Fix propagation bug in Unsubtyping - #8468
#8468Merged
tlively merged 2 commits intoMar 16, 2026
mainWebAssembly/binaryen:mainfrom
unsubtyping-fix-propagationWebAssembly/binaryen:unsubtyping-fix-propagationCopy head branch name to clipboard
Merged
Fix propagation bug in Unsubtyping#8468tlively merged 2 commits intomainWebAssembly/binaryen:mainfrom unsubtyping-fix-propagationWebAssembly/binaryen:unsubtyping-fix-propagationCopy head branch name to clipboard
tlively merged 2 commits into
mainWebAssembly/binaryen:mainfrom
unsubtyping-fix-propagationWebAssembly/binaryen:unsubtyping-fix-propagationCopy head branch name to clipboard
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Unsubtyping has to propagate a `subtypesExposedToJS` marker from supertypes to subtypes. It previously did this by propagating from supertype to subtype whenever a new subtyping relationship was found. But subtyping trees are not always built from top to bottom. In cases where the newly discovered subtype already had subtypes, the previous propagation scheme would fail to propagate to those transitive subtypes. Fix the problem by propagating to the full subtype tree rooted at a newly discovered subtype. Use a DFS over the tree and avoid traversing subtrees that have already been marked to avoid introducing possible quadratic behavior.
kripken
approved these changes
Mar 16, 2026
| ;; CHECK-NEXT: (unreachable) | ||
| ;; CHECK-NEXT: ) | ||
| (@binaryen.js.called) | ||
| (func $expose-structref (result anyref) |
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| (func $expose-structref (result anyref) | |
| (func $expose-anyref (result anyref) |
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Unsubtyping has to propagate a
subtypesExposedToJSmarker from supertypes to subtypes. It previously did this by propagating from supertype to subtype whenever a new subtyping relationship was found. But subtyping trees are not always built from top to bottom. In cases where the newly discovered subtype already had subtypes, the previous propagation scheme would fail to propagate to those transitive subtypes.Fix the problem by propagating to the full subtype tree rooted at a newly discovered subtype. Use a DFS over the tree and avoid traversing subtrees that have already been marked to avoid introducing possible quadratic behavior.