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[Heap2Local] Fix cmpxchg with same ref and expected - #9333
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When a non-escaping struct allocation flows into both the `ref` and `expected` operands of a `struct.atomic.rmw.cmpxchg`, Struct2Local replaces `expected` with a dummy `ref.null` before visiting the cmpxchg. Previously, `visitStructCmpxchg` checked whether the allocation flowed into `ref` and emitted a `ref.eq` comparison between the field local and `expected`, which ended up comparing the field local against `null` and spuriously writing `replacement` into the field local whenever the field held `null`. Since a non-escaping allocation can never be stored into any struct field, the cmpxchg comparison against `expected` can never succeed; fix this by just dropping the cmpxchg children and reading the field local when the allocation flows into both `ref` and `expected`.
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This pull request optimizes struct.atomic.rmw.cmpxchg operations within the Heap2Local pass when the expected operand flows from an unescaped allocation. Because the allocation does not escape, it cannot match the value already in the struct, allowing the cmpxchg to be simplified to a read operation that drops its operands and retrieves the local variable. Corresponding test cases have been updated and added in heap2local-rmw.wast to validate this optimization. There are no review comments, so I have no feedback to provide.
aheejin
approved these changes
Nov 2, 2026
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When a non-escaping struct allocation flows into both the
refandexpectedoperands of astruct.atomic.rmw.cmpxchg, Struct2Local replacesexpectedwith a dummyref.nullbefore visiting the cmpxchg. Previously,visitStructCmpxchgchecked whether the allocation flowed intorefand emitted aref.eqcomparison between the field local andexpected, which ended up comparing the field local againstnulland spuriously writingreplacementinto the field local whenever the field heldnull. Since a non-escaping allocation can never be stored into any struct field, the cmpxchg comparison againstexpectedcan never succeed; fix this by just dropping the cmpxchg children and reading the field local when the allocation flows into bothrefandexpected.