Add opaque TypeId handles for CTFE

22 files changed, 236 insertions, 56 deletions

diff --git a/compiler/rustc_codegen_cranelift/src/constant.rs b/compiler/rustc_codegen_cranelift/src/constant.rs
index ed06423b260..85adf0f3716 100644
--- a/compiler/rustc_codegen_cranelift/src/constant.rs
+++ b/compiler/rustc_codegen_cranelift/src/constant.rs
@@ -175,6 +175,13 @@ pub(crate) fn codegen_const_value<'tcx>(
                             fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
                         fx.bcx.ins().global_value(fx.pointer_type, local_data_id)
                     }
+                    GlobalAlloc::TypeId { .. } => {
+                        return CValue::const_val(
+                            fx,
+                            layout,
+                            ScalarInt::try_from_target_usize(offset.bytes(), fx.tcx).unwrap(),
+                        );
+                    }
                     GlobalAlloc::Static(def_id) => {
                         assert!(fx.tcx.is_static(def_id));
                         let data_id = data_id_for_static(
@@ -360,6 +367,7 @@ fn define_all_allocs(tcx: TyCtxt<'_>, module: &mut dyn Module, cx: &mut Constant
                     GlobalAlloc::Memory(alloc) => alloc,
                     GlobalAlloc::Function { .. }
                     | GlobalAlloc::Static(_)
+                    | GlobalAlloc::TypeId { .. }
                     | GlobalAlloc::VTable(..) => {
                         unreachable!()
                     }
@@ -471,6 +479,11 @@ fn define_all_allocs(tcx: TyCtxt<'_>, module: &mut dyn Module, cx: &mut Constant
                         .principal()
                         .map(|principal| tcx.instantiate_bound_regions_with_erased(principal)),
                 ),
+                GlobalAlloc::TypeId { .. } => {
+                    // Nothing to do, the bytes/offset of this pointer have already been written together with all other bytes,
+                    // so we just need to drop this provenance.
+                    continue;
+                }
                 GlobalAlloc::Static(def_id) => {
                     if tcx.codegen_fn_attrs(def_id).flags.contains(CodegenFnAttrFlags::THREAD_LOCAL)
                     {
diff --git a/compiler/rustc_codegen_gcc/src/common.rs b/compiler/rustc_codegen_gcc/src/common.rs
index 32713eb56c6..28848ca6184 100644
--- a/compiler/rustc_codegen_gcc/src/common.rs
+++ b/compiler/rustc_codegen_gcc/src/common.rs
@@ -1,7 +1,6 @@
 use gccjit::{LValue, RValue, ToRValue, Type};
-use rustc_abi as abi;
-use rustc_abi::HasDataLayout;
 use rustc_abi::Primitive::Pointer;
+use rustc_abi::{self as abi, HasDataLayout};
 use rustc_codegen_ssa::traits::{
     BaseTypeCodegenMethods, ConstCodegenMethods, MiscCodegenMethods, StaticCodegenMethods,
 };
@@ -282,6 +281,13 @@ impl<'gcc, 'tcx> ConstCodegenMethods for CodegenCx<'gcc, 'tcx> {
                         let init = self.const_data_from_alloc(alloc);
                         self.static_addr_of(init, alloc.inner().align, None)
                     }
+                    GlobalAlloc::TypeId { .. } => {
+                        let val = self.const_usize(offset.bytes());
+                        // This is still a variable of pointer type, even though we only use the provenance
+                        // of that pointer in CTFE and Miri. But to make LLVM's type system happy,
+                        // we need an int-to-ptr cast here (it doesn't matter at all which provenance that picks).
+                        return self.context.new_cast(None, val, ty);
+                    }
                     GlobalAlloc::Static(def_id) => {
                         assert!(self.tcx.is_static(def_id));
                         self.get_static(def_id).get_address(None)
diff --git a/compiler/rustc_codegen_llvm/src/common.rs b/compiler/rustc_codegen_llvm/src/common.rs
index 92f38565eef..b9b5c776d86 100644
--- a/compiler/rustc_codegen_llvm/src/common.rs
+++ b/compiler/rustc_codegen_llvm/src/common.rs
@@ -3,9 +3,8 @@
 use std::borrow::Borrow;
 
