Merge from rustc

175 files changed, 1022 insertions, 691 deletions

diff --git a/compiler/rustc_ast_lowering/messages.ftl b/compiler/rustc_ast_lowering/messages.ftl
index 9ed93d481e7..a5ee6713be8 100644
--- a/compiler/rustc_ast_lowering/messages.ftl
+++ b/compiler/rustc_ast_lowering/messages.ftl
@@ -167,11 +167,21 @@ ast_lowering_template_modifier = template modifier
 
 ast_lowering_this_not_async = this is not `async`
 
+ast_lowering_underscore_array_length_unstable =
+    using `_` for array lengths is unstable
+
 ast_lowering_underscore_expr_lhs_assign =
     in expressions, `_` can only be used on the left-hand side of an assignment
     .label = `_` not allowed here
 
+ast_lowering_unstable_inline_assembly = inline assembly is not stable yet on this architecture
+ast_lowering_unstable_inline_assembly_label_operands =
+    label operands for inline assembly are unstable
+ast_lowering_unstable_may_unwind = the `may_unwind` option is unstable
+
 ast_lowering_use_angle_brackets = use angle brackets instead
+
+ast_lowering_yield = yield syntax is experimental
 ast_lowering_yield_in_closure =
     `yield` can only be used in `#[coroutine]` closures, or `gen` blocks
     .suggestion = use `#[coroutine]` to make this closure a coroutine
diff --git a/compiler/rustc_ast_lowering/src/asm.rs b/compiler/rustc_ast_lowering/src/asm.rs
index ea7b8c114f4..7d9d689e6d7 100644
--- a/compiler/rustc_ast_lowering/src/asm.rs
+++ b/compiler/rustc_ast_lowering/src/asm.rs
@@ -19,10 +19,12 @@ use super::errors::{
     InvalidRegisterClass, RegisterClassOnlyClobber, RegisterConflict,
 };
 use super::LoweringContext;
-use crate::{ImplTraitContext, ImplTraitPosition, ParamMode, ResolverAstLoweringExt};
+use crate::{
+    fluent_generated as fluent, ImplTraitContext, ImplTraitPosition, ParamMode,
+    ResolverAstLoweringExt,
+};
 
 impl<'a, 'hir> LoweringContext<'a, 'hir> {
-    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     pub(crate) fn lower_inline_asm(
         &mut self,
         sp: Span,
@@ -52,7 +54,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     &self.tcx.sess,
                     sym::asm_experimental_arch,
                     sp,
-                    "inline assembly is not stable yet on this architecture",
+                    fluent::ast_lowering_unstable_inline_assembly,
                 )
                 .emit();
             }
@@ -64,8 +66,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             self.dcx().emit_err(AttSyntaxOnlyX86 { span: sp });
         }
         if asm.options.contains(InlineAsmOptions::MAY_UNWIND) && !self.tcx.features().asm_unwind {
-            feature_err(&self.tcx.sess, sym::asm_unwind, sp, "the `may_unwind` option is unstable")
-                .emit();
+            feature_err(
+                &self.tcx.sess,
+                sym::asm_unwind,
+                sp,
+                fluent::ast_lowering_unstable_may_unwind,
+            )
+            .emit();
         }
 
         let mut clobber_abis = FxIndexMap::default();
@@ -176,20 +183,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             out_expr: out_expr.as_ref().map(|expr| self.lower_expr(expr)),
                         }
                     }
-                    InlineAsmOperand::Const { anon_const } => {
-                        if !self.tcx.features().asm_const {
-                            feature_err(
-                                sess,
-                                sym::asm_const,
-                                *op_sp,
-                                "const operands for inline assembly are unstable",
-                            )
-                            .emit();
-                        }
-                        hir::InlineAsmOperand::Const {
-                            anon_const: self.lower_anon_const_to_anon_const(anon_const),
-                        }
-                    }
+                    InlineAsmOperand::Const { anon_const } => hir::InlineAsmOperand::Const {
+                        anon_const: self.lower_anon_const_to_anon_const(anon_const),
+                    },
                     InlineAsmOperand::Sym { sym } => {
                         let static_def_id = self
                             .resolver
@@ -246,7 +242,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                                 sess,
                                 sym::asm_goto,
                                 *op_sp,
-                                "label operands for inline assembly are unstable",
+                                fluent::ast_lowering_unstable_inline_assembly_label_operands,
                             )
                             .emit();
                         }
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index 124fe6bd380..b5d8a547a8f 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -23,7 +23,7 @@ use super::{
     ImplTraitContext, LoweringContext, ParamMode, ParenthesizedGenericArgs, ResolverAstLoweringExt,
 };
 use crate::errors::YieldInClosure;
-use crate::{FnDeclKind, ImplTraitPosition};
+use crate::{fluent_generated, FnDeclKind, ImplTraitPosition};
 
 impl<'hir> LoweringContext<'_, 'hir> {
     fn lower_exprs(&mut self, exprs: &[AstP<Expr>]) -> &'hir [hir::Expr<'hir>] {
@@ -1540,7 +1540,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
         }
     }
 
-    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn lower_expr_yield(&mut self, span: Span, opt_expr: Option<&Expr>) -> hir::ExprKind<'hir> {
         let yielded =
             opt_expr.as_ref().map(|x| self.lower_expr(x)).unwrap_or_else(|| self.expr_unit(span));
@@ -1575,7 +1574,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         &self.tcx.sess,
                         sym::coroutines,
                         span,
-                        "yield syntax is experimental",
+                        fluent_generated::ast_lowering_yield,
                     )
                     .emit();
                 }
@@ -1587,7 +1586,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         &self.tcx.sess,
                         sym::coroutines,
                         span,
-                        "yield syntax is experimental",
+                        fluent_generated::ast_lowering_yield,
                     )
                     .emit();
                 }
diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index 224787c335b..81d17a9dec2 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -2326,7 +2326,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         self.expr_block(block)
     }
 
-    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn lower_array_length(&mut self, c: &AnonConst) -> hir::ArrayLen<'hir> {
         match c.value.kind {
             ExprKind::Underscore => {
@@ -2340,7 +2339,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         &self.tcx.sess,
                         sym::generic_arg_infer,
                         c.value.span,
-                        "using `_` for array lengths is unstable",
+                        fluent_generated::ast_lowering_underscore_array_length_unstable,
                     )
                     .stash(c.value.span, StashKey::UnderscoreForArrayLengths);
                     hir::ArrayLen::Body(self.lower_anon_const_to_const_arg(c))
diff --git a/compiler/rustc_attr/messages.ftl b/compiler/rustc_attr/messages.ftl
index eb51e568f81..5d9ac23ec49 100644
--- a/compiler/rustc_attr/messages.ftl
+++ b/compiler/rustc_attr/messages.ftl
@@ -104,6 +104,9 @@ attr_unknown_meta_item =
 attr_unknown_version_literal =
     unknown version literal format, assuming it refers to a future version
 
+attr_unstable_cfg_target_compact =
+    compact `cfg(target(..))` is experimental and subject to change
+
 attr_unsupported_literal_cfg_string =
     literal in `cfg` predicate value must be a string
 attr_unsupported_literal_deprecated_kv_pair =
diff --git a/compiler/rustc_attr/src/builtin.rs b/compiler/rustc_attr/src/builtin.rs
index cf86a6942da..d057dcfdf9d 100644
--- a/compiler/rustc_attr/src/builtin.rs
+++ b/compiler/rustc_attr/src/builtin.rs
@@ -20,6 +20,7 @@ use rustc_span::hygiene::Transparency;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::Span;
 
+use crate::fluent_generated;
 use crate::session_diagnostics::{self, IncorrectReprFormatGenericCause};
 
 /// The version placeholder that recently stabilized features contain inside the
@@ -521,7 +522,6 @@ pub struct Condition {
 }
 
 /// Tests if a cfg-pattern matches the cfg set
-#[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
 pub fn cfg_matches(
     cfg: &ast::MetaItem,
     sess: &Session,
@@ -593,7 +593,6 @@ pub fn parse_version(s: Symbol) -> Option<RustcVersion> {
 
 /// Evaluate a cfg-like condition (with `any` and `all`), using `eval` to
 /// evaluate individual items.
-#[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
 pub fn eval_condition(
     cfg: &ast::MetaItem,
     sess: &Session,
@@ -680,7 +679,7 @@ pub fn eval_condition(
                             sess,
                             sym::cfg_target_compact,
                             cfg.span,
-                            "compact `cfg(target(..))` is experimental and subject to change",
+                            fluent_generated::attr_unstable_cfg_target_compact,
                         )
                         .emit();
                     }
diff --git a/compiler/rustc_borrowck/messages.ftl b/compiler/rustc_borrowck/messages.ftl
index c14a617eb91..edb25e12864 100644
--- a/compiler/rustc_borrowck/messages.ftl
+++ b/compiler/rustc_borrowck/messages.ftl
@@ -62,6 +62,9 @@ borrowck_could_not_normalize =
 borrowck_could_not_prove =
     could not prove `{$predicate}`
 
+borrowck_dereference_suggestion =
+    dereference the return value
+
 borrowck_func_take_self_moved_place =
     `{$func}` takes ownership of the receiver `self`, which moves {$place_name}
 
@@ -74,9 +77,24 @@ borrowck_higher_ranked_lifetime_error =
 borrowck_higher_ranked_subtype_error =
     higher-ranked subtype error
 
+borrowck_implicit_static =
+    this has an implicit `'static` lifetime requirement
+
+borrowck_implicit_static_introduced =
+    calling this method introduces the `impl`'s `'static` requirement
+
+borrowck_implicit_static_relax =
+    consider relaxing the implicit `'static` requirement
+
 borrowck_lifetime_constraints_error =
     lifetime may not live long enough
 
+borrowck_limitations_implies_static =
+    due to current limitations in the borrow checker, this implies a `'static` lifetime
+
+borrowck_move_closure_suggestion =
+    consider adding 'move' keyword before the nested closure
+
 borrowck_move_out_place_here =
     {$place} is moved here
 
@@ -163,6 +181,9 @@ borrowck_partial_var_move_by_use_in_coroutine =
         *[false] moved
     } due to use in coroutine
 
+borrowck_restrict_to_static =
+    consider restricting the type parameter to the `'static` lifetime
+
 borrowck_returned_async_block_escaped =
     returns an `async` block that contains a reference to a captured variable, which then escapes the closure body
 
diff --git a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
index a58c7c43246..2b46e5597f7 100644
--- a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
@@ -3989,7 +3989,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
             } else {
                 let ty = self.infcx.tcx.type_of(self.mir_def_id()).instantiate_identity();
                 match ty.kind() {
-                    ty::FnDef(_, _) | ty::FnPtr(_) => self.annotate_fn_sig(
+                    ty::FnDef(_, _) | ty::FnPtr(..) => self.annotate_fn_sig(
                         self.mir_def_id(),
                         self.infcx.tcx.fn_sig(self.mir_def_id()).instantiate_identity(),
                     ),
diff --git a/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs b/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs
index 3590e12274c..d85959c9a29 100644
--- a/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs
@@ -3,6 +3,8 @@
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
 
+use std::assert_matches::assert_matches;
+
 use rustc_errors::{Applicability, Diag};
 use rustc_hir as hir;
 use rustc_hir::intravisit::Visitor;
@@ -116,7 +118,7 @@ impl<'tcx> BorrowExplanation<'tcx> {
                     // path_span must be `Some` as otherwise the if condition is true
                     let path_span = path_span.unwrap();
                     // path_span is only present in the case of closure capture
-                    assert!(matches!(later_use_kind, LaterUseKind::ClosureCapture));
+                    assert_matches!(later_use_kind, LaterUseKind::ClosureCapture);
                     if !borrow_span.is_some_and(|sp| sp.overlaps(var_or_use_span)) {
                         let path_label = "used here by closure";
                         let capture_kind_label = message;
@@ -147,7 +149,7 @@ impl<'tcx> BorrowExplanation<'tcx> {
                     // path_span must be `Some` as otherwise the if condition is true
                     let path_span = path_span.unwrap();
                     // path_span is only present in the case of closure capture
-                    assert!(matches!(later_use_kind, LaterUseKind::ClosureCapture));
+                    assert_matches!(later_use_kind, LaterUseKind::ClosureCapture);
                     if borrow_span.map(|sp| !sp.overlaps(var_or_use_span)).unwrap_or(true) {
                         let path_label = "used here by closure";
                         let capture_kind_label = message;
diff --git a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
index 82df9760d8e..451e8bcb16d 100644
--- a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs
@@ -35,7 +35,7 @@ use crate::session_diagnostics::{
     LifetimeReturnCategoryErr, RequireStaticErr, VarHereDenote,
 };
 use crate::universal_regions::DefiningTy;
-use crate::{borrowck_errors, MirBorrowckCtxt};
+use crate::{borrowck_errors, fluent_generated as fluent, MirBorrowckCtxt};
 
 impl<'tcx> ConstraintDescription for ConstraintCategory<'tcx> {
     fn description(&self) -> &'static str {
@@ -198,7 +198,6 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
     // from higher-ranked trait bounds (HRTB). Try to locate span of the trait
     // and the span which bounded to the trait for adding 'static lifetime suggestion
     #[allow(rustc::diagnostic_outside_of_impl)]
-    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn suggest_static_lifetime_for_gat_from_hrtb(
         &self,
         diag: &mut Diag<'_>,
@@ -251,23 +250,28 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
         debug!(?hrtb_bounds);
 
         hrtb_bounds.iter().for_each(|bound| {
-            let Trait(PolyTraitRef { trait_ref, span: trait_span, .. }, _) = bound else { return; };
-            diag.span_note(
-                *trait_span,
-                "due to current limitations in the borrow checker, this implies a `'static` lifetime"
-            );
-            let Some(generics_fn) = hir.get_generics(self.body.source.def_id().expect_local()) else { return; };
-            let Def(_, trait_res_defid) = trait_ref.path.res else { return; };
+            let Trait(PolyTraitRef { trait_ref, span: trait_span, .. }, _) = bound else {
+                return;
+            };
+            diag.span_note(*trait_span, fluent::borrowck_limitations_implies_static);
+            let Some(generics_fn) = hir.get_generics(self.body.source.def_id().expect_local())
+            else {
+                return;
+            };
+            let Def(_, trait_res_defid) = trait_ref.path.res else {
+                return;
+            };
             debug!(?generics_fn);
             generics_fn.predicates.iter().for_each(|predicate| {
-                let BoundPredicate(
-                    WhereBoundPredicate {
-                        span: bounded_span,
-                        bounded_ty,
-                        bounds,
-                        ..
-                    }
-                ) = predicate else { return; };
+                let BoundPredicate(WhereBoundPredicate {
+                    span: bounded_span,
+                    bounded_ty,
+                    bounds,
+                    ..
+                }) = predicate
+                else {
+                    return;
+                };
                 bounds.iter().for_each(|bd| {
                     if let Trait(PolyTraitRef { trait_ref: tr_ref, .. }, _) = bd
                         && let Def(_, res_defid) = tr_ref.path.res
@@ -277,16 +281,17 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                         && generics_fn.params
                             .iter()
                             .rfind(|param| param.def_id.to_def_id() == defid)
-                            .is_some() {
-                            suggestions.push((bounded_span.shrink_to_hi(), " + 'static".to_string()));
-                        }
+                            .is_some()
+                    {
+                        suggestions.push((bounded_span.shrink_to_hi(), " + 'static".to_string()));
+                    }
                 });
             });
         });
         if suggestions.len() > 0 {
             suggestions.dedup();
             diag.multipart_suggestion_verbose(
-                "consider restricting the type parameter to the `'static` lifetime",
+                fluent::borrowck_restrict_to_static,
                 suggestions,
                 Applicability::MaybeIncorrect,
             );
@@ -976,7 +981,6 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
     }
 
     #[allow(rustc::diagnostic_outside_of_impl)]
-    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     #[instrument(skip(self, err), level = "debug")]
     fn suggest_constrain_dyn_trait_in_impl(
         &self,
@@ -994,16 +998,12 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
             debug!("trait spans found: {:?}", traits);
             for span in &traits {
                 let mut multi_span: MultiSpan = vec![*span].into();
-                multi_span
-                    .push_span_label(*span, "this has an implicit `'static` lifetime requirement");
-                multi_span.push_span_label(
-                    ident.span,
-                    "calling this method introduces the `impl`'s `'static` requirement",
-                );
+                multi_span.push_span_label(*span, fluent::borrowck_implicit_static);
+                multi_span.push_span_label(ident.span, fluent::borrowck_implicit_static_introduced);
                 err.subdiagnostic(RequireStaticErr::UsedImpl { multi_span });
                 err.span_suggestion_verbose(
                     span.shrink_to_hi(),
-                    "consider relaxing the implicit `'static` requirement",
+                    fluent::borrowck_implicit_static_relax,
                     " + '_",
                     Applicability::MaybeIncorrect,
                 );
@@ -1045,7 +1045,6 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
     }
 
     #[allow(rustc::diagnostic_outside_of_impl)]
-    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     /// When encountering a lifetime error caused by the return type of a closure, check the
     /// corresponding trait bound and see if dereferencing the closure return value would satisfy
     /// them. If so, we produce a structured suggestion.
@@ -1166,7 +1165,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
         if ocx.select_all_or_error().is_empty() && count > 0 {
             diag.span_suggestion_verbose(
                 tcx.hir().body(*body).value.peel_blocks().span.shrink_to_lo(),
-                "dereference the return value",
+                fluent::borrowck_dereference_suggestion,
                 "*".repeat(count),
                 Applicability::MachineApplicable,
             );
@@ -1174,7 +1173,6 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
     }
 
     #[allow(rustc::diagnostic_outside_of_impl)]
-    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn suggest_move_on_borrowing_closure(&self, diag: &mut Diag<'_>) {
         let map = self.infcx.tcx.hir();
         let body = map.body_owned_by(self.mir_def_id());
@@ -1213,7 +1211,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
         if let Some(closure_span) = closure_span {
             diag.span_suggestion_verbose(
                 closure_span,
-                "consider adding 'move' keyword before the nested closure",
+                fluent::borrowck_move_closure_suggestion,
                 "move ",
                 Applicability::MaybeIncorrect,
             );
diff --git a/compiler/rustc_borrowck/src/lib.rs b/compiler/rustc_borrowck/src/lib.rs
index 9c2a0036bef..30dd45d847c 100644
--- a/compiler/rustc_borrowck/src/lib.rs
+++ b/compiler/rustc_borrowck/src/lib.rs
@@ -1644,7 +1644,7 @@ impl<'mir, 'tcx> MirBorrowckCtxt<'_, 'mir, '_, 'tcx> {
                     | ty::Pat(_, _)
                     | ty::Slice(_)
                     | ty::FnDef(_, _)
-                    | ty::FnPtr(_)
+                    | ty::FnPtr(..)
                     | ty::Dynamic(_, _, _)
                     | ty::Closure(_, _)
                     | ty::CoroutineClosure(_, _)
@@ -1689,7 +1689,7 @@ impl<'mir, 'tcx> MirBorrowckCtxt<'_, 'mir, '_, 'tcx> {
                     | ty::RawPtr(_, _)
                     | ty::Ref(_, _, _)
                     | ty::FnDef(_, _)
-                    | ty::FnPtr(_)
+                    | ty::FnPtr(..)
                     | ty::Dynamic(_, _, _)
                     | ty::CoroutineWitness(..)
                     | ty::Never
diff --git a/compiler/rustc_borrowck/src/type_check/canonical.rs b/compiler/rustc_borrowck/src/type_check/canonical.rs
index 86cd8b918fc..b58691fbeae 100644
--- a/compiler/rustc_borrowck/src/type_check/canonical.rs
+++ b/compiler/rustc_borrowck/src/type_check/canonical.rs
@@ -7,6 +7,7 @@ use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, Upcast};
 use rustc_span::def_id::DefId;
 use rustc_span::Span;
+use rustc_trait_selection::traits::query::type_op::custom::CustomTypeOp;
 use rustc_trait_selection::traits::query::type_op::{self, TypeOpOutput};
 use rustc_trait_selection::traits::ObligationCause;
 
@@ -166,6 +167,52 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
     }
 
     #[instrument(skip(self), level = "debug")]
+    pub(super) fn struct_tail(
+        &mut self,
+        ty: Ty<'tcx>,
+        location: impl NormalizeLocation,
+    ) -> Ty<'tcx> {
+        let tcx = self.tcx();
+        if self.infcx.next_trait_solver() {
+            let body = self.body;
+            let param_env = self.param_env;
+            self.fully_perform_op(
+                location.to_locations(),
+                ConstraintCategory::Boring,
+                CustomTypeOp::new(
+                    |ocx| {
+                        let structurally_normalize = |ty| {
+                            ocx.structurally_normalize(
+                                &ObligationCause::misc(
+                                    location.to_locations().span(body),
+                                    body.source.def_id().expect_local(),
+                                ),
+                                param_env,
+                                ty,
+                            )
+                            .unwrap_or_else(|_| bug!("struct tail should have been computable, since we computed it in HIR"))
+                        };
+
+                        let tail = tcx.struct_tail_raw(
+                            ty,
+                            structurally_normalize,
+                            || {},
+                        );
+
+                        Ok(tail)
+                    },
+                    "normalizing struct tail",
+                ),
+            )
+            .unwrap_or_else(|guar| Ty::new_error(tcx, guar))
+        } else {
+            let mut normalize = |ty| self.normalize(ty, location);
+            let tail = tcx.struct_tail_raw(ty, &mut normalize, || {});
+            normalize(tail)
+        }
+    }
+
+    #[instrument(skip(self), level = "debug")]
     pub(super) fn ascribe_user_type(
         &mut self,
         mir_ty: Ty<'tcx>,
diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index b13773ffe14..a2669da1b04 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -1364,7 +1364,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 debug!("func_ty.kind: {:?}", func_ty.kind());
 
                 let sig = match func_ty.kind() {
-                    ty::FnDef(..) | ty::FnPtr(_) => func_ty.fn_sig(tcx),
+                    ty::FnDef(..) | ty::FnPtr(..) => func_ty.fn_sig(tcx),
                     _ => {
                         span_mirbug!(self, term, "call to non-function {:?}", func_ty);
                         return;
@@ -1989,9 +1989,9 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
 
                         let ty_fn_ptr_from = Ty::new_fn_ptr(tcx, fn_sig);
 
-                        if let Err(terr) = self.eq_types(
-                            *ty,
+                        if let Err(terr) = self.sub_types(
                             ty_fn_ptr_from,
+                            *ty,
                             location.to_locations(),
                             ConstraintCategory::Cast { unsize_to: None },
                         ) {
@@ -2014,9 +2014,9 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                         let ty_fn_ptr_from =
                             Ty::new_fn_ptr(tcx, tcx.signature_unclosure(sig, *safety));
 
-                        if let Err(terr) = self.eq_types(
-                            *ty,
+                        if let Err(terr) = self.sub_types(
                             ty_fn_ptr_from,
+                            *ty,
                             location.to_locations(),
                             ConstraintCategory::Cast { unsize_to: None },
                         ) {
@@ -2329,17 +2329,8 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                         let cast_ty_to = CastTy::from_ty(*ty);
                         match (cast_ty_from, cast_ty_to) {
                             (Some(CastTy::Ptr(src)), Some(CastTy::Ptr(dst))) => {
-                                let mut normalize = |t| self.normalize(t, location);
-
-                                // N.B. `struct_tail_with_normalize` only "structurally resolves"
-                                // the type. It is not fully normalized, so we have to normalize it
-                                // afterwards.
-                                let src_tail =
-                                    tcx.struct_tail_with_normalize(src.ty, &mut normalize, || ());
-                                let src_tail = normalize(src_tail);
-                                let dst_tail =
-                                    tcx.struct_tail_with_normalize(dst.ty, &mut normalize, || ());
-                                let dst_tail = normalize(dst_tail);
+                                let src_tail = self.struct_tail(src.ty, location);
+                                let dst_tail = self.struct_tail(dst.ty, location);
 
                                 // This checks (lifetime part of) vtable validity for pointer casts,
                                 // which is irrelevant when there are aren't principal traits on both sides (aka only auto traits).
@@ -2420,7 +2411,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 let ty_left = left.ty(body, tcx);
                 match ty_left.kind() {
                     // Types with regions are comparable if they have a common super-type.
-                    ty::RawPtr(_, _) | ty::FnPtr(_) => {
+                    ty::RawPtr(_, _) | ty::FnPtr(..) => {
                         let ty_right = right.ty(body, tcx);
                         let common_ty = self.infcx.next_ty_var(body.source_info(location).span);
                         self.sub_types(
diff --git a/compiler/rustc_codegen_cranelift/src/common.rs b/compiler/rustc_codegen_cranelift/src/common.rs
index a1b29a42225..b9000a3874f 100644
--- a/compiler/rustc_codegen_cranelift/src/common.rs
+++ b/compiler/rustc_codegen_cranelift/src/common.rs
@@ -69,7 +69,7 @@ fn clif_type_from_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Option<types::Typ
             FloatTy::F64 => types::F64,
             FloatTy::F128 => unimplemented!("f16_f128"),
         },
-        ty::FnPtr(_) => pointer_ty(tcx),
+        ty::FnPtr(..) => pointer_ty(tcx),
         ty::RawPtr(pointee_ty, _) | ty::Ref(_, pointee_ty, _) => {
             if has_ptr_meta(tcx, *pointee_ty) {
                 return None;
diff --git a/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs b/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
index b21c559e668..29deac60730 100644
--- a/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
+++ b/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
@@ -725,7 +725,8 @@ fn codegen_regular_intrinsic_call<'tcx>(
 
             // Cranelift treats stores as volatile by default
             // FIXME correctly handle unaligned_volatile_store
-            // FIXME actually do nontemporal stores if requested
+            // FIXME actually do nontemporal stores if requested (but do not just emit MOVNT on x86;
+            // see the LLVM backend for details)
             let dest = CPlace::for_ptr(Pointer::new(ptr), val.layout());
             dest.write_cvalue(fx, val);
         }
diff --git a/compiler/rustc_codegen_cranelift/src/value_and_place.rs b/compiler/rustc_codegen_cranelift/src/value_and_place.rs
index 8eb2095e523..fd77502224e 100644
--- a/compiler/rustc_codegen_cranelift/src/value_and_place.rs
+++ b/compiler/rustc_codegen_cranelift/src/value_and_place.rs
@@ -874,7 +874,7 @@ pub(crate) fn assert_assignable<'tcx>(
         (ty::Ref(_, a, _), ty::RawPtr(b, _)) | (ty::RawPtr(a, _), ty::Ref(_, b, _)) => {
             assert_assignable(fx, *a, *b, limit - 1);
         }
-        (ty::FnPtr(_), ty::FnPtr(_)) => {
+        (ty::FnPtr(..), ty::FnPtr(..)) => {
             let from_sig = fx.tcx.normalize_erasing_late_bound_regions(
                 ParamEnv::reveal_all(),
                 from_ty.fn_sig(fx.tcx),
diff --git a/compiler/rustc_codegen_gcc/build_system/src/test.rs b/compiler/rustc_codegen_gcc/build_system/src/test.rs
index dabf6c5aa3e..83fa8059b1a 100644
--- a/compiler/rustc_codegen_gcc/build_system/src/test.rs
+++ b/compiler/rustc_codegen_gcc/build_system/src/test.rs
@@ -552,7 +552,7 @@ fn asm_tests(env: &Env, args: &TestArg) -> Result<(), String> {
             &"--stage",
             &"0",
             &"tests/assembly/asm",
-            &"--rustc-args",
+            &"--compiletest-rustc-args",
             &rustc_args,
         ],
         Some(&rust_dir),
@@ -1020,7 +1020,7 @@ where
             &"--stage",
             &"0",
             &format!("tests/{}", test_type),
-            &"--rustc-args",
+            &"--compiletest-rustc-args",
             &rustc_args,
         ],
         Some(&rust_path),
diff --git a/compiler/rustc_codegen_gcc/src/builder.rs b/compiler/rustc_codegen_gcc/src/builder.rs
index a64371a3d89..47b378cc1cd 100644
--- a/compiler/rustc_codegen_gcc/src/builder.rs
+++ b/compiler/rustc_codegen_gcc/src/builder.rs
@@ -1127,6 +1127,8 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
         self.llbb().add_assignment(self.location, aligned_destination, val);
         // TODO(antoyo): handle align and flags.
         // NOTE: dummy value here since it's never used. FIXME(antoyo): API should not return a value here?
+        // When adding support for NONTEMPORAL, make sure to not just emit MOVNT on x86; see the
+        // LLVM backend for details.
         self.cx.context.new_rvalue_zero(self.type_i32())
     }
 
diff --git a/compiler/rustc_codegen_gcc/src/common.rs b/compiler/rustc_codegen_gcc/src/common.rs
index 7a456e1c5d6..dca6b6494f9 100644
--- a/compiler/rustc_codegen_gcc/src/common.rs
+++ b/compiler/rustc_codegen_gcc/src/common.rs
@@ -160,6 +160,11 @@ impl<'gcc, 'tcx> ConstMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
         self.context.new_struct_constructor(None, struct_type.as_type(), None, values)
     }
 
+    fn const_vector(&self, values: &[RValue<'gcc>]) -> RValue<'gcc> {
+        let typ = self.type_vector(values[0].get_type(), values.len() as u64);
+        self.context.new_rvalue_from_vector(None, typ, values)
+    }
+
     fn const_to_opt_uint(&self, _v: RValue<'gcc>) -> Option<u64> {
         // TODO(antoyo)
         None
diff --git a/compiler/rustc_codegen_gcc/src/type_of.rs b/compiler/rustc_codegen_gcc/src/type_of.rs
index d85ed4f12ff..b7b1be5369c 100644
--- a/compiler/rustc_codegen_gcc/src/type_of.rs
+++ b/compiler/rustc_codegen_gcc/src/type_of.rs
@@ -213,9 +213,8 @@ impl<'tcx> LayoutGccExt<'tcx> for TyAndLayout<'tcx> {
                 // NOTE: we cannot remove this match like in the LLVM codegen because the call
                 // to fn_ptr_backend_type handle the on-stack attribute.
                 // TODO(antoyo): find a less hackish way to hande the on-stack attribute.
-                ty::FnPtr(sig) => {
-                    cx.fn_ptr_backend_type(cx.fn_abi_of_fn_ptr(sig, ty::List::empty()))
-                }
+                ty::FnPtr(sig_tys, hdr) => cx
+                    .fn_ptr_backend_type(cx.fn_abi_of_fn_ptr(sig_tys.with(hdr), ty::List::empty())),
                 _ => self.scalar_gcc_type_at(cx, scalar, Size::ZERO),
             };
             cx.scalar_types.borrow_mut().insert(self.ty, ty);
diff --git a/compiler/rustc_codegen_gcc/tests/run/asm.rs b/compiler/rustc_codegen_gcc/tests/run/asm.rs
index 56f2aac3d0a..4e05d026868 100644
--- a/compiler/rustc_codegen_gcc/tests/run/asm.rs
+++ b/compiler/rustc_codegen_gcc/tests/run/asm.rs
@@ -3,12 +3,10 @@
 // Run-time:
 //   status: 0
 
-#![feature(asm_const)]
-
-#[cfg(target_arch="x86_64")]
+#[cfg(target_arch = "x86_64")]
 use std::arch::{asm, global_asm};
 
-#[cfg(target_arch="x86_64")]
+#[cfg(target_arch = "x86_64")]
 global_asm!(
     "
     .global add_asm
@@ -22,7 +20,7 @@ extern "C" {
     fn add_asm(a: i64, b: i64) -> i64;
 }
 
