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Clarify MIR semantics of storage statements

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This commit is contained in:
Jakob Degen 2022-07-08 00:58:48 -07:00
parent 7665c35430
commit 4939f6c64b
2 changed files with 18 additions and 12 deletions
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8
compiler/rustc_const_eval/src/transform/validate.rs
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@ -205,7 +205,13 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
}
if self.reachable_blocks.contains(location.block) && context.is_use() {
// Uses of locals must occur while the local's storage is allocated.
// We check that the local is live whenever it is used. Technically, violating this
// restriction is only UB and not actually indicative of not well-formed MIR. This means
// that an optimization which turns MIR that already has UB into MIR that fails this
// check is not necessarily wrong. However, we have no such optimizations at the moment,
// and so we include this check anyway to help us catch bugs. If you happen to write an
// optimization that might cause this to incorrectly fire, feel free to remove this
// check.
self.storage_liveness.seek_after_primary_effect(location);
let locals_with_storage = self.storage_liveness.get();
if !locals_with_storage.contains(local) {