From d0192e62914f3ca48314f5f04a1a9e9c486e8f3e Mon Sep 17 00:00:00 2001 From: Ralf Jung Date: Tue, 22 Feb 2022 19:09:11 -0500 Subject: [PATCH] Miri: extend comments on downcast operation --- compiler/rustc_const_eval/src/interpret/operand.rs | 4 +++- compiler/rustc_const_eval/src/interpret/place.rs | 4 +++- 2 files changed, 6 insertions(+), 2 deletions(-) diff --git a/compiler/rustc_const_eval/src/interpret/operand.rs b/compiler/rustc_const_eval/src/interpret/operand.rs index bc4dca4c146..cd147b03bca 100644 --- a/compiler/rustc_const_eval/src/interpret/operand.rs +++ b/compiler/rustc_const_eval/src/interpret/operand.rs @@ -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 } } diff --git a/compiler/rustc_const_eval/src/interpret/place.rs b/compiler/rustc_const_eval/src/interpret/place.rs index e9b2df53a33..b1784b12c65 100644 --- a/compiler/rustc_const_eval/src/interpret/place.rs +++ b/compiler/rustc_const_eval/src/interpret/place.rs @@ -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 }) }