                     .dcx()
                     .emit_err(errors::MutablePtrInFinal { span: ecx.tcx.span, kind: intern_kind }),
             )));
         }
+        Err(InternError::ConstAllocNotGlobal) => {
+            throw_inval!(AlreadyReported(ReportedErrorInfo::non_const_eval_error(
+                ecx.tcx.dcx().emit_err(errors::ConstHeapPtrInFinal { span: ecx.tcx.span }),
+            )));
+        }
     }
 
     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 52fc898192a..f24fb18f83b 100644
--- a/compiler/rustc_const_eval/src/const_eval/machine.rs
+++ b/compiler/rustc_const_eval/src/const_eval/machine.rs
@@ -169,13 +169,19 @@ pub type CompileTimeInterpCx<'tcx> = InterpCx<'tcx, CompileTimeMachine<'tcx>>;
 
 #[derive(Debug, PartialEq, Eq, Copy, Clone)]
 pub enum MemoryKind {
-    Heap,
+    Heap {
+        /// Indicates whether `make_global` was called on this allocation.
+        /// If this is `true`, the allocation must be immutable.
+        was_made_global: bool,
+    },
 }
 
 impl fmt::Display for MemoryKind {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
-            MemoryKind::Heap => write!(f, "heap allocation"),
+            MemoryKind::Heap { was_made_global } => {
+                write!(f, "heap allocation{}", if *was_made_global { " (made global)" } else { "" })
+            }
         }
     }
 }
@@ -184,7 +190,7 @@ impl interpret::MayLeak for MemoryKind {
     #[inline(always)]
     fn may_leak(self) -> bool {
         match self {
-            MemoryKind::Heap => false,
+            MemoryKind::Heap { was_made_global } => was_made_global,
         }
     }
 }
@@ -314,8 +320,6 @@ impl<'tcx> CompileTimeMachine<'tcx> {
 impl<'tcx> interpret::Machine<'tcx> for CompileTimeMachine<'tcx> {
     compile_time_machine!(<'tcx>);
 
-    type MemoryKind = MemoryKind;
-
     const PANIC_ON_ALLOC_FAIL: bool = false; // will be raised as a proper error
 
     #[inline(always)]
@@ -359,8 +363,8 @@ impl<'tcx> interpret::Machine<'tcx> for CompileTimeMachine<'tcx> {
         if let ty::InstanceKind::Item(def) = instance.def {
             // Execution might have wandered off into other crates, so we cannot do a stability-
             // sensitive check here. But we can at least rule out functions that are not const at
-            // all. That said, we have to allow calling functions inside a trait marked with
-            // #[const_trait]. These *are* const-checked!
+            // all. That said, we have to allow calling functions inside a `const trait`. These
+            // *are* const-checked!
             if !ecx.tcx.is_const_fn(def) || ecx.tcx.has_attr(def, sym::rustc_do_not_const_check) {
                 // We certainly do *not* want to actually call the fn
                 // though, so be sure we return here.
@@ -420,7 +424,7 @@ impl<'tcx> interpret::Machine<'tcx> for CompileTimeMachine<'tcx> {
                 let ptr = ecx.allocate_ptr(
                     Size::from_bytes(size),
                     align,
-                    interpret::MemoryKind::Machine(MemoryKind::Heap),
+                    interpret::MemoryKind::Machine(MemoryKind::Heap { was_made_global: false }),
                     AllocInit::Uninit,
                 )?;
                 ecx.write_pointer(ptr, dest)?;
@@ -453,10 +457,17 @@ impl<'tcx> interpret::Machine<'tcx> for CompileTimeMachine<'tcx> {
                     ecx.deallocate_ptr(
                         ptr,
                         Some((size, align)),
-                        interpret::MemoryKind::Machine(MemoryKind::Heap),
+                        interpret::MemoryKind::Machine(MemoryKind::Heap { was_made_global: false }),
                     )?;
                 }
             }
+
+            sym::const_make_global => {
+                let ptr = ecx.read_pointer(&args[0])?;
+                ecx.make_const_heap_ptr_global(ptr)?;
+                ecx.write_pointer(ptr, dest)?;
+            }
+
             // The intrinsic represents whether the value is known to the optimizer (LLVM).
             // We're not doing any optimizations here, so there is no optimizer that could know the value.
             // (We know the value here in the machine of course, but this is the runtime of that code,
diff --git a/compiler/rustc_const_eval/src/errors.rs b/compiler/rustc_const_eval/src/errors.rs
index 49cd7138748..b6a64035261 100644
--- a/compiler/rustc_const_eval/src/errors.rs
+++ b/compiler/rustc_const_eval/src/errors.rs
@@ -44,6 +44,14 @@ pub(crate) struct MutablePtrInFinal {
 }
 
 #[derive(Diagnostic)]
+#[diag(const_eval_const_heap_ptr_in_final)]
+#[note]
+pub(crate) struct ConstHeapPtrInFinal {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
 #[diag(const_eval_unstable_in_stable_exposed)]
 pub(crate) struct UnstableInStableExposed {
     pub gate: String,
diff --git a/compiler/rustc_const_eval/src/interpret/call.rs b/compiler/rustc_const_eval/src/interpret/call.rs
index ad3e02580f3..1503f3bcd99 100644
--- a/compiler/rustc_const_eval/src/interpret/call.rs
+++ b/compiler/rustc_const_eval/src/interpret/call.rs
@@ -6,7 +6,7 @@ use std::borrow::Cow;
 use either::{Left, Right};
 use rustc_abi::{self as abi, ExternAbi, FieldIdx, Integer, VariantIdx};
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::layout::{FnAbiOf, IntegerExt, TyAndLayout};
+use rustc_middle::ty::layout::{IntegerExt, TyAndLayout};
 use rustc_middle::ty::{self, AdtDef, Instance, Ty, VariantDef};
 use rustc_middle::{bug, mir, span_bug};
 use rustc_span::sym;
diff --git a/compiler/rustc_const_eval/src/interpret/eval_context.rs b/compiler/rustc_const_eval/src/interpret/eval_context.rs
index 41fc8d47cd3..11e7706fe60 100644
--- a/compiler/rustc_const_eval/src/interpret/eval_context.rs
+++ b/compiler/rustc_const_eval/src/interpret/eval_context.rs
@@ -7,8 +7,8 @@ use rustc_hir::def_id::DefId;
 use rustc_middle::mir::interpret::{ErrorHandled, InvalidMetaKind, ReportedErrorInfo};
 use rustc_middle::query::TyCtxtAt;
 use rustc_middle::ty::layout::{
-    self, FnAbiError, FnAbiOfHelpers, FnAbiRequest, LayoutError, LayoutOf, LayoutOfHelpers,
-    TyAndLayout,
+    self, FnAbiError, FnAbiOf, FnAbiOfHelpers, FnAbiRequest, LayoutError, LayoutOf,
+    LayoutOfHelpers, TyAndLayout,
 };
 use rustc_middle::ty::{self, GenericArgsRef, Ty, TyCtxt, TypeFoldable, TypingEnv, Variance};
 use rustc_middle::{mir, span_bug};
@@ -92,20 +92,6 @@ impl<'tcx, M: Machine<'tcx>> LayoutOfHelpers<'tcx> for InterpCx<'tcx, M> {
     }
 }
 
-impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
-    /// This inherent method takes priority over the trait method with the same name in LayoutOf,
-    /// and allows wrapping the actual [LayoutOf::layout_of] with a tracing span.
-    /// See [LayoutOf::layout_of] for the original documentation.
-    #[inline(always)]
-    pub fn layout_of(
-        &self,
-        ty: Ty<'tcx>,
-    ) -> <InterpCx<'tcx, M> as LayoutOfHelpers<'tcx>>::LayoutOfResult {
-        let _span = enter_trace_span!(M, "InterpCx::layout_of", "ty = {:?}", ty.kind());
-        LayoutOf::layout_of(self, ty)
-    }
-}
-
 impl<'tcx, M: Machine<'tcx>> FnAbiOfHelpers<'tcx> for InterpCx<'tcx, M> {
     type FnAbiOfResult = Result<&'tcx FnAbi<'tcx, Ty<'tcx>>, InterpErrorKind<'tcx>>;
 
@@ -121,6 +107,43 @@ impl<'tcx, M: Machine<'tcx>> FnAbiOfHelpers<'tcx> for InterpCx<'tcx, M> {
     }
 }
 
+impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
+    /// This inherent method takes priority over the trait method with the same name in LayoutOf,
+    /// and allows wrapping the actual [LayoutOf::layout_of] with a tracing span.
+    /// 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, "InterpCx::layout_of", ty = ?ty.kind());
+        LayoutOf::layout_of(self, ty)
+    }
+
+    /// This inherent method takes priority over the trait method with the same name in FnAbiOf,
+    /// and allows wrapping the actual [FnAbiOf::fn_abi_of_fn_ptr] with a tracing span.
+    /// See [FnAbiOf::fn_abi_of_fn_ptr] for the original documentation.
+    #[inline(always)]
+    pub fn fn_abi_of_fn_ptr(
+        &self,
+        sig: ty::PolyFnSig<'tcx>,
+        extra_args: &'tcx ty::List<Ty<'tcx>>,
+    ) -> <Self as FnAbiOfHelpers<'tcx>>::FnAbiOfResult {
+        let _span = enter_trace_span!(M, "InterpCx::fn_abi_of_fn_ptr", ?sig, ?extra_args);
+        FnAbiOf::fn_abi_of_fn_ptr(self, sig, extra_args)
+    }
+
+    /// This inherent method takes priority over the trait method with the same name in FnAbiOf,
+    /// and allows wrapping the actual [FnAbiOf::fn_abi_of_instance] with a tracing span.
+    /// See [FnAbiOf::fn_abi_of_instance] for the original documentation.
+    #[inline(always)]
+    pub fn fn_abi_of_instance(
+        &self,
+        instance: ty::Instance<'tcx>,
+        extra_args: &'tcx ty::List<Ty<'tcx>>,
+    ) -> <Self as FnAbiOfHelpers<'tcx>>::FnAbiOfResult {
+        let _span = enter_trace_span!(M, "InterpCx::fn_abi_of_instance", ?instance, ?extra_args);
+        FnAbiOf::fn_abi_of_instance(self, instance, extra_args)
+    }
+}
+
 /// Test if it is valid for a MIR assignment to assign `src`-typed place to `dest`-typed value.
 /// This test should be symmetric, as it is primarily about layout compatibility.
 pub(super) fn mir_assign_valid_types<'tcx>(
diff --git a/compiler/rustc_const_eval/src/interpret/intern.rs b/compiler/rustc_const_eval/src/interpret/intern.rs
index f0f958d069e..bb59b9f5418 100644
--- a/compiler/rustc_const_eval/src/interpret/intern.rs
+++ b/compiler/rustc_const_eval/src/interpret/intern.rs
@@ -26,21 +26,18 @@ use rustc_middle::ty::layout::TyAndLayout;
 use rustc_span::def_id::LocalDefId;
 use tracing::{instrument, trace};
 
-use super::{
-    AllocId, Allocation, InterpCx, MPlaceTy, Machine, MemoryKind, PlaceTy, err_ub, interp_ok,
-};
-use crate::const_eval;
+use super::{AllocId, Allocation, InterpCx, MPlaceTy, Machine, MemoryKind, PlaceTy, interp_ok};
 use crate::const_eval::DummyMachine;
-use crate::errors::NestedStaticInThreadLocal;
+use crate::{const_eval, errors};
 
-pub trait CompileTimeMachine<'tcx, T> = Machine<
+pub trait CompileTimeMachine<'tcx> = Machine<
         'tcx,
-        MemoryKind = T,
+        MemoryKind = const_eval::MemoryKind,
         Provenance = CtfeProvenance,
         ExtraFnVal = !,
         FrameExtra = (),
         AllocExtra = (),
-        MemoryMap = FxIndexMap<AllocId, (MemoryKind<T>, Allocation)>,
+        MemoryMap = FxIndexMap<AllocId, (MemoryKind<const_eval::MemoryKind>, Allocation)>,
     > + HasStaticRootDefId;
 
 pub trait HasStaticRootDefId {
@@ -62,18 +59,32 @@ impl HasStaticRootDefId for const_eval::CompileTimeMachine<'_> {
 /// already mutable (as a sanity check).
 ///
 /// Returns an iterator over all relocations referred to by this allocation.
-fn intern_shallow<'tcx, T, M: CompileTimeMachine<'tcx, T>>(
+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, ()> {
+) -> 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(());
+    let Some((kind, mut alloc)) = ecx.memory.alloc_map.swap_remove(&alloc_id) else {
+        return Err(InternError::DanglingPointer);
     };
+
+    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));
+                return Err(InternError::ConstAllocNotGlobal);
+            }
+        }
+        MemoryKind::Stack | MemoryKind::CallerLocation => {}
+    }
+
     // 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.
@@ -99,7 +110,7 @@ fn intern_shallow<'tcx, T, M: CompileTimeMachine<'tcx, T>>(
     } else {
         ecx.tcx.set_alloc_id_memory(alloc_id, alloc);
     }
-    Ok(alloc.0.0.provenance().ptrs().iter().map(|&(_, prov)| prov))
+    Ok(alloc.inner().provenance().ptrs().iter().map(|&(_, prov)| prov))
 }
 
 /// Creates a new `DefId` and feeds all the right queries to make this `DefId`
@@ -125,7 +136,7 @@ fn intern_as_new_static<'tcx>(
     tcx.set_nested_alloc_id_static(alloc_id, feed.def_id());
 
     if tcx.is_thread_local_static(static_id.into()) {
-        tcx.dcx().emit_err(NestedStaticInThreadLocal { span: tcx.def_span(static_id) });
+        tcx.dcx().emit_err(errors::NestedStaticInThreadLocal { span: tcx.def_span(static_id) });
     }
 
     // These do not inherit the codegen attrs of the parent static allocation, since
@@ -151,9 +162,10 @@ pub enum InternKind {
 }
 
 #[derive(Debug)]
-pub enum InternResult {
-    FoundBadMutablePointer,
-    FoundDanglingPointer,
+pub enum InternError {
+    BadMutablePointer,
+    DanglingPointer,
+    ConstAllocNotGlobal,
 }
 
 /// Intern `ret` and everything it references.
@@ -163,11 +175,11 @@ pub enum InternResult {
 ///
 /// For `InternKind::Static` the root allocation will not be interned, but must be handled by the caller.
 #[instrument(level = "debug", skip(ecx))]
-pub fn intern_const_alloc_recursive<'tcx, M: CompileTimeMachine<'tcx, const_eval::MemoryKind>>(
+pub fn intern_const_alloc_recursive<'tcx, M: CompileTimeMachine<'tcx>>(
     ecx: &mut InterpCx<'tcx, M>,
     intern_kind: InternKind,
     ret: &MPlaceTy<'tcx>,
-) -> Result<(), InternResult> {
+) -> Result<(), InternError> {
     let mut disambiguator = DisambiguatorState::new();
 
     // We are interning recursively, and for mutability we are distinguishing the "root" allocation
@@ -181,7 +193,7 @@ pub fn intern_const_alloc_recursive<'tcx, M: CompileTimeMachine<'tcx, const_eval
         }
         InternKind::Static(Mutability::Not) => {
             (
-                // Outermost allocation is mutable if `!Freeze`.
+                // Outermost allocation is mutable if `!Freeze` i.e. contains interior mutable types.
                 if ret.layout.ty.is_freeze(*ecx.tcx, ecx.typing_env) {
                     Mutability::Not
                 } else {
@@ -224,6 +236,7 @@ pub fn intern_const_alloc_recursive<'tcx, M: CompileTimeMachine<'tcx, const_eval
     // 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.
     // We show errors if there are dangling pointers, or mutable pointers in immutable contexts
@@ -278,18 +291,7 @@ pub fn intern_const_alloc_recursive<'tcx, M: CompileTimeMachine<'tcx, const_eval
             // when there is memory there that someone might expect to be mutable, but we make it immutable.
             let dangling = !is_already_global && !ecx.memory.alloc_map.contains_key(&alloc_id);
             if !dangling {
-                // Found a mutable pointer inside a const where inner allocations should be
-                // immutable.
-                if !ecx.tcx.sess.opts.unstable_opts.unleash_the_miri_inside_of_you {
-                    span_bug!(
-                        ecx.tcx.span,
-                        "the static const safety checks accepted a mutable pointer they should not have accepted"
-                    );
-                }
-                // Prefer dangling pointer errors over mutable pointer errors
-                if result.is_ok() {
-                    result = Err(InternResult::FoundBadMutablePointer);
-                }
+                found_bad_mutable_ptr = true;
             }
         }
         if ecx.tcx.try_get_global_alloc(alloc_id).is_some() {
@@ -310,18 +312,31 @@ pub fn intern_const_alloc_recursive<'tcx, M: CompileTimeMachine<'tcx, const_eval
         just_interned.insert(alloc_id);
         match intern_shallow(ecx, alloc_id, inner_mutability, Some(&mut disambiguator)) {
             Ok(nested) => todo.extend(nested),
-            Err(()) => {
-                ecx.tcx.dcx().delayed_bug("found dangling pointer during const interning");
-                result = Err(InternResult::FoundDanglingPointer);
+            Err(err) => {
+                ecx.tcx.dcx().delayed_bug("error during const interning");
+                result = Err(err);
             }
         }
     }
+    if found_bad_mutable_ptr && result.is_ok() {
+        // 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);
+        } else {
+            span_bug!(
+                ecx.tcx.span,
+                "the static const safety checks accepted a mutable pointer they should not have accepted"
+            );
+        }
+    }
     result
 }
 
 /// Intern `ret`. This function assumes that `ret` references no other allocation.
 #[instrument(level = "debug", skip(ecx))]
-pub fn intern_const_alloc_for_constprop<'tcx, T, M: CompileTimeMachine<'tcx, T>>(
+pub fn intern_const_alloc_for_constprop<'tcx, M: CompileTimeMachine<'tcx>>(
     ecx: &mut InterpCx<'tcx, M>,
     alloc_id: AllocId,
 ) -> InterpResult<'tcx, ()> {
@@ -330,10 +345,7 @@ pub fn intern_const_alloc_for_constprop<'tcx, T, M: CompileTimeMachine<'tcx, T>>
         return interp_ok(());
     }
     // Move allocation to `tcx`.
-    if let Some(_) = intern_shallow(ecx, alloc_id, Mutability::Not, None)
-        .map_err(|()| err_ub!(DeadLocal))?
-        .next()
-    {
+    if let Some(_) = intern_shallow(ecx, alloc_id, Mutability::Not, None).unwrap().next() {
         // We are not doing recursive interning, so we don't currently support provenance.
         // (If this assertion ever triggers, we should just implement a
         // proper recursive interning loop -- or just call `intern_const_alloc_recursive`.
diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics.rs b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
index 22d29eda913..e24a355891d 100644
--- a/compiler/rustc_const_eval/src/interpret/intrinsics.rs
+++ b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
@@ -4,8 +4,9 @@
 
 use std::assert_matches::assert_matches;
 
-use rustc_abi::{FieldIdx, Size};
+use rustc_abi::{FieldIdx, HasDataLayout, Size};
 use rustc_apfloat::ieee::{Double, Half, Quad, Single};
+use rustc_middle::mir::interpret::{read_target_uint, write_target_uint};
 use rustc_middle::mir::{self, BinOp, ConstValue, NonDivergingIntrinsic};
 use rustc_middle::ty::layout::TyAndLayout;
 use rustc_middle::ty::{Ty, TyCtxt};
@@ -30,7 +31,7 @@ pub(crate) fn alloc_type_name<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> ConstAll
 }
 impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     /// Generates a value of `TypeId` for `ty` in-place.
-    pub(crate) fn write_type_id(
+    fn write_type_id(
         &mut self,
         ty: Ty<'tcx>,
         dest: &PlaceTy<'tcx, M::Provenance>,
@@ -48,8 +49,8 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         // Here we rely on `TypeId` being a newtype around an array of pointers, so we
         // first project to its only field and then the array elements.
         let alloc_id = tcx.reserve_and_set_type_id_alloc(ty);
-        let first = self.project_field(dest, FieldIdx::ZERO)?;
-        let mut elem_iter = self.project_array_fields(&first)?;
+        let arr = self.project_field(dest, FieldIdx::ZERO)?;
+        let mut elem_iter = self.project_array_fields(&arr)?;
         while let Some((_, elem)) = elem_iter.next(self)? {
             // Decorate this part of the hash with provenance; leave the integer part unchanged.
             let hash_fragment = self.read_scalar(&elem)?.to_target_usize(&tcx)?;
@@ -61,6 +62,52 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         interp_ok(())
     }
 
+    /// Read a value of type `TypeId`, returning the type it represents.
+    pub(crate) fn read_type_id(
+        &self,
+        op: &OpTy<'tcx, M::Provenance>,
+    ) -> InterpResult<'tcx, Ty<'tcx>> {
+        // `TypeId` is a newtype around an array of pointers. All pointers must have the same
+        // provenance, and that provenance represents the type.
+        let ptr_size = self.pointer_size().bytes_usize();
+        let arr = self.project_field(op, FieldIdx::ZERO)?;
+
+        let mut ty_and_hash = None;
+        let mut elem_iter = self.project_array_fields(&arr)?;
+        while let Some((idx, elem)) = elem_iter.next(self)? {
+            let elem = self.read_pointer(&elem)?;
+            let (elem_ty, elem_hash) = self.get_ptr_type_id(elem)?;
+            // If this is the first element, remember the type and its hash.
+            // If this is not the first element, ensure it is consistent with the previous ones.
+            let full_hash = match ty_and_hash {
+                None => {
+                    let hash = self.tcx.type_id_hash(elem_ty).as_u128();
+                    let mut hash_bytes = [0u8; 16];
+                    write_target_uint(self.data_layout().endian, &mut hash_bytes, hash).unwrap();
+                    ty_and_hash = Some((elem_ty, hash_bytes));
+                    hash_bytes
+                }
+                Some((ty, hash_bytes)) => {
+                    if ty != elem_ty {
+                        throw_ub_format!(
+                            "invalid `TypeId` value: not all bytes carry the same type id metadata"
+                        );
+                    }
+                    hash_bytes
+                }
+            };
+            // Ensure the elem_hash matches the corresponding part of the full hash.
+            let hash_frag = &full_hash[(idx as usize) * ptr_size..][..ptr_size];
+            if read_target_uint(self.data_layout().endian, hash_frag).unwrap() != elem_hash.into() {
+                throw_ub_format!(
+                    "invalid `TypeId` value: the hash does not match the type id metadata"
+                );
+            }
+        }
+
+        interp_ok(ty_and_hash.unwrap().0)
+    }
+
     /// Returns `true` if emulation happened.
     /// Here we implement the intrinsics that are common to all Miri instances; individual machines can add their own
     /// intrinsic handling.
@@ -97,47 +144,9 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 self.write_type_id(tp_ty, dest)?;
             }
             sym::type_id_eq => {
-                // Both operands are `TypeId`, which is a newtype around an array of pointers.
-                // Project until we have the array elements.
-                let a_fields = self.project_field(&args[0], FieldIdx::ZERO)?;
-                let b_fields = self.project_field(&args[1], FieldIdx::ZERO)?;
-
-                let mut a_fields = self.project_array_fields(&a_fields)?;
-                let mut b_fields = self.project_array_fields(&b_fields)?;
-
-                let mut provenance_a = None;
-                let mut provenance_b = None;
-                let mut provenance_matches = true;
-
-                while let Some((i, a)) = a_fields.next(self)? {
-                    let (_, b) = b_fields.next(self)?.unwrap();
-
-                    let a = self.deref_pointer(&a)?;
-                    let (a, offset_a) = self.get_ptr_type_id(a.ptr())?;
-
-                    let b = self.deref_pointer(&b)?;
-                    let (b, offset_b) = self.get_ptr_type_id(b.ptr())?;
-
-                    if *provenance_a.get_or_insert(a) != a {
-                        throw_ub_format!(
-                            "type_id_eq: the first TypeId argument is invalid, the provenance of chunk {i} does not match the first chunk's"
-                        )
-                    }
-                    if *provenance_b.get_or_insert(b) != b {
-                        throw_ub_format!(
-                            "type_id_eq: the second TypeId argument is invalid, the provenance of chunk {i} does not match the first chunk's"
-                        )
-                    }
-                    provenance_matches &= a == b;
-
-                    if offset_a != offset_b && provenance_matches {
-                        throw_ub_format!(
-                            "type_id_eq: one of the TypeId arguments is invalid, chunk {i} of the hash does not match the type it represents"
-                        )
-                    }
-                }
-
-                self.write_scalar(Scalar::from_bool(provenance_matches), dest)?;
+                let a_ty = self.read_type_id(&args[0])?;
+                let b_ty = self.read_type_id(&args[1])?;
+                self.write_scalar(Scalar::from_bool(a_ty == b_ty), dest)?;
             }
             sym::variant_count => {
                 let tp_ty = instance.args.type_at(0);
diff --git a/compiler/rustc_const_eval/src/interpret/machine.rs b/compiler/rustc_const_eval/src/interpret/machine.rs
index d150ed69250..e981f3973ae 100644
--- a/compiler/rustc_const_eval/src/interpret/machine.rs
+++ b/compiler/rustc_const_eval/src/interpret/machine.rs
@@ -649,6 +649,7 @@ pub macro compile_time_machine(<$tcx: lifetime>) {
 
     type ExtraFnVal = !;
 
+    type MemoryKind = $crate::const_eval::MemoryKind;
     type MemoryMap =
         rustc_data_structures::fx::FxIndexMap<AllocId, (MemoryKind<Self::MemoryKind>, Allocation)>;
     const GLOBAL_KIND: Option<Self::MemoryKind> = None; // no copying of globals from `tcx` to machine memory
diff --git a/compiler/rustc_const_eval/src/interpret/memory.rs b/compiler/rustc_const_eval/src/interpret/memory.rs
index 6414821e21d..47228de5213 100644
--- a/compiler/rustc_const_eval/src/interpret/memory.rs
+++ b/compiler/rustc_const_eval/src/interpret/memory.rs
@@ -26,6 +26,7 @@ use super::{
     Misalignment, Pointer, PointerArithmetic, Provenance, Scalar, alloc_range, err_ub,
     err_ub_custom, interp_ok, throw_ub, throw_ub_custom, throw_unsup, throw_unsup_format,
 };
+use crate::const_eval::ConstEvalErrKind;
 use crate::fluent_generated as fluent;
 
 #[derive(Debug, PartialEq, Copy, Clone)]
@@ -311,6 +312,51 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         interp_ok(new_ptr)
     }
 
+    /// Mark the `const_allocate`d allocation `ptr` points to as immutable so we can intern it.
+    pub fn make_const_heap_ptr_global(
+        &mut self,
+        ptr: Pointer<Option<CtfeProvenance>>,
+    ) -> InterpResult<'tcx>
+    where
+        M: Machine<'tcx, MemoryKind = crate::const_eval::MemoryKind, Provenance = CtfeProvenance>,
+    {
+        let (alloc_id, offset, _) = self.ptr_get_alloc_id(ptr, 0)?;
+        if offset.bytes() != 0 {
+            return Err(ConstEvalErrKind::ConstMakeGlobalWithOffset(ptr)).into();
+        }
+
+        if matches!(self.tcx.try_get_global_alloc(alloc_id), Some(_)) {
+            // This points to something outside the current interpreter.
+            return Err(ConstEvalErrKind::ConstMakeGlobalPtrIsNonHeap(ptr)).into();
+        }
+
+        // If we can't find it in `alloc_map` it must be dangling (because we don't use
+        // `extra_fn_ptr_map` in const-eval).
+        let (kind, alloc) = self
+            .memory
+            .alloc_map
+            .get_mut_or(alloc_id, || Err(ConstEvalErrKind::ConstMakeGlobalWithDanglingPtr(ptr)))?;
+
+        // Ensure this is actually a *heap* allocation, and record it as made-global.
+        match kind {
+            MemoryKind::Stack | MemoryKind::CallerLocation => {
+                return Err(ConstEvalErrKind::ConstMakeGlobalPtrIsNonHeap(ptr)).into();
+            }
+            MemoryKind::Machine(crate::const_eval::MemoryKind::Heap { was_made_global }) => {
+                if *was_made_global {
+                    return Err(ConstEvalErrKind::ConstMakeGlobalPtrAlreadyMadeGlobal(alloc_id))
+                        .into();
+                }
+                *was_made_global = true;
+            }
+        }
+
+        // Prevent further mutation, this is now an immutable global.
+        alloc.mutability = Mutability::Not;
+
+        interp_ok(())
+    }
+
     #[instrument(skip(self), level = "debug")]
     pub fn deallocate_ptr(
         &mut self,
@@ -890,7 +936,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         if let Some(fn_val) = self.get_fn_alloc(id) {
             let align = match fn_val {
                 FnVal::Instance(instance) => {
-                    self.tcx.codegen_fn_attrs(instance.def_id()).alignment.unwrap_or(Align::ONE)
+                    self.tcx.codegen_instance_attrs(instance.def).alignment.unwrap_or(Align::ONE)
                 }
                 // Machine-specific extra functions currently do not support alignment restrictions.
                 FnVal::Other(_) => Align::ONE,
@@ -951,12 +997,12 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     pub fn get_ptr_type_id(
         &self,
         ptr: Pointer<Option<M::Provenance>>,
-    ) -> InterpResult<'tcx, (Ty<'tcx>, Size)> {
+    ) -> InterpResult<'tcx, (Ty<'tcx>, u64)> {
         let (alloc_id, offset, _meta) = self.ptr_get_alloc_id(ptr, 0)?;
         let GlobalAlloc::TypeId { ty } = self.tcx.global_alloc(alloc_id) else {
-            throw_ub_format!("type_id_eq: `TypeId` provenance is not a type id")
+            throw_ub_format!("invalid `TypeId` value: not all bytes carry type id metadata")
         };
-        interp_ok((ty, offset))
+        interp_ok((ty, offset.bytes()))
     }
 
     pub fn get_ptr_fn(
diff --git a/compiler/rustc_const_eval/src/interpret/mod.rs b/compiler/rustc_const_eval/src/interpret/mod.rs
index 2fc372dd019..2f365ec77b3 100644
--- a/compiler/rustc_const_eval/src/interpret/mod.rs
+++ b/compiler/rustc_const_eval/src/interpret/mod.rs
@@ -26,7 +26,7 @@ pub use self::call::FnArg;
 pub use self::eval_context::{InterpCx, format_interp_error};
 use self::eval_context::{from_known_layout, mir_assign_valid_types};
 pub use self::intern::{
-    HasStaticRootDefId, InternKind, InternResult, intern_const_alloc_for_constprop,
+    HasStaticRootDefId, InternError, InternKind, intern_const_alloc_for_constprop,
     intern_const_alloc_recursive,
 };
 pub use self::machine::{AllocMap, Machine, MayLeak, ReturnAction, compile_time_machine};
diff --git a/compiler/rustc_const_eval/src/interpret/stack.rs b/compiler/rustc_const_eval/src/interpret/stack.rs
index b6ba069526c..2e99bb4209f 100644
--- a/compiler/rustc_const_eval/src/interpret/stack.rs
+++ b/compiler/rustc_const_eval/src/interpret/stack.rs
@@ -12,6 +12,7 @@ use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_middle::{bug, mir};
 use rustc_mir_dataflow::impls::always_storage_live_locals;
 use rustc_span::Span;
+use tracing::field::Empty;
 use tracing::{info_span, instrument, trace};
 
 use super::{
@@ -396,7 +397,11 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         // Finish things up.
         M::after_stack_push(self)?;
         self.frame_mut().loc = Left(mir::Location::START);
-        let span = info_span!("frame", "{}", instance);
+        // `tracing_separate_thread` is used to instruct the chrome_tracing [tracing::Layer] in Miri
+        // to put the "frame" span on a separate trace thread/line than other spans, to make the
+        // visualization in https://ui.perfetto.dev easier to interpret. It is set to a value of
+        // [tracing::field::Empty] so that other tracing layers (e.g. the logger) will ignore it.
+        let span = info_span!("frame", tracing_separate_thread = Empty, "{}", instance);
         self.frame_mut().tracing_span.enter(span);
 
         interp_ok(())
diff --git a/compiler/rustc_const_eval/src/interpret/step.rs b/compiler/rustc_const_eval/src/interpret/step.rs
index 833fcc38817..629dcc3523c 100644
--- a/compiler/rustc_const_eval/src/interpret/step.rs
+++ b/compiler/rustc_const_eval/src/interpret/step.rs
@@ -5,7 +5,6 @@
 use either::Either;
 use rustc_abi::{FIRST_VARIANT, FieldIdx};
 use rustc_index::IndexSlice;
-use rustc_middle::ty::layout::FnAbiOf;
 use rustc_middle::ty::{self, Instance, Ty};
 use rustc_middle::{bug, mir, span_bug};
 use rustc_span::source_map::Spanned;
diff --git a/compiler/rustc_const_eval/src/interpret/validity.rs b/compiler/rustc_const_eval/src/interpret/validity.rs
index fc44490c96d..62f591ceaa9 100644
--- a/compiler/rustc_const_eval/src/interpret/validity.rs
+++ b/compiler/rustc_const_eval/src/interpret/validity.rs
@@ -558,7 +558,15 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
                 {
                     // Everything should be already interned.
                     let Some(global_alloc) = self.ecx.tcx.try_get_global_alloc(alloc_id) else {
-                        assert!(self.ecx.memory.alloc_map.get(alloc_id).is_none());
+                        if self.ecx.memory.alloc_map.contains_key(&alloc_id) {
+                            // This can happen when interning didn't complete due to, e.g.
+                            // missing `make_global`. This must mean other errors are already
+                            // being reported.
+                            self.ecx.tcx.dcx().delayed_bug(
+                                "interning did not complete, there should be an error",
+                            );
+                            return interp_ok(());
+                        }
                         // We can't have *any* references to non-existing allocations in const-eval
                         // as the rest of rustc isn't happy with them... so we throw an error, even
                         // though for zero-sized references this isn't really UB.
diff --git a/compiler/rustc_const_eval/src/util/check_validity_requirement.rs b/compiler/rustc_const_eval/src/util/check_validity_requirement.rs
index 4ca39bbc68e..b1f29598750 100644
--- a/compiler/rustc_const_eval/src/util/check_validity_requirement.rs
+++ b/compiler/rustc_const_eval/src/util/check_validity_requirement.rs
@@ -52,9 +52,9 @@ fn check_validity_requirement_strict<'tcx>(
 
     let mut cx = InterpCx::new(cx.tcx(), DUMMY_SP, cx.typing_env, machine);
 
-    let allocated = cx
-        .allocate(ty, MemoryKind::Machine(crate::const_eval::MemoryKind::Heap))
-        .expect("OOM: failed to allocate for uninit check");
+    // It doesn't really matter which `MemoryKind` we use here, `Stack` is the least wrong.
+    let allocated =
+        cx.allocate(ty, MemoryKind::Stack).expect("OOM: failed to allocate for uninit check");
 
     if kind == ValidityRequirement::Zero {
         cx.write_bytes_ptr(
@@ -184,9 +184,10 @@ pub(crate) fn validate_scalar_in_layout<'tcx>(
     let Ok(layout) = cx.layout_of(ty) else {
         bug!("could not compute layout of {scalar:?}:{ty:?}")
     };
-    let allocated = cx
-        .allocate(layout, MemoryKind::Machine(crate::const_eval::MemoryKind::Heap))
-        .expect("OOM: failed to allocate for uninit check");
+
+    // It doesn't really matter which `MemoryKind` we use here, `Stack` is the least wrong.
+    let allocated =
+        cx.allocate(layout, MemoryKind::Stack).expect("OOM: failed to allocate for uninit check");
 
     cx.write_scalar(scalar, &allocated).unwrap();
 
diff --git a/compiler/rustc_driver_impl/src/lib.rs b/compiler/rustc_driver_impl/src/lib.rs
index 18490385455..f3ed6042105 100644
--- a/compiler/rustc_driver_impl/src/lib.rs
+++ b/compiler/rustc_driver_impl/src/lib.rs
@@ -1237,9 +1237,55 @@ pub fn handle_options(early_dcx: &EarlyDiagCtxt, args: &[String]) -> Option<geto
         return None;
     }
 
+    warn_on_confusing_output_filename_flag(early_dcx, &matches, args);
+
     Some(matches)
 }
 
+/// Warn if `-o` is used without a space between the flag name and the value
+/// and the value is a high-value confusables,
+/// e.g. `-optimize` instead of `-o optimize`, see issue #142812.
+fn warn_on_confusing_output_filename_flag(
+    early_dcx: &EarlyDiagCtxt,
+    matches: &getopts::Matches,
+    args: &[String],
+) {
+    fn eq_ignore_separators(s1: &str, s2: &str) -> bool {
+        let s1 = s1.replace('-', "_");
+        let s2 = s2.replace('-', "_");
+        s1 == s2
+    }
+
+    if let Some(name) = matches.opt_str("o")
+        && let Some(suspect) = args.iter().find(|arg| arg.starts_with("-o") && *arg != "-o")
+    {
+        let filename = suspect.strip_prefix("-").unwrap_or(suspect);
+        let optgroups = config::rustc_optgroups();
+        let fake_args = ["optimize", "o0", "o1", "o2", "o3", "ofast", "og", "os", "oz"];
+
+        // Check if provided filename might be confusing in conjunction with `-o` flag,
+        // i.e. consider `-o{filename}` such as `-optimize` with `filename` being `ptimize`.
+        // There are high-value confusables, for example:
+        // - Long name of flags, e.g. `--out-dir` vs `-out-dir`
+        // - C compiler flag, e.g. `optimize`, `o0`, `o1`, `o2`, `o3`, `ofast`.
+        // - Codegen flags, e.g. `pt-level` of `-opt-level`.
+        if optgroups.iter().any(|option| eq_ignore_separators(option.long_name(), filename))
+            || config::CG_OPTIONS.iter().any(|option| eq_ignore_separators(option.name(), filename))
+            || fake_args.iter().any(|arg| eq_ignore_separators(arg, filename))
+        {
+            early_dcx.early_warn(
+                "option `-o` has no space between flag name and value, which can be confusing",
+            );
+            early_dcx.early_note(format!(
+                "output filename `-o {name}` is applied instead of a flag named `o{name}`"
+            ));
+            early_dcx.early_help(format!(
+                "insert a space between `-o` and `{name}` if this is intentional: `-o {name}`"
+            ));
+        }
+    }
+}
+
 fn parse_crate_attrs<'a>(sess: &'a Session) -> PResult<'a, ast::AttrVec> {
     let mut parser = unwrap_or_emit_fatal(match &sess.io.input {
         Input::File(file) => new_parser_from_file(&sess.psess, file, None),
diff --git a/compiler/rustc_expand/src/base.rs b/compiler/rustc_expand/src/base.rs
index ce3006c2604..1928cfd9048 100644
--- a/compiler/rustc_expand/src/base.rs
+++ b/compiler/rustc_expand/src/base.rs
@@ -1062,7 +1062,7 @@ pub trait ResolverExpand {
     fn next_node_id(&mut self) -> NodeId;
     fn invocation_parent(&self, id: LocalExpnId) -> LocalDefId;
 
-    fn resolve_dollar_crates(&mut self);
+    fn resolve_dollar_crates(&self);
     fn visit_ast_fragment_with_placeholders(
         &mut self,
         expn_id: LocalExpnId,
diff --git a/compiler/rustc_expand/src/build.rs b/compiler/rustc_expand/src/build.rs
index 85683c1a03f..51d6e43ab67 100644
--- a/compiler/rustc_expand/src/build.rs
+++ b/compiler/rustc_expand/src/build.rs
@@ -3,8 +3,8 @@ use rustc_ast::token::Delimiter;
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::util::literal;
 use rustc_ast::{
-    self as ast, AnonConst, AttrVec, BlockCheckMode, Expr, LocalKind, MatchKind, PatKind, UnOp,
-    attr, token, tokenstream,
+    self as ast, AnonConst, AttrItem, AttrVec, BlockCheckMode, Expr, LocalKind, MatchKind, PatKind,
+    UnOp, attr, token, tokenstream,
 };
 use rustc_span::source_map::Spanned;
 use rustc_span::{DUMMY_SP, Ident, Span, Symbol, kw, sym};
@@ -766,4 +766,10 @@ impl<'a> ExtCtxt<'a> {
             span,
         )
     }
+
+    // Builds an attribute fully manually.
+    pub fn attr_nested(&self, inner: AttrItem, span: Span) -> ast::Attribute {
+        let g = &self.sess.psess.attr_id_generator;
+        attr::mk_attr_from_item(g, inner, None, ast::AttrStyle::Outer, span)
+    }
 }
diff --git a/compiler/rustc_expand/src/config.rs b/compiler/rustc_expand/src/config.rs
index 6922ddfd6bd..83a8d601afe 100644
--- a/compiler/rustc_expand/src/config.rs
+++ b/compiler/rustc_expand/src/config.rs
@@ -12,7 +12,7 @@ use rustc_ast::{
 };
 use rustc_attr_parsing as attr;
 use rustc_attr_parsing::{
-    AttributeParser, CFG_TEMPLATE, EvalConfigResult, eval_config_entry, parse_cfg_attr,
+    AttributeParser, CFG_TEMPLATE, EvalConfigResult, ShouldEmit, eval_config_entry, parse_cfg_attr,
 };
 use rustc_data_structures::flat_map_in_place::FlatMapInPlace;
 use rustc_feature::{
@@ -167,7 +167,9 @@ pub fn pre_configure_attrs(sess: &Session, attrs: &[Attribute]) -> ast::AttrVec
         .flat_map(|attr| strip_unconfigured.process_cfg_attr(attr))
         .take_while(|attr| {
             !is_cfg(attr)
-                || strip_unconfigured.cfg_true(attr, strip_unconfigured.lint_node_id).as_bool()
+                || strip_unconfigured
+                    .cfg_true(attr, strip_unconfigured.lint_node_id, ShouldEmit::Nothing)
+                    .as_bool()
         })
         .collect()
 }
@@ -401,10 +403,18 @@ impl<'a> StripUnconfigured<'a> {
 
     /// Determines if a node with the given attributes should be included in this configuration.
     fn in_cfg(&self, attrs: &[Attribute]) -> bool {
-        attrs.iter().all(|attr| !is_cfg(attr) || self.cfg_true(attr, self.lint_node_id).as_bool())
+        attrs.iter().all(|attr| {
+            !is_cfg(attr)
+                || self.cfg_true(attr, self.lint_node_id, ShouldEmit::ErrorsAndLints).as_bool()
+        })
     }
 
-    pub(crate) fn cfg_true(&self, attr: &Attribute, node: NodeId) -> EvalConfigResult {
+    pub(crate) fn cfg_true(
+        &self,
+        attr: &Attribute,
+        node: NodeId,
+        emit_errors: ShouldEmit,
+    ) -> EvalConfigResult {
         // We need to run this to do basic validation of the attribute, such as that lits are valid, etc
         // FIXME(jdonszelmann) this should not be necessary in the future
         match validate_attr::parse_meta(&self.sess.psess, attr) {
@@ -428,7 +438,7 @@ impl<'a> StripUnconfigured<'a> {
             attr.span,
             node,
             self.features,
-            true,
+            emit_errors,
             parse_cfg_attr,
             &CFG_TEMPLATE,
         ) else {
@@ -436,7 +446,7 @@ impl<'a> StripUnconfigured<'a> {
             return EvalConfigResult::True;
         };
 
-        eval_config_entry(self.sess, &cfg, self.lint_node_id, self.features)
+        eval_config_entry(self.sess, &cfg, self.lint_node_id, self.features, emit_errors)
     }
 
     /// If attributes are not allowed on expressions, emit an error for `attr`
diff --git a/compiler/rustc_expand/src/expand.rs b/compiler/rustc_expand/src/expand.rs
index f99060e9a21..79ec79a2fdf 100644
--- a/compiler/rustc_expand/src/expand.rs
+++ b/compiler/rustc_expand/src/expand.rs
@@ -13,7 +13,7 @@ use rustc_ast::{
     MetaItemKind, ModKind, NodeId, PatKind, StmtKind, TyKind, token,
 };
 use rustc_ast_pretty::pprust;
-use rustc_attr_parsing::EvalConfigResult;
+use rustc_attr_parsing::{EvalConfigResult, ShouldEmit};
 use rustc_data_structures::flat_map_in_place::FlatMapInPlace;
 use rustc_errors::PResult;
 use rustc_feature::Features;
@@ -2171,7 +2171,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
         attr: ast::Attribute,
         pos: usize,
     ) -> EvalConfigResult {
-        let res = self.cfg().cfg_true(&attr, node.node_id());
+        let res = self.cfg().cfg_true(&attr, node.node_id(), ShouldEmit::ErrorsAndLints);
         if res.as_bool() {
             // A trace attribute left in AST in place of the original `cfg` attribute.
             // It can later be used by lints or other diagnostics.
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
index 7d9915d7f68..74872504b79 100644
--- a/compiler/rustc_feature/src/builtin_attrs.rs
+++ b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -614,6 +614,7 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
 
     // RFC 2632
+    // FIXME(const_trait_impl) remove this
     gated!(
         const_trait, Normal, template!(Word), WarnFollowing, EncodeCrossCrate::No, const_trait_impl,
         "`const_trait` is a temporary placeholder for marking a trait that is suitable for `const` \
@@ -684,6 +685,10 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         EncodeCrossCrate::Yes
     ),
     ungated!(
+        unstable_feature_bound, Normal, template!(Word, List: "feat1, feat2, ..."),
+        DuplicatesOk, EncodeCrossCrate::No,
+    ),
+    ungated!(
         rustc_const_unstable, Normal, template!(List: r#"feature = "name""#),
         DuplicatesOk, EncodeCrossCrate::Yes
     ),
diff --git a/compiler/rustc_hir/src/def.rs b/compiler/rustc_hir/src/def.rs
index df010f87098..ca57c4f3164 100644
--- a/compiler/rustc_hir/src/def.rs
+++ b/compiler/rustc_hir/src/def.rs
@@ -295,6 +295,12 @@ impl DefKind {
         }
     }
 
