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When the same optimized allocation flows into both the `ref` and `expected` fields of a StructCmpxchg, we previously (arbitrarily) prioritized optimizing based on the flow through `expected`. But this optimization stores the `ref` in a scratch local and then creates a new struct.get of its value. Since the same optimized allocation is also flowing through the `ref` field, that means we end up trying to do a struct.get on a null, which traps. To fix the problem, prioritize doing the optimization based on the flow through `ref` instead. This drops the other expressions and does not introduce any new accesses of the optimized value. Fixes #8563.
tlively
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aheejin and
kripken
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a team
kripken
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Apr 1, 2026
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When the same optimized allocation flows into both the
refandexpectedfields of a StructCmpxchg, we previously (arbitrarily) prioritized optimizing based on the flow throughexpected. But this optimization stores therefin a scratch local and then creates a new struct.get of its value. Since the same optimized allocation is also flowing through thereffield, that means we end up trying to do a struct.get on a null, which traps. To fix the problem, prioritize doing the optimization based on the flow throughrefinstead. This drops the other expressions and does not introduce any new accesses of the optimized value.Fixes #8563.