 use libc::{c_char, c_uint};
-use rustc_abi as abi;
-use rustc_abi::HasDataLayout;
 use rustc_abi::Primitive::Pointer;
+use rustc_abi::{self as abi, HasDataLayout as _};
 use rustc_ast::Mutability;
 use rustc_codegen_ssa::common::TypeKind;
 use rustc_codegen_ssa::traits::*;
@@ -284,7 +283,8 @@ impl<'ll, 'tcx> ConstCodegenMethods for CodegenCx<'ll, 'tcx> {
                                 self.const_bitcast(llval, llty)
                             };
                         } else {
-                            let init = const_alloc_to_llvm(self, alloc, /*static*/ false);
+                            let init =
+                                const_alloc_to_llvm(self, alloc.inner(), /*static*/ false);
                             let alloc = alloc.inner();
                             let value = match alloc.mutability {
                                 Mutability::Mut => self.static_addr_of_mut(init, alloc.align, None),
@@ -316,15 +316,19 @@ impl<'ll, 'tcx> ConstCodegenMethods for CodegenCx<'ll, 'tcx> {
                                 }),
                             )))
                             .unwrap_memory();
-                        let init = const_alloc_to_llvm(self, alloc, /*static*/ false);
-                        let value = self.static_addr_of_impl(init, alloc.inner().align, None);
-                        value
+                        let init = const_alloc_to_llvm(self, alloc.inner(), /*static*/ false);
+                        self.static_addr_of_impl(init, alloc.inner().align, None)
                     }
                     GlobalAlloc::Static(def_id) => {
                         assert!(self.tcx.is_static(def_id));
                         assert!(!self.tcx.is_thread_local_static(def_id));
                         self.get_static(def_id)
                     }
+                    GlobalAlloc::TypeId { .. } => {
+                        // Drop the provenance, the offset contains the bytes of the hash
+                        let llval = self.const_usize(offset.bytes());
+                        return unsafe { llvm::LLVMConstIntToPtr(llval, llty) };
+                    }
                 };
                 let base_addr_space = global_alloc.address_space(self);
                 let llval = unsafe {
@@ -346,7 +350,7 @@ impl<'ll, 'tcx> ConstCodegenMethods for CodegenCx<'ll, 'tcx> {
     }
 
     fn const_data_from_alloc(&self, alloc: ConstAllocation<'_>) -> Self::Value {
-        const_alloc_to_llvm(self, alloc, /*static*/ false)
+        const_alloc_to_llvm(self, alloc.inner(), /*static*/ false)
     }
 
     fn const_ptr_byte_offset(&self, base_addr: Self::Value, offset: abi::Size) -> Self::Value {
diff --git a/compiler/rustc_codegen_llvm/src/consts.rs b/compiler/rustc_codegen_llvm/src/consts.rs
index 28f5282c6b0..21524fd2eb8 100644
--- a/compiler/rustc_codegen_llvm/src/consts.rs
+++ b/compiler/rustc_codegen_llvm/src/consts.rs
@@ -27,10 +27,9 @@ use crate::{base, debuginfo};
 
 pub(crate) fn const_alloc_to_llvm<'ll>(
     cx: &CodegenCx<'ll, '_>,
-    alloc: ConstAllocation<'_>,
+    alloc: &Allocation,
     is_static: bool,
 ) -> &'ll Value {
-    let alloc = alloc.inner();
     // We expect that callers of const_alloc_to_llvm will instead directly codegen a pointer or
     // integer for any &ZST where the ZST is a constant (i.e. not a static). We should never be
     // producing empty LLVM allocations as they're just adding noise to binaries and forcing less
@@ -141,7 +140,7 @@ fn codegen_static_initializer<'ll, 'tcx>(
     def_id: DefId,
 ) -> Result<(&'ll Value, ConstAllocation<'tcx>), ErrorHandled> {
     let alloc = cx.tcx.eval_static_initializer(def_id)?;
-    Ok((const_alloc_to_llvm(cx, alloc, /*static*/ true), alloc))
+    Ok((const_alloc_to_llvm(cx, alloc.inner(), /*static*/ true), alloc))
 }
 
 fn set_global_alignment<'ll>(cx: &CodegenCx<'ll, '_>, gv: &'ll Value, mut align: Align) {
diff --git a/compiler/rustc_codegen_ssa/src/mir/operand.rs b/compiler/rustc_codegen_ssa/src/mir/operand.rs
index 2896dfd5463..a639803ea60 100644
--- a/compiler/rustc_codegen_ssa/src/mir/operand.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/operand.rs
@@ -186,7 +186,7 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
         offset: Size,
     ) -> Self {
         let alloc_align = alloc.inner().align;
-        assert!(alloc_align >= layout.align.abi);
+        assert!(alloc_align >= layout.align.abi, "{alloc_align:?} < {:?}", layout.align.abi);
 
         let read_scalar = |start, size, s: abi::Scalar, ty| {
             match alloc.0.read_scalar(
diff --git a/compiler/rustc_const_eval/messages.ftl b/compiler/rustc_const_eval/messages.ftl
index 22a1894ee72..b767ca9a3c2 100644
--- a/compiler/rustc_const_eval/messages.ftl
+++ b/compiler/rustc_const_eval/messages.ftl
@@ -78,6 +78,8 @@ const_eval_dealloc_kind_mismatch =
 