+    /// This is a "module" in name resolution sense.
+    #[inline]
+    pub fn is_module_like(self) -> bool {
+        matches!(self, DefKind::Mod | DefKind::Enum | DefKind::Trait)
+    }
+
     #[inline]
     pub fn is_fn_like(self) -> bool {
         matches!(
@@ -720,6 +726,15 @@ impl<Id> Res<Id> {
         }
     }
 
+    /// If this is a "module" in name resolution sense, return its `DefId`.
+    #[inline]
+    pub fn module_like_def_id(&self) -> Option<DefId> {
+        match self {
+            Res::Def(def_kind, def_id) if def_kind.is_module_like() => Some(*def_id),
+            _ => None,
+        }
+    }
+
     /// A human readable name for the res kind ("function", "module", etc.).
     pub fn descr(&self) -> &'static str {
         match *self {
diff --git a/compiler/rustc_hir/src/definitions.rs b/compiler/rustc_hir/src/definitions.rs
index f93b9e5af53..698406d53a4 100644
--- a/compiler/rustc_hir/src/definitions.rs
+++ b/compiler/rustc_hir/src/definitions.rs
@@ -140,7 +140,9 @@ impl DefKey {
     pub(crate) fn compute_stable_hash(&self, parent: DefPathHash) -> DefPathHash {
         let mut hasher = StableHasher::new();
 
-        parent.hash(&mut hasher);
+        // The new path is in the same crate as `parent`, and will contain the stable_crate_id.
+        // Therefore, we only need to include information of the parent's local hash.
+        parent.local_hash().hash(&mut hasher);
 
         let DisambiguatedDefPathData { ref data, disambiguator } = self.disambiguated_data;
 
@@ -181,32 +183,26 @@ pub struct DisambiguatedDefPathData {
 }
 
 impl DisambiguatedDefPathData {
-    pub fn fmt_maybe_verbose(&self, writer: &mut impl Write, verbose: bool) -> fmt::Result {
+    pub fn as_sym(&self, verbose: bool) -> Symbol {
         match self.data.name() {
             DefPathDataName::Named(name) => {
                 if verbose && self.disambiguator != 0 {
-                    write!(writer, "{}#{}", name, self.disambiguator)
+                    Symbol::intern(&format!("{}#{}", name, self.disambiguator))
                 } else {
-                    writer.write_str(name.as_str())
+                    name
                 }
             }
             DefPathDataName::Anon { namespace } => {
                 if let DefPathData::AnonAssocTy(method) = self.data {
-                    write!(writer, "{}::{{{}#{}}}", method, namespace, self.disambiguator)
+                    Symbol::intern(&format!("{}::{{{}#{}}}", method, namespace, self.disambiguator))
                 } else {
-                    write!(writer, "{{{}#{}}}", namespace, self.disambiguator)
+                    Symbol::intern(&format!("{{{}#{}}}", namespace, self.disambiguator))
                 }
             }
         }
     }
 }
 
-impl fmt::Display for DisambiguatedDefPathData {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        self.fmt_maybe_verbose(f, true)
-    }
-}
-
 #[derive(Clone, Debug, Encodable, Decodable)]
 pub struct DefPath {
     /// The path leading from the crate root to the item.
@@ -250,7 +246,7 @@ impl DefPath {
         let mut s = String::with_capacity(self.data.len() * 16);
 
         for component in &self.data {
-            write!(s, "::{component}").unwrap();
+            write!(s, "::{}", component.as_sym(true)).unwrap();
         }
 
         s
@@ -266,7 +262,7 @@ impl DefPath {
         for component in &self.data {
             s.extend(opt_delimiter);
             opt_delimiter = Some('-');
-            write!(s, "{component}").unwrap();
+            write!(s, "{}", component.as_sym(true)).unwrap();
         }
 
         s
@@ -361,8 +357,16 @@ impl Definitions {
             },
         };
 
-        let parent_hash = DefPathHash::new(stable_crate_id, Hash64::ZERO);
-        let def_path_hash = key.compute_stable_hash(parent_hash);
+        // We want *both* halves of a DefPathHash to depend on the crate-id of the defining crate.
+        // The crate-id can be more easily changed than the DefPath of an item, so, in the case of
+        // a crate-local DefPathHash collision, the user can simply "roll the dice again" for all
+        // DefPathHashes in the crate by changing the crate disambiguator (e.g. via bumping the
+        // crate's version number).
+        //
+        // Children paths will only hash the local portion, and still inherit the change to the
+        // root hash.
+        let def_path_hash =
+            DefPathHash::new(stable_crate_id, Hash64::new(stable_crate_id.as_u64()));
 
         // Create the root definition.
         let mut table = DefPathTable::new(stable_crate_id);
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 159518a8d87..e7898648c2b 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -7,7 +7,7 @@ use rustc_ast::token::CommentKind;
 use rustc_ast::util::parser::ExprPrecedence;
 use rustc_ast::{
     self as ast, FloatTy, InlineAsmOptions, InlineAsmTemplatePiece, IntTy, Label, LitIntType,
-    LitKind, TraitObjectSyntax, UintTy, UnsafeBinderCastKind,
+    LitKind, TraitObjectSyntax, UintTy, UnsafeBinderCastKind, join_path_idents,
 };
 pub use rustc_ast::{
     AssignOp, AssignOpKind, AttrId, AttrStyle, BinOp, BinOpKind, BindingMode, BorrowKind,
@@ -1168,7 +1168,7 @@ impl AttrPath {
 
 impl fmt::Display for AttrPath {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, "{}", self.segments.iter().map(|i| i.to_string()).collect::<Vec<_>>().join("::"))
+        write!(f, "{}", join_path_idents(&self.segments))
     }
 }
 
@@ -4163,6 +4163,7 @@ impl<'hir> Item<'hir> {
 
         expect_trait,
             (
+                Constness,
                 IsAuto,
                 Safety,
                 Ident,
@@ -4170,8 +4171,8 @@ impl<'hir> Item<'hir> {
                 GenericBounds<'hir>,
                 &'hir [TraitItemId]
             ),
-            ItemKind::Trait(is_auto, safety, ident, generics, bounds, items),
-            (*is_auto, *safety, *ident, generics, bounds, items);
+            ItemKind::Trait(constness, is_auto, safety, ident, generics, bounds, items),
+            (*constness, *is_auto, *safety, *ident, generics, bounds, items);
 
         expect_trait_alias, (Ident, &'hir Generics<'hir>, GenericBounds<'hir>),
             ItemKind::TraitAlias(ident, generics, bounds), (*ident, generics, bounds);
@@ -4341,7 +4342,15 @@ pub enum ItemKind<'hir> {
     /// A union definition, e.g., `union Foo<A, B> {x: A, y: B}`.
     Union(Ident, &'hir Generics<'hir>, VariantData<'hir>),
     /// A trait definition.
-    Trait(IsAuto, Safety, Ident, &'hir Generics<'hir>, GenericBounds<'hir>, &'hir [TraitItemId]),
+    Trait(
+        Constness,
+        IsAuto,
+        Safety,
+        Ident,
+        &'hir Generics<'hir>,
+        GenericBounds<'hir>,
+        &'hir [TraitItemId],
+    ),
     /// A trait alias.
     TraitAlias(Ident, &'hir Generics<'hir>, GenericBounds<'hir>),
 
@@ -4385,7 +4394,7 @@ impl ItemKind<'_> {
             | ItemKind::Enum(ident, ..)
             | ItemKind::Struct(ident, ..)
             | ItemKind::Union(ident, ..)
-            | ItemKind::Trait(_, _, ident, ..)
+            | ItemKind::Trait(_, _, _, ident, ..)
             | ItemKind::TraitAlias(ident, ..) => Some(ident),
 
             ItemKind::Use(_, UseKind::Glob | UseKind::ListStem)
@@ -4403,7 +4412,7 @@ impl ItemKind<'_> {
             | ItemKind::Enum(_, generics, _)
             | ItemKind::Struct(_, generics, _)
             | ItemKind::Union(_, generics, _)
-            | ItemKind::Trait(_, _, _, generics, _, _)
+            | ItemKind::Trait(_, _, _, _, generics, _, _)
             | ItemKind::TraitAlias(_, generics, _)
             | ItemKind::Impl(Impl { generics, .. }) => generics,
             _ => return None,
diff --git a/compiler/rustc_hir/src/intravisit.rs b/compiler/rustc_hir/src/intravisit.rs
index 3edb94c28da..f33915d5b07 100644
--- a/compiler/rustc_hir/src/intravisit.rs
+++ b/compiler/rustc_hir/src/intravisit.rs
@@ -618,7 +618,15 @@ 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_variant_data(struct_definition));
         }
-        ItemKind::Trait(_is_auto, _safety, ident, ref generics, bounds, trait_item_refs) => {
+        ItemKind::Trait(
+            _constness,
+            _is_auto,
+            _safety,
+            ident,
+            ref generics,
+            bounds,
+            trait_item_refs,
+        ) => {
             try_visit!(visitor.visit_ident(ident));
             try_visit!(visitor.visit_generics(generics));
             walk_list!(visitor, visit_param_bound, bounds);
diff --git a/compiler/rustc_hir/src/tests.rs b/compiler/rustc_hir/src/tests.rs
index 18c2bfdac8c..3b797c1f103 100644
--- a/compiler/rustc_hir/src/tests.rs
+++ b/compiler/rustc_hir/src/tests.rs
@@ -28,7 +28,8 @@ fn def_path_hash_depends_on_crate_id() {
         assert_ne!(h0.local_hash(), h1.local_hash());
 
         fn mk_test_hash(stable_crate_id: StableCrateId) -> DefPathHash {
-            let parent_hash = DefPathHash::new(stable_crate_id, Hash64::ZERO);
+            let parent_hash =
+                DefPathHash::new(stable_crate_id, Hash64::new(stable_crate_id.as_u64()));
 
             let key = DefKey {
                 parent: None,
diff --git a/compiler/rustc_hir_analysis/messages.ftl b/compiler/rustc_hir_analysis/messages.ftl
index 529d3578985..e38ca9e80ce 100644
--- a/compiler/rustc_hir_analysis/messages.ftl
+++ b/compiler/rustc_hir_analysis/messages.ftl
@@ -117,15 +117,15 @@ hir_analysis_coercion_between_struct_same_note = expected coercion between the s
 
 hir_analysis_coercion_between_struct_single_note = expected a single field to be coerced, none found
 
-hir_analysis_const_bound_for_non_const_trait = `{$modifier}` can only be applied to `#[const_trait]` traits
+hir_analysis_const_bound_for_non_const_trait = `{$modifier}` can only be applied to `const` traits
     .label = can't be applied to `{$trait_name}`
-    .note = `{$trait_name}` can't be used with `{$modifier}` because it isn't annotated with `#[const_trait]`
-    .suggestion = {$suggestion_pre}mark `{$trait_name}` as `#[const_trait]` to allow it to have `const` implementations
+    .note = `{$trait_name}` can't be used with `{$modifier}` because it isn't `const`
+    .suggestion = {$suggestion_pre}mark `{$trait_name}` as `const` to allow it to have `const` implementations
 
-hir_analysis_const_impl_for_non_const_trait = const `impl` for trait `{$trait_name}` which is not marked with `#[const_trait]`
+hir_analysis_const_impl_for_non_const_trait = const `impl` for trait `{$trait_name}` which is not `const`
     .label = this trait is not `const`
-    .suggestion = {$suggestion_pre}mark `{$trait_name}` as `#[const_trait]` to allow it to have `const` implementations
-    .note = marking a trait with `#[const_trait]` ensures all default method bodies are `const`
+    .suggestion = {$suggestion_pre}mark `{$trait_name}` as `const` to allow it to have `const` implementations
+    .note = marking a trait with `const` ensures all default method bodies are `const`
     .adding = adding a non-const method body in the future would be a breaking change
 
 hir_analysis_const_param_ty_impl_on_non_adt =
@@ -158,7 +158,7 @@ hir_analysis_dispatch_from_dyn_zst = the trait `DispatchFromDyn` may only be imp
 hir_analysis_drop_impl_negative = negative `Drop` impls are not supported
 
 hir_analysis_drop_impl_on_wrong_item =
-    the `Drop` trait may only be implemented for local structs, enums, and unions
+    the `{$trait_}` trait may only be implemented for local structs, enums, and unions
     .label = must be a struct, enum, or union in the current crate
 
 hir_analysis_drop_impl_reservation = reservation `Drop` impls are not supported
diff --git a/compiler/rustc_hir_analysis/src/check/check.rs b/compiler/rustc_hir_analysis/src/check/check.rs
index 70fbb8a543e..03c026cd6c8 100644
--- a/compiler/rustc_hir_analysis/src/check/check.rs
+++ b/compiler/rustc_hir_analysis/src/check/check.rs
@@ -889,8 +889,6 @@ pub(crate) fn check_item_type(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Result<(),
             tcx.ensure_ok().predicates_of(def_id);
             tcx.ensure_ok().explicit_item_bounds(def_id);
             tcx.ensure_ok().explicit_item_self_bounds(def_id);
-            tcx.ensure_ok().item_bounds(def_id);
-            tcx.ensure_ok().item_self_bounds(def_id);
             if tcx.is_conditionally_const(def_id) {
                 tcx.ensure_ok().explicit_implied_const_bounds(def_id);
                 tcx.ensure_ok().const_conditions(def_id);
@@ -1044,8 +1042,12 @@ pub(crate) fn check_item_type(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Result<(),
             let has_type = match assoc_item.container {
                 ty::AssocItemContainer::Impl => true,
                 ty::AssocItemContainer::Trait => {
-                    tcx.ensure_ok().item_bounds(def_id);
-                    tcx.ensure_ok().item_self_bounds(def_id);
+                    tcx.ensure_ok().explicit_item_bounds(def_id);
+                    tcx.ensure_ok().explicit_item_self_bounds(def_id);
+                    if tcx.is_conditionally_const(def_id) {
+                        tcx.ensure_ok().explicit_implied_const_bounds(def_id);
+                        tcx.ensure_ok().const_conditions(def_id);
+                    }
                     res = res.and(check_trait_item(tcx, def_id));
                     assoc_item.defaultness(tcx).has_value()
                 }
diff --git a/compiler/rustc_hir_analysis/src/check/intrinsic.rs b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
index dcab6ef1c5a..6e5fe3823ab 100644
--- a/compiler/rustc_hir_analysis/src/check/intrinsic.rs
+++ b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
@@ -422,6 +422,9 @@ pub(crate) fn check_intrinsic_type(
             vec![Ty::new_mut_ptr(tcx, tcx.types.u8), tcx.types.usize, tcx.types.usize],
             tcx.types.unit,
         ),
+        sym::const_make_global => {
+            (0, 0, vec![Ty::new_mut_ptr(tcx, tcx.types.u8)], Ty::new_imm_ptr(tcx, tcx.types.u8))
+        }
 
         sym::ptr_offset_from => (
             1,
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index 607028f4d9a..14ec82ede1c 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -2212,12 +2212,16 @@ impl<'tcx> WfCheckingCtxt<'_, 'tcx> {
         let implied_obligations = traits::elaborate(tcx, predicates_with_span);
 
         for (pred, obligation_span) in implied_obligations {
-            // We lower empty bounds like `Vec<dyn Copy>:` as
-            // `WellFormed(Vec<dyn Copy>)`, which will later get checked by
-            // regular WF checking
-            if let ty::ClauseKind::WellFormed(..) = pred.kind().skip_binder() {
-                continue;
+            match pred.kind().skip_binder() {
+                // We lower empty bounds like `Vec<dyn Copy>:` as
+                // `WellFormed(Vec<dyn Copy>)`, which will later get checked by
+                // regular WF checking
+                ty::ClauseKind::WellFormed(..)
+                // Unstable feature goals cannot be proven in an empty environment so skip them
+                | ty::ClauseKind::UnstableFeature(..) => continue,
+                _ => {}
             }
+
             // Match the existing behavior.
             if pred.is_global() && !pred.has_type_flags(TypeFlags::HAS_BINDER_VARS) {
                 let pred = self.normalize(span, None, pred);
diff --git a/compiler/rustc_hir_analysis/src/coherence/builtin.rs b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
index 8356a0af63c..27948f50a4a 100644
--- a/compiler/rustc_hir_analysis/src/coherence/builtin.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
@@ -37,6 +37,7 @@ pub(super) fn check_trait<'tcx>(
     let lang_items = tcx.lang_items();
     let checker = Checker { tcx, trait_def_id, impl_def_id, impl_header };
     checker.check(lang_items.drop_trait(), visit_implementation_of_drop)?;
+    checker.check(lang_items.async_drop_trait(), visit_implementation_of_drop)?;
     checker.check(lang_items.copy_trait(), visit_implementation_of_copy)?;
     checker.check(lang_items.const_param_ty_trait(), |checker| {
         visit_implementation_of_const_param_ty(checker, LangItem::ConstParamTy)
@@ -83,7 +84,10 @@ fn visit_implementation_of_drop(checker: &Checker<'_>) -> Result<(), ErrorGuaran
 
     let impl_ = tcx.hir_expect_item(impl_did).expect_impl();
 
-    Err(tcx.dcx().emit_err(errors::DropImplOnWrongItem { span: impl_.self_ty.span }))
+    Err(tcx.dcx().emit_err(errors::DropImplOnWrongItem {
+        span: impl_.self_ty.span,
+        trait_: tcx.item_name(checker.impl_header.trait_ref.skip_binder().def_id),
+    }))
 }
 
 fn visit_implementation_of_copy(checker: &Checker<'_>) -> Result<(), ErrorGuaranteed> {
diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
index 28a8758178f..0728b24eb14 100644
--- a/compiler/rustc_hir_analysis/src/collect.rs
+++ b/compiler/rustc_hir_analysis/src/collect.rs
@@ -844,15 +844,20 @@ fn adt_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::AdtDef<'_> {
 fn trait_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::TraitDef {
     let item = tcx.hir_expect_item(def_id);
 
-    let (is_alias, is_auto, safety) = match item.kind {
-        hir::ItemKind::Trait(is_auto, safety, ..) => (false, is_auto == hir::IsAuto::Yes, safety),
-        hir::ItemKind::TraitAlias(..) => (true, false, hir::Safety::Safe),
+    let (constness, is_alias, is_auto, safety) = match item.kind {
+        hir::ItemKind::Trait(constness, is_auto, safety, ..) => {
+            (constness, false, is_auto == hir::IsAuto::Yes, safety)
+        }
+        hir::ItemKind::TraitAlias(..) => (hir::Constness::NotConst, true, false, hir::Safety::Safe),
         _ => span_bug!(item.span, "trait_def_of_item invoked on non-trait"),
     };
 
     let attrs = tcx.get_all_attrs(def_id);
     // Only regular traits can be const.
-    let constness = if !is_alias && find_attr!(attrs, AttributeKind::ConstTrait(_)) {
+    // FIXME(const_trait_impl): remove this
+    let constness = if constness == hir::Constness::Const
+        || !is_alias && find_attr!(attrs, AttributeKind::ConstTrait(_))
+    {
         hir::Constness::Const
     } else {
         hir::Constness::NotConst
diff --git a/compiler/rustc_hir_analysis/src/collect/item_bounds.rs b/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
index e51ef46afb7..548ba343aae 100644
--- a/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
+++ b/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
@@ -38,12 +38,13 @@ fn associated_type_bounds<'tcx>(
         let icx = ItemCtxt::new(tcx, assoc_item_def_id);
         let mut bounds = Vec::new();
         icx.lowerer().lower_bounds(item_ty, hir_bounds, &mut bounds, ty::List::empty(), filter);
-        // Implicit bounds are added to associated types unless a `?Trait` bound is found
+
         match filter {
             PredicateFilter::All
             | PredicateFilter::SelfOnly
             | PredicateFilter::SelfTraitThatDefines(_)
             | PredicateFilter::SelfAndAssociatedTypeBounds => {
+                // Implicit bounds are added to associated types unless a `?Trait` bound is found.
                 icx.lowerer().add_sizedness_bounds(
                     &mut bounds,
                     item_ty,
@@ -53,37 +54,48 @@ fn associated_type_bounds<'tcx>(
                     span,
                 );
                 icx.lowerer().add_default_traits(&mut bounds, item_ty, hir_bounds, None, span);
+
+                // Also collect `where Self::Assoc: Trait` from the parent trait's where clauses.
+                let trait_def_id = tcx.local_parent(assoc_item_def_id);
+                let trait_predicates = tcx.trait_explicit_predicates_and_bounds(trait_def_id);
+
+                let item_trait_ref =
+                    ty::TraitRef::identity(tcx, tcx.parent(assoc_item_def_id.to_def_id()));
+                bounds.extend(trait_predicates.predicates.iter().copied().filter_map(
+                    |(clause, span)| {
+                        remap_gat_vars_and_recurse_into_nested_projections(
+                            tcx,
+                            filter,
+                            item_trait_ref,
+                            assoc_item_def_id,
+                            span,
+                            clause,
+                        )
+                    },
+                ));
             }
             // `ConstIfConst` is only interested in `[const]` bounds.
-            PredicateFilter::ConstIfConst | PredicateFilter::SelfConstIfConst => {}
+            PredicateFilter::ConstIfConst | PredicateFilter::SelfConstIfConst => {
+                // FIXME(const_trait_impl): We *could* uplift the
+                // `where Self::Assoc: [const] Trait` bounds from the parent trait
+                // here too, but we'd need to split `const_conditions` into two
+                // queries (like we do for `trait_explicit_predicates_and_bounds`)
+                // since we need to also filter the predicates *out* of the const
+                // conditions or they lead to cycles in the trait solver when
+                // utilizing these bounds. For now, let's do nothing.
+            }
         }
 
-        let trait_def_id = tcx.local_parent(assoc_item_def_id);
-        let trait_predicates = tcx.trait_explicit_predicates_and_bounds(trait_def_id);
-
-        let item_trait_ref = ty::TraitRef::identity(tcx, tcx.parent(assoc_item_def_id.to_def_id()));
-        let bounds_from_parent =
-            trait_predicates.predicates.iter().copied().filter_map(|(clause, span)| {
-                remap_gat_vars_and_recurse_into_nested_projections(
-                    tcx,
-                    filter,
-                    item_trait_ref,
-                    assoc_item_def_id,
-                    span,
-                    clause,
-                )
-            });
-
-        let all_bounds = tcx.arena.alloc_from_iter(bounds.into_iter().chain(bounds_from_parent));
+        let bounds = tcx.arena.alloc_from_iter(bounds);
         debug!(
             "associated_type_bounds({}) = {:?}",
             tcx.def_path_str(assoc_item_def_id.to_def_id()),
-            all_bounds
+            bounds
         );
 
-        assert_only_contains_predicates_from(filter, all_bounds, item_ty);
+        assert_only_contains_predicates_from(filter, bounds, item_ty);
 
-        all_bounds
+        bounds
     })
 }
 
@@ -112,6 +124,7 @@ fn remap_gat_vars_and_recurse_into_nested_projections<'tcx>(
         ty::ClauseKind::Trait(tr) => tr.self_ty(),
         ty::ClauseKind::Projection(proj) => proj.projection_term.self_ty(),
         ty::ClauseKind::TypeOutlives(outlives) => outlives.0,
+        ty::ClauseKind::HostEffect(host) => host.self_ty(),
         _ => return None,
     };
 
diff --git a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
index a93e58b101f..f2f1560d8b2 100644
--- a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
@@ -1,6 +1,7 @@
 use std::assert_matches::assert_matches;
 
 use hir::Node;
+use rustc_attr_data_structures::{AttributeKind, find_attr};
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
@@ -162,7 +163,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
                         .map(|t| ty::Binder::dummy(t.instantiate_identity()));
                 }
             }
-            ItemKind::Trait(_, _, _, _, self_bounds, ..)
+            ItemKind::Trait(_, _, _, _, _, self_bounds, ..)
             | ItemKind::TraitAlias(_, _, self_bounds) => {
                 is_trait = Some((self_bounds, item.span));
             }
@@ -333,6 +334,19 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
         predicates.extend(const_evaluatable_predicates_of(tcx, def_id, &predicates));
     }
 
+    let attrs = tcx.hir_attrs(tcx.local_def_id_to_hir_id(def_id));
+    // FIXME(staged_api): We might want to look at the normal stability attributes too but
+    // first we would need a way to let std/core use APIs with unstable feature bounds from
+    // within stable APIs.
+    let allow_unstable_feature_attr =
+        find_attr!(attrs, AttributeKind::UnstableFeatureBound(i) => i)
+            .map(|i| i.as_slice())
+            .unwrap_or_default();
+
+    for (feat_name, span) in allow_unstable_feature_attr {
+        predicates.insert((ty::ClauseKind::UnstableFeature(*feat_name).upcast(tcx), *span));
+    }
+
     let mut predicates: Vec<_> = predicates.into_iter().collect();
 
     // Subtle: before we store the predicates into the tcx, we
@@ -764,6 +778,7 @@ pub(super) fn assert_only_contains_predicates_from<'tcx>(
                     ty::ClauseKind::RegionOutlives(_)
                     | ty::ClauseKind::ConstArgHasType(_, _)
                     | ty::ClauseKind::WellFormed(_)
+                    | ty::ClauseKind::UnstableFeature(_)
                     | ty::ClauseKind::ConstEvaluatable(_) => {
                         bug!(
                             "unexpected non-`Self` predicate when computing \
@@ -791,6 +806,7 @@ pub(super) fn assert_only_contains_predicates_from<'tcx>(
                     | ty::ClauseKind::ConstArgHasType(_, _)
                     | ty::ClauseKind::WellFormed(_)
                     | ty::ClauseKind::ConstEvaluatable(_)
+                    | ty::ClauseKind::UnstableFeature(_)
                     | ty::ClauseKind::HostEffect(..) => {
                         bug!(
                             "unexpected non-`Self` predicate when computing \
@@ -1006,7 +1022,7 @@ pub(super) fn const_conditions<'tcx>(
         Node::Item(item) => match item.kind {
             hir::ItemKind::Impl(impl_) => (impl_.generics, None, false),
             hir::ItemKind::Fn { generics, .. } => (generics, None, false),
-            hir::ItemKind::Trait(_, _, _, generics, supertraits, _) => {
+            hir::ItemKind::Trait(_, _, _, _, generics, supertraits, _) => {
                 (generics, Some((item.owner_id.def_id, supertraits)), false)
             }
             _ => bug!("const_conditions called on wrong item: {def_id:?}"),
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 8d7ac7db67b..77e63e38c8c 100644
--- a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
+++ b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
@@ -634,7 +634,7 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
             | hir::ItemKind::Enum(_, generics, _)
             | hir::ItemKind::Struct(_, generics, _)
             | hir::ItemKind::Union(_, generics, _)
-            | hir::ItemKind::Trait(_, _, _, generics, ..)
+            | hir::ItemKind::Trait(_, _, _, _, generics, ..)
             | hir::ItemKind::TraitAlias(_, generics, ..)
             | hir::ItemKind::Impl(&hir::Impl { generics, .. }) => {
                 // These kinds of items have only early-bound lifetime parameters.
diff --git a/compiler/rustc_hir_analysis/src/errors.rs b/compiler/rustc_hir_analysis/src/errors.rs
index c1c82839212..fbd21f8b100 100644
--- a/compiler/rustc_hir_analysis/src/errors.rs
+++ b/compiler/rustc_hir_analysis/src/errors.rs
@@ -205,6 +205,7 @@ pub(crate) struct DropImplOnWrongItem {
     #[primary_span]
     #[label]
     pub span: Span,
+    pub trait_: Symbol,
 }
 
 #[derive(Diagnostic)]
@@ -525,6 +526,7 @@ pub(crate) struct ConstImplForNonConstTrait {
     pub trait_name: String,
     #[suggestion(
         applicability = "machine-applicable",
+        // FIXME(const_trait_impl) fix this suggestion
         code = "#[const_trait] ",
         style = "verbose"
     )]
@@ -548,6 +550,7 @@ pub(crate) struct ConstBoundForNonConstTrait {
     pub suggestion_pre: &'static str,
     #[suggestion(
         applicability = "machine-applicable",
+        // FIXME(const_trait_impl) fix this suggestion
         code = "#[const_trait] ",
         style = "verbose"
     )]
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 3f928fd056e..2d60c9561a9 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
@@ -635,7 +635,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
                 self.suggest_adding_type_and_const_args(err);
             }
             ExcessTypesOrConsts { .. } => {
-                // this can happen with `[const] T` where T isn't a const_trait.
+                // this can happen with `[const] T` where T isn't a `const trait`.
             }
             _ => unreachable!(),
         }
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 4784cfb5235..9a752aeccdd 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
@@ -334,7 +334,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         };
 
         let (trait_generics, trait_bounds) = match parent_trait.kind {
-            hir::ItemKind::Trait(_, _, _, generics, supertraits, _) => (generics, supertraits),
+            hir::ItemKind::Trait(_, _, _, _, generics, supertraits, _) => (generics, supertraits),
             hir::ItemKind::TraitAlias(_, generics, supertraits) => (generics, supertraits),
             _ => unreachable!(),
         };
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 574d19a5aa5..0043f0c7117 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
@@ -499,6 +499,7 @@ fn trait_specialization_kind<'tcx>(
         | ty::ClauseKind::ConstArgHasType(..)
         | ty::ClauseKind::WellFormed(_)
         | ty::ClauseKind::ConstEvaluatable(..)
+        | ty::ClauseKind::UnstableFeature(_)
         | ty::ClauseKind::HostEffect(..) => None,
     }
 }
diff --git a/compiler/rustc_hir_analysis/src/outlives/explicit.rs b/compiler/rustc_hir_analysis/src/outlives/explicit.rs
index 2c1d443f951..d3a57a4d8e5 100644
--- a/compiler/rustc_hir_analysis/src/outlives/explicit.rs
+++ b/compiler/rustc_hir_analysis/src/outlives/explicit.rs
@@ -54,6 +54,7 @@ impl<'tcx> ExplicitPredicatesMap<'tcx> {
                     | ty::ClauseKind::ConstArgHasType(_, _)
                     | ty::ClauseKind::WellFormed(_)
                     | ty::ClauseKind::ConstEvaluatable(_)
+                    | ty::ClauseKind::UnstableFeature(_)
                     | ty::ClauseKind::HostEffect(..) => {}
                 }
             }
diff --git a/compiler/rustc_hir_analysis/src/outlives/utils.rs b/compiler/rustc_hir_analysis/src/outlives/utils.rs
index 301f5de9424..99a633e2b7d 100644
--- a/compiler/rustc_hir_analysis/src/outlives/utils.rs
+++ b/compiler/rustc_hir_analysis/src/outlives/utils.rs
@@ -7,8 +7,7 @@ use smallvec::smallvec;
 
 /// Tracks the `T: 'a` or `'a: 'a` predicates that we have inferred
 /// must be added to the struct header.
-pub(crate) type RequiredPredicates<'tcx> =
-    FxIndexMap<ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>, Span>;
+pub(crate) type RequiredPredicates<'tcx> = FxIndexMap<ty::ArgOutlivesPredicate<'tcx>, Span>;
 
 /// Given a requirement `T: 'a` or `'b: 'a`, deduce the
 /// outlives_component and add it to `required_predicates`
diff --git a/compiler/rustc_hir_pretty/src/lib.rs b/compiler/rustc_hir_pretty/src/lib.rs
index 2c13c9ef438..bda02042aa6 100644
--- a/compiler/rustc_hir_pretty/src/lib.rs
+++ b/compiler/rustc_hir_pretty/src/lib.rs
@@ -735,8 +735,17 @@ impl<'a> State<'a> {
                 }
                 self.bclose(item.span, cb);
             }
-            hir::ItemKind::Trait(is_auto, safety, ident, generics, bounds, trait_items) => {
+            hir::ItemKind::Trait(
+                constness,
+                is_auto,
+                safety,
+                ident,
+                generics,
+                bounds,
+                trait_items,
+            ) => {
                 let (cb, ib) = self.head("");
+                self.print_constness(constness);
                 self.print_is_auto(is_auto);
                 self.print_safety(safety);
                 self.word_nbsp("trait");
diff --git a/compiler/rustc_hir_typeck/src/closure.rs b/compiler/rustc_hir_typeck/src/closure.rs
index 459c0498d50..a413f805873 100644
--- a/compiler/rustc_hir_typeck/src/closure.rs
+++ b/compiler/rustc_hir_typeck/src/closure.rs
@@ -161,16 +161,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // Resume type defaults to `()` if the coroutine has no argument.
                 let resume_ty = liberated_sig.inputs().get(0).copied().unwrap_or(tcx.types.unit);
 
-                // In the new solver, we can just instantiate this eagerly
-                // with the witness. This will ensure that goals that don't need
-                // to stall on interior types will get processed eagerly.
-                let interior = if self.next_trait_solver() {
-                    Ty::new_coroutine_witness(tcx, expr_def_id.to_def_id(), parent_args)
-                } else {
-                    self.next_ty_var(expr_span)
-                };
-
-                self.deferred_coroutine_interiors.borrow_mut().push((expr_def_id, interior));
+                let interior = Ty::new_coroutine_witness(tcx, expr_def_id.to_def_id(), parent_args);
 
                 // Coroutines that come from coroutine closures have not yet determined
                 // their kind ty, so make a fresh infer var which will be constrained
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
index af1fc045ac8..0b3d50ff219 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
@@ -625,50 +625,23 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // trigger query cycle ICEs, as doing so requires MIR.
         self.select_obligations_where_possible(|_| {});
 
-        let coroutines = std::mem::take(&mut *self.deferred_coroutine_interiors.borrow_mut());
-        debug!(?coroutines);
-
-        let mut obligations = vec![];
-
-        if !self.next_trait_solver() {
-            for &(coroutine_def_id, interior) in coroutines.iter() {
-                debug!(?coroutine_def_id);
-
-                // Create the `CoroutineWitness` type that we will unify with `interior`.
-                let args = ty::GenericArgs::identity_for_item(
-                    self.tcx,
-                    self.tcx.typeck_root_def_id(coroutine_def_id.to_def_id()),
-                );
-                let witness =
-                    Ty::new_coroutine_witness(self.tcx, coroutine_def_id.to_def_id(), args);
-
-                // Unify `interior` with `witness` and collect all the resulting obligations.
-                let span = self.tcx.hir_body_owned_by(coroutine_def_id).value.span;
-                let ty::Infer(ty::InferTy::TyVar(_)) = interior.kind() else {
-                    span_bug!(span, "coroutine interior witness not infer: {:?}", interior.kind())
-                };
-                let ok = self
-                    .at(&self.misc(span), self.param_env)
-                    // Will never define opaque types, as all we do is instantiate a type variable.
-                    .eq(DefineOpaqueTypes::Yes, interior, witness)
-                    .expect("Failed to unify coroutine interior type");
-
-                obligations.extend(ok.obligations);
-            }
-        }
+        let ty::TypingMode::Analysis { defining_opaque_types_and_generators } = self.typing_mode()
+        else {
+            bug!();
+        };
 
-        if !coroutines.is_empty() {
-            obligations.extend(
+        if defining_opaque_types_and_generators
+            .iter()
+            .any(|def_id| self.tcx.is_coroutine(def_id.to_def_id()))
+        {
+            self.typeck_results.borrow_mut().coroutine_stalled_predicates.extend(
                 self.fulfillment_cx
                     .borrow_mut()
-                    .drain_stalled_obligations_for_coroutines(&self.infcx),
+                    .drain_stalled_obligations_for_coroutines(&self.infcx)
+                    .into_iter()
+                    .map(|o| (o.predicate, o.cause)),
             );
         }
-
-        self.typeck_results
-            .borrow_mut()
-            .coroutine_stalled_predicates
-            .extend(obligations.into_iter().map(|o| (o.predicate, o.cause)));
     }
 
     #[instrument(skip(self), level = "debug")]
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/inspect_obligations.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/inspect_obligations.rs
index e4c62bf027b..367e2b6b372 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/inspect_obligations.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/inspect_obligations.rs
@@ -54,6 +54,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             | ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(..))
             | ty::PredicateKind::ConstEquate(..)
             | ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(..))
+            | ty::PredicateKind::Clause(ty::ClauseKind::UnstableFeature(_))
             | ty::PredicateKind::Ambiguous => false,
         }
     }
diff --git a/compiler/rustc_hir_typeck/src/method/prelude_edition_lints.rs b/compiler/rustc_hir_typeck/src/method/prelude_edition_lints.rs
index 0037d5ac042..38413cca633 100644
--- a/compiler/rustc_hir_typeck/src/method/prelude_edition_lints.rs
+++ b/compiler/rustc_hir_typeck/src/method/prelude_edition_lints.rs
@@ -2,6 +2,7 @@ use std::fmt::Write;
 
 use hir::def_id::DefId;
 use hir::{HirId, ItemKind};
+use rustc_ast::join_path_idents;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_lint::{ARRAY_INTO_ITER, BOXED_SLICE_INTO_ITER};
@@ -383,13 +384,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // All that is left is `_`! We need to use the full path. It doesn't matter which one we
         // pick, so just take the first one.
         match import_items[0].kind {
-            ItemKind::Use(path, _) => Some(
-                path.segments
-                    .iter()
-                    .map(|segment| segment.ident.to_string())
-                    .collect::<Vec<_>>()
-                    .join("::"),
-            ),
+            ItemKind::Use(path, _) => {
+                Some(join_path_idents(path.segments.iter().map(|seg| seg.ident)))
+            }
             _ => {
                 span_bug!(span, "unexpected item kind, expected a use: {:?}", import_items[0].kind);
             }
diff --git a/compiler/rustc_hir_typeck/src/method/probe.rs b/compiler/rustc_hir_typeck/src/method/probe.rs
index 94c93e73627..3261327a9fd 100644
--- a/compiler/rustc_hir_typeck/src/method/probe.rs
+++ b/compiler/rustc_hir_typeck/src/method/probe.rs
@@ -921,6 +921,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 | ty::ClauseKind::ConstArgHasType(_, _)
                 | ty::ClauseKind::WellFormed(_)
                 | ty::ClauseKind::ConstEvaluatable(_)
+                | ty::ClauseKind::UnstableFeature(_)
                 | ty::ClauseKind::HostEffect(..) => None,
             }
         });
diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index 2815621ffde..dbfa7e6273c 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -1189,7 +1189,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         entry.1.insert((self_ty.span, ""));
                     }
                     Some(Node::Item(hir::Item {
-                        kind: hir::ItemKind::Trait(rustc_ast::ast::IsAuto::Yes, ..),
+                        kind: hir::ItemKind::Trait(_, rustc_ast::ast::IsAuto::Yes, ..),
                         span: item_span,
                         ..
                     })) => {
@@ -1201,7 +1201,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     Some(
                         Node::Item(hir::Item {
                             kind:
-                                hir::ItemKind::Trait(_, _, ident, ..)
+                                hir::ItemKind::Trait(_, _, _, ident, ..)
                                 | hir::ItemKind::TraitAlias(ident, ..),
                             ..
                         })
@@ -4084,7 +4084,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             return;
                         }
                         Node::Item(hir::Item {
-                            kind: hir::ItemKind::Trait(_, _, ident, _, bounds, _),
+                            kind: hir::ItemKind::Trait(_, _, _, ident, _, bounds, _),
                             ..
                         }) => {
                             let (sp, sep, article) = if bounds.is_empty() {
diff --git a/compiler/rustc_hir_typeck/src/typeck_root_ctxt.rs b/compiler/rustc_hir_typeck/src/typeck_root_ctxt.rs
index 26be5fc6d19..9f4ab8ca5d4 100644
--- a/compiler/rustc_hir_typeck/src/typeck_root_ctxt.rs
+++ b/compiler/rustc_hir_typeck/src/typeck_root_ctxt.rs
@@ -63,8 +63,6 @@ pub(crate) struct TypeckRootCtxt<'tcx> {
 
     pub(super) deferred_asm_checks: RefCell<Vec<(&'tcx hir::InlineAsm<'tcx>, HirId)>>,
 
-    pub(super) deferred_coroutine_interiors: RefCell<Vec<(LocalDefId, Ty<'tcx>)>>,
-
     pub(super) deferred_repeat_expr_checks:
         RefCell<Vec<(&'tcx hir::Expr<'tcx>, Ty<'tcx>, ty::Const<'tcx>)>>,
 
@@ -103,7 +101,6 @@ impl<'tcx> TypeckRootCtxt<'tcx> {
             deferred_cast_checks: RefCell::new(Vec::new()),
             deferred_transmute_checks: RefCell::new(Vec::new()),
             deferred_asm_checks: RefCell::new(Vec::new()),
-            deferred_coroutine_interiors: RefCell::new(Vec::new()),
             deferred_repeat_expr_checks: RefCell::new(Vec::new()),
             diverging_type_vars: RefCell::new(Default::default()),
             infer_var_info: RefCell::new(Default::default()),
diff --git a/compiler/rustc_infer/src/infer/canonical/query_response.rs b/compiler/rustc_infer/src/infer/canonical/query_response.rs
index d5d49e3188a..6be53c948c8 100644
--- a/compiler/rustc_infer/src/infer/canonical/query_response.rs
+++ b/compiler/rustc_infer/src/infer/canonical/query_response.rs
@@ -116,9 +116,15 @@ impl<'tcx> InferCtxt<'tcx> {
         }
 
         let region_obligations = self.take_registered_region_obligations();
+        let region_assumptions = self.take_registered_region_assumptions();
         debug!(?region_obligations);
         let region_constraints = self.with_region_constraints(|region_constraints| {
-            make_query_region_constraints(tcx, region_obligations, region_constraints)
+            make_query_region_constraints(
+                tcx,
+                region_obligations,
+                region_constraints,
+                region_assumptions,
+            )
         });
         debug!(?region_constraints);
 
@@ -169,6 +175,11 @@ impl<'tcx> InferCtxt<'tcx> {
             self.register_outlives_constraint(predicate, cause);
         }
 
+        for assumption in &query_response.value.region_constraints.assumptions {
+            let assumption = instantiate_value(self.tcx, &result_args, *assumption);
+            self.register_region_assumption(assumption);
+        }
+
         let user_result: R =
             query_response.instantiate_projected(self.tcx, &result_args, |q_r| q_r.value.clone());
 
@@ -292,6 +303,18 @@ impl<'tcx> InferCtxt<'tcx> {
             }),
         );
 
+        // FIXME(higher_ranked_auto): Optimize this to instantiate all assumptions
+        // at once, rather than calling `instantiate_value` repeatedly which may
+        // create more universes.
+        output_query_region_constraints.assumptions.extend(
+            query_response
+                .value
+                .region_constraints
+                .assumptions
+                .iter()
+                .map(|&r_c| instantiate_value(self.tcx, &result_args, r_c)),
+        );
+
         let user_result: R =
             query_response.instantiate_projected(self.tcx, &result_args, |q_r| q_r.value.clone());
 
@@ -567,6 +590,7 @@ pub fn make_query_region_constraints<'tcx>(
     tcx: TyCtxt<'tcx>,
     outlives_obligations: Vec<TypeOutlivesConstraint<'tcx>>,
     region_constraints: &RegionConstraintData<'tcx>,
+    assumptions: Vec<ty::ArgOutlivesPredicate<'tcx>>,
 ) -> QueryRegionConstraints<'tcx> {
     let RegionConstraintData { constraints, verifys } = region_constraints;
 
@@ -602,5 +626,5 @@ pub fn make_query_region_constraints<'tcx>(
         }))
         .collect();
 
-    QueryRegionConstraints { outlives }
+    QueryRegionConstraints { outlives, assumptions }
 }
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index cc3ad921489..2d269e320b6 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -149,6 +149,13 @@ pub struct InferCtxtInner<'tcx> {
     /// that all type inference variables have been bound and so forth.
     region_obligations: Vec<TypeOutlivesConstraint<'tcx>>,
 
+    /// The outlives bounds that we assume must hold about placeholders that
+    /// come from instantiating the binder of coroutine-witnesses. These bounds
+    /// are deduced from the well-formedness of the witness's types, and are
+    /// necessary because of the way we anonymize the regions in a coroutine,
+    /// which may cause types to no longer be considered well-formed.
+    region_assumptions: Vec<ty::ArgOutlivesPredicate<'tcx>>,
+
     /// Caches for opaque type inference.
     opaque_type_storage: OpaqueTypeStorage<'tcx>,
 }
@@ -164,7 +171,8 @@ impl<'tcx> InferCtxtInner<'tcx> {
             int_unification_storage: Default::default(),
             float_unification_storage: Default::default(),
             region_constraint_storage: Some(Default::default()),
-            region_obligations: vec![],
+            region_obligations: Default::default(),
+            region_assumptions: Default::default(),
             opaque_type_storage: Default::default(),
         }
     }
@@ -175,6 +183,11 @@ impl<'tcx> InferCtxtInner<'tcx> {
     }
 
     #[inline]
+    pub fn region_assumptions(&self) -> &[ty::ArgOutlivesPredicate<'tcx>] {
+        &self.region_assumptions
+    }
+
+    #[inline]
     pub fn projection_cache(&mut self) -> traits::ProjectionCache<'_, 'tcx> {
         self.projection_cache.with_log(&mut self.undo_log)
     }
diff --git a/compiler/rustc_infer/src/infer/outlives/env.rs b/compiler/rustc_infer/src/infer/outlives/env.rs
index cb5a33c5c97..47b738a4079 100644
--- a/compiler/rustc_infer/src/infer/outlives/env.rs
+++ b/compiler/rustc_infer/src/infer/outlives/env.rs
@@ -1,4 +1,4 @@
-use rustc_data_structures::fx::FxIndexSet;
+use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
 use rustc_data_structures::transitive_relation::TransitiveRelationBuilder;
 use rustc_middle::{bug, ty};
 use tracing::debug;
@@ -39,6 +39,9 @@ pub struct OutlivesEnvironment<'tcx> {
     /// optimized in the future, though.
     region_bound_pairs: RegionBoundPairs<'tcx>,
     known_type_outlives: Vec<ty::PolyTypeOutlivesPredicate<'tcx>>,
+    /// Assumptions that come from the well-formedness of coroutines that we prove
+    /// auto trait bounds for during the type checking of this body.
+    higher_ranked_assumptions: FxHashSet<ty::ArgOutlivesPredicate<'tcx>>,
 }
 
