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Rollup merge of #135182 - scottmcm:box-deref-via-transmute, r=oli-obk

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Transmute from NonNull to pointer when elaborating a box deref (MCP807)

Since per https://github.com/rust-lang/compiler-team/issues/807 we have to stop projecting into `NonNull`.

cc https://github.com/rust-lang/rust/issues/133652
This commit is contained in:
Guillaume Gomez 2025-01-07 15:30:25 +01:00 • committed by GitHub
commit a33da79fa9
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12 changed files with 29 additions and 28 deletions
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27
compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
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@ -29,13 +29,8 @@ fn build_ptr_tys<'tcx>(
pub(super) fn build_projection<'tcx>(
unique_ty: Ty<'tcx>,
nonnull_ty: Ty<'tcx>,
ptr_ty: Ty<'tcx>,
) -> [PlaceElem<'tcx>; 3] {
[
PlaceElem::Field(FieldIdx::ZERO, unique_ty),
PlaceElem::Field(FieldIdx::ZERO, nonnull_ty),
PlaceElem::Field(FieldIdx::ZERO, ptr_ty),
]
) -> [PlaceElem<'tcx>; 2] {
[PlaceElem::Field(FieldIdx::ZERO, unique_ty), PlaceElem::Field(FieldIdx::ZERO, nonnull_ty)]
}
struct ElaborateBoxDerefVisitor<'a, 'tcx> {
@ -75,10 +70,14 @@ impl<'a, 'tcx> MutVisitor<'tcx> for ElaborateBoxDerefVisitor<'a, 'tcx> {
self.patch.add_assign(
location,
Place::from(ptr_local),
Rvalue::Use(Operand::Copy(
Place::from(place.local)
.project_deeper(&build_projection(unique_ty, nonnull_ty, ptr_ty), tcx),
)),
Rvalue::Cast(
CastKind::Transmute,
Operand::Copy(
Place::from(place.local)
.project_deeper(&build_projection(unique_ty, nonnull_ty), tcx),
),
ptr_ty,
),
);
place.local = ptr_local;
@ -133,8 +132,10 @@ impl<'tcx> crate::MirPass<'tcx> for ElaborateBoxDerefs {
let (unique_ty, nonnull_ty, ptr_ty) =
build_ptr_tys(tcx, boxed_ty, unique_did, nonnull_did);
new_projections
.extend_from_slice(&build_projection(unique_ty, nonnull_ty, ptr_ty));
new_projections.extend_from_slice(&build_projection(unique_ty, nonnull_ty));
// While we can't project into `NonNull<_>` in a basic block
// due to MCP#807, this is debug info where it's fine.
new_projections.push(PlaceElem::Field(FieldIdx::ZERO, ptr_ty));
new_projections.push(PlaceElem::Deref);
} else if let Some(new_projections) = new_projections.as_mut() {
// Keep building up our projections list once we've started it.