 const_eval_deref_function_pointer =
     accessing {$allocation} which contains a function
+const_eval_deref_typeid_pointer =
+    accessing {$allocation} which contains a `TypeId`
 const_eval_deref_vtable_pointer =
     accessing {$allocation} which contains a vtable
 const_eval_division_by_zero =
diff --git a/compiler/rustc_const_eval/src/errors.rs b/compiler/rustc_const_eval/src/errors.rs
index 9133a5fc8ef..49cd7138748 100644
--- a/compiler/rustc_const_eval/src/errors.rs
+++ b/compiler/rustc_const_eval/src/errors.rs
@@ -475,6 +475,7 @@ impl<'a> ReportErrorExt for UndefinedBehaviorInfo<'a> {
             WriteToReadOnly(_) => const_eval_write_to_read_only,
             DerefFunctionPointer(_) => const_eval_deref_function_pointer,
             DerefVTablePointer(_) => const_eval_deref_vtable_pointer,
+            DerefTypeIdPointer(_) => const_eval_deref_typeid_pointer,
             InvalidBool(_) => const_eval_invalid_bool,
             InvalidChar(_) => const_eval_invalid_char,
             InvalidTag(_) => const_eval_invalid_tag,
@@ -588,7 +589,10 @@ impl<'a> ReportErrorExt for UndefinedBehaviorInfo<'a> {
                 diag.arg("has", has.bytes());
                 diag.arg("msg", format!("{msg:?}"));
             }
-            WriteToReadOnly(alloc) | DerefFunctionPointer(alloc) | DerefVTablePointer(alloc) => {
+            WriteToReadOnly(alloc)
+            | DerefFunctionPointer(alloc)
+            | DerefVTablePointer(alloc)
+            | DerefTypeIdPointer(alloc) => {
                 diag.arg("allocation", alloc);
             }
             InvalidBool(b) => {
diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics.rs b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
index 378ed6d0e10..ee5382af0b2 100644
--- a/compiler/rustc_const_eval/src/interpret/intrinsics.rs
+++ b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
@@ -4,8 +4,10 @@
 
 use std::assert_matches::assert_matches;
 
-use rustc_abi::Size;
+use rustc_abi::{FieldIdx, Size};
 use rustc_apfloat::ieee::{Double, Half, Quad, Single};
+use rustc_ast::Mutability;
+use rustc_middle::mir::interpret::{AllocId, AllocInit, alloc_range};
 use rustc_middle::mir::{self, BinOp, ConstValue, NonDivergingIntrinsic};
 use rustc_middle::ty::layout::TyAndLayout;
 use rustc_middle::ty::{Ty, TyCtxt};
@@ -29,6 +31,37 @@ pub(crate) fn alloc_type_name<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> ConstAll
     tcx.mk_const_alloc(alloc)
 }
 