 /// "Region-bound pairs" tracks outlives relations that are known to
@@ -52,6 +55,7 @@ impl<'tcx> OutlivesEnvironment<'tcx> {
         param_env: ty::ParamEnv<'tcx>,
         known_type_outlives: Vec<ty::PolyTypeOutlivesPredicate<'tcx>>,
         extra_bounds: impl IntoIterator<Item = OutlivesBound<'tcx>>,
+        higher_ranked_assumptions: FxHashSet<ty::ArgOutlivesPredicate<'tcx>>,
     ) -> Self {
         let mut region_relation = TransitiveRelationBuilder::default();
         let mut region_bound_pairs = RegionBoundPairs::default();
@@ -88,6 +92,7 @@ impl<'tcx> OutlivesEnvironment<'tcx> {
             known_type_outlives,
             free_region_map: FreeRegionMap { relation: region_relation.freeze() },
             region_bound_pairs,
+            higher_ranked_assumptions,
         }
     }
 
@@ -102,4 +107,8 @@ impl<'tcx> OutlivesEnvironment<'tcx> {
     pub fn known_type_outlives(&self) -> &[ty::PolyTypeOutlivesPredicate<'tcx>] {
         &self.known_type_outlives
     }
+
+    pub fn higher_ranked_assumptions(&self) -> &FxHashSet<ty::ArgOutlivesPredicate<'tcx>> {
+        &self.higher_ranked_assumptions
+    }
 }
diff --git a/compiler/rustc_infer/src/infer/outlives/mod.rs b/compiler/rustc_infer/src/infer/outlives/mod.rs
index 2a4544c1140..19911bfbd48 100644
--- a/compiler/rustc_infer/src/infer/outlives/mod.rs
+++ b/compiler/rustc_infer/src/infer/outlives/mod.rs
@@ -10,6 +10,7 @@ use super::region_constraints::{RegionConstraintData, UndoLog};
 use super::{InferCtxt, RegionResolutionError, SubregionOrigin};
 use crate::infer::free_regions::RegionRelations;
 use crate::infer::lexical_region_resolve;
+use crate::infer::region_constraints::Constraint;
 
 pub mod env;
 pub mod for_liveness;
@@ -54,18 +55,29 @@ impl<'tcx> InferCtxt<'tcx> {
             }
         };
 
-        let storage = {
+        let mut storage = {
             let mut inner = self.inner.borrow_mut();
             let inner = &mut *inner;
             assert!(
                 self.tainted_by_errors().is_some() || inner.region_obligations.is_empty(),
                 "region_obligations not empty: {:#?}",
-                inner.region_obligations
+                inner.region_obligations,
             );
             assert!(!UndoLogs::<UndoLog<'_>>::in_snapshot(&inner.undo_log));
             inner.region_constraint_storage.take().expect("regions already resolved")
         };
 
+        // Filter out any region-region outlives assumptions that are implied by
+        // coroutine well-formedness.
+        if self.tcx.sess.opts.unstable_opts.higher_ranked_assumptions {
+            storage.data.constraints.retain(|(constraint, _)| match *constraint {
+                Constraint::RegSubReg(r1, r2) => !outlives_env
+                    .higher_ranked_assumptions()
+                    .contains(&ty::OutlivesPredicate(r2.into(), r1)),
+                _ => true,
+            });
+        }
+
         let region_rels = &RegionRelations::new(self.tcx, outlives_env.free_region_map());
 
         let (lexical_region_resolutions, errors) =
@@ -93,6 +105,11 @@ impl<'tcx> InferCtxt<'tcx> {
             "region_obligations not empty: {:#?}",
             self.inner.borrow().region_obligations
         );
+        assert!(
+            self.inner.borrow().region_assumptions.is_empty(),
+            "region_assumptions not empty: {:#?}",
+            self.inner.borrow().region_assumptions
+        );
 
         self.inner.borrow_mut().unwrap_region_constraints().take_and_reset_data()
     }
diff --git a/compiler/rustc_infer/src/infer/outlives/obligations.rs b/compiler/rustc_infer/src/infer/outlives/obligations.rs
index 43504bd77c1..a8520c0e71d 100644
--- a/compiler/rustc_infer/src/infer/outlives/obligations.rs
+++ b/compiler/rustc_infer/src/infer/outlives/obligations.rs
@@ -84,7 +84,7 @@ use crate::traits::{ObligationCause, ObligationCauseCode};
 impl<'tcx> InferCtxt<'tcx> {
     pub fn register_outlives_constraint(
         &self,
-        ty::OutlivesPredicate(arg, r2): ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>,
+        ty::OutlivesPredicate(arg, r2): ty::ArgOutlivesPredicate<'tcx>,
         cause: &ObligationCause<'tcx>,
     ) {
         match arg.kind() {
@@ -170,6 +170,16 @@ impl<'tcx> InferCtxt<'tcx> {
         std::mem::take(&mut self.inner.borrow_mut().region_obligations)
     }
 
+    pub fn register_region_assumption(&self, assumption: ty::ArgOutlivesPredicate<'tcx>) {
+        let mut inner = self.inner.borrow_mut();
+        inner.undo_log.push(UndoLog::PushRegionAssumption);
+        inner.region_assumptions.push(assumption);
+    }
+
+    pub fn take_registered_region_assumptions(&self) -> Vec<ty::ArgOutlivesPredicate<'tcx>> {
+        std::mem::take(&mut self.inner.borrow_mut().region_assumptions)
+    }
+
     /// Process the region obligations that must be proven (during
     /// `regionck`) for the given `body_id`, given information about
     /// the region bounds in scope and so forth.
@@ -220,6 +230,14 @@ impl<'tcx> InferCtxt<'tcx> {
                 let (sup_type, sub_region) =
                     (sup_type, sub_region).fold_with(&mut OpportunisticRegionResolver::new(self));
 
+                if self.tcx.sess.opts.unstable_opts.higher_ranked_assumptions
+                    && outlives_env
+                        .higher_ranked_assumptions()
+                        .contains(&ty::OutlivesPredicate(sup_type.into(), sub_region))
+                {
+                    continue;
+                }
+
                 debug!(?sup_type, ?sub_region, ?origin);
 
                 let outlives = &mut TypeOutlives::new(
diff --git a/compiler/rustc_infer/src/infer/snapshot/undo_log.rs b/compiler/rustc_infer/src/infer/snapshot/undo_log.rs
index 34e649afedc..40e4c329446 100644
--- a/compiler/rustc_infer/src/infer/snapshot/undo_log.rs
+++ b/compiler/rustc_infer/src/infer/snapshot/undo_log.rs
@@ -28,6 +28,7 @@ pub(crate) enum UndoLog<'tcx> {
     RegionUnificationTable(sv::UndoLog<ut::Delegate<RegionVidKey<'tcx>>>),
     ProjectionCache(traits::UndoLog<'tcx>),
     PushTypeOutlivesConstraint,
+    PushRegionAssumption,
 }
 
 macro_rules! impl_from {
@@ -77,6 +78,9 @@ impl<'tcx> Rollback<UndoLog<'tcx>> for InferCtxtInner<'tcx> {
                 let popped = self.region_obligations.pop();
                 assert_matches!(popped, Some(_), "pushed region constraint but could not pop it");
             }
+            UndoLog::PushRegionAssumption => {
+                self.region_assumptions.pop();
+            }
         }
     }
 }
diff --git a/compiler/rustc_lint/messages.ftl b/compiler/rustc_lint/messages.ftl
index 8d9f2385b71..1a1cfc9fa6f 100644
--- a/compiler/rustc_lint/messages.ftl
+++ b/compiler/rustc_lint/messages.ftl
@@ -440,6 +440,7 @@ lint_invalid_asm_label_named = avoid using named labels in inline assembly
     .help = only local labels of the form `<number>:` should be used in inline asm
     .note = see the asm section of Rust By Example <https://doc.rust-lang.org/nightly/rust-by-example/unsafe/asm.html#labels> for more information
 lint_invalid_asm_label_no_span = the label may be declared in the expansion of a macro
+
 lint_invalid_crate_type_value = invalid `crate_type` value
     .suggestion = did you mean
 
@@ -508,27 +509,50 @@ lint_metavariable_still_repeating = variable `{$name}` is still repeating at thi
 
 lint_metavariable_wrong_operator = meta-variable repeats with different Kleene operator
 
-lint_mismatched_lifetime_syntaxes =
-    lifetime flowing from input to output with different syntax can be confusing
-    .label_mismatched_lifetime_syntaxes_inputs =
-        {$n_inputs ->
-            [one] this lifetime flows
-            *[other] these lifetimes flow
-        } to the output
-    .label_mismatched_lifetime_syntaxes_outputs =
-        the {$n_outputs ->
-            [one] lifetime gets
-            *[other] lifetimes get
-        } resolved as `{$lifetime_name}`
+lint_mismatched_lifetime_syntaxes_eliding_while_named =
+    eliding a lifetime that's named elsewhere is confusing
+
+lint_mismatched_lifetime_syntaxes_help =
+    the same lifetime is referred to in inconsistent ways, making the signature confusing
+
+lint_mismatched_lifetime_syntaxes_hiding_and_eliding_while_named =
+    hiding or eliding a lifetime that's named elsewhere is confusing
+
+lint_mismatched_lifetime_syntaxes_hiding_while_elided =
+    hiding a lifetime that's elided elsewhere is confusing
+
+lint_mismatched_lifetime_syntaxes_hiding_while_named =
+    hiding a lifetime that's named elsewhere is confusing
+
+lint_mismatched_lifetime_syntaxes_input_elided =
+    the lifetime is elided here
+
+lint_mismatched_lifetime_syntaxes_input_hidden =
+    the lifetime is hidden here
+
+lint_mismatched_lifetime_syntaxes_input_named =
+    the lifetime is named here
+
+lint_mismatched_lifetime_syntaxes_output_elided =
+    the same lifetime is elided here
+
+lint_mismatched_lifetime_syntaxes_output_hidden =
+    the same lifetime is hidden here
+
+lint_mismatched_lifetime_syntaxes_output_named =
+    the same lifetime is named here
 
 lint_mismatched_lifetime_syntaxes_suggestion_explicit =
-    one option is to consistently use `{$lifetime_name}`
+    consistently use `{$lifetime_name}`
 
 lint_mismatched_lifetime_syntaxes_suggestion_implicit =
-    one option is to consistently remove the lifetime
+    remove the lifetime name from references
 
 lint_mismatched_lifetime_syntaxes_suggestion_mixed =
-    one option is to remove the lifetime for references and use the anonymous lifetime for paths
+    remove the lifetime name from references and use `'_` for type paths
+
+lint_mismatched_lifetime_syntaxes_suggestion_mixed_only_paths =
+    use `'_` for type paths
 
 lint_missing_unsafe_on_extern = extern blocks should be unsafe
     .suggestion = needs `unsafe` before the extern keyword
@@ -744,6 +768,9 @@ lint_redundant_semicolons_suggestion = remove {$multiple_semicolons ->
         *[false] this semicolon
     }
 
+lint_reexport_private_dependency =
+    {$kind} `{$name}` from private dependency '{$krate}' is re-exported
+
 lint_remove_mut_from_pattern = remove `mut` from the parameter
 
 lint_removed_lint = lint `{$name}` has been removed: {$reason}
@@ -790,6 +817,9 @@ lint_supertrait_as_deref_target = this `Deref` implementation is covered by an i
     .label2 = target type is a supertrait of `{$self_ty}`
     .help = consider removing this implementation or replacing it with a method instead
 
+lint_surrogate_char_cast = surrogate values are not valid for `char`
+    .note = `0xD800..=0xDFFF` are reserved for Unicode surrogates and are not valid `char` values
+
 lint_suspicious_double_ref_clone =
     using `.clone()` on a double reference, which returns `{$ty}` instead of cloning the inner type
 
@@ -799,6 +829,9 @@ lint_suspicious_double_ref_deref =
 lint_symbol_intern_string_literal = using `Symbol::intern` on a string literal
     .help = consider adding the symbol to `compiler/rustc_span/src/symbol.rs`
 
+lint_too_large_char_cast = value exceeds maximum `char` value
+    .note = maximum valid `char` value is `0x10FFFF`
+
 lint_trailing_semi_macro = trailing semicolon in macro used in expression position
     .note1 = macro invocations at the end of a block are treated as expressions
     .note2 = to ignore the value produced by the macro, add a semicolon after the invocation of `{$name}`
diff --git a/compiler/rustc_lint/src/builtin.rs b/compiler/rustc_lint/src/builtin.rs
index 255ff56f62b..73e68834232 100644
--- a/compiler/rustc_lint/src/builtin.rs
+++ b/compiler/rustc_lint/src/builtin.rs
@@ -1519,8 +1519,9 @@ impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
                     ClauseKind::TypeOutlives(..) |
                     ClauseKind::RegionOutlives(..) => "lifetime",
 
+                    ClauseKind::UnstableFeature(_)
                     // `ConstArgHasType` is never global as `ct` is always a param
-                    ClauseKind::ConstArgHasType(..)
+                    | ClauseKind::ConstArgHasType(..)
                     // Ignore projections, as they can only be global
                     // if the trait bound is global
                     | ClauseKind::Projection(..)
@@ -1584,6 +1585,8 @@ impl EarlyLintPass for DoubleNegations {
         if let ExprKind::Unary(UnOp::Neg, ref inner) = expr.kind
             && let ExprKind::Unary(UnOp::Neg, ref inner2) = inner.kind
             && !matches!(inner2.kind, ExprKind::Unary(UnOp::Neg, _))
+            // Don't lint if this jumps macro expansion boundary (Issue #143980)
+            && expr.span.eq_ctxt(inner.span)
         {
             cx.emit_span_lint(
                 DOUBLE_NEGATIONS,
diff --git a/compiler/rustc_lint/src/early/diagnostics.rs b/compiler/rustc_lint/src/early/diagnostics.rs
index 653559009cc..f0fbf5bc81e 100644
--- a/compiler/rustc_lint/src/early/diagnostics.rs
+++ b/compiler/rustc_lint/src/early/diagnostics.rs
@@ -351,6 +351,9 @@ pub fn decorate_builtin_lint(
             }
             .decorate_lint(diag);
         }
+        BuiltinLintDiag::ReexportPrivateDependency { name, kind, krate } => {
+            lints::ReexportPrivateDependency { name, kind, krate }.decorate_lint(diag);
+        }
         BuiltinLintDiag::UnusedQualifications { removal_span } => {
             lints::UnusedQualifications { removal_span }.decorate_lint(diag);
         }
diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
index 419124d5144..f06757b3c23 100644
--- a/compiler/rustc_lint/src/lib.rs
+++ b/compiler/rustc_lint/src/lib.rs
@@ -55,7 +55,7 @@ mod invalid_from_utf8;
 mod late;
 mod let_underscore;
 mod levels;
-mod lifetime_syntax;
+pub mod lifetime_syntax;
 mod lints;
 mod macro_expr_fragment_specifier_2024_migration;
 mod map_unit_fn;
diff --git a/compiler/rustc_lint/src/lifetime_syntax.rs b/compiler/rustc_lint/src/lifetime_syntax.rs
index 5465968e984..2a5a34cdc6e 100644
--- a/compiler/rustc_lint/src/lifetime_syntax.rs
+++ b/compiler/rustc_lint/src/lifetime_syntax.rs
@@ -140,43 +140,115 @@ fn report_mismatches<'tcx>(
     }
 }
 
-fn lifetimes_use_matched_syntax(input_info: &[Info<'_>], output_info: &[Info<'_>]) -> bool {
-    // Categorize lifetimes into source/syntax buckets.
-    let mut n_hidden = 0;
-    let mut n_elided = 0;
-    let mut n_named = 0;
+#[derive(Debug, Copy, Clone, PartialEq)]
+enum LifetimeSyntaxCategory {
+    Hidden,
+    Elided,
+    Named,
+}
 
-    for info in input_info.iter().chain(output_info) {
+impl LifetimeSyntaxCategory {
+    fn new(syntax_source: (hir::LifetimeSyntax, LifetimeSource)) -> Option<Self> {
         use LifetimeSource::*;
         use hir::LifetimeSyntax::*;
 
-        let syntax_source = (info.lifetime.syntax, info.lifetime.source);
-
         match syntax_source {
-            // Ignore any other kind of lifetime.
-            (_, Other) => continue,
-
             // E.g. `&T`.
-            (Implicit, Reference | OutlivesBound | PreciseCapturing) |
+            (Implicit, Reference) |
             // E.g. `&'_ T`.
-            (ExplicitAnonymous, Reference | OutlivesBound | PreciseCapturing) |
+            (ExplicitAnonymous, Reference) |
             // E.g. `ContainsLifetime<'_>`.
-            (ExplicitAnonymous, Path { .. }) => n_elided += 1,
+            (ExplicitAnonymous, Path { .. }) |
+            // E.g. `+ '_`, `+ use<'_>`.
+            (ExplicitAnonymous, OutlivesBound | PreciseCapturing) => {
+                Some(Self::Elided)
+            }
 
             // E.g. `ContainsLifetime`.
-            (Implicit, Path { .. }) => n_hidden += 1,
+            (Implicit, Path { .. }) => {
+                Some(Self::Hidden)
+            }
 
             // E.g. `&'a T`.
-            (ExplicitBound, Reference | OutlivesBound | PreciseCapturing) |
+            (ExplicitBound, Reference) |
             // E.g. `ContainsLifetime<'a>`.
-            (ExplicitBound, Path { .. }) => n_named += 1,
-        };
+            (ExplicitBound, Path { .. }) |
+            // E.g. `+ 'a`, `+ use<'a>`.
+            (ExplicitBound, OutlivesBound | PreciseCapturing) => {
+                Some(Self::Named)
+            }
+
+            (Implicit, OutlivesBound | PreciseCapturing) |
+            (_, Other) => {
+                None
+            }
+        }
+    }
+}
+
+#[derive(Debug, Default)]
+pub struct LifetimeSyntaxCategories<T> {
+    pub hidden: T,
+    pub elided: T,
+    pub named: T,
+}
+
+impl<T> LifetimeSyntaxCategories<T> {
+    fn select(&mut self, category: LifetimeSyntaxCategory) -> &mut T {
+        use LifetimeSyntaxCategory::*;
+
+        match category {
+            Elided => &mut self.elided,
+            Hidden => &mut self.hidden,
+            Named => &mut self.named,
+        }
+    }
+}
+
+impl<T> LifetimeSyntaxCategories<Vec<T>> {
+    pub fn len(&self) -> LifetimeSyntaxCategories<usize> {
+        LifetimeSyntaxCategories {
+            hidden: self.hidden.len(),
+            elided: self.elided.len(),
+            named: self.named.len(),
+        }
+    }
+
+    pub fn flatten(&self) -> impl Iterator<Item = &T> {
+        let Self { hidden, elided, named } = self;
+        [hidden.iter(), elided.iter(), named.iter()].into_iter().flatten()
+    }
+}
+
+impl std::ops::Add for LifetimeSyntaxCategories<usize> {
+    type Output = Self;
+
+    fn add(self, rhs: Self) -> Self::Output {
+        Self {
+            hidden: self.hidden + rhs.hidden,
+            elided: self.elided + rhs.elided,
+            named: self.named + rhs.named,
+        }
+    }
+}
+
+fn lifetimes_use_matched_syntax(input_info: &[Info<'_>], output_info: &[Info<'_>]) -> bool {
+    let mut syntax_counts = LifetimeSyntaxCategories::<usize>::default();
+
+    for info in input_info.iter().chain(output_info) {
+        if let Some(category) = info.lifetime_syntax_category() {
+            *syntax_counts.select(category) += 1;
+        }
     }
 
-    let syntax_counts = (n_hidden, n_elided, n_named);
     tracing::debug!(?syntax_counts);
 
-    matches!(syntax_counts, (_, 0, 0) | (0, _, 0) | (0, 0, _))
+    matches!(
+        syntax_counts,
+        LifetimeSyntaxCategories { hidden: _, elided: 0, named: 0 }
+            | LifetimeSyntaxCategories { hidden: 0, elided: _, named: 0 }
+            | LifetimeSyntaxCategories { hidden: 0, elided: 0, named: _ }
+    )
 }
 
 fn emit_mismatch_diagnostic<'tcx>(
@@ -238,7 +310,7 @@ fn emit_mismatch_diagnostic<'tcx>(
         use LifetimeSource::*;
         use hir::LifetimeSyntax::*;
 
-        let syntax_source = (info.lifetime.syntax, info.lifetime.source);
+        let syntax_source = info.syntax_source();
 
         if let (_, Other) = syntax_source {
             // Ignore any other kind of lifetime.
@@ -259,7 +331,6 @@ fn emit_mismatch_diagnostic<'tcx>(
             // E.g. `&'_ T`.
             (ExplicitAnonymous, Reference) => {
                 suggest_change_to_implicit.push(info);
-                suggest_change_to_mixed_implicit.push(info);
                 suggest_change_to_explicit_bound.push(info);
             }
 
@@ -319,12 +390,22 @@ fn emit_mismatch_diagnostic<'tcx>(
         }
     }
 
+    let categorize = |infos: &[Info<'_>]| {
+        let mut categories = LifetimeSyntaxCategories::<Vec<_>>::default();
+        for info in infos {
+            if let Some(category) = info.lifetime_syntax_category() {
+                categories.select(category).push(info.reporting_span());
+            }
+        }
+        categories
+    };
+
+    let inputs = categorize(input_info);
+    let outputs = categorize(output_info);
+
     let make_implicit_suggestions =
         |infos: &[&Info<'_>]| infos.iter().map(|i| i.removing_span()).collect::<Vec<_>>();
 
-    let inputs = input_info.iter().map(|info| info.reporting_span()).collect();
-    let outputs = output_info.iter().map(|info| info.reporting_span()).collect();
-
     let explicit_bound_suggestion = bound_lifetime.map(|info| {
         build_mismatch_suggestion(info.lifetime_name(), &suggest_change_to_explicit_bound)
     });
@@ -399,8 +480,6 @@ fn emit_mismatch_diagnostic<'tcx>(
         ?explicit_anonymous_suggestion,
     );
 
-    let lifetime_name = bound_lifetime.map(|info| info.lifetime_name()).unwrap_or("'_").to_owned();
-
     // We can produce a number of suggestions which may overwhelm
     // the user. Instead, we order the suggestions based on Rust
     // idioms. The "best" choice is shown to the user and the
@@ -413,8 +492,8 @@ fn emit_mismatch_diagnostic<'tcx>(
 
     cx.emit_span_lint(
         MISMATCHED_LIFETIME_SYNTAXES,
-        Vec::clone(&inputs),
-        lints::MismatchedLifetimeSyntaxes { lifetime_name, inputs, outputs, suggestions },
+        inputs.flatten().copied().collect::<Vec<_>>(),
+        lints::MismatchedLifetimeSyntaxes { inputs, outputs, suggestions },
     );
 }
 
@@ -422,12 +501,12 @@ fn build_mismatch_suggestion(
     lifetime_name: &str,
     infos: &[&Info<'_>],
 ) -> lints::MismatchedLifetimeSyntaxesSuggestion {
-    let lifetime_name_sugg = lifetime_name.to_owned();
+    let lifetime_name = lifetime_name.to_owned();
 
     let suggestions = infos.iter().map(|info| info.suggestion(&lifetime_name)).collect();
 
     lints::MismatchedLifetimeSyntaxesSuggestion::Explicit {
-        lifetime_name_sugg,
+        lifetime_name,
         suggestions,
         tool_only: false,
     }
@@ -441,6 +520,14 @@ struct Info<'tcx> {
 }
 
 impl<'tcx> Info<'tcx> {
+    fn syntax_source(&self) -> (hir::LifetimeSyntax, LifetimeSource) {
+        (self.lifetime.syntax, self.lifetime.source)
+    }
+
+    fn lifetime_syntax_category(&self) -> Option<LifetimeSyntaxCategory> {
+        LifetimeSyntaxCategory::new(self.syntax_source())
+    }
+
     fn lifetime_name(&self) -> &str {
         self.lifetime.ident.as_str()
     }
diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs
index 21148833eaf..fd8d0f832aa 100644
--- a/compiler/rustc_lint/src/lints.rs
+++ b/compiler/rustc_lint/src/lints.rs
@@ -21,6 +21,7 @@ use rustc_span::{Ident, MacroRulesNormalizedIdent, Span, Symbol, sym};
 
 use crate::builtin::{InitError, ShorthandAssocTyCollector, TypeAliasBounds};
 use crate::errors::{OverruledAttributeSub, RequestedLevel};
+use crate::lifetime_syntax::LifetimeSyntaxCategories;
 use crate::{LateContext, fluent_generated as fluent};
 
 // array_into_iter.rs
@@ -1747,6 +1748,20 @@ pub(crate) struct OverflowingLiteral<'a> {
 }
 
 #[derive(LintDiagnostic)]
+#[diag(lint_surrogate_char_cast)]
+#[note]
+pub(crate) struct SurrogateCharCast {
+    pub literal: u128,
+}
+
+#[derive(LintDiagnostic)]
+#[diag(lint_too_large_char_cast)]
+#[note]
+pub(crate) struct TooLargeCharCast {
+    pub literal: u128,
+}
+
+#[derive(LintDiagnostic)]
 #[diag(lint_uses_power_alignment)]
 pub(crate) struct UsesPowerAlignment;
 
@@ -3081,6 +3096,14 @@ pub(crate) struct HiddenGlobReexports {
 }
 
 #[derive(LintDiagnostic)]
+#[diag(lint_reexport_private_dependency)]
+pub(crate) struct ReexportPrivateDependency {
+    pub name: String,
+    pub kind: String,
+    pub krate: Symbol,
+}
+
+#[derive(LintDiagnostic)]
 #[diag(lint_unnecessary_qualification)]
 pub(crate) struct UnusedQualifications {
     #[suggestion(style = "verbose", code = "", applicability = "machine-applicable")]
@@ -3194,31 +3217,60 @@ pub(crate) struct ReservedMultihash {
 
 #[derive(Debug)]
 pub(crate) struct MismatchedLifetimeSyntaxes {
-    pub lifetime_name: String,
-    pub inputs: Vec<Span>,
-    pub outputs: Vec<Span>,
+    pub inputs: LifetimeSyntaxCategories<Vec<Span>>,
+    pub outputs: LifetimeSyntaxCategories<Vec<Span>>,
 
     pub suggestions: Vec<MismatchedLifetimeSyntaxesSuggestion>,
 }
 
 impl<'a, G: EmissionGuarantee> LintDiagnostic<'a, G> for MismatchedLifetimeSyntaxes {
     fn decorate_lint<'b>(self, diag: &'b mut Diag<'a, G>) {
-        diag.primary_message(fluent::lint_mismatched_lifetime_syntaxes);
+        let counts = self.inputs.len() + self.outputs.len();
+        let message = match counts {
+            LifetimeSyntaxCategories { hidden: 0, elided: 0, named: 0 } => {
+                panic!("No lifetime mismatch detected")
+            }
 
-        diag.arg("lifetime_name", self.lifetime_name);
+            LifetimeSyntaxCategories { hidden: _, elided: _, named: 0 } => {
+                fluent::lint_mismatched_lifetime_syntaxes_hiding_while_elided
+            }
+
+            LifetimeSyntaxCategories { hidden: _, elided: 0, named: _ } => {
+                fluent::lint_mismatched_lifetime_syntaxes_hiding_while_named
+            }
+
+            LifetimeSyntaxCategories { hidden: 0, elided: _, named: _ } => {
+                fluent::lint_mismatched_lifetime_syntaxes_eliding_while_named
+            }
+
+            LifetimeSyntaxCategories { hidden: _, elided: _, named: _ } => {
+                fluent::lint_mismatched_lifetime_syntaxes_hiding_and_eliding_while_named
+            }
+        };
+        diag.primary_message(message);
 
-        diag.arg("n_inputs", self.inputs.len());
-        for input in self.inputs {
-            let a = diag.eagerly_translate(fluent::lint_label_mismatched_lifetime_syntaxes_inputs);
-            diag.span_label(input, a);
+        for s in self.inputs.hidden {
+            diag.span_label(s, fluent::lint_mismatched_lifetime_syntaxes_input_hidden);
+        }
+        for s in self.inputs.elided {
+            diag.span_label(s, fluent::lint_mismatched_lifetime_syntaxes_input_elided);
+        }
+        for s in self.inputs.named {
+            diag.span_label(s, fluent::lint_mismatched_lifetime_syntaxes_input_named);
         }
 
-        diag.arg("n_outputs", self.outputs.len());
-        for output in self.outputs {
-            let a = diag.eagerly_translate(fluent::lint_label_mismatched_lifetime_syntaxes_outputs);
-            diag.span_label(output, a);
+        for s in self.outputs.hidden {
+            diag.span_label(s, fluent::lint_mismatched_lifetime_syntaxes_output_hidden);
+        }
+        for s in self.outputs.elided {
+            diag.span_label(s, fluent::lint_mismatched_lifetime_syntaxes_output_elided);
+        }
+        for s in self.outputs.named {
+            diag.span_label(s, fluent::lint_mismatched_lifetime_syntaxes_output_named);
         }
 
+        diag.help(fluent::lint_mismatched_lifetime_syntaxes_help);
+
         let mut suggestions = self.suggestions.into_iter();
         if let Some(s) = suggestions.next() {
             diag.subdiagnostic(s);
@@ -3245,7 +3297,7 @@ pub(crate) enum MismatchedLifetimeSyntaxesSuggestion {
     },
 
     Explicit {
-        lifetime_name_sugg: String,
+        lifetime_name: String,
         suggestions: Vec<(Span, String)>,
         tool_only: bool,
     },
@@ -3285,6 +3337,12 @@ impl Subdiagnostic for MismatchedLifetimeSyntaxesSuggestion {
             }
 
             Mixed { implicit_suggestions, explicit_anonymous_suggestions, tool_only } => {
+                let message = if implicit_suggestions.is_empty() {
+                    fluent::lint_mismatched_lifetime_syntaxes_suggestion_mixed_only_paths
+                } else {
+                    fluent::lint_mismatched_lifetime_syntaxes_suggestion_mixed
+                };
+
                 let implicit_suggestions =
                     implicit_suggestions.into_iter().map(|s| (s, String::new()));
 
@@ -3292,19 +3350,19 @@ impl Subdiagnostic for MismatchedLifetimeSyntaxesSuggestion {
                     implicit_suggestions.chain(explicit_anonymous_suggestions).collect();
 
                 diag.multipart_suggestion_with_style(
-                    fluent::lint_mismatched_lifetime_syntaxes_suggestion_mixed,
+                    message,
                     suggestions,
                     Applicability::MaybeIncorrect,
                     style(tool_only),
                 );
             }
 
-            Explicit { lifetime_name_sugg, suggestions, tool_only } => {
-                diag.arg("lifetime_name_sugg", lifetime_name_sugg);
+            Explicit { lifetime_name, suggestions, tool_only } => {
+                diag.arg("lifetime_name", lifetime_name);
                 let msg = diag.eagerly_translate(
                     fluent::lint_mismatched_lifetime_syntaxes_suggestion_explicit,
                 );
-                diag.remove_arg("lifetime_name_sugg");
+                diag.remove_arg("lifetime_name");
                 diag.multipart_suggestion_with_style(
                     msg,
                     suggestions,
diff --git a/compiler/rustc_lint/src/multiple_supertrait_upcastable.rs b/compiler/rustc_lint/src/multiple_supertrait_upcastable.rs
index 3cc55eaa0f2..5513c703f1d 100644
--- a/compiler/rustc_lint/src/multiple_supertrait_upcastable.rs
+++ b/compiler/rustc_lint/src/multiple_supertrait_upcastable.rs
@@ -39,7 +39,7 @@ impl<'tcx> LateLintPass<'tcx> for MultipleSupertraitUpcastable {
         let def_id = item.owner_id.to_def_id();
         // NOTE(nbdd0121): use `dyn_compatibility_violations` instead of `is_dyn_compatible` because
         // the latter will report `where_clause_object_safety` lint.
-        if let hir::ItemKind::Trait(_, _, ident, ..) = item.kind
+        if let hir::ItemKind::Trait(_, _, _, ident, ..) = item.kind
             && cx.tcx.is_dyn_compatible(def_id)
         {
             let direct_super_traits_iter = cx
diff --git a/compiler/rustc_lint/src/types/literal.rs b/compiler/rustc_lint/src/types/literal.rs
index d44f45177bd..2bac58ba23d 100644
--- a/compiler/rustc_lint/src/types/literal.rs
+++ b/compiler/rustc_lint/src/types/literal.rs
@@ -12,7 +12,7 @@ use crate::context::LintContext;
 use crate::lints::{
     OnlyCastu8ToChar, OverflowingBinHex, OverflowingBinHexSign, OverflowingBinHexSignBitSub,
     OverflowingBinHexSub, OverflowingInt, OverflowingIntHelp, OverflowingLiteral, OverflowingUInt,
-    RangeEndpointOutOfRange, UseInclusiveRange,
+    RangeEndpointOutOfRange, SurrogateCharCast, TooLargeCharCast, UseInclusiveRange,
 };
 use crate::types::{OVERFLOWING_LITERALS, TypeLimits};
 
@@ -38,12 +38,18 @@ fn lint_overflowing_range_endpoint<'tcx>(
 
     // We only want to handle exclusive (`..`) ranges,
     // which are represented as `ExprKind::Struct`.
-    let Node::ExprField(field) = cx.tcx.parent_hir_node(hir_id) else { return false };
-    let Node::Expr(struct_expr) = cx.tcx.parent_hir_node(field.hir_id) else { return false };
+    let Node::ExprField(field) = cx.tcx.parent_hir_node(hir_id) else {
+        return false;
+    };
+    let Node::Expr(struct_expr) = cx.tcx.parent_hir_node(field.hir_id) else {
+        return false;
+    };
     if !is_range_literal(struct_expr) {
         return false;
     };
-    let ExprKind::Struct(_, [start, end], _) = &struct_expr.kind else { return false };
+    let ExprKind::Struct(_, [start, end], _) = &struct_expr.kind else {
+        return false;
+    };
 
     // We can suggest using an inclusive range
     // (`..=`) instead only if it is the `end` that is
@@ -61,7 +67,9 @@ fn lint_overflowing_range_endpoint<'tcx>(
     };
 
     let sub_sugg = if span.lo() == lit_span.lo() {
-        let Ok(start) = cx.sess().source_map().span_to_snippet(start.span) else { return false };
+        let Ok(start) = cx.sess().source_map().span_to_snippet(start.span) else {
+            return false;
+        };
         UseInclusiveRange::WithoutParen {
             sugg: struct_expr.span.shrink_to_lo().to(lit_span.shrink_to_hi()),
             start,
@@ -316,11 +324,25 @@ fn lint_uint_literal<'tcx>(
             match par_e.kind {
                 hir::ExprKind::Cast(..) => {
                     if let ty::Char = cx.typeck_results().expr_ty(par_e).kind() {
-                        cx.emit_span_lint(
-                            OVERFLOWING_LITERALS,
-                            par_e.span,
-                            OnlyCastu8ToChar { span: par_e.span, literal: lit_val },
-                        );
+                        if lit_val > 0x10FFFF {
+                            cx.emit_span_lint(
+                                OVERFLOWING_LITERALS,
+                                par_e.span,
+                                TooLargeCharCast { literal: lit_val },
+                            );
+                        } else if (0xD800..=0xDFFF).contains(&lit_val) {
+                            cx.emit_span_lint(
+                                OVERFLOWING_LITERALS,
+                                par_e.span,
+                                SurrogateCharCast { literal: lit_val },
+                            );
+                        } else {
+                            cx.emit_span_lint(
+                                OVERFLOWING_LITERALS,
+                                par_e.span,
+                                OnlyCastu8ToChar { span: par_e.span, literal: lit_val },
+                            );
+                        }
                         return;
                     }
                 }
diff --git a/compiler/rustc_lint_defs/src/lib.rs b/compiler/rustc_lint_defs/src/lib.rs
index cd402c9234f..fe068d96b74 100644
--- a/compiler/rustc_lint_defs/src/lib.rs
+++ b/compiler/rustc_lint_defs/src/lib.rs
@@ -739,6 +739,11 @@ pub enum BuiltinLintDiag {
         /// The local binding that shadows the glob reexport.
         private_item_span: Span,
     },
+    ReexportPrivateDependency {
+        name: String,
+        kind: String,
+        krate: Symbol,
+    },
     UnusedQualifications {
         /// The span of the unnecessarily-qualified path to remove.
         removal_span: Span,
diff --git a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
index 19954459cb5..57a672c45f7 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
@@ -3,7 +3,7 @@ use std::mem;
 use std::sync::Arc;
 
 use rustc_attr_data_structures::Deprecation;
-use rustc_hir::def::{CtorKind, DefKind, Res};
+use rustc_hir::def::{CtorKind, DefKind};
 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LOCAL_CRATE};
 use rustc_hir::definitions::{DefKey, DefPath, DefPathHash};
 use rustc_middle::arena::ArenaAllocatable;
@@ -510,10 +510,7 @@ pub(in crate::rmeta) fn provide(providers: &mut Providers) {
                         }
                         Entry::Vacant(entry) => {
                             entry.insert(parent);
-                            if matches!(
-                                child.res,
-                                Res::Def(DefKind::Mod | DefKind::Enum | DefKind::Trait, _)
-                            ) {
+                            if child.res.module_like_def_id().is_some() {
                                 bfs_queue.push_back(def_id);
                             }
                         }
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index b50453cb0df..5cd98038fc6 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -1131,7 +1131,7 @@ fn should_encode_mir(
                     && reachable_set.contains(&def_id)
                     && (generics.requires_monomorphization(tcx)
                         || tcx.cross_crate_inlinable(def_id)));
-            // The function has a `const` modifier or is in a `#[const_trait]`.
+            // The function has a `const` modifier or is in a `const trait`.
             let is_const_fn = tcx.is_const_fn(def_id.to_def_id())
                 || tcx.is_const_default_method(def_id.to_def_id());
             (is_const_fn, opt)
diff --git a/compiler/rustc_middle/src/hir/map.rs b/compiler/rustc_middle/src/hir/map.rs
index 84710e5e636..42a1e7377f4 100644
--- a/compiler/rustc_middle/src/hir/map.rs
+++ b/compiler/rustc_middle/src/hir/map.rs
@@ -940,7 +940,7 @@ impl<'tcx> TyCtxt<'tcx> {
             }) => until_within(*outer_span, ty.span),
             // With generics and bounds.
             Node::Item(Item {
-                kind: ItemKind::Trait(_, _, _, generics, bounds, _),
+                kind: ItemKind::Trait(_, _, _, _, generics, bounds, _),
                 span: outer_span,
                 ..
             })
diff --git a/compiler/rustc_middle/src/infer/canonical.rs b/compiler/rustc_middle/src/infer/canonical.rs
index 2bbc48b633c..4fe4c2dadee 100644
--- a/compiler/rustc_middle/src/infer/canonical.rs
+++ b/compiler/rustc_middle/src/infer/canonical.rs
@@ -81,13 +81,18 @@ pub struct QueryResponse<'tcx, R> {
 #[derive(HashStable, TypeFoldable, TypeVisitable)]
 pub struct QueryRegionConstraints<'tcx> {
     pub outlives: Vec<QueryOutlivesConstraint<'tcx>>,
+    pub assumptions: Vec<ty::ArgOutlivesPredicate<'tcx>>,
 }
 
 impl QueryRegionConstraints<'_> {
-    /// Represents an empty (trivially true) set of region
-    /// constraints.
+    /// Represents an empty (trivially true) set of region constraints.
+    ///
+    /// FIXME(higher_ranked_auto): This could still just be true if there are only assumptions?
+    /// Because I don't expect for us to get cases where an assumption from one query would
+    /// discharge a requirement from another query, which is a potential problem if we did throw
+    /// away these assumptions because there were no constraints.
     pub fn is_empty(&self) -> bool {
-        self.outlives.is_empty()
+        self.outlives.is_empty() && self.assumptions.is_empty()
     }
 }
 
@@ -130,8 +135,7 @@ impl<'tcx, R> QueryResponse<'tcx, R> {
     }
 }
 
-pub type QueryOutlivesConstraint<'tcx> =
-    (ty::OutlivesPredicate<'tcx, GenericArg<'tcx>>, ConstraintCategory<'tcx>);
+pub type QueryOutlivesConstraint<'tcx> = (ty::ArgOutlivesPredicate<'tcx>, ConstraintCategory<'tcx>);
 
 #[derive(Default)]
 pub struct CanonicalParamEnvCache<'tcx> {
diff --git a/compiler/rustc_middle/src/middle/codegen_fn_attrs.rs b/compiler/rustc_middle/src/middle/codegen_fn_attrs.rs
index 2f16d385efb..6eae3b51e29 100644
--- a/compiler/rustc_middle/src/middle/codegen_fn_attrs.rs
+++ b/compiler/rustc_middle/src/middle/codegen_fn_attrs.rs
@@ -1,3 +1,5 @@
+use std::borrow::Cow;
+
 use rustc_abi::Align;
 use rustc_ast::expand::autodiff_attrs::AutoDiffAttrs;
 use rustc_attr_data_structures::{InlineAttr, InstructionSetAttr, OptimizeAttr};
@@ -6,6 +8,26 @@ use rustc_span::Symbol;
 use rustc_target::spec::SanitizerSet;
 
 use crate::mir::mono::Linkage;
+use crate::ty::{InstanceKind, TyCtxt};
+
+impl<'tcx> TyCtxt<'tcx> {
+    pub fn codegen_instance_attrs(
+        self,
+        instance_kind: InstanceKind<'_>,
+    ) -> Cow<'tcx, CodegenFnAttrs> {
+        let mut attrs = Cow::Borrowed(self.codegen_fn_attrs(instance_kind.def_id()));
+
+        // Drop the `#[naked]` attribute on non-item `InstanceKind`s, like the shims that
+        // are generated for indirect function calls.
+        if !matches!(instance_kind, InstanceKind::Item(_)) {
+            if attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
+                attrs.to_mut().flags.remove(CodegenFnAttrFlags::NAKED);
+            }
+        }
+
+        attrs
+    }
+}
 
 #[derive(Clone, TyEncodable, TyDecodable, HashStable, Debug)]
 pub struct CodegenFnAttrs {
diff --git a/compiler/rustc_middle/src/mir/interpret/error.rs b/compiler/rustc_middle/src/mir/interpret/error.rs
index 71e0c943fbb..3e68afbfabd 100644
--- a/compiler/rustc_middle/src/mir/interpret/error.rs
+++ b/compiler/rustc_middle/src/mir/interpret/error.rs
@@ -257,7 +257,7 @@ pub enum InvalidProgramInfo<'tcx> {
 /// Details of why a pointer had to be in-bounds.
 #[derive(Debug, Copy, Clone)]
 pub enum CheckInAllocMsg {
-    /// We are access memory.
+    /// We are accessing memory.
     MemoryAccess,
     /// We are doing pointer arithmetic.
     InboundsPointerArithmetic,
diff --git a/compiler/rustc_middle/src/mir/mono.rs b/compiler/rustc_middle/src/mir/mono.rs
index 47ba850d50d..2d7ddd105bd 100644
--- a/compiler/rustc_middle/src/mir/mono.rs
+++ b/compiler/rustc_middle/src/mir/mono.rs
@@ -152,7 +152,7 @@ impl<'tcx> MonoItem<'tcx> {
         // If the function is #[naked] or contains any other attribute that requires exactly-once
         // instantiation:
         // We emit an unused_attributes lint for this case, which should be kept in sync if possible.
-        let codegen_fn_attrs = tcx.codegen_fn_attrs(instance.def_id());
+        let codegen_fn_attrs = tcx.codegen_instance_attrs(instance.def);
         if codegen_fn_attrs.contains_extern_indicator()
             || codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED)
         {
@@ -219,7 +219,7 @@ impl<'tcx> MonoItem<'tcx> {
         // functions the same as those that unconditionally get LocalCopy codegen. It's only when
         // we get here that we can at least not codegen a #[inline(never)] generic function in all
         // of our CGUs.
-        if let InlineAttr::Never = tcx.codegen_fn_attrs(instance.def_id()).inline
+        if let InlineAttr::Never = codegen_fn_attrs.inline
             && self.is_generic_fn()
         {
             return InstantiationMode::GloballyShared { may_conflict: true };
@@ -234,14 +234,13 @@ impl<'tcx> MonoItem<'tcx> {
     }
 
     pub fn explicit_linkage(&self, tcx: TyCtxt<'tcx>) -> Option<Linkage> {
-        let def_id = match *self {
-            MonoItem::Fn(ref instance) => instance.def_id(),
-            MonoItem::Static(def_id) => def_id,
+        let instance_kind = match *self {
+            MonoItem::Fn(ref instance) => instance.def,
+            MonoItem::Static(def_id) => InstanceKind::Item(def_id),
             MonoItem::GlobalAsm(..) => return None,
         };
 
-        let codegen_fn_attrs = tcx.codegen_fn_attrs(def_id);
-        codegen_fn_attrs.linkage
+        tcx.codegen_instance_attrs(instance_kind).linkage
     }
 
     /// Returns `true` if this instance is instantiable - whether it has no unsatisfied
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 935cc889574..d5c2b6de4ae 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -988,7 +988,7 @@ rustc_queries! {
     }
 
     query coroutine_hidden_types(
-        def_id: DefId
+        def_id: DefId,
     ) -> ty::EarlyBinder<'tcx, ty::Binder<'tcx, ty::CoroutineWitnessTypes<TyCtxt<'tcx>>>> {
         desc { "looking up the hidden types stored across await points in a coroutine" }
     }
@@ -1505,6 +1505,15 @@ rustc_queries! {
         separate_provide_extern
     }
 