-#[cfg(target_arch="x86_64")]
+#[cfg(target_arch = "x86_64")]
 pub unsafe fn mem_cpy(dst: *mut u8, src: *const u8, len: usize) {
     asm!(
         "rep movsb",
@@ -33,7 +31,7 @@ pub unsafe fn mem_cpy(dst: *mut u8, src: *const u8, len: usize) {
     );
 }
 
-#[cfg(target_arch="x86_64")]
+#[cfg(target_arch = "x86_64")]
 fn asm() {
     unsafe {
         asm!("nop");
@@ -178,9 +176,8 @@ fn asm() {
     assert_eq!(array1, array2);
 }
 
-#[cfg(not(target_arch="x86_64"))]
-fn asm() {
-}
+#[cfg(not(target_arch = "x86_64"))]
+fn asm() {}
 
 fn main() {
     asm();
diff --git a/compiler/rustc_codegen_llvm/src/abi.rs b/compiler/rustc_codegen_llvm/src/abi.rs
index 1277b7898c2..5ff580e295a 100644
--- a/compiler/rustc_codegen_llvm/src/abi.rs
+++ b/compiler/rustc_codegen_llvm/src/abi.rs
@@ -430,9 +430,32 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
             i += 1;
             i - 1
         };
+
+        let apply_range_attr = |idx: AttributePlace, scalar: rustc_target::abi::Scalar| {
+            if cx.sess().opts.optimize != config::OptLevel::No
+                && llvm_util::get_version() >= (19, 0, 0)
+                && matches!(scalar.primitive(), Int(..))
+                // If the value is a boolean, the range is 0..2 and that ultimately
+                // become 0..0 when the type becomes i1, which would be rejected
+                // by the LLVM verifier.
+                && !scalar.is_bool()
+                // LLVM also rejects full range.
+                && !scalar.is_always_valid(cx)
+            {
+                attributes::apply_to_llfn(
+                    llfn,
+                    idx,
+                    &[llvm::CreateRangeAttr(cx.llcx, scalar.size(cx), scalar.valid_range(cx))],
+                );
+            }
+        };
+
         match &self.ret.mode {
             PassMode::Direct(attrs) => {
                 attrs.apply_attrs_to_llfn(llvm::AttributePlace::ReturnValue, cx, llfn);
+                if let abi::Abi::Scalar(scalar) = self.ret.layout.abi {
+                    apply_range_attr(llvm::AttributePlace::ReturnValue, scalar);
+                }
             }
             PassMode::Indirect { attrs, meta_attrs: _, on_stack } => {
                 assert!(!on_stack);
@@ -471,8 +494,13 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
                     );
                     attributes::apply_to_llfn(llfn, llvm::AttributePlace::Argument(i), &[byval]);
                 }
-                PassMode::Direct(attrs)
-                | PassMode::Indirect { attrs, meta_attrs: None, on_stack: false } => {
+                PassMode::Direct(attrs) => {
+                    let i = apply(attrs);
+                    if let abi::Abi::Scalar(scalar) = arg.layout.abi {
+                        apply_range_attr(llvm::AttributePlace::Argument(i), scalar);
+                    }
+                }
+                PassMode::Indirect { attrs, meta_attrs: None, on_stack: false } => {
                     apply(attrs);
                 }
                 PassMode::Indirect { attrs, meta_attrs: Some(meta_attrs), on_stack } => {
@@ -481,8 +509,12 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
                     apply(meta_attrs);
                 }
                 PassMode::Pair(a, b) => {
-                    apply(a);
-                    apply(b);
+                    let i = apply(a);
+                    let ii = apply(b);
+                    if let abi::Abi::ScalarPair(scalar_a, scalar_b) = arg.layout.abi {
+                        apply_range_attr(llvm::AttributePlace::Argument(i), scalar_a);
+                        apply_range_attr(llvm::AttributePlace::Argument(ii), scalar_b);
+                    }
                 }
                 PassMode::Cast { cast, pad_i32 } => {
                     if *pad_i32 {
@@ -537,15 +569,18 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
             }
             _ => {}
         }
-        if let abi::Abi::Scalar(scalar) = self.ret.layout.abi {
-            // If the value is a boolean, the range is 0..2 and that ultimately
-            // become 0..0 when the type becomes i1, which would be rejected
-            // by the LLVM verifier.
-            if let Int(..) = scalar.primitive() {
-                if !scalar.is_bool() && !scalar.is_always_valid(bx) {
-                    bx.range_metadata(callsite, scalar.valid_range(bx));
-                }
-            }
+        if bx.cx.sess().opts.optimize != config::OptLevel::No
+                && llvm_util::get_version() < (19, 0, 0)
+                && let abi::Abi::Scalar(scalar) = self.ret.layout.abi
+                && matches!(scalar.primitive(), Int(..))
+                // If the value is a boolean, the range is 0..2 and that ultimately
+                // become 0..0 when the type becomes i1, which would be rejected
+                // by the LLVM verifier.
+                && !scalar.is_bool()
+                // LLVM also rejects full range.
+                && !scalar.is_always_valid(bx)
+        {
+            bx.range_metadata(callsite, scalar.valid_range(bx));
         }
         for arg in self.args.iter() {
             match &arg.mode {
diff --git a/compiler/rustc_codegen_llvm/src/asm.rs b/compiler/rustc_codegen_llvm/src/asm.rs
index aea8395441a..f931698c38f 100644
--- a/compiler/rustc_codegen_llvm/src/asm.rs
+++ b/compiler/rustc_codegen_llvm/src/asm.rs
@@ -1,3 +1,5 @@
+use std::assert_matches::assert_matches;
+
 use libc::{c_char, c_uint};
 use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
 use rustc_codegen_ssa::mir::operand::OperandValue;
@@ -89,7 +91,7 @@ impl<'ll, 'tcx> AsmBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
                         // if the target feature needed by the register class is
                         // disabled. This is necessary otherwise LLVM will try
                         // to actually allocate a register for the dummy output.
-                        assert!(matches!(reg, InlineAsmRegOrRegClass::Reg(_)));
+                        assert_matches!(reg, InlineAsmRegOrRegClass::Reg(_));
                         clobbers.push(format!("~{}", reg_to_llvm(reg, None)));
                         continue;
                     } else {
diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs
index 0f44c5dba5e..cc081f29e12 100644
--- a/compiler/rustc_codegen_llvm/src/builder.rs
+++ b/compiler/rustc_codegen_llvm/src/builder.rs
@@ -728,13 +728,32 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
                 llvm::LLVMSetVolatile(store, llvm::True);
             }
             if flags.contains(MemFlags::NONTEMPORAL) {
-                // According to LLVM [1] building a nontemporal store must
-                // *always* point to a metadata value of the integer 1.
-                //
-                // [1]: https://llvm.org/docs/LangRef.html#store-instruction
-                let one = self.cx.const_i32(1);
-                let node = llvm::LLVMMDNodeInContext(self.cx.llcx, &one, 1);
-                llvm::LLVMSetMetadata(store, llvm::MD_nontemporal as c_uint, node);
+                // Make sure that the current target architectures supports "sane" non-temporal
+                // stores, i.e., non-temporal stores that are equivalent to regular stores except
+                // for performance. LLVM doesn't seem to care about this, and will happily treat
+                // `!nontemporal` stores as-if they were normal stores (for reordering optimizations
+                // etc) even on x86, despite later lowering them to MOVNT which do *not* behave like
+                // regular stores but require special fences.
+                // So we keep a list of architectures where `!nontemporal` is known to be truly just
+                // a hint, and use regular stores everywhere else.
+                // (In the future, we could alternatively ensure that an sfence gets emitted after a sequence of movnt
+                // before any kind of synchronizing operation. But it's not clear how to do that with LLVM.)
+                // For more context, see <https://github.com/rust-lang/rust/issues/114582> and
+                // <https://github.com/llvm/llvm-project/issues/64521>.
+                const WELL_BEHAVED_NONTEMPORAL_ARCHS: &[&str] =
+                    &["aarch64", "arm", "riscv32", "riscv64"];
+
+                let use_nontemporal =
+                    WELL_BEHAVED_NONTEMPORAL_ARCHS.contains(&&*self.cx.tcx.sess.target.arch);
+                if use_nontemporal {
+                    // According to LLVM [1] building a nontemporal store must
+                    // *always* point to a metadata value of the integer 1.
+                    //
+                    // [1]: https://llvm.org/docs/LangRef.html#store-instruction
+                    let one = self.cx.const_i32(1);
+                    let node = llvm::LLVMMDNodeInContext(self.cx.llcx, &one, 1);
+                    llvm::LLVMSetMetadata(store, llvm::MD_nontemporal as c_uint, node);
+                }
             }
             store
         }
diff --git a/compiler/rustc_codegen_llvm/src/common.rs b/compiler/rustc_codegen_llvm/src/common.rs
index 65f974c5689..a3997900184 100644
--- a/compiler/rustc_codegen_llvm/src/common.rs
+++ b/compiler/rustc_codegen_llvm/src/common.rs
@@ -97,11 +97,6 @@ impl<'ll> CodegenCx<'ll, '_> {
         unsafe { llvm::LLVMConstArray2(ty, elts.as_ptr(), len) }
     }
 
-    pub fn const_vector(&self, elts: &[&'ll Value]) -> &'ll Value {
-        let len = c_uint::try_from(elts.len()).expect("LLVMConstVector elements len overflow");
-        unsafe { llvm::LLVMConstVector(elts.as_ptr(), len) }
-    }
-
     pub fn const_bytes(&self, bytes: &[u8]) -> &'ll Value {
         bytes_in_context(self.llcx, bytes)
     }
@@ -221,6 +216,11 @@ impl<'ll, 'tcx> ConstMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         struct_in_context(self.llcx, elts, packed)
     }
 
+    fn const_vector(&self, elts: &[&'ll Value]) -> &'ll Value {
+        let len = c_uint::try_from(elts.len()).expect("LLVMConstVector elements len overflow");
+        unsafe { llvm::LLVMConstVector(elts.as_ptr(), len) }
+    }
+
     fn const_to_opt_uint(&self, v: &'ll Value) -> Option<u64> {
         try_as_const_integral(v).and_then(|v| unsafe {
             let mut i = 0u64;
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
index ad638588612..87bea22d8dd 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
@@ -456,7 +456,7 @@ pub fn type_di_node<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>, t: Ty<'tcx>) -> &'ll D
         {
             build_pointer_or_reference_di_node(cx, t, t.boxed_ty(), unique_type_id)
         }
-        ty::FnDef(..) | ty::FnPtr(_) => build_subroutine_type_di_node(cx, unique_type_id),
+        ty::FnDef(..) | ty::FnPtr(..) => build_subroutine_type_di_node(cx, unique_type_id),
         ty::Closure(..) => build_closure_env_di_node(cx, unique_type_id),
         ty::CoroutineClosure(..) => build_closure_env_di_node(cx, unique_type_id),
         ty::Coroutine(..) => enums::build_coroutine_di_node(cx, unique_type_id),
diff --git a/compiler/rustc_codegen_llvm/src/intrinsic.rs b/compiler/rustc_codegen_llvm/src/intrinsic.rs
index 57d5f6fdf50..f5558723d11 100644
--- a/compiler/rustc_codegen_llvm/src/intrinsic.rs
+++ b/compiler/rustc_codegen_llvm/src/intrinsic.rs
@@ -1,3 +1,4 @@
+use std::assert_matches::assert_matches;
 use std::cmp::Ordering;
 
 use rustc_codegen_ssa::base::{compare_simd_types, wants_msvc_seh, wants_wasm_eh};
@@ -1142,7 +1143,7 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
     if cfg!(debug_assertions) {
         for (ty, arg) in arg_tys.iter().zip(args) {
             if ty.is_simd() {
-                assert!(matches!(arg.val, OperandValue::Immediate(_)));
+                assert_matches!(arg.val, OperandValue::Immediate(_));
             }
         }
     }
diff --git a/compiler/rustc_codegen_llvm/src/lib.rs b/compiler/rustc_codegen_llvm/src/lib.rs
index 518a86e0cb0..43164390a1c 100644
--- a/compiler/rustc_codegen_llvm/src/lib.rs
+++ b/compiler/rustc_codegen_llvm/src/lib.rs
@@ -8,6 +8,7 @@
 #![allow(internal_features)]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
+#![feature(assert_matches)]
 #![feature(exact_size_is_empty)]
 #![feature(extern_types)]
 #![feature(hash_raw_entry)]
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 80b13c0e1d4..faabbcb020d 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -1575,6 +1575,12 @@ extern "C" {
     pub fn LLVMRustCreateAllocSizeAttr(C: &Context, size_arg: u32) -> &Attribute;
     pub fn LLVMRustCreateAllocKindAttr(C: &Context, size_arg: u64) -> &Attribute;
     pub fn LLVMRustCreateMemoryEffectsAttr(C: &Context, effects: MemoryEffects) -> &Attribute;
+    pub fn LLVMRustCreateRangeAttribute(
+        C: &Context,
+        num_bits: c_uint,
+        lower_words: *const u64,
+        upper_words: *const u64,
+    ) -> &Attribute;
 
     // Operations on functions
     pub fn LLVMRustGetOrInsertFunction<'a>(
diff --git a/compiler/rustc_codegen_llvm/src/llvm/mod.rs b/compiler/rustc_codegen_llvm/src/llvm/mod.rs
index 72691907c0d..d0db350a149 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/mod.rs
@@ -8,7 +8,7 @@ use std::string::FromUtf8Error;
 use libc::c_uint;
 use rustc_data_structures::small_c_str::SmallCStr;
 use rustc_llvm::RustString;
-use rustc_target::abi::Align;
+use rustc_target::abi::{Align, Size, WrappingRange};
 
 pub use self::AtomicRmwBinOp::*;
 pub use self::CallConv::*;
@@ -105,6 +105,21 @@ pub fn CreateAllocKindAttr(llcx: &Context, kind_arg: AllocKindFlags) -> &Attribu
     unsafe { LLVMRustCreateAllocKindAttr(llcx, kind_arg.bits()) }
 }
 
+pub fn CreateRangeAttr(llcx: &Context, size: Size, range: WrappingRange) -> &Attribute {
+    let lower = range.start;
+    let upper = range.end.wrapping_add(1);
+    let lower_words = [lower as u64, (lower >> 64) as u64];
+    let upper_words = [upper as u64, (upper >> 64) as u64];
+    unsafe {
+        LLVMRustCreateRangeAttribute(
+            llcx,
+            size.bits().try_into().unwrap(),
+            lower_words.as_ptr(),
+            upper_words.as_ptr(),
+        )
+    }
+}
+
 #[derive(Copy, Clone)]
 pub enum AttributePlace {
     ReturnValue,
diff --git a/compiler/rustc_codegen_ssa/src/back/write.rs b/compiler/rustc_codegen_ssa/src/back/write.rs
index bea12747a51..70b45a852ca 100644
--- a/compiler/rustc_codegen_ssa/src/back/write.rs
+++ b/compiler/rustc_codegen_ssa/src/back/write.rs
@@ -1,4 +1,5 @@
 use std::any::Any;
+use std::assert_matches::assert_matches;
 use std::marker::PhantomData;
 use std::path::{Path, PathBuf};
 use std::sync::mpsc::{channel, Receiver, Sender};
@@ -1963,7 +1964,7 @@ impl SharedEmitterMain {
                     sess.dcx().abort_if_errors();
                 }
                 Ok(SharedEmitterMessage::InlineAsmError(cookie, msg, level, source)) => {
-                    assert!(matches!(level, Level::Error | Level::Warning | Level::Note));
+                    assert_matches!(level, Level::Error | Level::Warning | Level::Note);
                     let msg = msg.strip_prefix("error: ").unwrap_or(&msg).to_string();
                     let mut err = Diag::<()>::new(sess.dcx(), level, msg);
 
diff --git a/compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs b/compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs
index 27558038927..359043a6d78 100644
--- a/compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs
+++ b/compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs
@@ -331,7 +331,7 @@ fn push_debuginfo_type_name<'tcx>(
                 output.push(')');
             }
         }
-        ty::FnDef(..) | ty::FnPtr(_) => {
+        ty::FnDef(..) | ty::FnPtr(..) => {
             // We've encountered a weird 'recursive type'
             // Currently, the only way to generate such a type
             // is by using 'impl trait':
diff --git a/compiler/rustc_codegen_ssa/src/lib.rs b/compiler/rustc_codegen_ssa/src/lib.rs
index 1b029660433..cb6d9d6f66e 100644
--- a/compiler/rustc_codegen_ssa/src/lib.rs
+++ b/compiler/rustc_codegen_ssa/src/lib.rs
@@ -4,6 +4,7 @@
 #![allow(rustc::untranslatable_diagnostic)]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
+#![feature(assert_matches)]
 #![feature(box_patterns)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index bc3076528da..817e2ca72ec 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -846,7 +846,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 ),
                 None,
             ),
-            ty::FnPtr(_) => (None, Some(callee.immediate())),
+            ty::FnPtr(..) => (None, Some(callee.immediate())),
             _ => bug!("{} is not callable", callee.layout.ty),
         };
 
@@ -923,8 +923,12 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         // third argument must be constant. This is
                         // checked by the type-checker.
                         if i == 2 && intrinsic.name == sym::simd_shuffle {
+                            // FIXME: the simd_shuffle argument is actually an array,
+                            // not a vector, so we need this special hack to make sure
+                            // it is passed as an immediate. We should pass the
+                            // shuffle indices as a vector instead to avoid this hack.
                             if let mir::Operand::Constant(constant) = &arg.node {
-                                let (llval, ty) = self.simd_shuffle_indices(bx, constant);
+                                let (llval, ty) = self.immediate_const_vector(bx, constant);
                                 return OperandRef {
                                     val: Immediate(llval),
                                     layout: bx.layout_of(ty),
diff --git a/compiler/rustc_codegen_ssa/src/mir/constant.rs b/compiler/rustc_codegen_ssa/src/mir/constant.rs
index f4d974f7036..0aa85b82038 100644
--- a/compiler/rustc_codegen_ssa/src/mir/constant.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/constant.rs
@@ -1,6 +1,6 @@
 use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::ty::layout::HasTyCtxt;
-use rustc_middle::ty::{self, Ty};
+use rustc_middle::ty::{self, Ty, ValTree};
 use rustc_middle::{bug, mir, span_bug};
 use rustc_target::abi::Abi;
 
@@ -28,7 +28,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             .expect("erroneous constant missed by mono item collection")
     }
 
-    /// This is a convenience helper for `simd_shuffle_indices`. It has the precondition
+    /// This is a convenience helper for `immediate_const_vector`. It has the precondition
     /// that the given `constant` is an `Const::Unevaluated` and must be convertible to
     /// a `ValTree`. If you want a more general version of this, talk to `wg-const-eval` on zulip.
     ///
@@ -59,23 +59,42 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         self.cx.tcx().const_eval_resolve_for_typeck(ty::ParamEnv::reveal_all(), uv, constant.span)
     }
 
-    /// process constant containing SIMD shuffle indices
-    pub fn simd_shuffle_indices(
+    /// process constant containing SIMD shuffle indices & constant vectors
+    pub fn immediate_const_vector(
         &mut self,
         bx: &Bx,
         constant: &mir::ConstOperand<'tcx>,
     ) -> (Bx::Value, Ty<'tcx>) {
         let ty = self.monomorphize(constant.ty());
+        let ty_is_simd = ty.is_simd();
+        // FIXME: ideally we'd assert that this is a SIMD type, but simd_shuffle
+        // in its current form relies on a regular array being passed as an
+        // immediate argument. This hack can be removed once that is fixed.
+        let field_ty = if ty_is_simd {
+            ty.simd_size_and_type(bx.tcx()).1
+        } else {
+            ty.builtin_index().unwrap()
+        };
+
         let val = self
             .eval_unevaluated_mir_constant_to_valtree(constant)
             .ok()
             .map(|x| x.ok())
             .flatten()
             .map(|val| {
-                let field_ty = ty.builtin_index().unwrap();
-                let values: Vec<_> = val
-                    .unwrap_branch()
-                    .iter()
+                // Depending on whether this is a SIMD type with an array field
+                // or a type with many fields (one for each elements), the valtree
+                // is either a single branch with N children, or a root node
+                // with exactly one child which then in turn has many children.
+                // So we look at the first child to determine whether it is a
+                // leaf or whether we have to go one more layer down.
+                let branch_or_leaf = val.unwrap_branch();
+                let first = branch_or_leaf.get(0).unwrap();
+                let field_iter = match first {
+                    ValTree::Branch(_) => first.unwrap_branch().iter(),
+                    ValTree::Leaf(_) => branch_or_leaf.iter(),
+                };
+                let values: Vec<_> = field_iter
                     .map(|field| {
                         if let Some(prim) = field.try_to_scalar() {
                             let layout = bx.layout_of(field_ty);
@@ -84,11 +103,11 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                             };
                             bx.scalar_to_backend(prim, scalar, bx.immediate_backend_type(layout))
                         } else {
-                            bug!("simd shuffle field {:?}", field)
+                            bug!("field is not a scalar {:?}", field)
                         }
                     })
                     .collect();
-                bx.const_struct(&values, false)
+                if ty_is_simd { bx.const_vector(&values) } else { bx.const_struct(&values, false) }
             })
             .unwrap_or_else(|| {
                 bx.tcx().dcx().emit_err(errors::ShuffleIndicesEvaluation { span: constant.span });
diff --git a/compiler/rustc_codegen_ssa/src/mir/operand.rs b/compiler/rustc_codegen_ssa/src/mir/operand.rs
index 2bc2d0f70bf..1891de8c0eb 100644
--- a/compiler/rustc_codegen_ssa/src/mir/operand.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/operand.rs
@@ -1,3 +1,4 @@
+use std::assert_matches::assert_matches;
 use std::fmt;
 
 use arrayvec::ArrayVec;
@@ -389,7 +390,7 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
             }
             // Newtype vector of array, e.g. #[repr(simd)] struct S([i32; 4]);
             (OperandValue::Immediate(llval), Abi::Aggregate { sized: true }) => {
-                assert!(matches!(self.layout.abi, Abi::Vector { .. }));
+                assert_matches!(self.layout.abi, Abi::Vector { .. });
 
                 let llfield_ty = bx.cx().backend_type(field);
 
@@ -635,7 +636,24 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 self.codegen_consume(bx, place.as_ref())
             }
 
-            mir::Operand::Constant(ref constant) => self.eval_mir_constant_to_operand(bx, constant),
+            mir::Operand::Constant(ref constant) => {
+                let constant_ty = self.monomorphize(constant.ty());
+                // Most SIMD vector constants should be passed as immediates.
+                // (In particular, some intrinsics really rely on this.)
+                if constant_ty.is_simd() {
+                    // However, some SIMD types do not actually use the vector ABI
+                    // (in particular, packed SIMD types do not). Ensure we exclude those.
+                    let layout = bx.layout_of(constant_ty);
+                    if let Abi::Vector { .. } = layout.abi {
+                        let (llval, ty) = self.immediate_const_vector(bx, constant);
+                        return OperandRef {
+                            val: OperandValue::Immediate(llval),
+                            layout: bx.layout_of(ty),
+                        };
+                    }
+                }
+                self.eval_mir_constant_to_operand(bx, constant)
+            }
         }
     }
 }
diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
index d91a118bc71..3c2c29ac7f7 100644
--- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
@@ -1,3 +1,5 @@
+use std::assert_matches::assert_matches;
+
 use arrayvec::ArrayVec;
 use rustc_middle::ty::adjustment::PointerCoercion;
 use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf, TyAndLayout};
@@ -220,7 +222,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         match operand.val {
             OperandValue::Ref(source_place_val) => {
                 assert_eq!(source_place_val.llextra, None);
-                assert!(matches!(operand_kind, OperandValueKind::Ref));
+                assert_matches!(operand_kind, OperandValueKind::Ref);
                 Some(bx.load_operand(source_place_val.with_type(cast)).val)
             }
             OperandValue::ZeroSized => {
diff --git a/compiler/rustc_codegen_ssa/src/traits/builder.rs b/compiler/rustc_codegen_ssa/src/traits/builder.rs
index 2b802240e03..6cf84a012f0 100644
--- a/compiler/rustc_codegen_ssa/src/traits/builder.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/builder.rs
@@ -1,3 +1,5 @@
+use std::assert_matches::assert_matches;
+
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
 use rustc_middle::ty::layout::{HasParamEnv, TyAndLayout};
 use rustc_middle::ty::{Instance, Ty};
@@ -254,10 +256,10 @@ pub trait BuilderMethods<'a, 'tcx>:
         } else {
             (in_ty, dest_ty)
         };
-        assert!(matches!(
+        assert_matches!(
             self.cx().type_kind(float_ty),
             TypeKind::Half | TypeKind::Float | TypeKind::Double | TypeKind::FP128
-        ));
+        );
         assert_eq!(self.cx().type_kind(int_ty), TypeKind::Integer);
 
         if let Some(false) = self.cx().sess().opts.unstable_opts.saturating_float_casts {
diff --git a/compiler/rustc_codegen_ssa/src/traits/consts.rs b/compiler/rustc_codegen_ssa/src/traits/consts.rs
index d93b3e06ca6..c15f1fa8e56 100644
--- a/compiler/rustc_codegen_ssa/src/traits/consts.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/consts.rs
@@ -30,6 +30,7 @@ pub trait ConstMethods<'tcx>: BackendTypes {
 
     fn const_str(&self, s: &str) -> (Self::Value, Self::Value);
     fn const_struct(&self, elts: &[Self::Value], packed: bool) -> Self::Value;
+    fn const_vector(&self, elts: &[Self::Value]) -> Self::Value;
 
     fn const_to_opt_uint(&self, v: Self::Value) -> Option<u64>;
     fn const_to_opt_u128(&self, v: Self::Value, sign_ext: bool) -> Option<u128>;
diff --git a/compiler/rustc_const_eval/messages.ftl b/compiler/rustc_const_eval/messages.ftl
index c64c73b2323..1442f1832b9 100644
--- a/compiler/rustc_const_eval/messages.ftl
+++ b/compiler/rustc_const_eval/messages.ftl
@@ -41,6 +41,8 @@ const_eval_const_context = {$kind ->
     *[other] {""}
 }
 
+const_eval_const_stable = const-stable functions can only call other const-stable functions
+
 const_eval_copy_nonoverlapping_overlapping =
     `copy_nonoverlapping` called on overlapping ranges
 
@@ -201,6 +203,9 @@ const_eval_invalid_vtable_pointer =
 const_eval_invalid_vtable_trait =
     using vtable for trait `{$vtable_trait}` but trait `{$expected_trait}` was expected
 
+const_eval_lazy_lock =
+    consider wrapping this expression in `std::sync::LazyLock::new(|| ...)`
+
 const_eval_live_drop =
     destructor of `{$dropped_ty}` cannot be evaluated at compile-time
     .label = the destructor for this type cannot be evaluated in {const_eval_const_context}s
diff --git a/compiler/rustc_const_eval/src/check_consts/check.rs b/compiler/rustc_const_eval/src/check_consts/check.rs
index 3ded81b90ff..32a9247bcc7 100644
--- a/compiler/rustc_const_eval/src/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/check_consts/check.rs
@@ -1,5 +1,6 @@
 //! The `Visitor` responsible for actually checking a `mir::Body` for invalid operations.
 