+pub(crate) fn alloc_type_id<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> AllocId {
+    let size = Size::from_bytes(16);
+    let align = tcx.data_layout.pointer_align();
+    let mut alloc = Allocation::new(size, *align, AllocInit::Uninit, ());
+    let ptr_size = tcx.data_layout.pointer_size();
+    let type_id_hash = tcx.type_id_hash(ty).as_u128();
+    alloc
+        .write_scalar(
+            &tcx,
+            alloc_range(Size::ZERO, Size::from_bytes(16)),
+            Scalar::from_u128(type_id_hash),
+        )
+        .unwrap();
+
+    // Give the first pointer-size bytes provenance that knows about the type id
+
+    let alloc_id = tcx.reserve_and_set_type_id_alloc(ty);
+    let offset = alloc
+        .read_scalar(&tcx, alloc_range(Size::ZERO, ptr_size), false)
+        .unwrap()
+        .to_target_usize(&tcx)
+        .unwrap();
+    let ptr = Pointer::new(alloc_id.into(), Size::from_bytes(offset));
+    let val = Scalar::from_pointer(ptr, &tcx);
+    alloc.write_scalar(&tcx, alloc_range(Size::ZERO, ptr_size), val).unwrap();
+
+    alloc.mutability = Mutability::Not;
+
+    tcx.reserve_and_set_memory_alloc(tcx.mk_const_alloc(alloc))
+}
+
 impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     /// Returns `true` if emulation happened.
     /// Here we implement the intrinsics that are common to all Miri instances; individual machines can add their own
@@ -63,10 +96,52 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             sym::type_id => {
                 let tp_ty = instance.args.type_at(0);
                 ensure_monomorphic_enough(tcx, tp_ty)?;
-                let val = ConstValue::from_u128(tcx.type_id_hash(tp_ty).as_u128());
+                let alloc_id = alloc_type_id(tcx, tp_ty);
+                let val = ConstValue::Indirect { alloc_id, offset: Size::ZERO };
                 let val = self.const_val_to_op(val, dest.layout.ty, Some(dest.layout))?;
                 self.copy_op(&val, dest)?;
             }
+            sym::type_id_eq => {
+                // Both operands are `TypeId`, which is a newtype around an array of pointers.
+                // Project until we have the array elements.
+                let a_fields = self.project_field(&args[0], FieldIdx::ZERO)?;
+                let b_fields = self.project_field(&args[1], FieldIdx::ZERO)?;
+
+                let mut a_fields = self.project_array_fields(&a_fields)?;
+                let mut b_fields = self.project_array_fields(&b_fields)?;
+
+                let (_idx, a) = a_fields
+                    .next(self)?
+                    .expect("we know the layout of TypeId has at least 2 array elements");
+                let a = self.deref_pointer(&a)?;
+                let (a, offset_a) = self.get_ptr_type_id(a.ptr())?;
+
+                let (_idx, b) = b_fields
+                    .next(self)?
+                    .expect("we know the layout of TypeId has at least 2 array elements");
+                let b = self.deref_pointer(&b)?;
+                let (b, offset_b) = self.get_ptr_type_id(b.ptr())?;
+
+                let provenance_matches = a == b;
+
+                let mut eq_id = offset_a == offset_b;
+
+                while let Some((_, a)) = a_fields.next(self)? {
+                    let (_, b) = b_fields.next(self)?.unwrap();
+
+                    let a = self.read_target_usize(&a)?;
+                    let b = self.read_target_usize(&b)?;
+                    eq_id &= a == b;
+                }
+
+                if !eq_id && provenance_matches {
+                    throw_ub_format!(
+                        "type_id_eq: one of the TypeId arguments is invalid, the hash does not match the type it represents"
+                    )
+                }
+
+                self.write_scalar(Scalar::from_bool(provenance_matches), dest)?;
+            }
             sym::variant_count => {
                 let tp_ty = instance.args.type_at(0);
                 let ty = match tp_ty.kind() {
diff --git a/compiler/rustc_const_eval/src/interpret/memory.rs b/compiler/rustc_const_eval/src/interpret/memory.rs
index 524023b8104..bb301600135 100644
--- a/compiler/rustc_const_eval/src/interpret/memory.rs
+++ b/compiler/rustc_const_eval/src/interpret/memory.rs
@@ -15,9 +15,9 @@ use std::{fmt, ptr};
 use rustc_abi::{Align, HasDataLayout, Size};
 use rustc_ast::Mutability;
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
-use rustc_middle::bug;
 use rustc_middle::mir::display_allocation;
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
+use rustc_middle::{bug, throw_ub_format};
 use tracing::{debug, instrument, trace};
 
 use super::{
@@ -346,6 +346,13 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                         kind = "vtable",
                     )
                 }
+                Some(GlobalAlloc::TypeId { .. }) => {
+                    err_ub_custom!(
+                        fluent::const_eval_invalid_dealloc,
+                        alloc_id = alloc_id,
+                        kind = "typeid",
+                    )
+                }
                 Some(GlobalAlloc::Static(..) | GlobalAlloc::Memory(..)) => {
                     err_ub_custom!(
                         fluent::const_eval_invalid_dealloc,
@@ -615,6 +622,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             }
             Some(GlobalAlloc::Function { .. }) => throw_ub!(DerefFunctionPointer(id)),
             Some(GlobalAlloc::VTable(..)) => throw_ub!(DerefVTablePointer(id)),
+            Some(GlobalAlloc::TypeId { .. }) => throw_ub!(DerefTypeIdPointer(id)),
             None => throw_ub!(PointerUseAfterFree(id, CheckInAllocMsg::MemoryAccess)),
             Some(GlobalAlloc::Static(def_id)) => {
                 assert!(self.tcx.is_static(def_id));
@@ -896,7 +904,9 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             let (size, align) = global_alloc.size_and_align(*self.tcx, self.typing_env);
             let mutbl = global_alloc.mutability(*self.tcx, self.typing_env);
             let kind = match global_alloc {
-                GlobalAlloc::Static { .. } | GlobalAlloc::Memory { .. } => AllocKind::LiveData,
+                GlobalAlloc::TypeId { .. }
+                | GlobalAlloc::Static { .. }
+                | GlobalAlloc::Memory { .. } => AllocKind::LiveData,
                 GlobalAlloc::Function { .. } => bug!("We already checked function pointers above"),
                 GlobalAlloc::VTable { .. } => AllocKind::VTable,
             };
@@ -936,6 +946,19 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         }
     }
 
