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Fix unreachable BrOn branch analysis #8970

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Fix unreachable BrOn branch analysis #8970

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4 changes: 1 addition & 3 deletions src/ir/effects.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1044,10 +1044,8 @@ class EffectAnalyzer {
}
void visitRefGetDesc(RefGetDesc* curr) { trapOnNull(curr->ref); }
void visitBrOn(BrOn* curr) {
if (trapOnNull(curr->desc)) {
return;
}
parent.breakTargets.insert(curr->name);
trapOnNull(curr->desc);
}
void visitStructNew(StructNew* curr) { trapOnNull(curr->desc); }
void visitStructGet(StructGet* curr) {
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64 changes: 64 additions & 0 deletions test/lit/passes/monomorphize-desc.wast
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Original file line number Diff line number Diff line change
@@ -0,0 +1,64 @@
;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.

;; RUN: foreach %s %t wasm-opt --monomorphize -all -S -o - | filecheck %s

(module
(rec
;; CHECK: (rec
;; CHECK-NEXT: (type $A (descriptor $B) (struct))
(type $A (descriptor $B) (struct))
;; CHECK: (type $B (describes $A) (struct))
(type $B (describes $A) (struct))
)

;; CHECK: (type $2 (func (param i32)))

;; CHECK: (type $3 (func (result anyref)))

;; CHECK: (type $4 (func (param nullref)))

;; CHECK: (func $target (type $2) (param $0 i32)
;; CHECK-NEXT: (nop)
;; CHECK-NEXT: )
(func $target (param i32)
)

;; CHECK: (func $test (type $3) (result anyref)
;; CHECK-NEXT: (block $block (result (ref $A))
;; CHECK-NEXT: (call $target_2
;; CHECK-NEXT: (block ;; (replaces unreachable BrOn we can't emit)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (ref.null none)
;; CHECK-NEXT: )
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (ref.null none)
;; CHECK-NEXT: )
;; CHECK-NEXT: (unreachable)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (unreachable)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $test (result anyref)
;; We can monomorphize the call to $target, pushing the ref.is_null into
;; $target_2. The parameter we send there is now nullref, so everything there
;; gets optimized away. In this function, after refinalizing we end up with
;; an unreachable br_on, and while doing so, we should not hit an internal

@tlively tlively Aug 7, 2026

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The br_on is not actually unreachable, right? It just unconditionally traps because of the null descriptor.

;; error on how we process that now-unreachable instruction.
(block $block (result (ref $A))
(call $target
(ref.is_null
(br_on_cast_desc_eq $block anyref (ref $A)
(ref.null none)
(ref.null none)
)
)
)
(unreachable)
)
)
)

;; CHECK: (func $target_2 (type $4) (param $0 nullref)
;; CHECK-NEXT: (nop)
;; CHECK-NEXT: )
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