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, 4 deletions

diff --git a/compiler/rustc_codegen_gcc/src/common.rs b/compiler/rustc_codegen_gcc/src/common.rs
index 19127c7612d..b056b6d4730 100644
--- a/compiler/rustc_codegen_gcc/src/common.rs
+++ b/compiler/rustc_codegen_gcc/src/common.rs
@@ -158,14 +158,14 @@ impl<'gcc, 'tcx> ConstMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
     }
 
     fn scalar_to_backend(&self, cv: Scalar, layout: abi::Scalar, ty: Type<'gcc>) -> RValue<'gcc> {
-        let bitsize = if layout.is_bool() { 1 } else { layout.value.size(self).bits() };
+        let bitsize = if layout.is_bool() { 1 } else { layout.size(self).bits() };
         match cv {
             Scalar::Int(ScalarInt::ZST) => {
-                assert_eq!(0, layout.value.size(self).bytes());
+                assert_eq!(0, layout.size(self).bytes());
                 self.const_undef(self.type_ix(0))
             }
             Scalar::Int(int) => {
-                let data = int.assert_bits(layout.value.size(self));
+                let data = int.assert_bits(layout.size(self));
 
                 // FIXME(antoyo): there's some issues with using the u128 code that follows, so hard-code
                 // the paths for floating-point values.
@@ -209,7 +209,7 @@ impl<'gcc, 'tcx> ConstMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
                 let base_addr = self.const_bitcast(base_addr, self.usize_type);
                 let offset = self.context.new_rvalue_from_long(self.usize_type, offset.bytes() as i64);
                 let ptr = self.const_bitcast(base_addr + offset, ptr_type);
-                if layout.value != Pointer {
+                if layout.primitive() != Pointer {
                     self.const_bitcast(ptr.dereference(None).to_rvalue(), ty)
                 }
                 else {