+    /// Takes a pointer that is the first chunk of a `TypeId` and return the type that its
+    /// provenance refers to, as well as the segment of the hash that this pointer covers.
+    pub fn get_ptr_type_id(
+        &self,
+        ptr: Pointer<Option<M::Provenance>>,
+    ) -> InterpResult<'tcx, (Ty<'tcx>, Size)> {
+        let (alloc_id, offset, _meta) = self.ptr_get_alloc_id(ptr, 0)?;
+        let GlobalAlloc::TypeId { ty } = self.tcx.global_alloc(alloc_id) else {
+            throw_ub_format!("type_id_eq: `TypeId` provenance is not a type id")
+        };
+        interp_ok((ty, offset))
+    }
+
     pub fn get_ptr_fn(
         &self,
         ptr: Pointer<Option<M::Provenance>>,
@@ -1197,6 +1220,9 @@ impl<'a, 'tcx, M: Machine<'tcx>> std::fmt::Debug for DumpAllocs<'a, 'tcx, M> {
                         Some(GlobalAlloc::VTable(ty, dyn_ty)) => {
                             write!(fmt, " (vtable: impl {dyn_ty} for {ty})")?;
                         }
+                        Some(GlobalAlloc::TypeId { ty }) => {
+                            write!(fmt, " (typeid for {ty})")?;
+                        }
                         Some(GlobalAlloc::Static(did)) => {
                             write!(fmt, " (static: {})", self.ecx.tcx.def_path_str(did))?;
                         }
diff --git a/compiler/rustc_const_eval/src/interpret/projection.rs b/compiler/rustc_const_eval/src/interpret/projection.rs
index 306697d4ec9..f72c4418081 100644
--- a/compiler/rustc_const_eval/src/interpret/projection.rs
+++ b/compiler/rustc_const_eval/src/interpret/projection.rs
@@ -296,7 +296,11 @@ where
         base: &'a P,
     ) -> InterpResult<'tcx, ArrayIterator<'a, 'tcx, M::Provenance, P>> {
         let abi::FieldsShape::Array { stride, .. } = base.layout().fields else {
-            span_bug!(self.cur_span(), "project_array_fields: expected an array layout");
+            span_bug!(
+                self.cur_span(),
+                "project_array_fields: expected an array layout, got {:#?}",
+                base.layout()
+            );
         };
         let len = base.len(self)?;
         let field_layout = base.layout().field(self, 0);
diff --git a/compiler/rustc_const_eval/src/interpret/validity.rs b/compiler/rustc_const_eval/src/interpret/validity.rs
index fc4d13af8c4..fc44490c96d 100644
--- a/compiler/rustc_const_eval/src/interpret/validity.rs
+++ b/compiler/rustc_const_eval/src/interpret/validity.rs
@@ -571,40 +571,42 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
                     let alloc_actual_mutbl =
                         global_alloc.mutability(*self.ecx.tcx, self.ecx.typing_env);
 
-                    if let GlobalAlloc::Static(did) = global_alloc {
-                        let DefKind::Static { nested, .. } = self.ecx.tcx.def_kind(did) else {
-                            bug!()
-                        };
-                        // Special handling for pointers to statics (irrespective of their type).
-                        assert!(!self.ecx.tcx.is_thread_local_static(did));
-                        assert!(self.ecx.tcx.is_static(did));
-                        // Mode-specific checks
-                        match ctfe_mode {
-                            CtfeValidationMode::Static { .. }
-                            | CtfeValidationMode::Promoted { .. } => {
-                                // We skip recursively checking other statics. These statics must be sound by
-                                // themselves, and the only way to get broken statics here is by using
-                                // unsafe code.
-                                // The reasons we don't check other statics is twofold. For one, in all
-                                // sound cases, the static was already validated on its own, and second, we
-                                // trigger cycle errors if we try to compute the value of the other static
-                                // and that static refers back to us (potentially through a promoted).
-                                // This could miss some UB, but that's fine.
-                                // We still walk nested allocations, as they are fundamentally part of this validation run.
-                                // This means we will also recurse into nested statics of *other*
-                                // statics, even though we do not recurse into other statics directly.
-                                // That's somewhat inconsistent but harmless.
-                                skip_recursive_check = !nested;
-                            }
-                            CtfeValidationMode::Const { .. } => {
-                                // If this is mutable memory or an `extern static`, there's no point in checking it -- we'd
-                                // just get errors trying to read the value.
-                                if alloc_actual_mutbl.is_mut() || self.ecx.tcx.is_foreign_item(did)
-                                {
-                                    skip_recursive_check = true;
+                    match global_alloc {
+                        GlobalAlloc::Static(did) => {
+                            let DefKind::Static { nested, .. } = self.ecx.tcx.def_kind(did) else {
+                                bug!()
+                            };
+                            assert!(!self.ecx.tcx.is_thread_local_static(did));
+                            assert!(self.ecx.tcx.is_static(did));
+                            match ctfe_mode {
+                                CtfeValidationMode::Static { .. }
+                                | CtfeValidationMode::Promoted { .. } => {
+                                    // We skip recursively checking other statics. These statics must be sound by
+                                    // themselves, and the only way to get broken statics here is by using
+                                    // unsafe code.
+                                    // The reasons we don't check other statics is twofold. For one, in all
+                                    // sound cases, the static was already validated on its own, and second, we
+                                    // trigger cycle errors if we try to compute the value of the other static
+                                    // and that static refers back to us (potentially through a promoted).
+                                    // This could miss some UB, but that's fine.
+                                    // We still walk nested allocations, as they are fundamentally part of this validation run.
+                                    // This means we will also recurse into nested statics of *other*
+                                    // statics, even though we do not recurse into other statics directly.
+                                    // That's somewhat inconsistent but harmless.
+                                    skip_recursive_check = !nested;
+                                }
+                                CtfeValidationMode::Const { .. } => {
+                                    // If this is mutable memory or an `extern static`, there's no point in checking it -- we'd
+                                    // just get errors trying to read the value.
+                                    if alloc_actual_mutbl.is_mut()
+                                        || self.ecx.tcx.is_foreign_item(did)
+                                    {
+                                        skip_recursive_check = true;
+                                    }
                                 }
                             }
                         }
+                        _ => (),
                     }
 
