diff options
Diffstat (limited to 'compiler/rustc_mir_transform/src/jump_threading.rs')
| -rw-r--r-- | compiler/rustc_mir_transform/src/jump_threading.rs | 31 |
1 files changed, 7 insertions, 24 deletions
diff --git a/compiler/rustc_mir_transform/src/jump_threading.rs b/compiler/rustc_mir_transform/src/jump_threading.rs index beed007589b..8feb90ff7a0 100644 --- a/compiler/rustc_mir_transform/src/jump_threading.rs +++ b/compiler/rustc_mir_transform/src/jump_threading.rs @@ -35,7 +35,6 @@ //! Likewise, applying the optimisation can create a lot of new MIR, so we bound the instruction //! cost by `MAX_COST`. -use rustc_abi::{TagEncoding, Variants}; use rustc_arena::DroplessArena; use rustc_const_eval::const_eval::DummyMachine; use rustc_const_eval::interpret::{ImmTy, Immediate, InterpCx, OpTy, Projectable}; @@ -565,31 +564,15 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> { StatementKind::SetDiscriminant { box place, variant_index } => { let Some(discr_target) = self.map.find_discr(place.as_ref()) else { return }; let enum_ty = place.ty(self.body, self.tcx).ty; - // `SetDiscriminant` may be a no-op if the assigned variant is the untagged variant - // of a niche encoding. If we cannot ensure that we write to the discriminant, do - // nothing. - let Ok(enum_layout) = self.ecx.layout_of(enum_ty) else { + // `SetDiscriminant` guarantees that the discriminant is now `variant_index`. + // Even if the discriminant write does nothing due to niches, it is UB to set the + // discriminant when the data does not encode the desired discriminant. + let Some(discr) = + self.ecx.discriminant_for_variant(enum_ty, *variant_index).discard_err() + else { return; }; - let writes_discriminant = match enum_layout.variants { - Variants::Single { index } => { - assert_eq!(index, *variant_index); - true - } - Variants::Multiple { tag_encoding: TagEncoding::Direct, .. } => true, - Variants::Multiple { - tag_encoding: TagEncoding::Niche { untagged_variant, .. }, - .. - } => *variant_index != untagged_variant, - }; - if writes_discriminant { - let Some(discr) = - self.ecx.discriminant_for_variant(enum_ty, *variant_index).discard_err() - else { - return; - }; - self.process_immediate(bb, discr_target, discr, state); - } + self.process_immediate(bb, discr_target, discr, state); } // If we expect `lhs ?= true`, we have an opportunity if we assume `lhs == true`. StatementKind::Intrinsic(box NonDivergingIntrinsic::Assume( |