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Miri: extend comments on downcast operation

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This commit is contained in:
Ralf Jung 2022-02-22 19:09:11 -05:00
parent 68369a041c
commit d0192e6291
2 changed files with 6 additions and 2 deletions
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4
compiler/rustc_const_eval/src/interpret/operand.rs
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@ -405,10 +405,12 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
op: &OpTy<'tcx, M::PointerTag>,
variant: VariantIdx,
) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
// Downcasts only change the layout
Ok(match op.try_as_mplace() {
Ok(ref mplace) => self.mplace_downcast(mplace, variant)?.into(),
Err(..) => {
// Downcasts only change the layout.
// (In particular, no check about whether this is even the active variant -- that's by design,
// see https://github.com/rust-lang/rust/issues/93688#issuecomment-1032929496.)
let layout = op.layout.for_variant(self, variant);
OpTy { layout, ..*op }
}

4
compiler/rustc_const_eval/src/interpret/place.rs
View file

@ -479,7 +479,9 @@ where
base: &MPlaceTy<'tcx, M::PointerTag>,
variant: VariantIdx,
) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
// Downcasts only change the layout
// Downcasts only change the layout.
// (In particular, no check about whether this is even the active variant -- that's by design,
// see https://github.com/rust-lang/rust/issues/93688#issuecomment-1032929496.)
assert!(!base.meta.has_meta());
Ok(MPlaceTy { layout: base.layout.for_variant(self, variant), ..*base })
}