+use std::assert_matches::assert_matches;
 use std::mem;
 use std::ops::Deref;
 
@@ -170,7 +171,7 @@ struct LocalReturnTyVisitor<'ck, 'mir, 'tcx> {
 impl<'ck, 'mir, 'tcx> TypeVisitor<TyCtxt<'tcx>> for LocalReturnTyVisitor<'ck, 'mir, 'tcx> {
     fn visit_ty(&mut self, t: Ty<'tcx>) {
         match t.kind() {
-            ty::FnPtr(_) => {}
+            ty::FnPtr(..) => {}
             ty::Ref(_, _, hir::Mutability::Mut) => {
                 self.checker.check_op(ops::mut_ref::MutRef(self.kind));
                 t.super_visit_with(self)
@@ -590,7 +591,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                 if is_int_bool_or_char(lhs_ty) && is_int_bool_or_char(rhs_ty) {
                     // Int, bool, and char operations are fine.
                 } else if lhs_ty.is_fn_ptr() || lhs_ty.is_unsafe_ptr() {
-                    assert!(matches!(
+                    assert_matches!(
                         op,
                         BinOp::Eq
                             | BinOp::Ne
@@ -599,7 +600,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                             | BinOp::Ge
                             | BinOp::Gt
                             | BinOp::Offset
-                    ));
+                    );
 
                     self.check_op(ops::RawPtrComparison);
                 } else if lhs_ty.is_floating_point() || rhs_ty.is_floating_point() {
@@ -725,7 +726,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                 let (mut callee, mut fn_args) = match *fn_ty.kind() {
                     ty::FnDef(def_id, fn_args) => (def_id, fn_args),
 
-                    ty::FnPtr(_) => {
+                    ty::FnPtr(..) => {
                         self.check_op(ops::FnCallIndirect);
                         return;
                     }
diff --git a/compiler/rustc_const_eval/src/check_consts/ops.rs b/compiler/rustc_const_eval/src/check_consts/ops.rs
index f47a2ec8f75..c6361710ac9 100644
--- a/compiler/rustc_const_eval/src/check_consts/ops.rs
+++ b/compiler/rustc_const_eval/src/check_consts/ops.rs
@@ -23,7 +23,7 @@ use rustc_trait_selection::traits::SelectionContext;
 use tracing::debug;
 
 use super::ConstCx;
-use crate::errors;
+use crate::{errors, fluent_generated};
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum Status {
@@ -310,7 +310,7 @@ impl<'tcx> NonConstOp<'tcx> for FnCallNonConst<'tcx> {
         }
 
         if let ConstContext::Static(_) = ccx.const_kind() {
-            err.note("consider wrapping this expression in `std::sync::LazyLock::new(|| ...)`");
+            err.note(fluent_generated::const_eval_lazy_lock);
         }
 
         err
@@ -334,7 +334,7 @@ impl<'tcx> NonConstOp<'tcx> for FnCallUnstable {
         // FIXME: make this translatable
         #[allow(rustc::untranslatable_diagnostic)]
         if ccx.is_const_stable_const_fn() {
-            err.help("const-stable functions can only call other const-stable functions");
+            err.help(fluent_generated::const_eval_const_stable);
         } else if ccx.tcx.sess.is_nightly_build() {
             if let Some(feature) = feature {
                 err.help(format!("add `#![feature({feature})]` to the crate attributes to enable"));
@@ -605,8 +605,6 @@ impl<'tcx> NonConstOp<'tcx> for StaticAccess {
             span,
             format!("referencing statics in {}s is unstable", ccx.const_kind(),),
         );
-        // FIXME: make this translatable
-        #[allow(rustc::untranslatable_diagnostic)]
         err
             .note("`static` and `const` variables can refer to other `const` variables. A `const` variable, however, cannot refer to a `static` variable.")
             .help("to fix this, the value can be extracted to a `const` and then used.");
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 ff27e400016..96b3ec6f187 100644
--- a/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
+++ b/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
@@ -226,7 +226,7 @@ pub(super) fn op_to_const<'tcx>(
                 let pointee_ty = imm.layout.ty.builtin_deref(false).unwrap(); // `false` = no raw ptrs
                 debug_assert!(
                     matches!(
-                        ecx.tcx.struct_tail_without_normalization(pointee_ty).kind(),
+                        ecx.tcx.struct_tail_for_codegen(pointee_ty, ecx.param_env).kind(),
                         ty::Str | ty::Slice(..),
                     ),
                     "`ConstValue::Slice` is for slice-tailed types only, but got {}",
diff --git a/compiler/rustc_const_eval/src/const_eval/valtrees.rs b/compiler/rustc_const_eval/src/const_eval/valtrees.rs
index 8227c045948..c96296eddb8 100644
--- a/compiler/rustc_const_eval/src/const_eval/valtrees.rs
+++ b/compiler/rustc_const_eval/src/const_eval/valtrees.rs
@@ -132,7 +132,7 @@ fn const_to_valtree_inner<'tcx>(
 
         // Technically we could allow function pointers (represented as `ty::Instance`), but this is not guaranteed to
         // agree with runtime equality tests.
-        ty::FnPtr(_) => Err(ValTreeCreationError::NonSupportedType(ty)),
+        ty::FnPtr(..) => Err(ValTreeCreationError::NonSupportedType(ty)),
 
         ty::Ref(_, _, _)  => {
             let derefd_place = ecx.deref_pointer(place)?;
@@ -195,7 +195,7 @@ fn reconstruct_place_meta<'tcx>(
 
     let mut last_valtree = valtree;
     // Traverse the type, and update `last_valtree` as we go.
-    let tail = tcx.struct_tail_with_normalize(
+    let tail = tcx.struct_tail_raw(
         layout.ty,
         |ty| ty,
         || {
@@ -353,7 +353,7 @@ pub fn valtree_to_const_value<'tcx>(
         | ty::CoroutineClosure(..)
         | ty::Coroutine(..)
         | ty::CoroutineWitness(..)
-        | ty::FnPtr(_)
+        | ty::FnPtr(..)
         | ty::Str
         | ty::Slice(_)
         | ty::Dynamic(..) => bug!("no ValTree should have been created for type {:?}", ty.kind()),
diff --git a/compiler/rustc_const_eval/src/interpret/call.rs b/compiler/rustc_const_eval/src/interpret/call.rs
index fdbdfc7e1b8..917a2fa7c6d 100644
--- a/compiler/rustc_const_eval/src/interpret/call.rs
+++ b/compiler/rustc_const_eval/src/interpret/call.rs
@@ -1,5 +1,6 @@
 //! Manages calling a concrete function (with known MIR body) with argument passing,
 //! and returning the return value to the caller.
+use std::assert_matches::assert_matches;
 use std::borrow::Cow;
 
 use either::{Left, Right};
@@ -557,7 +558,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                     unwind,
                 )? {
                     assert!(!self.tcx.intrinsic(fallback.def_id()).unwrap().must_be_overridden);
-                    assert!(matches!(fallback.def, ty::InstanceKind::Item(_)));
+                    assert_matches!(fallback.def, ty::InstanceKind::Item(_));
                     return self.init_fn_call(
                         FnVal::Instance(fallback),
                         (caller_abi, caller_fn_abi),
diff --git a/compiler/rustc_const_eval/src/interpret/cast.rs b/compiler/rustc_const_eval/src/interpret/cast.rs
index c3d7f2234ed..4901e4b2a41 100644
--- a/compiler/rustc_const_eval/src/interpret/cast.rs
+++ b/compiler/rustc_const_eval/src/interpret/cast.rs
@@ -97,7 +97,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             CastKind::PointerCoercion(PointerCoercion::UnsafeFnPointer) => {
                 let src = self.read_immediate(src)?;
                 match cast_ty.kind() {
-                    ty::FnPtr(_) => {
+                    ty::FnPtr(..) => {
                         // No change to value
                         self.write_immediate(*src, dest)?;
                     }
@@ -230,7 +230,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         src: &ImmTy<'tcx, M::Provenance>,
         cast_to: TyAndLayout<'tcx>,
     ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
-        assert_matches!(src.layout.ty.kind(), ty::RawPtr(_, _) | ty::FnPtr(_));
+        assert_matches!(src.layout.ty.kind(), ty::RawPtr(_, _) | ty::FnPtr(..));
         assert!(cast_to.ty.is_integral());
 
         let scalar = src.to_scalar();
@@ -400,6 +400,12 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             }
             (ty::Dynamic(data_a, _, ty::Dyn), ty::Dynamic(data_b, _, ty::Dyn)) => {
                 let val = self.read_immediate(src)?;
+                // MIR building generates odd NOP casts, prevent them from causing unexpected trouble.
+                // See <https://github.com/rust-lang/rust/issues/128880>.
+                // FIXME: ideally we wouldn't have to do this.
+                if data_a == data_b {
+                    return self.write_immediate(*val, dest);
+                }
                 // Take apart the old pointer, and find the dynamic type.
                 let (old_data, old_vptr) = val.to_scalar_pair();
                 let old_data = old_data.to_pointer(self)?;
diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics.rs b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
index 9210ec4e16f..aef39b9af2f 100644
--- a/compiler/rustc_const_eval/src/interpret/intrinsics.rs
+++ b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
@@ -2,6 +2,8 @@
 //! looking at their MIR. Intrinsics/functions supported here are shared by CTFE
 //! and miri.
 
+use std::assert_matches::assert_matches;
+
 use rustc_hir::def_id::DefId;
 use rustc_middle::mir::{self, BinOp, ConstValue, NonDivergingIntrinsic};
 use rustc_middle::ty::layout::{LayoutOf as _, TyAndLayout, ValidityRequirement};
@@ -79,7 +81,7 @@ pub(crate) fn eval_nullary_intrinsic<'tcx>(
             | ty::RawPtr(_, _)
             | ty::Ref(_, _, _)
             | ty::FnDef(_, _)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Dynamic(_, _, _)
             | ty::Closure(_, _)
             | ty::CoroutineClosure(_, _)
@@ -510,7 +512,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         dest: &MPlaceTy<'tcx, M::Provenance>,
     ) -> InterpResult<'tcx> {
         assert_eq!(a.layout.ty, b.layout.ty);
-        assert!(matches!(a.layout.ty.kind(), ty::Int(..) | ty::Uint(..)));
+        assert_matches!(a.layout.ty.kind(), ty::Int(..) | ty::Uint(..));
 
         // Performs an exact division, resulting in undefined behavior where
         // `x % y != 0` or `y == 0` or `x == T::MIN && y == -1`.
@@ -536,8 +538,8 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         r: &ImmTy<'tcx, M::Provenance>,
     ) -> InterpResult<'tcx, Scalar<M::Provenance>> {
         assert_eq!(l.layout.ty, r.layout.ty);
-        assert!(matches!(l.layout.ty.kind(), ty::Int(..) | ty::Uint(..)));
-        assert!(matches!(mir_op, BinOp::Add | BinOp::Sub));
+        assert_matches!(l.layout.ty.kind(), ty::Int(..) | ty::Uint(..));
+        assert_matches!(mir_op, BinOp::Add | BinOp::Sub);
 
         let (val, overflowed) =
             self.binary_op(mir_op.wrapping_to_overflowing().unwrap(), l, r)?.to_scalar_pair();
diff --git a/compiler/rustc_const_eval/src/interpret/machine.rs b/compiler/rustc_const_eval/src/interpret/machine.rs
index 7af4e0c285b..761ab81e228 100644
--- a/compiler/rustc_const_eval/src/interpret/machine.rs
+++ b/compiler/rustc_const_eval/src/interpret/machine.rs
@@ -19,7 +19,7 @@ use rustc_target::spec::abi::Abi as CallAbi;
 use super::{
     throw_unsup, throw_unsup_format, AllocBytes, AllocId, AllocKind, AllocRange, Allocation,
     ConstAllocation, CtfeProvenance, FnArg, Frame, ImmTy, InterpCx, InterpResult, MPlaceTy,
-    MemoryKind, Misalignment, OpTy, PlaceTy, Pointer, Provenance,
+    MemoryKind, Misalignment, OpTy, PlaceTy, Pointer, Provenance, CTFE_ALLOC_SALT,
 };
 
 /// Data returned by [`Machine::after_stack_pop`], and consumed by
@@ -575,6 +575,14 @@ pub trait Machine<'tcx>: Sized {
     {
         eval(ecx, val, span, layout)
     }
+
+    /// Returns the salt to be used for a deduplicated global alloation.
+    /// If the allocation is for a function, the instance is provided as well
+    /// (this lets Miri ensure unique addresses for some functions).
+    fn get_global_alloc_salt(
+        ecx: &InterpCx<'tcx, Self>,
+        instance: Option<ty::Instance<'tcx>>,
+    ) -> usize;
 }
 
 /// A lot of the flexibility above is just needed for `Miri`, but all "compile-time" machines
@@ -677,4 +685,12 @@ pub macro compile_time_machine(<$tcx: lifetime>) {
         let (prov, offset) = ptr.into_parts();
         Some((prov.alloc_id(), offset, prov.immutable()))
     }
+
+    #[inline(always)]
+    fn get_global_alloc_salt(
+        _ecx: &InterpCx<$tcx, Self>,
+        _instance: Option<ty::Instance<$tcx>>,
+    ) -> usize {
+        CTFE_ALLOC_SALT
+    }
 }
diff --git a/compiler/rustc_const_eval/src/interpret/memory.rs b/compiler/rustc_const_eval/src/interpret/memory.rs
index 2e5d0ae7736..910aec9b8e1 100644
--- a/compiler/rustc_const_eval/src/interpret/memory.rs
+++ b/compiler/rustc_const_eval/src/interpret/memory.rs
@@ -195,7 +195,10 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
 
     pub fn fn_ptr(&mut self, fn_val: FnVal<'tcx, M::ExtraFnVal>) -> Pointer<M::Provenance> {
         let id = match fn_val {
-            FnVal::Instance(instance) => self.tcx.reserve_and_set_fn_alloc(instance),
+            FnVal::Instance(instance) => {
+                let salt = M::get_global_alloc_salt(self, Some(instance));
+                self.tcx.reserve_and_set_fn_alloc(instance, salt)
+            }
             FnVal::Other(extra) => {
                 // FIXME(RalfJung): Should we have a cache here?
                 let id = self.tcx.reserve_alloc_id();
diff --git a/compiler/rustc_const_eval/src/interpret/operand.rs b/compiler/rustc_const_eval/src/interpret/operand.rs
index 4ced009ab39..ad87d6953d3 100644
--- a/compiler/rustc_const_eval/src/interpret/operand.rs
+++ b/compiler/rustc_const_eval/src/interpret/operand.rs
@@ -342,7 +342,7 @@ impl<'tcx, Prov: Provenance> ImmTy<'tcx, Prov> {
             }
             // extract fields from types with `ScalarPair` ABI
             (Immediate::ScalarPair(a_val, b_val), Abi::ScalarPair(a, b)) => {
-                assert!(matches!(layout.abi, Abi::Scalar(..)));
+                assert_matches!(layout.abi, Abi::Scalar(..));
                 Immediate::from(if offset.bytes() == 0 {
                     debug_assert_eq!(layout.size, a.size(cx));
                     a_val
diff --git a/compiler/rustc_const_eval/src/interpret/place.rs b/compiler/rustc_const_eval/src/interpret/place.rs
index 470a62026b9..2afdd02c880 100644
--- a/compiler/rustc_const_eval/src/interpret/place.rs
+++ b/compiler/rustc_const_eval/src/interpret/place.rs
@@ -1008,7 +1008,8 @@ where
         // Use cache for immutable strings.
         let ptr = if mutbl.is_not() {
             // Use dedup'd allocation function.
-            let id = tcx.allocate_bytes_dedup(str.as_bytes());
+            let salt = M::get_global_alloc_salt(self, None);
+            let id = tcx.allocate_bytes_dedup(str.as_bytes(), salt);
 
             // Turn untagged "global" pointers (obtained via `tcx`) into the machine pointer to the allocation.
             M::adjust_alloc_root_pointer(&self, Pointer::from(id), Some(kind))?
diff --git a/compiler/rustc_const_eval/src/interpret/stack.rs b/compiler/rustc_const_eval/src/interpret/stack.rs
index 50dbced6a2a..0f6bf5c0336 100644
--- a/compiler/rustc_const_eval/src/interpret/stack.rs
+++ b/compiler/rustc_const_eval/src/interpret/stack.rs
@@ -483,7 +483,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 | ty::Bool
                 | ty::Float(_)
                 | ty::FnDef(..)
-                | ty::FnPtr(_)
+                | ty::FnPtr(..)
                 | ty::RawPtr(..)
                 | ty::Char
                 | ty::Ref(..)
diff --git a/compiler/rustc_const_eval/src/interpret/step.rs b/compiler/rustc_const_eval/src/interpret/step.rs
index 2527eca3446..aaee6f6d247 100644
--- a/compiler/rustc_const_eval/src/interpret/step.rs
+++ b/compiler/rustc_const_eval/src/interpret/step.rs
@@ -424,7 +424,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             self.tcx.mk_type_list_from_iter(extra_args.iter().map(|arg| arg.layout().ty));
 
         let (callee, fn_abi, with_caller_location) = match *func.layout.ty.kind() {
-            ty::FnPtr(_sig) => {
+            ty::FnPtr(..) => {
                 let fn_ptr = self.read_pointer(&func)?;
                 let fn_val = self.get_ptr_fn(fn_ptr)?;
                 (fn_val, self.fn_abi_of_fn_ptr(fn_sig_binder, extra_args)?, false)
diff --git a/compiler/rustc_const_eval/src/interpret/traits.rs b/compiler/rustc_const_eval/src/interpret/traits.rs
index fb50661b826..cd4faf06655 100644
--- a/compiler/rustc_const_eval/src/interpret/traits.rs
+++ b/compiler/rustc_const_eval/src/interpret/traits.rs
@@ -28,7 +28,9 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         ensure_monomorphic_enough(*self.tcx, ty)?;
         ensure_monomorphic_enough(*self.tcx, poly_trait_ref)?;
 
-        let vtable_symbolic_allocation = self.tcx.reserve_and_set_vtable_alloc(ty, poly_trait_ref);
+        let salt = M::get_global_alloc_salt(self, None);
+        let vtable_symbolic_allocation =
+            self.tcx.reserve_and_set_vtable_alloc(ty, poly_trait_ref, salt);
         let vtable_ptr = self.global_root_pointer(Pointer::from(vtable_symbolic_allocation))?;
         Ok(vtable_ptr.into())
     }
diff --git a/compiler/rustc_const_eval/src/interpret/validity.rs b/compiler/rustc_const_eval/src/interpret/validity.rs
index fadc4ee6c8a..26b7251f6db 100644
--- a/compiler/rustc_const_eval/src/interpret/validity.rs
+++ b/compiler/rustc_const_eval/src/interpret/validity.rs
@@ -616,7 +616,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
                 self.check_safe_pointer(value, PointerKind::Ref(*mutbl))?;
                 Ok(true)
             }
-            ty::FnPtr(_sig) => {
+            ty::FnPtr(..) => {
                 let value = self.read_scalar(value, ExpectedKind::FnPtr)?;
 
                 // If we check references recursively, also check that this points to a function.
diff --git a/compiler/rustc_const_eval/src/util/type_name.rs b/compiler/rustc_const_eval/src/util/type_name.rs
index 3aa3b3b74e0..36c7bed5c11 100644
--- a/compiler/rustc_const_eval/src/util/type_name.rs
+++ b/compiler/rustc_const_eval/src/util/type_name.rs
@@ -35,7 +35,7 @@ impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
             | ty::Slice(_)
             | ty::RawPtr(_, _)
             | ty::Ref(_, _, _)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Never
             | ty::Tuple(_)
             | ty::Dynamic(_, _, _) => self.pretty_print_type(ty),
diff --git a/compiler/rustc_data_structures/src/graph/scc/mod.rs b/compiler/rustc_data_structures/src/graph/scc/mod.rs
index 96fc8ae3887..2a457ffb70b 100644
--- a/compiler/rustc_data_structures/src/graph/scc/mod.rs
+++ b/compiler/rustc_data_structures/src/graph/scc/mod.rs
@@ -8,6 +8,7 @@
 //! Typical examples would include: minimum element in SCC, maximum element
 //! reachable from it, etc.
 
+use std::assert_matches::debug_assert_matches;
 use std::fmt::Debug;
 use std::ops::Range;
 
@@ -569,7 +570,7 @@ where
                     // This None marks that we still have the initialize this node's frame.
                     debug!(?depth, ?node);
 
-                    debug_assert!(matches!(self.node_states[node], NodeState::NotVisited));
+                    debug_assert_matches!(self.node_states[node], NodeState::NotVisited);
 
                     // Push `node` onto the stack.
                     self.node_states[node] = NodeState::BeingVisited {
diff --git a/compiler/rustc_data_structures/src/lib.rs b/compiler/rustc_data_structures/src/lib.rs
index 403136e78f4..a35f5b1f17d 100644
--- a/compiler/rustc_data_structures/src/lib.rs
+++ b/compiler/rustc_data_structures/src/lib.rs
@@ -18,6 +18,7 @@
 #![feature(array_windows)]
 #![feature(ascii_char)]
 #![feature(ascii_char_variants)]
+#![feature(assert_matches)]
 #![feature(auto_traits)]
 #![feature(cfg_match)]
 #![feature(core_intrinsics)]
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index aefbf05a1fc..fd203c38318 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -10,6 +10,7 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(array_windows)]
+#![feature(assert_matches)]
 #![feature(associated_type_defaults)]
 #![feature(box_into_inner)]
 #![feature(box_patterns)]
@@ -28,6 +29,7 @@
 
 extern crate self as rustc_errors;
 
+use std::assert_matches::assert_matches;
 use std::backtrace::{Backtrace, BacktraceStatus};
 use std::borrow::Cow;
 use std::cell::Cell;
@@ -1490,7 +1492,7 @@ impl DiagCtxtInner {
             // Future breakages aren't emitted if they're `Level::Allow` or
             // `Level::Expect`, but they still need to be constructed and
             // stashed below, so they'll trigger the must_produce_diag check.
-            assert!(matches!(diagnostic.level, Error | Warning | Allow | Expect(_)));
+            assert_matches!(diagnostic.level, Error | Warning | Allow | Expect(_));
             self.future_breakage_diagnostics.push(diagnostic.clone());
         }
 
@@ -1835,23 +1837,23 @@ impl DelayedDiagInner {
     }
 }
 
-/// Level              is_error  EmissionGuarantee         Top-level  Sub   Used in lints?
-/// -----              --------  -----------------         ---------  ---   --------------
-/// Bug                yes       BugAbort                  yes        -     -
-/// Fatal              yes       FatalAbort/FatalError(*)  yes        -     -
-/// Error              yes       ErrorGuaranteed           yes        -     yes
-/// DelayedBug         yes       ErrorGuaranteed           yes        -     -
-/// ForceWarning       -         ()                        yes        -     lint-only
-/// Warning            -         ()                        yes        yes   yes
-/// Note               -         ()                        rare       yes   -
-/// OnceNote           -         ()                        -          yes   lint-only
-/// Help               -         ()                        rare       yes   -
-/// OnceHelp           -         ()                        -          yes   lint-only
-/// FailureNote        -         ()                        rare       -     -
-/// Allow              -         ()                        yes        -     lint-only
-/// Expect             -         ()                        yes        -     lint-only
+/// | Level        | is_error | EmissionGuarantee            | Top-level | Sub | Used in lints?
+/// | -----        | -------- | -----------------            | --------- | --- | --------------
+/// | Bug          | yes      | BugAbort                     | yes       | -   | -
+/// | Fatal        | yes      | FatalAbort/FatalError[^star] | yes       | -   | -
+/// | Error        | yes      | ErrorGuaranteed              | yes       | -   | yes
+/// | DelayedBug   | yes      | ErrorGuaranteed              | yes       | -   | -
+/// | ForceWarning | -        | ()                           | yes       | -   | lint-only
+/// | Warning      | -        | ()                           | yes       | yes | yes
+/// | Note         | -        | ()                           | rare      | yes | -
+/// | OnceNote     | -        | ()                           | -         | yes | lint-only
+/// | Help         | -        | ()                           | rare      | yes | -
+/// | OnceHelp     | -        | ()                           | -         | yes | lint-only
+/// | FailureNote  | -        | ()                           | rare      | -   | -
+/// | Allow        | -        | ()                           | yes       | -   | lint-only
+/// | Expect       | -        | ()                           | yes       | -   | lint-only
 ///
-/// (*) `FatalAbort` normally, `FatalError` in the non-aborting "almost fatal" case that is
+/// [^star]: `FatalAbort` normally, `FatalError` in the non-aborting "almost fatal" case that is
 ///     occasionally used.
 ///
 #[derive(Copy, PartialEq, Eq, Clone, Hash, Debug, Encodable, Decodable)]
diff --git a/compiler/rustc_expand/messages.ftl b/compiler/rustc_expand/messages.ftl
index 18d95a398fd..766d96e268f 100644
--- a/compiler/rustc_expand/messages.ftl
+++ b/compiler/rustc_expand/messages.ftl
@@ -129,6 +129,9 @@ expand_module_multiple_candidates =
 expand_must_repeat_once =
     this must repeat at least once
 
+expand_non_inline_modules_in_proc_macro_input_are_unstable =
+    non-inline modules in proc macro input are unstable
+
 expand_not_a_meta_item =
     not a meta item
 
diff --git a/compiler/rustc_expand/src/base.rs b/compiler/rustc_expand/src/base.rs
index 7712915d490..8f9104135cd 100644
--- a/compiler/rustc_expand/src/base.rs
+++ b/compiler/rustc_expand/src/base.rs
@@ -1398,8 +1398,6 @@ fn pretty_printing_compatibility_hack(item: &Item, sess: &Session) {
         };
 
         if crate_matches {
-            // FIXME: make this translatable
-            #[allow(rustc::untranslatable_diagnostic)]
             sess.dcx().emit_fatal(errors::ProcMacroBackCompat {
                 crate_name: "rental".to_string(),
                 fixed_version: "0.5.6".to_string(),
diff --git a/compiler/rustc_expand/src/expand.rs b/compiler/rustc_expand/src/expand.rs
index d8cb367e3fa..37679e17b90 100644
--- a/compiler/rustc_expand/src/expand.rs
+++ b/compiler/rustc_expand/src/expand.rs
@@ -39,6 +39,7 @@ use crate::errors::{
     RecursionLimitReached, RemoveExprNotSupported, RemoveNodeNotSupported, UnsupportedKeyValue,
     WrongFragmentKind,
 };
+use crate::fluent_generated;
 use crate::mbe::diagnostics::annotate_err_with_kind;
 use crate::module::{mod_dir_path, parse_external_mod, DirOwnership, ParsedExternalMod};
 use crate::placeholders::{placeholder, PlaceholderExpander};
@@ -882,7 +883,6 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         }
 
         impl<'ast, 'a> Visitor<'ast> for GateProcMacroInput<'a> {
-            #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
             fn visit_item(&mut self, item: &'ast ast::Item) {
                 match &item.kind {
                     ItemKind::Mod(_, mod_kind)
@@ -892,7 +892,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                             self.sess,
                             sym::proc_macro_hygiene,
                             item.span,
-                            "non-inline modules in proc macro input are unstable",
+                            fluent_generated::expand_non_inline_modules_in_proc_macro_input_are_unstable,
                         )
                         .emit();
                     }
@@ -1876,7 +1876,6 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
 
     // Detect use of feature-gated or invalid attributes on macro invocations
     // since they will not be detected after macro expansion.
-    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn check_attributes(&self, attrs: &[ast::Attribute], call: &ast::MacCall) {
         let features = self.cx.ecfg.features;
         let mut attrs = attrs.iter().peekable();
diff --git a/compiler/rustc_feature/src/accepted.rs b/compiler/rustc_feature/src/accepted.rs
index 44286cfeeef..03b40e28f8b 100644
--- a/compiler/rustc_feature/src/accepted.rs
+++ b/compiler/rustc_feature/src/accepted.rs
@@ -60,6 +60,8 @@ declare_features! (
     (accepted, adx_target_feature, "1.61.0", Some(44839)),
     /// Allows explicit discriminants on non-unit enum variants.
     (accepted, arbitrary_enum_discriminant, "1.66.0", Some(60553)),
+    /// Allows using `const` operands in inline assembly.
+    (accepted, asm_const, "CURRENT_RUSTC_VERSION", Some(93332)),
     /// Allows using `sym` operands in inline assembly.
     (accepted, asm_sym, "1.66.0", Some(93333)),
     /// Allows the definition of associated constants in `trait` or `impl` blocks.
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
index 72ea55d5999..d593f05c8c6 100644
--- a/compiler/rustc_feature/src/builtin_attrs.rs
+++ b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -643,8 +643,8 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         through unstable paths"
     ),
     rustc_attr!(
-        rustc_deprecated_safe_2024, Normal, template!(Word), WarnFollowing,
-        EncodeCrossCrate::Yes,
+        rustc_deprecated_safe_2024, Normal, template!(List: r#"audit_that = "...""#),
+        ErrorFollowing, EncodeCrossCrate::Yes,
         "rustc_deprecated_safe_2024 is supposed to be used in libstd only",
     ),
 
diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
index 47810bc9165..24f691ea7fa 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -348,8 +348,6 @@ declare_features! (
     (unstable, alloc_error_handler, "1.29.0", Some(51540)),
     /// Allows trait methods with arbitrary self types.
     (unstable, arbitrary_self_types, "1.23.0", Some(44874)),
-    /// Allows using `const` operands in inline assembly.
-    (unstable, asm_const, "1.58.0", Some(93332)),
     /// Enables experimental inline assembly support for additional architectures.
     (unstable, asm_experimental_arch, "1.58.0", Some(93335)),
     /// Allows using `label` operands in inline assembly.
diff --git a/compiler/rustc_hir_analysis/src/check/intrinsicck.rs b/compiler/rustc_hir_analysis/src/check/intrinsicck.rs
index 847a1e64706..3d5a22fce85 100644
--- a/compiler/rustc_hir_analysis/src/check/intrinsicck.rs
+++ b/compiler/rustc_hir_analysis/src/check/intrinsicck.rs
@@ -1,3 +1,5 @@
+use std::assert_matches::debug_assert_matches;
+
 use rustc_ast::InlineAsmTemplatePiece;
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir::{self as hir, LangItem};
@@ -66,7 +68,7 @@ impl<'a, 'tcx> InlineAsmCtxt<'a, 'tcx> {
             ty::Float(FloatTy::F32) => Some(InlineAsmType::F32),
             ty::Float(FloatTy::F64) => Some(InlineAsmType::F64),
             ty::Float(FloatTy::F128) => Some(InlineAsmType::F128),
-            ty::FnPtr(_) => Some(asm_ty_isize),
+            ty::FnPtr(..) => Some(asm_ty_isize),
             ty::RawPtr(ty, _) if self.is_thin_ptr_ty(ty) => Some(asm_ty_isize),
             ty::Adt(adt, args) if adt.repr().simd() => {
                 let fields = &adt.non_enum_variant().fields;
@@ -457,17 +459,17 @@ impl<'a, 'tcx> InlineAsmCtxt<'a, 'tcx> {
                 }
                 // Typeck has checked that Const operands are integers.
                 hir::InlineAsmOperand::Const { anon_const } => {
-                    debug_assert!(matches!(
+                    debug_assert_matches!(
                         self.tcx.type_of(anon_const.def_id).instantiate_identity().kind(),
                         ty::Error(_) | ty::Int(_) | ty::Uint(_)
-                    ));
+                    );
                 }
                 // Typeck has checked that SymFn refers to a function.
                 hir::InlineAsmOperand::SymFn { anon_const } => {
-                    debug_assert!(matches!(
+                    debug_assert_matches!(
                         self.tcx.type_of(anon_const.def_id).instantiate_identity().kind(),
                         ty::Error(_) | ty::FnDef(..)
-                    ));
+                    );
                 }
                 // AST lowering guarantees that SymStatic points to a static.
                 hir::InlineAsmOperand::SymStatic { .. } => {}
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index a9f8630741a..d3b928fc17c 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -951,7 +951,7 @@ fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) -> Result<(),
             } else {
                 let mut diag = match ty.kind() {
                     ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Error(_) => return Ok(()),
-                    ty::FnPtr(_) => tcx.dcx().struct_span_err(
+                    ty::FnPtr(..) => tcx.dcx().struct_span_err(
                         hir_ty.span,
                         "using function pointers as const generic parameters is forbidden",
                     ),
diff --git a/compiler/rustc_hir_analysis/src/coherence/builtin.rs b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
index bdb5f5b7205..fecd78bc38f 100644
--- a/compiler/rustc_hir_analysis/src/coherence/builtin.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
@@ -1,6 +1,7 @@
 //! Check properties that are required by built-in traits and set
 //! up data structures required by type-checking/codegen.
 
