Merge from rustc

16 files changed, 139 insertions, 166 deletions

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(_) => {}