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[RemoveUnusedBrs] Skip BrOn when descriptor is unreachable #9268

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Merged
tlively merged 1 commit into from
Oct 16, 2026
Merged

[RemoveUnusedBrs] Skip BrOn when descriptor is unreachable #9268

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11 changes: 6 additions & 5 deletions src/passes/RemoveUnusedBrs.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -855,12 +855,13 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {

void visitBrOn(BrOn* curr) {
// Ignore unreachable BrOns which we cannot improve anyhow. Note that
// we must check the ref field manually, as we may be changing types as
// we go here. (Another option would be to use a TypeUpdater here
// instead of calling ReFinalize at the very end, but that would be more
// complex and slower.)
// we must check the ref and desc fields manually, as we may be changing
// types as we go here. (Another option would be to use a TypeUpdater
// here instead of calling ReFinalize at the very end, but that would be
// more complex and slower.)
if (curr->type == Type::unreachable ||
curr->ref->type == Type::unreachable) {
curr->ref->type == Type::unreachable ||
(curr->desc && curr->desc->type == Type::unreachable)) {
return;
}

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32 changes: 32 additions & 0 deletions test/lit/passes/remove-unused-brs-desc.wast
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Expand Up @@ -783,4 +783,36 @@
)
)
)

;; CHECK: (func $unreachable-desc (type $17) (param $any anyref) (param $d (ref (exact $super.desc))) (result anyref)
;; CHECK-NEXT: (block $block (result (ref (exact $super.desc)))
;; CHECK-NEXT: (block (result (ref (exact $super.desc)))
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (local.tee $any
;; CHECK-NEXT: (ref.i31
;; CHECK-NEXT: (i32.const 0)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.get $d)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $unreachable-desc (param $any anyref) (param $d (ref (exact $super.desc))) (result anyref)
;; The inner br_on_cast is optimized into an unconditional br, making the
;; descriptor operand of the outer br_on_cast_desc_eq unreachable before
;; ReFinalize runs.
(block $block (result anyref)
(br_on_cast_desc_eq $block anyref (ref null (exact $super))
(local.tee $any
(ref.i31
(i32.const 0)
)
)
(br_on_cast $block (ref (exact $super.desc)) (ref (exact $super.desc))
(local.get $d)
)
)
)
)
)
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