+    /// Returns the `CodegenFnAttrs` for the item at `def_id`.
+    ///
+    /// If possible, use `tcx.codegen_instance_attrs` instead. That function takes the
+    /// instance kind into account.
+    ///
+    /// For example, the `#[naked]` attribute should be applied for `InstanceKind::Item`,
+    /// but should not be applied if the instance kind is `InstanceKind::ReifyShim`.
+    /// Using this query would include the attribute regardless of the actual instance
+    /// kind at the call site.
     query codegen_fn_attrs(def_id: DefId) -> &'tcx CodegenFnAttrs {
         desc { |tcx| "computing codegen attributes of `{}`", tcx.def_path_str(def_id) }
         arena_cache
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 98b2ce01d89..81c13e55dd8 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -137,6 +137,7 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
     type FnInputTys = &'tcx [Ty<'tcx>];
     type ParamTy = ParamTy;
     type BoundTy = ty::BoundTy;
+    type Symbol = Symbol;
 
     type PlaceholderTy = ty::PlaceholderType;
     type ErrorGuaranteed = ErrorGuaranteed;
@@ -162,6 +163,8 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
     type BoundRegion = ty::BoundRegion;
     type PlaceholderRegion = ty::PlaceholderRegion;
 
+    type RegionAssumptions = &'tcx ty::List<ty::ArgOutlivesPredicate<'tcx>>;
+
     type ParamEnv = ty::ParamEnv<'tcx>;
     type Predicate = Predicate<'tcx>;
 
@@ -713,17 +716,13 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
         self,
         defining_anchor: Self::LocalDefId,
     ) -> Self::LocalDefIds {
-        if self.next_trait_solver_globally() {
-            let coroutines_defined_by = self
-                .nested_bodies_within(defining_anchor)
-                .iter()
-                .filter(|def_id| self.is_coroutine(def_id.to_def_id()));
-            self.mk_local_def_ids_from_iter(
-                self.opaque_types_defined_by(defining_anchor).iter().chain(coroutines_defined_by),
-            )
-        } else {
-            self.opaque_types_defined_by(defining_anchor)
-        }
+        let coroutines_defined_by = self
+            .nested_bodies_within(defining_anchor)
+            .iter()
+            .filter(|def_id| self.is_coroutine(def_id.to_def_id()));
+        self.mk_local_def_ids_from_iter(
+            self.opaque_types_defined_by(defining_anchor).iter().chain(coroutines_defined_by),
+        )
     }
 }
 
@@ -833,6 +832,13 @@ impl<'tcx> rustc_type_ir::inherent::Features<TyCtxt<'tcx>> for &'tcx rustc_featu
     fn associated_const_equality(self) -> bool {
         self.associated_const_equality()
     }
+
+    fn feature_bound_holds_in_crate(self, symbol: Symbol) -> bool {
+        // We don't consider feature bounds to hold in the crate when `staged_api` feature is
+        // enabled, even if it is enabled through `#[feature]`.
+        // This is to prevent accidentally leaking unstable APIs to stable.
+        !self.staged_api() && self.enabled(symbol)
+    }
 }
 
 impl<'tcx> rustc_type_ir::inherent::Span<TyCtxt<'tcx>> for Span {
@@ -874,6 +880,7 @@ pub struct CtxtInterners<'tcx> {
     offset_of: InternedSet<'tcx, List<(VariantIdx, FieldIdx)>>,
     valtree: InternedSet<'tcx, ty::ValTreeKind<'tcx>>,
     patterns: InternedSet<'tcx, List<ty::Pattern<'tcx>>>,
+    outlives: InternedSet<'tcx, List<ty::ArgOutlivesPredicate<'tcx>>>,
 }
 
 impl<'tcx> CtxtInterners<'tcx> {
@@ -911,6 +918,7 @@ impl<'tcx> CtxtInterners<'tcx> {
             offset_of: InternedSet::with_capacity(N),
             valtree: InternedSet::with_capacity(N),
             patterns: InternedSet::with_capacity(N),
+            outlives: InternedSet::with_capacity(N),
         }
     }
 
@@ -2692,6 +2700,7 @@ slice_interners!(
     captures: intern_captures(&'tcx ty::CapturedPlace<'tcx>),
     offset_of: pub mk_offset_of((VariantIdx, FieldIdx)),
     patterns: pub mk_patterns(Pattern<'tcx>),
+    outlives: pub mk_outlives(ty::ArgOutlivesPredicate<'tcx>),
 );
 
 impl<'tcx> TyCtxt<'tcx> {
@@ -3107,6 +3116,17 @@ impl<'tcx> TyCtxt<'tcx> {
         T::collect_and_apply(iter, |xs| self.mk_bound_variable_kinds(xs))
     }
 
+    pub fn mk_outlives_from_iter<I, T>(self, iter: I) -> T::Output
+    where
+        I: Iterator<Item = T>,
+        T: CollectAndApply<
+                ty::ArgOutlivesPredicate<'tcx>,
+                &'tcx ty::List<ty::ArgOutlivesPredicate<'tcx>>,
+            >,
+    {
+        T::collect_and_apply(iter, |xs| self.mk_outlives(xs))
+    }
+
     /// Emit a lint at `span` from a lint struct (some type that implements `LintDiagnostic`,
     /// typically generated by `#[derive(LintDiagnostic)]`).
     #[track_caller]
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 6e8f1e8fdd5..a7cde2ad485 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -88,7 +88,7 @@ pub use self::opaque_types::OpaqueTypeKey;
 pub use self::parameterized::ParameterizedOverTcx;
 pub use self::pattern::{Pattern, PatternKind};
 pub use self::predicate::{
-    AliasTerm, Clause, ClauseKind, CoercePredicate, ExistentialPredicate,
+    AliasTerm, ArgOutlivesPredicate, Clause, ClauseKind, CoercePredicate, ExistentialPredicate,
     ExistentialPredicateStableCmpExt, ExistentialProjection, ExistentialTraitRef,
     HostEffectPredicate, NormalizesTo, OutlivesPredicate, PolyCoercePredicate,
     PolyExistentialPredicate, PolyExistentialProjection, PolyExistentialTraitRef,
diff --git a/compiler/rustc_middle/src/ty/predicate.rs b/compiler/rustc_middle/src/ty/predicate.rs
index bc2ac42b6b1..46f254e9d30 100644
--- a/compiler/rustc_middle/src/ty/predicate.rs
+++ b/compiler/rustc_middle/src/ty/predicate.rs
@@ -26,6 +26,7 @@ pub type SubtypePredicate<'tcx> = ir::SubtypePredicate<TyCtxt<'tcx>>;
 pub type OutlivesPredicate<'tcx, T> = ir::OutlivesPredicate<TyCtxt<'tcx>, T>;
 pub type RegionOutlivesPredicate<'tcx> = OutlivesPredicate<'tcx, ty::Region<'tcx>>;
 pub type TypeOutlivesPredicate<'tcx> = OutlivesPredicate<'tcx, Ty<'tcx>>;
+pub type ArgOutlivesPredicate<'tcx> = OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>;
 pub type PolyTraitPredicate<'tcx> = ty::Binder<'tcx, TraitPredicate<'tcx>>;
 pub type PolyRegionOutlivesPredicate<'tcx> = ty::Binder<'tcx, RegionOutlivesPredicate<'tcx>>;
 pub type PolyTypeOutlivesPredicate<'tcx> = ty::Binder<'tcx, TypeOutlivesPredicate<'tcx>>;
@@ -131,6 +132,7 @@ impl<'tcx> Predicate<'tcx> {
             | PredicateKind::Clause(ClauseKind::TypeOutlives(_))
             | PredicateKind::Clause(ClauseKind::Projection(_))
             | PredicateKind::Clause(ClauseKind::ConstArgHasType(..))
+            | PredicateKind::Clause(ClauseKind::UnstableFeature(_))
             | PredicateKind::DynCompatible(_)
             | PredicateKind::Subtype(_)
             | PredicateKind::Coerce(_)
@@ -649,6 +651,7 @@ impl<'tcx> Predicate<'tcx> {
             PredicateKind::Clause(ClauseKind::Projection(..))
             | PredicateKind::Clause(ClauseKind::HostEffect(..))
             | PredicateKind::Clause(ClauseKind::ConstArgHasType(..))
+            | PredicateKind::Clause(ClauseKind::UnstableFeature(_))
             | PredicateKind::NormalizesTo(..)
             | PredicateKind::AliasRelate(..)
             | PredicateKind::Subtype(..)
@@ -670,6 +673,7 @@ impl<'tcx> Predicate<'tcx> {
             PredicateKind::Clause(ClauseKind::Trait(..))
             | PredicateKind::Clause(ClauseKind::HostEffect(..))
             | PredicateKind::Clause(ClauseKind::ConstArgHasType(..))
+            | PredicateKind::Clause(ClauseKind::UnstableFeature(_))
             | PredicateKind::NormalizesTo(..)
             | PredicateKind::AliasRelate(..)
             | PredicateKind::Subtype(..)
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index 7c48a4b0885..2eb530f328d 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -2430,7 +2430,7 @@ impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
         }
 
         let verbose = self.should_print_verbose();
-        disambiguated_data.fmt_maybe_verbose(self, verbose)?;
+        write!(self, "{}", disambiguated_data.as_sym(verbose))?;
 
         self.empty_path = false;
 
@@ -3237,6 +3237,7 @@ define_print! {
             ty::ClauseKind::ConstEvaluatable(ct) => {
                 p!("the constant `", print(ct), "` can be evaluated")
             }
+            ty::ClauseKind::UnstableFeature(symbol) => p!("unstable feature: ", write("`{}`", symbol)),
         }
     }
 
@@ -3454,9 +3455,7 @@ fn for_each_def(tcx: TyCtxt<'_>, mut collect_fn: impl for<'b> FnMut(&'b Ident, N
                         collect_fn(&child.ident, ns, def_id);
                     }
 
-                    if matches!(defkind, DefKind::Mod | DefKind::Enum | DefKind::Trait)
-                        && seen_defs.insert(def_id)
-                    {
+                    if defkind.is_module_like() && seen_defs.insert(def_id) {
                         queue.push(def_id);
                     }
                 }
diff --git a/compiler/rustc_middle/src/ty/structural_impls.rs b/compiler/rustc_middle/src/ty/structural_impls.rs
index af9c98bd87d..ab31d943408 100644
--- a/compiler/rustc_middle/src/ty/structural_impls.rs
+++ b/compiler/rustc_middle/src/ty/structural_impls.rs
@@ -802,4 +802,5 @@ list_fold! {
     &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>> : mk_poly_existential_predicates,
     &'tcx ty::List<PlaceElem<'tcx>> : mk_place_elems,
     &'tcx ty::List<ty::Pattern<'tcx>> : mk_patterns,
+    &'tcx ty::List<ty::ArgOutlivesPredicate<'tcx>> : mk_outlives,
 }
diff --git a/compiler/rustc_middle/src/ty/trait_def.rs b/compiler/rustc_middle/src/ty/trait_def.rs
index ea25ce65f77..59e2b2a034d 100644
--- a/compiler/rustc_middle/src/ty/trait_def.rs
+++ b/compiler/rustc_middle/src/ty/trait_def.rs
@@ -20,7 +20,7 @@ pub struct TraitDef {
 
     pub safety: hir::Safety,
 
-    /// Whether this trait has been annotated with `#[const_trait]`.
+    /// Whether this trait is `const`.
     pub constness: hir::Constness,
 
     /// If `true`, then this trait had the `#[rustc_paren_sugar]`
diff --git a/compiler/rustc_mir_transform/src/coverage/query.rs b/compiler/rustc_mir_transform/src/coverage/query.rs
index ccf76dc7108..986c001de5e 100644
--- a/compiler/rustc_mir_transform/src/coverage/query.rs
+++ b/compiler/rustc_mir_transform/src/coverage/query.rs
@@ -1,3 +1,4 @@
+use rustc_attr_data_structures::{AttributeKind, CoverageStatus, find_attr};
 use rustc_index::bit_set::DenseBitSet;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::mir::coverage::{BasicCoverageBlock, CoverageIdsInfo, CoverageKind, MappingKind};
@@ -5,7 +6,6 @@ use rustc_middle::mir::{Body, Statement, StatementKind};
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_middle::util::Providers;
 use rustc_span::def_id::LocalDefId;
-use rustc_span::sym;
 use tracing::trace;
 
 use crate::coverage::counters::node_flow::make_node_counters;
@@ -58,26 +58,20 @@ fn is_eligible_for_coverage(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
 /// Query implementation for `coverage_attr_on`.
 fn coverage_attr_on(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
     // Check for annotations directly on this def.
-    if let Some(attr) = tcx.get_attr(def_id, sym::coverage) {
-        match attr.meta_item_list().as_deref() {
-            Some([item]) if item.has_name(sym::off) => return false,
-            Some([item]) if item.has_name(sym::on) => return true,
-            Some(_) | None => {
-                // Other possibilities should have been rejected by `rustc_parse::validate_attr`.
-                // Use `span_delayed_bug` to avoid an ICE in failing builds (#127880).
-                tcx.dcx().span_delayed_bug(attr.span(), "unexpected value of coverage attribute");
-            }
+    if let Some(coverage_status) =
+        find_attr!(tcx.get_all_attrs(def_id), AttributeKind::Coverage(_, status) => status)
+    {
+        *coverage_status == CoverageStatus::On
+    } else {
+        match tcx.opt_local_parent(def_id) {
+            // Check the parent def (and so on recursively) until we find an
+            // enclosing attribute or reach the crate root.
+            Some(parent) => tcx.coverage_attr_on(parent),
+            // We reached the crate root without seeing a coverage attribute, so
+            // allow coverage instrumentation by default.
+            None => true,
         }
     }
-
-    match tcx.opt_local_parent(def_id) {
-        // Check the parent def (and so on recursively) until we find an
-        // enclosing attribute or reach the crate root.
-        Some(parent) => tcx.coverage_attr_on(parent),
-        // We reached the crate root without seeing a coverage attribute, so
-        // allow coverage instrumentation by default.
-        None => true,
-    }
 }
 
 /// Query implementation for `coverage_ids_info`.
diff --git a/compiler/rustc_mir_transform/src/gvn.rs b/compiler/rustc_mir_transform/src/gvn.rs
index 6b11706d2b5..07717b7c069 100644
--- a/compiler/rustc_mir_transform/src/gvn.rs
+++ b/compiler/rustc_mir_transform/src/gvn.rs
@@ -105,7 +105,6 @@ use rustc_middle::mir::*;
 use rustc_middle::ty::layout::HasTypingEnv;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::DUMMY_SP;
-use rustc_span::def_id::DefId;
 use smallvec::SmallVec;
 use tracing::{debug, instrument, trace};
 
@@ -130,7 +129,7 @@ impl<'tcx> crate::MirPass<'tcx> for GVN {
         let mut state = VnState::new(tcx, body, typing_env, &ssa, dominators, &body.local_decls);
 
         for local in body.args_iter().filter(|&local| ssa.is_ssa(local)) {
-            let opaque = state.new_opaque();
+            let opaque = state.new_opaque(body.local_decls[local].ty);
             state.assign(local, opaque);
         }
 
@@ -155,22 +154,6 @@ newtype_index! {
     struct VnIndex {}
 }
 
-/// Computing the aggregate's type can be quite slow, so we only keep the minimal amount of
-/// information to reconstruct it when needed.
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
-enum AggregateTy<'tcx> {
-    /// Invariant: this must not be used for an empty array.
-    Array,
-    Tuple,
-    Def(DefId, ty::GenericArgsRef<'tcx>),
-    RawPtr {
-        /// Needed for cast propagation.
-        data_pointer_ty: Ty<'tcx>,
-        /// The data pointer can be anything thin, so doesn't determine the output.
-        output_pointer_ty: Ty<'tcx>,
-    },
-}
-
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
 enum AddressKind {
     Ref(BorrowKind),
@@ -193,7 +176,14 @@ enum Value<'tcx> {
     },
     /// An aggregate value, either tuple/closure/struct/enum.
     /// This does not contain unions, as we cannot reason with the value.
-    Aggregate(AggregateTy<'tcx>, VariantIdx, Vec<VnIndex>),
+    Aggregate(VariantIdx, Vec<VnIndex>),
+    /// A raw pointer aggregate built from a thin pointer and metadata.
+    RawPtr {
+        /// Thin pointer component. This is field 0 in MIR.
+        pointer: VnIndex,
+        /// Metadata component. This is field 1 in MIR.
+        metadata: VnIndex,
+    },
     /// This corresponds to a `[value; count]` expression.
     Repeat(VnIndex, ty::Const<'tcx>),
     /// The address of a place.
@@ -206,7 +196,7 @@ enum Value<'tcx> {
 
     // Extractions.
     /// This is the *value* obtained by projecting another value.
-    Projection(VnIndex, ProjectionElem<VnIndex, Ty<'tcx>>),
+    Projection(VnIndex, ProjectionElem<VnIndex, ()>),
     /// Discriminant of the given value.
     Discriminant(VnIndex),
     /// Length of an array or slice.
@@ -219,8 +209,6 @@ enum Value<'tcx> {
     Cast {
         kind: CastKind,
         value: VnIndex,
-        from: Ty<'tcx>,
-        to: Ty<'tcx>,
     },
 }
 
@@ -228,12 +216,13 @@ struct VnState<'body, 'tcx> {
     tcx: TyCtxt<'tcx>,
     ecx: InterpCx<'tcx, DummyMachine>,
     local_decls: &'body LocalDecls<'tcx>,
+    is_coroutine: bool,
     /// Value stored in each local.
     locals: IndexVec<Local, Option<VnIndex>>,
     /// Locals that are assigned that value.
     // This vector does not hold all the values of `VnIndex` that we create.
     rev_locals: IndexVec<VnIndex, SmallVec<[Local; 1]>>,
-    values: FxIndexSet<Value<'tcx>>,
+    values: FxIndexSet<(Value<'tcx>, Ty<'tcx>)>,
     /// Values evaluated as constants if possible.
     evaluated: IndexVec<VnIndex, Option<OpTy<'tcx>>>,
     /// Counter to generate different values.
@@ -265,6 +254,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             tcx,
             ecx: InterpCx::new(tcx, DUMMY_SP, typing_env, DummyMachine),
             local_decls,
+            is_coroutine: body.coroutine.is_some(),
             locals: IndexVec::from_elem(None, local_decls),
             rev_locals: IndexVec::with_capacity(num_values),
             values: FxIndexSet::with_capacity_and_hasher(num_values, Default::default()),
@@ -282,8 +272,8 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
     }
 
     #[instrument(level = "trace", skip(self), ret)]
-    fn insert(&mut self, value: Value<'tcx>) -> VnIndex {
-        let (index, new) = self.values.insert_full(value);
+    fn insert(&mut self, ty: Ty<'tcx>, value: Value<'tcx>) -> VnIndex {
+        let (index, new) = self.values.insert_full((value, ty));
         let index = VnIndex::from_usize(index);
         if new {
             // Grow `evaluated` and `rev_locals` here to amortize the allocations.
@@ -305,20 +295,33 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
     /// Create a new `Value` for which we have no information at all, except that it is distinct
     /// from all the others.
     #[instrument(level = "trace", skip(self), ret)]
-    fn new_opaque(&mut self) -> VnIndex {
+    fn new_opaque(&mut self, ty: Ty<'tcx>) -> VnIndex {
         let value = Value::Opaque(self.next_opaque());
-        self.insert(value)
+        self.insert(ty, value)
     }
 
     /// Create a new `Value::Address` distinct from all the others.
     #[instrument(level = "trace", skip(self), ret)]
     fn new_pointer(&mut self, place: Place<'tcx>, kind: AddressKind) -> VnIndex {
+        let pty = place.ty(self.local_decls, self.tcx).ty;
+        let ty = match kind {
+            AddressKind::Ref(bk) => {
+                Ty::new_ref(self.tcx, self.tcx.lifetimes.re_erased, pty, bk.to_mutbl_lossy())
+            }
+            AddressKind::Address(mutbl) => Ty::new_ptr(self.tcx, pty, mutbl.to_mutbl_lossy()),
+        };
         let value = Value::Address { place, kind, provenance: self.next_opaque() };
-        self.insert(value)
+        self.insert(ty, value)
     }
 
+    #[inline]
     fn get(&self, index: VnIndex) -> &Value<'tcx> {
-        self.values.get_index(index.as_usize()).unwrap()
+        &self.values.get_index(index.as_usize()).unwrap().0
+    }
+
+    #[inline]
+    fn ty(&self, index: VnIndex) -> Ty<'tcx> {
+        self.values.get_index(index.as_usize()).unwrap().1
     }
 
     /// Record that `local` is assigned `value`. `local` must be SSA.
@@ -341,29 +344,29 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             debug_assert_ne!(disambiguator, 0);
             disambiguator
         };
-        self.insert(Value::Constant { value, disambiguator })
+        self.insert(value.ty(), Value::Constant { value, disambiguator })
     }
 
     fn insert_bool(&mut self, flag: bool) -> VnIndex {
         // Booleans are deterministic.
         let value = Const::from_bool(self.tcx, flag);
         debug_assert!(value.is_deterministic());
-        self.insert(Value::Constant { value, disambiguator: 0 })
+        self.insert(self.tcx.types.bool, Value::Constant { value, disambiguator: 0 })
     }
 
-    fn insert_scalar(&mut self, scalar: Scalar, ty: Ty<'tcx>) -> VnIndex {
+    fn insert_scalar(&mut self, ty: Ty<'tcx>, scalar: Scalar) -> VnIndex {
         // Scalars are deterministic.
         let value = Const::from_scalar(self.tcx, scalar, ty);
         debug_assert!(value.is_deterministic());
-        self.insert(Value::Constant { value, disambiguator: 0 })
+        self.insert(ty, Value::Constant { value, disambiguator: 0 })
     }
 
-    fn insert_tuple(&mut self, values: Vec<VnIndex>) -> VnIndex {
-        self.insert(Value::Aggregate(AggregateTy::Tuple, VariantIdx::ZERO, values))
+    fn insert_tuple(&mut self, ty: Ty<'tcx>, values: Vec<VnIndex>) -> VnIndex {
+        self.insert(ty, Value::Aggregate(VariantIdx::ZERO, values))
     }
 
-    fn insert_deref(&mut self, value: VnIndex) -> VnIndex {
-        let value = self.insert(Value::Projection(value, ProjectionElem::Deref));
+    fn insert_deref(&mut self, ty: Ty<'tcx>, value: VnIndex) -> VnIndex {
+        let value = self.insert(ty, Value::Projection(value, ProjectionElem::Deref));
         self.derefs.push(value);
         value
     }
@@ -371,14 +374,23 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
     fn invalidate_derefs(&mut self) {
         for deref in std::mem::take(&mut self.derefs) {
             let opaque = self.next_opaque();
-            *self.values.get_index_mut2(deref.index()).unwrap() = Value::Opaque(opaque);
+            self.values.get_index_mut2(deref.index()).unwrap().0 = Value::Opaque(opaque);
         }
     }
 
     #[instrument(level = "trace", skip(self), ret)]
     fn eval_to_const(&mut self, value: VnIndex) -> Option<OpTy<'tcx>> {
         use Value::*;
+        let ty = self.ty(value);
+        // Avoid computing layouts inside a coroutine, as that can cause cycles.
+        let ty = if !self.is_coroutine || ty.is_scalar() {
+            self.ecx.layout_of(ty).ok()?
+        } else {
+            return None;
+        };
         let op = match *self.get(value) {
+            _ if ty.is_zst() => ImmTy::uninit(ty).into(),
+
             Opaque(_) => return None,
             // Do not bother evaluating repeat expressions. This would uselessly consume memory.
             Repeat(..) => return None,
@@ -386,42 +398,14 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             Constant { ref value, disambiguator: _ } => {
                 self.ecx.eval_mir_constant(value, DUMMY_SP, None).discard_err()?
             }
-            Aggregate(kind, variant, ref fields) => {
+            Aggregate(variant, ref fields) => {
                 let fields = fields
                     .iter()
                     .map(|&f| self.evaluated[f].as_ref())
                     .collect::<Option<Vec<_>>>()?;
-                let ty = match kind {
-                    AggregateTy::Array => {
-                        assert!(fields.len() > 0);
-                        Ty::new_array(self.tcx, fields[0].layout.ty, fields.len() as u64)
-                    }
-                    AggregateTy::Tuple => {
-                        Ty::new_tup_from_iter(self.tcx, fields.iter().map(|f| f.layout.ty))
-                    }
-                    AggregateTy::Def(def_id, args) => {
-                        self.tcx.type_of(def_id).instantiate(self.tcx, args)
-                    }
-                    AggregateTy::RawPtr { output_pointer_ty, .. } => output_pointer_ty,
-                };
-                let variant = if ty.is_enum() { Some(variant) } else { None };
-                let ty = self.ecx.layout_of(ty).ok()?;
-                if ty.is_zst() {
-                    ImmTy::uninit(ty).into()
-                } else if matches!(kind, AggregateTy::RawPtr { .. }) {
-                    // Pointers don't have fields, so don't `project_field` them.
-                    let data = self.ecx.read_pointer(fields[0]).discard_err()?;
-                    let meta = if fields[1].layout.is_zst() {
-                        MemPlaceMeta::None
-                    } else {
-                        MemPlaceMeta::Meta(self.ecx.read_scalar(fields[1]).discard_err()?)
-                    };
-                    let ptr_imm = Immediate::new_pointer_with_meta(data, meta, &self.ecx);
-                    ImmTy::from_immediate(ptr_imm, ty).into()
-                } else if matches!(
-                    ty.backend_repr,
-                    BackendRepr::Scalar(..) | BackendRepr::ScalarPair(..)
-                ) {
+                let variant = if ty.ty.is_enum() { Some(variant) } else { None };
+                if matches!(ty.backend_repr, BackendRepr::Scalar(..) | BackendRepr::ScalarPair(..))
+                {
                     let dest = self.ecx.allocate(ty, MemoryKind::Stack).discard_err()?;
                     let variant_dest = if let Some(variant) = variant {
                         self.ecx.project_downcast(&dest, variant).discard_err()?
@@ -446,32 +430,46 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                     return None;
                 }
             }
+            RawPtr { pointer, metadata } => {
+                let pointer = self.evaluated[pointer].as_ref()?;
+                let metadata = self.evaluated[metadata].as_ref()?;
+
+                // Pointers don't have fields, so don't `project_field` them.
+                let data = self.ecx.read_pointer(pointer).discard_err()?;
+                let meta = if metadata.layout.is_zst() {
+                    MemPlaceMeta::None
+                } else {
+                    MemPlaceMeta::Meta(self.ecx.read_scalar(metadata).discard_err()?)
+                };
+                let ptr_imm = Immediate::new_pointer_with_meta(data, meta, &self.ecx);
+                ImmTy::from_immediate(ptr_imm, ty).into()
+            }
 
             Projection(base, elem) => {
-                let value = self.evaluated[base].as_ref()?;
+                let base = self.evaluated[base].as_ref()?;
                 let elem = match elem {
                     ProjectionElem::Deref => ProjectionElem::Deref,
                     ProjectionElem::Downcast(name, read_variant) => {
                         ProjectionElem::Downcast(name, read_variant)
                     }
-                    ProjectionElem::Field(f, ty) => ProjectionElem::Field(f, ty),
+                    ProjectionElem::Field(f, ()) => ProjectionElem::Field(f, ty.ty),
                     ProjectionElem::ConstantIndex { offset, min_length, from_end } => {
                         ProjectionElem::ConstantIndex { offset, min_length, from_end }
                     }
                     ProjectionElem::Subslice { from, to, from_end } => {
                         ProjectionElem::Subslice { from, to, from_end }
                     }
-                    ProjectionElem::OpaqueCast(ty) => ProjectionElem::OpaqueCast(ty),
-                    ProjectionElem::Subtype(ty) => ProjectionElem::Subtype(ty),
-                    ProjectionElem::UnwrapUnsafeBinder(ty) => {
-                        ProjectionElem::UnwrapUnsafeBinder(ty)
+                    ProjectionElem::OpaqueCast(()) => ProjectionElem::OpaqueCast(ty.ty),
+                    ProjectionElem::Subtype(()) => ProjectionElem::Subtype(ty.ty),
+                    ProjectionElem::UnwrapUnsafeBinder(()) => {
+                        ProjectionElem::UnwrapUnsafeBinder(ty.ty)
                     }
                     // This should have been replaced by a `ConstantIndex` earlier.
                     ProjectionElem::Index(_) => return None,
                 };
-                self.ecx.project(value, elem).discard_err()?
+                self.ecx.project(base, elem).discard_err()?
             }
-            Address { place, kind, provenance: _ } => {
+            Address { place, kind: _, provenance: _ } => {
                 if !place.is_indirect_first_projection() {
                     return None;
                 }
@@ -487,19 +485,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                     mplace = self.ecx.project(&mplace, proj).discard_err()?;
                 }
                 let pointer = mplace.to_ref(&self.ecx);
-                let ty = match kind {
-                    AddressKind::Ref(bk) => Ty::new_ref(
-                        self.tcx,
-                        self.tcx.lifetimes.re_erased,
-                        mplace.layout.ty,
-                        bk.to_mutbl_lossy(),
-                    ),
-                    AddressKind::Address(mutbl) => {
-                        Ty::new_ptr(self.tcx, mplace.layout.ty, mutbl.to_mutbl_lossy())
-                    }
-                };
-                let layout = self.ecx.layout_of(ty).ok()?;
-                ImmTy::from_immediate(pointer, layout).into()
+                ImmTy::from_immediate(pointer, ty).into()
             }
 
             Discriminant(base) => {
@@ -511,32 +497,28 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             }
             Len(slice) => {
                 let slice = self.evaluated[slice].as_ref()?;
-                let usize_layout = self.ecx.layout_of(self.tcx.types.usize).unwrap();
                 let len = slice.len(&self.ecx).discard_err()?;
-                let imm = ImmTy::from_uint(len, usize_layout);
-                imm.into()
+                ImmTy::from_uint(len, ty).into()
             }
-            NullaryOp(null_op, ty) => {
-                let layout = self.ecx.layout_of(ty).ok()?;
+            NullaryOp(null_op, arg_ty) => {
+                let arg_layout = self.ecx.layout_of(arg_ty).ok()?;
                 if let NullOp::SizeOf | NullOp::AlignOf = null_op
-                    && layout.is_unsized()
+                    && arg_layout.is_unsized()
                 {
                     return None;
                 }
                 let val = match null_op {
-                    NullOp::SizeOf => layout.size.bytes(),
-                    NullOp::AlignOf => layout.align.abi.bytes(),
+                    NullOp::SizeOf => arg_layout.size.bytes(),
+                    NullOp::AlignOf => arg_layout.align.abi.bytes(),
                     NullOp::OffsetOf(fields) => self
                         .ecx
                         .tcx
-                        .offset_of_subfield(self.typing_env(), layout, fields.iter())
+                        .offset_of_subfield(self.typing_env(), arg_layout, fields.iter())
                         .bytes(),
                     NullOp::UbChecks => return None,
                     NullOp::ContractChecks => return None,
                 };
-                let usize_layout = self.ecx.layout_of(self.tcx.types.usize).unwrap();
-                let imm = ImmTy::from_uint(val, usize_layout);
-                imm.into()
+                ImmTy::from_uint(val, ty).into()
             }
             UnaryOp(un_op, operand) => {
                 let operand = self.evaluated[operand].as_ref()?;
@@ -552,30 +534,27 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                 let val = self.ecx.binary_op(bin_op, &lhs, &rhs).discard_err()?;
                 val.into()
             }
-            Cast { kind, value, from: _, to } => match kind {
+            Cast { kind, value } => match kind {
                 CastKind::IntToInt | CastKind::IntToFloat => {
                     let value = self.evaluated[value].as_ref()?;
                     let value = self.ecx.read_immediate(value).discard_err()?;
-                    let to = self.ecx.layout_of(to).ok()?;
-                    let res = self.ecx.int_to_int_or_float(&value, to).discard_err()?;
+                    let res = self.ecx.int_to_int_or_float(&value, ty).discard_err()?;
                     res.into()
                 }
                 CastKind::FloatToFloat | CastKind::FloatToInt => {
                     let value = self.evaluated[value].as_ref()?;
                     let value = self.ecx.read_immediate(value).discard_err()?;
-                    let to = self.ecx.layout_of(to).ok()?;
-                    let res = self.ecx.float_to_float_or_int(&value, to).discard_err()?;
+                    let res = self.ecx.float_to_float_or_int(&value, ty).discard_err()?;
                     res.into()
                 }
                 CastKind::Transmute => {
                     let value = self.evaluated[value].as_ref()?;
-                    let to = self.ecx.layout_of(to).ok()?;
                     // `offset` for immediates generally only supports projections that match the
                     // type of the immediate. However, as a HACK, we exploit that it can also do
                     // limited transmutes: it only works between types with the same layout, and
                     // cannot transmute pointers to integers.
                     if value.as_mplace_or_imm().is_right() {
-                        let can_transmute = match (value.layout.backend_repr, to.backend_repr) {
+                        let can_transmute = match (value.layout.backend_repr, ty.backend_repr) {
                             (BackendRepr::Scalar(s1), BackendRepr::Scalar(s2)) => {
                                 s1.size(&self.ecx) == s2.size(&self.ecx)
                                     && !matches!(s1.primitive(), Primitive::Pointer(..))
@@ -595,13 +574,12 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                             return None;
                         }
                     }
-                    value.offset(Size::ZERO, to, &self.ecx).discard_err()?
+                    value.offset(Size::ZERO, ty, &self.ecx).discard_err()?
                 }
                 CastKind::PointerCoercion(ty::adjustment::PointerCoercion::Unsize, _) => {
                     let src = self.evaluated[value].as_ref()?;
-                    let to = self.ecx.layout_of(to).ok()?;
-                    let dest = self.ecx.allocate(to, MemoryKind::Stack).discard_err()?;
-                    self.ecx.unsize_into(src, to, &dest.clone().into()).discard_err()?;
+                    let dest = self.ecx.allocate(ty, MemoryKind::Stack).discard_err()?;
+                    self.ecx.unsize_into(src, ty, &dest.clone().into()).discard_err()?;
                     self.ecx
                         .alloc_mark_immutable(dest.ptr().provenance.unwrap().alloc_id())
                         .discard_err()?;
@@ -610,15 +588,13 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                 CastKind::FnPtrToPtr | CastKind::PtrToPtr => {
                     let src = self.evaluated[value].as_ref()?;
                     let src = self.ecx.read_immediate(src).discard_err()?;
-                    let to = self.ecx.layout_of(to).ok()?;
-                    let ret = self.ecx.ptr_to_ptr(&src, to).discard_err()?;
+                    let ret = self.ecx.ptr_to_ptr(&src, ty).discard_err()?;
                     ret.into()
                 }
                 CastKind::PointerCoercion(ty::adjustment::PointerCoercion::UnsafeFnPointer, _) => {
                     let src = self.evaluated[value].as_ref()?;
                     let src = self.ecx.read_immediate(src).discard_err()?;
-                    let to = self.ecx.layout_of(to).ok()?;
-                    ImmTy::from_immediate(*src, to).into()
+                    ImmTy::from_immediate(*src, ty).into()
                 }
                 _ => return None,
             },
@@ -628,31 +604,30 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
 
     fn project(
         &mut self,
-        place: PlaceRef<'tcx>,
+        place_ty: PlaceTy<'tcx>,
         value: VnIndex,
         proj: PlaceElem<'tcx>,
         from_non_ssa_index: &mut bool,
-    ) -> Option<VnIndex> {
+    ) -> Option<(PlaceTy<'tcx>, VnIndex)> {
+        let projection_ty = place_ty.projection_ty(self.tcx, proj);
         let proj = match proj {
             ProjectionElem::Deref => {
-                let ty = place.ty(self.local_decls, self.tcx).ty;
-                if let Some(Mutability::Not) = ty.ref_mutability()
-                    && let Some(pointee_ty) = ty.builtin_deref(true)
-                    && pointee_ty.is_freeze(self.tcx, self.typing_env())
+                if let Some(Mutability::Not) = place_ty.ty.ref_mutability()
+                    && projection_ty.ty.is_freeze(self.tcx, self.typing_env())
                 {
                     // An immutable borrow `_x` always points to the same value for the
                     // lifetime of the borrow, so we can merge all instances of `*_x`.
-                    return Some(self.insert_deref(value));
+                    return Some((projection_ty, self.insert_deref(projection_ty.ty, value)));
                 } else {
                     return None;
                 }
             }
             ProjectionElem::Downcast(name, index) => ProjectionElem::Downcast(name, index),
-            ProjectionElem::Field(f, ty) => {
-                if let Value::Aggregate(_, _, fields) = self.get(value) {
-                    return Some(fields[f.as_usize()]);
+            ProjectionElem::Field(f, _) => {
+                if let Value::Aggregate(_, fields) = self.get(value) {
+                    return Some((projection_ty, fields[f.as_usize()]));
                 } else if let Value::Projection(outer_value, ProjectionElem::Downcast(_, read_variant)) = self.get(value)
-                    && let Value::Aggregate(_, written_variant, fields) = self.get(*outer_value)
+                    && let Value::Aggregate(written_variant, fields) = self.get(*outer_value)
                     // This pass is not aware of control-flow, so we do not know whether the
                     // replacement we are doing is actually reachable. We could be in any arm of
                     // ```
@@ -670,14 +645,14 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                     // a downcast to an inactive variant.
                     && written_variant == read_variant
                 {
-                    return Some(fields[f.as_usize()]);
+                    return Some((projection_ty, fields[f.as_usize()]));
                 }
-                ProjectionElem::Field(f, ty)
+                ProjectionElem::Field(f, ())
             }
             ProjectionElem::Index(idx) => {
                 if let Value::Repeat(inner, _) = self.get(value) {
                     *from_non_ssa_index |= self.locals[idx].is_none();
-                    return Some(*inner);
+                    return Some((projection_ty, *inner));
                 }
                 let idx = self.locals[idx]?;
                 ProjectionElem::Index(idx)
@@ -685,15 +660,16 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             ProjectionElem::ConstantIndex { offset, min_length, from_end } => {
                 match self.get(value) {
                     Value::Repeat(inner, _) => {
-                        return Some(*inner);
+                        return Some((projection_ty, *inner));
                     }
-                    Value::Aggregate(AggregateTy::Array, _, operands) => {
+                    Value::Aggregate(_, operands) => {
                         let offset = if from_end {
                             operands.len() - offset as usize
                         } else {
                             offset as usize
                         };
-                        return operands.get(offset).copied();
+                        let value = operands.get(offset).copied()?;
+                        return Some((projection_ty, value));
                     }
                     _ => {}
                 };
@@ -702,12 +678,13 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             ProjectionElem::Subslice { from, to, from_end } => {
                 ProjectionElem::Subslice { from, to, from_end }
             }
-            ProjectionElem::OpaqueCast(ty) => ProjectionElem::OpaqueCast(ty),
-            ProjectionElem::Subtype(ty) => ProjectionElem::Subtype(ty),
-            ProjectionElem::UnwrapUnsafeBinder(ty) => ProjectionElem::UnwrapUnsafeBinder(ty),
+            ProjectionElem::OpaqueCast(_) => ProjectionElem::OpaqueCast(()),
+            ProjectionElem::Subtype(_) => ProjectionElem::Subtype(()),
+            ProjectionElem::UnwrapUnsafeBinder(_) => ProjectionElem::UnwrapUnsafeBinder(()),
         };
 
-        Some(self.insert(Value::Projection(value, proj)))
+        let value = self.insert(projection_ty.ty, Value::Projection(value, proj));
+        Some((projection_ty, value))
     }
 
     /// Simplify the projection chain if we know better.
@@ -769,6 +746,8 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
 
         // Invariant: `value` holds the value up-to the `index`th projection excluded.
         let mut value = self.locals[place.local]?;
+        // Invariant: `value` has type `place_ty`, with optional downcast variant if needed.
+        let mut place_ty = PlaceTy::from_ty(self.local_decls[place.local].ty);
         let mut from_non_ssa_index = false;
         for (index, proj) in place.projection.iter().enumerate() {
             if let Value::Projection(pointer, ProjectionElem::Deref) = *self.get(value)
@@ -786,8 +765,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                 place_ref = PlaceRef { local, projection: &place.projection[index..] };
             }
 
-            let base = PlaceRef { local: place.local, projection: &place.projection[..index] };
-            value = self.project(base, value, proj, &mut from_non_ssa_index)?;
+            (place_ty, value) = self.project(place_ty, value, proj, &mut from_non_ssa_index)?;
         }
 
         if let Value::Projection(pointer, ProjectionElem::Deref) = *self.get(value)
@@ -864,14 +842,9 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                 self.simplify_place_projection(place, location);
                 return Some(self.new_pointer(*place, AddressKind::Address(mutbl)));
             }
-            Rvalue::WrapUnsafeBinder(ref mut op, ty) => {
+            Rvalue::WrapUnsafeBinder(ref mut op, _) => {
                 let value = self.simplify_operand(op, location)?;
-                Value::Cast {
-                    kind: CastKind::Transmute,
-                    value,
-                    from: op.ty(self.local_decls, self.tcx),
-                    to: ty,
-                }
+                Value::Cast { kind: CastKind::Transmute, value }
             }
 
             // Operations.
@@ -896,18 +869,17 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             // Unsupported values.
             Rvalue::ThreadLocalRef(..) | Rvalue::ShallowInitBox(..) => return None,
         };
-        debug!(?value);
-        Some(self.insert(value))
+        let ty = rvalue.ty(self.local_decls, self.tcx);
+        Some(self.insert(ty, value))
     }
 
     fn simplify_discriminant(&mut self, place: VnIndex) -> Option<VnIndex> {
-        if let Value::Aggregate(enum_ty, variant, _) = *self.get(place)
-            && let AggregateTy::Def(enum_did, enum_args) = enum_ty
-            && let DefKind::Enum = self.tcx.def_kind(enum_did)
+        let enum_ty = self.ty(place);
+        if enum_ty.is_enum()
+            && let Value::Aggregate(variant, _) = *self.get(place)
         {
-            let enum_ty = self.tcx.type_of(enum_did).instantiate(self.tcx, enum_args);
             let discr = self.ecx.discriminant_for_variant(enum_ty, variant).discard_err()?;
-            return Some(self.insert_scalar(discr.to_scalar(), discr.layout.ty));
+            return Some(self.insert_scalar(discr.layout.ty, discr.to_scalar()));
         }
 
         None
@@ -915,12 +887,13 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
 
     fn try_as_place_elem(
         &mut self,
-        proj: ProjectionElem<VnIndex, Ty<'tcx>>,
+        ty: Ty<'tcx>,
+        proj: ProjectionElem<VnIndex, ()>,
         loc: Location,
     ) -> Option<PlaceElem<'tcx>> {
         Some(match proj {
             ProjectionElem::Deref => ProjectionElem::Deref,
-            ProjectionElem::Field(idx, ty) => ProjectionElem::Field(idx, ty),
+            ProjectionElem::Field(idx, ()) => ProjectionElem::Field(idx, ty),
             ProjectionElem::Index(idx) => {
                 let Some(local) = self.try_as_local(idx, loc) else {
                     return None;
@@ -935,9 +908,9 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                 ProjectionElem::Subslice { from, to, from_end }
             }
             ProjectionElem::Downcast(symbol, idx) => ProjectionElem::Downcast(symbol, idx),
-            ProjectionElem::OpaqueCast(idx) => ProjectionElem::OpaqueCast(idx),
-            ProjectionElem::Subtype(idx) => ProjectionElem::Subtype(idx),
-            ProjectionElem::UnwrapUnsafeBinder(ty) => ProjectionElem::UnwrapUnsafeBinder(ty),
+            ProjectionElem::OpaqueCast(()) => ProjectionElem::OpaqueCast(ty),
+            ProjectionElem::Subtype(()) => ProjectionElem::Subtype(ty),
+            ProjectionElem::UnwrapUnsafeBinder(()) => ProjectionElem::UnwrapUnsafeBinder(ty),
         })
     }
 
@@ -983,8 +956,8 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
 
         // Allow introducing places with non-constant offsets, as those are still better than
         // reconstructing an aggregate.
-        if let Some(place) = self.try_as_place(copy_from_local_value, location, true)
-            && rvalue.ty(self.local_decls, self.tcx) == place.ty(self.local_decls, self.tcx).ty
+        if self.ty(copy_from_local_value) == rvalue.ty(self.local_decls, self.tcx)
+            && let Some(place) = self.try_as_place(copy_from_local_value, location, true)
         {
             // Avoid creating `*a = copy (*b)`, as they might be aliases resulting in overlapping assignments.
             // FIXME: This also avoids any kind of projection, not just derefs. We can add allowed projections.
@@ -1004,9 +977,11 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
         rvalue: &mut Rvalue<'tcx>,
         location: Location,
     ) -> Option<VnIndex> {
+        let tcx = self.tcx;
+        let ty = rvalue.ty(self.local_decls, tcx);
+
         let Rvalue::Aggregate(box ref kind, ref mut field_ops) = *rvalue else { bug!() };
 
-        let tcx = self.tcx;
         if field_ops.is_empty() {
             let is_zst = match *kind {
                 AggregateKind::Array(..)
@@ -1021,87 +996,72 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             };
 
             if is_zst {
-                let ty = rvalue.ty(self.local_decls, tcx);
                 return Some(self.insert_constant(Const::zero_sized(ty)));
             }
         }
 
