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[Flatten] Use target block type for Switch temps - #9312
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When lowering a Switch with a concrete value, Flatten previously passed the switch value's type rather than the target block's type to getTempForBreakTarget. When the switch value had a narrower subtype than the target block (such as nullfuncref flowing to a funcref block), the break temp local was allocated with the narrower subtype, failing validation when the block read the local at the block's result type or when another branch wrote a supertype value. Look up findBreakTarget(name)->type for each Switch target, matching Break.
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This pull request fixes an issue in the Flatten pass where a br_table sending a subtype of its target block's result type would incorrectly allocate the break target local with the narrower sent value type instead of the target block's type. The fix retrieves the actual target block's type to allocate the local correctly. A corresponding test case switch_subtype has been added to verify this behavior. I have no further feedback to provide.
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Found relatively quickly by the fuzzer after #9303 landed. |
kripken
approved these changes
Oct 28, 2026
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When lowering a Switch with a concrete value, Flatten previously passed the switch value's type rather than the target block's type to getTempForBreakTarget. When the switch value had a narrower subtype than the target block (such as nullfuncref flowing to a funcref block), the break temp local was allocated with the narrower subtype, failing validation when the block read the local at the block's result type or when another branch wrote a supertype value. Look up findBreakTarget(name)->type for each Switch target, matching Break.