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Auto merge of #118482 - RalfJung:interpret-local-type, r=WaffleLapkin

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explain a good reason for why LocalValue does not store the type of the local

As found out by `@lcnr` in https://github.com/rust-lang/rust/pull/112307, storing the type here can lead to subtle bugs when it gets out of sync with the MIR body. That's not the reason why the interpreter does it this way I think, but good thing we dodged that bullet. :)
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bors 2023-12-01 04:08:22 +00:00
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compiler/rustc_const_eval/src/interpret/eval_context.rs
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@ -173,6 +173,9 @@ impl<Prov: Provenance> std::fmt::Debug for LocalState<'_, Prov> {
}
/// Current value of a local variable
///
/// This does not store the type of the local; the type is given by `body.local_decls` and can never
/// change, so by not storing here we avoid having to maintain that as an invariant.
#[derive(Copy, Clone, Debug)] // Miri debug-prints these
pub(super) enum LocalValue<Prov: Provenance = AllocId> {
/// This local is not currently alive, and cannot be used at all.