-        let (mut ty, variant_index) = match *kind {
-            AggregateKind::Array(..) => {
-                assert!(!field_ops.is_empty());
-                (AggregateTy::Array, FIRST_VARIANT)
-            }
-            AggregateKind::Tuple => {
+        let fields: Vec<_> = field_ops
+            .iter_mut()
+            .map(|op| {
+                self.simplify_operand(op, location)
+                    .unwrap_or_else(|| self.new_opaque(op.ty(self.local_decls, self.tcx)))
+            })
+            .collect();
+
+        let variant_index = match *kind {
+            AggregateKind::Array(..) | AggregateKind::Tuple => {
                 assert!(!field_ops.is_empty());
-                (AggregateTy::Tuple, FIRST_VARIANT)
-            }
-            AggregateKind::Closure(did, args)
-            | AggregateKind::CoroutineClosure(did, args)
-            | AggregateKind::Coroutine(did, args) => (AggregateTy::Def(did, args), FIRST_VARIANT),
-            AggregateKind::Adt(did, variant_index, args, _, None) => {
-                (AggregateTy::Def(did, args), variant_index)
+                FIRST_VARIANT
             }
+            AggregateKind::Closure(..)
+            | AggregateKind::CoroutineClosure(..)
+            | AggregateKind::Coroutine(..) => FIRST_VARIANT,
+            AggregateKind::Adt(_, variant_index, _, _, None) => variant_index,
             // Do not track unions.
             AggregateKind::Adt(_, _, _, _, Some(_)) => return None,
-            AggregateKind::RawPtr(pointee_ty, mtbl) => {
+            AggregateKind::RawPtr(..) => {
                 assert_eq!(field_ops.len(), 2);
-                let data_pointer_ty = field_ops[FieldIdx::ZERO].ty(self.local_decls, self.tcx);
-                let output_pointer_ty = Ty::new_ptr(self.tcx, pointee_ty, mtbl);
-                (AggregateTy::RawPtr { data_pointer_ty, output_pointer_ty }, FIRST_VARIANT)
-            }
-        };
-
-        let mut fields: Vec<_> = field_ops
-            .iter_mut()
-            .map(|op| self.simplify_operand(op, location).unwrap_or_else(|| self.new_opaque()))
-            .collect();
-
-        if let AggregateTy::RawPtr { data_pointer_ty, output_pointer_ty } = &mut ty {
-            let mut was_updated = false;
+                let [mut pointer, metadata] = fields.try_into().unwrap();
+
+                // Any thin pointer of matching mutability is fine as the data pointer.
+                let mut was_updated = false;
+                while let Value::Cast { kind: CastKind::PtrToPtr, value: cast_value } =
+                    self.get(pointer)
+                    && let ty::RawPtr(from_pointee_ty, from_mtbl) = self.ty(*cast_value).kind()
+                    && let ty::RawPtr(_, output_mtbl) = ty.kind()
+                    && from_mtbl == output_mtbl
+                    && from_pointee_ty.is_sized(self.tcx, self.typing_env())
+                {
+                    pointer = *cast_value;
+                    was_updated = true;
+                }
 
-            // Any thin pointer of matching mutability is fine as the data pointer.
-            while let Value::Cast {
-                kind: CastKind::PtrToPtr,
-                value: cast_value,
-                from: cast_from,
-                to: _,
-            } = self.get(fields[0])
-                && let ty::RawPtr(from_pointee_ty, from_mtbl) = cast_from.kind()
-                && let ty::RawPtr(_, output_mtbl) = output_pointer_ty.kind()
-                && from_mtbl == output_mtbl
-                && from_pointee_ty.is_sized(self.tcx, self.typing_env())
-            {
-                fields[0] = *cast_value;
-                *data_pointer_ty = *cast_from;
-                was_updated = true;
-            }
+                if was_updated && let Some(op) = self.try_as_operand(pointer, location) {
+                    field_ops[FieldIdx::ZERO] = op;
+                }
 
-            if was_updated && let Some(op) = self.try_as_operand(fields[0], location) {
-                field_ops[FieldIdx::ZERO] = op;
+                return Some(self.insert(ty, Value::RawPtr { pointer, metadata }));
             }
-        }
+        };
 
-        if let AggregateTy::Array = ty
-            && fields.len() > 4
-        {
+        if ty.is_array() && fields.len() > 4 {
             let first = fields[0];
             if fields.iter().all(|&v| v == first) {
                 let len = ty::Const::from_target_usize(self.tcx, fields.len().try_into().unwrap());
                 if let Some(op) = self.try_as_operand(first, location) {
                     *rvalue = Rvalue::Repeat(op, len);
                 }
-                return Some(self.insert(Value::Repeat(first, len)));
+                return Some(self.insert(ty, Value::Repeat(first, len)));
             }
         }
 
-        if let AggregateTy::Def(_, _) = ty
-            && let Some(value) =
-                self.simplify_aggregate_to_copy(lhs, rvalue, location, &fields, variant_index)
+        if let Some(value) =
+            self.simplify_aggregate_to_copy(lhs, rvalue, location, &fields, variant_index)
         {
             return Some(value);
         }
 
-        Some(self.insert(Value::Aggregate(ty, variant_index, fields)))
+        Some(self.insert(ty, Value::Aggregate(variant_index, fields)))
     }
 
     #[instrument(level = "trace", skip(self), ret)]
@@ -1112,6 +1072,8 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
         location: Location,
     ) -> Option<VnIndex> {
         let mut arg_index = self.simplify_operand(arg_op, location)?;
+        let arg_ty = self.ty(arg_index);
+        let ret_ty = op.ty(self.tcx, arg_ty);
 
         // PtrMetadata doesn't care about *const vs *mut vs & vs &mut,
         // so start by removing those distinctions so we can update the `Operand`
@@ -1127,8 +1089,8 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                     // we can't always know exactly what the metadata are.
                     // To allow things like `*mut (?A, ?T)` <-> `*mut (?B, ?T)`,
                     // it's fine to get a projection as the type.
-                    Value::Cast { kind: CastKind::PtrToPtr, value: inner, from, to }
-                        if self.pointers_have_same_metadata(*from, *to) =>
+                    Value::Cast { kind: CastKind::PtrToPtr, value: inner }
+                        if self.pointers_have_same_metadata(self.ty(*inner), arg_ty) =>
                     {
                         arg_index = *inner;
                         was_updated = true;
@@ -1165,26 +1127,22 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             (UnOp::Not, Value::BinaryOp(BinOp::Ne, lhs, rhs)) => {
                 Value::BinaryOp(BinOp::Eq, *lhs, *rhs)
             }
-            (UnOp::PtrMetadata, Value::Aggregate(AggregateTy::RawPtr { .. }, _, fields)) => {
-                return Some(fields[1]);
-            }
+            (UnOp::PtrMetadata, Value::RawPtr { metadata, .. }) => return Some(*metadata),
             // We have an unsizing cast, which assigns the length to wide pointer metadata.
             (
                 UnOp::PtrMetadata,
                 Value::Cast {
                     kind: CastKind::PointerCoercion(ty::adjustment::PointerCoercion::Unsize, _),
-                    from,
-                    to,
-                    ..
+                    value: inner,
                 },
-            ) if let ty::Slice(..) = to.builtin_deref(true).unwrap().kind()
-                && let ty::Array(_, len) = from.builtin_deref(true).unwrap().kind() =>
+            ) if let ty::Slice(..) = arg_ty.builtin_deref(true).unwrap().kind()
+                && let ty::Array(_, len) = self.ty(*inner).builtin_deref(true).unwrap().kind() =>
             {
                 return Some(self.insert_constant(Const::Ty(self.tcx.types.usize, *len)));
             }
             _ => Value::UnaryOp(op, arg_index),
         };
-        Some(self.insert(value))
+        Some(self.insert(ret_ty, value))
     }
 
     #[instrument(level = "trace", skip(self), ret)]
@@ -1197,25 +1155,23 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
     ) -> Option<VnIndex> {
         let lhs = self.simplify_operand(lhs_operand, location);
         let rhs = self.simplify_operand(rhs_operand, location);
+
         // Only short-circuit options after we called `simplify_operand`
         // on both operands for side effect.
         let mut lhs = lhs?;
         let mut rhs = rhs?;
 
-        let lhs_ty = lhs_operand.ty(self.local_decls, self.tcx);
+        let lhs_ty = self.ty(lhs);
 
         // If we're comparing pointers, remove `PtrToPtr` casts if the from
         // types of both casts and the metadata all match.
         if let BinOp::Eq | BinOp::Ne | BinOp::Lt | BinOp::Le | BinOp::Gt | BinOp::Ge = op
             && lhs_ty.is_any_ptr()
-            && let Value::Cast {
-                kind: CastKind::PtrToPtr, value: lhs_value, from: lhs_from, ..
-            } = self.get(lhs)
-            && let Value::Cast {
-                kind: CastKind::PtrToPtr, value: rhs_value, from: rhs_from, ..
-            } = self.get(rhs)
-            && lhs_from == rhs_from
-            && self.pointers_have_same_metadata(*lhs_from, lhs_ty)
+            && let Value::Cast { kind: CastKind::PtrToPtr, value: lhs_value } = self.get(lhs)
+            && let Value::Cast { kind: CastKind::PtrToPtr, value: rhs_value } = self.get(rhs)
+            && let lhs_from = self.ty(*lhs_value)
+            && lhs_from == self.ty(*rhs_value)
+            && self.pointers_have_same_metadata(lhs_from, lhs_ty)
         {
             lhs = *lhs_value;
             rhs = *rhs_value;
@@ -1230,8 +1186,9 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
         if let Some(value) = self.simplify_binary_inner(op, lhs_ty, lhs, rhs) {
             return Some(value);
         }
+        let ty = op.ty(self.tcx, lhs_ty, self.ty(rhs));
         let value = Value::BinaryOp(op, lhs, rhs);
-        Some(self.insert(value))
+        Some(self.insert(ty, value))
     }
 
     fn simplify_binary_inner(
@@ -1323,19 +1280,19 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                 | BinOp::Shr,
                 Left(0),
                 _,
-            ) => self.insert_scalar(Scalar::from_uint(0u128, layout.size), lhs_ty),
+            ) => self.insert_scalar(lhs_ty, Scalar::from_uint(0u128, layout.size)),
             // Attempt to simplify `x | ALL_ONES` to `ALL_ONES`.
             (BinOp::BitOr, _, Left(ones)) | (BinOp::BitOr, Left(ones), _)
                 if ones == layout.size.truncate(u128::MAX)
                     || (layout.ty.is_bool() && ones == 1) =>
             {
-                self.insert_scalar(Scalar::from_uint(ones, layout.size), lhs_ty)
+                self.insert_scalar(lhs_ty, Scalar::from_uint(ones, layout.size))
             }
             // Sub/Xor with itself.
             (BinOp::Sub | BinOp::SubWithOverflow | BinOp::SubUnchecked | BinOp::BitXor, a, b)
                 if a == b =>
             {
-                self.insert_scalar(Scalar::from_uint(0u128, layout.size), lhs_ty)
+                self.insert_scalar(lhs_ty, Scalar::from_uint(0u128, layout.size))
             }
             // Comparison:
             // - if both operands can be computed as bits, just compare the bits;
@@ -1349,8 +1306,9 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
         };
 
         if op.is_overflowing() {
+            let ty = Ty::new_tup(self.tcx, &[self.ty(result), self.tcx.types.bool]);
             let false_val = self.insert_bool(false);
-            Some(self.insert_tuple(vec![result, false_val]))
+            Some(self.insert_tuple(ty, vec![result, false_val]))
         } else {
             Some(result)
         }
@@ -1366,9 +1324,9 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
         use CastKind::*;
         use rustc_middle::ty::adjustment::PointerCoercion::*;
 
-        let mut from = initial_operand.ty(self.local_decls, self.tcx);
         let mut kind = *initial_kind;
         let mut value = self.simplify_operand(initial_operand, location)?;
+        let mut from = self.ty(value);
         if from == to {
             return Some(value);
         }
@@ -1376,7 +1334,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
         if let CastKind::PointerCoercion(ReifyFnPointer | ClosureFnPointer(_), _) = kind {
             // Each reification of a generic fn may get a different pointer.
             // Do not try to merge them.
-            return Some(self.new_opaque());
+            return Some(self.new_opaque(to));
         }
 
         let mut was_ever_updated = false;
@@ -1399,23 +1357,22 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             // If a cast just casts away the metadata again, then we can get it by
             // casting the original thin pointer passed to `from_raw_parts`
             if let PtrToPtr = kind
-                && let Value::Aggregate(AggregateTy::RawPtr { data_pointer_ty, .. }, _, fields) =
-                    self.get(value)
+                && let Value::RawPtr { pointer, .. } = self.get(value)
                 && let ty::RawPtr(to_pointee, _) = to.kind()
                 && to_pointee.is_sized(self.tcx, self.typing_env())
             {
-                from = *data_pointer_ty;
-                value = fields[0];
+                from = self.ty(*pointer);
+                value = *pointer;
                 was_updated_this_iteration = true;
-                if *data_pointer_ty == to {
-                    return Some(fields[0]);
+                if from == to {
+                    return Some(*pointer);
                 }
             }
 
             // Aggregate-then-Transmute can just transmute the original field value,
             // so long as the bytes of a value from only from a single field.
             if let Transmute = kind
-                && let Value::Aggregate(_aggregate_ty, variant_idx, field_values) = self.get(value)
+                && let Value::Aggregate(variant_idx, field_values) = self.get(value)
                 && let Some((field_idx, field_ty)) =
                     self.value_is_all_in_one_field(from, *variant_idx)
             {
@@ -1428,13 +1385,8 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             }
 
             // Various cast-then-cast cases can be simplified.
-            if let Value::Cast {
-                kind: inner_kind,
-                value: inner_value,
-                from: inner_from,
-                to: inner_to,
-            } = *self.get(value)
-            {
+            if let Value::Cast { kind: inner_kind, value: inner_value } = *self.get(value) {
+                let inner_from = self.ty(inner_value);
                 let new_kind = match (inner_kind, kind) {
                     // Even if there's a narrowing cast in here that's fine, because
                     // things like `*mut [i32] -> *mut i32 -> *const i32` and
@@ -1443,9 +1395,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                     // PtrToPtr-then-Transmute is fine so long as the pointer cast is identity:
                     // `*const T -> *mut T -> NonNull<T>` is fine, but we need to check for narrowing
                     // to skip things like `*const [i32] -> *const i32 -> NonNull<T>`.
-                    (PtrToPtr, Transmute)
-                        if self.pointers_have_same_metadata(inner_from, inner_to) =>
-                    {
+                    (PtrToPtr, Transmute) if self.pointers_have_same_metadata(inner_from, from) => {
                         Some(Transmute)
                     }
                     // Similarly, for Transmute-then-PtrToPtr. Note that we need to check different
@@ -1456,7 +1406,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                     // If would be legal to always do this, but we don't want to hide information
                     // from the backend that it'd otherwise be able to use for optimizations.
                     (Transmute, Transmute)
-                        if !self.type_may_have_niche_of_interest_to_backend(inner_to) =>
+                        if !self.type_may_have_niche_of_interest_to_backend(from) =>
                     {
                         Some(Transmute)
                     }
@@ -1485,7 +1435,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             *initial_kind = kind;
         }
 
-        Some(self.insert(Value::Cast { kind, value, from, to }))
+        Some(self.insert(to, Value::Cast { kind, value }))
     }
 
     fn simplify_len(&mut self, place: &mut Place<'tcx>, location: Location) -> Option<VnIndex> {
@@ -1507,18 +1457,18 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
         }
 
         // We have an unsizing cast, which assigns the length to wide pointer metadata.
-        if let Value::Cast { kind, from, to, .. } = self.get(inner)
+        if let Value::Cast { kind, value: from } = self.get(inner)
             && let CastKind::PointerCoercion(ty::adjustment::PointerCoercion::Unsize, _) = kind
-            && let Some(from) = from.builtin_deref(true)
+            && let Some(from) = self.ty(*from).builtin_deref(true)
             && let ty::Array(_, len) = from.kind()
-            && let Some(to) = to.builtin_deref(true)
+            && let Some(to) = self.ty(inner).builtin_deref(true)
             && let ty::Slice(..) = to.kind()
         {
             return Some(self.insert_constant(Const::Ty(self.tcx.types.usize, *len)));
         }
 
         // Fallback: a symbolic `Len`.
-        Some(self.insert(Value::Len(inner)))
+        Some(self.insert(self.tcx.types.usize, Value::Len(inner)))
     }
 
     fn pointers_have_same_metadata(&self, left_ptr_ty: Ty<'tcx>, right_ptr_ty: Ty<'tcx>) -> bool {
@@ -1727,7 +1677,7 @@ impl<'tcx> VnState<'_, 'tcx> {
                 return Some(place);
             } else if let Value::Projection(pointer, proj) = *self.get(index)
                 && (allow_complex_projection || proj.is_stable_offset())
-                && let Some(proj) = self.try_as_place_elem(proj, loc)
+                && let Some(proj) = self.try_as_place_elem(self.ty(index), proj, loc)
             {
                 projection.push(proj);
                 index = pointer;
@@ -1755,7 +1705,7 @@ impl<'tcx> MutVisitor<'tcx> for VnState<'_, 'tcx> {
 
     fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
         self.simplify_place_projection(place, location);
-        if context.is_mutating_use() && !place.projection.is_empty() {
+        if context.is_mutating_use() && place.is_indirect() {
             // Non-local mutation maybe invalidate deref.
             self.invalidate_derefs();
         }
@@ -1767,36 +1717,42 @@ impl<'tcx> MutVisitor<'tcx> for VnState<'_, 'tcx> {
         self.super_operand(operand, location);
     }
 
-    fn visit_statement(&mut self, stmt: &mut Statement<'tcx>, location: Location) {
-        if let StatementKind::Assign(box (ref mut lhs, ref mut rvalue)) = stmt.kind {
-            self.simplify_place_projection(lhs, location);
-
-            let value = self.simplify_rvalue(lhs, rvalue, location);
-            let value = if let Some(local) = lhs.as_local()
-                && self.ssa.is_ssa(local)
-                // FIXME(#112651) `rvalue` may have a subtype to `local`. We can only mark
-                // `local` as reusable if we have an exact type match.
-                && self.local_decls[local].ty == rvalue.ty(self.local_decls, self.tcx)
+    fn visit_assign(
+        &mut self,
+        lhs: &mut Place<'tcx>,
+        rvalue: &mut Rvalue<'tcx>,
+        location: Location,
+    ) {
+        self.simplify_place_projection(lhs, location);
+
+        let value = self.simplify_rvalue(lhs, rvalue, location);
+        if let Some(value) = value {
+            if let Some(const_) = self.try_as_constant(value) {
+                *rvalue = Rvalue::Use(Operand::Constant(Box::new(const_)));
+            } else if let Some(place) = self.try_as_place(value, location, false)
+                && *rvalue != Rvalue::Use(Operand::Move(place))
+                && *rvalue != Rvalue::Use(Operand::Copy(place))
             {
-                let value = value.unwrap_or_else(|| self.new_opaque());
-                self.assign(local, value);
-                Some(value)
-            } else {
-                value
-            };
-            if let Some(value) = value {
-                if let Some(const_) = self.try_as_constant(value) {
-                    *rvalue = Rvalue::Use(Operand::Constant(Box::new(const_)));
-                } else if let Some(place) = self.try_as_place(value, location, false)
-                    && *rvalue != Rvalue::Use(Operand::Move(place))
-                    && *rvalue != Rvalue::Use(Operand::Copy(place))
-                {
-                    *rvalue = Rvalue::Use(Operand::Copy(place));
-                    self.reused_locals.insert(place.local);
-                }
+                *rvalue = Rvalue::Use(Operand::Copy(place));
+                self.reused_locals.insert(place.local);
             }
         }
-        self.super_statement(stmt, location);
+
+        if lhs.is_indirect() {
+            // Non-local mutation maybe invalidate deref.
+            self.invalidate_derefs();
+        }
+
+        if let Some(local) = lhs.as_local()
+            && self.ssa.is_ssa(local)
+            && let rvalue_ty = rvalue.ty(self.local_decls, self.tcx)
+            // FIXME(#112651) `rvalue` may have a subtype to `local`. We can only mark
+            // `local` as reusable if we have an exact type match.
+            && self.local_decls[local].ty == rvalue_ty
+        {
+            let value = value.unwrap_or_else(|| self.new_opaque(rvalue_ty));
+            self.assign(local, value);
+        }
     }
 
     fn visit_terminator(&mut self, terminator: &mut Terminator<'tcx>, location: Location) {
@@ -1804,7 +1760,8 @@ impl<'tcx> MutVisitor<'tcx> for VnState<'_, 'tcx> {
             if let Some(local) = destination.as_local()
                 && self.ssa.is_ssa(local)
             {
-                let opaque = self.new_opaque();
+                let ty = self.local_decls[local].ty;
+                let opaque = self.new_opaque(ty);
                 self.assign(local, opaque);
             }
         }
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 b42587618b5..ce9b794d40d 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
@@ -22,6 +22,7 @@ use crate::delegate::SolverDelegate;
 use crate::placeholder::BoundVarReplacer;
 use crate::solve::inspect::{self, ProofTreeBuilder};
 use crate::solve::search_graph::SearchGraph;
+use crate::solve::ty::may_use_unstable_feature;
 use crate::solve::{
     CanonicalInput, Certainty, FIXPOINT_STEP_LIMIT, Goal, GoalEvaluation, GoalEvaluationKind,
     GoalSource, GoalStalledOn, HasChanged, NestedNormalizationGoals, NoSolution, QueryInput,
@@ -550,6 +551,9 @@ where
                 ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, ty)) => {
                     self.compute_const_arg_has_type_goal(Goal { param_env, predicate: (ct, ty) })
                 }
+                ty::PredicateKind::Clause(ty::ClauseKind::UnstableFeature(symbol)) => {
+                    self.compute_unstable_feature_goal(param_env, symbol)
+                }
                 ty::PredicateKind::Subtype(predicate) => {
                     self.compute_subtype_goal(Goal { param_env, predicate })
                 }
@@ -1177,6 +1181,14 @@ where
     ) -> T {
         BoundVarReplacer::replace_bound_vars(&**self.delegate, universes, t).0
     }
+
+    pub(super) fn may_use_unstable_feature(
+        &self,
+        param_env: I::ParamEnv,
+        symbol: I::Symbol,
+    ) -> bool {
+        may_use_unstable_feature(&**self.delegate, param_env, symbol)
+    }
 }
 
 /// Eagerly replace aliases with inference variables, emitting `AliasRelate`
diff --git a/compiler/rustc_next_trait_solver/src/solve/mod.rs b/compiler/rustc_next_trait_solver/src/solve/mod.rs
index e68ea22c7a2..5ea3f0d1061 100644
--- a/compiler/rustc_next_trait_solver/src/solve/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/mod.rs
@@ -148,6 +148,20 @@ where
         }
     }
 
+    fn compute_unstable_feature_goal(
+        &mut self,
+        param_env: <I as Interner>::ParamEnv,
+        symbol: <I as Interner>::Symbol,
+    ) -> QueryResult<I> {
+        if self.may_use_unstable_feature(param_env, symbol) {
+            self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+        } else {
+            self.evaluate_added_goals_and_make_canonical_response(Certainty::Maybe(
+                MaybeCause::Ambiguity,
+            ))
+        }
+    }
+
     #[instrument(level = "trace", skip(self))]
     fn compute_const_evaluatable_goal(
         &mut self,
diff --git a/compiler/rustc_parse/Cargo.toml b/compiler/rustc_parse/Cargo.toml
index c4a0ae2ce9d..a92012f8329 100644
--- a/compiler/rustc_parse/Cargo.toml
+++ b/compiler/rustc_parse/Cargo.toml
@@ -6,7 +6,7 @@ edition = "2024"
 [dependencies]
 # tidy-alphabetical-start
 bitflags = "2.4.1"
-rustc-literal-escaper = "0.0.4"
+rustc-literal-escaper = "0.0.5"
 rustc_ast = { path = "../rustc_ast" }
 rustc_ast_pretty = { path = "../rustc_ast_pretty" }
 rustc_data_structures = { path = "../rustc_data_structures" }
diff --git a/compiler/rustc_parse/messages.ftl b/compiler/rustc_parse/messages.ftl
index af9f8735549..859118a4ade 100644
--- a/compiler/rustc_parse/messages.ftl
+++ b/compiler/rustc_parse/messages.ftl
@@ -855,6 +855,7 @@ parse_trailing_vert_not_allowed = a trailing `|` is not allowed in an or-pattern
     .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_transpose_dyn_or_impl = `for<...>` expected after `{$kw}`, not before
diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index 7f1b0991f0c..4aaaba01fae 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/compiler/rustc_parse/src/errors.rs
@@ -1962,6 +1962,14 @@ pub(crate) struct TraitAliasCannotBeAuto {
 }
 
 #[derive(Diagnostic)]
+#[diag(parse_trait_alias_cannot_be_const)]
+pub(crate) struct TraitAliasCannotBeConst {
+    #[primary_span]
+    #[label(parse_trait_alias_cannot_be_const)]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
 #[diag(parse_trait_alias_cannot_be_unsafe)]
 pub(crate) struct TraitAliasCannotBeUnsafe {
     #[primary_span]
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index d6cc98d505c..b767b0fcf99 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -244,6 +244,9 @@ impl<'a> Parser<'a> {
             self.bump(); // `static`
             let mutability = self.parse_mutability();
             self.parse_static_item(safety, mutability)?
+        } else if self.check_keyword(exp!(Trait)) || self.check_trait_front_matter() {
+            // TRAIT ITEM
+            self.parse_item_trait(attrs, lo)?
         } else if let Const::Yes(const_span) = self.parse_constness(Case::Sensitive) {
             // CONST ITEM
             if self.token.is_keyword(kw::Impl) {
@@ -262,9 +265,6 @@ impl<'a> Parser<'a> {
                     define_opaque: None,
                 }))
             }
-        } else if self.check_keyword(exp!(Trait)) || self.check_auto_or_unsafe_trait_item() {
-            // TRAIT ITEM
-            self.parse_item_trait(attrs, lo)?
         } else if self.check_keyword(exp!(Impl))
             || self.check_keyword(exp!(Unsafe)) && self.is_keyword_ahead(1, &[kw::Impl])
         {
@@ -373,7 +373,7 @@ impl<'a> Parser<'a> {
     pub(super) fn is_path_start_item(&mut self) -> bool {
         self.is_kw_followed_by_ident(kw::Union) // no: `union::b`, yes: `union U { .. }`
         || self.is_reuse_path_item()
-        || self.check_auto_or_unsafe_trait_item() // no: `auto::b`, yes: `auto trait X { .. }`
+        || self.check_trait_front_matter() // no: `auto::b`, yes: `auto trait X { .. }`
         || self.is_async_fn() // no(2015): `async::b`, yes: `async fn`
         || matches!(self.is_macro_rules_item(), IsMacroRulesItem::Yes{..}) // no: `macro_rules::b`, yes: `macro_rules! mac`
     }
@@ -872,16 +872,19 @@ impl<'a> Parser<'a> {
         }
     }
 
-    /// Is this an `(unsafe auto? | auto) trait` item?
-    fn check_auto_or_unsafe_trait_item(&mut self) -> bool {
+    /// Is this an `(const unsafe? auto?| unsafe auto? | auto) trait` item?
+    fn check_trait_front_matter(&mut self) -> bool {
         // auto trait
         self.check_keyword(exp!(Auto)) && self.is_keyword_ahead(1, &[kw::Trait])
             // unsafe auto trait
             || self.check_keyword(exp!(Unsafe)) && self.is_keyword_ahead(1, &[kw::Trait, kw::Auto])
+            || self.check_keyword(exp!(Const)) && ((self.is_keyword_ahead(1, &[kw::Trait]) || self.is_keyword_ahead(1, &[kw::Auto]) && self.is_keyword_ahead(2, &[kw::Trait]))
+                || self.is_keyword_ahead(1, &[kw::Unsafe]) && self.is_keyword_ahead(2, &[kw::Trait, kw::Auto]))
     }
 
     /// Parses `unsafe? auto? trait Foo { ... }` or `trait Foo = Bar;`.
     fn parse_item_trait(&mut self, attrs: &mut AttrVec, lo: Span) -> PResult<'a, ItemKind> {
+        let constness = self.parse_constness(Case::Sensitive);
         let safety = self.parse_safety(Case::Sensitive);
         // Parse optional `auto` prefix.
         let is_auto = if self.eat_keyword(exp!(Auto)) {
@@ -913,6 +916,9 @@ impl<'a> Parser<'a> {
             self.expect_semi()?;
 
             let whole_span = lo.to(self.prev_token.span);
+            if let Const::Yes(_) = constness {
+                self.dcx().emit_err(errors::TraitAliasCannotBeConst { span: whole_span });
+            }
             if is_auto == IsAuto::Yes {
                 self.dcx().emit_err(errors::TraitAliasCannotBeAuto { span: whole_span });
             }
@@ -927,7 +933,15 @@ impl<'a> Parser<'a> {
             // It's a normal trait.
             generics.where_clause = self.parse_where_clause()?;
             let items = self.parse_item_list(attrs, |p| p.parse_trait_item(ForceCollect::No))?;
-            Ok(ItemKind::Trait(Box::new(Trait { is_auto, safety, ident, generics, bounds, items })))
+            Ok(ItemKind::Trait(Box::new(Trait {
+                constness,
+                is_auto,
+                safety,
+                ident,
+                generics,
+                bounds,
+                items,
+            })))
         }
     }
 
diff --git a/compiler/rustc_parse/src/validate_attr.rs b/compiler/rustc_parse/src/validate_attr.rs
index 783d79d978a..a476f0db37e 100644
--- a/compiler/rustc_parse/src/validate_attr.rs
+++ b/compiler/rustc_parse/src/validate_attr.rs
@@ -318,6 +318,7 @@ pub fn check_builtin_meta_item(
                 | sym::rustc_layout_scalar_valid_range_end
                 | sym::no_implicit_prelude
                 | sym::automatically_derived
+                | sym::coverage
         ) {
             return;
         }
diff --git a/compiler/rustc_parse_format/Cargo.toml b/compiler/rustc_parse_format/Cargo.toml
index 0666ae29409..d178fcda1fb 100644
--- a/compiler/rustc_parse_format/Cargo.toml
+++ b/compiler/rustc_parse_format/Cargo.toml
@@ -5,7 +5,7 @@ edition = "2024"
 
 [dependencies]
 # tidy-alphabetical-start
-rustc-literal-escaper = "0.0.4"
+rustc-literal-escaper = "0.0.5"
 rustc_lexer = { path = "../rustc_lexer" }
 # tidy-alphabetical-end
 
diff --git a/compiler/rustc_passes/messages.ftl b/compiler/rustc_passes/messages.ftl
index 3418d997b83..d1b856ca415 100644
--- a/compiler/rustc_passes/messages.ftl
+++ b/compiler/rustc_passes/messages.ftl
@@ -667,6 +667,10 @@ 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 = {$on_crate ->
@@ -780,7 +784,7 @@ passes_unused_capture_maybe_capture_ref = value captured by `{$name}` is never r
     .help = did you mean to capture by reference instead?
 
 passes_unused_default_method_body_const_note =
-    `default_method_body_is_const` has been replaced with `#[const_trait]` on traits
+    `default_method_body_is_const` has been replaced with `const` on traits
 
 passes_unused_duplicate =
     unused attribute
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index 2009ddc1e2d..2766b14bb8d 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};
+use rustc_ast::{AttrStyle, LitKind, MetaItemInner, MetaItemKind, ast, join_path_syms};
 use rustc_attr_data_structures::{AttributeKind, InlineAttr, ReprAttr, find_attr};
 use rustc_attr_parsing::{AttributeParser, Late};
 use rustc_data_structures::fx::FxHashMap;
@@ -247,6 +247,9 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 &Attribute::Parsed(AttributeKind::FfiPure(attr_span)) => {
                     self.check_ffi_pure(attr_span, attrs, target)
                 }
+                Attribute::Parsed(AttributeKind::UnstableFeatureBound(syms)) => {
+                    self.check_unstable_feature_bound(syms.first().unwrap().1, span, target)
+                }
                 Attribute::Parsed(
                     AttributeKind::BodyStability { .. }
                     | AttributeKind::ConstStabilityIndirect
@@ -285,6 +288,9 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 &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::Unparsed(attr_item) => {
                     style = Some(attr_item.style);
                     match attr.path().as_slice() {
@@ -294,7 +300,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                         [sym::diagnostic, sym::on_unimplemented, ..] => {
                             self.check_diagnostic_on_unimplemented(attr.span(), hir_id, target)
                         }
-                        [sym::coverage, ..] => self.check_coverage(attr, span, target),
                         [sym::no_sanitize, ..] => {
                             self.check_no_sanitize(attr, span, target)
                         }
@@ -585,7 +590,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
 
     /// Checks that `#[coverage(..)]` is applied to a function/closure/method,
     /// or to an impl block or module.
-    fn check_coverage(&self, attr: &Attribute, target_span: Span, target: Target) {
+    fn check_coverage(&self, attr_span: Span, target_span: Span, target: Target) {
         let mut not_fn_impl_mod = None;
         let mut no_body = None;
 
@@ -608,7 +613,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
 
         self.dcx().emit_err(errors::CoverageAttributeNotAllowed {
-            attr_span: attr.span(),
+            attr_span,
             not_fn_impl_mod,
             no_body,
             help: (),
@@ -678,9 +683,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         allowed_target: Target,
     ) {
         if target != allowed_target {
-            let path = attr.path();
-            let path: Vec<_> = path.iter().map(|s| s.as_str()).collect();
-            let attr_name = path.join("::");
+            let attr_name = join_path_syms(attr.path());
             self.tcx.emit_node_span_lint(
                 UNUSED_ATTRIBUTES,
                 hir_id,
@@ -1159,7 +1162,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         match item.kind {
             ItemKind::Enum(_, generics, _) | ItemKind::Struct(_, generics, _)
                 if generics.params.len() != 0 => {}
-            ItemKind::Trait(_, _, _, generics, _, items)
+            ItemKind::Trait(_, _, _, _, generics, _, items)
                 if generics.params.len() != 0
                     || items.iter().any(|item| {
                         matches!(self.tcx.def_kind(item.owner_id), DefKind::AssocTy)
@@ -2267,6 +2270,47 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
+    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 => {}
diff --git a/compiler/rustc_passes/src/errors.rs b/compiler/rustc_passes/src/errors.rs
index 093a2b38804..37330c0ed6e 100644
--- a/compiler/rustc_passes/src/errors.rs
+++ b/compiler/rustc_passes/src/errors.rs
@@ -687,6 +687,15 @@ 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]
diff --git a/compiler/rustc_passes/src/stability.rs b/compiler/rustc_passes/src/stability.rs
index adda94fda8f..e5530d52686 100644
--- a/compiler/rustc_passes/src/stability.rs
+++ b/compiler/rustc_passes/src/stability.rs
@@ -802,12 +802,28 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
                     // FIXME(jdonszelmann): make it impossible to miss the or_else in the typesystem
                     let const_stab = attrs::find_attr!(attrs, AttributeKind::ConstStability{stability, ..} => *stability);
 
+                    let unstable_feature_stab =
+                        find_attr!(attrs, AttributeKind::UnstableFeatureBound(i) => i)
+                            .map(|i| i.as_slice())
+                            .unwrap_or_default();
+
                     // If this impl block has an #[unstable] attribute, give an
                     // error if all involved types and traits are stable, because
                     // it will have no effect.
                     // See: https://github.com/rust-lang/rust/issues/55436
+                    //
+                    // The exception is when there are both  #[unstable_feature_bound(..)] and
+                    //  #![unstable(feature = "..", issue = "..")] that have the same symbol because
+                    // that can effectively mark an impl as unstable.
+                    //
+                    // For example:
+                    // ```
+                    // #[unstable_feature_bound(feat_foo)]
+                    // #[unstable(feature = "feat_foo", issue = "none")]
+                    // impl Foo for Bar {}
+                    // ```
                     if let Some((
-                        Stability { level: attrs::StabilityLevel::Unstable { .. }, .. },
+                        Stability { level: attrs::StabilityLevel::Unstable { .. }, feature },
                         span,
                     )) = stab
                     {
@@ -815,9 +831,21 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
                         c.visit_ty_unambig(self_ty);
                         c.visit_trait_ref(t);
 
+                        // Skip the lint if the impl is marked as unstable using
+                        // #[unstable_feature_bound(..)]
+                        let mut unstable_feature_bound_in_effect = false;
+                        for (unstable_bound_feat_name, _) in unstable_feature_stab {
+                            if *unstable_bound_feat_name == feature {
+                                unstable_feature_bound_in_effect = true;
+                            }
+                        }
+
                         // do not lint when the trait isn't resolved, since resolution error should
                         // be fixed first
-                        if t.path.res != Res::Err && c.fully_stable {
+                        if t.path.res != Res::Err
+                            && c.fully_stable
+                            && !unstable_feature_bound_in_effect
+                        {
                             self.tcx.emit_node_span_lint(
                                 INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
                                 item.hir_id(),
diff --git a/compiler/rustc_privacy/src/lib.rs b/compiler/rustc_privacy/src/lib.rs
index ab2433234aa..80c13e44d7d 100644
--- a/compiler/rustc_privacy/src/lib.rs
+++ b/compiler/rustc_privacy/src/lib.rs
@@ -156,6 +156,7 @@ where
             }
             ty::ClauseKind::ConstEvaluatable(ct) => ct.visit_with(self),
             ty::ClauseKind::WellFormed(term) => term.visit_with(self),
+            ty::ClauseKind::UnstableFeature(_) => V::Result::output(),
         }
     }
 
diff --git a/compiler/rustc_proc_macro/Cargo.toml b/compiler/rustc_proc_macro/Cargo.toml
index 748fa944e28..762acf9a1eb 100644
--- a/compiler/rustc_proc_macro/Cargo.toml
+++ b/compiler/rustc_proc_macro/Cargo.toml
@@ -15,7 +15,7 @@ test = false
 doctest = false
 
 [dependencies]
-rustc-literal-escaper = "0.0.4"
+rustc-literal-escaper = "0.0.5"
 
 [features]
 rustc-dep-of-std = []
diff --git a/compiler/rustc_public/src/unstable/convert/stable/ty.rs b/compiler/rustc_public/src/unstable/convert/stable/ty.rs
index 75c29788787..6b226b8a24d 100644
--- a/compiler/rustc_public/src/unstable/convert/stable/ty.rs
+++ b/compiler/rustc_public/src/unstable/convert/stable/ty.rs
@@ -764,6 +764,9 @@ impl<'tcx> Stable<'tcx> for ty::ClauseKind<'tcx> {
             ClauseKind::HostEffect(..) => {
                 todo!()
             }
+            ClauseKind::UnstableFeature(_) => {
+                todo!()
+            }
         }
     }
 }
diff --git a/compiler/rustc_resolve/src/build_reduced_graph.rs b/compiler/rustc_resolve/src/build_reduced_graph.rs
index 6979d89a8e7..e56aabfd414 100644
--- a/compiler/rustc_resolve/src/build_reduced_graph.rs
+++ b/compiler/rustc_resolve/src/build_reduced_graph.rs
@@ -20,9 +20,9 @@ use rustc_hir::def::{self, *};
 use rustc_hir::def_id::{CRATE_DEF_ID, DefId, LocalDefId};
 use rustc_index::bit_set::DenseBitSet;
 use rustc_metadata::creader::LoadedMacro;
+use rustc_middle::bug;
 use rustc_middle::metadata::ModChild;
-use rustc_middle::ty::Feed;
-use rustc_middle::{bug, ty};
+use rustc_middle::ty::{Feed, Visibility};
 use rustc_span::hygiene::{ExpnId, LocalExpnId, MacroKind};
 use rustc_span::{Ident, Span, Symbol, kw, sym};
 use tracing::debug;
@@ -33,54 +33,42 @@ use crate::imports::{ImportData, ImportKind};
 use crate::macros::{MacroRulesBinding, MacroRulesScope, MacroRulesScopeRef};
 use crate::{
     BindingKey, ExternPreludeEntry, Finalize, MacroData, Module, ModuleKind, ModuleOrUniformRoot,
-    NameBinding, NameBindingData, NameBindingKind, ParentScope, PathResult, ResolutionError,
-    Resolver, ResolverArenas, Segment, ToNameBinding, Used, VisResolutionError, errors,
+    NameBinding, ParentScope, PathResult, ResolutionError, Resolver, Segment, Used,
+    VisResolutionError, errors,
 };
 
 type Res = def::Res<NodeId>;
 
-impl<'ra, Id: Into<DefId>> ToNameBinding<'ra>
-    for (Module<'ra>, ty::Visibility<Id>, Span, LocalExpnId)
-{
-    fn to_name_binding(self, arenas: &'ra ResolverArenas<'ra>) -> NameBinding<'ra> {
-        arenas.alloc_name_binding(NameBindingData {
-            kind: NameBindingKind::Module(self.0),
-            ambiguity: None,
-            warn_ambiguity: false,
-            vis: self.1.to_def_id(),
-            span: self.2,
-            expansion: self.3,
-        })
-    }
-}
-
-impl<'ra, Id: Into<DefId>> ToNameBinding<'ra> for (Res, ty::Visibility<Id>, Span, LocalExpnId) {
-    fn to_name_binding(self, arenas: &'ra ResolverArenas<'ra>) -> NameBinding<'ra> {
-        arenas.alloc_name_binding(NameBindingData {
-            kind: NameBindingKind::Res(self.0),
-            ambiguity: None,
-            warn_ambiguity: false,
-            vis: self.1.to_def_id(),
-            span: self.2,
-            expansion: self.3,
-        })
-    }
-}
-
 impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     /// Defines `name` in namespace `ns` of module `parent` to be `def` if it is not yet defined;
     /// otherwise, reports an error.
-    pub(crate) fn define<T>(&mut self, parent: Module<'ra>, ident: Ident, ns: Namespace, def: T)
-    where
-        T: ToNameBinding<'ra>,
-    {
-        let binding = def.to_name_binding(self.arenas);
+    pub(crate) fn define_binding(
+        &mut self,
+        parent: Module<'ra>,
+        ident: Ident,
+        ns: Namespace,
+        binding: NameBinding<'ra>,
+    ) {
         let key = self.new_disambiguated_key(ident, ns);
         if let Err(old_binding) = self.try_define(parent, key, binding, false) {
             self.report_conflict(parent, ident, ns, old_binding, binding);
         }
     }
 
+    fn define(
+        &mut self,
+        parent: Module<'ra>,
+        ident: Ident,
+        ns: Namespace,
+        res: Res,
+        vis: Visibility<impl Into<DefId>>,
+        span: Span,
+        expn_id: LocalExpnId,
+    ) {
+        let binding = self.arenas.new_res_binding(res, vis.to_def_id(), span, expn_id);
+        self.define_binding(parent, ident, ns, binding)
+    }
+
     /// Walks up the tree of definitions starting at `def_id`,
     /// stopping at the first encountered module.
     /// Parent block modules for arbitrary def-ids are not recorded for the local crate,
@@ -97,7 +85,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     /// Reachable macros with block module parents exist due to `#[macro_export] macro_rules!`,
     /// but they cannot use def-site hygiene, so the assumption holds
     /// (<https://github.com/rust-lang/rust/pull/77984#issuecomment-712445508>).
-    pub(crate) fn get_nearest_non_block_module(&mut self, mut def_id: DefId) -> Module<'ra> {
+    pub(crate) fn get_nearest_non_block_module(&self, mut def_id: DefId) -> Module<'ra> {
         loop {
             match self.get_module(def_id) {
                 Some(module) => return module,
@@ -106,44 +94,47 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         }
     }
 
-    pub(crate) fn expect_module(&mut self, def_id: DefId) -> Module<'ra> {
+    pub(crate) fn expect_module(&self, def_id: DefId) -> Module<'ra> {
         self.get_module(def_id).expect("argument `DefId` is not a module")
     }
 
     /// If `def_id` refers to a module (in resolver's sense, i.e. a module item, crate root, enum,
     /// or trait), then this function returns that module's resolver representation, otherwise it
     /// returns `None`.
-    pub(crate) fn get_module(&mut self, def_id: DefId) -> Option<Module<'ra>> {
-        if let module @ Some(..) = self.module_map.get(&def_id) {
-            return module.copied();
-        }
+    pub(crate) fn get_module(&self, def_id: DefId) -> Option<Module<'ra>> {
+        match def_id.as_local() {
+            Some(local_def_id) => self.local_module_map.get(&local_def_id).copied(),
+            None => {
+                if let module @ Some(..) = self.extern_module_map.borrow().get(&def_id) {
+                    return module.copied();
+                }
 
-        if !def_id.is_local() {
-            // Query `def_kind` is not used because query system overhead is too expensive here.
-            let def_kind = self.cstore().def_kind_untracked(def_id);
-            if let DefKind::Mod | DefKind::Enum | DefKind::Trait = def_kind {
-                let parent = self
-                    .tcx
-                    .opt_parent(def_id)
-                    .map(|parent_id| self.get_nearest_non_block_module(parent_id));
-                // Query `expn_that_defined` is not used because
-                // hashing spans in its result is expensive.
-                let expn_id = self.cstore().expn_that_defined_untracked(def_id, self.tcx.sess);
-                return Some(self.new_module(
-                    parent,
-                    ModuleKind::Def(def_kind, def_id, Some(self.tcx.item_name(def_id))),
-                    expn_id,
-                    self.def_span(def_id),
-                    // FIXME: Account for `#[no_implicit_prelude]` attributes.
-                    parent.is_some_and(|module| module.no_implicit_prelude),
-                ));
+                // Query `def_kind` is not used because query system overhead is too expensive here.
+                let def_kind = self.cstore().def_kind_untracked(def_id);
+                if def_kind.is_module_like() {
+                    let parent = self
+                        .tcx
+                        .opt_parent(def_id)
+                        .map(|parent_id| self.get_nearest_non_block_module(parent_id));
+                    // Query `expn_that_defined` is not used because
+                    // hashing spans in its result is expensive.
+                    let expn_id = self.cstore().expn_that_defined_untracked(def_id, self.tcx.sess);
+                    return Some(self.new_extern_module(
+                        parent,
+                        ModuleKind::Def(def_kind, def_id, Some(self.tcx.item_name(def_id))),
+                        expn_id,
+                        self.def_span(def_id),
+                        // FIXME: Account for `#[no_implicit_prelude]` attributes.
+                        parent.is_some_and(|module| module.no_implicit_prelude),
+                    ));
+                }
+
+                None
             }
         }
-
-        None
     }
 
-    pub(crate) fn expn_def_scope(&mut self, expn_id: ExpnId) -> Module<'ra> {
+    pub(crate) fn expn_def_scope(&self, expn_id: ExpnId) -> Module<'ra> {
         match expn_id.expn_data().macro_def_id {
             Some(def_id) => self.macro_def_scope(def_id),
             None => expn_id
@@ -153,7 +144,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         }
     }
 
