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Auto merge of #113892 - RalfJung:uninit-undef-poison, r=wesleywiser

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clarify MIR uninit vs LLVM undef/poison

In [this LLVM discussion](https://discourse.llvm.org/t/rfc-load-instruction-uninitialized-memory-semantics/67481) I learned that mapping our uninitialized memory in MIR to poison in LLVM would be quite problematic due to the lack of a byte type. I am not sure where to write down this insight but this seems like a reasonable start.
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bors 2023-07-21 19:32:17 +00:00
commit d908a5b08e
2 changed files with 7 additions and 1 deletions
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compiler/rustc_const_eval/src/interpret/operand.rs
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@ -31,7 +31,7 @@ pub enum Immediate<Prov: Provenance = AllocId> {
/// A pair of two scalar value (must have `ScalarPair` ABI where both fields are
/// `Scalar::Initialized`).
ScalarPair(Scalar<Prov>, Scalar<Prov>),
/// A value of fully uninitialized memory. Can have and size and layout.
/// A value of fully uninitialized memory. Can have arbitrary size and layout.
Uninit,
}