+use std::assert_matches::assert_matches;
 use std::collections::BTreeMap;
 
 use rustc_data_structures::fx::FxHashSet;
@@ -129,7 +130,7 @@ fn visit_implementation_of_const_param_ty(
     checker: &Checker<'_>,
     kind: LangItem,
 ) -> Result<(), ErrorGuaranteed> {
-    assert!(matches!(kind, LangItem::ConstParamTy | LangItem::UnsizedConstParamTy));
+    assert_matches!(kind, LangItem::ConstParamTy | LangItem::UnsizedConstParamTy);
 
     let tcx = checker.tcx;
     let header = checker.impl_header;
diff --git a/compiler/rustc_hir_analysis/src/coherence/inherent_impls.rs b/compiler/rustc_hir_analysis/src/coherence/inherent_impls.rs
index e2d3ff558cf..89acb778d6c 100644
--- a/compiler/rustc_hir_analysis/src/coherence/inherent_impls.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/inherent_impls.rs
@@ -172,7 +172,7 @@ impl<'tcx> InherentCollect<'tcx> {
             | ty::RawPtr(_, _)
             | ty::Ref(..)
             | ty::Never
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Tuple(..) => self.check_primitive_impl(id, self_ty),
             ty::Alias(ty::Projection | ty::Inherent | ty::Opaque, _) | ty::Param(_) => {
                 Err(self.tcx.dcx().emit_err(errors::InherentNominal { span: item_span }))
diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
index 8c1e5e78b75..91fa066ec6a 100644
--- a/compiler/rustc_hir_analysis/src/collect.rs
+++ b/compiler/rustc_hir_analysis/src/collect.rs
@@ -1700,6 +1700,8 @@ fn impl_trait_header(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<ty::ImplTrai
             trait_ref: ty::EarlyBinder::bind(trait_ref),
             safety: impl_.safety,
             polarity: polarity_of_impl(tcx, def_id, impl_, item.span),
+            do_not_recommend: tcx.features().do_not_recommend
+                && tcx.has_attrs_with_path(def_id, &[sym::diagnostic, sym::do_not_recommend]),
         }
     })
 }
diff --git a/compiler/rustc_hir_analysis/src/collect/generics_of.rs b/compiler/rustc_hir_analysis/src/collect/generics_of.rs
index 60e2c2eb30e..28d6cab4b43 100644
--- a/compiler/rustc_hir_analysis/src/collect/generics_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/generics_of.rs
@@ -1,3 +1,4 @@
+use std::assert_matches::assert_matches;
 use std::ops::ControlFlow;
 
 use hir::intravisit::{self, Visitor};
@@ -207,9 +208,9 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                 ..
             }) => {
                 if in_trait {
-                    assert!(matches!(tcx.def_kind(fn_def_id), DefKind::AssocFn))
+                    assert_matches!(tcx.def_kind(fn_def_id), DefKind::AssocFn);
                 } else {
-                    assert!(matches!(tcx.def_kind(fn_def_id), DefKind::AssocFn | DefKind::Fn))
+                    assert_matches!(tcx.def_kind(fn_def_id), DefKind::AssocFn | DefKind::Fn);
                 }
                 Some(fn_def_id.to_def_id())
             }
@@ -218,9 +219,9 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                 ..
             }) => {
                 if in_assoc_ty {
-                    assert!(matches!(tcx.def_kind(parent), DefKind::AssocTy));
+                    assert_matches!(tcx.def_kind(parent), DefKind::AssocTy);
                 } else {
-                    assert!(matches!(tcx.def_kind(parent), DefKind::TyAlias));
+                    assert_matches!(tcx.def_kind(parent), DefKind::TyAlias);
                 }
                 debug!("generics_of: parent of opaque ty {:?} is {:?}", def_id, parent);
                 // Opaque types are always nested within another item, and
diff --git a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
index a5a56cb845d..6ac4802b195 100644
--- a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
@@ -1,3 +1,5 @@
+use std::assert_matches::assert_matches;
+
 use hir::{HirId, Node};
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
@@ -601,7 +603,7 @@ pub(super) fn implied_predicates_with_filter(
     let Some(trait_def_id) = trait_def_id.as_local() else {
         // if `assoc_name` is None, then the query should've been redirected to an
         // external provider
-        assert!(matches!(filter, PredicateFilter::SelfThatDefines(_)));
+        assert_matches!(filter, PredicateFilter::SelfThatDefines(_));
         return tcx.explicit_super_predicates_of(trait_def_id);
     };
 
diff --git a/compiler/rustc_hir_analysis/src/delegation.rs b/compiler/rustc_hir_analysis/src/delegation.rs
index ca62ef92b83..20aaa43219f 100644
--- a/compiler/rustc_hir_analysis/src/delegation.rs
+++ b/compiler/rustc_hir_analysis/src/delegation.rs
@@ -1,3 +1,5 @@
+use std::assert_matches::debug_assert_matches;
+
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LocalDefId};
@@ -63,7 +65,7 @@ enum FnKind {
 }
 
 fn fn_kind<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> FnKind {
-    debug_assert!(matches!(tcx.def_kind(def_id), DefKind::Fn | DefKind::AssocFn));
+    debug_assert_matches!(tcx.def_kind(def_id), DefKind::Fn | DefKind::AssocFn);
 
     let parent = tcx.parent(def_id);
     match tcx.def_kind(parent) {
diff --git a/compiler/rustc_hir_analysis/src/impl_wf_check.rs b/compiler/rustc_hir_analysis/src/impl_wf_check.rs
index a8ae620f7a4..ab441ed4cde 100644
--- a/compiler/rustc_hir_analysis/src/impl_wf_check.rs
+++ b/compiler/rustc_hir_analysis/src/impl_wf_check.rs
@@ -8,6 +8,8 @@
 //! specialization errors. These things can (and probably should) be
 //! fixed, but for the moment it's easier to do these checks early.
 
+use std::assert_matches::debug_assert_matches;
+
 use min_specialization::check_min_specialization;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::codes::*;
@@ -54,7 +56,7 @@ mod min_specialization;
 pub fn check_impl_wf(tcx: TyCtxt<'_>, impl_def_id: LocalDefId) -> Result<(), ErrorGuaranteed> {
     let min_specialization = tcx.features().min_specialization;
     let mut res = Ok(());
-    debug_assert!(matches!(tcx.def_kind(impl_def_id), DefKind::Impl { .. }));
+    debug_assert_matches!(tcx.def_kind(impl_def_id), DefKind::Impl { .. });
     res = res.and(enforce_impl_params_are_constrained(tcx, impl_def_id));
     if min_specialization {
         res = res.and(check_min_specialization(tcx, impl_def_id));
diff --git a/compiler/rustc_hir_analysis/src/lib.rs b/compiler/rustc_hir_analysis/src/lib.rs
index 061db14ad0a..291d57f2a17 100644
--- a/compiler/rustc_hir_analysis/src/lib.rs
+++ b/compiler/rustc_hir_analysis/src/lib.rs
@@ -62,6 +62,7 @@ This API is completely unstable and subject to change.
 #![allow(rustc::untranslatable_diagnostic)]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
+#![feature(assert_matches)]
 #![feature(control_flow_enum)]
 #![feature(if_let_guard)]
 #![feature(iter_intersperse)]
diff --git a/compiler/rustc_hir_analysis/src/variance/constraints.rs b/compiler/rustc_hir_analysis/src/variance/constraints.rs
index 92baa41e07f..ce9e73bf245 100644
--- a/compiler/rustc_hir_analysis/src/variance/constraints.rs
+++ b/compiler/rustc_hir_analysis/src/variance/constraints.rs
@@ -317,8 +317,8 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
                 self.add_constraint(current, data.index, variance);
             }
 
-            ty::FnPtr(sig) => {
-                self.add_constraints_from_sig(current, sig, variance);
+            ty::FnPtr(sig_tys, hdr) => {
+                self.add_constraints_from_sig(current, sig_tys.with(hdr), variance);
             }
 
             ty::Error(_) => {
diff --git a/compiler/rustc_hir_typeck/src/callee.rs b/compiler/rustc_hir_typeck/src/callee.rs
index 07f64ead6f6..44cb08e44eb 100644
--- a/compiler/rustc_hir_typeck/src/callee.rs
+++ b/compiler/rustc_hir_typeck/src/callee.rs
@@ -137,7 +137,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // If the callee is a bare function or a closure, then we're all set.
         match *adjusted_ty.kind() {
-            ty::FnDef(..) | ty::FnPtr(_) => {
+            ty::FnDef(..) | ty::FnPtr(..) => {
                 let adjustments = self.adjust_steps(autoderef);
                 self.apply_adjustments(callee_expr, adjustments);
                 return Some(CallStep::Builtin(adjusted_ty));
@@ -467,7 +467,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 (fn_sig, Some(def_id))
             }
             // FIXME(effects): these arms should error because we can't enforce them
-            ty::FnPtr(sig) => (sig, None),
+            ty::FnPtr(sig_tys, hdr) => (sig_tys.with(hdr), None),
             _ => {
                 for arg in arg_exprs {
                     self.check_expr(arg);
diff --git a/compiler/rustc_hir_typeck/src/cast.rs b/compiler/rustc_hir_typeck/src/cast.rs
index de702733904..7cd97166ed1 100644
--- a/compiler/rustc_hir_typeck/src/cast.rs
+++ b/compiler/rustc_hir_typeck/src/cast.rs
@@ -97,6 +97,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             return Ok(Some(PointerKind::Thin));
         }
 
+        let t = self.try_structurally_resolve_type(span, t);
+
         Ok(match *t.kind() {
             ty::Slice(_) | ty::Str => Some(PointerKind::Length),
             ty::Dynamic(tty, _, ty::Dyn) => Some(PointerKind::VTable(tty)),
diff --git a/compiler/rustc_hir_typeck/src/check.rs b/compiler/rustc_hir_typeck/src/check.rs
index 89df464cca0..cd357e4a7ad 100644
--- a/compiler/rustc_hir_typeck/src/check.rs
+++ b/compiler/rustc_hir_typeck/src/check.rs
@@ -160,15 +160,11 @@ pub(super) fn check_fn<'a, 'tcx>(
     fcx.demand_suptype(span, ret_ty, actual_return_ty);
 
     // Check that a function marked as `#[panic_handler]` has signature `fn(&PanicInfo) -> !`
-    if let Some(panic_impl_did) = tcx.lang_items().panic_impl()
-        && panic_impl_did == fn_def_id.to_def_id()
-    {
-        check_panic_info_fn(tcx, panic_impl_did.expect_local(), fn_sig);
+    if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::PanicImpl) {
+        check_panic_info_fn(tcx, fn_def_id, fn_sig);
     }
 
-    if let Some(lang_start_defid) = tcx.lang_items().start_fn()
-        && lang_start_defid == fn_def_id.to_def_id()
-    {
+    if tcx.is_lang_item(fn_def_id.to_def_id(), LangItem::Start) {
         check_lang_start_fn(tcx, fn_sig, fn_def_id);
     }
 
diff --git a/compiler/rustc_hir_typeck/src/closure.rs b/compiler/rustc_hir_typeck/src/closure.rs
index a7953acc95c..589a9c5a719 100644
--- a/compiler/rustc_hir_typeck/src/closure.rs
+++ b/compiler/rustc_hir_typeck/src/closure.rs
@@ -336,9 +336,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     .into_iter()
                     .map(|obl| (obl.predicate, obl.cause.span)),
             ),
-            ty::FnPtr(sig) => match closure_kind {
+            ty::FnPtr(sig_tys, hdr) => match closure_kind {
                 hir::ClosureKind::Closure => {
-                    let expected_sig = ExpectedSig { cause_span: None, sig };
+                    let expected_sig = ExpectedSig { cause_span: None, sig: sig_tys.with(hdr) };
                     (Some(expected_sig), Some(ty::ClosureKind::Fn))
                 }
                 hir::ClosureKind::Coroutine(_) | hir::ClosureKind::CoroutineClosure(_) => {
diff --git a/compiler/rustc_hir_typeck/src/coercion.rs b/compiler/rustc_hir_typeck/src/coercion.rs
index fcd3798eb48..d53df251a15 100644
--- a/compiler/rustc_hir_typeck/src/coercion.rs
+++ b/compiler/rustc_hir_typeck/src/coercion.rs
@@ -137,7 +137,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
                 at.lub(DefineOpaqueTypes::Yes, b, a)
             } else {
                 at.sup(DefineOpaqueTypes::Yes, b, a)
-                    .map(|InferOk { value: (), obligations }| InferOk { value: a, obligations })
+                    .map(|InferOk { value: (), obligations }| InferOk { value: b, obligations })
             };
 
             // In the new solver, lazy norm may allow us to shallowly equate
@@ -225,10 +225,10 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
                 // items to drop the unsafe qualifier.
                 self.coerce_from_fn_item(a, b)
             }
-            ty::FnPtr(a_f) => {
+            ty::FnPtr(a_sig_tys, a_hdr) => {
                 // We permit coercion of fn pointers to drop the
                 // unsafe qualifier.
-                self.coerce_from_fn_pointer(a, a_f, b)
+                self.coerce_from_fn_pointer(a, a_sig_tys.with(a_hdr), b)
             }
             ty::Closure(closure_def_id_a, args_a) => {
                 // Non-capturing closures are coercible to
@@ -788,9 +788,8 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         self.commit_if_ok(|snapshot| {
             let outer_universe = self.infcx.universe();
 
-            let result = if let ty::FnPtr(fn_ty_b) = b.kind()
-                && let (hir::Safety::Safe, hir::Safety::Unsafe) =
-                    (fn_ty_a.safety(), fn_ty_b.safety())
+            let result = if let ty::FnPtr(_, hdr_b) = b.kind()
+                && let (hir::Safety::Safe, hir::Safety::Unsafe) = (fn_ty_a.safety(), hdr_b.safety)
             {
                 let unsafe_a = self.tcx.safe_to_unsafe_fn_ty(fn_ty_a);
                 self.unify_and(unsafe_a, b, to_unsafe)
@@ -842,7 +841,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         debug!("coerce_from_fn_item(a={:?}, b={:?})", a, b);
 
         match b.kind() {
-            ty::FnPtr(b_sig) => {
+            ty::FnPtr(_, b_hdr) => {
                 let a_sig = a.fn_sig(self.tcx);
                 if let ty::FnDef(def_id, _) = *a.kind() {
                     // Intrinsics are not coercible to function pointers
@@ -852,7 +851,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
 
                     // Safe `#[target_feature]` functions are not assignable to safe fn pointers (RFC 2396).
 
-                    if b_sig.safety() == hir::Safety::Safe
+                    if b_hdr.safety == hir::Safety::Safe
                         && !self.tcx.codegen_fn_attrs(def_id).target_features.is_empty()
                     {
                         return Err(TypeError::TargetFeatureCast(def_id));
@@ -910,7 +909,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
             //
             // All we care here is if any variable is being captured and not the exact paths,
             // so we check `upvars_mentioned` for root variables being captured.
-            ty::FnPtr(fn_ty)
+            ty::FnPtr(_, hdr)
                 if self
                     .tcx
                     .upvars_mentioned(closure_def_id_a.expect_local())
@@ -923,7 +922,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
                 // or
                 //     `unsafe fn(arg0,arg1,...) -> _`
                 let closure_sig = args_a.as_closure().sig();
-                let safety = fn_ty.safety();
+                let safety = hdr.safety;
                 let pointer_ty =
                     Ty::new_fn_ptr(self.tcx, self.tcx.signature_unclosure(closure_sig, safety));
                 debug!("coerce_closure_to_fn(a={:?}, b={:?}, pty={:?})", a, b, pointer_ty);
diff --git a/compiler/rustc_hir_typeck/src/expectation.rs b/compiler/rustc_hir_typeck/src/expectation.rs
index 91deae4174b..76ae41db5c5 100644
--- a/compiler/rustc_hir_typeck/src/expectation.rs
+++ b/compiler/rustc_hir_typeck/src/expectation.rs
@@ -70,7 +70,8 @@ impl<'a, 'tcx> Expectation<'tcx> {
     /// See the test case `test/ui/coerce-expect-unsized.rs` and #20169
     /// for examples of where this comes up,.
     pub(super) fn rvalue_hint(fcx: &FnCtxt<'a, 'tcx>, ty: Ty<'tcx>) -> Expectation<'tcx> {
-        match fcx.tcx.struct_tail_without_normalization(ty).kind() {
+        // FIXME: This is not right, even in the old solver...
+        match fcx.tcx.struct_tail_raw(ty, |ty| ty, || {}).kind() {
             ty::Slice(_) | ty::Str | ty::Dynamic(..) => ExpectRvalueLikeUnsized(ty),
             _ => ExpectHasType(ty),
         }
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
index 841d25b54cc..b169f75796b 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
@@ -404,7 +404,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         code: traits::ObligationCauseCode<'tcx>,
     ) {
         if !ty.references_error() {
-            let tail = self.tcx.struct_tail_with_normalize(
+            let tail = self.tcx.struct_tail_raw(
                 ty,
                 |ty| {
                     if self.next_trait_solver() {
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
index 89e7227eda2..7720faddba3 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
@@ -1530,7 +1530,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     ty::Int(_) | ty::Uint(_) => Some(ty),
                     ty::Char => Some(tcx.types.u8),
                     ty::RawPtr(..) => Some(tcx.types.usize),
-                    ty::FnDef(..) | ty::FnPtr(_) => Some(tcx.types.usize),
+                    ty::FnDef(..) | ty::FnPtr(..) => Some(tcx.types.usize),
                     _ => None,
                 });
                 opt_ty.unwrap_or_else(|| self.next_int_var())
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
index 6b4edcd95d9..703273968c5 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
@@ -604,7 +604,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         expected: Ty<'tcx>,
         found: Ty<'tcx>,
     ) -> bool {
-        if let (ty::FnPtr(_), ty::Closure(def_id, _)) = (expected.kind(), found.kind()) {
+        if let (ty::FnPtr(..), ty::Closure(def_id, _)) = (expected.kind(), found.kind()) {
             if let Some(upvars) = self.tcx.upvars_mentioned(*def_id) {
                 // Report upto four upvars being captured to reduce the amount error messages
                 // reported back to the user.
diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index 61287d98676..3b71e2f19b1 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -50,7 +50,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // Not all of these (e.g., unsafe fns) implement `FnOnce`,
             // so we look for these beforehand.
             // FIXME(async_closures): These don't impl `FnOnce` by default.
-            ty::Closure(..) | ty::FnDef(..) | ty::FnPtr(_) => true,
+            ty::Closure(..) | ty::FnDef(..) | ty::FnPtr(..) => true,
             // If it's not a simple function, look for things which implement `FnOnce`.
             _ => {
                 let Some(fn_once) = tcx.lang_items().fn_once_trait() else {
diff --git a/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs b/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
index 3bcb92d8029..db5139172b0 100644
--- a/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
+++ b/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
@@ -438,7 +438,7 @@ impl<'cx, 'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'cx, 'tcx> {
             | ty::RawPtr(..)
             | ty::Ref(..)
             | ty::FnDef(..)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Dynamic(..)
             | ty::Never
             | ty::Tuple(..)
diff --git a/compiler/rustc_infer/src/infer/outlives/verify.rs b/compiler/rustc_infer/src/infer/outlives/verify.rs
index c3d37d9986f..1908e1e09c3 100644
--- a/compiler/rustc_infer/src/infer/outlives/verify.rs
+++ b/compiler/rustc_infer/src/infer/outlives/verify.rs
@@ -1,3 +1,5 @@
+use std::assert_matches::assert_matches;
+
 use rustc_middle::ty::{self, OutlivesPredicate, Ty, TyCtxt};
 use rustc_type_ir::outlives::{compute_alias_components_recursive, Component};
 use smallvec::smallvec;
@@ -181,7 +183,7 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
         &self,
         generic_ty: Ty<'tcx>,
     ) -> Vec<ty::PolyTypeOutlivesPredicate<'tcx>> {
-        assert!(matches!(generic_ty.kind(), ty::Param(_) | ty::Placeholder(_)));
+        assert_matches!(generic_ty.kind(), ty::Param(_) | ty::Placeholder(_));
         self.declared_generic_bounds_from_env_for_erased_ty(generic_ty)
     }
 
diff --git a/compiler/rustc_infer/src/lib.rs b/compiler/rustc_infer/src/lib.rs
index b65ac859667..25ac8ba974b 100644
--- a/compiler/rustc_infer/src/lib.rs
+++ b/compiler/rustc_infer/src/lib.rs
@@ -18,6 +18,7 @@
 #![allow(rustc::untranslatable_diagnostic)]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
+#![feature(assert_matches)]
 #![feature(box_patterns)]
 #![feature(control_flow_enum)]
 #![feature(extend_one)]
diff --git a/compiler/rustc_interface/src/util.rs b/compiler/rustc_interface/src/util.rs
index 6f53b1c9031..761d288a7c2 100644
--- a/compiler/rustc_interface/src/util.rs
+++ b/compiler/rustc_interface/src/util.rs
@@ -386,7 +386,6 @@ fn get_codegen_sysroot(
     }
 }
 
-#[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
 pub(crate) fn check_attr_crate_type(
     sess: &Session,
     attrs: &[ast::Attribute],
diff --git a/compiler/rustc_lint/src/for_loops_over_fallibles.rs b/compiler/rustc_lint/src/for_loops_over_fallibles.rs
index 6cb5263ac54..2793d48dc51 100644
--- a/compiler/rustc_lint/src/for_loops_over_fallibles.rs
+++ b/compiler/rustc_lint/src/for_loops_over_fallibles.rs
@@ -1,5 +1,5 @@
 use hir::{Expr, Pat};
-use rustc_hir as hir;
+use rustc_hir::{self as hir, LangItem};
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::traits::ObligationCause;
 use rustc_middle::ty;
@@ -126,7 +126,10 @@ fn extract_iterator_next_call<'tcx>(
 ) -> Option<&'tcx Expr<'tcx>> {
     // This won't work for `Iterator::next(iter)`, is this an issue?
     if let hir::ExprKind::MethodCall(_, recv, _, _) = expr.kind
-        && cx.typeck_results().type_dependent_def_id(expr.hir_id) == cx.tcx.lang_items().next_fn()
+        && cx
+            .typeck_results()
+            .type_dependent_def_id(expr.hir_id)
+            .is_some_and(|def_id| cx.tcx.is_lang_item(def_id, LangItem::IteratorNext))
     {
         Some(recv)
     } else {
diff --git a/compiler/rustc_lint/src/levels.rs b/compiler/rustc_lint/src/levels.rs
index 72920fd045f..44117e5d7a5 100644
--- a/compiler/rustc_lint/src/levels.rs
+++ b/compiler/rustc_lint/src/levels.rs
@@ -717,7 +717,6 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
         };
     }
 
-    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn add(&mut self, attrs: &[ast::Attribute], is_crate_node: bool, source_hir_id: Option<HirId>) {
         let sess = self.sess;
         for (attr_index, attr) in attrs.iter().enumerate() {
@@ -1039,7 +1038,6 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
             let (level, src) = self.lint_level(builtin::UNKNOWN_LINTS);
             // FIXME: make this translatable
             #[allow(rustc::diagnostic_outside_of_impl)]
-            #[allow(rustc::untranslatable_diagnostic)]
             lint_level(self.sess, lint, level, src, Some(span.into()), |lint| {
                 lint.primary_message(fluent::lint_unknown_gated_lint);
                 lint.arg("name", lint_id.lint.name_lower());
diff --git a/compiler/rustc_lint/src/traits.rs b/compiler/rustc_lint/src/traits.rs
index fea96b5366e..a0fe4b5af74 100644
--- a/compiler/rustc_lint/src/traits.rs
+++ b/compiler/rustc_lint/src/traits.rs
@@ -114,7 +114,7 @@ impl<'tcx> LateLintPass<'tcx> for DropTraitConstraints {
         let hir::TyKind::TraitObject(bounds, _lifetime, _syntax) = &ty.kind else { return };
         for (bound, modifier) in &bounds[..] {
             let def_id = bound.trait_ref.trait_def_id();
-            if cx.tcx.lang_items().drop_trait() == def_id
+            if def_id.is_some_and(|def_id| cx.tcx.is_lang_item(def_id, LangItem::Drop))
                 && *modifier != hir::TraitBoundModifier::Maybe
             {
                 let Some(def_id) = cx.tcx.get_diagnostic_item(sym::needs_drop) else { return };
diff --git a/compiler/rustc_lint/src/types.rs b/compiler/rustc_lint/src/types.rs
index 51896da893c..54bf73a40dd 100644
--- a/compiler/rustc_lint/src/types.rs
+++ b/compiler/rustc_lint/src/types.rs
@@ -1022,7 +1022,7 @@ fn ty_is_known_nonnull<'tcx>(
     let ty = tcx.try_normalize_erasing_regions(param_env, ty).unwrap_or(ty);
 
     match ty.kind() {
-        ty::FnPtr(_) => true,
+        ty::FnPtr(..) => true,
         ty::Ref(..) => true,
         ty::Adt(def, _) if def.is_box() && matches!(mode, CItemKind::Definition) => true,
         ty::Adt(def, args) if def.repr().transparent() && !def.is_union() => {
@@ -1473,7 +1473,8 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 
             ty::Array(inner_ty, _) => self.check_type_for_ffi(cache, inner_ty),
 
-            ty::FnPtr(sig) => {
+            ty::FnPtr(sig_tys, hdr) => {
+                let sig = sig_tys.with(hdr);
                 if self.is_internal_abi(sig.abi()) {
                     return FfiUnsafe {
                         ty,
@@ -1709,8 +1710,8 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
             type Result = ControlFlow<Ty<'tcx>>;
 
             fn visit_ty(&mut self, ty: Ty<'tcx>) -> Self::Result {
-                if let ty::FnPtr(sig) = ty.kind()
-                    && !self.visitor.is_internal_abi(sig.abi())
+                if let ty::FnPtr(_, hdr) = ty.kind()
+                    && !self.visitor.is_internal_abi(hdr.abi)
                 {
                     self.tys.push(ty);
                 }
diff --git a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
index 2ff7335a0fc..79a68b2ff0e 100644
--- a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
@@ -397,6 +397,18 @@ LLVMRustCreateAllocSizeAttr(LLVMContextRef C, uint32_t ElementSizeArg) {
                                               std::nullopt));
 }
 
+extern "C" LLVMAttributeRef
+LLVMRustCreateRangeAttribute(LLVMContextRef C, unsigned NumBits,
+                             const uint64_t LowerWords[],
+                             const uint64_t UpperWords[]) {
+#if LLVM_VERSION_GE(19, 0)
+  return LLVMCreateConstantRangeAttribute(C, Attribute::Range, NumBits,
+                                          LowerWords, UpperWords);
+#else
+  report_fatal_error("LLVM 19.0 is required for Range Attribute");
+#endif
+}
+
 // These values **must** match ffi::AllocKindFlags.
 // It _happens_ to match the LLVM values of llvm::AllocFnKind,
 // but that's happenstance and we do explicit conversions before
diff --git a/compiler/rustc_metadata/messages.ftl b/compiler/rustc_metadata/messages.ftl
index 24fe1ebc07e..d80aa0cc4f4 100644
--- a/compiler/rustc_metadata/messages.ftl
+++ b/compiler/rustc_metadata/messages.ftl
@@ -134,12 +134,18 @@ metadata_lib_framework_apple =
 metadata_lib_required =
     crate `{$crate_name}` required to be available in {$kind} format, but was not found in this form
 
+metadata_link_arg_unstable =
+    link kind `link-arg` is unstable
+
 metadata_link_cfg_form =
     link cfg must be of the form `cfg(/* predicate */)`
 
 metadata_link_cfg_single_predicate =
     link cfg must have a single predicate argument
 
+metadata_link_cfg_unstable =
+    link cfg is unstable
+
 metadata_link_framework_apple =
     link kind `framework` is only supported on Apple targets
 
diff --git a/compiler/rustc_metadata/src/creader.rs b/compiler/rustc_metadata/src/creader.rs
index 2fca443ffa0..14a1a7f67e5 100644
--- a/compiler/rustc_metadata/src/creader.rs
+++ b/compiler/rustc_metadata/src/creader.rs
@@ -949,7 +949,6 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
         }
     }
 
-    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn report_unused_deps(&mut self, krate: &ast::Crate) {
         // Make a point span rather than covering the whole file
         let span = krate.spans.inner_span.shrink_to_lo();
diff --git a/compiler/rustc_metadata/src/native_libs.rs b/compiler/rustc_metadata/src/native_libs.rs
index b19493d12ff..34497f5ac53 100644
--- a/compiler/rustc_metadata/src/native_libs.rs
+++ b/compiler/rustc_metadata/src/native_libs.rs
@@ -17,7 +17,7 @@ use rustc_span::def_id::{DefId, LOCAL_CRATE};
 use rustc_span::symbol::{sym, Symbol};
 use rustc_target::spec::abi::Abi;
 
-use crate::errors;
+use crate::{errors, fluent_generated};
 
 pub fn find_native_static_library(name: &str, verbatim: bool, sess: &Session) -> PathBuf {
     let formats = if verbatim {
@@ -87,7 +87,6 @@ struct Collector<'tcx> {
 }
 
 impl<'tcx> Collector<'tcx> {
-    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn process_module(&mut self, module: &ForeignModule) {
         let ForeignModule { def_id, abi, ref foreign_items } = *module;
         let def_id = def_id.expect_local();
@@ -161,7 +160,7 @@ impl<'tcx> Collector<'tcx> {
                                         sess,
                                         sym::link_arg_attribute,
                                         span,
-                                        "link kind `link-arg` is unstable",
+                                        fluent_generated::metadata_link_arg_unstable,
                                     )
                                     .emit();
                                 }
@@ -201,8 +200,13 @@ impl<'tcx> Collector<'tcx> {
                             continue;
                         };
                         if !features.link_cfg {
-                            feature_err(sess, sym::link_cfg, item.span(), "link cfg is unstable")
-                                .emit();
+                            feature_err(
+                                sess,
+                                sym::link_cfg,
+                                item.span(),
+                                fluent_generated::metadata_link_cfg_unstable,
+                            )
+                            .emit();
                         }
                         cfg = Some(link_cfg.clone());
                     }
@@ -266,6 +270,8 @@ impl<'tcx> Collector<'tcx> {
 
                     macro report_unstable_modifier($feature: ident) {
                         if !features.$feature {
+                            // FIXME: make this translatable
+                            #[expect(rustc::untranslatable_diagnostic)]
                             feature_err(
                                 sess,
                                 sym::$feature,
diff --git a/compiler/rustc_middle/src/mir/interpret/mod.rs b/compiler/rustc_middle/src/mir/interpret/mod.rs
index 1851a61d753..91e71c12cae 100644
--- a/compiler/rustc_middle/src/mir/interpret/mod.rs
+++ b/compiler/rustc_middle/src/mir/interpret/mod.rs
@@ -13,7 +13,6 @@ use std::num::NonZero;
 use std::{fmt, io};
 
 use rustc_ast::LitKind;
-use rustc_attr::InlineAttr;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::Lock;
 use rustc_errors::ErrorGuaranteed;
@@ -46,7 +45,7 @@ pub use self::pointer::{CtfeProvenance, Pointer, PointerArithmetic, Provenance};
 pub use self::value::Scalar;
 use crate::mir;
 use crate::ty::codec::{TyDecoder, TyEncoder};
-use crate::ty::{self, GenericArgKind, Instance, Ty, TyCtxt};
+use crate::ty::{self, Instance, Ty, TyCtxt};
 
 /// Uniquely identifies one of the following:
 /// - A constant
@@ -126,11 +125,10 @@ pub fn specialized_encode_alloc_id<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>>(
             AllocDiscriminant::Alloc.encode(encoder);
             alloc.encode(encoder);
         }
-        GlobalAlloc::Function { instance, unique } => {
+        GlobalAlloc::Function { instance } => {
             trace!("encoding {:?} with {:#?}", alloc_id, instance);
             AllocDiscriminant::Fn.encode(encoder);
             instance.encode(encoder);
-            unique.encode(encoder);
         }
         GlobalAlloc::VTable(ty, poly_trait_ref) => {
             trace!("encoding {:?} with {ty:#?}, {poly_trait_ref:#?}", alloc_id);
@@ -219,38 +217,32 @@ impl<'s> AllocDecodingSession<'s> {
         }
 
         // Now decode the actual data.
-        let alloc_id = decoder.with_position(pos, |decoder| {
-            match alloc_kind {
-                AllocDiscriminant::Alloc => {
-                    trace!("creating memory alloc ID");
-                    let alloc = <ConstAllocation<'tcx> as Decodable<_>>::decode(decoder);
-                    trace!("decoded alloc {:?}", alloc);
-                    decoder.interner().reserve_and_set_memory_alloc(alloc)
-                }
-                AllocDiscriminant::Fn => {
-                    trace!("creating fn alloc ID");
-                    let instance = ty::Instance::decode(decoder);
-                    trace!("decoded fn alloc instance: {:?}", instance);
-                    let unique = bool::decode(decoder);
-                    // Here we cannot call `reserve_and_set_fn_alloc` as that would use a query, which
-                    // is not possible in this context. That's why the allocation stores
-                    // whether it is unique or not.
-                    decoder.interner().reserve_and_set_fn_alloc_internal(instance, unique)
-                }
-                AllocDiscriminant::VTable => {
-                    trace!("creating vtable alloc ID");
-                    let ty = <Ty<'_> as Decodable<D>>::decode(decoder);
-                    let poly_trait_ref =
-                        <Option<ty::PolyExistentialTraitRef<'_>> as Decodable<D>>::decode(decoder);
-                    trace!("decoded vtable alloc instance: {ty:?}, {poly_trait_ref:?}");
-                    decoder.interner().reserve_and_set_vtable_alloc(ty, poly_trait_ref)
-                }
-                AllocDiscriminant::Static => {
-                    trace!("creating extern static alloc ID");
-                    let did = <DefId as Decodable<D>>::decode(decoder);
-                    trace!("decoded static def-ID: {:?}", did);
-                    decoder.interner().reserve_and_set_static_alloc(did)
-                }
+        let alloc_id = decoder.with_position(pos, |decoder| match alloc_kind {
+            AllocDiscriminant::Alloc => {
+                trace!("creating memory alloc ID");
+                let alloc = <ConstAllocation<'tcx> as Decodable<_>>::decode(decoder);
+                trace!("decoded alloc {:?}", alloc);
+                decoder.interner().reserve_and_set_memory_alloc(alloc)
+            }
+            AllocDiscriminant::Fn => {
+                trace!("creating fn alloc ID");
+                let instance = ty::Instance::decode(decoder);
+                trace!("decoded fn alloc instance: {:?}", instance);
+                decoder.interner().reserve_and_set_fn_alloc(instance, CTFE_ALLOC_SALT)
+            }
+            AllocDiscriminant::VTable => {
+                trace!("creating vtable alloc ID");
+                let ty = <Ty<'_> as Decodable<D>>::decode(decoder);
+                let poly_trait_ref =
+                    <Option<ty::PolyExistentialTraitRef<'_>> as Decodable<D>>::decode(decoder);
+                trace!("decoded vtable alloc instance: {ty:?}, {poly_trait_ref:?}");
+                decoder.interner().reserve_and_set_vtable_alloc(ty, poly_trait_ref, CTFE_ALLOC_SALT)
+            }
+            AllocDiscriminant::Static => {
+                trace!("creating extern static alloc ID");
+                let did = <DefId as Decodable<D>>::decode(decoder);
+                trace!("decoded static def-ID: {:?}", did);
+                decoder.interner().reserve_and_set_static_alloc(did)
             }
         });
 
