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add test for GVN issue; cleanup in dataflow_const_prop

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Ralf Jung 2024-01-26 10:30:46 +01:00
parent 1025a12b64
commit 64cd13ff3b
5 changed files with 98 additions and 7 deletions
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6
compiler/rustc_const_eval/src/interpret/operand.rs
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@ -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,