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

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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`
This commit is contained in:
bors 2022-02-13 00:14:52 +00:00
commit 5c30d65683
13 changed files with 94 additions and 91 deletions
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8
compiler/rustc_middle/src/ty/layout.rs
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@ -3051,9 +3051,10 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
layout: TyAndLayout<'tcx>,
offset: Size,
is_return: bool| {
// Booleans are always an i1 that needs to be zero-extended.
// Booleans are always a noundef i1 that needs to be zero-extended.
if scalar.is_bool() {
attrs.ext(ArgExtension::Zext);
attrs.set(ArgAttribute::NoUndef);
return;
}
@ -3078,6 +3079,11 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
_ => pointee.size,
};
// `Box`, `&T`, and `&mut T` cannot be undef.
// Note that this only applies to the value of the pointer itself;
// this attribute doesn't make it UB for the pointed-to data to be undef.
attrs.set(ArgAttribute::NoUndef);
// `Box` pointer parameters never alias because ownership is transferred
// `&mut` pointer parameters never alias other parameters,
// or mutable global data