@@ -265,12 +257,7 @@ impl<'s> AllocDecodingSession<'s> {
 #[derive(Debug, Clone, Eq, PartialEq, Hash, TyDecodable, TyEncodable, HashStable)]
 pub enum GlobalAlloc<'tcx> {
     /// The alloc ID is used as a function pointer.
-    Function {
-        instance: Instance<'tcx>,
-        /// Stores whether this instance is unique, i.e. all pointers to this function use the same
-        /// alloc ID.
-        unique: bool,
-    },
+    Function { instance: Instance<'tcx> },
     /// This alloc ID points to a symbolic (not-reified) vtable.
     VTable(Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>),
     /// The alloc ID points to a "lazy" static variable that did not get computed (yet).
@@ -323,14 +310,17 @@ impl<'tcx> GlobalAlloc<'tcx> {
     }
 }
 
+pub const CTFE_ALLOC_SALT: usize = 0;
+
 pub(crate) struct AllocMap<'tcx> {
     /// Maps `AllocId`s to their corresponding allocations.
     alloc_map: FxHashMap<AllocId, GlobalAlloc<'tcx>>,
 
-    /// Used to ensure that statics and functions only get one associated `AllocId`.
-    //
-    // FIXME: Should we just have two separate dedup maps for statics and functions each?
-    dedup: FxHashMap<GlobalAlloc<'tcx>, AllocId>,
+    /// Used to deduplicate global allocations: functions, vtables, string literals, ...
+    ///
+    /// The `usize` is a "salt" used by Miri to make deduplication imperfect, thus better emulating
+    /// the actual guarantees.
+    dedup: FxHashMap<(GlobalAlloc<'tcx>, usize), AllocId>,
 
     /// The `AllocId` to assign to the next requested ID.
     /// Always incremented; never gets smaller.
@@ -368,74 +358,40 @@ impl<'tcx> TyCtxt<'tcx> {
 
     /// Reserves a new ID *if* this allocation has not been dedup-reserved before.
     /// Should not be used for mutable memory.
-    fn reserve_and_set_dedup(self, alloc: GlobalAlloc<'tcx>) -> AllocId {
+    fn reserve_and_set_dedup(self, alloc: GlobalAlloc<'tcx>, salt: usize) -> AllocId {
         let mut alloc_map = self.alloc_map.lock();
         if let GlobalAlloc::Memory(mem) = alloc {
             if mem.inner().mutability.is_mut() {
                 bug!("trying to dedup-reserve mutable memory");
             }
         }
-        if let Some(&alloc_id) = alloc_map.dedup.get(&alloc) {
+        let alloc_salt = (alloc, salt);
+        if let Some(&alloc_id) = alloc_map.dedup.get(&alloc_salt) {
             return alloc_id;
         }
         let id = alloc_map.reserve();
-        debug!("creating alloc {alloc:?} with id {id:?}");
-        alloc_map.alloc_map.insert(id, alloc.clone());
-        alloc_map.dedup.insert(alloc, id);
+        debug!("creating alloc {:?} with id {id:?}", alloc_salt.0);
+        alloc_map.alloc_map.insert(id, alloc_salt.0.clone());
+        alloc_map.dedup.insert(alloc_salt, id);
         id
     }
 
     /// Generates an `AllocId` for a memory allocation. If the exact same memory has been
     /// allocated before, this will return the same `AllocId`.
-    pub fn reserve_and_set_memory_dedup(self, mem: ConstAllocation<'tcx>) -> AllocId {
-        self.reserve_and_set_dedup(GlobalAlloc::Memory(mem))
+    pub fn reserve_and_set_memory_dedup(self, mem: ConstAllocation<'tcx>, salt: usize) -> AllocId {
+        self.reserve_and_set_dedup(GlobalAlloc::Memory(mem), salt)
     }
 
     /// Generates an `AllocId` for a static or return a cached one in case this function has been
     /// called on the same static before.
     pub fn reserve_and_set_static_alloc(self, static_id: DefId) -> AllocId {
-        self.reserve_and_set_dedup(GlobalAlloc::Static(static_id))
-    }
-
-    /// Generates an `AllocId` for a function. The caller must already have decided whether this
-    /// function obtains a unique AllocId or gets de-duplicated via the cache.
-    fn reserve_and_set_fn_alloc_internal(self, instance: Instance<'tcx>, unique: bool) -> AllocId {
-        let alloc = GlobalAlloc::Function { instance, unique };
-        if unique {
-            // Deduplicate.
-            self.reserve_and_set_dedup(alloc)
-        } else {
-            // Get a fresh ID.
-            let mut alloc_map = self.alloc_map.lock();
-            let id = alloc_map.reserve();
-            alloc_map.alloc_map.insert(id, alloc);
-            id
-        }
+        let salt = 0; // Statics have a guaranteed unique address, no salt added.
+        self.reserve_and_set_dedup(GlobalAlloc::Static(static_id), salt)
     }
 
-    /// Generates an `AllocId` for a function. Depending on the function type,
-    /// this might get deduplicated or assigned a new ID each time.
-    pub fn reserve_and_set_fn_alloc(self, instance: Instance<'tcx>) -> AllocId {
-        // Functions cannot be identified by pointers, as asm-equal functions can get deduplicated
-        // by the linker (we set the "unnamed_addr" attribute for LLVM) and functions can be
-        // duplicated across crates. We thus generate a new `AllocId` for every mention of a
-        // function. This means that `main as fn() == main as fn()` is false, while `let x = main as
-        // fn(); x == x` is true. However, as a quality-of-life feature it can be useful to identify
-        // certain functions uniquely, e.g. for backtraces. So we identify whether codegen will
-        // actually emit duplicate functions. It does that when they have non-lifetime generics, or
-        // when they can be inlined. All other functions are given a unique address.
-        // This is not a stable guarantee! The `inline` attribute is a hint and cannot be relied
-        // upon for anything. But if we don't do this, backtraces look terrible.
-        let is_generic = instance
-            .args
-            .into_iter()
-            .any(|kind| !matches!(kind.unpack(), GenericArgKind::Lifetime(_)));
-        let can_be_inlined = match self.codegen_fn_attrs(instance.def_id()).inline {
-            InlineAttr::Never => false,
-            _ => true,
-        };
-        let unique = !is_generic && !can_be_inlined;
-        self.reserve_and_set_fn_alloc_internal(instance, unique)
+    /// Generates an `AllocId` for a function. Will get deduplicated.
+    pub fn reserve_and_set_fn_alloc(self, instance: Instance<'tcx>, salt: usize) -> AllocId {
+        self.reserve_and_set_dedup(GlobalAlloc::Function { instance }, salt)
     }
 
     /// Generates an `AllocId` for a (symbolic, not-reified) vtable. Will get deduplicated.
@@ -443,8 +399,9 @@ impl<'tcx> TyCtxt<'tcx> {
         self,
         ty: Ty<'tcx>,
         poly_trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
+        salt: usize,
     ) -> AllocId {
-        self.reserve_and_set_dedup(GlobalAlloc::VTable(ty, poly_trait_ref))
+        self.reserve_and_set_dedup(GlobalAlloc::VTable(ty, poly_trait_ref), salt)
     }
 
     /// Interns the `Allocation` and return a new `AllocId`, even if there's already an identical
diff --git a/compiler/rustc_middle/src/ty/consts/kind.rs b/compiler/rustc_middle/src/ty/consts/kind.rs
index 7f096dd36f8..c7c2e8afa1e 100644
--- a/compiler/rustc_middle/src/ty/consts/kind.rs
+++ b/compiler/rustc_middle/src/ty/consts/kind.rs
@@ -1,3 +1,5 @@
+use std::assert_matches::assert_matches;
+
 use rustc_macros::{extension, HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable};
 
 use super::Const;
@@ -80,7 +82,7 @@ impl<'tcx> Expr<'tcx> {
     }
 
     pub fn binop_args(self) -> (Ty<'tcx>, Ty<'tcx>, Const<'tcx>, Const<'tcx>) {
-        assert!(matches!(self.kind, ExprKind::Binop(_)));
+        assert_matches!(self.kind, ExprKind::Binop(_));
 
         match self.args().as_slice() {
             [lhs_ty, rhs_ty, lhs_ct, rhs_ct] => (
@@ -101,7 +103,7 @@ impl<'tcx> Expr<'tcx> {
     }
 
     pub fn unop_args(self) -> (Ty<'tcx>, Const<'tcx>) {
-        assert!(matches!(self.kind, ExprKind::UnOp(_)));
+        assert_matches!(self.kind, ExprKind::UnOp(_));
 
         match self.args().as_slice() {
             [ty, ct] => (ty.expect_ty(), ct.expect_const()),
@@ -125,7 +127,7 @@ impl<'tcx> Expr<'tcx> {
     }
 
     pub fn call_args(self) -> (Ty<'tcx>, Const<'tcx>, impl Iterator<Item = Const<'tcx>>) {
-        assert!(matches!(self.kind, ExprKind::FunctionCall));
+        assert_matches!(self.kind, ExprKind::FunctionCall);
 
         match self.args().as_slice() {
             [func_ty, func, rest @ ..] => (
@@ -152,7 +154,7 @@ impl<'tcx> Expr<'tcx> {
     }
 
     pub fn cast_args(self) -> (Ty<'tcx>, Const<'tcx>, Ty<'tcx>) {
-        assert!(matches!(self.kind, ExprKind::Cast(_)));
+        assert_matches!(self.kind, ExprKind::Cast(_));
 
         match self.args().as_slice() {
             [value_ty, value, to_ty] => {
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 8198b2fdc89..9b39b849704 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -418,7 +418,7 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
             | ty::RawPtr(_, _)
             | ty::Ref(_, _, _)
             | ty::FnDef(_, _)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Dynamic(_, _, _)
             | ty::Closure(..)
             | ty::CoroutineClosure(..)
@@ -1429,11 +1429,11 @@ impl<'tcx> TyCtxt<'tcx> {
 
     /// Allocates a read-only byte or string literal for `mir::interpret`.
     /// Returns the same `AllocId` if called again with the same bytes.
-    pub fn allocate_bytes_dedup(self, bytes: &[u8]) -> interpret::AllocId {
+    pub fn allocate_bytes_dedup(self, bytes: &[u8], salt: usize) -> interpret::AllocId {
         // Create an allocation that just contains these bytes.
         let alloc = interpret::Allocation::from_bytes_byte_aligned_immutable(bytes);
         let alloc = self.mk_const_alloc(alloc);
-        self.reserve_and_set_memory_dedup(alloc)
+        self.reserve_and_set_memory_dedup(alloc, salt)
     }
 
     /// Returns a range of the start/end indices specified with the
@@ -3167,6 +3167,12 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn impl_polarity(self, def_id: impl IntoQueryParam<DefId>) -> ty::ImplPolarity {
         self.impl_trait_header(def_id).map_or(ty::ImplPolarity::Positive, |h| h.polarity)
     }
+
+    /// Whether this is a trait implementation that has `#[diagnostic::do_not_recommend]`
+    pub fn do_not_recommend_impl(self, def_id: DefId) -> bool {
+        matches!(self.def_kind(def_id), DefKind::Impl { of_trait: true })
+            && self.impl_trait_header(def_id).is_some_and(|header| header.do_not_recommend)
+    }
 }
 
 /// Parameter attributes that can only be determined by examining the body of a function instead
diff --git a/compiler/rustc_middle/src/ty/diagnostics.rs b/compiler/rustc_middle/src/ty/diagnostics.rs
index 5acc0b7ac7f..c14dadc68c9 100644
--- a/compiler/rustc_middle/src/ty/diagnostics.rs
+++ b/compiler/rustc_middle/src/ty/diagnostics.rs
@@ -6,10 +6,9 @@ use std::ops::ControlFlow;
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::{into_diag_arg_using_display, Applicability, Diag, DiagArgValue, IntoDiagArg};
-use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
-use rustc_hir::{PredicateOrigin, WherePredicate};
+use rustc_hir::{self as hir, LangItem, PredicateOrigin, WherePredicate};
 use rustc_span::{BytePos, Span};
 use rustc_type_ir::TyKind::*;
 
@@ -290,8 +289,9 @@ pub fn suggest_constraining_type_params<'a>(
         let Some(param) = param else { return false };
 
         {
-            let mut sized_constraints =
-                constraints.extract_if(|(_, def_id)| *def_id == tcx.lang_items().sized_trait());
+            let mut sized_constraints = constraints.extract_if(|(_, def_id)| {
+                def_id.is_some_and(|def_id| tcx.is_lang_item(def_id, LangItem::Sized))
+            });
             if let Some((_, def_id)) = sized_constraints.next() {
                 applicability = Applicability::MaybeIncorrect;
 
diff --git a/compiler/rustc_middle/src/ty/error.rs b/compiler/rustc_middle/src/ty/error.rs
index 2f9bdb16bb0..d974a86a303 100644
--- a/compiler/rustc_middle/src/ty/error.rs
+++ b/compiler/rustc_middle/src/ty/error.rs
@@ -130,7 +130,7 @@ impl<'tcx> Ty<'tcx> {
                 DefKind::Ctor(CtorOf::Variant, _) => "enum constructor".into(),
                 _ => "fn item".into(),
             },
-            ty::FnPtr(_) => "fn pointer".into(),
+            ty::FnPtr(..) => "fn pointer".into(),
             ty::Dynamic(inner, ..) if let Some(principal) = inner.principal() => {
                 format!("`dyn {}`", tcx.def_path_str(principal.def_id())).into()
             }
@@ -194,7 +194,7 @@ impl<'tcx> Ty<'tcx> {
                 DefKind::Ctor(CtorOf::Variant, _) => "enum constructor".into(),
                 _ => "fn item".into(),
             },
-            ty::FnPtr(_) => "fn pointer".into(),
+            ty::FnPtr(..) => "fn pointer".into(),
             ty::Dynamic(..) => "trait object".into(),
             ty::Closure(..) | ty::CoroutineClosure(..) => "closure".into(),
             ty::Coroutine(def_id, ..) => {
diff --git a/compiler/rustc_middle/src/ty/flags.rs b/compiler/rustc_middle/src/ty/flags.rs
index c3430b58406..fc079592583 100644
--- a/compiler/rustc_middle/src/ty/flags.rs
+++ b/compiler/rustc_middle/src/ty/flags.rs
@@ -250,9 +250,8 @@ impl FlagComputation {
                 self.add_args(args);
             }
 
-            &ty::FnPtr(fn_sig) => self.bound_computation(fn_sig, |computation, fn_sig| {
-                computation.add_tys(fn_sig.inputs());
-                computation.add_ty(fn_sig.output());
+            &ty::FnPtr(sig_tys, _) => self.bound_computation(sig_tys, |computation, sig_tys| {
+                computation.add_tys(sig_tys.inputs_and_output);
             }),
         }
     }
diff --git a/compiler/rustc_middle/src/ty/instance.rs b/compiler/rustc_middle/src/ty/instance.rs
index 0496c571f5e..6f19739de45 100644
--- a/compiler/rustc_middle/src/ty/instance.rs
+++ b/compiler/rustc_middle/src/ty/instance.rs
@@ -838,7 +838,7 @@ impl<'tcx> Instance<'tcx> {
             return None;
         };
 
-        if tcx.lang_items().get(coroutine_callable_item) == Some(trait_item_id) {
+        if tcx.is_lang_item(trait_item_id, coroutine_callable_item) {
             let ty::Coroutine(_, id_args) = *tcx.type_of(coroutine_def_id).skip_binder().kind()
             else {
                 bug!()
diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs
index 9204405d58f..619981bf021 100644
--- a/compiler/rustc_middle/src/ty/layout.rs
+++ b/compiler/rustc_middle/src/ty/layout.rs
@@ -362,7 +362,7 @@ impl<'tcx> SizeSkeleton<'tcx> {
             ty::Ref(_, pointee, _) | ty::RawPtr(pointee, _) => {
                 let non_zero = !ty.is_unsafe_ptr();
 
-                let tail = tcx.struct_tail_with_normalize(
+                let tail = tcx.struct_tail_raw(
                     pointee,
                     |ty| match tcx.try_normalize_erasing_regions(param_env, ty) {
                         Ok(ty) => ty,
@@ -801,7 +801,7 @@ where
                 | ty::Int(_)
                 | ty::Uint(_)
                 | ty::Float(_)
-                | ty::FnPtr(_)
+                | ty::FnPtr(..)
                 | ty::Never
                 | ty::FnDef(..)
                 | ty::CoroutineWitness(..)
@@ -986,9 +986,11 @@ where
                     safe: None,
                 })
             }
-            ty::FnPtr(fn_sig) if offset.bytes() == 0 => {
-                tcx.layout_of(param_env.and(Ty::new_fn_ptr(tcx, fn_sig))).ok().map(|layout| {
-                    PointeeInfo { size: layout.size, align: layout.align.abi, safe: None }
+            ty::FnPtr(..) if offset.bytes() == 0 => {
+                tcx.layout_of(param_env.and(this.ty)).ok().map(|layout| PointeeInfo {
+                    size: layout.size,
+                    align: layout.align.abi,
+                    safe: None,
                 })
             }
             ty::Ref(_, ty, mt) if offset.bytes() == 0 => {
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 9736428e6f7..1e3b5800cba 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -262,6 +262,7 @@ pub struct ImplTraitHeader<'tcx> {
     pub trait_ref: ty::EarlyBinder<'tcx, ty::TraitRef<'tcx>>,
     pub polarity: ImplPolarity,
     pub safety: hir::Safety,
+    pub do_not_recommend: bool,
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, Debug, TypeFoldable, TypeVisitable)]
@@ -2149,6 +2150,6 @@ mod size_asserts {
     use super::*;
     // tidy-alphabetical-start
     static_assert_size!(PredicateKind<'_>, 32);
-    static_assert_size!(WithCachedTypeInfo<TyKind<'_>>, 56);
+    static_assert_size!(WithCachedTypeInfo<TyKind<'_>>, 48);
     // tidy-alphabetical-end
 }
diff --git a/compiler/rustc_middle/src/ty/print/mod.rs b/compiler/rustc_middle/src/ty/print/mod.rs
index 6cce79dfdc1..cc746746760 100644
--- a/compiler/rustc_middle/src/ty/print/mod.rs
+++ b/compiler/rustc_middle/src/ty/print/mod.rs
@@ -290,7 +290,7 @@ fn characteristic_def_id_of_type_cached<'a>(
         | ty::Int(_)
         | ty::Uint(_)
         | ty::Str
-        | ty::FnPtr(_)
+        | ty::FnPtr(..)
         | ty::Alias(..)
         | ty::Placeholder(..)
         | ty::Param(_)
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index 29d72183dd3..56ddf146636 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -696,7 +696,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                     p!(print(sig), " {{", print_value_path(def_id, args), "}}");
                 }
             }
-            ty::FnPtr(ref bare_fn) => p!(print(bare_fn)),
+            ty::FnPtr(ref sig_tys, hdr) => p!(print(sig_tys.with(hdr))),
             ty::Infer(infer_ty) => {
                 if self.should_print_verbose() {
                     p!(write("{:?}", ty.kind()));
@@ -1145,7 +1145,9 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                         let term = if let Some(ty) = term.skip_binder().as_type()
                             && let ty::Alias(ty::Projection, proj) = ty.kind()
                             && let Some(assoc) = tcx.opt_associated_item(proj.def_id)
-                            && assoc.trait_container(tcx) == tcx.lang_items().coroutine_trait()
+                            && assoc
+                                .trait_container(tcx)
+                                .is_some_and(|def_id| tcx.is_lang_item(def_id, LangItem::Coroutine))
                             && assoc.name == rustc_span::sym::Return
                         {
                             if let ty::Coroutine(_, args) = args.type_at(0).kind() {
@@ -1678,7 +1680,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                     }
                 }
             }
-            ty::FnPtr(_) => {
+            ty::FnPtr(..) => {
                 // FIXME: We should probably have a helper method to share code with the "Byte strings"
                 // printing above (which also has to handle pointers to all sorts of things).
                 if let Some(GlobalAlloc::Function { instance, .. }) =
@@ -1741,7 +1743,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                 p!(write("{:?}", char::try_from(int).unwrap()))
             }
             // Pointer types
-            ty::Ref(..) | ty::RawPtr(_, _) | ty::FnPtr(_) => {
+            ty::Ref(..) | ty::RawPtr(_, _) | ty::FnPtr(..) => {
                 let data = int.to_bits(self.tcx().data_layout.pointer_size);
                 self.typed_value(
                     |this| {
diff --git a/compiler/rustc_middle/src/ty/structural_impls.rs b/compiler/rustc_middle/src/ty/structural_impls.rs
index 8fb44a5f0b1..80b33c2cda9 100644
--- a/compiler/rustc_middle/src/ty/structural_impls.rs
+++ b/compiler/rustc_middle/src/ty/structural_impls.rs
@@ -374,7 +374,7 @@ impl<'tcx> TypeSuperFoldable<TyCtxt<'tcx>> for Ty<'tcx> {
             ),
             ty::Tuple(ts) => ty::Tuple(ts.try_fold_with(folder)?),
             ty::FnDef(def_id, args) => ty::FnDef(def_id, args.try_fold_with(folder)?),
-            ty::FnPtr(f) => ty::FnPtr(f.try_fold_with(folder)?),
+            ty::FnPtr(sig_tys, hdr) => ty::FnPtr(sig_tys.try_fold_with(folder)?, hdr),
             ty::Ref(r, ty, mutbl) => {
                 ty::Ref(r.try_fold_with(folder)?, ty.try_fold_with(folder)?, mutbl)
             }
@@ -424,7 +424,7 @@ impl<'tcx> TypeSuperVisitable<TyCtxt<'tcx>> for Ty<'tcx> {
             }
             ty::Tuple(ts) => ts.visit_with(visitor),
             ty::FnDef(_, args) => args.visit_with(visitor),
-            ty::FnPtr(ref f) => f.visit_with(visitor),
+            ty::FnPtr(ref sig_tys, _) => sig_tys.visit_with(visitor),
             ty::Ref(r, ty, _) => {
                 try_visit!(r.visit_with(visitor));
                 ty.visit_with(visitor)
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 8c97de1c59b..0a277fea49c 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -658,7 +658,8 @@ impl<'tcx> Ty<'tcx> {
 
     #[inline]
     pub fn new_fn_ptr(tcx: TyCtxt<'tcx>, fty: PolyFnSig<'tcx>) -> Ty<'tcx> {
-        Ty::new(tcx, FnPtr(fty))
+        let (sig_tys, hdr) = fty.split();
+        Ty::new(tcx, FnPtr(sig_tys, hdr))
     }
 
     #[inline]
@@ -1182,7 +1183,7 @@ impl<'tcx> Ty<'tcx> {
                 | Float(_)
                 | Uint(_)
                 | FnDef(..)
-                | FnPtr(_)
+                | FnPtr(..)
                 | RawPtr(_, _)
                 | Infer(IntVar(_) | FloatVar(_))
         )
@@ -1333,7 +1334,7 @@ impl<'tcx> Ty<'tcx> {
     pub fn fn_sig(self, tcx: TyCtxt<'tcx>) -> PolyFnSig<'tcx> {
         match self.kind() {
             FnDef(def_id, args) => tcx.fn_sig(*def_id).instantiate(tcx, args),
-            FnPtr(f) => *f,
+            FnPtr(sig_tys, hdr) => sig_tys.with(*hdr),
             Error(_) => {
                 // ignore errors (#54954)
                 Binder::dummy(ty::FnSig {
@@ -1352,12 +1353,12 @@ impl<'tcx> Ty<'tcx> {
 
     #[inline]
     pub fn is_fn(self) -> bool {
-        matches!(self.kind(), FnDef(..) | FnPtr(_))
+        matches!(self.kind(), FnDef(..) | FnPtr(..))
     }
 
     #[inline]
     pub fn is_fn_ptr(self) -> bool {
-        matches!(self.kind(), FnPtr(_))
+        matches!(self.kind(), FnPtr(..))
     }
 
     #[inline]
@@ -1590,7 +1591,7 @@ impl<'tcx> Ty<'tcx> {
         tcx: TyCtxt<'tcx>,
         normalize: impl FnMut(Ty<'tcx>) -> Ty<'tcx>,
     ) -> Result<Ty<'tcx>, Ty<'tcx>> {
-        let tail = tcx.struct_tail_with_normalize(self, normalize, || {});
+        let tail = tcx.struct_tail_raw(self, normalize, || {});
         match tail.kind() {
             // Sized types
             ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
@@ -1599,7 +1600,7 @@ impl<'tcx> Ty<'tcx> {
             | ty::Bool
             | ty::Float(_)
             | ty::FnDef(..)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::RawPtr(..)
             | ty::Char
             | ty::Ref(..)
@@ -1614,10 +1615,10 @@ impl<'tcx> Ty<'tcx> {
             | ty::Foreign(..)
             // `dyn*` has metadata = ().
             | ty::Dynamic(_, _, ty::DynStar)
-            // If returned by `struct_tail_with_normalize` this is a unit struct
+            // If returned by `struct_tail_raw` this is a unit struct
             // without any fields, or not a struct, and therefore is Sized.
             | ty::Adt(..)
-            // If returned by `struct_tail_with_normalize` this is the empty tuple,
+            // If returned by `struct_tail_raw` this is the empty tuple,
             // a.k.a. unit type, which is Sized
             | ty::Tuple(..) => Ok(tcx.types.unit),
 
@@ -1791,7 +1792,7 @@ impl<'tcx> Ty<'tcx> {
             | ty::Bool
             | ty::Float(_)
             | ty::FnDef(..)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::RawPtr(..)
             | ty::Char
             | ty::Ref(..)
@@ -1915,7 +1916,7 @@ impl<'tcx> Ty<'tcx> {
 
     pub fn is_c_void(self, tcx: TyCtxt<'_>) -> bool {
         match self.kind() {
-            ty::Adt(adt, _) => tcx.lang_items().get(LangItem::CVoid) == Some(adt.did()),
+            ty::Adt(adt, _) => tcx.is_lang_item(adt.did(), LangItem::CVoid),
             _ => false,
         }
     }
@@ -1941,7 +1942,7 @@ impl<'tcx> Ty<'tcx> {
             | RawPtr(_, _)
             | Ref(_, _, _)
             | FnDef(_, _)
-            | FnPtr(_)
+            | FnPtr(..)
             | Dynamic(_, _, _)
             | Closure(_, _)
             | CoroutineClosure(_, _)
@@ -1955,9 +1956,12 @@ impl<'tcx> Ty<'tcx> {
 }
 
 impl<'tcx> rustc_type_ir::inherent::Tys<TyCtxt<'tcx>> for &'tcx ty::List<Ty<'tcx>> {
-    fn split_inputs_and_output(self) -> (&'tcx [Ty<'tcx>], Ty<'tcx>) {
-        let (output, inputs) = self.split_last().unwrap();
-        (inputs, *output)
+    fn inputs(self) -> &'tcx [Ty<'tcx>] {
+        self.split_last().unwrap().1
+    }
+
+    fn output(self) -> Ty<'tcx> {
+        *self.split_last().unwrap().0
     }
 }
 
@@ -1969,6 +1973,6 @@ mod size_asserts {
     use super::*;
     // tidy-alphabetical-start
     static_assert_size!(ty::RegionKind<'_>, 24);
-    static_assert_size!(ty::TyKind<'_>, 32);
+    static_assert_size!(ty::TyKind<'_>, 24);
     // tidy-alphabetical-end
 }
diff --git a/compiler/rustc_middle/src/ty/util.rs b/compiler/rustc_middle/src/ty/util.rs
index 365f434a264..b9bf17cbb5c 100644
--- a/compiler/rustc_middle/src/ty/util.rs
+++ b/compiler/rustc_middle/src/ty/util.rs
@@ -171,14 +171,6 @@ impl<'tcx> TyCtxt<'tcx> {
         }
     }
 
-    /// Attempts to returns the deeply last field of nested structures, but
-    /// does not apply any normalization in its search. Returns the same type
-    /// if input `ty` is not a structure at all.
-    pub fn struct_tail_without_normalization(self, ty: Ty<'tcx>) -> Ty<'tcx> {
-        let tcx = self;
-        tcx.struct_tail_with_normalize(ty, |ty| ty, || {})
-    }
-
     /// Returns the deeply last field of nested structures, or the same type if
     /// not a structure at all. Corresponds to the only possible unsized field,
     /// and its type can be used to determine unsizing strategy.
@@ -188,7 +180,7 @@ impl<'tcx> TyCtxt<'tcx> {
     /// normalization attempt may cause compiler bugs.
     pub fn struct_tail_for_codegen(self, ty: Ty<'tcx>, param_env: ty::ParamEnv<'tcx>) -> Ty<'tcx> {
         let tcx = self;
-        tcx.struct_tail_with_normalize(ty, |ty| tcx.normalize_erasing_regions(param_env, ty), || {})
+        tcx.struct_tail_raw(ty, |ty| tcx.normalize_erasing_regions(param_env, ty), || {})
     }
 
