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Rollup merge of #126154 - RalfJung:storage-live, r=compiler-errors

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StorageLive: refresh storage (instead of UB) when local is already live

Blocked on [this FCP](https://github.com/rust-lang/rust/issues/99160#issuecomment-2155924538), which also contains the motivation.

Fixes https://github.com/rust-lang/rust/issues/99160
Fixes https://github.com/rust-lang/rust/issues/98896 (by declaring it not-a-bug)
Fixes https://github.com/rust-lang/rust/issues/119366
Fixes https://github.com/rust-lang/unsafe-code-guidelines/issues/129
This commit is contained in:
León Orell Valerian Liehr 2024-06-19 13:04:58 +02:00 • committed by GitHub
commit 035285b464
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7 changed files with 71 additions and 11 deletions
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8
compiler/rustc_const_eval/src/interpret/eval_context.rs
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@ -1100,11 +1100,9 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
Operand::Immediate(Immediate::Uninit)
});
// StorageLive expects the local to be dead, and marks it live.
// If the local is already live, deallocate its old memory.
let old = mem::replace(&mut self.frame_mut().locals[local].value, local_val);
if !matches!(old, LocalValue::Dead) {
throw_ub_custom!(fluent::const_eval_double_storage_live);
}
self.deallocate_local(old)?;
Ok(())
}
@ -1118,7 +1116,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
assert!(local != mir::RETURN_PLACE, "Cannot make return place dead");
trace!("{:?} is now dead", local);
// It is entirely okay for this local to be already dead (at least that's how we currently generate MIR)
// If the local is already dead, this is a NOP.
let old = mem::replace(&mut self.frame_mut().locals[local].value, LocalValue::Dead);
self.deallocate_local(old)?;
Ok(())