Rollup merge of #99050 - JakobDegen:storage-docs, r=tmiasko
Clarify MIR semantics of storage statements Seems worthwhile to start closing out some of the less controversial open questions about MIR semantics. Hopefully this is fairly non-controversial - it's what we implement already, and I see no reason to do anything more restrictive. cc ``@tmiasko`` who commented on this when it was discussed in the original PR that added these docs.
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2 changed files with 18 additions and 12 deletions
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@ -206,7 +206,13 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
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}
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if self.reachable_blocks.contains(location.block) && context.is_use() {
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// Uses of locals must occur while the local's storage is allocated.
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// We check that the local is live whenever it is used. Technically, violating this
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// restriction is only UB and not actually indicative of not well-formed MIR. This means
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// that an optimization which turns MIR that already has UB into MIR that fails this
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// check is not necessarily wrong. However, we have no such optimizations at the moment,
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// and so we include this check anyway to help us catch bugs. If you happen to write an
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// optimization that might cause this to incorrectly fire, feel free to remove this
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// check.
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self.storage_liveness.seek_after_primary_effect(location);
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let locals_with_storage = self.storage_liveness.get();
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if !locals_with_storage.contains(local) {
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