     /// Returns the deeply last field of nested structures, or the same type if
@@ -196,12 +188,14 @@ impl<'tcx> TyCtxt<'tcx> {
     /// and its type can be used to determine unsizing strategy.
     ///
     /// This is parameterized over the normalization strategy (i.e. how to
-    /// handle `<T as Trait>::Assoc` and `impl Trait`); pass the identity
-    /// function to indicate no normalization should take place.
+    /// handle `<T as Trait>::Assoc` and `impl Trait`). You almost certainly do
+    /// **NOT** want to pass the identity function here, unless you know what
+    /// you're doing, or you're within normalization code itself and will handle
+    /// an unnormalized tail recursively.
     ///
     /// See also `struct_tail_for_codegen`, which is suitable for use
     /// during codegen.
-    pub fn struct_tail_with_normalize(
+    pub fn struct_tail_raw(
         self,
         mut ty: Ty<'tcx>,
         mut normalize: impl FnMut(Ty<'tcx>) -> Ty<'tcx>,
@@ -281,7 +275,7 @@ impl<'tcx> TyCtxt<'tcx> {
         param_env: ty::ParamEnv<'tcx>,
     ) -> (Ty<'tcx>, Ty<'tcx>) {
         let tcx = self;
-        tcx.struct_lockstep_tails_with_normalize(source, target, |ty| {
+        tcx.struct_lockstep_tails_raw(source, target, |ty| {
             tcx.normalize_erasing_regions(param_env, ty)
         })
     }
@@ -294,7 +288,7 @@ impl<'tcx> TyCtxt<'tcx> {
     ///
     /// See also `struct_lockstep_tails_for_codegen`, which is suitable for use
     /// during codegen.
-    pub fn struct_lockstep_tails_with_normalize(
+    pub fn struct_lockstep_tails_raw(
         self,
         source: Ty<'tcx>,
         target: Ty<'tcx>,
@@ -1278,7 +1272,7 @@ impl<'tcx> Ty<'tcx> {
             | ty::RawPtr(_, _)
             | ty::FnDef(..)
             | ty::Error(_)
-            | ty::FnPtr(_) => true,
+            | ty::FnPtr(..) => true,
             ty::Tuple(fields) => fields.iter().all(Self::is_trivially_freeze),
             ty::Pat(ty, _) | ty::Slice(ty) | ty::Array(ty, _) => ty.is_trivially_freeze(),
             ty::Adt(..)
@@ -1318,7 +1312,7 @@ impl<'tcx> Ty<'tcx> {
             | ty::RawPtr(_, _)
             | ty::FnDef(..)
             | ty::Error(_)
-            | ty::FnPtr(_) => true,
+            | ty::FnPtr(..) => true,
             ty::Tuple(fields) => fields.iter().all(Self::is_trivially_unpin),
             ty::Pat(ty, _) | ty::Slice(ty) | ty::Array(ty, _) => ty.is_trivially_unpin(),
             ty::Adt(..)
@@ -1357,7 +1351,7 @@ impl<'tcx> Ty<'tcx> {
             | ty::Ref(..)
             | ty::RawPtr(..)
             | ty::FnDef(..)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Infer(ty::FreshIntTy(_))
             | ty::Infer(ty::FreshFloatTy(_)) => AsyncDropGlueMorphology::Noop,
 
@@ -1540,7 +1534,7 @@ impl<'tcx> Ty<'tcx> {
             ty::Pat(..) | ty::Ref(..) | ty::Array(..) | ty::Slice(_) | ty::Tuple(..) => true,
 
             // Raw pointers use bitwise comparison.
-            ty::RawPtr(_, _) | ty::FnPtr(_) => true,
+            ty::RawPtr(_, _) | ty::FnPtr(..) => true,
 
             // Floating point numbers are not `Eq`.
             ty::Float(_) => false,
@@ -1671,7 +1665,7 @@ pub fn needs_drop_components_with_async<'tcx>(
         | ty::Float(_)
         | ty::Never
         | ty::FnDef(..)
-        | ty::FnPtr(_)
+        | ty::FnPtr(..)
         | ty::Char
         | ty::RawPtr(_, _)
         | ty::Ref(..)
@@ -1738,7 +1732,7 @@ pub fn is_trivially_const_drop(ty: Ty<'_>) -> bool {
         | ty::RawPtr(_, _)
         | ty::Ref(..)
         | ty::FnDef(..)
-        | ty::FnPtr(_)
+        | ty::FnPtr(..)
         | ty::Never
         | ty::Foreign(_) => true,
 
diff --git a/compiler/rustc_middle/src/ty/vtable.rs b/compiler/rustc_middle/src/ty/vtable.rs
index f38f27b84f0..951112dfe85 100644
--- a/compiler/rustc_middle/src/ty/vtable.rs
+++ b/compiler/rustc_middle/src/ty/vtable.rs
@@ -3,7 +3,7 @@ use std::fmt;
 use rustc_ast::Mutability;
 use rustc_macros::HashStable;
 
-use crate::mir::interpret::{alloc_range, AllocId, Allocation, Pointer, Scalar};
+use crate::mir::interpret::{alloc_range, AllocId, Allocation, Pointer, Scalar, CTFE_ALLOC_SALT};
 use crate::ty::{self, Instance, PolyTraitRef, Ty, TyCtxt};
 
 #[derive(Clone, Copy, PartialEq, HashStable)]
@@ -73,6 +73,11 @@ pub(crate) fn vtable_min_entries<'tcx>(
 
 /// Retrieves an allocation that represents the contents of a vtable.
 /// Since this is a query, allocations are cached and not duplicated.
+///
+/// This is an "internal" `AllocId` that should never be used as a value in the interpreted program.
+/// The interpreter should use `AllocId` that refer to a `GlobalAlloc::VTable` instead.
+/// (This is similar to statics, which also have a similar "internal" `AllocId` storing their
+/// initial contents.)
 pub(super) fn vtable_allocation_provider<'tcx>(
     tcx: TyCtxt<'tcx>,
     key: (Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>),
@@ -114,7 +119,7 @@ pub(super) fn vtable_allocation_provider<'tcx>(
             VtblEntry::MetadataDropInPlace => {
                 if ty.needs_drop(tcx, ty::ParamEnv::reveal_all()) {
                     let instance = ty::Instance::resolve_drop_in_place(tcx, ty);
-                    let fn_alloc_id = tcx.reserve_and_set_fn_alloc(instance);
+                    let fn_alloc_id = tcx.reserve_and_set_fn_alloc(instance, CTFE_ALLOC_SALT);
                     let fn_ptr = Pointer::from(fn_alloc_id);
                     Scalar::from_pointer(fn_ptr, &tcx)
                 } else {
@@ -127,7 +132,7 @@ pub(super) fn vtable_allocation_provider<'tcx>(
             VtblEntry::Method(instance) => {
                 // Prepare the fn ptr we write into the vtable.
                 let instance = instance.polymorphize(tcx);
-                let fn_alloc_id = tcx.reserve_and_set_fn_alloc(instance);
+                let fn_alloc_id = tcx.reserve_and_set_fn_alloc(instance, CTFE_ALLOC_SALT);
                 let fn_ptr = Pointer::from(fn_alloc_id);
                 Scalar::from_pointer(fn_ptr, &tcx)
             }
diff --git a/compiler/rustc_middle/src/ty/walk.rs b/compiler/rustc_middle/src/ty/walk.rs
index 2dd7a96f192..abd6df17514 100644
--- a/compiler/rustc_middle/src/ty/walk.rs
+++ b/compiler/rustc_middle/src/ty/walk.rs
@@ -189,9 +189,10 @@ fn push_inner<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>)
                 stack.extend(args.iter().rev());
             }
             ty::Tuple(ts) => stack.extend(ts.iter().rev().map(GenericArg::from)),
-            ty::FnPtr(sig) => {
-                stack.push(sig.skip_binder().output().into());
-                stack.extend(sig.skip_binder().inputs().iter().copied().rev().map(|ty| ty.into()));
+            ty::FnPtr(sig_tys, _hdr) => {
+                stack.extend(
+                    sig_tys.skip_binder().inputs_and_output.iter().rev().map(|ty| ty.into()),
+                );
             }
         },
         GenericArgKind::Lifetime(_) => {}
diff --git a/compiler/rustc_mir_build/messages.ftl b/compiler/rustc_mir_build/messages.ftl
index dda4debecec..7baf0256dd8 100644
--- a/compiler/rustc_mir_build/messages.ftl
+++ b/compiler/rustc_mir_build/messages.ftl
@@ -30,7 +30,7 @@ mir_build_call_to_deprecated_safe_fn_requires_unsafe =
     call to deprecated safe function `{$function}` is unsafe and requires unsafe block
     .note = consult the function's documentation for information on how to avoid undefined behavior
     .label = call to unsafe function
-    .suggestion = you can wrap the call in an `unsafe` block if you can guarantee the code is only ever called from single-threaded code
+    .suggestion = you can wrap the call in an `unsafe` block if you can guarantee {$guarantee}
 
 mir_build_call_to_fn_with_requires_unsafe =
     call to function `{$function}` with `#[target_feature]` is unsafe and requires unsafe block
diff --git a/compiler/rustc_mir_build/src/build/expr/as_constant.rs b/compiler/rustc_mir_build/src/build/expr/as_constant.rs
index 10cf545f1b7..4430aab73a8 100644
--- a/compiler/rustc_mir_build/src/build/expr/as_constant.rs
+++ b/compiler/rustc_mir_build/src/build/expr/as_constant.rs
@@ -2,7 +2,9 @@
 
 use rustc_ast as ast;
 use rustc_hir::LangItem;
-use rustc_middle::mir::interpret::{Allocation, LitToConstError, LitToConstInput, Scalar};
+use rustc_middle::mir::interpret::{
+    Allocation, LitToConstError, LitToConstInput, Scalar, CTFE_ALLOC_SALT,
+};
 use rustc_middle::mir::*;
 use rustc_middle::thir::*;
 use rustc_middle::ty::{
@@ -140,7 +142,7 @@ fn lit_to_mir_constant<'tcx>(
             ConstValue::Slice { data: allocation, meta: allocation.inner().size().bytes() }
         }
         (ast::LitKind::ByteStr(data, _), ty::Ref(_, inner_ty, _)) if inner_ty.is_array() => {
-            let id = tcx.allocate_bytes_dedup(data);
+            let id = tcx.allocate_bytes_dedup(data, CTFE_ALLOC_SALT);
             ConstValue::Scalar(Scalar::from_pointer(id.into(), &tcx))
         }
         (ast::LitKind::CStr(data, _), ty::Ref(_, inner_ty, _)) if matches!(inner_ty.kind(), ty::Adt(def, _) if tcx.is_lang_item(def.did(), LangItem::CStr)) =>
diff --git a/compiler/rustc_mir_build/src/check_unsafety.rs b/compiler/rustc_mir_build/src/check_unsafety.rs
index 54a4204da71..9b85ad0ad08 100644
--- a/compiler/rustc_mir_build/src/check_unsafety.rs
+++ b/compiler/rustc_mir_build/src/check_unsafety.rs
@@ -96,9 +96,32 @@ impl<'tcx> UnsafetyVisitor<'_, 'tcx> {
             // from an edition before 2024.
             &UnsafeOpKind::CallToUnsafeFunction(Some(id))
                 if !span.at_least_rust_2024()
-                    && self.tcx.has_attr(id, sym::rustc_deprecated_safe_2024) =>
+                    && let Some(attr) = self.tcx.get_attr(id, sym::rustc_deprecated_safe_2024) =>
             {
+                let suggestion = attr
+                    .meta_item_list()
+                    .unwrap_or_default()
+                    .into_iter()
+                    .find(|item| item.has_name(sym::audit_that))
+                    .map(|item| {
+                        item.value_str().expect(
+                            "`#[rustc_deprecated_safe_2024(audit_that)]` must have a string value",
+                        )
+                    });
+
                 let sm = self.tcx.sess.source_map();
+                let guarantee = suggestion
+                    .as_ref()
+                    .map(|suggestion| format!("that {}", suggestion))
+                    .unwrap_or_else(|| String::from("its unsafe preconditions"));
+                let suggestion = suggestion
+                    .and_then(|suggestion| {
+                        sm.indentation_before(span).map(|indent| {
+                            format!("{}// TODO: Audit that {}.\n", indent, suggestion) // ignore-tidy-todo
+                        })
+                    })
+                    .unwrap_or_default();
+
                 self.tcx.emit_node_span_lint(
                     DEPRECATED_SAFE_2024,
                     self.hir_context,
@@ -106,8 +129,9 @@ impl<'tcx> UnsafetyVisitor<'_, 'tcx> {
                     CallToDeprecatedSafeFnRequiresUnsafe {
                         span,
                         function: with_no_trimmed_paths!(self.tcx.def_path_str(id)),
+                        guarantee,
                         sub: CallToDeprecatedSafeFnRequiresUnsafeSub {
-                            indent: sm.indentation_before(span).unwrap_or_default(),
+                            start_of_line_suggestion: suggestion,
                             start_of_line: sm.span_extend_to_line(span).shrink_to_lo(),
                             left: span.shrink_to_lo(),
                             right: span.shrink_to_hi(),
diff --git a/compiler/rustc_mir_build/src/errors.rs b/compiler/rustc_mir_build/src/errors.rs
index 42eca71ca3f..34577f102d1 100644
--- a/compiler/rustc_mir_build/src/errors.rs
+++ b/compiler/rustc_mir_build/src/errors.rs
@@ -28,6 +28,7 @@ pub(crate) struct CallToDeprecatedSafeFnRequiresUnsafe {
     #[label]
     pub(crate) span: Span,
     pub(crate) function: String,
+    pub(crate) guarantee: String,
     #[subdiagnostic]
     pub(crate) sub: CallToDeprecatedSafeFnRequiresUnsafeSub,
 }
@@ -35,10 +36,8 @@ pub(crate) struct CallToDeprecatedSafeFnRequiresUnsafe {
 #[derive(Subdiagnostic)]
 #[multipart_suggestion(mir_build_suggestion, applicability = "machine-applicable")]
 pub(crate) struct CallToDeprecatedSafeFnRequiresUnsafeSub {
-    pub(crate) indent: String,
-    #[suggestion_part(
-        code = "{indent}// TODO: Audit that the environment access only happens in single-threaded code.\n" // ignore-tidy-todo
-    )]
+    pub(crate) start_of_line_suggestion: String,
+    #[suggestion_part(code = "{start_of_line_suggestion}")]
     pub(crate) start_of_line: Span,
     #[suggestion_part(code = "unsafe {{ ")]
     pub(crate) left: Span,
diff --git a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
index 07bf222fcca..85b9dacb129 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/check_match.rs
@@ -702,10 +702,12 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
             && adt.is_enum()
             && let Constructor::Variant(variant_index) = witness_1.ctor()
         {
-            let variant = adt.variant(*variant_index);
-            let inhabited = variant.inhabited_predicate(self.tcx, *adt).instantiate(self.tcx, args);
-            assert!(inhabited.apply(self.tcx, cx.param_env, cx.module));
-            !inhabited.apply_ignore_module(self.tcx, cx.param_env)
+            let variant_inhabited = adt
+                .variant(*variant_index)
+                .inhabited_predicate(self.tcx, *adt)
+                .instantiate(self.tcx, args);
+            variant_inhabited.apply(self.tcx, cx.param_env, cx.module)
+                && !variant_inhabited.apply_ignore_module(self.tcx, cx.param_env)
         } else {
             false
         };
diff --git a/compiler/rustc_mir_dataflow/src/impls/initialized.rs b/compiler/rustc_mir_dataflow/src/impls/initialized.rs
index e9e8ddefa02..7822fb17f72 100644
--- a/compiler/rustc_mir_dataflow/src/impls/initialized.rs
+++ b/compiler/rustc_mir_dataflow/src/impls/initialized.rs
@@ -1,3 +1,5 @@
+use std::assert_matches::assert_matches;
+
 use rustc_index::bit_set::{BitSet, ChunkedBitSet};
 use rustc_index::Idx;
 use rustc_middle::bug;
@@ -496,7 +498,7 @@ impl<'tcx> GenKillAnalysis<'tcx> for MaybeUninitializedPlaces<'_, '_, 'tcx> {
         });
         if self.skip_unreachable_unwind.contains(location.block) {
             let mir::TerminatorKind::Drop { target, unwind, .. } = terminator.kind else { bug!() };
-            assert!(matches!(unwind, mir::UnwindAction::Cleanup(_)));
+            assert_matches!(unwind, mir::UnwindAction::Cleanup(_));
             TerminatorEdges::Single(target)
         } else {
             terminator.edges()
diff --git a/compiler/rustc_mir_dataflow/src/lib.rs b/compiler/rustc_mir_dataflow/src/lib.rs
index b0808ba2067..8708bebeeb0 100644
--- a/compiler/rustc_mir_dataflow/src/lib.rs
+++ b/compiler/rustc_mir_dataflow/src/lib.rs
@@ -1,4 +1,5 @@
 // tidy-alphabetical-start
+#![feature(assert_matches)]
 #![feature(associated_type_defaults)]
 #![feature(box_patterns)]
 #![feature(exact_size_is_empty)]
diff --git a/compiler/rustc_mir_dataflow/src/move_paths/builder.rs b/compiler/rustc_mir_dataflow/src/move_paths/builder.rs
index c26a72e4543..86091379f5a 100644
--- a/compiler/rustc_mir_dataflow/src/move_paths/builder.rs
+++ b/compiler/rustc_mir_dataflow/src/move_paths/builder.rs
@@ -158,7 +158,7 @@ impl<'b, 'a, 'tcx, F: Fn(Ty<'tcx>) -> bool> Gatherer<'b, 'a, 'tcx, F> {
                     | ty::Pat(_, _)
                     | ty::Slice(_)
                     | ty::FnDef(_, _)
-                    | ty::FnPtr(_)
+                    | ty::FnPtr(..)
                     | ty::Dynamic(_, _, _)
                     | ty::Closure(..)
                     | ty::CoroutineClosure(..)
@@ -201,7 +201,7 @@ impl<'b, 'a, 'tcx, F: Fn(Ty<'tcx>) -> bool> Gatherer<'b, 'a, 'tcx, F> {
                     | ty::RawPtr(_, _)
                     | ty::Ref(_, _, _)
                     | ty::FnDef(_, _)
-                    | ty::FnPtr(_)
+                    | ty::FnPtr(..)
                     | ty::Dynamic(_, _, _)
                     | ty::CoroutineWitness(..)
                     | ty::Never
diff --git a/compiler/rustc_mir_dataflow/src/value_analysis.rs b/compiler/rustc_mir_dataflow/src/value_analysis.rs
index ca8a2777045..139fd592f69 100644
--- a/compiler/rustc_mir_dataflow/src/value_analysis.rs
+++ b/compiler/rustc_mir_dataflow/src/value_analysis.rs
@@ -32,6 +32,7 @@
 //! Because of that, we can assume that the only way to change the value behind a tracked place is
 //! by direct assignment.
 
+use std::assert_matches::assert_matches;
 use std::fmt::{Debug, Formatter};
 use std::ops::Range;
 
@@ -54,7 +55,7 @@ use crate::{Analysis, AnalysisDomain, JoinSemiLattice, SwitchIntEdgeEffects};
 
 pub trait ValueAnalysis<'tcx> {
     /// For each place of interest, the analysis tracks a value of the given type.
-    type Value: Clone + JoinSemiLattice + HasBottom + HasTop;
+    type Value: Clone + JoinSemiLattice + HasBottom + HasTop + Debug;
 
     const NAME: &'static str;
 
@@ -344,7 +345,7 @@ impl<'tcx, T: ValueAnalysis<'tcx>> AnalysisDomain<'tcx> for ValueAnalysisWrapper
 
     fn initialize_start_block(&self, body: &Body<'tcx>, state: &mut Self::Domain) {
         // The initial state maps all tracked places of argument projections to ⊤ and the rest to ⊥.
-        assert!(matches!(state, State::Unreachable));
+        assert_matches!(state, State::Unreachable);
         *state = State::new_reachable();
         for arg in body.args_iter() {
             state.flood(PlaceRef { local: arg, projection: &[] }, self.0.map());
diff --git a/compiler/rustc_mir_transform/src/abort_unwinding_calls.rs b/compiler/rustc_mir_transform/src/abort_unwinding_calls.rs
index f52a4524d78..edb6bc4fbea 100644
--- a/compiler/rustc_mir_transform/src/abort_unwinding_calls.rs
+++ b/compiler/rustc_mir_transform/src/abort_unwinding_calls.rs
@@ -64,7 +64,7 @@ impl<'tcx> MirPass<'tcx> for AbortUnwindingCalls {
                     let ty = func.ty(body, tcx);
                     let sig = ty.fn_sig(tcx);
                     let fn_def_id = match ty.kind() {
-                        ty::FnPtr(_) => None,
+                        ty::FnPtr(..) => None,
                         &ty::FnDef(def_id, _) => Some(def_id),
                         _ => span_bug!(span, "invalid callee of type {:?}", ty),
                     };
diff --git a/compiler/rustc_mir_transform/src/ffi_unwind_calls.rs b/compiler/rustc_mir_transform/src/ffi_unwind_calls.rs
index 4132e604f20..9a2cc057232 100644
--- a/compiler/rustc_mir_transform/src/ffi_unwind_calls.rs
+++ b/compiler/rustc_mir_transform/src/ffi_unwind_calls.rs
@@ -57,7 +57,7 @@ fn has_ffi_unwind_calls(tcx: TyCtxt<'_>, local_def_id: LocalDefId) -> bool {
         };
 
         let fn_def_id = match ty.kind() {
-            ty::FnPtr(_) => None,
+            ty::FnPtr(..) => None,
             &ty::FnDef(def_id, _) => {
                 // Rust calls cannot themselves create foreign unwinds (even if they use a non-Rust ABI).
                 // So the leak of the foreign unwind into Rust can only be elsewhere, not here.
diff --git a/compiler/rustc_mir_transform/src/promote_consts.rs b/compiler/rustc_mir_transform/src/promote_consts.rs
index dc8e50ac8cd..48a3266ae6f 100644
--- a/compiler/rustc_mir_transform/src/promote_consts.rs
+++ b/compiler/rustc_mir_transform/src/promote_consts.rs
@@ -468,7 +468,7 @@ impl<'tcx> Validator<'_, 'tcx> {
 
                 if let ty::RawPtr(_, _) | ty::FnPtr(..) = lhs_ty.kind() {
                     // Raw and fn pointer operations are not allowed inside consts and thus not promotable.
-                    assert!(matches!(
+                    assert_matches!(
                         op,
                         BinOp::Eq
                             | BinOp::Ne
@@ -477,7 +477,7 @@ impl<'tcx> Validator<'_, 'tcx> {
                             | BinOp::Ge
                             | BinOp::Gt
                             | BinOp::Offset
-                    ));
+                    );
                     return Err(Unpromotable);
                 }
 
diff --git a/compiler/rustc_mir_transform/src/shim.rs b/compiler/rustc_mir_transform/src/shim.rs
index f41f3ef656c..09b4e5e0711 100644
--- a/compiler/rustc_mir_transform/src/shim.rs
+++ b/compiler/rustc_mir_transform/src/shim.rs
@@ -437,7 +437,7 @@ fn build_clone_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -
     let src = tcx.mk_place_deref(Place::from(Local::new(1 + 0)));
 
     match self_ty.kind() {
-        ty::FnDef(..) | ty::FnPtr(_) => builder.copy_shim(),
+        ty::FnDef(..) | ty::FnPtr(..) => builder.copy_shim(),
         ty::Closure(_, args) => builder.tuple_like_shim(dest, src, args.as_closure().upvar_tys()),
         ty::CoroutineClosure(_, args) => {
             builder.tuple_like_shim(dest, src, args.as_coroutine_closure().upvar_tys())
@@ -996,7 +996,7 @@ pub fn build_adt_ctor(tcx: TyCtxt<'_>, ctor_id: DefId) -> Body<'_> {
 /// }
 /// ```
 fn build_fn_ptr_addr_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Ty<'tcx>) -> Body<'tcx> {
-    assert!(matches!(self_ty.kind(), ty::FnPtr(..)), "expected fn ptr, found {self_ty}");
+    assert_matches!(self_ty.kind(), ty::FnPtr(..), "expected fn ptr, found {self_ty}");
     let span = tcx.def_span(def_id);
     let Some(sig) = tcx.fn_sig(def_id).instantiate(tcx, &[self_ty.into()]).no_bound_vars() else {
         span_bug!(span, "FnPtr::addr with bound vars for `{self_ty}`");
diff --git a/compiler/rustc_monomorphize/src/partitioning.rs b/compiler/rustc_monomorphize/src/partitioning.rs
index 65a3d8d1742..f96329a3403 100644
--- a/compiler/rustc_monomorphize/src/partitioning.rs
+++ b/compiler/rustc_monomorphize/src/partitioning.rs
@@ -648,7 +648,9 @@ fn characteristic_def_id_of_mono_item<'tcx>(
 
             if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
                 if tcx.sess.opts.incremental.is_some()
-                    && tcx.trait_id_of_impl(impl_def_id) == tcx.lang_items().drop_trait()
+                    && tcx
+                        .trait_id_of_impl(impl_def_id)
+                        .is_some_and(|def_id| tcx.is_lang_item(def_id, LangItem::Drop))
                 {
                     // Put `Drop::drop` into the same cgu as `drop_in_place`
                     // since `drop_in_place` is the only thing that can
diff --git a/compiler/rustc_next_trait_solver/src/canonicalizer.rs b/compiler/rustc_next_trait_solver/src/canonicalizer.rs
index 82488088e30..394518daa42 100644
--- a/compiler/rustc_next_trait_solver/src/canonicalizer.rs
+++ b/compiler/rustc_next_trait_solver/src/canonicalizer.rs
@@ -360,7 +360,7 @@ impl<D: SolverDelegate<Interner = I>, I: Interner> TypeFolder<I> for Canonicaliz
             | ty::Ref(_, _, _)
             | ty::Pat(_, _)
             | ty::FnDef(_, _)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Dynamic(_, _, _)
             | ty::Closure(..)
             | ty::CoroutineClosure(..)
diff --git a/compiler/rustc_next_trait_solver/src/coherence.rs b/compiler/rustc_next_trait_solver/src/coherence.rs
index f22ea41c512..2461ef0c0df 100644
--- a/compiler/rustc_next_trait_solver/src/coherence.rs
+++ b/compiler/rustc_next_trait_solver/src/coherence.rs
@@ -334,7 +334,7 @@ where
             | ty::Str
             | ty::FnDef(..)
             | ty::Pat(..)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Array(..)
             | ty::Slice(..)
             | ty::RawPtr(..)
diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
index 84921e87fb3..bb05eb4c256 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
@@ -533,7 +533,7 @@ where
             | ty::RawPtr(_, _)
             | ty::Ref(_, _, _)
             | ty::FnDef(_, _)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Dynamic(..)
             | ty::Closure(..)
             | ty::CoroutineClosure(..)
@@ -620,7 +620,7 @@ where
             | ty::RawPtr(_, _)
             | ty::Ref(_, _, _)
             | ty::FnDef(_, _)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Alias(..)
             | ty::Closure(..)
             | ty::CoroutineClosure(..)
diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
index 00837f7cdd8..a57338acaab 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
@@ -31,7 +31,7 @@ where
         | ty::Bool
         | ty::Float(_)
         | ty::FnDef(..)
-        | ty::FnPtr(_)
+        | ty::FnPtr(..)
         | ty::Error(_)
         | ty::Never
         | ty::Char => Ok(vec![]),
@@ -117,7 +117,7 @@ where
         | ty::Bool
         | ty::Float(_)
         | ty::FnDef(..)
-        | ty::FnPtr(_)
+        | ty::FnPtr(..)
         | ty::RawPtr(..)
         | ty::Char
         | ty::Ref(..)
@@ -178,7 +178,7 @@ where
 {
     match ty.kind() {
         // impl Copy/Clone for FnDef, FnPtr
-        ty::FnDef(..) | ty::FnPtr(_) | ty::Error(_) => Ok(vec![]),
+        ty::FnDef(..) | ty::FnPtr(..) | ty::Error(_) => Ok(vec![]),
 
         // Implementations are provided in core
         ty::Uint(_)
@@ -269,7 +269,8 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_callable<I: Intern
             }
         }
         // keep this in sync with assemble_fn_pointer_candidates until the old solver is removed.
-        ty::FnPtr(sig) => {
+        ty::FnPtr(sig_tys, hdr) => {
+            let sig = sig_tys.with(hdr);
             if sig.is_fn_trait_compatible() {
                 Ok(Some(
                     sig.map_bound(|sig| (Ty::new_tup(cx, sig.inputs().as_slice()), sig.output())),
@@ -460,7 +461,7 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_async_callable<I:
 
         ty::FnDef(def_id, _) => {
             let sig = self_ty.fn_sig(cx);
-            if sig.skip_binder().is_fn_trait_compatible() && !cx.has_target_features(def_id) {
+            if sig.is_fn_trait_compatible() && !cx.has_target_features(def_id) {
                 fn_item_to_async_callable(cx, sig)
             } else {
                 Err(NoSolution)
@@ -468,7 +469,7 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_async_callable<I:
         }
         ty::FnPtr(..) => {
             let sig = self_ty.fn_sig(cx);
-            if sig.skip_binder().is_fn_trait_compatible() {
+            if sig.is_fn_trait_compatible() {
                 fn_item_to_async_callable(cx, sig)
             } else {
                 Err(NoSolution)
diff --git a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
index b1dba712f79..1314b7eb6ff 100644
--- a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
@@ -1145,7 +1145,7 @@ where
             | ty::RawPtr(_, _)
             | ty::Ref(_, _, _)
             | ty::FnDef(_, _)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Closure(..)
             | ty::CoroutineClosure(..)
             | ty::Coroutine(_, _)
diff --git a/compiler/rustc_parse/src/lib.rs b/compiler/rustc_parse/src/lib.rs
index e6b04080c8d..37079271493 100644
--- a/compiler/rustc_parse/src/lib.rs
+++ b/compiler/rustc_parse/src/lib.rs
@@ -5,6 +5,7 @@
 #![allow(rustc::diagnostic_outside_of_impl)]
 #![allow(rustc::untranslatable_diagnostic)]
 #![feature(array_windows)]
+#![feature(assert_matches)]
 #![feature(box_patterns)]
 #![feature(debug_closure_helpers)]
 #![feature(if_let_guard)]
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index 4b8e4c25e16..9b3b6d5f9ad 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -10,6 +10,7 @@ mod path;
 mod stmt;
 mod ty;
 
+use std::assert_matches::debug_assert_matches;
 use std::ops::Range;
 use std::{fmt, mem, slice};
 
@@ -1166,10 +1167,12 @@ impl<'a> Parser<'a> {
             match self.token_cursor.tree_cursor.look_ahead(0) {
                 Some(tree) => {
                     // Indexing stayed within the current token tree.
-                    return match tree {
-                        TokenTree::Token(token, _) => looker(token),
-                        TokenTree::Delimited(dspan, _, delim, _) => {
-                            looker(&Token::new(token::OpenDelim(*delim), dspan.open))
+                    match tree {
+                        TokenTree::Token(token, _) => return looker(token),
+                        &TokenTree::Delimited(dspan, _, delim, _) => {
+                            if delim != Delimiter::Invisible {
+                                return looker(&Token::new(token::OpenDelim(delim), dspan.open));
+                            }
                         }
                     };
                 }
@@ -1385,7 +1388,7 @@ impl<'a> Parser<'a> {
                     // can capture these tokens if necessary.
                     self.bump();
                     if self.token_cursor.stack.len() == target_depth {
-                        debug_assert!(matches!(self.token.kind, token::CloseDelim(_)));
+                        debug_assert_matches!(self.token.kind, token::CloseDelim(_));
                         break;
                     }
                 }
diff --git a/compiler/rustc_parse/src/parser/tests.rs b/compiler/rustc_parse/src/parser/tests.rs
index 2d82742f66c..cb8e8d30988 100644
--- a/compiler/rustc_parse/src/parser/tests.rs
+++ b/compiler/rustc_parse/src/parser/tests.rs
@@ -1,3 +1,4 @@
+use std::assert_matches::assert_matches;
 use std::io::prelude::*;
 use std::iter::Peekable;
 use std::path::{Path, PathBuf};
@@ -1747,7 +1748,7 @@ fn out_of_line_mod() {
         .unwrap();
 
         let ast::ItemKind::Mod(_, mod_kind) = &item.kind else { panic!() };
-        assert!(matches!(mod_kind, ast::ModKind::Loaded(items, ..) if items.len() == 2));
+        assert_matches!(mod_kind, ast::ModKind::Loaded(items, ..) if items.len() == 2);
     });
 }
 
diff --git a/compiler/rustc_passes/messages.ftl b/compiler/rustc_passes/messages.ftl
index 59c9d1e49f5..0318d34fb73 100644
--- a/compiler/rustc_passes/messages.ftl
+++ b/compiler/rustc_passes/messages.ftl
@@ -223,6 +223,9 @@ passes_doc_masked_only_extern_crate =
     .not_an_extern_crate_label = not an `extern crate` item
     .note = read <https://doc.rust-lang.org/unstable-book/language-features/doc-masked.html> for more information
 
