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Explain that this is UB catching instead of malformed MIR.

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This commit is contained in:
Camille GILLOT 2023-02-25 16:29:06 +00:00
parent 9aa4f6acb2
commit bf46b9cb28
1 changed files with 7 additions and 0 deletions
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7
compiler/rustc_const_eval/src/transform/validate.rs
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@ -756,6 +756,13 @@ fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
} }
} }
StatementKind::StorageLive(local) => { StatementKind::StorageLive(local) => {
// We check that the local is not live when entering a `StorageLive` for it.
// 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.
if self.reachable_blocks.contains(location.block) { if self.reachable_blocks.contains(location.block) {
self.storage_liveness.seek_before_primary_effect(location); self.storage_liveness.seek_before_primary_effect(location);
let locals_with_storage = self.storage_liveness.get(); let locals_with_storage = self.storage_liveness.get();