diff options
Diffstat (limited to 'compiler')
4 files changed, 10 insertions, 26 deletions
diff --git a/compiler/rustc_const_eval/src/interpret/operand.rs b/compiler/rustc_const_eval/src/interpret/operand.rs index 80d4bda4827..4653c9016c6 100644 --- a/compiler/rustc_const_eval/src/interpret/operand.rs +++ b/compiler/rustc_const_eval/src/interpret/operand.rs @@ -260,8 +260,12 @@ impl<'tcx, Prov: Provenance> ImmTy<'tcx, Prov> { // This makes several assumptions about what layouts we will encounter; we match what // codegen does as good as we can (see `extract_field` in `rustc_codegen_ssa/src/mir/operand.rs`). let inner_val: Immediate<_> = match (**self, self.layout.abi) { - // if the entire value is uninit, then so is the field (can happen in ConstProp) + // If the entire value is uninit, then so is the field (can happen in ConstProp). (Immediate::Uninit, _) => Immediate::Uninit, + // If the field is uninhabited, we can forget the data (can happen in ConstProp). + // `enum S { A(!), B, C }` is an example of an enum with Scalar layout that + // has an `Uninhabited` variant, which means this case is possible. + _ if layout.abi.is_uninhabited() => Immediate::Uninit, // the field contains no information, can be left uninit // (Scalar/ScalarPair can contain even aligned ZST, not just 1-ZST) _ if layout.is_zst() => Immediate::Uninit, diff --git a/compiler/rustc_const_eval/src/interpret/projection.rs b/compiler/rustc_const_eval/src/interpret/projection.rs index bd60e066f72..3a441c1d649 100644 --- a/compiler/rustc_const_eval/src/interpret/projection.rs +++ b/compiler/rustc_const_eval/src/interpret/projection.rs @@ -201,25 +201,8 @@ where // see https://github.com/rust-lang/rust/issues/93688#issuecomment-1032929496.) // So we just "offset" by 0. let layout = base.layout().for_variant(self, variant); - // In the future we might want to allow this to permit code like this: - // (this is a Rust/MIR pseudocode mix) - // ``` - // enum Option2 { - // Some(i32, !), - // None, - // } - // - // fn panic() -> ! { panic!() } - // - // let x: Option2; - // x.Some.0 = 42; - // x.Some.1 = panic(); - // SetDiscriminant(x, Some); - // ``` - // However, for now we don't generate such MIR, and this check here *has* found real - // bugs (see https://github.com/rust-lang/rust/issues/115145), so we will keep rejecting - // it. - assert!(!layout.abi.is_uninhabited()); + // This variant may in fact be uninhabited. + // See <https://github.com/rust-lang/rust/issues/120337>. // This cannot be `transmute` as variants *can* have a smaller size than the entire enum. base.offset(Size::ZERO, layout, self) diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs index a5c229879a7..a4b6c4f9c3f 100644 --- a/compiler/rustc_middle/src/mir/syntax.rs +++ b/compiler/rustc_middle/src/mir/syntax.rs @@ -1074,6 +1074,8 @@ pub enum ProjectionElem<V, T> { /// "Downcast" to a variant of an enum or a coroutine. /// /// The included Symbol is the name of the variant, used for printing MIR. + /// + /// This operation itself is never UB, all it does is change the type of the place. Downcast(Option<Symbol>, VariantIdx), /// Like an explicit cast from an opaque type to a concrete type, but without diff --git a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs index d5f22b2cdbc..ad12bce9b02 100644 --- a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs +++ b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs @@ -403,12 +403,7 @@ impl<'a, 'tcx> ConstAnalysis<'a, 'tcx> { operand, &mut |elem, op| match elem { TrackElem::Field(idx) => self.ecx.project_field(op, idx.as_usize()).ok(), - TrackElem::Variant(idx) => { - if op.layout.for_variant(&self.ecx, idx).abi.is_uninhabited() { - return None; - } - self.ecx.project_downcast(op, idx).ok() - } + TrackElem::Variant(idx) => self.ecx.project_downcast(op, idx).ok(), TrackElem::Discriminant => { let variant = self.ecx.read_discriminant(op).ok()?; let discr_value = |