-    pub(crate) fn macro_def_scope(&mut self, def_id: DefId) -> Module<'ra> {
+    pub(crate) fn macro_def_scope(&self, def_id: DefId) -> Module<'ra> {
         if let Some(id) = def_id.as_local() {
             self.local_macro_def_scopes[&id]
         } else {
@@ -223,12 +214,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         let expansion = parent_scope.expansion;
         // Record primary definitions.
         match res {
-            Res::Def(DefKind::Mod | DefKind::Enum | DefKind::Trait, def_id) => {
-                let module = self.expect_module(def_id);
-                self.define(parent, ident, TypeNS, (module, vis, span, expansion));
-            }
             Res::Def(
-                DefKind::Struct
+                DefKind::Mod
+                | DefKind::Enum
+                | DefKind::Trait
+                | DefKind::Struct
                 | DefKind::Union
                 | DefKind::Variant
                 | DefKind::TyAlias
@@ -239,7 +229,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 _,
             )
             | Res::PrimTy(..)
-            | Res::ToolMod => self.define(parent, ident, TypeNS, (res, vis, span, expansion)),
+            | Res::ToolMod => self.define(parent, ident, TypeNS, res, vis, span, expansion),
             Res::Def(
                 DefKind::Fn
                 | DefKind::AssocFn
@@ -248,9 +238,9 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 | DefKind::AssocConst
                 | DefKind::Ctor(..),
                 _,
-            ) => self.define(parent, ident, ValueNS, (res, vis, span, expansion)),
+            ) => self.define(parent, ident, ValueNS, res, vis, span, expansion),
             Res::Def(DefKind::Macro(..), _) | Res::NonMacroAttr(..) => {
-                self.define(parent, ident, MacroNS, (res, vis, span, expansion))
+                self.define(parent, ident, MacroNS, res, vis, span, expansion)
             }
             Res::Def(
                 DefKind::TyParam
@@ -294,10 +284,10 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
         Res::Def(self.r.tcx.def_kind(def_id), def_id)
     }
 
-    fn resolve_visibility(&mut self, vis: &ast::Visibility) -> ty::Visibility {
+    fn resolve_visibility(&mut self, vis: &ast::Visibility) -> Visibility {
         self.try_resolve_visibility(vis, true).unwrap_or_else(|err| {
             self.r.report_vis_error(err);
-            ty::Visibility::Public
+            Visibility::Public
         })
     }
 
@@ -305,10 +295,10 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
         &mut self,
         vis: &'ast ast::Visibility,
         finalize: bool,
-    ) -> Result<ty::Visibility, VisResolutionError<'ast>> {
+    ) -> Result<Visibility, VisResolutionError<'ast>> {
         let parent_scope = &self.parent_scope;
         match vis.kind {
-            ast::VisibilityKind::Public => Ok(ty::Visibility::Public),
+            ast::VisibilityKind::Public => Ok(Visibility::Public),
             ast::VisibilityKind::Inherited => {
                 Ok(match self.parent_scope.module.kind {
                     // Any inherited visibility resolved directly inside an enum or trait
@@ -318,7 +308,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                         self.r.tcx.visibility(def_id).expect_local()
                     }
                     // Otherwise, the visibility is restricted to the nearest parent `mod` item.
-                    _ => ty::Visibility::Restricted(
+                    _ => Visibility::Restricted(
                         self.parent_scope.module.nearest_parent_mod().expect_local(),
                     ),
                 })
@@ -366,9 +356,9 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                         }
                         if module.is_normal() {
                             match res {
-                                Res::Err => Ok(ty::Visibility::Public),
+                                Res::Err => Ok(Visibility::Public),
                                 _ => {
-                                    let vis = ty::Visibility::Restricted(res.def_id());
+                                    let vis = Visibility::Restricted(res.def_id());
                                     if self.r.is_accessible_from(vis, parent_scope.module) {
                                         Ok(vis.expect_local())
                                     } else {
@@ -416,7 +406,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
         self.r.field_visibility_spans.insert(def_id, field_vis);
     }
 
-    fn block_needs_anonymous_module(&mut self, block: &Block) -> bool {
+    fn block_needs_anonymous_module(&self, block: &Block) -> bool {
         // If any statements are items, we need to create an anonymous module
         block
             .stmts
@@ -433,7 +423,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
         item: &ast::Item,
         root_span: Span,
         root_id: NodeId,
-        vis: ty::Visibility,
+        vis: Visibility,
     ) {
         let current_module = self.parent_scope.module;
         let import = self.r.arenas.alloc_import(ImportData {
@@ -481,7 +471,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
         list_stem: bool,
         // The whole `use` item
         item: &Item,
-        vis: ty::Visibility,
+        vis: Visibility,
         root_span: Span,
     ) {
         debug!(
@@ -690,7 +680,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                         true,
                         // The whole `use` item
                         item,
-                        ty::Visibility::Restricted(
+                        Visibility::Restricted(
                             self.parent_scope.module.nearest_parent_mod().expect_local(),
                         ),
                         root_span,
@@ -706,7 +696,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
         ident: Ident,
         feed: Feed<'tcx, LocalDefId>,
         adt_res: Res,
-        adt_vis: ty::Visibility,
+        adt_vis: Visibility,
         adt_span: Span,
     ) {
         let parent_scope = &self.parent_scope;
@@ -714,7 +704,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
         let expansion = parent_scope.expansion;
 
         // Define a name in the type namespace if it is not anonymous.
-        self.r.define(parent, ident, TypeNS, (adt_res, adt_vis, adt_span, expansion));
+        self.r.define(parent, ident, TypeNS, adt_res, adt_vis, adt_span, expansion);
         self.r.feed_visibility(feed, adt_vis);
         let def_id = feed.key();
 
@@ -766,7 +756,12 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
             }
 
             ItemKind::Mod(_, ident, ref mod_kind) => {
-                let module = self.r.new_module(
+                self.r.define(parent, ident, TypeNS, res, vis, sp, expansion);
+
+                if let ast::ModKind::Loaded(_, _, _, Err(_)) = mod_kind {
+                    self.r.mods_with_parse_errors.insert(def_id);
+                }
+                self.parent_scope.module = self.r.new_local_module(
                     Some(parent),
                     ModuleKind::Def(def_kind, def_id, Some(ident.name)),
                     expansion.to_expn_id(),
@@ -774,24 +769,16 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                     parent.no_implicit_prelude
                         || ast::attr::contains_name(&item.attrs, sym::no_implicit_prelude),
                 );
-                self.r.define(parent, ident, TypeNS, (module, vis, sp, expansion));
-
-                if let ast::ModKind::Loaded(_, _, _, Err(_)) = mod_kind {
-                    self.r.mods_with_parse_errors.insert(def_id);
-                }
-
-                // Descend into the module.
-                self.parent_scope.module = module;
             }
 
             // These items live in the value namespace.
             ItemKind::Const(box ConstItem { ident, .. })
             | ItemKind::Delegation(box Delegation { ident, .. })
             | ItemKind::Static(box StaticItem { ident, .. }) => {
-                self.r.define(parent, ident, ValueNS, (res, vis, sp, expansion));
+                self.r.define(parent, ident, ValueNS, res, vis, sp, expansion);
             }
             ItemKind::Fn(box Fn { ident, .. }) => {
-                self.r.define(parent, ident, ValueNS, (res, vis, sp, expansion));
+                self.r.define(parent, ident, ValueNS, res, vis, sp, expansion);
 
                 // Functions introducing procedural macros reserve a slot
                 // in the macro namespace as well (see #52225).
@@ -800,19 +787,19 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
 
             // These items live in the type namespace.
             ItemKind::TyAlias(box TyAlias { ident, .. }) | ItemKind::TraitAlias(ident, ..) => {
-                self.r.define(parent, ident, TypeNS, (res, vis, sp, expansion));
+                self.r.define(parent, ident, TypeNS, res, vis, sp, expansion);
             }
 
             ItemKind::Enum(ident, _, _) | ItemKind::Trait(box ast::Trait { ident, .. }) => {
-                let module = self.r.new_module(
+                self.r.define(parent, ident, TypeNS, res, vis, sp, expansion);
+
+                self.parent_scope.module = self.r.new_local_module(
                     Some(parent),
                     ModuleKind::Def(def_kind, def_id, Some(ident.name)),
                     expansion.to_expn_id(),
                     item.span,
                     parent.no_implicit_prelude,
                 );
-                self.r.define(parent, ident, TypeNS, (module, vis, sp, expansion));
-                self.parent_scope.module = module;
             }
 
             // These items live in both the type and value namespaces.
@@ -834,7 +821,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                     let mut ctor_vis = if vis.is_public()
                         && ast::attr::contains_name(&item.attrs, sym::non_exhaustive)
                     {
-                        ty::Visibility::Restricted(CRATE_DEF_ID)
+                        Visibility::Restricted(CRATE_DEF_ID)
                     } else {
                         vis
                     };
@@ -847,7 +834,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                         // constructor visibility should still be determined correctly.
                         let field_vis = self
                             .try_resolve_visibility(&field.vis, false)
-                            .unwrap_or(ty::Visibility::Public);
+                            .unwrap_or(Visibility::Public);
                         if ctor_vis.is_at_least(field_vis, self.r.tcx) {
                             ctor_vis = field_vis;
                         }
@@ -856,7 +843,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                     let feed = self.r.feed(ctor_node_id);
                     let ctor_def_id = feed.key();
                     let ctor_res = self.res(ctor_def_id);
-                    self.r.define(parent, ident, ValueNS, (ctor_res, ctor_vis, sp, expansion));
+                    self.r.define(parent, ident, ValueNS, ctor_res, ctor_vis, sp, expansion);
                     self.r.feed_visibility(feed, ctor_vis);
                     // We need the field visibility spans also for the constructor for E0603.
                     self.insert_field_visibilities_local(ctor_def_id.to_def_id(), vdata.fields());
@@ -896,7 +883,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
         item: &Item,
         ident: Ident,
         local_def_id: LocalDefId,
-        vis: ty::Visibility,
+        vis: Visibility,
         parent: Module<'ra>,
     ) {
         let sp = item.span;
@@ -920,8 +907,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
         }
         .map(|module| {
             let used = self.process_macro_use_imports(item, module);
-            let vis = ty::Visibility::<LocalDefId>::Public;
-            let binding = (module, vis, sp, expansion).to_name_binding(self.r.arenas);
+            let binding = self.r.arenas.new_pub_res_binding(module.res().unwrap(), sp, expansion);
             (used, Some(ModuleOrUniformRoot::Module(module)), binding)
         })
         .unwrap_or((true, None, self.r.dummy_binding));
@@ -978,7 +964,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                 );
             }
         }
-        self.r.define(parent, ident, TypeNS, imported_binding);
+        self.r.define_binding(parent, ident, TypeNS, imported_binding);
     }
 
     /// Constructs the reduced graph for one foreign item.
@@ -995,7 +981,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
         let parent = self.parent_scope.module;
         let expansion = self.parent_scope.expansion;
         let vis = self.resolve_visibility(&item.vis);
-        self.r.define(parent, ident, ns, (self.res(def_id), vis, item.span, expansion));
+        self.r.define(parent, ident, ns, self.res(def_id), vis, item.span, expansion);
         self.r.feed_visibility(feed, vis);
     }
 
@@ -1003,7 +989,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
         let parent = self.parent_scope.module;
         let expansion = self.parent_scope.expansion;
         if self.block_needs_anonymous_module(block) {
-            let module = self.r.new_module(
+            let module = self.r.new_local_module(
                 Some(parent),
                 ModuleKind::Block,
                 expansion.to_expn_id(),
@@ -1081,7 +1067,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                 root_span: span,
                 span,
                 module_path: Vec::new(),
-                vis: ty::Visibility::Restricted(CRATE_DEF_ID),
+                vis: Visibility::Restricted(CRATE_DEF_ID),
             })
         };
 
@@ -1135,7 +1121,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
     }
 
     /// Returns `true` if this attribute list contains `macro_use`.
-    fn contains_macro_use(&mut self, attrs: &[ast::Attribute]) -> bool {
+    fn contains_macro_use(&self, attrs: &[ast::Attribute]) -> bool {
         for attr in attrs {
             if attr.has_name(sym::macro_escape) {
                 let inner_attribute = matches!(attr.style, ast::AttrStyle::Inner);
@@ -1231,11 +1217,11 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
             self.r.macro_names.insert(ident);
             let is_macro_export = ast::attr::contains_name(&item.attrs, sym::macro_export);
             let vis = if is_macro_export {
-                ty::Visibility::Public
+                Visibility::Public
             } else {
-                ty::Visibility::Restricted(CRATE_DEF_ID)
+                Visibility::Restricted(CRATE_DEF_ID)
             };
-            let binding = (res, vis, span, expansion).to_name_binding(self.r.arenas);
+            let binding = self.r.arenas.new_res_binding(res, vis.to_def_id(), span, expansion);
             self.r.set_binding_parent_module(binding, parent_scope.module);
             self.r.all_macro_rules.insert(ident.name);
             if is_macro_export {
@@ -1254,7 +1240,7 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                 });
                 self.r.import_use_map.insert(import, Used::Other);
                 let import_binding = self.r.import(binding, import);
-                self.r.define(self.r.graph_root, ident, MacroNS, import_binding);
+                self.r.define_binding(self.r.graph_root, ident, MacroNS, import_binding);
             } else {
                 self.r.check_reserved_macro_name(ident, res);
                 self.insert_unused_macro(ident, def_id, item.id);
@@ -1275,14 +1261,14 @@ impl<'a, 'ra, 'tcx> BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
                 // Visibilities must not be resolved non-speculatively twice
                 // and we already resolved this one as a `fn` item visibility.
                 ItemKind::Fn(..) => {
-                    self.try_resolve_visibility(&item.vis, false).unwrap_or(ty::Visibility::Public)
+                    self.try_resolve_visibility(&item.vis, false).unwrap_or(Visibility::Public)
                 }
                 _ => self.resolve_visibility(&item.vis),
             };
             if !vis.is_public() {
                 self.insert_unused_macro(ident, def_id, item.id);
             }
-            self.r.define(module, ident, MacroNS, (res, vis, span, expansion));
+            self.r.define(module, ident, MacroNS, res, vis, span, expansion);
             self.r.feed_visibility(feed, vis);
             self.parent_scope.macro_rules
         }
@@ -1418,7 +1404,7 @@ impl<'a, 'ra, 'tcx> Visitor<'a> for BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
         if ctxt == AssocCtxt::Trait {
             let parent = self.parent_scope.module;
             let expansion = self.parent_scope.expansion;
-            self.r.define(parent, ident, ns, (self.res(def_id), vis, item.span, expansion));
+            self.r.define(parent, ident, ns, self.res(def_id), vis, item.span, expansion);
         } else if !matches!(&item.kind, AssocItemKind::Delegation(deleg) if deleg.from_glob) {
             let impl_def_id = self.r.tcx.local_parent(local_def_id);
             let key = BindingKey::new(ident.normalize_to_macros_2_0(), ns);
@@ -1503,13 +1489,13 @@ impl<'a, 'ra, 'tcx> Visitor<'a> for BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
         let feed = self.r.feed(variant.id);
         let def_id = feed.key();
         let vis = self.resolve_visibility(&variant.vis);
-        self.r.define(parent, ident, TypeNS, (self.res(def_id), vis, variant.span, expn_id));
+        self.r.define(parent, ident, TypeNS, self.res(def_id), vis, variant.span, expn_id);
         self.r.feed_visibility(feed, vis);
 
         // If the variant is marked as non_exhaustive then lower the visibility to within the crate.
         let ctor_vis =
             if vis.is_public() && ast::attr::contains_name(&variant.attrs, sym::non_exhaustive) {
-                ty::Visibility::Restricted(CRATE_DEF_ID)
+                Visibility::Restricted(CRATE_DEF_ID)
             } else {
                 vis
             };
@@ -1519,7 +1505,7 @@ impl<'a, 'ra, 'tcx> Visitor<'a> for BuildReducedGraphVisitor<'a, 'ra, 'tcx> {
             let feed = self.r.feed(ctor_node_id);
             let ctor_def_id = feed.key();
             let ctor_res = self.res(ctor_def_id);
-            self.r.define(parent, ident, ValueNS, (ctor_res, ctor_vis, variant.span, expn_id));
+            self.r.define(parent, ident, ValueNS, ctor_res, ctor_vis, variant.span, expn_id);
             self.r.feed_visibility(feed, ctor_vis);
         }
 
diff --git a/compiler/rustc_resolve/src/def_collector.rs b/compiler/rustc_resolve/src/def_collector.rs
index 781e2ce9704..7d51fef28d3 100644
--- a/compiler/rustc_resolve/src/def_collector.rs
+++ b/compiler/rustc_resolve/src/def_collector.rs
@@ -2,7 +2,7 @@ use std::mem;
 
 use rustc_ast::visit::FnKind;
 use rustc_ast::*;
-use rustc_attr_parsing::{AttributeParser, Early, OmitDoc};
+use rustc_attr_parsing::{AttributeParser, Early, OmitDoc, ShouldEmit};
 use rustc_expand::expand::AstFragment;
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, CtorOf, DefKind};
@@ -132,7 +132,7 @@ impl<'a, 'ra, 'tcx> visit::Visitor<'a> for DefCollector<'a, 'ra, 'tcx> {
                     &self.resolver.tcx.sess,
                     self.resolver.tcx.features(),
                     Vec::new(),
-                    Early { emit_errors: false },
+                    Early { emit_errors: ShouldEmit::Nothing },
                 );
                 let attrs = parser.parse_attribute_list(
                     &i.attrs,
diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index 93d848787ef..f6f45adabe9 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -1,6 +1,8 @@
 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};
+use rustc_ast::{
+    self as ast, CRATE_NODE_ID, Crate, ItemKind, ModKind, NodeId, Path, join_path_idents,
+};
 use rustc_ast_pretty::pprust;
 use rustc_attr_data_structures::{
     self as attr, AttributeKind, CfgEntry, Stability, StrippedCfgItem, find_attr,
@@ -232,12 +234,12 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             return;
         }
 
-        let old_kind = match (ns, old_binding.module()) {
+        let old_kind = match (ns, old_binding.res()) {
             (ValueNS, _) => "value",
             (MacroNS, _) => "macro",
             (TypeNS, _) if old_binding.is_extern_crate() => "extern crate",
-            (TypeNS, Some(module)) if module.is_normal() => "module",
-            (TypeNS, Some(module)) if module.is_trait() => "trait",
+            (TypeNS, Res::Def(DefKind::Mod, _)) => "module",
+            (TypeNS, Res::Def(DefKind::Trait, _)) => "trait",
             (TypeNS, _) => "type",
         };
 
@@ -1319,7 +1321,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 }
 
                 // collect submodules to explore
-                if let Some(module) = name_binding.module() {
+                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));
@@ -1339,14 +1341,14 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
                     if !is_extern_crate_that_also_appears_in_prelude || alias_import {
                         // add the module to the lookup
-                        if seen_modules.insert(module.def_id()) {
+                        if seen_modules.insert(def_id) {
                             if via_import { &mut worklist_via_import } else { &mut worklist }.push(
                                 (
-                                    module,
+                                    this.expect_module(def_id),
                                     path_segments,
                                     child_accessible,
                                     child_doc_visible,
-                                    is_stable && this.is_stable(module.def_id(), name_binding.span),
+                                    is_stable && this.is_stable(def_id, name_binding.span),
                                 ),
                             );
                         }
@@ -2018,7 +2020,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             }
         }
 
-        let mut sugg_paths = vec![];
+        let mut sugg_paths: Vec<(Vec<Ident>, bool)> = vec![];
         if let Some(mut def_id) = res.opt_def_id() {
             // We can't use `def_path_str` in resolve.
             let mut path = vec![def_id];
@@ -2031,16 +2033,16 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 }
             }
             // We will only suggest importing directly if it is accessible through that path.
-            let path_names: Option<Vec<String>> = path
+            let path_names: Option<Vec<Ident>> = path
                 .iter()
                 .rev()
                 .map(|def_id| {
-                    self.tcx.opt_item_name(*def_id).map(|n| {
-                        if def_id.is_top_level_module() {
-                            "crate".to_string()
+                    self.tcx.opt_item_name(*def_id).map(|name| {
+                        Ident::with_dummy_span(if def_id.is_top_level_module() {
+                            kw::Crate
                         } else {
-                            n.to_string()
-                        }
+                            name
+                        })
                     })
                 })
                 .collect();
@@ -2084,17 +2086,14 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             match binding.kind {
                 NameBindingKind::Import { import, .. } => {
                     for segment in import.module_path.iter().skip(1) {
-                        path.push(segment.ident.to_string());
+                        path.push(segment.ident);
                     }
                     sugg_paths.push((
-                        path.iter()
-                            .cloned()
-                            .chain(vec![ident.to_string()].into_iter())
-                            .collect::<Vec<_>>(),
+                        path.iter().cloned().chain(std::iter::once(ident)).collect::<Vec<_>>(),
                         true, // re-export
                     ));
                 }
-                NameBindingKind::Res(_) | NameBindingKind::Module(_) => {}
+                NameBindingKind::Res(_) => {}
             }
             let first = binding == first_binding;
             let def_span = self.tcx.sess.source_map().guess_head_span(binding.span);
@@ -2126,7 +2125,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             err.subdiagnostic(note);
         }
         // We prioritize shorter paths, non-core imports and direct imports over the alternatives.
-        sugg_paths.sort_by_key(|(p, reexport)| (p.len(), p[0] == "core", *reexport));
+        sugg_paths.sort_by_key(|(p, reexport)| (p.len(), p[0].name == sym::core, *reexport));
         for (sugg, reexport) in sugg_paths {
             if not_publicly_reexported {
                 break;
@@ -2136,7 +2135,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 // `tests/ui/imports/issue-55884-2.rs`
                 continue;
             }
-            let path = sugg.join("::");
+            let path = join_path_idents(sugg);
             let sugg = if reexport {
                 errors::ImportIdent::ThroughReExport { span: dedup_span, ident, path }
             } else {
@@ -2150,7 +2149,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     }
 
     pub(crate) fn find_similarly_named_module_or_crate(
-        &mut self,
+        &self,
         ident: Symbol,
         current_module: Module<'ra>,
     ) -> Option<Symbol> {
@@ -2159,7 +2158,16 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             .keys()
             .map(|ident| ident.name)
             .chain(
-                self.module_map
+                self.local_module_map
+                    .iter()
+                    .filter(|(_, module)| {
+                        current_module.is_ancestor_of(**module) && current_module != **module
+                    })
+                    .flat_map(|(_, module)| module.kind.name()),
+            )
+            .chain(
+                self.extern_module_map
+                    .borrow()
                     .iter()
                     .filter(|(_, module)| {
                         current_module.is_ancestor_of(**module) && current_module != **module
@@ -2306,25 +2314,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     .ok()
                 };
                 if let Some(binding) = binding {
-                    let mut found = |what| {
-                        msg = format!(
-                            "expected {}, found {} `{}` in {}",
-                            ns.descr(),
-                            what,
-                            ident,
-                            parent
-                        )
-                    };
-                    if binding.module().is_some() {
-                        found("module")
-                    } else {
-                        match binding.res() {
-                            // Avoid using TyCtxt::def_kind_descr in the resolver, because it
-                            // indirectly *calls* the resolver, and would cause a query cycle.
-                            Res::Def(kind, id) => found(kind.descr(id)),
-                            _ => found(ns_to_try.descr()),
-                        }
-                    }
+                    msg = format!(
+                        "expected {}, found {} `{ident}` in {parent}",
+                        ns.descr(),
+                        binding.res().descr(),
+                    );
                 };
             }
             (msg, None)
@@ -2449,7 +2443,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     }
 
     fn undeclared_module_suggest_declare(
-        &mut self,
+        &self,
         ident: Ident,
         path: std::path::PathBuf,
     ) -> Option<(Vec<(Span, String)>, String, Applicability)> {
@@ -2464,7 +2458,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         ))
     }
 
-    fn undeclared_module_exists(&mut self, ident: Ident) -> Option<std::path::PathBuf> {
+    fn undeclared_module_exists(&self, ident: Ident) -> Option<std::path::PathBuf> {
         let map = self.tcx.sess.source_map();
 
         let src = map.span_to_filename(ident.span).into_local_path()?;
@@ -2823,24 +2817,23 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     return cached;
                 }
                 visited.insert(parent_module, false);
-                let res = r.module_map.get(&parent_module).is_some_and(|m| {
-                    for importer in m.glob_importers.borrow().iter() {
-                        if let Some(next_parent_module) = importer.parent_scope.module.opt_def_id()
+                let m = r.expect_module(parent_module);
+                let mut res = false;
+                for importer in m.glob_importers.borrow().iter() {
+                    if let Some(next_parent_module) = importer.parent_scope.module.opt_def_id() {
+                        if next_parent_module == module
+                            || comes_from_same_module_for_glob(
+                                r,
+                                next_parent_module,
+                                module,
+                                visited,
+                            )
                         {
-                            if next_parent_module == module
-                                || comes_from_same_module_for_glob(
-                                    r,
-                                    next_parent_module,
-                                    module,
-                                    visited,
-                                )
-                            {
-                                return true;
-                            }
+                            res = true;
+                            break;
                         }
                     }
-                    false
-                });
+                }
                 visited.insert(parent_module, res);
                 res
             }
diff --git a/compiler/rustc_resolve/src/effective_visibilities.rs b/compiler/rustc_resolve/src/effective_visibilities.rs
index 5de80de3f8d..34d1e9552fd 100644
--- a/compiler/rustc_resolve/src/effective_visibilities.rs
+++ b/compiler/rustc_resolve/src/effective_visibilities.rs
@@ -38,11 +38,11 @@ pub(crate) struct EffectiveVisibilitiesVisitor<'a, 'ra, 'tcx> {
 }
 
 impl Resolver<'_, '_> {
-    fn nearest_normal_mod(&mut self, def_id: LocalDefId) -> LocalDefId {
+    fn nearest_normal_mod(&self, def_id: LocalDefId) -> LocalDefId {
         self.get_nearest_non_block_module(def_id.to_def_id()).nearest_parent_mod().expect_local()
     }
 
-    fn private_vis_import(&mut self, binding: NameBinding<'_>) -> Visibility {
+    fn private_vis_import(&self, binding: NameBinding<'_>) -> Visibility {
         let NameBindingKind::Import { import, .. } = binding.kind else { unreachable!() };
         Visibility::Restricted(
             import
@@ -52,7 +52,7 @@ impl Resolver<'_, '_> {
         )
     }
 
-    fn private_vis_def(&mut self, def_id: LocalDefId) -> Visibility {
+    fn private_vis_def(&self, def_id: LocalDefId) -> Visibility {
         // For mod items `nearest_normal_mod` returns its argument, but we actually need its parent.
         let normal_mod_id = self.nearest_normal_mod(def_id);
         if normal_mod_id == def_id {
@@ -113,8 +113,7 @@ impl<'a, 'ra, 'tcx> EffectiveVisibilitiesVisitor<'a, 'ra, 'tcx> {
     /// Update effective visibilities of bindings in the given module,
     /// including their whole reexport chains.
     fn set_bindings_effective_visibilities(&mut self, module_id: LocalDefId) {
-        assert!(self.r.module_map.contains_key(&module_id.to_def_id()));
-        let module = self.r.get_module(module_id.to_def_id()).unwrap();
+        let module = self.r.expect_module(module_id.to_def_id());
         let resolutions = self.r.resolutions(module);
 
         for (_, name_resolution) in resolutions.borrow().iter() {
diff --git a/compiler/rustc_resolve/src/ident.rs b/compiler/rustc_resolve/src/ident.rs
index 99297de40d5..34941398a2b 100644
--- a/compiler/rustc_resolve/src/ident.rs
+++ b/compiler/rustc_resolve/src/ident.rs
@@ -3,11 +3,10 @@ use Namespace::*;
 use rustc_ast::{self as ast, NodeId};
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def::{DefKind, Namespace, NonMacroAttrKind, PartialRes, PerNS};
-use rustc_middle::{bug, ty};
+use rustc_middle::bug;
 use rustc_session::lint::BuiltinLintDiag;
 use rustc_session::lint::builtin::PROC_MACRO_DERIVE_RESOLUTION_FALLBACK;
 use rustc_session::parse::feature_err;
-use rustc_span::def_id::LocalDefId;
 use rustc_span::hygiene::{ExpnId, ExpnKind, LocalExpnId, MacroKind, SyntaxContext};
 use rustc_span::{Ident, Span, kw, sym};
 use tracing::{debug, instrument};
@@ -20,11 +19,9 @@ use crate::{
     AmbiguityError, AmbiguityErrorMisc, AmbiguityKind, BindingKey, Determinacy, Finalize,
     ImportKind, LexicalScopeBinding, Module, ModuleKind, ModuleOrUniformRoot, NameBinding,
     NameBindingKind, ParentScope, PathResult, PrivacyError, Res, ResolutionError, Resolver, Scope,
-    ScopeSet, Segment, ToNameBinding, Used, Weak, errors,
+    ScopeSet, Segment, Used, Weak, errors,
 };
 
-type Visibility = ty::Visibility<LocalDefId>;
-
 #[derive(Copy, Clone)]
 pub enum UsePrelude {
     No,
@@ -222,7 +219,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     }
 
     fn hygienic_lexical_parent(
-        &mut self,
+        &self,
         module: Module<'ra>,
         ctxt: &mut SyntaxContext,
         derive_fallback_lint_id: Option<NodeId>,
@@ -464,13 +461,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                             ) {
                                 Ok((Some(ext), _)) => {
                                     if ext.helper_attrs.contains(&ident.name) {
-                                        let binding = (
+                                        let binding = this.arenas.new_pub_res_binding(
                                             Res::NonMacroAttr(NonMacroAttrKind::DeriveHelperCompat),
-                                            Visibility::Public,
                                             derive.span,
                                             LocalExpnId::ROOT,
-                                        )
-                                            .to_name_binding(this.arenas);
+                                        );
                                         result = Ok((binding, Flags::empty()));
                                         break;
                                     }
@@ -846,7 +841,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 if ns == TypeNS {
                     if ident.name == kw::Crate || ident.name == kw::DollarCrate {
                         let module = self.resolve_crate_root(ident);
-                        return Ok(self.module_self_bindings[&module]);
+                        return Ok(module.self_binding.unwrap());
                     } else if ident.name == kw::Super || ident.name == kw::SelfLower {
                         // FIXME: Implement these with renaming requirements so that e.g.
                         // `use super;` doesn't work, but `use super as name;` does.
@@ -890,7 +885,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             );
         }
 
-        let check_usable = |this: &mut Self, binding: NameBinding<'ra>| {
+        let check_usable = |this: &Self, binding: NameBinding<'ra>| {
             let usable = this.is_accessible_from(binding.vis, parent_scope.module);
             if usable { Ok(binding) } else { Err((Determined, Weak::No)) }
         };
@@ -1637,11 +1632,11 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     }
 
                     let maybe_assoc = opt_ns != Some(MacroNS) && PathSource::Type.is_expected(res);
-                    if let Some(next_module) = binding.module() {
-                        if self.mods_with_parse_errors.contains(&next_module.def_id()) {
+                    if let Some(def_id) = binding.res().module_like_def_id() {
+                        if self.mods_with_parse_errors.contains(&def_id) {
                             module_had_parse_errors = true;
                         }
-                        module = Some(ModuleOrUniformRoot::Module(next_module));
+                        module = Some(ModuleOrUniformRoot::Module(self.expect_module(def_id)));
                         record_segment_res(self, res);
                     } else if res == Res::ToolMod && !is_last && opt_ns.is_some() {
                         if binding.is_import() {
diff --git a/compiler/rustc_resolve/src/imports.rs b/compiler/rustc_resolve/src/imports.rs
index 40c63a3edf3..0a4c25b0eb0 100644
--- a/compiler/rustc_resolve/src/imports.rs
+++ b/compiler/rustc_resolve/src/imports.rs
@@ -11,11 +11,12 @@ use rustc_errors::{Applicability, MultiSpan, pluralize, struct_span_code_err};
 use rustc_hir::def::{self, DefKind, PartialRes};
 use rustc_hir::def_id::DefId;
 use rustc_middle::metadata::{ModChild, Reexport};
-use rustc_middle::{span_bug, ty};
+use rustc_middle::span_bug;
+use rustc_middle::ty::Visibility;
 use rustc_session::lint::BuiltinLintDiag;
 use rustc_session::lint::builtin::{
-    AMBIGUOUS_GLOB_REEXPORTS, HIDDEN_GLOB_REEXPORTS, PUB_USE_OF_PRIVATE_EXTERN_CRATE,
-    REDUNDANT_IMPORTS, UNUSED_IMPORTS,
+    AMBIGUOUS_GLOB_REEXPORTS, EXPORTED_PRIVATE_DEPENDENCIES, HIDDEN_GLOB_REEXPORTS,
+    PUB_USE_OF_PRIVATE_EXTERN_CRATE, REDUNDANT_IMPORTS, UNUSED_IMPORTS,
 };
 use rustc_session::parse::feature_err;
 use rustc_span::edit_distance::find_best_match_for_name;
@@ -88,7 +89,7 @@ pub(crate) enum ImportKind<'ra> {
         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<ty::Visibility>>,
+        max_vis: Cell<Option<Visibility>>,
         id: NodeId,
     },
     ExternCrate {
@@ -185,7 +186,7 @@ pub(crate) struct ImportData<'ra> {
     /// |`use ::foo`      | `ModuleOrUniformRoot::CrateRootAndExternPrelude`    | a special case in 2015 edition |
     /// |`use foo`        | `ModuleOrUniformRoot::CurrentScope`                 | - |
     pub imported_module: Cell<Option<ModuleOrUniformRoot<'ra>>>,
-    pub vis: ty::Visibility,
+    pub vis: Visibility,
 }
 
 /// All imports are unique and allocated on a same arena,
@@ -455,7 +456,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         f: F,
     ) -> T
     where
-        F: FnOnce(&mut Resolver<'ra, 'tcx>, &mut NameResolution<'ra>) -> T,
+        F: FnOnce(&Resolver<'ra, 'tcx>, &mut NameResolution<'ra>) -> T,
     {
         // Ensure that `resolution` isn't borrowed when defining in the module's glob importers,
         // during which the resolution might end up getting re-defined via a glob cycle.
@@ -634,10 +635,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         }
     }
 
-    pub(crate) fn check_hidden_glob_reexports(
-        &mut self,
-        exported_ambiguities: FxHashSet<NameBinding<'ra>>,
-    ) {
+    pub(crate) fn lint_reexports(&mut self, exported_ambiguities: FxHashSet<NameBinding<'ra>>) {
         for module in self.arenas.local_modules().iter() {
             for (key, resolution) in self.resolutions(*module).borrow().iter() {
                 let resolution = resolution.borrow();
@@ -679,9 +677,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                             NameBindingKind::Res(res) => {
                                 Some(self.def_id_to_node_id(res.def_id().expect_local()))
                             }
-                            NameBindingKind::Module(module) => {
-                                Some(self.def_id_to_node_id(module.def_id().expect_local()))
-                            }
                             NameBindingKind::Import { import, .. } => import.id(),
                         };
                         if let Some(binding_id) = binding_id {
@@ -699,6 +694,27 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         }
                     }
                 }
+
+                if let NameBindingKind::Import { import, .. } = binding.kind
+                    && let Some(binding_id) = import.id()
+                    && let import_def_id = self.local_def_id(binding_id)
+                    && self.effective_visibilities.is_exported(import_def_id)
+                    && let Res::Def(reexported_kind, reexported_def_id) = binding.res()
+                    && !matches!(reexported_kind, DefKind::Ctor(..))
+                    && !reexported_def_id.is_local()
+                    && self.tcx.is_private_dep(reexported_def_id.krate)
+                {
+                    self.lint_buffer.buffer_lint(
+                        EXPORTED_PRIVATE_DEPENDENCIES,
+                        binding_id,
+                        binding.span,
+                        BuiltinLintDiag::ReexportPrivateDependency {
+                            kind: binding.res().descr().to_string(),
+                            name: key.ident.name.to_string(),
+                            krate: self.tcx.crate_name(reexported_def_id.krate),
+                        },
+                    );
+                }
             }
         }
     }
@@ -875,7 +891,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                         }
                         // We need the `target`, `source` can be extracted.
                         let imported_binding = this.import(binding, import);
-                        this.define(parent, target, ns, imported_binding);
+                        this.define_binding(parent, target, ns, imported_binding);
                         PendingBinding::Ready(Some(imported_binding))
                     }
                     Err(Determinacy::Determined) => {
@@ -1283,7 +1299,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
             if !binding.vis.is_at_least(import.vis, this.tcx) {
                 reexport_error = Some((ns, binding));
-                if let ty::Visibility::Restricted(binding_def_id) = binding.vis
+                if let Visibility::Restricted(binding_def_id) = binding.vis
                     && binding_def_id.is_top_level_module()
                 {
                     crate_private_reexport = true;
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index 44a567f7810..93cec8daa5a 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -28,7 +28,7 @@ use rustc_hir::def::{self, CtorKind, DefKind, LifetimeRes, NonMacroAttrKind, Par
 use rustc_hir::def_id::{CRATE_DEF_ID, DefId, LOCAL_CRATE, LocalDefId};
 use rustc_hir::{MissingLifetimeKind, PrimTy, TraitCandidate};
 use rustc_middle::middle::resolve_bound_vars::Set1;
-use rustc_middle::ty::DelegationFnSig;
+use rustc_middle::ty::{DelegationFnSig, Visibility};
 use rustc_middle::{bug, span_bug};
 use rustc_session::config::{CrateType, ResolveDocLinks};
 use rustc_session::lint::{self, BuiltinLintDiag};
@@ -638,8 +638,8 @@ impl PathSource<'_, '_, '_> {
 enum MaybeExported<'a> {
     Ok(NodeId),
     Impl(Option<DefId>),
-    ImplItem(Result<DefId, &'a Visibility>),
-    NestedUse(&'a Visibility),
+    ImplItem(Result<DefId, &'a ast::Visibility>),
+    NestedUse(&'a ast::Visibility),
 }
 
 impl MaybeExported<'_> {
@@ -2491,7 +2491,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
 
     /// Searches the current set of local scopes for labels. Returns the `NodeId` of the resolved
     /// label and reports an error if the label is not found or is unreachable.
-    fn resolve_label(&mut self, mut label: Ident) -> Result<(NodeId, Span), ResolutionError<'ra>> {
+    fn resolve_label(&self, mut label: Ident) -> Result<(NodeId, Span), ResolutionError<'ra>> {
         let mut suggestion = None;
 
         for i in (0..self.label_ribs.len()).rev() {
@@ -2899,9 +2899,21 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
                 }
 
                 if param.ident.name == kw::UnderscoreLifetime {
+                    // To avoid emitting two similar errors,
+                    // we need to check if the span is a raw underscore lifetime, see issue #143152
+                    let is_raw_underscore_lifetime = self
+                        .r
+                        .tcx
+                        .sess
+                        .psess
+                        .raw_identifier_spans
+                        .iter()
+                        .any(|span| span == param.span());
+
                     self.r
                         .dcx()
-                        .emit_err(errors::UnderscoreLifetimeIsReserved { span: param.ident.span });
+                        .create_err(errors::UnderscoreLifetimeIsReserved { span: param.ident.span })
+                        .emit_unless(is_raw_underscore_lifetime);
                     // Record lifetime res, so lowering knows there is something fishy.
                     self.record_lifetime_param(param.id, LifetimeRes::Error);
                     continue;
@@ -3463,7 +3475,7 @@ impl<'a, 'ast, 'ra, 'tcx> LateResolutionVisitor<'a, 'ast, 'ra, 'tcx> {
                     span,
                     "error should be emitted when an unexpected trait item is used",
                 );
-                rustc_middle::ty::Visibility::Public
+                Visibility::Public
             };
             this.r.feed_visibility(this.r.feed(id), vis);
         };
diff --git a/compiler/rustc_resolve/src/late/diagnostics.rs b/compiler/rustc_resolve/src/late/diagnostics.rs
index b669796bb02..ee462d90764 100644
--- a/compiler/rustc_resolve/src/late/diagnostics.rs
+++ b/compiler/rustc_resolve/src/late/diagnostics.rs
@@ -926,7 +926,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                     continue;
                 };
                 if let Res::Def(DefKind::Mod, module) = res.expect_full_res()
-                    && let Some(module) = self.r.get_module(module)
+                    && let module = self.r.expect_module(module)
                     && let item = path[idx + 1].ident
                     && let Some(did) = find_doc_alias_name(self.r, module, item.name)
                 {
@@ -939,7 +939,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
     }
 
     fn suggest_trait_and_bounds(
-        &mut self,
+        &self,
         err: &mut Diag<'_>,
         source: PathSource<'_, '_, '_>,
         res: Option<Res>,
@@ -1140,7 +1140,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
 
     /// Emit special messages for unresolved `Self` and `self`.
     fn suggest_self_ty(
-        &mut self,
+        &self,
         err: &mut Diag<'_>,
         source: PathSource<'_, '_, '_>,
         path: &[Segment],
@@ -1256,7 +1256,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
     }
 
     fn detect_missing_binding_available_from_pattern(
-        &mut self,
+        &self,
         err: &mut Diag<'_>,
         path: &[Segment],
         following_seg: Option<&Segment>,
@@ -1302,11 +1302,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
         }
     }
 
-    fn suggest_at_operator_in_slice_pat_with_range(
-        &mut self,
-        err: &mut Diag<'_>,
-        path: &[Segment],
-    ) {
+    fn suggest_at_operator_in_slice_pat_with_range(&self, err: &mut Diag<'_>, path: &[Segment]) {
         let Some(pat) = self.diag_metadata.current_pat else { return };
         let (bound, side, range) = match &pat.kind {
             ast::PatKind::Range(Some(bound), None, range) => (bound, Side::Start, range),
@@ -1367,7 +1363,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
     }
 
     fn explain_functions_in_pattern(
-        &mut self,
+        &self,
         err: &mut Diag<'_>,
         res: Option<Res>,
         source: PathSource<'_, '_, '_>,
@@ -1379,7 +1375,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
     }
 
     fn suggest_changing_type_to_const_param(
-        &mut self,
+        &self,
         err: &mut Diag<'_>,
         res: Option<Res>,
         source: PathSource<'_, '_, '_>,
@@ -1429,7 +1425,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
     }
 
     fn suggest_pattern_match_with_let(
-        &mut self,
+        &self,
         err: &mut Diag<'_>,
         source: PathSource<'_, '_, '_>,
         span: Span,
@@ -1485,7 +1481,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
     }
 
     /// Given `where <T as Bar>::Baz: String`, suggest `where T: Bar<Baz = String>`.
-    fn restrict_assoc_type_in_where_clause(&mut self, span: Span, err: &mut Diag<'_>) -> bool {
+    fn restrict_assoc_type_in_where_clause(&self, span: Span, err: &mut Diag<'_>) -> bool {
         // Detect that we are actually in a `where` predicate.
         let (bounded_ty, bounds, where_span) = if let Some(ast::WherePredicate {
             kind:
@@ -1633,7 +1629,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
         let ns = source.namespace();
         let is_expected = &|res| source.is_expected(res);
 
-        let path_sep = |this: &mut Self, err: &mut Diag<'_>, expr: &Expr, kind: DefKind| {
+        let path_sep = |this: &Self, err: &mut Diag<'_>, expr: &Expr, kind: DefKind| {
             const MESSAGE: &str = "use the path separator to refer to an item";
 
             let (lhs_span, rhs_span) = match &expr.kind {
@@ -2531,16 +2527,14 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                     // FIXME: this is not totally accurate, but mostly works
                     suggestion.candidate != following_seg.ident.name
                 }
-                Res::Def(DefKind::Mod, def_id) => self.r.get_module(def_id).map_or_else(
-                    || false,
-                    |module| {
-                        self.r
-                            .resolutions(module)
-                            .borrow()
-                            .iter()
-                            .any(|(key, _)| key.ident.name == following_seg.ident.name)
-                    },
-                ),
+                Res::Def(DefKind::Mod, def_id) => {
+                    let module = self.r.expect_module(def_id);
+                    self.r
+                        .resolutions(module)
+                        .borrow()
+                        .iter()
+                        .any(|(key, _)| key.ident.name == following_seg.ident.name)
+                }
                 _ => true,
             });
         }
@@ -2589,7 +2583,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
 
     // try to give a suggestion for this pattern: `name = blah`, which is common in other languages
     // suggest `let name = blah` to introduce a new binding
-    fn let_binding_suggestion(&mut self, err: &mut Diag<'_>, ident_span: Span) -> bool {
+    fn let_binding_suggestion(&self, err: &mut Diag<'_>, ident_span: Span) -> bool {
         if ident_span.from_expansion() {
             return false;
         }
@@ -2656,18 +2650,17 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                 if result.is_some() || !name_binding.vis.is_visible_locally() {
                     return;
                 }
-                if let Some(module) = name_binding.module() {
+                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));
-                    let module_def_id = module.def_id();
                     let doc_visible = doc_visible
                         && (module_def_id.is_local() || !r.tcx.is_doc_hidden(module_def_id));
                     if module_def_id == def_id {
                         let path =
                             Path { span: name_binding.span, segments: path_segments, tokens: None };
                         result = Some((
-                            module,
+                            r.expect_module(module_def_id),
                             ImportSuggestion {
                                 did: Some(def_id),
                                 descr: "module",
@@ -2682,6 +2675,7 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                     } else {
                         // add the module to the lookup
                         if seen_modules.insert(module_def_id) {
+                            let module = r.expect_module(module_def_id);
                             worklist.push((module, path_segments, doc_visible));
                         }
                     }
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index c2b3451d4a1..dae30b77ec1 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/compiler/rustc_resolve/src/lib.rs
@@ -65,7 +65,7 @@ use rustc_middle::query::Providers;
 use rustc_middle::span_bug;
 use rustc_middle::ty::{
     self, DelegationFnSig, Feed, MainDefinition, RegisteredTools, ResolverGlobalCtxt,
-    ResolverOutputs, TyCtxt, TyCtxtFeed,
+    ResolverOutputs, TyCtxt, TyCtxtFeed, Visibility,
 };
 use rustc_query_system::ich::StableHashingContext;
 use rustc_session::lint::builtin::PRIVATE_MACRO_USE;
@@ -579,12 +579,16 @@ 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>)]>>>,
+    traits: RefCell<Option<Box<[(Ident, NameBinding<'ra>, Option<Module<'ra>>)]>>>,
 
