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Auto merge of #100064 - RalfJung:disaligned, r=petrochenkov

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fix is_disaligned logic for nested packed structs

https://github.com/rust-lang/rust/pull/83605 broke the `is_disaligned` logic by bailing out of the loop in `is_within_packed` early. This PR fixes that problem and adds suitable tests.

Fixes https://github.com/rust-lang/rust/issues/99838
This commit is contained in:
bors 2022-08-03 16:09:56 +00:00
commit d6b96b61e7
4 changed files with 162 additions and 17 deletions
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28
compiler/rustc_const_eval/src/util/alignment.rs
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@ -48,20 +48,16 @@ fn is_within_packed<'tcx, L>(
where
L: HasLocalDecls<'tcx>,
{
for (place_base, elem) in place.iter_projections().rev() {
match elem {
// encountered a Deref, which is ABI-aligned
ProjectionElem::Deref => break,
ProjectionElem::Field(..) => {
let ty = place_base.ty(local_decls, tcx).ty;
match ty.kind() {
ty::Adt(def, _) => return def.repr().pack,
_ => {}
}
}
_ => {}
}
}
None
place
.iter_projections()
.rev()
// Stop at `Deref`; standard ABI alignment applies there.
.take_while(|(_base, elem)| !matches!(elem, ProjectionElem::Deref))
// Consider the packed alignments at play here...
.filter_map(|(base, _elem)| {
base.ty(local_decls, tcx).ty.ty_adt_def().and_then(|adt| adt.repr().pack)
})
// ... and compute their minimum.
// The overall smallest alignment is what matters.
.min()
}