+passes_doc_rust_logo =
+    the `#[doc(rust_logo)]` attribute is used for Rust branding
+
 passes_doc_test_literal = `#![doc(test(...)]` does not take a literal
 
 passes_doc_test_takes_list =
@@ -595,6 +598,9 @@ passes_remove_fields =
      *[other] fields
     }
 
+passes_repr_align_function =
+    `repr(align)` attributes on functions are unstable
+
 passes_repr_conflicting =
     conflicting representation hints
 
diff --git a/compiler/rustc_passes/src/abi_test.rs b/compiler/rustc_passes/src/abi_test.rs
index 839b96fb3de..d0cc123c41a 100644
--- a/compiler/rustc_passes/src/abi_test.rs
+++ b/compiler/rustc_passes/src/abi_test.rs
@@ -127,14 +127,17 @@ fn dump_abi_of_fn_type(tcx: TyCtxt<'_>, item_def_id: LocalDefId, attr: &Attribut
     for meta_item in meta_items {
         match meta_item.name_or_empty() {
             sym::debug => {
-                let ty::FnPtr(sig) = ty.kind() else {
+                let ty::FnPtr(sig_tys, hdr) = ty.kind() else {
                     span_bug!(
                         meta_item.span(),
                         "`#[rustc_abi(debug)]` on a type alias requires function pointer type"
                     );
                 };
                 let abi = unwrap_fn_abi(
-                    tcx.fn_abi_of_fn_ptr(param_env.and((*sig, /* extra_args */ ty::List::empty()))),
+                    tcx.fn_abi_of_fn_ptr(
+                        param_env
+                            .and((sig_tys.with(*hdr), /* extra_args */ ty::List::empty())),
+                    ),
                     tcx,
                     item_def_id,
                 );
@@ -155,7 +158,7 @@ fn dump_abi_of_fn_type(tcx: TyCtxt<'_>, item_def_id: LocalDefId, attr: &Attribut
                         "`#[rustc_abi(assert_eq)]` on a type alias requires pair type"
                     );
                 };
-                let ty::FnPtr(sig1) = field1.kind() else {
+                let ty::FnPtr(sig_tys1, hdr1) = field1.kind() else {
                     span_bug!(
                         meta_item.span(),
                         "`#[rustc_abi(assert_eq)]` on a type alias requires pair of function pointer types"
@@ -163,12 +166,13 @@ fn dump_abi_of_fn_type(tcx: TyCtxt<'_>, item_def_id: LocalDefId, attr: &Attribut
                 };
                 let abi1 = unwrap_fn_abi(
                     tcx.fn_abi_of_fn_ptr(
-                        param_env.and((*sig1, /* extra_args */ ty::List::empty())),
+                        param_env
+                            .and((sig_tys1.with(*hdr1), /* extra_args */ ty::List::empty())),
                     ),
                     tcx,
                     item_def_id,
                 );
-                let ty::FnPtr(sig2) = field2.kind() else {
+                let ty::FnPtr(sig_tys2, hdr2) = field2.kind() else {
                     span_bug!(
                         meta_item.span(),
                         "`#[rustc_abi(assert_eq)]` on a type alias requires pair of function pointer types"
@@ -176,7 +180,8 @@ fn dump_abi_of_fn_type(tcx: TyCtxt<'_>, item_def_id: LocalDefId, attr: &Attribut
                 };
                 let abi2 = unwrap_fn_abi(
                     tcx.fn_abi_of_fn_ptr(
-                        param_env.and((*sig2, /* extra_args */ ty::List::empty())),
+                        param_env
+                            .and((sig_tys2.with(*hdr2), /* extra_args */ ty::List::empty())),
                     ),
                     tcx,
                     item_def_id,
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index 2a63ecfe658..bd157d1d619 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -1142,7 +1142,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
     /// of one item. Read the documentation of [`check_doc_inline`] for more information.
     ///
     /// [`check_doc_inline`]: Self::check_doc_inline
-    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn check_doc_attrs(
         &self,
         attr: &Attribute,
@@ -1220,7 +1219,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                                     &self.tcx.sess,
                                     sym::rustdoc_internals,
                                     meta.span(),
-                                    "the `#[doc(rust_logo)]` attribute is used for Rust branding",
+                                    fluent::passes_doc_rust_logo,
                                 )
                                 .emit();
                             }
@@ -1736,7 +1735,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
     }
 
     /// Checks if the `#[repr]` attributes on `item` are valid.
-    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
     fn check_repr(
         &self,
         attrs: &[Attribute],
@@ -1793,7 +1791,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                             &self.tcx.sess,
                             sym::fn_align,
                             hint.span(),
-                            "`repr(align)` attributes on functions are unstable",
+                            fluent::passes_repr_align_function,
                         )
                         .emit();
                     }
diff --git a/compiler/rustc_passes/src/entry.rs b/compiler/rustc_passes/src/entry.rs
index 48f55d4c3a0..ecb345bb51a 100644
--- a/compiler/rustc_passes/src/entry.rs
+++ b/compiler/rustc_passes/src/entry.rs
@@ -106,7 +106,6 @@ fn check_and_search_item(id: ItemId, ctxt: &mut EntryContext<'_>) {
     }
 }
 
-#[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
 fn configure_main(tcx: TyCtxt<'_>, visitor: &EntryContext<'_>) -> Option<(DefId, EntryFnType)> {
     if let Some((def_id, _)) = visitor.start_fn {
         Some((def_id.to_def_id(), EntryFnType::Start))
diff --git a/compiler/rustc_pattern_analysis/src/rustc.rs b/compiler/rustc_pattern_analysis/src/rustc.rs
index 10b7968a1a7..bcd3d3092c3 100644
--- a/compiler/rustc_pattern_analysis/src/rustc.rs
+++ b/compiler/rustc_pattern_analysis/src/rustc.rs
@@ -413,7 +413,7 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
             | ty::Foreign(_)
             | ty::RawPtr(_, _)
             | ty::FnDef(_, _)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Pat(_, _)
             | ty::Dynamic(_, _, _)
             | ty::Closure(..)
diff --git a/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/encode.rs b/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/encode.rs
index 61de338eab1..a4e4f50e8f2 100644
--- a/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/encode.rs
+++ b/compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/encode.rs
@@ -607,10 +607,15 @@ pub fn encode_ty<'tcx>(
             typeid.push_str(&s);
         }
 
-        ty::FnPtr(fn_sig) => {
+        ty::FnPtr(sig_tys, hdr) => {
             // PF<return-type><parameter-type1..parameter-typeN>E
             let mut s = String::from("P");
-            s.push_str(&encode_fnsig(tcx, &fn_sig.skip_binder(), dict, TypeIdOptions::empty()));
+            s.push_str(&encode_fnsig(
+                tcx,
+                &sig_tys.with(*hdr).skip_binder(),
+                dict,
+                TypeIdOptions::empty(),
+            ));
             compress(dict, DictKey::Ty(ty, TyQ::None), &mut s);
             typeid.push_str(&s);
         }
diff --git a/compiler/rustc_smir/src/rustc_internal/internal.rs b/compiler/rustc_smir/src/rustc_internal/internal.rs
index a4577461094..f52cb010a87 100644
--- a/compiler/rustc_smir/src/rustc_internal/internal.rs
+++ b/compiler/rustc_smir/src/rustc_internal/internal.rs
@@ -131,7 +131,10 @@ impl RustcInternal for RigidTy {
             RigidTy::FnDef(def, args) => {
                 rustc_ty::TyKind::FnDef(def.0.internal(tables, tcx), args.internal(tables, tcx))
             }
-            RigidTy::FnPtr(sig) => rustc_ty::TyKind::FnPtr(sig.internal(tables, tcx)),
+            RigidTy::FnPtr(sig) => {
+                let (sig_tys, hdr) = sig.internal(tables, tcx).split();
+                rustc_ty::TyKind::FnPtr(sig_tys, hdr)
+            }
             RigidTy::Closure(def, args) => {
                 rustc_ty::TyKind::Closure(def.0.internal(tables, tcx), args.internal(tables, tcx))
             }
diff --git a/compiler/rustc_smir/src/rustc_smir/convert/ty.rs b/compiler/rustc_smir/src/rustc_smir/convert/ty.rs
index ef2eb7d52ea..332fe22d869 100644
--- a/compiler/rustc_smir/src/rustc_smir/convert/ty.rs
+++ b/compiler/rustc_smir/src/rustc_smir/convert/ty.rs
@@ -352,7 +352,9 @@ impl<'tcx> Stable<'tcx> for ty::TyKind<'tcx> {
             ty::FnDef(def_id, generic_args) => {
                 TyKind::RigidTy(RigidTy::FnDef(tables.fn_def(*def_id), generic_args.stable(tables)))
             }
-            ty::FnPtr(poly_fn_sig) => TyKind::RigidTy(RigidTy::FnPtr(poly_fn_sig.stable(tables))),
+            ty::FnPtr(sig_tys, hdr) => {
+                TyKind::RigidTy(RigidTy::FnPtr(sig_tys.with(*hdr).stable(tables)))
+            }
             ty::Dynamic(existential_predicates, region, dyn_kind) => {
                 TyKind::RigidTy(RigidTy::Dynamic(
                     existential_predicates
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 9cb729ec485..a2e94492f8c 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -472,6 +472,7 @@ symbols! {
         attr,
         attr_literals,
         attributes,
+        audit_that,
         augmented_assignments,
         auto_traits,
         automatically_derived,
diff --git a/compiler/rustc_symbol_mangling/src/v0.rs b/compiler/rustc_symbol_mangling/src/v0.rs
index c2451c08d11..3a606f244e3 100644
--- a/compiler/rustc_symbol_mangling/src/v0.rs
+++ b/compiler/rustc_symbol_mangling/src/v0.rs
@@ -427,7 +427,8 @@ impl<'tcx> Printer<'tcx> for SymbolMangler<'tcx> {
                 self.print_def_path(def_id, &[])?;
             }
 
-            ty::FnPtr(sig) => {
+            ty::FnPtr(sig_tys, hdr) => {
+                let sig = sig_tys.with(hdr);
                 self.push("F");
                 self.in_binder(&sig, |cx, sig| {
                     if sig.safety == hir::Safety::Unsafe {
diff --git a/compiler/rustc_target/src/abi/call/powerpc64.rs b/compiler/rustc_target/src/abi/call/powerpc64.rs
index 11a6cb52bab..749eea0ef63 100644
--- a/compiler/rustc_target/src/abi/call/powerpc64.rs
+++ b/compiler/rustc_target/src/abi/call/powerpc64.rs
@@ -41,64 +41,23 @@ where
     })
 }
 
-fn classify_ret<'a, Ty, C>(cx: &C, ret: &mut ArgAbi<'a, Ty>, abi: ABI)
+fn classify<'a, Ty, C>(cx: &C, arg: &mut ArgAbi<'a, Ty>, abi: ABI, is_ret: bool)
 where
     Ty: TyAbiInterface<'a, C> + Copy,
     C: HasDataLayout,
 {
-    if !ret.layout.is_sized() {
+    if arg.is_ignore() || !arg.layout.is_sized() {
         // Not touching this...
         return;
     }
-    if !ret.layout.is_aggregate() {
-        ret.extend_integer_width_to(64);
+    if !arg.layout.is_aggregate() {
+        arg.extend_integer_width_to(64);
         return;
     }
 
     // The ELFv1 ABI doesn't return aggregates in registers
-    if abi == ELFv1 {
-        ret.make_indirect();
-        return;
-    }
-
-    if let Some(uniform) = is_homogeneous_aggregate(cx, ret, abi) {
-        ret.cast_to(uniform);
-        return;
-    }
-
-    let size = ret.layout.size;
-    let bits = size.bits();
-    if bits <= 128 {
-        let unit = if cx.data_layout().endian == Endian::Big {
-            Reg { kind: RegKind::Integer, size }
-        } else if bits <= 8 {
-            Reg::i8()
-        } else if bits <= 16 {
-            Reg::i16()
-        } else if bits <= 32 {
-            Reg::i32()
-        } else {
-            Reg::i64()
-        };
-
-        ret.cast_to(Uniform::new(unit, size));
-        return;
-    }
-
-    ret.make_indirect();
-}
-
-fn classify_arg<'a, Ty, C>(cx: &C, arg: &mut ArgAbi<'a, Ty>, abi: ABI)
-where
-    Ty: TyAbiInterface<'a, C> + Copy,
-    C: HasDataLayout,
-{
-    if !arg.layout.is_sized() {
-        // Not touching this...
-        return;
-    }
-    if !arg.layout.is_aggregate() {
-        arg.extend_integer_width_to(64);
+    if is_ret && abi == ELFv1 {
+        arg.make_indirect();
         return;
     }
 
@@ -108,7 +67,10 @@ where
     }
 
     let size = arg.layout.size;
-    if size.bits() <= 64 {
+    if is_ret && size.bits() > 128 {
+        // Non-homogeneous aggregates larger than two doublewords are returned indirectly.
+        arg.make_indirect();
+    } else if size.bits() <= 64 {
         // Aggregates smaller than a doubleword should appear in
         // the least-significant bits of the parameter doubleword.
         arg.cast_to(Reg { kind: RegKind::Integer, size })
@@ -138,14 +100,9 @@ where
         }
     };
 
-    if !fn_abi.ret.is_ignore() {
-        classify_ret(cx, &mut fn_abi.ret, abi);
-    }
+    classify(cx, &mut fn_abi.ret, abi, true);
 
     for arg in fn_abi.args.iter_mut() {
-        if arg.is_ignore() {
-            continue;
-        }
-        classify_arg(cx, arg, abi);
+        classify(cx, arg, abi, false);
     }
 }
diff --git a/compiler/rustc_target/src/spec/abi/tests.rs b/compiler/rustc_target/src/spec/abi/tests.rs
index 251a12fe7aa..4823058dd69 100644
--- a/compiler/rustc_target/src/spec/abi/tests.rs
+++ b/compiler/rustc_target/src/spec/abi/tests.rs
@@ -1,3 +1,5 @@
+use std::assert_matches::assert_matches;
+
 use super::*;
 
 #[allow(non_snake_case)]
@@ -16,7 +18,7 @@ fn lookup_cdecl() {
 #[test]
 fn lookup_baz() {
     let abi = lookup("baz");
-    assert!(matches!(abi, Err(AbiUnsupported::Unrecognized)))
+    assert_matches!(abi, Err(AbiUnsupported::Unrecognized));
 }
 
 #[test]
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 8ccb2a8483a..5193333be8e 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs
@@ -1087,9 +1087,9 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 values
             }
 
-            (ty::FnDef(did1, args1), ty::FnPtr(sig2)) => {
+            (ty::FnDef(did1, args1), ty::FnPtr(sig_tys2, hdr2)) => {
                 let sig1 = self.tcx.fn_sig(*did1).instantiate(self.tcx, args1);
-                let mut values = self.cmp_fn_sig(&sig1, sig2);
+                let mut values = self.cmp_fn_sig(&sig1, &sig_tys2.with(*hdr2));
                 values.0.push_highlighted(format!(
                     " {{{}}}",
                     self.tcx.def_path_str_with_args(*did1, args1)
@@ -1097,16 +1097,18 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 values
             }
 
-            (ty::FnPtr(sig1), ty::FnDef(did2, args2)) => {
+            (ty::FnPtr(sig_tys1, hdr1), ty::FnDef(did2, args2)) => {
                 let sig2 = self.tcx.fn_sig(*did2).instantiate(self.tcx, args2);
-                let mut values = self.cmp_fn_sig(sig1, &sig2);
+                let mut values = self.cmp_fn_sig(&sig_tys1.with(*hdr1), &sig2);
                 values
                     .1
                     .push_normal(format!(" {{{}}}", self.tcx.def_path_str_with_args(*did2, args2)));
                 values
             }
 
-            (ty::FnPtr(sig1), ty::FnPtr(sig2)) => self.cmp_fn_sig(sig1, sig2),
+            (ty::FnPtr(sig_tys1, hdr1), ty::FnPtr(sig_tys2, hdr2)) => {
+                self.cmp_fn_sig(&sig_tys1.with(*hdr1), &sig_tys2.with(*hdr2))
+            }
 
             _ => {
                 let mut strs = (DiagStyledString::new(), DiagStyledString::new());
diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs
index 864510bb650..05c79170902 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/note_and_explain.rs
@@ -4,6 +4,7 @@ use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_middle::traits::{ObligationCause, ObligationCauseCode};
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
+use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
 use rustc_middle::ty::print::{FmtPrinter, Printer};
 use rustc_middle::ty::{self, suggest_constraining_type_param, Ty};
 use rustc_span::def_id::DefId;
@@ -313,11 +314,15 @@ impl<T> Trait<T> for X {
                     (ty::Dynamic(t, _, ty::DynKind::Dyn), _)
                         if let Some(def_id) = t.principal_def_id() =>
                     {
-                        let mut impl_def_ids = vec![];
+                        let mut has_matching_impl = false;
                         tcx.for_each_relevant_impl(def_id, values.found, |did| {
-                            impl_def_ids.push(did)
+                            if DeepRejectCtxt::new(tcx, TreatParams::ForLookup)
+                                .types_may_unify(values.found, tcx.type_of(did).skip_binder())
+                            {
+                                has_matching_impl = true;
+                            }
                         });
-                        if let [_] = &impl_def_ids[..] {
+                        if has_matching_impl {
                             let trait_name = tcx.item_name(def_id);
                             diag.help(format!(
                                 "`{}` implements `{trait_name}` so you could box the found value \
@@ -330,11 +335,15 @@ impl<T> Trait<T> for X {
                     (_, ty::Dynamic(t, _, ty::DynKind::Dyn))
                         if let Some(def_id) = t.principal_def_id() =>
                     {
-                        let mut impl_def_ids = vec![];
+                        let mut has_matching_impl = false;
                         tcx.for_each_relevant_impl(def_id, values.expected, |did| {
-                            impl_def_ids.push(did)
+                            if DeepRejectCtxt::new(tcx, TreatParams::ForLookup)
+                                .types_may_unify(values.expected, tcx.type_of(did).skip_binder())
+                            {
+                                has_matching_impl = true;
+                            }
                         });
-                        if let [_] = &impl_def_ids[..] {
+                        if has_matching_impl {
                             let trait_name = tcx.item_name(def_id);
                             diag.help(format!(
                                 "`{}` implements `{trait_name}` so you could change the expected \
@@ -346,11 +355,15 @@ impl<T> Trait<T> for X {
                     (ty::Dynamic(t, _, ty::DynKind::DynStar), _)
                         if let Some(def_id) = t.principal_def_id() =>
                     {
-                        let mut impl_def_ids = vec![];
+                        let mut has_matching_impl = false;
                         tcx.for_each_relevant_impl(def_id, values.found, |did| {
-                            impl_def_ids.push(did)
+                            if DeepRejectCtxt::new(tcx, TreatParams::ForLookup)
+                                .types_may_unify(values.found, tcx.type_of(did).skip_binder())
+                            {
+                                has_matching_impl = true;
+                            }
                         });
-                        if let [_] = &impl_def_ids[..] {
+                        if has_matching_impl {
                             let trait_name = tcx.item_name(def_id);
                             diag.help(format!(
                                 "`{}` implements `{trait_name}`, `#[feature(dyn_star)]` is likely \
@@ -441,9 +454,9 @@ impl<T> Trait<T> for X {
                             }
                         }
                     }
-                    (ty::FnPtr(sig), ty::FnDef(def_id, _))
-                    | (ty::FnDef(def_id, _), ty::FnPtr(sig)) => {
-                        if tcx.fn_sig(def_id).skip_binder().safety() < sig.safety() {
+                    (ty::FnPtr(_, hdr), ty::FnDef(def_id, _))
+                    | (ty::FnDef(def_id, _), ty::FnPtr(_, hdr)) => {
+                        if tcx.fn_sig(def_id).skip_binder().safety() < hdr.safety {
                             diag.note(
                                 "unsafe functions cannot be coerced into safe function pointers",
                             );
diff --git a/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs b/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs
index ee159aa0b77..35f68a56d2d 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/infer/suggest.rs
@@ -383,8 +383,9 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             return;
         }
         match (&expected_inner.kind(), &found_inner.kind()) {
-            (ty::FnPtr(sig), ty::FnDef(did, args)) => {
-                let expected_sig = &(self.normalize_fn_sig)(*sig);
+            (ty::FnPtr(sig_tys, hdr), ty::FnDef(did, args)) => {
+                let sig = sig_tys.with(*hdr);
+                let expected_sig = &(self.normalize_fn_sig)(sig);
                 let found_sig =
                     &(self.normalize_fn_sig)(self.tcx.fn_sig(*did).instantiate(self.tcx, args));
 
@@ -402,11 +403,11 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     (false, true) => FunctionPointerSuggestion::RemoveRef { span, fn_name },
                     (true, true) => {
                         diag.subdiagnostic(FnItemsAreDistinct);
-                        FunctionPointerSuggestion::CastRef { span, fn_name, sig: *sig }
+                        FunctionPointerSuggestion::CastRef { span, fn_name, sig }
                     }
                     (false, false) => {
                         diag.subdiagnostic(FnItemsAreDistinct);
-                        FunctionPointerSuggestion::Cast { span, fn_name, sig: *sig }
+                        FunctionPointerSuggestion::Cast { span, fn_name, sig }
                     }
                 };
                 diag.subdiagnostic(sugg);
@@ -449,10 +450,10 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
 
                 diag.subdiagnostic(sug);
             }
-            (ty::FnDef(did, args), ty::FnPtr(sig)) => {
+            (ty::FnDef(did, args), ty::FnPtr(sig_tys, hdr)) => {
                 let expected_sig =
                     &(self.normalize_fn_sig)(self.tcx.fn_sig(*did).instantiate(self.tcx, args));
-                let found_sig = &(self.normalize_fn_sig)(*sig);
+                let found_sig = &(self.normalize_fn_sig)(sig_tys.with(*hdr));
 
                 if !self.same_type_modulo_infer(*found_sig, *expected_sig) {
                     return;
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 95d4509c100..326a0e4e35c 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
@@ -230,8 +230,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                             post_message,
                         );
 
-                        let (err_msg, safe_transmute_explanation) = if Some(main_trait_ref.def_id())
-                            == self.tcx.lang_items().transmute_trait()
+                        let (err_msg, safe_transmute_explanation) = if self.tcx.is_lang_item(main_trait_ref.def_id(), LangItem::TransmuteTrait)
                         {
                             // Recompute the safe transmute reason and use that for the error reporting
                             match self.get_safe_transmute_error_and_reason(
@@ -375,7 +374,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         let impl_candidates = self.find_similar_impl_candidates(leaf_trait_predicate);
                         suggested = if let &[cand] = &impl_candidates[..] {
                             let cand = cand.trait_ref;
-                            if let (ty::FnPtr(_), ty::FnDef(..)) =
+                            if let (ty::FnPtr(..), ty::FnDef(..)) =
                                 (cand.self_ty().kind(), main_trait_ref.self_ty().skip_binder().kind())
                             {
                                 err.span_suggestion(
@@ -687,10 +686,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         let mut applied_do_not_recommend = false;
         loop {
             if let ObligationCauseCode::ImplDerived(ref c) = base_cause {
-                if self.tcx.has_attrs_with_path(
-                    c.impl_or_alias_def_id,
-                    &[sym::diagnostic, sym::do_not_recommend],
-                ) {
+                if self.tcx.do_not_recommend_impl(c.impl_or_alias_def_id) {
                     let code = (*c.derived.parent_code).clone();
                     obligation.cause.map_code(|_| code);
                     obligation.predicate = c.derived.parent_trait_pred.upcast(self.tcx);
@@ -793,8 +789,8 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             // is unimplemented is because async closures don't implement `Fn`/`FnMut`
             // if they have captures.
             if let Some(by_ref_captures) = by_ref_captures
-                && let ty::FnPtr(sig) = by_ref_captures.kind()
-                && !sig.skip_binder().output().is_unit()
+                && let ty::FnPtr(sig_tys, _) = by_ref_captures.kind()
+                && !sig_tys.skip_binder().output().is_unit()
             {
                 let mut err = self.dcx().create_err(AsyncClosureNotFn {
                     span: self.tcx.def_span(closure_def_id),
@@ -1060,7 +1056,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     "`{ty}` is forbidden as the type of a const generic parameter",
                 )
             }
-            ty::FnPtr(_) => {
+            ty::FnPtr(..) => {
                 struct_span_code_err!(
                     self.dcx(),
                     span,
@@ -1629,11 +1625,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 .tcx
                 .all_impls(def_id)
                 // ignore `do_not_recommend` items
-                .filter(|def_id| {
-                    !self
-                        .tcx
-                        .has_attrs_with_path(*def_id, &[sym::diagnostic, sym::do_not_recommend])
-                })
+                .filter(|def_id| !self.tcx.do_not_recommend_impl(*def_id))
                 // Ignore automatically derived impls and `!Trait` impls.
                 .filter_map(|def_id| self.tcx.impl_trait_header(def_id))
                 .filter_map(|header| {
@@ -1843,10 +1835,10 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             if let &[cand] = &candidates[..] {
                 let (desc, mention_castable) =
                     match (cand.self_ty().kind(), trait_ref.self_ty().skip_binder().kind()) {
-                        (ty::FnPtr(_), ty::FnDef(..)) => {
+                        (ty::FnPtr(..), ty::FnDef(..)) => {
                             (" implemented for fn pointer `", ", cast using `as`")
                         }
-                        (ty::FnPtr(_), _) => (" implemented for fn pointer `", ""),
+                        (ty::FnPtr(..), _) => (" implemented for fn pointer `", ""),
                         _ => (" implemented for `", ""),
                     };
                 err.highlighted_help(vec![
@@ -1903,12 +1895,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         let impl_candidates = impl_candidates
             .into_iter()
             .cloned()
-            .filter(|cand| {
-                !self.tcx.has_attrs_with_path(
-                    cand.impl_def_id,
-                    &[sym::diagnostic, sym::do_not_recommend],
-                )
-            })
+            .filter(|cand| !self.tcx.do_not_recommend_impl(cand.impl_def_id))
             .collect::<Vec<_>>();
 
         let def_id = trait_ref.def_id();
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 9269177eb50..d0f76f0d50e 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs
@@ -1077,10 +1077,10 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         let Some((def_id_or_name, output, inputs)) =
             (self.autoderef_steps)(found).into_iter().find_map(|(found, _)| {
                 match *found.kind() {
-                    ty::FnPtr(fn_sig) => Some((
+                    ty::FnPtr(sig_tys, _) => Some((
                         DefIdOrName::Name("function pointer"),
-                        fn_sig.output(),
-                        fn_sig.inputs(),
+                        sig_tys.output(),
+                        sig_tys.inputs(),
                     )),
                     ty::FnDef(def_id, _) => {
                         let fn_sig = found.fn_sig(self.tcx);
@@ -1977,20 +1977,22 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
         let ObligationCauseCode::FunctionArg { arg_hir_id, .. } = cause else {
             return;
         };
-        let ty::FnPtr(expected) = expected.kind() else {
+        let ty::FnPtr(sig_tys, hdr) = expected.kind() else {
             return;
         };
-        let ty::FnPtr(found) = found.kind() else {
+        let expected = sig_tys.with(*hdr);
+        let ty::FnPtr(sig_tys, hdr) = found.kind() else {
             return;
         };
+        let found = sig_tys.with(*hdr);
         let Node::Expr(arg) = self.tcx.hir_node(*arg_hir_id) else {
             return;
         };
         let hir::ExprKind::Path(path) = arg.kind else {
             return;
         };
-        let expected_inputs = self.tcx.instantiate_bound_regions_with_erased(*expected).inputs();
-        let found_inputs = self.tcx.instantiate_bound_regions_with_erased(*found).inputs();
+        let expected_inputs = self.tcx.instantiate_bound_regions_with_erased(expected).inputs();
+        let found_inputs = self.tcx.instantiate_bound_regions_with_erased(found).inputs();
         let both_tys = expected_inputs.iter().copied().zip(found_inputs.iter().copied());
 
         let arg_expr = |infcx: &InferCtxt<'tcx>, name, expected: Ty<'tcx>, found: Ty<'tcx>| {
@@ -2829,7 +2831,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                                     // Do not suggest relaxing if there is an explicit `Sized` obligation.
                                     && !bounds.iter()
                                         .filter_map(|bound| bound.trait_ref())
-                                        .any(|tr| tr.trait_def_id() == tcx.lang_items().sized_trait())
+                                        .any(|tr| tr.trait_def_id().is_some_and(|def_id| tcx.is_lang_item(def_id, LangItem::Sized)))
                                 {
                                     let (span, separator) = if let [.., last] = bounds {
                                         (last.span().shrink_to_hi(), " +")
@@ -4790,13 +4792,13 @@ fn hint_missing_borrow<'tcx>(
     }
 
     let found_args = match found.kind() {
-        ty::FnPtr(f) => infcx.enter_forall(*f, |f| f.inputs().iter()),
+        ty::FnPtr(sig_tys, _) => infcx.enter_forall(*sig_tys, |sig_tys| sig_tys.inputs().iter()),
         kind => {
             span_bug!(span, "found was converted to a FnPtr above but is now {:?}", kind)
         }
     };
     let expected_args = match expected.kind() {
-        ty::FnPtr(f) => infcx.enter_forall(*f, |f| f.inputs().iter()),
+        ty::FnPtr(sig_tys, _) => infcx.enter_forall(*sig_tys, |sig_tys| sig_tys.inputs().iter()),
         kind => {
             span_bug!(span, "expected was converted to a FnPtr above but is now {:?}", kind)
         }
diff --git a/compiler/rustc_trait_selection/src/solve/fulfill.rs b/compiler/rustc_trait_selection/src/solve/fulfill.rs
index 49fa775a0a1..de8951ef720 100644
--- a/compiler/rustc_trait_selection/src/solve/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/solve/fulfill.rs
@@ -13,7 +13,6 @@ use rustc_middle::bug;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_next_trait_solver::solve::{GenerateProofTree, SolverDelegateEvalExt as _};
-use rustc_span::symbol::sym;
 
 use super::delegate::SolverDelegate;
 use super::inspect::{self, ProofTreeInferCtxtExt, ProofTreeVisitor};
@@ -440,10 +439,7 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
             source: CandidateSource::Impl(impl_def_id),
             result: _,
         } = candidate.kind()
-            && goal
-                .infcx()
-                .tcx
-                .has_attrs_with_path(impl_def_id, &[sym::diagnostic, sym::do_not_recommend])
+            && goal.infcx().tcx.do_not_recommend_impl(impl_def_id)
         {
             return ControlFlow::Break(self.obligation.clone());
         }
diff --git a/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs b/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
index 4e4022830d4..51dda25d8ad 100644
--- a/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
+++ b/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
@@ -9,6 +9,8 @@
 //! coherence right now and was annoying to implement, so I am leaving it
 //! as is until we start using it for something else.
 
