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Do not flatten derefs with ProjectionElem::Index.

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This commit is contained in:
Camille Gillot 2025-08-07 02:22:24 +00:00
parent 8a87857320
commit ebd60b9b8f
3 changed files with 15 additions and 6 deletions
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15
compiler/rustc_mir_transform/src/gvn.rs
View file

@ -756,7 +756,13 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
&& let Some(v) = self.simplify_place_value(&mut pointee, location)
{
value = v;
place_ref = pointee.project_deeper(&place.projection[index..], self.tcx).as_ref();
// `pointee` holds a `Place`, so `ProjectionElem::Index` holds a `Local`.
// That local is SSA, but we otherwise have no guarantee on that local's value at
// the current location compared to its value where `pointee` was borrowed.
if pointee.projection.iter().all(|elem| !matches!(elem, ProjectionElem::Index(_))) {
place_ref =
pointee.project_deeper(&place.projection[index..], self.tcx).as_ref();
}
}
if let Some(local) = self.try_as_local(value, location) {
// Both `local` and `Place { local: place.local, projection: projection[..index] }`
@ -774,7 +780,12 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
&& let Some(v) = self.simplify_place_value(&mut pointee, location)
{
value = v;
place_ref = pointee.project_deeper(&[], self.tcx).as_ref();
// `pointee` holds a `Place`, so `ProjectionElem::Index` holds a `Local`.
// That local is SSA, but we otherwise have no guarantee on that local's value at
// the current location compared to its value where `pointee` was borrowed.
if pointee.projection.iter().all(|elem| !matches!(elem, ProjectionElem::Index(_))) {
place_ref = pointee.project_deeper(&[], self.tcx).as_ref();
}
}
if let Some(new_local) = self.try_as_local(value, location) {
place_ref = PlaceRef { local: new_local, projection: &[] };

3
tests/mir-opt/gvn.dereference_indexing.GVN.panic-abort.diff
View file

@ -43,8 +43,7 @@
+ nop;
StorageLive(_8);
StorageLive(_9);
- _9 = copy (*_3);
+ _9 = copy _1[_4];
_9 = copy (*_3);
_8 = opaque::<u8>(move _9) -> [return: bb2, unwind unreachable];
}

3
tests/mir-opt/gvn.dereference_indexing.GVN.panic-unwind.diff
View file

@ -43,8 +43,7 @@
+ nop;
StorageLive(_8);
StorageLive(_9);
- _9 = copy (*_3);
+ _9 = copy _1[_4];
_9 = copy (*_3);
_8 = opaque::<u8>(move _9) -> [return: bb2, unwind continue];
}