                     // If this allocation has size zero, there is no actual mutability here.
diff --git a/compiler/rustc_hir/src/lang_items.rs b/compiler/rustc_hir/src/lang_items.rs
index c11db63ba11..6347f1bfa71 100644
--- a/compiler/rustc_hir/src/lang_items.rs
+++ b/compiler/rustc_hir/src/lang_items.rs
@@ -274,6 +274,8 @@ language_item_table! {
     PartialOrd,              sym::partial_ord,         partial_ord_trait,          Target::Trait,          GenericRequirement::Exact(1);
     CVoid,                   sym::c_void,              c_void,                     Target::Enum,           GenericRequirement::None;
 
+    TypeId,                  sym::type_id,             type_id,                    Target::Struct,         GenericRequirement::None;
+
     // A number of panic-related lang items. The `panic` item corresponds to divide-by-zero and
     // various panic cases with `match`. The `panic_bounds_check` item is for indexing arrays.
     //
diff --git a/compiler/rustc_hir_analysis/src/check/intrinsic.rs b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
index cebf7d1b532..e3532ade32f 100644
--- a/compiler/rustc_hir_analysis/src/check/intrinsic.rs
+++ b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
@@ -93,6 +93,7 @@ fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: LocalDefId) -> hi
         | sym::three_way_compare
         | sym::discriminant_value
         | sym::type_id
+        | sym::type_id_eq
         | sym::select_unpredictable
         | sym::cold_path
         | sym::ptr_guaranteed_cmp
@@ -220,7 +221,13 @@ pub(crate) fn check_intrinsic_type(
         sym::needs_drop => (1, 0, vec![], tcx.types.bool),
 
         sym::type_name => (1, 0, vec![], Ty::new_static_str(tcx)),
-        sym::type_id => (1, 0, vec![], tcx.types.u128),
+        sym::type_id => {
+            (1, 0, vec![], tcx.type_of(tcx.lang_items().type_id().unwrap()).instantiate_identity())
+        }
+        sym::type_id_eq => {
+            let type_id = tcx.type_of(tcx.lang_items().type_id().unwrap()).instantiate_identity();
+            (0, 0, vec![type_id, type_id], tcx.types.bool)
+        }
         sym::offset => (2, 0, vec![param(0), param(1)], param(0)),
         sym::arith_offset => (
             1,
diff --git a/compiler/rustc_middle/src/mir/interpret/error.rs b/compiler/rustc_middle/src/mir/interpret/error.rs
index 8acb8fa9f80..71e0c943fbb 100644
--- a/compiler/rustc_middle/src/mir/interpret/error.rs
+++ b/compiler/rustc_middle/src/mir/interpret/error.rs
@@ -392,6 +392,8 @@ pub enum UndefinedBehaviorInfo<'tcx> {
     DerefFunctionPointer(AllocId),
     /// Trying to access the data behind a vtable pointer.
     DerefVTablePointer(AllocId),
+    /// Trying to access the actual type id.
+    DerefTypeIdPointer(AllocId),
     /// Using a non-boolean `u8` as bool.
     InvalidBool(u8),
     /// Using a non-character `u32` as character.
diff --git a/compiler/rustc_middle/src/mir/interpret/mod.rs b/compiler/rustc_middle/src/mir/interpret/mod.rs
index 0b2645013ba..bed99a4ff2a 100644
--- a/compiler/rustc_middle/src/mir/interpret/mod.rs
+++ b/compiler/rustc_middle/src/mir/interpret/mod.rs
@@ -103,6 +103,7 @@ enum AllocDiscriminant {
     Fn,
     VTable,
     Static,
+    Type,
 }
 
