Auto merge of #94527 - oli-obk:undef_scalars, r=nagisa,erikdesjardin

Let CTFE to handle partially uninitialized unions without marking the entire value as uninitialized.

follow up to #94411

To fix https://github.com/rust-lang/rust/issues/69488 and by extension fix https://github.com/rust-lang/rust/issues/94371, we should stop treating types like `MaybeUninit<usize>` as something that the `Scalar` type in the interpreter engine can represent. So we add a new field to `abi::Primitive` that records whether the primitive is nested in a union

cc `@RalfJung`

r? `@ghost`

1 files changed, 4 insertions, 1 deletions

diff --git a/compiler/rustc_codegen_llvm/src/consts.rs b/compiler/rustc_codegen_llvm/src/consts.rs
index 413ef0ba764..cb4073528e1 100644
--- a/compiler/rustc_codegen_llvm/src/consts.rs
+++ b/compiler/rustc_codegen_llvm/src/consts.rs
@@ -109,7 +109,10 @@ pub fn const_alloc_to_llvm<'ll>(cx: &CodegenCx<'ll, '_>, alloc: ConstAllocation<
                 Pointer::new(alloc_id, Size::from_bytes(ptr_offset)),
                 &cx.tcx,
             ),
-            Scalar { value: Primitive::Pointer, valid_range: WrappingRange { start: 0, end: !0 } },
+            Scalar::Initialized {
+                value: Primitive::Pointer,
+                valid_range: WrappingRange::full(dl.pointer_size),
+            },
             cx.type_i8p_ext(address_space),
         ));
         next_offset = offset + pointer_size;