Auto merge of #93670 - erikdesjardins:noundef, r=nikic

Apply noundef attribute to &T, &mut T, Box<T>, bool

This doesn't handle `char` because it's a bit awkward to distinguish it from `u32` at this point in codegen.

Note that this _does not_ change whether or not it is UB for `&`, `&mut`, or `Box` to point to undef. It only applies to the pointer itself, not the pointed-to memory.

Fixes (partially) #74378.

r? `@nikic` cc `@RalfJung`

1 files changed, 6 insertions, 1 deletions

diff --git a/compiler/rustc_target/src/abi/call/mod.rs b/compiler/rustc_target/src/abi/call/mod.rs
index 0870b1054e4..34324a58297 100644
--- a/compiler/rustc_target/src/abi/call/mod.rs
+++ b/compiler/rustc_target/src/abi/call/mod.rs
@@ -74,6 +74,7 @@ mod attr_impl {
             // or not to actually emit the attribute. It can also be controlled
             // with the `-Zmutable-noalias` debugging option.
             const NoAliasMutRef = 1 << 6;
+            const NoUndef = 1 << 7;
         }
     }
 }
@@ -495,7 +496,11 @@ impl<'a, Ty> ArgAbi<'a, Ty> {
         // For non-immediate arguments the callee gets its own copy of
         // the value on the stack, so there are no aliases. It's also
         // program-invisible so can't possibly capture
-        attrs.set(ArgAttribute::NoAlias).set(ArgAttribute::NoCapture).set(ArgAttribute::NonNull);
+        attrs
+            .set(ArgAttribute::NoAlias)
+            .set(ArgAttribute::NoCapture)
+            .set(ArgAttribute::NonNull)
+            .set(ArgAttribute::NoUndef);
         attrs.pointee_size = layout.size;
         // FIXME(eddyb) We should be doing this, but at least on
         // i686-pc-windows-msvc, it results in wrong stack offsets.