+use std::assert_matches::assert_matches;
+
 use rustc_ast_ir::try_visit;
 use rustc_ast_ir::visit::VisitorResult;
 use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, InferOk};
@@ -273,10 +275,10 @@ impl<'a, 'tcx> InspectGoal<'a, 'tcx> {
                     steps.push(step)
                 }
                 inspect::ProbeStep::MakeCanonicalResponse { shallow_certainty: c } => {
-                    assert!(matches!(
+                    assert_matches!(
                         shallow_certainty.replace(c),
                         None | Some(Certainty::Maybe(MaybeCause::Ambiguity))
-                    ));
+                    );
                 }
                 inspect::ProbeStep::NestedProbe(ref probe) => {
                     match probe.kind {
diff --git a/compiler/rustc_trait_selection/src/solve/normalize.rs b/compiler/rustc_trait_selection/src/solve/normalize.rs
index 419d7e704de..c93c40b4826 100644
--- a/compiler/rustc_trait_selection/src/solve/normalize.rs
+++ b/compiler/rustc_trait_selection/src/solve/normalize.rs
@@ -1,3 +1,4 @@
+use std::assert_matches::assert_matches;
 use std::fmt::Debug;
 use std::marker::PhantomData;
 
@@ -63,7 +64,7 @@ where
     E: FromSolverError<'tcx, NextSolverError<'tcx>>,
 {
     fn normalize_alias_ty(&mut self, alias_ty: Ty<'tcx>) -> Result<Ty<'tcx>, Vec<E>> {
-        assert!(matches!(alias_ty.kind(), ty::Alias(..)));
+        assert_matches!(alias_ty.kind(), ty::Alias(..));
 
         let infcx = self.at.infcx;
         let tcx = infcx.tcx;
diff --git a/compiler/rustc_trait_selection/src/traits/misc.rs b/compiler/rustc_trait_selection/src/traits/misc.rs
index 9a127e752a6..3e65194577e 100644
--- a/compiler/rustc_trait_selection/src/traits/misc.rs
+++ b/compiler/rustc_trait_selection/src/traits/misc.rs
@@ -1,5 +1,7 @@
 //! Miscellaneous type-system utilities that are too small to deserve their own modules.
 
+use std::assert_matches::assert_matches;
+
 use hir::LangItem;
 use rustc_ast::Mutability;
 use rustc_data_structures::fx::FxIndexSet;
@@ -92,7 +94,7 @@ pub fn type_allowed_to_implement_const_param_ty<'tcx>(
     lang_item: LangItem,
     parent_cause: ObligationCause<'tcx>,
 ) -> Result<(), ConstParamTyImplementationError<'tcx>> {
-    assert!(matches!(lang_item, LangItem::ConstParamTy | LangItem::UnsizedConstParamTy));
+    assert_matches!(lang_item, LangItem::ConstParamTy | LangItem::UnsizedConstParamTy);
 
     let inner_tys: Vec<_> = match *self_type.kind() {
         // Trivially okay as these types are all:
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index 4b62a5c59b2..568214fe022 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -1110,7 +1110,7 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
                         | ty::Error(_) => false,
                     }
                 } else if tcx.is_lang_item(trait_ref.def_id, LangItem::PointeeTrait) {
-                    let tail = selcx.tcx().struct_tail_with_normalize(
+                    let tail = selcx.tcx().struct_tail_raw(
                         self_ty,
                         |ty| {
                             // We throw away any obligations we get from this, since we normalize
@@ -1149,10 +1149,10 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
                         | ty::Never
                         // Extern types have unit metadata, according to RFC 2850
                         | ty::Foreign(_)
-                        // If returned by `struct_tail_without_normalization` this is a unit struct
+                        // If returned by `struct_tail` this is a unit struct
                         // without any fields, or not a struct, and therefore is Sized.
                         | ty::Adt(..)
-                        // If returned by `struct_tail_without_normalization` this is the empty tuple.
+                        // If returned by `struct_tail` this is the empty tuple.
                         | ty::Tuple(..)
                         // Integers and floats are always Sized, and so have unit type metadata.
                         | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(..)) => true,
@@ -1636,7 +1636,7 @@ fn confirm_fn_pointer_candidate<'cx, 'tcx>(
             .generics_of(def_id)
             .host_effect_index
             .map_or(tcx.consts.true_, |idx| args.const_at(idx)),
-        ty::FnPtr(_) => tcx.consts.true_,
+        ty::FnPtr(..) => tcx.consts.true_,
         _ => unreachable!("only expected FnPtr or FnDef in `confirm_fn_pointer_candidate`"),
     };
 
diff --git a/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs b/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs
index d3a1ed52d2e..7d30e652449 100644
--- a/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs
@@ -33,7 +33,7 @@ pub fn trivial_dropck_outlives<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
         | ty::Float(_)
         | ty::Never
         | ty::FnDef(..)
-        | ty::FnPtr(_)
+        | ty::FnPtr(..)
         | ty::Char
         | ty::CoroutineWitness(..)
         | ty::RawPtr(_, _)
@@ -224,7 +224,7 @@ pub fn dtorck_constraint_for_ty_inner<'tcx>(
         | ty::RawPtr(..)
         | ty::Ref(..)
         | ty::FnDef(..)
-        | ty::FnPtr(_)
+        | ty::FnPtr(..)
         | ty::CoroutineWitness(..) => {
             // these types never have a destructor
         }
diff --git a/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs b/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs
index 294c6bfc124..d6687c762c3 100644
--- a/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs
@@ -1,3 +1,4 @@
+use rustc_hir::LangItem;
 use rustc_infer::traits::Obligation;
 pub use rustc_middle::traits::query::type_op::ProvePredicate;
 use rustc_middle::traits::query::NoSolution;
@@ -20,8 +21,7 @@ impl<'tcx> super::QueryTypeOp<'tcx> for ProvePredicate<'tcx> {
         // such cases.
         if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_ref)) =
             key.value.predicate.kind().skip_binder()
-            && let Some(sized_def_id) = tcx.lang_items().sized_trait()
-            && trait_ref.def_id() == sized_def_id
+            && tcx.is_lang_item(trait_ref.def_id(), LangItem::Sized)
             && trait_ref.self_ty().is_trivially_sized(tcx)
         {
             return Some(());
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 9de62031311..cb8deeaedb6 100644
--- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -468,8 +468,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 candidates.vec.push(AsyncClosureCandidate);
             }
             // Provide an impl, but only for suitable `fn` pointers.
-            ty::FnPtr(sig) => {
-                if sig.is_fn_trait_compatible() {
+            ty::FnPtr(sig_tys, hdr) => {
+                if sig_tys.with(hdr).is_fn_trait_compatible() {
                     candidates.vec.push(AsyncClosureCandidate);
                 }
             }
@@ -535,8 +535,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 candidates.ambiguous = true; // Could wind up being a fn() type.
             }
             // Provide an impl, but only for suitable `fn` pointers.
-            ty::FnPtr(sig) => {
-                if sig.is_fn_trait_compatible() {
+            ty::FnPtr(sig_tys, hdr) => {
+                if sig_tys.with(hdr).is_fn_trait_compatible() {
                     candidates
                         .vec
                         .push(FnPointerCandidate { fn_host_effect: self.tcx().consts.true_ });
@@ -819,7 +819,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 | ty::RawPtr(_, _)
                 | ty::Ref(..)
                 | ty::FnDef(..)
-                | ty::FnPtr(_)
+                | ty::FnPtr(..)
                 | ty::Closure(..)
                 | ty::CoroutineClosure(..)
                 | ty::Coroutine(..)
@@ -1207,7 +1207,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             | ty::RawPtr(_, _)
             | ty::Ref(..)
             | ty::FnDef(..)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Never
             | ty::Foreign(_)
             | ty::Array(..)
@@ -1290,7 +1290,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             | ty::Ref(_, _, _)
             | ty::FnDef(_, _)
             | ty::Pat(_, _)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Dynamic(_, _, _)
             | ty::Closure(..)
             | ty::CoroutineClosure(..)
@@ -1339,7 +1339,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let self_ty = self.infcx.resolve_vars_if_possible(obligation.self_ty());
 
         match self_ty.skip_binder().kind() {
-            ty::FnPtr(_) => candidates.vec.push(BuiltinCandidate { has_nested: false }),
+            ty::FnPtr(..) => candidates.vec.push(BuiltinCandidate { has_nested: false }),
             ty::Bool
             | ty::Char
             | ty::Int(_)
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index ddd8b970cc8..0d7ceca4301 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -1398,7 +1398,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 | ty::RawPtr(_, _)
                 | ty::Ref(..)
                 | ty::FnDef(..)
-                | ty::FnPtr(_)
+                | ty::FnPtr(..)
                 | ty::Never
                 | ty::Foreign(_) => {}
 
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 1b2767a6a62..f002fa27db2 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -2113,7 +2113,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
             | ty::Bool
             | ty::Float(_)
             | ty::FnDef(..)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::RawPtr(..)
             | ty::Char
             | ty::Ref(..)
@@ -2170,7 +2170,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
         use self::BuiltinImplConditions::{Ambiguous, None, Where};
 
         match *self_ty.kind() {
-            ty::FnDef(..) | ty::FnPtr(_) | ty::Error(_) => Where(ty::Binder::dummy(Vec::new())),
+            ty::FnDef(..) | ty::FnPtr(..) | ty::Error(_) => Where(ty::Binder::dummy(Vec::new())),
 
             ty::Uint(_)
             | ty::Int(_)
@@ -2332,7 +2332,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
             | ty::Bool
             | ty::Float(_)
             | ty::FnDef(..)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Error(_)
             | ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
             | ty::Never
diff --git a/compiler/rustc_trait_selection/src/traits/wf.rs b/compiler/rustc_trait_selection/src/traits/wf.rs
index 7e5fe7e3c94..a3982c3d987 100644
--- a/compiler/rustc_trait_selection/src/traits/wf.rs
+++ b/compiler/rustc_trait_selection/src/traits/wf.rs
@@ -812,7 +812,7 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
                 return upvars.visit_with(self);
             }
 
-            ty::FnPtr(_) => {
+            ty::FnPtr(..) => {
                 // Let the visitor iterate into the argument/return
                 // types appearing in the fn signature.
             }
diff --git a/compiler/rustc_ty_utils/src/abi.rs b/compiler/rustc_ty_utils/src/abi.rs
index d90c3bedc70..34c426f2aa6 100644
--- a/compiler/rustc_ty_utils/src/abi.rs
+++ b/compiler/rustc_ty_utils/src/abi.rs
@@ -621,7 +621,7 @@ fn fn_abi_new_uncached<'tcx>(
     let rust_abi = matches!(sig.abi, RustIntrinsic | Rust | RustCall);
 
     let is_drop_in_place =
-        fn_def_id.is_some() && fn_def_id == cx.tcx.lang_items().drop_in_place_fn();
+        fn_def_id.is_some_and(|def_id| cx.tcx.is_lang_item(def_id, LangItem::DropInPlace));
 
     let arg_of = |ty: Ty<'tcx>, arg_idx: Option<usize>| -> Result<_, &'tcx FnAbiError<'tcx>> {
         let span = tracing::debug_span!("arg_of");
diff --git a/compiler/rustc_ty_utils/src/instance.rs b/compiler/rustc_ty_utils/src/instance.rs
index 43e49138709..c7ed6e6110f 100644
--- a/compiler/rustc_ty_utils/src/instance.rs
+++ b/compiler/rustc_ty_utils/src/instance.rs
@@ -248,7 +248,7 @@ fn resolve_associated_item<'tcx>(
                 if name == sym::clone {
                     let self_ty = trait_ref.self_ty();
                     match self_ty.kind() {
-                        ty::FnDef(..) | ty::FnPtr(_) => (),
+                        ty::FnDef(..) | ty::FnPtr(..) => (),
                         ty::Coroutine(..)
                         | ty::CoroutineWitness(..)
                         | ty::Closure(..)
diff --git a/compiler/rustc_ty_utils/src/layout.rs b/compiler/rustc_ty_utils/src/layout.rs
index 1eb03fc3bd6..234e1a6d55e 100644
--- a/compiler/rustc_ty_utils/src/layout.rs
+++ b/compiler/rustc_ty_utils/src/layout.rs
@@ -184,7 +184,7 @@ fn layout_of_uncached<'tcx>(
         ty::Int(ity) => scalar(Int(Integer::from_int_ty(dl, ity), true)),
         ty::Uint(ity) => scalar(Int(Integer::from_uint_ty(dl, ity), false)),
         ty::Float(fty) => scalar(Float(Float::from_float_ty(fty))),
-        ty::FnPtr(_) => {
+        ty::FnPtr(..) => {
             let mut ptr = scalar_unit(Pointer(dl.instruction_address_space));
             ptr.valid_range_mut().start = 1;
             tcx.mk_layout(LayoutS::scalar(cx, ptr))
@@ -219,9 +219,13 @@ fn layout_of_uncached<'tcx>(
                             // its struct tail cannot be normalized either, so try to get a
                             // more descriptive layout error here, which will lead to less confusing
                             // diagnostics.
+                            //
+                            // We use the raw struct tail function here to get the first tail
+                            // that is an alias, which is likely the cause of the normalization
+                            // error.
                             match tcx.try_normalize_erasing_regions(
                                 param_env,
-                                tcx.struct_tail_without_normalization(pointee),
+                                tcx.struct_tail_raw(pointee, |ty| ty, || {}),
                             ) {
                                 Ok(_) => {}
                                 Err(better_err) => {
diff --git a/compiler/rustc_ty_utils/src/layout_sanity_check.rs b/compiler/rustc_ty_utils/src/layout_sanity_check.rs
index d8e0443c50b..2223aca28d1 100644
--- a/compiler/rustc_ty_utils/src/layout_sanity_check.rs
+++ b/compiler/rustc_ty_utils/src/layout_sanity_check.rs
@@ -249,7 +249,7 @@ pub(super) fn sanity_check_layout<'tcx>(
     if let Variants::Multiple { variants, .. } = &layout.variants {
         for variant in variants.iter() {
             // No nested "multiple".
-            assert!(matches!(variant.variants, Variants::Single { .. }));
+            assert_matches!(variant.variants, Variants::Single { .. });
             // Variants should have the same or a smaller size as the full thing,
             // and same for alignment.
             if variant.size > layout.size {
diff --git a/compiler/rustc_type_ir/src/binder.rs b/compiler/rustc_type_ir/src/binder.rs
index 8797288070e..d42efbc91e1 100644
--- a/compiler/rustc_type_ir/src/binder.rs
+++ b/compiler/rustc_type_ir/src/binder.rs
@@ -86,6 +86,7 @@ macro_rules! impl_binder_encode_decode {
 #[cfg(feature = "nightly")]
 impl_binder_encode_decode! {
     ty::FnSig<I>,
+    ty::FnSigTys<I>,
     ty::TraitPredicate<I>,
     ty::ExistentialPredicate<I>,
     ty::TraitRef<I>,
@@ -247,21 +248,6 @@ impl<I: Interner, T> Binder<I, T> {
         // `self.value` is equivalent to `self.skip_binder()`
         if self.value.has_escaping_bound_vars() { None } else { Some(self.skip_binder()) }
     }
-
-    /// Splits the contents into two things that share the same binder
-    /// level as the original, returning two distinct binders.
-    ///
-    /// `f` should consider bound regions at depth 1 to be free, and
-    /// anything it produces with bound regions at depth 1 will be
-    /// bound in the resulting return values.
-    pub fn split<U, V, F>(self, f: F) -> (Binder<I, U>, Binder<I, V>)
-    where
-        F: FnOnce(T) -> (U, V),
-    {
-        let Binder { value, bound_vars } = self;
-        let (u, v) = f(value);
-        (Binder { value: u, bound_vars }, Binder { value: v, bound_vars })
-    }
 }
 
 impl<I: Interner, T> Binder<I, Option<T>> {
diff --git a/compiler/rustc_type_ir/src/fast_reject.rs b/compiler/rustc_type_ir/src/fast_reject.rs
index 456accd1a1b..fab4a099117 100644
--- a/compiler/rustc_type_ir/src/fast_reject.rs
+++ b/compiler/rustc_type_ir/src/fast_reject.rs
@@ -135,7 +135,9 @@ pub fn simplify_type<I: Interner>(
         ty::CoroutineWitness(def_id, _) => Some(SimplifiedType::CoroutineWitness(def_id)),
         ty::Never => Some(SimplifiedType::Never),
         ty::Tuple(tys) => Some(SimplifiedType::Tuple(tys.len())),
-        ty::FnPtr(f) => Some(SimplifiedType::Function(f.skip_binder().inputs().len())),
+        ty::FnPtr(sig_tys, _hdr) => {
+            Some(SimplifiedType::Function(sig_tys.skip_binder().inputs().len()))
+        }
         ty::Placeholder(..) => Some(SimplifiedType::Placeholder),
         ty::Param(_) => match treat_params {
             TreatParams::ForLookup => Some(SimplifiedType::Placeholder),
@@ -307,17 +309,14 @@ impl<I: Interner> DeepRejectCtxt<I> {
                     obl_preds.principal_def_id() == impl_preds.principal_def_id()
                 )
             }
-            ty::FnPtr(obl_sig) => match k {
-                ty::FnPtr(impl_sig) => {
-                    let ty::FnSig { inputs_and_output, c_variadic, safety, abi } =
-                        obl_sig.skip_binder();
-                    let impl_sig = impl_sig.skip_binder();
+            ty::FnPtr(obl_sig_tys, obl_hdr) => match k {
+                ty::FnPtr(impl_sig_tys, impl_hdr) => {
+                    let obl_sig_tys = obl_sig_tys.skip_binder().inputs_and_output;
+                    let impl_sig_tys = impl_sig_tys.skip_binder().inputs_and_output;
 
-                    abi == impl_sig.abi
-                        && c_variadic == impl_sig.c_variadic
-                        && safety == impl_sig.safety
-                        && inputs_and_output.len() == impl_sig.inputs_and_output.len()
-                        && iter::zip(inputs_and_output.iter(), impl_sig.inputs_and_output.iter())
+                    obl_hdr == impl_hdr
+                        && obl_sig_tys.len() == impl_sig_tys.len()
+                        && iter::zip(obl_sig_tys.iter(), impl_sig_tys.iter())
                             .all(|(obl, imp)| self.types_may_unify(obl, imp))
                 }
                 _ => false,
diff --git a/compiler/rustc_type_ir/src/inherent.rs b/compiler/rustc_type_ir/src/inherent.rs
index 263ba676427..958360faede 100644
--- a/compiler/rustc_type_ir/src/inherent.rs
+++ b/compiler/rustc_type_ir/src/inherent.rs
@@ -133,12 +133,12 @@ pub trait Ty<I: Interner<Ty = Self>>:
     }
 
     fn is_fn_ptr(self) -> bool {
-        matches!(self.kind(), ty::FnPtr(_))
+        matches!(self.kind(), ty::FnPtr(..))
     }
 
     fn fn_sig(self, interner: I) -> ty::Binder<I, ty::FnSig<I>> {
         match self.kind() {
-            ty::FnPtr(sig) => sig,
+            ty::FnPtr(sig_tys, hdr) => sig_tys.with(hdr),
             ty::FnDef(def_id, args) => interner.fn_sig(def_id).instantiate(interner, args),
             ty::Error(_) => {
                 // ignore errors (#54954)
@@ -181,7 +181,7 @@ pub trait Ty<I: Interner<Ty = Self>>:
             | ty::RawPtr(_, _)
             | ty::Ref(_, _, _)
             | ty::FnDef(_, _)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Dynamic(_, _, _)
             | ty::Closure(_, _)
             | ty::CoroutineClosure(_, _)
@@ -203,7 +203,9 @@ pub trait Ty<I: Interner<Ty = Self>>:
 pub trait Tys<I: Interner<Tys = Self>>:
     Copy + Debug + Hash + Eq + SliceLike<Item = I::Ty> + TypeFoldable<I> + Default
 {
-    fn split_inputs_and_output(self) -> (I::FnInputTys, I::Ty);
+    fn inputs(self) -> I::FnInputTys;
+
+    fn output(self) -> I::Ty;
 }
 
 pub trait Abi<I: Interner<Abi = Self>>: Copy + Debug + Hash + Eq + Relate<I> {
diff --git a/compiler/rustc_type_ir/src/outlives.rs b/compiler/rustc_type_ir/src/outlives.rs
index 2f26a439183..bfcea6a81d3 100644
--- a/compiler/rustc_type_ir/src/outlives.rs
+++ b/compiler/rustc_type_ir/src/outlives.rs
@@ -186,7 +186,7 @@ impl<I: Interner> TypeVisitor<I> for OutlivesCollector<'_, I> {
             | ty::Slice(_)
             | ty::RawPtr(_, _)
             | ty::Ref(_, _, _)
-            | ty::FnPtr(_)
+            | ty::FnPtr(..)
             | ty::Dynamic(_, _, _)
             | ty::Tuple(_) => {
                 ty.super_visit_with(self);
diff --git a/compiler/rustc_type_ir/src/relate.rs b/compiler/rustc_type_ir/src/relate.rs
index 9fd3534d1fa..578436b622a 100644
--- a/compiler/rustc_type_ir/src/relate.rs
+++ b/compiler/rustc_type_ir/src/relate.rs
@@ -524,8 +524,8 @@ pub fn structurally_relate_tys<I: Interner, R: TypeRelation<I>>(
             Ok(Ty::new_fn_def(cx, a_def_id, args))
         }
 
-        (ty::FnPtr(a_fty), ty::FnPtr(b_fty)) => {
-            let fty = relation.relate(a_fty, b_fty)?;
+        (ty::FnPtr(a_sig_tys, a_hdr), ty::FnPtr(b_sig_tys, b_hdr)) => {
+            let fty = relation.relate(a_sig_tys.with(a_hdr), b_sig_tys.with(b_hdr))?;
             Ok(Ty::new_fn_ptr(cx, fty))
         }
 
diff --git a/compiler/rustc_type_ir/src/ty_kind.rs b/compiler/rustc_type_ir/src/ty_kind.rs
index 7e48f1b20a8..328b6739d97 100644
--- a/compiler/rustc_type_ir/src/ty_kind.rs
+++ b/compiler/rustc_type_ir/src/ty_kind.rs
@@ -143,7 +143,12 @@ pub enum TyKind<I: Interner> {
     /// fn foo() -> i32 { 1 }
     /// let bar: fn() -> i32 = foo;
     /// ```
-    FnPtr(ty::Binder<I, FnSig<I>>),
+    ///
+    /// These two fields are equivalent to a `ty::Binder<I, FnSig<I>>`. But by
+    /// splitting that into two pieces, we get a more compact data layout that
+    /// reduces the size of `TyKind` by 8 bytes. It is a very hot type, so it's
+    /// worth the mild inconvenience.
+    FnPtr(ty::Binder<I, FnSigTys<I>>, FnHeader<I>),
 
     /// A trait object. Written as `dyn for<'b> Trait<'b, Assoc = u32> + Send + 'a`.
     Dynamic(I::BoundExistentialPredicates, I::Region, DynKind),
@@ -288,7 +293,7 @@ impl<I: Interner> fmt::Debug for TyKind<I> {
             RawPtr(ty, mutbl) => write!(f, "*{} {:?}", mutbl.ptr_str(), ty),
             Ref(r, t, m) => write!(f, "&{:?} {}{:?}", r, m.prefix_str(), t),
             FnDef(d, s) => f.debug_tuple("FnDef").field(d).field(&s).finish(),
-            FnPtr(s) => write!(f, "{s:?}"),
+            FnPtr(sig_tys, hdr) => write!(f, "{:?}", sig_tys.with(*hdr)),
             Dynamic(p, r, repr) => match repr {
                 DynKind::Dyn => write!(f, "dyn {p:?} + {r:?}"),
                 DynKind::DynStar => write!(f, "dyn* {p:?} + {r:?}"),
@@ -868,16 +873,12 @@ pub struct FnSig<I: Interner> {
 }
 
 impl<I: Interner> FnSig<I> {
-    pub fn split_inputs_and_output(self) -> (I::FnInputTys, I::Ty) {
-        self.inputs_and_output.split_inputs_and_output()
-    }
-
     pub fn inputs(self) -> I::FnInputTys {
-        self.split_inputs_and_output().0
+        self.inputs_and_output.inputs()
     }
 
     pub fn output(self) -> I::Ty {
-        self.split_inputs_and_output().1
+        self.inputs_and_output.output()
     }
 
     pub fn is_fn_trait_compatible(self) -> bool {
@@ -922,6 +923,13 @@ impl<I: Interner> ty::Binder<I, FnSig<I>> {
     pub fn is_fn_trait_compatible(&self) -> bool {
         self.skip_binder().is_fn_trait_compatible()
     }
+
+    // Used to split a single value into the two fields in `TyKind::FnPtr`.
+    pub fn split(self) -> (ty::Binder<I, FnSigTys<I>>, FnHeader<I>) {
+        let hdr =
+            FnHeader { c_variadic: self.c_variadic(), safety: self.safety(), abi: self.abi() };
+        (self.map_bound(|sig| FnSigTys { inputs_and_output: sig.inputs_and_output }), hdr)
+    }
 }
 
 impl<I: Interner> fmt::Debug for FnSig<I> {
@@ -935,7 +943,7 @@ impl<I: Interner> fmt::Debug for FnSig<I> {
         }
 
         write!(f, "fn(")?;
-        let (inputs, output) = sig.split_inputs_and_output();
+        let inputs = sig.inputs();
         for (i, ty) in inputs.iter().enumerate() {
             if i > 0 {
                 write!(f, ", ")?;
@@ -951,9 +959,69 @@ impl<I: Interner> fmt::Debug for FnSig<I> {
         }
         write!(f, ")")?;
 
+        let output = sig.output();
         match output.kind() {
             Tuple(list) if list.is_empty() => Ok(()),
             _ => write!(f, " -> {:?}", sig.output()),
         }
     }
 }
+
+// This is just a `FnSig` without the `FnHeader` fields.
+#[derive_where(Clone, Copy, Debug, PartialEq, Eq, Hash; I: Interner)]
+#[cfg_attr(feature = "nightly", derive(TyEncodable, TyDecodable, HashStable_NoContext))]
+#[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
+pub struct FnSigTys<I: Interner> {
+    pub inputs_and_output: I::Tys,
+}
+
+impl<I: Interner> FnSigTys<I> {
+    pub fn inputs(self) -> I::FnInputTys {
+        self.inputs_and_output.inputs()
+    }
+
+    pub fn output(self) -> I::Ty {
+        self.inputs_and_output.output()
+    }
+}
+
+impl<I: Interner> ty::Binder<I, FnSigTys<I>> {
+    // Used to combine the two fields in `TyKind::FnPtr` into a single value.
+    pub fn with(self, hdr: FnHeader<I>) -> ty::Binder<I, FnSig<I>> {
+        self.map_bound(|sig_tys| FnSig {
+            inputs_and_output: sig_tys.inputs_and_output,
+            c_variadic: hdr.c_variadic,
+            safety: hdr.safety,
+            abi: hdr.abi,
+        })
+    }
+
+    #[inline]
+    pub fn inputs(self) -> ty::Binder<I, I::FnInputTys> {
+        self.map_bound(|sig_tys| sig_tys.inputs())
+    }
+
+    #[inline]
+    #[track_caller]
+    pub fn input(self, index: usize) -> ty::Binder<I, I::Ty> {
+        self.map_bound(|sig_tys| sig_tys.inputs().get(index).unwrap())
+    }
+
+    pub fn inputs_and_output(self) -> ty::Binder<I, I::Tys> {
+        self.map_bound(|sig_tys| sig_tys.inputs_and_output)
+    }
+
+    #[inline]
+    pub fn output(self) -> ty::Binder<I, I::Ty> {
+        self.map_bound(|sig_tys| sig_tys.output())
+    }
+}
+
+#[derive_where(Clone, Copy, Debug, PartialEq, Eq, Hash; I: Interner)]
+#[cfg_attr(feature = "nightly", derive(TyEncodable, TyDecodable, HashStable_NoContext))]
+#[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
+pub struct FnHeader<I: Interner> {
+    pub c_variadic: bool,
+    pub safety: I::Safety,
+    pub abi: I::Abi,
+}
diff --git a/compiler/rustc_type_ir/src/ty_kind/closure.rs b/compiler/rustc_type_ir/src/ty_kind/closure.rs
index 81717ce4a22..9d907baeeb3 100644
--- a/compiler/rustc_type_ir/src/ty_kind/closure.rs
+++ b/compiler/rustc_type_ir/src/ty_kind/closure.rs
@@ -197,7 +197,7 @@ impl<I: Interner> ClosureArgs<I> {
     /// Extracts the signature from the closure.
     pub fn sig(self) -> ty::Binder<I, ty::FnSig<I>> {
         match self.sig_as_fn_ptr_ty().kind() {
-            ty::FnPtr(sig) => sig,
+            ty::FnPtr(sig_tys, hdr) => sig_tys.with(hdr),
             ty => panic!("closure_sig_as_fn_ptr_ty is not a fn-ptr: {ty:?}"),
         }
     }
@@ -292,21 +292,23 @@ impl<I: Interner> CoroutineClosureArgs<I> {
 
     pub fn coroutine_closure_sig(self) -> ty::Binder<I, CoroutineClosureSignature<I>> {
         let interior = self.coroutine_witness_ty();
-        let ty::FnPtr(sig) = self.signature_parts_ty().kind() else { panic!() };
-        sig.map_bound(|sig| {
-            let [resume_ty, tupled_inputs_ty] = *sig.inputs().as_slice() else {
+        let ty::FnPtr(sig_tys, hdr) = self.signature_parts_ty().kind() else { panic!() };
+        sig_tys.map_bound(|sig_tys| {
+            let [resume_ty, tupled_inputs_ty] = *sig_tys.inputs().as_slice() else {
                 panic!();
             };
-            let [yield_ty, return_ty] = *sig.output().tuple_fields().as_slice() else { panic!() };
+            let [yield_ty, return_ty] = *sig_tys.output().tuple_fields().as_slice() else {
+                panic!()
+            };
             CoroutineClosureSignature {
                 interior,
                 tupled_inputs_ty,
                 resume_ty,
                 yield_ty,
                 return_ty,
-                c_variadic: sig.c_variadic,
-                safety: sig.safety,
-                abi: sig.abi,
+                c_variadic: hdr.c_variadic,
+                safety: hdr.safety,
+                abi: hdr.abi,
             }
         })
     }
@@ -321,7 +323,7 @@ impl<I: Interner> CoroutineClosureArgs<I> {
 
     pub fn has_self_borrows(&self) -> bool {
         match self.coroutine_captures_by_ref_ty().kind() {
-            ty::FnPtr(sig) => sig
+            ty::FnPtr(sig_tys, _) => sig_tys
                 .skip_binder()
                 .visit_with(&mut HasRegionsBoundAt { binder: ty::INNERMOST })
                 .is_break(),
@@ -460,11 +462,11 @@ impl<I: Interner> CoroutineClosureSignature<I> {
     ) -> I::Ty {
         match kind {
             ty::ClosureKind::Fn | ty::ClosureKind::FnMut => {
-                let ty::FnPtr(sig) = coroutine_captures_by_ref_ty.kind() else {
+                let ty::FnPtr(sig_tys, _) = coroutine_captures_by_ref_ty.kind() else {
                     panic!();
                 };
                 let coroutine_captures_by_ref_ty =
-                    sig.output().skip_binder().fold_with(&mut FoldEscapingRegions {
+                    sig_tys.output().skip_binder().fold_with(&mut FoldEscapingRegions {
                         interner: cx,
                         region: env_region,
                         debruijn: ty::INNERMOST,