Fix treeify soundness: never treeify (sink) effectful ops at all.#18
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The `last_non_pure` adjacency rule let a non-pure value (e.g. a load) be owned by its adjacent consumer; when that consumer's pure single-use chain was itself treeified under a later use, the load's code was emitted at the final owner's position, possibly sinking past intervening effects, including stores to the same address. Rather than build a full reordering analysis, this PR simply forces all non-pure ops to stay in-place as their own tree. This increases Wasm code size slightly (traffic through allocated locals to consume the result of every load), but in an optimizing Wasm engine the end result will be the same.
fitzgen
approved these changes
Jul 24, 2026
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The
last_non_pureadjacency rule let a non-pure value (e.g. a load) be owned by its adjacent consumer; when that consumer's pure single-use chain was itself treeified under a later use, the load's code was emitted at the final owner's position, possibly sinking past intervening effects, including stores to the same address.Rather than build a full reordering analysis, this PR simply forces all non-pure ops to stay in-place as their own tree. This increases Wasm code size slightly (traffic through allocated locals to consume the result of every load), but in an optimizing Wasm engine the end result will be the same.