     /// Span of the module itself. Used for error reporting.
     span: Span,
 
     expansion: ExpnId,
+
+    /// Binding for implicitly declared names that come with a module,
+    /// like `self` (not yet used), or `crate`/`$crate` (for root modules).
+    self_binding: Option<NameBinding<'ra>>,
 }
 
 /// All modules are unique and allocated on a same arena,
@@ -613,6 +617,7 @@ impl<'ra> ModuleData<'ra> {
         expansion: ExpnId,
         span: Span,
         no_implicit_prelude: bool,
+        self_binding: Option<NameBinding<'ra>>,
     ) -> Self {
         let is_foreign = match kind {
             ModuleKind::Def(_, def_id, _) => !def_id.is_local(),
@@ -630,6 +635,7 @@ impl<'ra> ModuleData<'ra> {
             traits: RefCell::new(None),
             span,
             expansion,
+            self_binding,
         }
     }
 }
@@ -655,12 +661,12 @@ impl<'ra> Module<'ra> {
         let mut traits = self.traits.borrow_mut();
         if traits.is_none() {
             let mut collected_traits = Vec::new();
-            self.for_each_child(resolver, |_, name, ns, binding| {
+            self.for_each_child(resolver, |r, name, ns, binding| {
                 if ns != TypeNS {
                     return;
                 }
-                if let Res::Def(DefKind::Trait | DefKind::TraitAlias, _) = binding.res() {
-                    collected_traits.push((name, binding))
+                if let Res::Def(DefKind::Trait | DefKind::TraitAlias, def_id) = binding.res() {
+                    collected_traits.push((name, binding, r.as_mut().get_module(def_id)))
                 }
             });
             *traits = Some(collected_traits.into_boxed_slice());
@@ -674,7 +680,6 @@ impl<'ra> Module<'ra> {
         }
     }
 
-    // Public for rustdoc.
     fn def_id(self) -> DefId {
         self.opt_def_id().expect("`ModuleData::def_id` is called on a block module")
     }
@@ -749,7 +754,7 @@ struct NameBindingData<'ra> {
     warn_ambiguity: bool,
     expansion: LocalExpnId,
     span: Span,
-    vis: ty::Visibility<DefId>,
+    vis: Visibility<DefId>,
 }
 
 /// All name bindings are unique and allocated on a same arena,
@@ -769,20 +774,9 @@ impl std::hash::Hash for NameBindingData<'_> {
     }
 }
 
-trait ToNameBinding<'ra> {
-    fn to_name_binding(self, arenas: &'ra ResolverArenas<'ra>) -> NameBinding<'ra>;
-}
-
-impl<'ra> ToNameBinding<'ra> for NameBinding<'ra> {
-    fn to_name_binding(self, _: &'ra ResolverArenas<'ra>) -> NameBinding<'ra> {
-        self
-    }
-}
-
 #[derive(Clone, Copy, Debug)]
 enum NameBindingKind<'ra> {
     Res(Res),
-    Module(Module<'ra>),
     Import { binding: NameBinding<'ra>, import: Import<'ra> },
 }
 
@@ -875,18 +869,9 @@ struct AmbiguityError<'ra> {
 }
 
 impl<'ra> NameBindingData<'ra> {
-    fn module(&self) -> Option<Module<'ra>> {
-        match self.kind {
-            NameBindingKind::Module(module) => Some(module),
-            NameBindingKind::Import { binding, .. } => binding.module(),
-            _ => None,
-        }
-    }
-
     fn res(&self) -> Res {
         match self.kind {
             NameBindingKind::Res(res) => res,
-            NameBindingKind::Module(module) => module.res().unwrap(),
             NameBindingKind::Import { binding, .. } => binding.res(),
         }
     }
@@ -921,7 +906,7 @@ impl<'ra> NameBindingData<'ra> {
                 DefKind::Variant | DefKind::Ctor(CtorOf::Variant, ..),
                 _,
             )) => true,
-            NameBindingKind::Res(..) | NameBindingKind::Module(..) => false,
+            NameBindingKind::Res(..) => false,
         }
     }
 
@@ -930,11 +915,7 @@ impl<'ra> NameBindingData<'ra> {
             NameBindingKind::Import { import, .. } => {
                 matches!(import.kind, ImportKind::ExternCrate { .. })
             }
-            NameBindingKind::Module(module)
-                if let ModuleKind::Def(DefKind::Mod, def_id, _) = module.kind =>
-            {
-                def_id.is_crate_root()
-            }
+            NameBindingKind::Res(Res::Def(_, def_id)) => def_id.is_crate_root(),
             _ => false,
         }
     }
@@ -1100,7 +1081,10 @@ pub struct Resolver<'ra, 'tcx> {
     /// some AST passes can generate identifiers that only resolve to local or
     /// lang items.
     empty_module: Module<'ra>,
-    module_map: FxIndexMap<DefId, Module<'ra>>,
+    /// Eagerly populated map of all local non-block modules.
+    local_module_map: FxIndexMap<LocalDefId, Module<'ra>>,
+    /// Lazily populated cache of modules loaded from external crates.
+    extern_module_map: RefCell<FxIndexMap<DefId, Module<'ra>>>,
     binding_parent_modules: FxHashMap<NameBinding<'ra>, Module<'ra>>,
 
     underscore_disambiguator: u32,
@@ -1108,7 +1092,7 @@ 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, ty::Visibility)>,
+    visibilities_for_hashing: Vec<(LocalDefId, Visibility)>,
     used_imports: FxHashSet<NodeId>,
     maybe_unused_trait_imports: FxIndexSet<LocalDefId>,
 
@@ -1126,17 +1110,14 @@ pub struct Resolver<'ra, 'tcx> {
     builtin_types_bindings: FxHashMap<Symbol, NameBinding<'ra>>,
     builtin_attrs_bindings: FxHashMap<Symbol, NameBinding<'ra>>,
     registered_tool_bindings: FxHashMap<Ident, NameBinding<'ra>>,
-    /// Binding for implicitly declared names that come with a module,
-    /// like `self` (not yet used), or `crate`/`$crate` (for root modules).
-    module_self_bindings: FxHashMap<Module<'ra>, NameBinding<'ra>>,
-
     used_extern_options: FxHashSet<Symbol>,
     macro_names: FxHashSet<Ident>,
     builtin_macros: FxHashMap<Symbol, SyntaxExtensionKind>,
     registered_tools: &'tcx RegisteredTools,
     macro_use_prelude: FxIndexMap<Symbol, NameBinding<'ra>>,
+    /// Eagerly populated map of all local macro definitions.
     local_macro_map: FxHashMap<LocalDefId, &'ra MacroData>,
-    /// Lazily populated cache of macros loaded from external crates.
+    /// Lazily populated cache of macro definitions loaded from external crates.
     extern_macro_map: RefCell<FxHashMap<DefId, &'ra MacroData>>,
     dummy_ext_bang: Arc<SyntaxExtension>,
     dummy_ext_derive: Arc<SyntaxExtension>,
@@ -1181,7 +1162,7 @@ pub struct Resolver<'ra, 'tcx> {
     /// Table for mapping struct IDs into struct constructor IDs,
     /// it's not used during normal resolution, only for better error reporting.
     /// Also includes of list of each fields visibility
-    struct_constructors: LocalDefIdMap<(Res, ty::Visibility<DefId>, Vec<ty::Visibility<DefId>>)>,
+    struct_constructors: LocalDefIdMap<(Res, Visibility<DefId>, Vec<Visibility<DefId>>)>,
 
     lint_buffer: LintBuffer,
 
@@ -1255,6 +1236,32 @@ pub struct ResolverArenas<'ra> {
 }
 
 impl<'ra> ResolverArenas<'ra> {
+    fn new_res_binding(
+        &'ra self,
+        res: Res,
+        vis: Visibility<DefId>,
+        span: Span,
+        expansion: LocalExpnId,
+    ) -> NameBinding<'ra> {
+        self.alloc_name_binding(NameBindingData {
+            kind: NameBindingKind::Res(res),
+            ambiguity: None,
+            warn_ambiguity: false,
+            vis,
+            span,
+            expansion,
+        })
+    }
+
+    fn new_pub_res_binding(
+        &'ra self,
+        res: Res,
+        span: Span,
+        expn_id: LocalExpnId,
+    ) -> NameBinding<'ra> {
+        self.new_res_binding(res, Visibility::Public, span, expn_id)
+    }
+
     fn new_module(
         &'ra self,
         parent: Option<Module<'ra>>,
@@ -1262,26 +1269,25 @@ impl<'ra> ResolverArenas<'ra> {
         expn_id: ExpnId,
         span: Span,
         no_implicit_prelude: bool,
-        module_map: &mut FxIndexMap<DefId, Module<'ra>>,
-        module_self_bindings: &mut FxHashMap<Module<'ra>, NameBinding<'ra>>,
     ) -> Module<'ra> {
+        let (def_id, self_binding) = match kind {
+            ModuleKind::Def(def_kind, def_id, _) => (
+                Some(def_id),
+                Some(self.new_pub_res_binding(Res::Def(def_kind, def_id), span, LocalExpnId::ROOT)),
+            ),
+            ModuleKind::Block => (None, None),
+        };
         let module = Module(Interned::new_unchecked(self.modules.alloc(ModuleData::new(
             parent,
             kind,
             expn_id,
             span,
             no_implicit_prelude,
+            self_binding,
         ))));
-        let def_id = module.opt_def_id();
         if def_id.is_none_or(|def_id| def_id.is_local()) {
             self.local_modules.borrow_mut().push(module);
         }
-        if let Some(def_id) = def_id {
-            module_map.insert(def_id, module);
-            let vis = ty::Visibility::<DefId>::Public;
-            let binding = (module, vis, module.span, LocalExpnId::ROOT).to_name_binding(self);
-            module_self_bindings.insert(module, binding);
-        }
         module
     }
     fn local_modules(&'ra self) -> std::cell::Ref<'ra, Vec<Module<'ra>>> {
@@ -1422,25 +1428,21 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         arenas: &'ra ResolverArenas<'ra>,
     ) -> Resolver<'ra, 'tcx> {
         let root_def_id = CRATE_DEF_ID.to_def_id();
-        let mut module_map = FxIndexMap::default();
-        let mut module_self_bindings = FxHashMap::default();
+        let mut local_module_map = FxIndexMap::default();
         let graph_root = arenas.new_module(
             None,
             ModuleKind::Def(DefKind::Mod, root_def_id, None),
             ExpnId::root(),
             crate_span,
             attr::contains_name(attrs, sym::no_implicit_prelude),
-            &mut module_map,
-            &mut module_self_bindings,
         );
+        local_module_map.insert(CRATE_DEF_ID, graph_root);
         let empty_module = arenas.new_module(
             None,
             ModuleKind::Def(DefKind::Mod, root_def_id, None),
             ExpnId::root(),
             DUMMY_SP,
             true,
-            &mut Default::default(),
-            &mut Default::default(),
         );
 
         let mut node_id_to_def_id = NodeMap::default();
@@ -1470,8 +1472,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         }
 
         let registered_tools = tcx.registered_tools(());
-
-        let pub_vis = ty::Visibility::<DefId>::Public;
         let edition = tcx.sess.edition();
 
         let mut resolver = Resolver {
@@ -1503,7 +1503,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             trait_map: NodeMap::default(),
             underscore_disambiguator: 0,
             empty_module,
-            module_map,
+            local_module_map,
+            extern_module_map: Default::default(),
             block_map: Default::default(),
             binding_parent_modules: FxHashMap::default(),
             ast_transform_scopes: FxHashMap::default(),
@@ -1520,12 +1521,12 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             macro_expanded_macro_export_errors: BTreeSet::new(),
 
             arenas,
-            dummy_binding: (Res::Err, pub_vis, DUMMY_SP, LocalExpnId::ROOT).to_name_binding(arenas),
+            dummy_binding: arenas.new_pub_res_binding(Res::Err, DUMMY_SP, LocalExpnId::ROOT),
             builtin_types_bindings: PrimTy::ALL
                 .iter()
                 .map(|prim_ty| {
-                    let binding = (Res::PrimTy(*prim_ty), pub_vis, DUMMY_SP, LocalExpnId::ROOT)
-                        .to_name_binding(arenas);
+                    let res = Res::PrimTy(*prim_ty);
+                    let binding = arenas.new_pub_res_binding(res, DUMMY_SP, LocalExpnId::ROOT);
                     (prim_ty.name(), binding)
                 })
                 .collect(),
@@ -1533,21 +1534,18 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 .iter()
                 .map(|builtin_attr| {
                     let res = Res::NonMacroAttr(NonMacroAttrKind::Builtin(builtin_attr.name));
-                    let binding =
-                        (res, pub_vis, DUMMY_SP, LocalExpnId::ROOT).to_name_binding(arenas);
+                    let binding = arenas.new_pub_res_binding(res, DUMMY_SP, LocalExpnId::ROOT);
                     (builtin_attr.name, binding)
                 })
                 .collect(),
             registered_tool_bindings: registered_tools
                 .iter()
                 .map(|ident| {
-                    let binding = (Res::ToolMod, pub_vis, ident.span, LocalExpnId::ROOT)
-                        .to_name_binding(arenas);
+                    let res = Res::ToolMod;
+                    let binding = arenas.new_pub_res_binding(res, ident.span, LocalExpnId::ROOT);
                     (*ident, binding)
                 })
                 .collect(),
-            module_self_bindings,
-
             used_extern_options: Default::default(),
             macro_names: FxHashSet::default(),
             builtin_macros: Default::default(),
@@ -1605,12 +1603,12 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
 
         let root_parent_scope = ParentScope::module(graph_root, &resolver);
         resolver.invocation_parent_scopes.insert(LocalExpnId::ROOT, root_parent_scope);
-        resolver.feed_visibility(crate_feed, ty::Visibility::Public);
+        resolver.feed_visibility(crate_feed, Visibility::Public);
 
         resolver
     }
 
-    fn new_module(
+    fn new_local_module(
         &mut self,
         parent: Option<Module<'ra>>,
         kind: ModuleKind,
@@ -1618,17 +1616,24 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         span: Span,
         no_implicit_prelude: bool,
     ) -> Module<'ra> {
-        let module_map = &mut self.module_map;
-        let module_self_bindings = &mut self.module_self_bindings;
-        self.arenas.new_module(
-            parent,
-            kind,
-            expn_id,
-            span,
-            no_implicit_prelude,
-            module_map,
-            module_self_bindings,
-        )
+        let module = self.arenas.new_module(parent, kind, expn_id, span, no_implicit_prelude);
+        if let Some(def_id) = module.opt_def_id() {
+            self.local_module_map.insert(def_id.expect_local(), module);
+        }
+        module
+    }
+
+    fn new_extern_module(
+        &self,
+        parent: Option<Module<'ra>>,
+        kind: ModuleKind,
+        expn_id: ExpnId,
+        span: Span,
+        no_implicit_prelude: bool,
+    ) -> Module<'ra> {
+        let module = self.arenas.new_module(parent, kind, expn_id, span, no_implicit_prelude);
+        self.extern_module_map.borrow_mut().insert(module.def_id(), module);
+        module
     }
 
     fn new_local_macro(&mut self, def_id: LocalDefId, macro_data: MacroData) -> &'ra MacroData {
@@ -1659,7 +1664,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         Default::default()
     }
 
-    fn feed_visibility(&mut self, feed: Feed<'tcx, LocalDefId>, vis: ty::Visibility) {
+    fn feed_visibility(&mut self, feed: Feed<'tcx, LocalDefId>, vis: Visibility) {
         let feed = feed.upgrade(self.tcx);
         feed.visibility(vis.to_def_id());
         self.visibilities_for_hashing.push((feed.def_id(), vis));
@@ -1775,9 +1780,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             let exported_ambiguities = self.tcx.sess.time("compute_effective_visibilities", || {
                 EffectiveVisibilitiesVisitor::compute_effective_visibilities(self, krate)
             });
-            self.tcx.sess.time("check_hidden_glob_reexports", || {
-                self.check_hidden_glob_reexports(exported_ambiguities)
-            });
+            self.tcx.sess.time("lint_reexports", || self.lint_reexports(exported_ambiguities));
             self.tcx
                 .sess
                 .time("finalize_macro_resolutions", || self.finalize_macro_resolutions(krate));
@@ -1837,10 +1840,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     ) {
         module.ensure_traits(self);
         let traits = module.traits.borrow();
-        for (trait_name, trait_binding) in traits.as_ref().unwrap().iter() {
-            if self.trait_may_have_item(trait_binding.module(), assoc_item) {
+        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);
                 found_traits.push(TraitCandidate { def_id, import_ids });
             }
         }
@@ -2016,7 +2019,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         }
     }
 
-    fn resolve_crate_root(&mut self, ident: Ident) -> Module<'ra> {
+    fn resolve_crate_root(&self, ident: Ident) -> Module<'ra> {
         debug!("resolve_crate_root({:?})", ident);
         let mut ctxt = ident.span.ctxt();
         let mark = if ident.name == kw::DollarCrate {
@@ -2089,7 +2092,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         module
     }
 
-    fn resolve_self(&mut self, ctxt: &mut SyntaxContext, module: Module<'ra>) -> Module<'ra> {
+    fn resolve_self(&self, ctxt: &mut SyntaxContext, module: Module<'ra>) -> Module<'ra> {
         let mut module = self.expect_module(module.nearest_parent_mod());
         while module.span.ctxt().normalize_to_macros_2_0() != *ctxt {
             let parent = module.parent.unwrap_or_else(|| self.expn_def_scope(ctxt.remove_mark()));
@@ -2110,11 +2113,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         self.pat_span_map.insert(node, span);
     }
 
-    fn is_accessible_from(
-        &self,
-        vis: ty::Visibility<impl Into<DefId>>,
-        module: Module<'ra>,
-    ) -> bool {
+    fn is_accessible_from(&self, vis: Visibility<impl Into<DefId>>, module: Module<'ra>) -> bool {
         vis.is_accessible_from(module.nearest_parent_mod(), self.tcx)
     }
 
@@ -2174,9 +2173,8 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 } else {
                     self.crate_loader(|c| c.maybe_process_path_extern(ident.name))?
                 };
-                let crate_root = self.expect_module(crate_id.as_def_id());
-                let vis = ty::Visibility::<DefId>::Public;
-                (crate_root, vis, DUMMY_SP, LocalExpnId::ROOT).to_name_binding(self.arenas)
+                let res = Res::Def(DefKind::Mod, crate_id.as_def_id());
+                self.arenas.new_pub_res_binding(res, DUMMY_SP, LocalExpnId::ROOT)
             })
         });
 
diff --git a/compiler/rustc_resolve/src/macros.rs b/compiler/rustc_resolve/src/macros.rs
index cbb24289f51..77ef7f56c09 100644
--- a/compiler/rustc_resolve/src/macros.rs
+++ b/compiler/rustc_resolve/src/macros.rs
@@ -20,7 +20,7 @@ use rustc_expand::expand::{
 use rustc_hir::def::{self, DefKind, Namespace, NonMacroAttrKind};
 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId};
 use rustc_middle::middle::stability;
-use rustc_middle::ty::{RegisteredTools, TyCtxt, Visibility};
+use rustc_middle::ty::{RegisteredTools, TyCtxt};
 use rustc_session::lint::BuiltinLintDiag;
 use rustc_session::lint::builtin::{
     LEGACY_DERIVE_HELPERS, OUT_OF_SCOPE_MACRO_CALLS, UNKNOWN_DIAGNOSTIC_ATTRIBUTES,
@@ -41,7 +41,7 @@ use crate::imports::Import;
 use crate::{
     BindingKey, DeriveData, Determinacy, Finalize, InvocationParent, MacroData, ModuleKind,
     ModuleOrUniformRoot, NameBinding, NameBindingKind, ParentScope, PathResult, ResolutionError,
-    Resolver, ScopeSet, Segment, ToNameBinding, Used,
+    Resolver, ScopeSet, Segment, Used,
 };
 
 type Res = def::Res<NodeId>;
@@ -170,7 +170,7 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
         self.invocation_parents[&id].parent_def
     }
 
-    fn resolve_dollar_crates(&mut self) {
+    fn resolve_dollar_crates(&self) {
         hygiene::update_dollar_crate_names(|ctxt| {
             let ident = Ident::new(kw::DollarCrate, DUMMY_SP.with_ctxt(ctxt));
             match self.resolve_crate_root(ident).kind {
@@ -436,8 +436,7 @@ impl<'ra, 'tcx> ResolverExpand for Resolver<'ra, 'tcx> {
             .iter()
             .map(|(_, ident)| {
                 let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
-                let binding = (res, Visibility::<DefId>::Public, ident.span, expn_id)
-                    .to_name_binding(self.arenas);
+                let binding = self.arenas.new_pub_res_binding(res, ident.span, expn_id);
                 (*ident, binding)
             })
             .collect();
@@ -836,7 +835,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
     }
 
     pub(crate) fn finalize_macro_resolutions(&mut self, krate: &Crate) {
-        let check_consistency = |this: &mut Self,
+        let check_consistency = |this: &Self,
                                  path: &[Segment],
                                  span,
                                  kind: MacroKind,
diff --git a/compiler/rustc_resolve/src/rustdoc.rs b/compiler/rustc_resolve/src/rustdoc.rs
index f61cd1f0adf..24e15ded94f 100644
--- a/compiler/rustc_resolve/src/rustdoc.rs
+++ b/compiler/rustc_resolve/src/rustdoc.rs
@@ -7,6 +7,7 @@ use pulldown_cmark::{
 };
 use rustc_ast as ast;
 use rustc_ast::attr::AttributeExt;
+use rustc_ast::join_path_syms;
 use rustc_ast::util::comments::beautify_doc_string;
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::unord::UnordSet;
@@ -259,7 +260,7 @@ pub fn main_body_opts() -> Options {
         | Options::ENABLE_SMART_PUNCTUATION
 }
 
-fn strip_generics_from_path_segment(segment: Vec<char>) -> Result<String, MalformedGenerics> {
+fn strip_generics_from_path_segment(segment: Vec<char>) -> Result<Symbol, MalformedGenerics> {
     let mut stripped_segment = String::new();
     let mut param_depth = 0;
 
@@ -284,7 +285,7 @@ fn strip_generics_from_path_segment(segment: Vec<char>) -> Result<String, Malfor
     }
 
     if param_depth == 0 {
-        Ok(stripped_segment)
+        Ok(Symbol::intern(&stripped_segment))
     } else {
         // The segment has unbalanced angle brackets, e.g. `Vec<T` or `Vec<T>>`
         Err(MalformedGenerics::UnbalancedAngleBrackets)
@@ -346,9 +347,8 @@ pub fn strip_generics_from_path(path_str: &str) -> Result<Box<str>, MalformedGen
 
     debug!("path_str: {path_str:?}\nstripped segments: {stripped_segments:?}");
 
-    let stripped_path = stripped_segments.join("::");
-
-    if !stripped_path.is_empty() {
+    if !stripped_segments.is_empty() {
+        let stripped_path = join_path_syms(stripped_segments);
         Ok(stripped_path.into())
     } else {
         Err(MalformedGenerics::MissingType)
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index a91e2140fd4..d6215e1de04 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -1708,6 +1708,11 @@ impl RustcOptGroup {
             OptionKind::FlagMulti => options.optflagmulti(short_name, long_name, desc),
         };
     }
+
+    /// This is for diagnostics-only.
+    pub fn long_name(&self) -> &str {
+        self.long_name
+    }
 }
 
 pub fn make_opt(
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 626262c8442..2bdde2f887a 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -2256,6 +2256,8 @@ options! {
         environment variable `RUSTC_GRAPHVIZ_FONT` (default: `Courier, monospace`)"),
     has_thread_local: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "explicitly enable the `cfg(target_thread_local)` directive"),
+    higher_ranked_assumptions: bool = (false, parse_bool, [TRACKED],
+        "allow deducing higher-ranked outlives assumptions from coroutines when proving auto traits"),
     hint_mostly_unused: bool = (false, parse_bool, [TRACKED],
         "hint that most of this crate will go unused, to minimize work for uncalled functions"),
     human_readable_cgu_names: bool = (false, parse_bool, [TRACKED],
diff --git a/compiler/rustc_session/src/parse.rs b/compiler/rustc_session/src/parse.rs
index 0118cdb1fc2..9097b27b86c 100644
--- a/compiler/rustc_session/src/parse.rs
+++ b/compiler/rustc_session/src/parse.rs
@@ -205,6 +205,46 @@ pub fn add_feature_diagnostics_for_issue<G: EmissionGuarantee>(
     }
 }
 
+/// This is only used by unstable_feature_bound as it does not have issue number information for now.
+/// This is basically the same as `feature_err_issue`
+/// but without the feature issue note. If we can do a lookup for issue number from feature name,
+/// then we should directly use `feature_err_issue` for ambiguity error of
+/// `#[unstable_feature_bound]`.
+#[track_caller]
+pub fn feature_err_unstable_feature_bound(
+    sess: &Session,
+    feature: Symbol,
+    span: impl Into<MultiSpan>,
+    explain: impl Into<DiagMessage>,
+) -> Diag<'_> {
+    let span = span.into();
+
+    // Cancel an earlier warning for this same error, if it exists.
+    if let Some(span) = span.primary_span() {
+        if let Some(err) = sess.dcx().steal_non_err(span, StashKey::EarlySyntaxWarning) {
+            err.cancel()
+        }
+    }
+
+    let mut err = sess.dcx().create_err(FeatureGateError { span, explain: explain.into() });
+
+    // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
+    if sess.psess.unstable_features.is_nightly_build() {
+        err.subdiagnostic(FeatureDiagnosticHelp { feature });
+
+        if feature == sym::rustc_attrs {
+            // We're unlikely to stabilize something out of `rustc_attrs`
+            // without at least renaming it, so pointing out how old
+            // the compiler is will do little good.
+        } else if sess.opts.unstable_opts.ui_testing {
+            err.subdiagnostic(SuggestUpgradeCompiler::ui_testing());
+        } else if let Some(suggestion) = SuggestUpgradeCompiler::new() {
+            err.subdiagnostic(suggestion);
+        }
+    }
+    err
+}
+
 /// Info about a parsing session.
 pub struct ParseSess {
     dcx: DiagCtxt,
diff --git a/compiler/rustc_span/src/def_id.rs b/compiler/rustc_span/src/def_id.rs
index 641bac88ad0..77f01548bca 100644
--- a/compiler/rustc_span/src/def_id.rs
+++ b/compiler/rustc_span/src/def_id.rs
@@ -110,6 +110,7 @@ impl DefPathHash {
 
     /// Builds a new [DefPathHash] with the given [StableCrateId] and
     /// `local_hash`, where `local_hash` must be unique within its crate.
+    #[inline]
     pub fn new(stable_crate_id: StableCrateId, local_hash: Hash64) -> DefPathHash {
         DefPathHash(Fingerprint::new(stable_crate_id.0, local_hash))
     }
@@ -404,21 +405,21 @@ rustc_data_structures::define_id_collections!(
 impl<CTX: HashStableContext> HashStable<CTX> for DefId {
     #[inline]
     fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
-        self.to_stable_hash_key(hcx).hash_stable(hcx, hasher);
+        hcx.def_path_hash(*self).hash_stable(hcx, hasher);
     }
 }
 
 impl<CTX: HashStableContext> HashStable<CTX> for LocalDefId {
     #[inline]
     fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
-        self.to_stable_hash_key(hcx).hash_stable(hcx, hasher);
+        hcx.def_path_hash(self.to_def_id()).local_hash().hash_stable(hcx, hasher);
     }
 }
 
 impl<CTX: HashStableContext> HashStable<CTX> for CrateNum {
     #[inline]
     fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
-        self.to_stable_hash_key(hcx).hash_stable(hcx, hasher);
+        self.as_def_id().to_stable_hash_key(hcx).stable_crate_id().hash_stable(hcx, hasher);
     }
 }
 
@@ -464,30 +465,36 @@ macro_rules! typed_def_id {
         pub struct $Name(DefId);
 
         impl $Name {
+            #[inline]
             pub const fn new_unchecked(def_id: DefId) -> Self {
                 Self(def_id)
             }
 
+            #[inline]
             pub fn to_def_id(self) -> DefId {
                 self.into()
             }
 
+            #[inline]
             pub fn is_local(self) -> bool {
                 self.0.is_local()
             }
 
+            #[inline]
             pub fn as_local(self) -> Option<$LocalName> {
                 self.0.as_local().map($LocalName::new_unchecked)
             }
         }
 
         impl From<$LocalName> for $Name {
+            #[inline]
             fn from(local: $LocalName) -> Self {
                 Self(local.0.to_def_id())
             }
         }
 
         impl From<$Name> for DefId {
+            #[inline]
             fn from(typed: $Name) -> Self {
                 typed.0
             }
@@ -500,26 +507,31 @@ macro_rules! typed_def_id {
         impl !PartialOrd for $LocalName {}
 
         impl $LocalName {
+            #[inline]
             pub const fn new_unchecked(def_id: LocalDefId) -> Self {
                 Self(def_id)
             }
 
+            #[inline]
             pub fn to_def_id(self) -> DefId {
                 self.0.into()
             }
 
+            #[inline]
             pub fn to_local_def_id(self) -> LocalDefId {
                 self.0
             }
         }
 
         impl From<$LocalName> for LocalDefId {
+            #[inline]
             fn from(typed: $LocalName) -> Self {
                 typed.0
             }
         }
 
         impl From<$LocalName> for DefId {
+            #[inline]
             fn from(typed: $LocalName) -> Self {
                 typed.0.into()
             }
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 8b12edf426c..d28a73bc139 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -715,6 +715,7 @@ symbols! {
         const_indexing,
         const_let,
         const_loop,
+        const_make_global,
         const_mut_refs,
         const_panic,
         const_panic_fmt,
@@ -839,6 +840,7 @@ symbols! {
         derive,
         derive_coerce_pointee,
         derive_const,
+        derive_const_issue: "118304",
         derive_default_enum,
         derive_smart_pointer,
         destruct,
@@ -2284,6 +2286,7 @@ symbols! {
         unsized_locals,
         unsized_tuple_coercion,
         unstable,
+        unstable_feature_bound,
         unstable_location_reason_default: "this crate is being loaded from the sysroot, an \
                           unstable location; did you mean to load this crate \
                           from crates.io via `Cargo.toml` instead?",
diff --git a/compiler/rustc_symbol_mangling/src/lib.rs b/compiler/rustc_symbol_mangling/src/lib.rs
index a9bf5eae445..6bcb7f6e093 100644
--- a/compiler/rustc_symbol_mangling/src/lib.rs
+++ b/compiler/rustc_symbol_mangling/src/lib.rs
@@ -180,7 +180,7 @@ fn compute_symbol_name<'tcx>(
 
     // FIXME(eddyb) Precompute a custom symbol name based on attributes.
     let attrs = if tcx.def_kind(def_id).has_codegen_attrs() {
-        tcx.codegen_fn_attrs(def_id)
+        &tcx.codegen_instance_attrs(instance.def)
     } else {
         CodegenFnAttrs::EMPTY
     };
diff --git a/compiler/rustc_target/src/spec/targets/mips64_unknown_linux_muslabi64.rs b/compiler/rustc_target/src/spec/targets/mips64_unknown_linux_muslabi64.rs
index fd509503053..f95ce756354 100644
--- a/compiler/rustc_target/src/spec/targets/mips64_unknown_linux_muslabi64.rs
+++ b/compiler/rustc_target/src/spec/targets/mips64_unknown_linux_muslabi64.rs
@@ -5,7 +5,7 @@ use crate::spec::{Target, TargetMetadata, TargetOptions, base};
 pub(crate) fn target() -> Target {
     let mut base = base::linux_musl::opts();
     base.cpu = "mips64r2".into();
-    base.features = "+mips64r2".into();
+    base.features = "+mips64r2,+xgot".into();
     base.max_atomic_width = Some(64);
     Target {
         // LLVM doesn't recognize "muslabi64" yet.
diff --git a/compiler/rustc_target/src/spec/targets/mips64el_unknown_linux_muslabi64.rs b/compiler/rustc_target/src/spec/targets/mips64el_unknown_linux_muslabi64.rs
index aa087b1a35a..d42e097b0fd 100644
--- a/compiler/rustc_target/src/spec/targets/mips64el_unknown_linux_muslabi64.rs
+++ b/compiler/rustc_target/src/spec/targets/mips64el_unknown_linux_muslabi64.rs
@@ -3,7 +3,7 @@ use crate::spec::{Target, TargetMetadata, TargetOptions, base};
 pub(crate) fn target() -> Target {
     let mut base = base::linux_musl::opts();
     base.cpu = "mips64r2".into();
-    base.features = "+mips64r2".into();
+    base.features = "+mips64r2,+xgot".into();
     base.max_atomic_width = Some(64);
     // FIXME(compiler-team#422): musl targets should be dynamically linked by default.
     base.crt_static_default = true;
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 bc464b099e2..b9acadc406e 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs
@@ -51,6 +51,7 @@ use std::path::PathBuf;
 use std::{cmp, fmt, iter};
 
 use rustc_abi::ExternAbi;
+use rustc_ast::join_path_syms;
 use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_errors::{
     Applicability, Diag, DiagStyledString, IntoDiagArg, MultiSpan, StringPart, pluralize,
@@ -73,7 +74,7 @@ use rustc_middle::ty::{
     TypeVisitableExt,
 };
 use rustc_span::def_id::LOCAL_CRATE;
-use rustc_span::{BytePos, DUMMY_SP, DesugaringKind, Pos, Span, sym};
+use rustc_span::{BytePos, DUMMY_SP, DesugaringKind, Pos, Span, Symbol, sym};
 use tracing::{debug, instrument};
 
 use crate::error_reporting::TypeErrCtxt;
@@ -225,7 +226,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
 
         struct AbsolutePathPrinter<'tcx> {
             tcx: TyCtxt<'tcx>,
-            segments: Vec<String>,
+            segments: Vec<Symbol>,
         }
 
         impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
@@ -253,7 +254,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             }
 
             fn path_crate(&mut self, cnum: CrateNum) -> Result<(), PrintError> {
-                self.segments = vec![self.tcx.crate_name(cnum).to_string()];
+                self.segments = vec![self.tcx.crate_name(cnum)];
                 Ok(())
             }
             fn path_qualified(
@@ -279,7 +280,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 disambiguated_data: &DisambiguatedDefPathData,
             ) -> Result<(), PrintError> {
                 print_prefix(self)?;
-                self.segments.push(disambiguated_data.to_string());
+                self.segments.push(disambiguated_data.as_sym(true));
                 Ok(())
             }
             fn path_generic_args(
@@ -314,7 +315,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 // 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 {
-                    (expected_abs.join("::"), found_abs.join("::"))
+                    (join_path_syms(&expected_abs), join_path_syms(&found_abs))
                 } else {
                     (expected_str.clone(), found_str.clone())
                 };
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 712e88300ff..98f67257fd1 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/ambiguity.rs
@@ -12,6 +12,7 @@ use rustc_infer::traits::{
     Obligation, ObligationCause, ObligationCauseCode, PolyTraitObligation, PredicateObligation,
 };
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitable as _, TypeVisitableExt as _};
+use rustc_session::parse::feature_err_unstable_feature_bound;
 use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span};
 use tracing::{debug, instrument};
 
@@ -611,6 +612,30 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 )
                 .with_span_label(span, format!("cannot normalize `{alias}`"))
             }
+            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(
+                        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})]`"));
+                } else {
+                    err = 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() {
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 cd3e6c4bc54..1ac309da101 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
@@ -647,6 +647,8 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     | ty::PredicateKind::ConstEquate { .. }
                     // Ambiguous predicates should never error
                     | ty::PredicateKind::Ambiguous
+                    // We never return Err when proving UnstableFeature goal.
+                    | ty::PredicateKind::Clause(ty::ClauseKind::UnstableFeature{ .. })
                     | ty::PredicateKind::NormalizesTo { .. }
                     | ty::PredicateKind::AliasRelate { .. }
                     | ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType { .. }) => {
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 d4cc1ceb280..1d8b934cef3 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs
@@ -453,7 +453,7 @@ pub fn report_dyn_incompatibility<'tcx>(
     let trait_str = tcx.def_path_str(trait_def_id);
     let trait_span = tcx.hir_get_if_local(trait_def_id).and_then(|node| match node {
         hir::Node::Item(item) => match item.kind {
-            hir::ItemKind::Trait(_, _, ident, ..) | hir::ItemKind::TraitAlias(ident, _, _) => {
+            hir::ItemKind::Trait(_, _, _, ident, ..) | hir::ItemKind::TraitAlias(ident, _, _) => {
                 Some(ident.span)
             }
             _ => unreachable!(),
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 bd1d29826e6..bf7d4257b62 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
@@ -22,6 +22,7 @@ use rustc_hir::{
     expr_needs_parens, is_range_literal,
 };
 use rustc_infer::infer::{BoundRegionConversionTime, DefineOpaqueTypes, InferCtxt, InferOk};
+use rustc_middle::middle::privacy::Level;
 use rustc_middle::traits::IsConstable;
 use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::print::{
@@ -267,7 +268,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             let node = self.tcx.hir_node_by_def_id(body_id);
             match node {
                 hir::Node::Item(hir::Item {
-                    kind: hir::ItemKind::Trait(_, _, ident, generics, bounds, _),
+                    kind: hir::ItemKind::Trait(_, _, _, ident, generics, bounds, _),
                     ..
                 }) if self_ty == self.tcx.types.self_param => {
                     assert!(param_ty);
@@ -330,7 +331,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 }
                 hir::Node::Item(hir::Item {
                     kind:
-                        hir::ItemKind::Trait(_, _, _, generics, ..)
+                        hir::ItemKind::Trait(_, _, _, _, generics, ..)
                         | hir::ItemKind::Impl(hir::Impl { generics, .. }),
                     ..
                 }) if projection.is_some() => {
@@ -354,7 +355,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         hir::ItemKind::Struct(_, generics, _)
                         | hir::ItemKind::Enum(_, generics, _)
                         | hir::ItemKind::Union(_, generics, _)
-                        | hir::ItemKind::Trait(_, _, _, generics, ..)
+                        | hir::ItemKind::Trait(_, _, _, _, generics, ..)
                         | hir::ItemKind::Impl(hir::Impl { generics, .. })
                         | hir::ItemKind::Fn { generics, .. }
                         | hir::ItemKind::TyAlias(_, generics, _)
@@ -414,7 +415,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         hir::ItemKind::Struct(_, generics, _)
                         | hir::ItemKind::Enum(_, generics, _)
                         | hir::ItemKind::Union(_, generics, _)
-                        | hir::ItemKind::Trait(_, _, _, generics, ..)
+                        | hir::ItemKind::Trait(_, _, _, _, generics, ..)
                         | hir::ItemKind::Impl(hir::Impl { generics, .. })
                         | hir::ItemKind::Fn { generics, .. }
                         | hir::ItemKind::TyAlias(_, generics, _)
@@ -2870,11 +2871,20 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         ty::ClauseKind::Trait(trait_pred) => {
                             let def_id = trait_pred.def_id();
                             let visible_item = if let Some(local) = def_id.as_local() {
-                                // Check for local traits being reachable.
-                                let vis = &tcx.resolutions(()).effective_visibilities;
-                                // Account for non-`pub` traits in the root of the local crate.
-                                let is_locally_reachable = tcx.parent(def_id).is_crate_root();
-                                vis.is_reachable(local) || is_locally_reachable
+                                let ty = trait_pred.self_ty();
+                                // when `TraitA: TraitB` and `S` only impl TraitA,
+                                // we check if `TraitB` can be reachable from `S`
+                                // to determine whether to note `TraitA` is sealed trait.
+                                if let ty::Adt(adt, _) = ty.kind() {
+                                    let visibilities = tcx.effective_visibilities(());
+                                    visibilities.effective_vis(local).is_none_or(|v| {
+                                        v.at_level(Level::Reexported)
+                                            .is_accessible_from(adt.did(), tcx)
+                                    })
+                                } else {
+                                    // FIXME(xizheyin): if the type is not ADT, we should not suggest it
+                                    true
+                                }
                             } else {
                                 // Check for foreign traits being reachable.
                                 tcx.visible_parent_map(()).get(&def_id).is_some()
@@ -3436,7 +3446,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 let mut is_auto_trait = false;
                 match tcx.hir_get_if_local(data.impl_or_alias_def_id) {
                     Some(Node::Item(hir::Item {
-                        kind: hir::ItemKind::Trait(is_auto, _, ident, ..),
+                        kind: hir::ItemKind::Trait(_, is_auto, _, ident, ..),
                         ..
                     })) => {
                         // FIXME: we should do something else so that it works even on crate foreign
diff --git a/compiler/rustc_trait_selection/src/errors.rs b/compiler/rustc_trait_selection/src/errors.rs
index 90cdf75265d..7901d52dffb 100644
--- a/compiler/rustc_trait_selection/src/errors.rs
+++ b/compiler/rustc_trait_selection/src/errors.rs
@@ -534,7 +534,7 @@ impl Subdiagnostic for AddLifetimeParamsSuggestion<'_> {
                     match self.tcx.parent_hir_node(self.tcx.local_def_id_to_hir_id(anon_reg.scope))
                     {
                         hir::Node::Item(hir::Item {
-                            kind: hir::ItemKind::Trait(_, _, _, generics, ..),
+                            kind: hir::ItemKind::Trait(_, _, _, _, generics, ..),
                             ..
                         })
                         | hir::Node::Item(hir::Item {
diff --git a/compiler/rustc_trait_selection/src/infer.rs b/compiler/rustc_trait_selection/src/infer.rs
index 0118321befb..7c6b7b14ecb 100644
--- a/compiler/rustc_trait_selection/src/infer.rs
+++ b/compiler/rustc_trait_selection/src/infer.rs
@@ -33,8 +33,8 @@ impl<'tcx> InferCtxt<'tcx> {
         let ty = self.resolve_vars_if_possible(ty);
 
         // FIXME(#132279): This should be removed as it causes us to incorrectly
-        // handle opaques in their defining scope.
-        if !self.next_trait_solver() && !(param_env, ty).has_infer() {
+        // handle opaques in their defining scope, and stalled coroutines.
+        if !self.next_trait_solver() && !(param_env, ty).has_infer() && !ty.has_coroutines() {
             return self.tcx.type_is_copy_modulo_regions(self.typing_env(param_env), ty);
         }
 
diff --git a/compiler/rustc_trait_selection/src/regions.rs b/compiler/rustc_trait_selection/src/regions.rs
index 068e90b00b8..2b33b8ac9f8 100644
--- a/compiler/rustc_trait_selection/src/regions.rs
+++ b/compiler/rustc_trait_selection/src/regions.rs
@@ -4,7 +4,7 @@ use rustc_infer::infer::{InferCtxt, RegionResolutionError};
 use rustc_macros::extension;
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::traits::query::NoSolution;
-use rustc_middle::ty::{self, Ty};
+use rustc_middle::ty::{self, Ty, elaborate};
 
 use crate::traits::ScrubbedTraitError;
 use crate::traits::outlives_bounds::InferCtxtExt;
@@ -46,6 +46,11 @@ impl<'tcx> OutlivesEnvironment<'tcx> {
             }
         }
 
+        // FIXME(-Znext-trait-solver): Normalize these.
+        let higher_ranked_assumptions = infcx.take_registered_region_assumptions();
+        let higher_ranked_assumptions =
+            elaborate::elaborate_outlives_assumptions(infcx.tcx, higher_ranked_assumptions);
+
         // FIXME: This needs to be modified so that we normalize the known type
         // outlives obligations then elaborate them into their region/type components.
         // Otherwise, `<W<'a> as Mirror>::Assoc: 'b` will not imply `'a: 'b` even
@@ -59,6 +64,7 @@ impl<'tcx> OutlivesEnvironment<'tcx> {
                 assumed_wf_tys,
                 disable_implied_bounds_hack,
             ),
+            higher_ranked_assumptions,
         )
     }
 }
diff --git a/compiler/rustc_trait_selection/src/solve.rs b/compiler/rustc_trait_selection/src/solve.rs
index 5a5d16167d2..f58961683a9 100644
--- a/compiler/rustc_trait_selection/src/solve.rs
+++ b/compiler/rustc_trait_selection/src/solve.rs
@@ -7,7 +7,7 @@ mod normalize;
 mod select;
 
 pub(crate) use delegate::SolverDelegate;
-pub use fulfill::{FulfillmentCtxt, NextSolverError};
+pub use fulfill::{FulfillmentCtxt, NextSolverError, StalledOnCoroutines};
 pub(crate) use normalize::deeply_normalize_for_diagnostics;
 pub use normalize::{
     deeply_normalize, deeply_normalize_with_skipped_universes,
diff --git a/compiler/rustc_trait_selection/src/solve/delegate.rs b/compiler/rustc_trait_selection/src/solve/delegate.rs
index 1a24254d57f..17429e15cce 100644
--- a/compiler/rustc_trait_selection/src/solve/delegate.rs
+++ b/compiler/rustc_trait_selection/src/solve/delegate.rs
@@ -206,14 +206,18 @@ impl<'tcx> rustc_next_trait_solver::delegate::SolverDelegate for SolverDelegate<
         .map(|obligations| obligations.into_iter().map(|obligation| obligation.as_goal()).collect())
     }
 
