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[Custom Descriptors] Fix GTO after #7937 #7938

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Merged
merged 1 commit into from
Oct 2, 2025
Merged

[Custom Descriptors] Fix GTO after #7937 #7938

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12 changes: 12 additions & 0 deletions src/passes/GlobalTypeOptimization.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -761,6 +761,18 @@ struct GlobalTypeOptimization : public Pass {
curr->index = newIndex;
}

void visitRefCast(RefCast* curr) {
// Unreachable ref.cast_desc instructions would not have been counted as
// reading the descriptor field, so their descriptor operands may no
// longer be descriptors. This is invalid, so replace such casts
// entirely.
if (curr->type == Type::unreachable && curr->desc &&
curr->desc->type != Type::unreachable) {
assert(curr->ref->type == Type::unreachable);
replaceCurrent(curr->ref);
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Don't we need to drop the desc for any effects it might have?

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No, because the preceding ref operand is unreachable. The desc operand will never be executed.

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Oh right, thanks.

}
}

void visitFunction(Function* curr) {
if (needEHFixups) {
EHUtils::handleBlockNestedPops(curr, *getModule());
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31 changes: 31 additions & 0 deletions test/lit/passes/gto-desc.wast
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Expand Up @@ -1396,3 +1396,34 @@
)
)

;; We can optimize away the descriptor since its only use is unreachable, but
;; we must update that use to remain valid despite being unreachable.
(module
(rec
;; CHECK: (rec
;; CHECK-NEXT: (type $struct (sub (struct)))
(type $struct (sub (descriptor $desc (struct))))
;; CHECK: (type $desc (sub (struct)))
(type $desc (sub (describes $struct (struct))))
)
;; CHECK: (type $2 (func))

;; CHECK: (func $test (type $2)
;; CHECK-NEXT: (local $struct (ref $struct))
;; CHECK-NEXT: (local $desc (ref $desc))
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (unreachable)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $test
(local $struct (ref $struct))
(local $desc (ref $desc))
(drop
(ref.cast_desc (ref $struct)
(unreachable)
(struct.new $desc)
)
)
)
)

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