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[RemoveUnusedBrs] Skip BrOn when descriptor is unreachable - #9268
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In `RemoveUnusedBrs::optimizeGC`, `Optimizer` walks and optimizes `BrOn` expressions bottom-up without running `ReFinalize` until the walk completes. When an inner `BrOn` in the `desc` operand of a `BrOnCastDescEq` or `BrOnCastDescEqFail` is optimized into an unconditional branch, `curr->desc->type` becomes `Type::unreachable` while `curr->type` still holds its old reference type. If the outer `BrOn` then refines `curr->castType` and calls `curr->finalize()`, `curr->type` becomes `Type::unreachable`, causing `maybeCast(curr, oldType)` to fail its reference-type assertion. Check `curr->desc && curr->desc->type == Type::unreachable` in the early return at the start of `Optimizer::visitBrOn` alongside `curr->ref->type == Type::unreachable`.
tlively
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kripken
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Oct 16, 2026
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In
RemoveUnusedBrs::optimizeGC,Optimizerwalks and optimizesBrOnexpressions bottom-up without runningReFinalizeuntil the walk completes. When an innerBrOnin thedescoperand of aBrOnCastDescEqorBrOnCastDescEqFailis optimized into an unconditional branch,curr->desc->typebecomesType::unreachablewhilecurr->typestill holds its old reference type. If the outerBrOnthen refinescurr->castTypeand callscurr->finalize(),curr->typebecomesType::unreachable, causingmaybeCast(curr, oldType)to fail its reference-type assertion. Checkcurr->desc && curr->desc->type == Type::unreachablein the early return at the start ofOptimizer::visitBrOnalongsidecurr->ref->type == Type::unreachable.