 pub fn specialized_encode_alloc_id<'tcx, E: TyEncoder<'tcx>>(
@@ -127,6 +128,11 @@ pub fn specialized_encode_alloc_id<'tcx, E: TyEncoder<'tcx>>(
             ty.encode(encoder);
             poly_trait_ref.encode(encoder);
         }
+        GlobalAlloc::TypeId { ty } => {
+            trace!("encoding {alloc_id:?} with {ty:#?}");
+            AllocDiscriminant::Type.encode(encoder);
+            ty.encode(encoder);
+        }
         GlobalAlloc::Static(did) => {
             assert!(!tcx.is_thread_local_static(did));
             // References to statics doesn't need to know about their allocations,
@@ -228,6 +234,12 @@ impl<'s> AllocDecodingSession<'s> {
                 trace!("decoded vtable alloc instance: {ty:?}, {poly_trait_ref:?}");
                 decoder.interner().reserve_and_set_vtable_alloc(ty, poly_trait_ref, CTFE_ALLOC_SALT)
             }
+            AllocDiscriminant::Type => {
+                trace!("creating typeid alloc ID");
+                let ty = Decodable::decode(decoder);
+                trace!("decoded typid: {ty:?}");
+                decoder.interner().reserve_and_set_type_id_alloc(ty)
+            }
             AllocDiscriminant::Static => {
                 trace!("creating extern static alloc ID");
                 let did = <DefId as Decodable<D>>::decode(decoder);
@@ -258,6 +270,9 @@ pub enum GlobalAlloc<'tcx> {
     Static(DefId),
     /// The alloc ID points to memory.
     Memory(ConstAllocation<'tcx>),
+    /// The first pointer-sized segment of a type id. On 64 bit systems, the 128 bit type id
+    /// is split into two segments, on 32 bit systems there are 4 segments, and so on.
+    TypeId { ty: Ty<'tcx> },
 }
 
 impl<'tcx> GlobalAlloc<'tcx> {
@@ -296,9 +311,10 @@ impl<'tcx> GlobalAlloc<'tcx> {
     pub fn address_space(&self, cx: &impl HasDataLayout) -> AddressSpace {
         match self {
             GlobalAlloc::Function { .. } => cx.data_layout().instruction_address_space,
-            GlobalAlloc::Static(..) | GlobalAlloc::Memory(..) | GlobalAlloc::VTable(..) => {
-                AddressSpace::ZERO
-            }
+            GlobalAlloc::TypeId { .. }
+            | GlobalAlloc::Static(..)
+            | GlobalAlloc::Memory(..)
+            | GlobalAlloc::VTable(..) => AddressSpace::ZERO,
         }
     }
 
@@ -334,7 +350,7 @@ impl<'tcx> GlobalAlloc<'tcx> {
                 }
             }
             GlobalAlloc::Memory(alloc) => alloc.inner().mutability,
-            GlobalAlloc::Function { .. } | GlobalAlloc::VTable(..) => {
+            GlobalAlloc::TypeId { .. } | GlobalAlloc::Function { .. } | GlobalAlloc::VTable(..) => {
                 // These are immutable.
                 Mutability::Not
             }
@@ -380,8 +396,10 @@ impl<'tcx> GlobalAlloc<'tcx> {
             GlobalAlloc::Function { .. } => (Size::ZERO, Align::ONE),
             GlobalAlloc::VTable(..) => {
                 // No data to be accessed here. But vtables are pointer-aligned.
-                return (Size::ZERO, tcx.data_layout.pointer_align().abi);
+                (Size::ZERO, tcx.data_layout.pointer_align().abi)
             }
+            // Fake allocation, there's nothing to access here
+            GlobalAlloc::TypeId { .. } => (Size::ZERO, Align::ONE),
         }
     }
 }
@@ -487,6 +505,11 @@ impl<'tcx> TyCtxt<'tcx> {
         self.reserve_and_set_dedup(GlobalAlloc::VTable(ty, dyn_ty), salt)
     }
 