-    fn make_deduplicated_outlives_constraints(
-        &self,
-    ) -> Vec<ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>> {
+    fn make_deduplicated_outlives_constraints(&self) -> Vec<ty::ArgOutlivesPredicate<'tcx>> {
         // Cannot use `take_registered_region_obligations` as we may compute the response
         // inside of a `probe` whenever we have multiple choices inside of the solver.
         let region_obligations = self.0.inner.borrow().region_obligations().to_owned();
+        let region_assumptions = self.0.inner.borrow().region_assumptions().to_owned();
         let region_constraints = self.0.with_region_constraints(|region_constraints| {
-            make_query_region_constraints(self.tcx, region_obligations, region_constraints)
+            make_query_region_constraints(
+                self.tcx,
+                region_obligations,
+                region_constraints,
+                region_assumptions,
+            )
         });
 
         let mut seen = FxHashSet::default();
diff --git a/compiler/rustc_trait_selection/src/solve/fulfill.rs b/compiler/rustc_trait_selection/src/solve/fulfill.rs
index d56042a5ca2..3ce0f025512 100644
--- a/compiler/rustc_trait_selection/src/solve/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/solve/fulfill.rs
@@ -10,7 +10,8 @@ use rustc_infer::traits::{
     FromSolverError, PredicateObligation, PredicateObligations, TraitEngine,
 };
 use rustc_middle::ty::{
-    self, DelayedSet, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor, TypingMode,
+    self, DelayedSet, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor,
+    TypingMode,
 };
 use rustc_next_trait_solver::delegate::SolverDelegate as _;
 use rustc_next_trait_solver::solve::{
@@ -254,7 +255,7 @@ where
         &mut self,
         infcx: &InferCtxt<'tcx>,
     ) -> PredicateObligations<'tcx> {
-        let stalled_generators = match infcx.typing_mode() {
+        let stalled_coroutines = match infcx.typing_mode() {
             TypingMode::Analysis { defining_opaque_types_and_generators } => {
                 defining_opaque_types_and_generators
             }
@@ -264,7 +265,7 @@ where
             | TypingMode::PostAnalysis => return Default::default(),
         };
 
-        if stalled_generators.is_empty() {
+        if stalled_coroutines.is_empty() {
             return Default::default();
         }
 
@@ -275,7 +276,7 @@ where
                         .visit_proof_tree(
                             obl.as_goal(),
                             &mut StalledOnCoroutines {
-                                stalled_generators,
+                                stalled_coroutines,
                                 span: obl.cause.span,
                                 cache: Default::default(),
                             },
@@ -297,10 +298,10 @@ where
 ///
 /// This function can be also return false positives, which will lead to poor diagnostics
 /// so we want to keep this visitor *precise* too.
-struct StalledOnCoroutines<'tcx> {
-    stalled_generators: &'tcx ty::List<LocalDefId>,
-    span: Span,
-    cache: DelayedSet<Ty<'tcx>>,
+pub struct StalledOnCoroutines<'tcx> {
+    pub stalled_coroutines: &'tcx ty::List<LocalDefId>,
+    pub span: Span,
+    pub cache: DelayedSet<Ty<'tcx>>,
 }
 
 impl<'tcx> inspect::ProofTreeVisitor<'tcx> for StalledOnCoroutines<'tcx> {
@@ -330,12 +331,14 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for StalledOnCoroutines<'tcx> {
         }
 
         if let ty::CoroutineWitness(def_id, _) = *ty.kind()
-            && def_id.as_local().is_some_and(|def_id| self.stalled_generators.contains(&def_id))
+            && def_id.as_local().is_some_and(|def_id| self.stalled_coroutines.contains(&def_id))
         {
-            return ControlFlow::Break(());
+            ControlFlow::Break(())
+        } else if ty.has_coroutines() {
+            ty.super_visit_with(self)
+        } else {
+            ControlFlow::Continue(())
         }
-
-        ty.super_visit_with(self)
     }
 }
 
diff --git a/compiler/rustc_trait_selection/src/traits/auto_trait.rs b/compiler/rustc_trait_selection/src/traits/auto_trait.rs
index 3ae908ec16b..759db1d18c0 100644
--- a/compiler/rustc_trait_selection/src/traits/auto_trait.rs
+++ b/compiler/rustc_trait_selection/src/traits/auto_trait.rs
@@ -800,6 +800,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
                 // FIXME(generic_const_exprs): you can absolutely add this as a where clauses
                 | ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(..))
                 | ty::PredicateKind::Coerce(..)
+                | ty::PredicateKind::Clause(ty::ClauseKind::UnstableFeature(_))
                 | ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(..)) => {}
                 ty::PredicateKind::Ambiguous => return false,
             };
diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs
index ce5a4edeaaa..f50f01a285b 100644
--- a/compiler/rustc_trait_selection/src/traits/coherence.rs
+++ b/compiler/rustc_trait_selection/src/traits/coherence.rs
@@ -461,6 +461,7 @@ fn impl_intersection_has_negative_obligation(
     // requirements, when proving the negated where clauses below.
     drop(equate_obligations);
     drop(infcx.take_registered_region_obligations());
+    drop(infcx.take_registered_region_assumptions());
     drop(infcx.take_and_reset_region_constraints());
 
     plug_infer_with_placeholders(
diff --git a/compiler/rustc_trait_selection/src/traits/dyn_compatibility.rs b/compiler/rustc_trait_selection/src/traits/dyn_compatibility.rs
index 9a4f3887bbb..ea1eed95723 100644
--- a/compiler/rustc_trait_selection/src/traits/dyn_compatibility.rs
+++ b/compiler/rustc_trait_selection/src/traits/dyn_compatibility.rs
@@ -238,6 +238,7 @@ fn predicate_references_self<'tcx>(
         // FIXME(generic_const_exprs): this can mention `Self`
         | ty::ClauseKind::ConstEvaluatable(..)
         | ty::ClauseKind::HostEffect(..)
+        | ty::ClauseKind::UnstableFeature(_)
          => None,
     }
 }
@@ -278,6 +279,7 @@ fn generics_require_sized_self(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
         | ty::ClauseKind::ConstArgHasType(_, _)
         | ty::ClauseKind::WellFormed(_)
         | ty::ClauseKind::ConstEvaluatable(_)
+        | ty::ClauseKind::UnstableFeature(_)
         | ty::ClauseKind::HostEffect(..) => false,
     })
 }
diff --git a/compiler/rustc_trait_selection/src/traits/fulfill.rs b/compiler/rustc_trait_selection/src/traits/fulfill.rs
index 64a51e0550b..e35f89358e9 100644
--- a/compiler/rustc_trait_selection/src/traits/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/traits/fulfill.rs
@@ -3,6 +3,7 @@ use std::marker::PhantomData;
 use rustc_data_structures::obligation_forest::{
     Error, ForestObligation, ObligationForest, ObligationProcessor, Outcome, ProcessResult,
 };
+use rustc_hir::def_id::LocalDefId;
 use rustc_infer::infer::DefineOpaqueTypes;
 use rustc_infer::traits::{
     FromSolverError, PolyTraitObligation, PredicateObligations, ProjectionCacheKey, SelectionError,
@@ -11,7 +12,11 @@ use rustc_infer::traits::{
 use rustc_middle::bug;
 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
-use rustc_middle::ty::{self, Binder, Const, GenericArgsRef, TypeVisitableExt, TypingMode};
+use rustc_middle::ty::{
+    self, Binder, Const, GenericArgsRef, TypeVisitable, TypeVisitableExt, TypingMode,
+    may_use_unstable_feature,
+};
+use rustc_span::DUMMY_SP;
 use thin_vec::{ThinVec, thin_vec};
 use tracing::{debug, debug_span, instrument};
 
@@ -24,6 +29,7 @@ use super::{
 };
 use crate::error_reporting::InferCtxtErrorExt;
 use crate::infer::{InferCtxt, TyOrConstInferVar};
+use crate::solve::StalledOnCoroutines;
 use crate::traits::normalize::normalize_with_depth_to;
 use crate::traits::project::{PolyProjectionObligation, ProjectionCacheKeyExt as _};
 use crate::traits::query::evaluate_obligation::InferCtxtExt;
@@ -166,8 +172,25 @@ where
         &mut self,
         infcx: &InferCtxt<'tcx>,
     ) -> PredicateObligations<'tcx> {
-        let mut processor =
-            DrainProcessor { removed_predicates: PredicateObligations::new(), infcx };
+        let stalled_coroutines = match infcx.typing_mode() {
+            TypingMode::Analysis { defining_opaque_types_and_generators } => {
+                defining_opaque_types_and_generators
+            }
+            TypingMode::Coherence
+            | TypingMode::Borrowck { defining_opaque_types: _ }
+            | TypingMode::PostBorrowckAnalysis { defined_opaque_types: _ }
+            | TypingMode::PostAnalysis => return Default::default(),
+        };
+
+        if stalled_coroutines.is_empty() {
+            return Default::default();
+        }
+
+        let mut processor = DrainProcessor {
+            infcx,
+            removed_predicates: PredicateObligations::new(),
+            stalled_coroutines,
+        };
         let outcome: Outcome<_, _> = self.predicates.process_obligations(&mut processor);
         assert!(outcome.errors.is_empty());
         return processor.removed_predicates;
@@ -175,6 +198,7 @@ where
         struct DrainProcessor<'a, 'tcx> {
             infcx: &'a InferCtxt<'tcx>,
             removed_predicates: PredicateObligations<'tcx>,
+            stalled_coroutines: &'tcx ty::List<LocalDefId>,
         }
 
         impl<'tcx> ObligationProcessor for DrainProcessor<'_, 'tcx> {
@@ -183,10 +207,14 @@ where
             type OUT = Outcome<Self::Obligation, Self::Error>;
 
             fn needs_process_obligation(&self, pending_obligation: &Self::Obligation) -> bool {
-                pending_obligation
-                    .stalled_on
-                    .iter()
-                    .any(|&var| self.infcx.ty_or_const_infer_var_changed(var))
+                self.infcx
+                    .resolve_vars_if_possible(pending_obligation.obligation.predicate)
+                    .visit_with(&mut StalledOnCoroutines {
+                        stalled_coroutines: self.stalled_coroutines,
+                        span: DUMMY_SP,
+                        cache: Default::default(),
+                    })
+                    .is_break()
             }
 
             fn process_obligation(
@@ -404,6 +432,9 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 ty::PredicateKind::AliasRelate(..) => {
                     bug!("AliasRelate is only used by the new solver")
                 }
+                ty::PredicateKind::Clause(ty::ClauseKind::UnstableFeature(_)) => {
+                   unreachable!("unexpected higher ranked `UnstableFeature` goal")
+                }
             },
             Some(pred) => match pred {
                 ty::PredicateKind::Clause(ty::ClauseKind::Trait(data)) => {
@@ -767,6 +798,13 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                         }
                     }
                 }
+                ty::PredicateKind::Clause(ty::ClauseKind::UnstableFeature(symbol)) => {
+                    if may_use_unstable_feature(self.selcx.infcx, obligation.param_env, symbol) {
+                        ProcessResult::Changed(Default::default())
+                    } else {
+                        ProcessResult::Unchanged
+                    }
+                }
             },
         }
     }
diff --git a/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs b/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
index 59d3ac21387..53518038f8d 100644
--- a/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
+++ b/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
@@ -78,7 +78,10 @@ fn implied_outlives_bounds<'a, 'tcx>(
     bounds.retain(|bound| !bound.has_placeholders());
 
     if !constraints.is_empty() {
-        let QueryRegionConstraints { outlives } = constraints;
+        // FIXME(higher_ranked_auto): Should we register assumptions here?
+        // We otherwise would get spurious errors if normalizing an implied
+        // outlives bound required proving some higher-ranked coroutine obl.
+        let QueryRegionConstraints { outlives, assumptions: _ } = constraints;
         let cause = ObligationCause::misc(span, body_id);
         for &(predicate, _) in &outlives {
             infcx.register_outlives_constraint(predicate, &cause);
diff --git a/compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs b/compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs
index 3b549244431..f027ba1c5cb 100644
--- a/compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs
@@ -80,6 +80,11 @@ where
         pre_obligations.is_empty(),
         "scrape_region_constraints: incoming region obligations = {pre_obligations:#?}",
     );
+    let pre_assumptions = infcx.take_registered_region_assumptions();
+    assert!(
+        pre_assumptions.is_empty(),
+        "scrape_region_constraints: incoming region assumptions = {pre_assumptions:#?}",
+    );
 
     let value = infcx.commit_if_ok(|_| {
         let ocx = ObligationCtxt::new(infcx);
@@ -100,11 +105,13 @@ where
     let value = infcx.resolve_vars_if_possible(value);
 
     let region_obligations = infcx.take_registered_region_obligations();
+    let region_assumptions = infcx.take_registered_region_assumptions();
     let region_constraint_data = infcx.take_and_reset_region_constraints();
     let region_constraints = query_response::make_query_region_constraints(
         infcx.tcx,
         region_obligations,
         &region_constraint_data,
+        region_assumptions,
     );
 
     if region_constraints.is_empty() {
diff --git a/compiler/rustc_trait_selection/src/traits/query/type_op/implied_outlives_bounds.rs b/compiler/rustc_trait_selection/src/traits/query/type_op/implied_outlives_bounds.rs
index e294f7839aa..7540cbe3fd1 100644
--- a/compiler/rustc_trait_selection/src/traits/query/type_op/implied_outlives_bounds.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/type_op/implied_outlives_bounds.rs
@@ -110,6 +110,7 @@ pub fn compute_implied_outlives_bounds_inner<'tcx>(
                 | ty::PredicateKind::ConstEquate(..)
                 | ty::PredicateKind::Ambiguous
                 | ty::PredicateKind::NormalizesTo(..)
+                | ty::PredicateKind::Clause(ty::ClauseKind::UnstableFeature(_))
                 | ty::PredicateKind::AliasRelate(..) => {}
 
                 // We need to search through *all* WellFormed predicates
diff --git a/compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs b/compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs
index 4bdf04311a0..018e9748cf0 100644
--- a/compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs
@@ -180,8 +180,9 @@ where
             span,
         )?;
         output.error_info = error_info;
-        if let Some(QueryRegionConstraints { outlives }) = output.constraints {
+        if let Some(QueryRegionConstraints { outlives, assumptions }) = output.constraints {
             region_constraints.outlives.extend(outlives.iter().cloned());
+            region_constraints.assumptions.extend(assumptions.iter().cloned());
         }
         output.constraints = if region_constraints.is_empty() {
             None
diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
index cc188a280aa..2c7089507a8 100644
--- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -842,6 +842,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     }
                 }
 
+                ty::CoroutineWitness(def_id, _) => {
+                    if self.should_stall_coroutine_witness(def_id) {
+                        candidates.ambiguous = true;
+                    } else {
+                        candidates.vec.push(AutoImplCandidate);
+                    }
+                }
+
                 ty::Bool
                 | ty::Char
                 | ty::Int(_)
@@ -861,7 +869,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 | ty::Coroutine(..)
                 | ty::Never
                 | ty::Tuple(_)
-                | ty::CoroutineWitness(..)
                 | ty::UnsafeBinder(_) => {
                     // Only consider auto impls of unsafe traits when there are
                     // no unsafe fields.
@@ -1119,12 +1126,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         match *self_ty.kind() {
             // These impls are built-in because we cannot express sufficiently
             // generic impls in libcore.
-            ty::FnDef(..)
-            | ty::FnPtr(..)
-            | ty::Error(_)
-            | ty::Tuple(..)
-            | ty::CoroutineWitness(..)
-            | ty::Pat(..) => {
+            ty::FnDef(..) | ty::FnPtr(..) | ty::Error(_) | ty::Tuple(..) | ty::Pat(..) => {
                 candidates.vec.push(BuiltinCandidate);
             }
 
@@ -1192,6 +1194,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 }
             }
 
+            ty::CoroutineWitness(coroutine_def_id, _) => {
+                if self.should_stall_coroutine_witness(coroutine_def_id) {
+                    candidates.ambiguous = true;
+                } else {
+                    candidates.vec.push(SizedCandidate);
+                }
+            }
+
             // Fallback to whatever user-defined impls or param-env clauses exist in this case.
             ty::Adt(..) | ty::Alias(..) | ty::Param(..) | ty::Placeholder(..) => {}
 
@@ -1229,7 +1239,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             | ty::Char
             | ty::Ref(..)
             | ty::Coroutine(..)
-            | ty::CoroutineWitness(..)
             | ty::Array(..)
             | ty::Closure(..)
             | ty::CoroutineClosure(..)
@@ -1238,6 +1247,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 candidates.vec.push(SizedCandidate);
             }
 
+            ty::CoroutineWitness(coroutine_def_id, _) => {
+                if self.should_stall_coroutine_witness(coroutine_def_id) {
+                    candidates.ambiguous = true;
+                } else {
+                    candidates.vec.push(SizedCandidate);
+                }
+            }
+
             // Conditionally `Sized`.
             ty::Tuple(..) | ty::Pat(..) | ty::Adt(..) | ty::UnsafeBinder(_) => {
                 candidates.vec.push(SizedCandidate);
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index ee8cef20279..488094b15ac 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -411,18 +411,33 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 obligation.predicate.self_ty().map_bound(|ty| self.infcx.shallow_resolve(ty));
             let self_ty = self.infcx.enter_forall_and_leak_universe(self_ty);
 
-            let types = self.constituent_types_for_ty(self_ty)?;
-            let types = self.infcx.enter_forall_and_leak_universe(types);
+            let constituents = self.constituent_types_for_auto_trait(self_ty)?;
+            let constituents = self.infcx.enter_forall_and_leak_universe(constituents);
 
             let cause = obligation.derived_cause(ObligationCauseCode::BuiltinDerived);
-            let obligations = self.collect_predicates_for_types(
+            let mut obligations = self.collect_predicates_for_types(
                 obligation.param_env,
-                cause,
+                cause.clone(),
                 obligation.recursion_depth + 1,
                 obligation.predicate.def_id(),
-                types,
+                constituents.types,
             );
 
+            // FIXME(coroutine_clone): We could uplift this into `collect_predicates_for_types`
+            // and do this for `Copy`/`Clone` too, but that's feature-gated so it doesn't really
+            // matter yet.
+            for assumption in constituents.assumptions {
+                let assumption = normalize_with_depth_to(
+                    self,
+                    obligation.param_env,
+                    cause.clone(),
+                    obligation.recursion_depth + 1,
+                    assumption,
+                    &mut obligations,
+                );
+                self.infcx.register_region_assumption(assumption);
+            }
+
             Ok(obligations)
         })
     }
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 2e65750db25..2b563c5b8d5 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -20,6 +20,7 @@ use rustc_infer::infer::DefineOpaqueTypes;
 use rustc_infer::infer::at::ToTrace;
 use rustc_infer::infer::relate::TypeRelation;
 use rustc_infer::traits::{PredicateObligations, TraitObligation};
+use rustc_macros::{TypeFoldable, TypeVisitable};
 use rustc_middle::bug;
 use rustc_middle::dep_graph::{DepNodeIndex, dep_kinds};
 pub use rustc_middle::traits::select::*;
@@ -28,7 +29,7 @@ use rustc_middle::ty::error::TypeErrorToStringExt;
 use rustc_middle::ty::print::{PrintTraitRefExt as _, with_no_trimmed_paths};
 use rustc_middle::ty::{
     self, DeepRejectCtxt, GenericArgsRef, PolyProjectionPredicate, SizedTraitKind, Ty, TyCtxt,
-    TypeFoldable, TypeVisitableExt, TypingMode, Upcast, elaborate,
+    TypeFoldable, TypeVisitableExt, TypingMode, Upcast, elaborate, may_use_unstable_feature,
 };
 use rustc_span::{Symbol, sym};
 use tracing::{debug, instrument, trace};
@@ -832,6 +833,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     }
                 }
 
+                ty::PredicateKind::Clause(ty::ClauseKind::UnstableFeature(symbol)) => {
+                    if may_use_unstable_feature(self.infcx, obligation.param_env, symbol) {
+                        Ok(EvaluatedToOk)
+                    } else {
+                        Ok(EvaluatedToAmbig)
+                    }
+                }
+
                 ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(uv)) => {
                     match const_evaluatable::is_const_evaluatable(
                         self.infcx,
@@ -1504,7 +1513,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 defining_opaque_types_and_generators: defining_opaque_types,
             }
             | TypingMode::Borrowck { defining_opaque_types } => {
-                defining_opaque_types.is_empty() || !pred.has_opaque_types()
+                defining_opaque_types.is_empty()
+                    || (!pred.has_opaque_types() && !pred.has_coroutines())
             }
             // The hidden types of `defined_opaque_types` is not local to the current
             // inference context, so we can freely move this to the global cache.
@@ -2247,10 +2257,10 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
     /// Zed<i32> where enum Zed { A(T), B(u32) } -> [i32, u32]
     /// ```
     #[instrument(level = "debug", skip(self), ret)]
-    fn constituent_types_for_ty(
+    fn constituent_types_for_auto_trait(
         &self,
         t: Ty<'tcx>,
-    ) -> Result<ty::Binder<'tcx, Vec<Ty<'tcx>>>, SelectionError<'tcx>> {
+    ) -> Result<ty::Binder<'tcx, AutoImplConstituents<'tcx>>, SelectionError<'tcx>> {
         Ok(match *t.kind() {
             ty::Uint(_)
             | ty::Int(_)
@@ -2261,17 +2271,26 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
             | ty::Error(_)
             | ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
             | ty::Never
-            | ty::Char => ty::Binder::dummy(Vec::new()),
+            | ty::Char => {
+                ty::Binder::dummy(AutoImplConstituents { types: vec![], assumptions: vec![] })
+            }
 
             // This branch is only for `experimental_default_bounds`.
             // Other foreign types were rejected earlier in
             // `assemble_candidates_from_auto_impls`.
-            ty::Foreign(..) => ty::Binder::dummy(Vec::new()),
+            ty::Foreign(..) => {
+                ty::Binder::dummy(AutoImplConstituents { types: vec![], assumptions: vec![] })
+            }
 
-            ty::UnsafeBinder(ty) => ty.map_bound(|ty| vec![ty]),
+            ty::UnsafeBinder(ty) => {
+                ty.map_bound(|ty| AutoImplConstituents { types: vec![ty], assumptions: vec![] })
+            }
 
             // Treat this like `struct str([u8]);`
-            ty::Str => ty::Binder::dummy(vec![Ty::new_slice(self.tcx(), self.tcx().types.u8)]),
+            ty::Str => ty::Binder::dummy(AutoImplConstituents {
+                types: vec![Ty::new_slice(self.tcx(), self.tcx().types.u8)],
+                assumptions: vec![],
+            }),
 
             ty::Placeholder(..)
             | ty::Dynamic(..)
@@ -2283,30 +2302,41 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
             }
 
             ty::RawPtr(element_ty, _) | ty::Ref(_, element_ty, _) => {
-                ty::Binder::dummy(vec![element_ty])
+                ty::Binder::dummy(AutoImplConstituents {
+                    types: vec![element_ty],
+                    assumptions: vec![],
+                })
             }
 
-            ty::Pat(ty, _) | ty::Array(ty, _) | ty::Slice(ty) => ty::Binder::dummy(vec![ty]),
+            ty::Pat(ty, _) | ty::Array(ty, _) | ty::Slice(ty) => {
+                ty::Binder::dummy(AutoImplConstituents { types: vec![ty], assumptions: vec![] })
+            }
 
             ty::Tuple(tys) => {
                 // (T1, ..., Tn) -- meets any bound that all of T1...Tn meet
-                ty::Binder::dummy(tys.iter().collect())
+                ty::Binder::dummy(AutoImplConstituents {
+                    types: tys.iter().collect(),
+                    assumptions: vec![],
+                })
             }
 
             ty::Closure(_, args) => {
                 let ty = self.infcx.shallow_resolve(args.as_closure().tupled_upvars_ty());
-                ty::Binder::dummy(vec![ty])
+                ty::Binder::dummy(AutoImplConstituents { types: vec![ty], assumptions: vec![] })
             }
 
             ty::CoroutineClosure(_, args) => {
                 let ty = self.infcx.shallow_resolve(args.as_coroutine_closure().tupled_upvars_ty());
-                ty::Binder::dummy(vec![ty])
+                ty::Binder::dummy(AutoImplConstituents { types: vec![ty], assumptions: vec![] })
             }
 
             ty::Coroutine(_, args) => {
                 let ty = self.infcx.shallow_resolve(args.as_coroutine().tupled_upvars_ty());
                 let witness = args.as_coroutine().witness();
-                ty::Binder::dummy([ty].into_iter().chain(iter::once(witness)).collect())
+                ty::Binder::dummy(AutoImplConstituents {
+                    types: [ty].into_iter().chain(iter::once(witness)).collect(),
+                    assumptions: vec![],
+                })
             }
 
             ty::CoroutineWitness(def_id, args) => self
@@ -2314,16 +2344,23 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
                 .tcx
                 .coroutine_hidden_types(def_id)
                 .instantiate(self.infcx.tcx, args)
-                .map_bound(|witness| witness.types.to_vec()),
+                .map_bound(|witness| AutoImplConstituents {
+                    types: witness.types.to_vec(),
+                    assumptions: witness.assumptions.to_vec(),
+                }),
 
             // For `PhantomData<T>`, we pass `T`.
             ty::Adt(def, args) if def.is_phantom_data() => {
-                ty::Binder::dummy(args.types().collect())
+                ty::Binder::dummy(AutoImplConstituents {
+                    types: args.types().collect(),
+                    assumptions: vec![],
+                })
             }
 
-            ty::Adt(def, args) => {
-                ty::Binder::dummy(def.all_fields().map(|f| f.ty(self.tcx(), args)).collect())
-            }
+            ty::Adt(def, args) => ty::Binder::dummy(AutoImplConstituents {
+                types: def.all_fields().map(|f| f.ty(self.tcx(), args)).collect(),
+                assumptions: vec![],
+            }),
 
             ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => {
                 if self.infcx.can_define_opaque_ty(def_id) {
@@ -2333,7 +2370,10 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
                     // which enforces a DAG between the functions requiring
                     // the auto trait bounds in question.
                     match self.tcx().type_of_opaque(def_id) {
-                        Ok(ty) => ty::Binder::dummy(vec![ty.instantiate(self.tcx(), args)]),
+                        Ok(ty) => ty::Binder::dummy(AutoImplConstituents {
+                            types: vec![ty.instantiate(self.tcx(), args)],
+                            assumptions: vec![],
+                        }),
                         Err(_) => {
                             return Err(SelectionError::OpaqueTypeAutoTraitLeakageUnknown(def_id));
                         }
@@ -2803,6 +2843,18 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
 
         obligations
     }
+
+    fn should_stall_coroutine_witness(&self, def_id: DefId) -> bool {
+        match self.infcx.typing_mode() {
+            TypingMode::Analysis { defining_opaque_types_and_generators: stalled_generators } => {
+                def_id.as_local().is_some_and(|def_id| stalled_generators.contains(&def_id))
+            }
+            TypingMode::Coherence
+            | TypingMode::PostAnalysis
+            | TypingMode::Borrowck { defining_opaque_types: _ }
+            | TypingMode::PostBorrowckAnalysis { defined_opaque_types: _ } => false,
+        }
+    }
 }
 
 impl<'o, 'tcx> TraitObligationStack<'o, 'tcx> {
@@ -3113,3 +3165,9 @@ pub(crate) enum ProjectionMatchesProjection {
     Ambiguous,
     No,
 }
+
+#[derive(Clone, Debug, TypeFoldable, TypeVisitable)]
+pub(crate) struct AutoImplConstituents<'tcx> {
+    pub types: Vec<Ty<'tcx>>,
+    pub assumptions: Vec<ty::ArgOutlivesPredicate<'tcx>>,
+}
diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
index 141454bfe37..0c14b124e25 100644
--- a/compiler/rustc_trait_selection/src/traits/util.rs
+++ b/compiler/rustc_trait_selection/src/traits/util.rs
@@ -80,6 +80,7 @@ pub fn expand_trait_aliases<'tcx>(
             | ty::ClauseKind::ConstArgHasType(_, _)
             | ty::ClauseKind::WellFormed(_)
             | ty::ClauseKind::ConstEvaluatable(_)
+            | ty::ClauseKind::UnstableFeature(_)
             | ty::ClauseKind::HostEffect(..) => {}
         }
     }
@@ -378,6 +379,13 @@ pub fn sizedness_fast_path<'tcx>(tcx: TyCtxt<'tcx>, predicate: ty::Predicate<'tc
             _ => return false,
         };
 
+        // FIXME(sized_hierarchy): this temporarily reverts the `sized_hierarchy` feature
+        // while a proper fix for `tests/ui/sized-hierarchy/incomplete-inference-issue-143992.rs`
+        // is pending a proper fix
+        if !tcx.features().sized_hierarchy() && matches!(sizedness, SizedTraitKind::MetaSized) {
+            return true;
+        }
+
         if trait_pred.self_ty().has_trivial_sizedness(tcx, sizedness) {
             debug!("fast path -- trivial sizedness");
             return true;
diff --git a/compiler/rustc_trait_selection/src/traits/wf.rs b/compiler/rustc_trait_selection/src/traits/wf.rs
index fed9f254cdf..adce9850b59 100644
--- a/compiler/rustc_trait_selection/src/traits/wf.rs
+++ b/compiler/rustc_trait_selection/src/traits/wf.rs
@@ -197,6 +197,7 @@ pub fn clause_obligations<'tcx>(
         ty::ClauseKind::ConstEvaluatable(ct) => {
             wf.add_wf_preds_for_term(ct.into());
         }
+        ty::ClauseKind::UnstableFeature(_) => {}
     }
 
     wf.normalize(infcx)
@@ -1095,6 +1096,7 @@ pub fn object_region_bounds<'tcx>(
                 | ty::ClauseKind::Projection(_)
                 | ty::ClauseKind::ConstArgHasType(_, _)
                 | ty::ClauseKind::WellFormed(_)
+                | ty::ClauseKind::UnstableFeature(_)
                 | ty::ClauseKind::ConstEvaluatable(_) => None,
             }
         })
diff --git a/compiler/rustc_traits/src/coroutine_witnesses.rs b/compiler/rustc_traits/src/coroutine_witnesses.rs
index 447e13126cc..87d17f3e131 100644
--- a/compiler/rustc_traits/src/coroutine_witnesses.rs
+++ b/compiler/rustc_traits/src/coroutine_witnesses.rs
@@ -1,5 +1,10 @@
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::{self, TyCtxt, fold_regions};
+use rustc_infer::infer::TyCtxtInferExt;
+use rustc_infer::infer::canonical::query_response::make_query_region_constraints;
+use rustc_infer::infer::resolve::OpportunisticRegionResolver;
+use rustc_infer::traits::{Obligation, ObligationCause};
+use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, TypeVisitableExt, fold_regions};
+use rustc_trait_selection::traits::{ObligationCtxt, with_replaced_escaping_bound_vars};
 
 /// Return the set of types that should be taken into account when checking
 /// trait bounds on a coroutine's internal state. This properly replaces
@@ -30,8 +35,57 @@ pub(crate) fn coroutine_hidden_types<'tcx>(
             }),
     );
 
+    let assumptions = compute_assumptions(tcx, def_id, bound_tys);
+
     ty::EarlyBinder::bind(ty::Binder::bind_with_vars(
-        ty::CoroutineWitnessTypes { types: bound_tys },
+        ty::CoroutineWitnessTypes { types: bound_tys, assumptions },
         tcx.mk_bound_variable_kinds(&vars),
     ))
 }
+
+fn compute_assumptions<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    def_id: DefId,
+    bound_tys: &'tcx ty::List<Ty<'tcx>>,
+) -> &'tcx ty::List<ty::ArgOutlivesPredicate<'tcx>> {
+    let infcx = tcx.infer_ctxt().build(ty::TypingMode::Analysis {
+        defining_opaque_types_and_generators: ty::List::empty(),
+    });
+    with_replaced_escaping_bound_vars(&infcx, &mut vec![None], bound_tys, |bound_tys| {
+        let param_env = tcx.param_env(def_id);
+        let ocx = ObligationCtxt::new(&infcx);
+
+        ocx.register_obligations(bound_tys.iter().map(|ty| {
+            Obligation::new(
+                tcx,
+                ObligationCause::dummy(),
+                param_env,
+                ty::ClauseKind::WellFormed(ty.into()),
+            )
+        }));
+        let _errors = ocx.select_all_or_error();
+
+        let region_obligations = infcx.take_registered_region_obligations();
+        let region_assumptions = infcx.take_registered_region_assumptions();
+        let region_constraints = infcx.take_and_reset_region_constraints();
+
+        let outlives = make_query_region_constraints(
+            tcx,
+            region_obligations,
+            &region_constraints,
+            region_assumptions,
+        )
+        .outlives
+        .fold_with(&mut OpportunisticRegionResolver::new(&infcx));
+
+        tcx.mk_outlives_from_iter(
+            outlives
+                .into_iter()
+                .map(|(o, _)| o)
+                // FIXME(higher_ranked_auto): We probably should deeply resolve these before
+                // filtering out infers which only correspond to unconstrained infer regions
+                // which we can sometimes get.
+                .filter(|o| !o.has_infer()),
+        )
+    })
+}
diff --git a/compiler/rustc_traits/src/normalize_erasing_regions.rs b/compiler/rustc_traits/src/normalize_erasing_regions.rs
index 68ff66bbce7..c1b848a2e79 100644
--- a/compiler/rustc_traits/src/normalize_erasing_regions.rs
+++ b/compiler/rustc_traits/src/normalize_erasing_regions.rs
@@ -57,6 +57,7 @@ fn not_outlives_predicate(p: ty::Predicate<'_>) -> bool {
         | ty::PredicateKind::Clause(ty::ClauseKind::Projection(..))
         | ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(..))
         | ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(..))
+        | ty::PredicateKind::Clause(ty::ClauseKind::UnstableFeature(_))
         | ty::PredicateKind::NormalizesTo(..)
         | ty::PredicateKind::AliasRelate(..)
         | ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(..))
diff --git a/compiler/rustc_ty_utils/src/opaque_types.rs b/compiler/rustc_ty_utils/src/opaque_types.rs
index 3b313edea6f..4a7263d0ccd 100644
--- a/compiler/rustc_ty_utils/src/opaque_types.rs
+++ b/compiler/rustc_ty_utils/src/opaque_types.rs
@@ -223,7 +223,10 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for OpaqueTypeCollector<'tcx> {
             }
             // Skips type aliases, as they are meant to be transparent.
             // FIXME(type_alias_impl_trait): can we require mentioning nested type aliases explicitly?
-            ty::Alias(ty::Free, alias_ty) if alias_ty.def_id.is_local() => {
+            ty::Alias(ty::Free, alias_ty) if let Some(def_id) = alias_ty.def_id.as_local() => {
+                if !self.seen.insert(def_id) {
+                    return;
+                }
                 self.tcx
                     .type_of(alias_ty.def_id)
                     .instantiate(self.tcx, alias_ty.args)
@@ -256,16 +259,16 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for OpaqueTypeCollector<'tcx> {
                                 return;
                             }
 
-                            let impl_args = alias_ty.args.rebase_onto(
+                            let alias_args = alias_ty.args.rebase_onto(
                                 self.tcx,
                                 impl_trait_ref.def_id,
                                 ty::GenericArgs::identity_for_item(self.tcx, parent),
                             );
 
-                            if self.tcx.check_args_compatible(assoc.def_id, impl_args) {
+                            if self.tcx.check_args_compatible(assoc.def_id, alias_args) {
                                 self.tcx
                                     .type_of(assoc.def_id)
-                                    .instantiate(self.tcx, impl_args)
+                                    .instantiate(self.tcx, alias_args)
                                     .visit_with(self);
                                 return;
                             } else {
diff --git a/compiler/rustc_type_ir/src/elaborate.rs b/compiler/rustc_type_ir/src/elaborate.rs
index 7ffcf7b5d96..dc15cc3eb55 100644
--- a/compiler/rustc_type_ir/src/elaborate.rs
+++ b/compiler/rustc_type_ir/src/elaborate.rs
@@ -234,6 +234,9 @@ impl<I: Interner, O: Elaboratable<I>> Elaborator<I, O> {
             ty::ClauseKind::ConstArgHasType(..) => {
                 // Nothing to elaborate
             }
+            ty::ClauseKind::UnstableFeature(_) => {
+                // Nothing to elaborate
+            }
         }
     }
 }
@@ -368,3 +371,54 @@ impl<I: Interner, It: Iterator<Item = I::Clause>> Iterator for FilterToTraits<I,
         (0, upper)
     }
 }
+
+pub fn elaborate_outlives_assumptions<I: Interner>(
+    cx: I,
+    assumptions: impl IntoIterator<Item = ty::OutlivesPredicate<I, I::GenericArg>>,
+) -> HashSet<ty::OutlivesPredicate<I, I::GenericArg>> {
+    let mut collected = HashSet::default();
+
+    for ty::OutlivesPredicate(arg1, r2) in assumptions {
+        collected.insert(ty::OutlivesPredicate(arg1, r2));
+        match arg1.kind() {
+            // Elaborate the components of an type, since we may have substituted a
+            // generic coroutine with a more specific type.
+            ty::GenericArgKind::Type(ty1) => {
+                let mut components = smallvec![];
+                push_outlives_components(cx, ty1, &mut components);
+                for c in components {
+                    match c {
+                        Component::Region(r1) => {
+                            if !r1.is_bound() {
+                                collected.insert(ty::OutlivesPredicate(r1.into(), r2));
+                            }
+                        }
+
+                        Component::Param(p) => {
+                            let ty = Ty::new_param(cx, p);
+                            collected.insert(ty::OutlivesPredicate(ty.into(), r2));
+                        }
+
+                        Component::Placeholder(p) => {
+                            let ty = Ty::new_placeholder(cx, p);
+                            collected.insert(ty::OutlivesPredicate(ty.into(), r2));
+                        }
+
+                        Component::Alias(alias_ty) => {
+                            collected.insert(ty::OutlivesPredicate(alias_ty.to_ty(cx).into(), r2));
+                        }
+
+                        Component::UnresolvedInferenceVariable(_) | Component::EscapingAlias(_) => {
+                        }
+                    }
+                }
+            }
+            // Nothing to elaborate for a region.
+            ty::GenericArgKind::Lifetime(_) => {}
+            // Consts don't really participate in outlives.
+            ty::GenericArgKind::Const(_) => {}
+        }
+    }
+
+    collected
+}
diff --git a/compiler/rustc_type_ir/src/flags.rs b/compiler/rustc_type_ir/src/flags.rs
index 37cc2baa402..d7b9e0ca340 100644
--- a/compiler/rustc_type_ir/src/flags.rs
+++ b/compiler/rustc_type_ir/src/flags.rs
@@ -130,6 +130,12 @@ bitflags::bitflags! {
 
         /// Does this have any binders with bound vars (e.g. that need to be anonymized)?
         const HAS_BINDER_VARS             = 1 << 23;
+
+        /// Does this type have any coroutine witnesses in it?
+        // FIXME: This should probably be changed to track whether the type has any
+        // *coroutines* in it, though this will happen if we remove coroutine witnesses
+        // altogether.
+        const HAS_TY_CORO                 = 1 << 24;
     }
 }
 
@@ -240,10 +246,12 @@ impl<I: Interner> FlagComputation<I> {
                 self.add_flags(TypeFlags::HAS_TY_PARAM);
             }
 
-            ty::Closure(_, args)
-            | ty::Coroutine(_, args)
-            | ty::CoroutineClosure(_, args)
-            | ty::CoroutineWitness(_, args) => {
+            ty::Closure(_, args) | ty::Coroutine(_, args) | ty::CoroutineClosure(_, args) => {
+                self.add_args(args.as_slice());
+            }
+
+            ty::CoroutineWitness(_, args) => {
+                self.add_flags(TypeFlags::HAS_TY_CORO);
                 self.add_args(args.as_slice());
             }
 
@@ -401,7 +409,6 @@ impl<I: Interner> FlagComputation<I> {
                 self.add_const(expected);
                 self.add_const(found);
             }
-            ty::PredicateKind::Ambiguous => {}
             ty::PredicateKind::NormalizesTo(ty::NormalizesTo { alias, term }) => {
                 self.add_alias_term(alias);
                 self.add_term(term);
@@ -410,6 +417,8 @@ impl<I: Interner> FlagComputation<I> {
                 self.add_term(t1);
                 self.add_term(t2);
             }
+            ty::PredicateKind::Clause(ty::ClauseKind::UnstableFeature(_sym)) => {}
+            ty::PredicateKind::Ambiguous => {}
         }
     }
 
diff --git a/compiler/rustc_type_ir/src/infer_ctxt.rs b/compiler/rustc_type_ir/src/infer_ctxt.rs
index 6c77a90250a..e86a2305e23 100644
--- a/compiler/rustc_type_ir/src/infer_ctxt.rs
+++ b/compiler/rustc_type_ir/src/infer_ctxt.rs
@@ -285,3 +285,40 @@ pub trait InferCtxtLike: Sized {
 
     fn reset_opaque_types(&self);
 }
+
+pub fn may_use_unstable_feature<'a, I: Interner, Infcx>(
+    infcx: &'a Infcx,
+    param_env: I::ParamEnv,
+    symbol: I::Symbol,
+) -> bool
+where
+    Infcx: InferCtxtLike<Interner = I>,
+{
+    // Iterate through all goals in param_env to find the one that has the same symbol.
+    for pred in param_env.caller_bounds().iter() {
+        if let ty::ClauseKind::UnstableFeature(sym) = pred.kind().skip_binder() {
+            if sym == symbol {
+                return true;
+            }
+        }
+    }
+
+    // During codegen we must assume that all feature bounds hold as we may be
+    // monomorphizing a body from an upstream crate which had an unstable feature
+    // enabled that we do not.
+    //
+    // Coherence should already report overlap errors involving unstable impls
+    // as the affected code would otherwise break when stabilizing this feature.
+    // It is also easily possible to accidentally cause unsoundness this way as
+    // we have to always enable unstable impls during codegen.
+    //
+    // Return ambiguity can also prevent people from writing code which depends on inference guidance
+    // that might no longer work after the impl is stabilised,
+    // tests/ui/unstable-feature-bound/unstable_impl_method_selection.rs is one of the example.
+    //
+    // Note: `feature_bound_holds_in_crate` does not consider a feature to be enabled
+    // if we are in std/core even if there is a corresponding `feature` attribute on the crate.
+
+    (infcx.typing_mode() == TypingMode::PostAnalysis)
+        || infcx.cx().features().feature_bound_holds_in_crate(symbol)
+}
diff --git a/compiler/rustc_type_ir/src/inherent.rs b/compiler/rustc_type_ir/src/inherent.rs
index 2754d40fd36..0e307e15d5b 100644
--- a/compiler/rustc_type_ir/src/inherent.rs
+++ b/compiler/rustc_type_ir/src/inherent.rs
@@ -630,6 +630,8 @@ pub trait Features<I: Interner>: Copy {
     fn coroutine_clone(self) -> bool;
 
     fn associated_const_equality(self) -> bool;
+
+    fn feature_bound_holds_in_crate(self, symbol: I::Symbol) -> bool;
 }
 
 pub trait DefId<I: Interner>: Copy + Debug + Hash + Eq + TypeFoldable<I> {
diff --git a/compiler/rustc_type_ir/src/interner.rs b/compiler/rustc_type_ir/src/interner.rs
index dd3cf1fc181..e3231244577 100644
--- a/compiler/rustc_type_ir/src/interner.rs
+++ b/compiler/rustc_type_ir/src/interner.rs
@@ -106,6 +106,7 @@ pub trait Interner:
     type ParamTy: ParamLike;
     type BoundTy: BoundVarLike<Self>;
     type PlaceholderTy: PlaceholderLike<Self, Bound = Self::BoundTy>;
+    type Symbol: Copy + Hash + PartialEq + Eq + Debug;
 
     // Things stored inside of tys
     type ErrorGuaranteed: Copy + Debug + Hash + Eq;
@@ -145,6 +146,13 @@ pub trait Interner:
     type BoundRegion: BoundVarLike<Self>;
     type PlaceholderRegion: PlaceholderLike<Self, Bound = Self::BoundRegion>;
 
+    type RegionAssumptions: Copy
+        + Debug
+        + Hash
+        + Eq
+        + SliceLike<Item = ty::OutlivesPredicate<Self, Self::GenericArg>>
+        + TypeFoldable<Self>;
+
     // Predicates
     type ParamEnv: ParamEnv<Self>;
     type Predicate: Predicate<Self>;
diff --git a/compiler/rustc_type_ir/src/predicate_kind.rs b/compiler/rustc_type_ir/src/predicate_kind.rs
index 4e41fd16ffd..8bc15ec4ff5 100644
--- a/compiler/rustc_type_ir/src/predicate_kind.rs
+++ b/compiler/rustc_type_ir/src/predicate_kind.rs
@@ -46,6 +46,13 @@ pub enum ClauseKind<I: Interner> {
     /// corresponding trait clause; this just enforces the *constness* of that
     /// implementation.
     HostEffect(ty::HostEffectPredicate<I>),
+
+    /// Support marking impl as unstable.
+    UnstableFeature(
+        #[type_foldable(identity)]
+        #[type_visitable(ignore)]
+        I::Symbol,
+    ),
 }
 
 #[derive_where(Clone, Copy, Hash, PartialEq, Eq; I: Interner)]
@@ -134,6 +141,9 @@ impl<I: Interner> fmt::Debug for ClauseKind<I> {
             ClauseKind::ConstEvaluatable(ct) => {
                 write!(f, "ConstEvaluatable({ct:?})")
             }
+            ClauseKind::UnstableFeature(feature_name) => {
+                write!(f, "UnstableFeature({feature_name:?})")
+            }
         }
     }
 }
diff --git a/compiler/rustc_type_ir/src/ty_kind.rs b/compiler/rustc_type_ir/src/ty_kind.rs
index db6fbefcf05..7c665424750 100644
--- a/compiler/rustc_type_ir/src/ty_kind.rs
+++ b/compiler/rustc_type_ir/src/ty_kind.rs
@@ -1150,4 +1150,5 @@ pub struct FnHeader<I: Interner> {
 #[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
 pub struct CoroutineWitnessTypes<I: Interner> {
     pub types: I::Tys,
+    pub assumptions: I::RegionAssumptions,
 }
diff --git a/compiler/rustc_type_ir/src/visit.rs b/compiler/rustc_type_ir/src/visit.rs
index a96ac97f785..5104484e9c4 100644
--- a/compiler/rustc_type_ir/src/visit.rs
+++ b/compiler/rustc_type_ir/src/visit.rs
@@ -269,6 +269,10 @@ pub trait TypeVisitableExt<I: Interner>: TypeVisitable<I> {
         self.has_type_flags(TypeFlags::HAS_TY_OPAQUE)
     }
 
+    fn has_coroutines(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_TY_CORO)
+    }
+
     fn references_error(&self) -> bool {
         self.has_type_flags(TypeFlags::HAS_ERROR)
     }