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Set branchesOut effect for call.without.effects #8695

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Set branchesOut effect for call.without.effects #8695

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3 changes: 3 additions & 0 deletions src/ir/effects.h
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Original file line number Diff line number Diff line change
Expand Up @@ -718,6 +718,9 @@ class EffectAnalyzer {

void visitCall(Call* curr) {
if (Intrinsics(parent.module).isCallWithoutEffects(curr)) {
if (curr->isReturn) {
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@kripken kripken May 12, 2026

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Suggested change
if (curr->isReturn) {
// The only effect this can have is to branch (which is an effect of the return, not the call).
if (curr->isReturn) {

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@kripken kripken May 12, 2026

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This explains why we special-case it.

parent.branchesOut = true;
}
return;
}

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21 changes: 21 additions & 0 deletions test/lit/passes/vacuum-intrinsics.wast
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Expand Up @@ -258,4 +258,25 @@
;; Helper function for the above.
(nop)
)

;; CHECK: (func $const (type $1) (result i32)
;; CHECK-NEXT: (i32.const 1)
;; CHECK-NEXT: )
(func $const (result i32)
(i32.const 1)
)

;; CHECK: (func $sets-branch-effect (type $1) (result i32)
;; CHECK-NEXT: (return_call $call.without.effects
;; CHECK-NEXT: (ref.func $const)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $sets-branch-effect (result i32)
;; $call-without-effects still has a branch effect, even though the callee
;; body is assumed to have no effects.
;; Without a branch effect, we'd be free to optimize this to (unreachable).
;; Also, we're free to optimize away the (unreachable).
(return_call $call.without.effects (ref.func $const))
(unreachable)
)
)
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