+    /// Generates an [AllocId] for a [core::any::TypeId]. Will get deduplicated.
+    pub fn reserve_and_set_type_id_alloc(self, ty: Ty<'tcx>) -> AllocId {
+        self.reserve_and_set_dedup(GlobalAlloc::TypeId { ty }, 0)
+    }
+
     /// Interns the `Allocation` and return a new `AllocId`, even if there's already an identical
     /// `Allocation` with a different `AllocId`.
     /// Statics with identical content will still point to the same `Allocation`, i.e.,
diff --git a/compiler/rustc_middle/src/mir/pretty.rs b/compiler/rustc_middle/src/mir/pretty.rs
index e9f3fb6ac8d..8e403dfddae 100644
--- a/compiler/rustc_middle/src/mir/pretty.rs
+++ b/compiler/rustc_middle/src/mir/pretty.rs
@@ -1621,6 +1621,7 @@ pub fn write_allocations<'tcx>(
             Some(GlobalAlloc::VTable(ty, dyn_ty)) => {
                 write!(w, " (vtable: impl {dyn_ty} for {ty})")?
             }
+            Some(GlobalAlloc::TypeId { ty }) => write!(w, " (typeid for {ty})")?,
             Some(GlobalAlloc::Static(did)) if !tcx.is_foreign_item(did) => {
                 write!(w, " (static: {}", tcx.def_path_str(did))?;
                 if body.phase <= MirPhase::Runtime(RuntimePhase::PostCleanup)
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index 4e078847815..7c48a4b0885 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -1773,6 +1773,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
                         }
                         Some(GlobalAlloc::Function { .. }) => p!("<function>"),
                         Some(GlobalAlloc::VTable(..)) => p!("<vtable>"),
+                        Some(GlobalAlloc::TypeId { .. }) => p!("<typeid>"),
                         None => p!("<dangling pointer>"),
                     }
                     return Ok(());
diff --git a/compiler/rustc_monomorphize/src/collector.rs b/compiler/rustc_monomorphize/src/collector.rs
index 131064f9832..91c8e64ce9a 100644
--- a/compiler/rustc_monomorphize/src/collector.rs
+++ b/compiler/rustc_monomorphize/src/collector.rs
@@ -1219,6 +1219,7 @@ fn collect_alloc<'tcx>(tcx: TyCtxt<'tcx>, alloc_id: AllocId, output: &mut MonoIt
             ));
             collect_alloc(tcx, alloc_id, output)
         }
+        GlobalAlloc::TypeId { .. } => {}
     }
 }
 
diff --git a/compiler/rustc_passes/src/reachable.rs b/compiler/rustc_passes/src/reachable.rs
index 7e15267a953..b49e8118fe3 100644
--- a/compiler/rustc_passes/src/reachable.rs
+++ b/compiler/rustc_passes/src/reachable.rs
@@ -325,6 +325,7 @@ impl<'tcx> ReachableContext<'tcx> {
                         self.visit(args);
                     }
                 }
+                GlobalAlloc::TypeId { ty, .. } => self.visit(ty),
                 GlobalAlloc::Memory(alloc) => self.propagate_from_alloc(alloc),
             }
         }
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 09f01d8704e..4df91cc3429 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -2194,6 +2194,7 @@ symbols! {
         type_changing_struct_update,
         type_const,
         type_id,
+        type_id_eq,
         type_ir,
         type_ir_infer_ctxt_like,
         type_ir_inherent,
diff --git a/compiler/stable_mir/src/mir/alloc.rs b/compiler/stable_mir/src/mir/alloc.rs
index 0d45e59885c..9a94551f3ec 100644
--- a/compiler/stable_mir/src/mir/alloc.rs
+++ b/compiler/stable_mir/src/mir/alloc.rs
@@ -23,6 +23,9 @@ pub enum GlobalAlloc {
     Static(StaticDef),
     /// The alloc ID points to memory.
     Memory(Allocation),
+    /// The first pointer-sized segment of a type id. On 64 bit systems, the 128 bit type id
+    /// is split into two segments, on 32 bit systems there are 4 segments, and so on.
+    TypeId { ty: Ty },
 }
 
 impl From<AllocId> for GlobalAlloc {
diff --git a/compiler/stable_mir/src/unstable/convert/stable/mir.rs b/compiler/stable_mir/src/unstable/convert/stable/mir.rs
index f6f4706e40b..ad39fc37600 100644
--- a/compiler/stable_mir/src/unstable/convert/stable/mir.rs
+++ b/compiler/stable_mir/src/unstable/convert/stable/mir.rs
@@ -864,6 +864,9 @@ impl<'tcx> Stable<'tcx> for mir::interpret::GlobalAlloc<'tcx> {
             mir::interpret::GlobalAlloc::Memory(alloc) => {
                 GlobalAlloc::Memory(alloc.stable(tables, cx))
             }
+            mir::interpret::GlobalAlloc::TypeId { ty } => {
+                GlobalAlloc::TypeId { ty: ty.stable(tables, cx) }
+            }
         }
     }
 }