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Merged
tlively merged 2 commits into from
Apr 2, 2026
+136 −34
Merged

More ArrayCmpxchg expected opts in Heap2Local #8567

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9a370c0
More ArrayCmpxchg expected opts in Heap2Local
tlively Apr 2, 2026
8c3bbec
address review comments
tlively Apr 2, 2026
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63 changes: 30 additions & 33 deletions src/passes/Heap2Local.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -461,40 +461,31 @@ struct EscapeAnalyzer {
}
}
void visitArraySet(ArraySet* curr) {
if (!curr->index->is<Const>()) {
// Array operations on nonconstant indexes do not escape in the normal
// sense, but they do escape from our being able to analyze them, so
// stop as soon as we see one.
return;
}

// As StructGet.
if (curr->ref == child) {
// Arrays flowing into array operations on nonconstant indexes do not
// escape in the normal sense, but they do escape from our being able to
// analyze them, so stop as soon as we see one.
if (child == curr->ref && curr->index->is<Const>()) {
escapes = false;
fullyConsumes = true;
}
}
void visitArrayGet(ArrayGet* curr) {
if (!curr->index->is<Const>()) {
return;
if (child == curr->ref && curr->index->is<Const>()) {
escapes = false;
fullyConsumes = true;
}
escapes = false;
fullyConsumes = true;
}
void visitArrayRMW(ArrayRMW* curr) {
if (!curr->index->is<Const>()) {
return;
}
if (curr->ref == child) {
if (child == curr->ref && curr->index->is<Const>()) {
escapes = false;
fullyConsumes = true;
}
}
void visitArrayCmpxchg(ArrayCmpxchg* curr) {
if (!curr->index->is<Const>()) {
return;
}
if (curr->ref == child || curr->expected == child) {
// Allocations flowing into `expected` are fully consumed and
// optimizable even if the index is not constant.
if (child == curr->expected ||
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@kripken kripken Apr 2, 2026

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Worth a comment here I think, as in the PR description.

(child == curr->ref && curr->index->is<Const>())) {
escapes = false;
fullyConsumes = true;
}
Expand Down Expand Up @@ -1233,9 +1224,15 @@ struct Struct2Local : PostWalker<Struct2Local> {
auto refScratch = builder.addVar(func, refType);
auto* setRefScratch = builder.makeLocalSet(refScratch, curr->ref);
auto* getRefScratch = builder.makeLocalGet(refScratch, refType);

auto indexScratch = builder.addVar(func, Type::i32);
auto* setIndexScratch = builder.makeLocalSet(indexScratch, curr->index);
auto* getIndexScratch = builder.makeLocalGet(indexScratch, Type::i32);

auto* arrayGet = builder.makeArrayGet(
getRefScratch, curr->index, curr->order, curr->type);
getRefScratch, getIndexScratch, curr->order, curr->type);
auto* block = builder.makeBlock({setRefScratch,
setIndexScratch,
builder.makeDrop(curr->expected),
builder.makeDrop(curr->replacement),
arrayGet});
Expand Down Expand Up @@ -1467,20 +1464,20 @@ struct Array2Struct : PostWalker<Array2Struct> {
return;
}

auto index = getIndex(curr->index);
if (index >= numFields) {
replaceCurrent(builder.makeBlock({builder.makeDrop(curr->ref),
builder.makeDrop(curr->expected),
builder.makeDrop(curr->replacement),
builder.makeUnreachable()}));
refinalize = true;
return;
}

// The allocation might flow into `ref` or `expected`, but not
// `replacement`, because then it would be considered to have escaped.
if (analyzer.getInteraction(curr->ref) == ParentChildInteraction::Flows) {
// The accessed array is being optimzied. Convert the ArrayCmpxchg into a
auto index = getIndex(curr->index);
if (index >= numFields) {
replaceCurrent(builder.makeBlock({builder.makeDrop(curr->ref),
builder.makeDrop(curr->expected),
builder.makeDrop(curr->replacement),
builder.makeUnreachable()}));
refinalize = true;
return;
}

// The accessed array is being optimized. Convert the ArrayCmpxchg into a
// StructCmpxchg.
replaceCurrent(builder.makeStructCmpxchg(
index, curr->ref, curr->expected, curr->replacement, curr->order));
Expand Down
107 changes: 106 additions & 1 deletion test/lit/passes/heap2local-rmw.wast
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Original file line number Diff line number Diff line change
Expand Up @@ -1465,11 +1465,15 @@
;; CHECK: (func $array-cmpxchg-expected (type $1) (param $array (ref $array))
;; CHECK-NEXT: (local $1 eqref)
;; CHECK-NEXT: (local $2 (ref null $array))
;; CHECK-NEXT: (local $3 i32)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (block (result eqref)
;; CHECK-NEXT: (local.set $2
;; CHECK-NEXT: (local.get $array)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $3
;; CHECK-NEXT: (i32.const 0)
;; CHECK-NEXT: )
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (block (result nullref)
;; CHECK-NEXT: (local.set $1
Expand All @@ -1483,7 +1487,7 @@
;; CHECK-NEXT: )
;; CHECK-NEXT: (array.atomic.get $array
;; CHECK-NEXT: (local.get $2)
;; CHECK-NEXT: (i32.const 0)
;; CHECK-NEXT: (local.get $3)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
Expand All @@ -1504,3 +1508,104 @@
)
)
)

(module
;; CHECK: (type $array (array (mut eqref)))
(type $array (array (mut eqref)))
;; CHECK: (type $1 (func (param (ref $array))))

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

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

;; CHECK: (import "" "" (func $effect-i32 (type $2) (result i32)))
(import "" "" (func $effect-i32 (result i32)))
;; CHECK: (import "" "" (func $effect-eq (type $3) (result eqref)))
(import "" "" (func $effect-eq (result eqref)))

;; CHECK: (func $array-cmpxchg-expected-index-effect (type $1) (param $array (ref $array))
;; CHECK-NEXT: (local $1 eqref)
;; CHECK-NEXT: (local $2 (ref null $array))
;; CHECK-NEXT: (local $3 i32)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (block (result eqref)
;; CHECK-NEXT: (local.set $2
;; CHECK-NEXT: (local.get $array)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $3
;; CHECK-NEXT: (call $effect-i32)
;; CHECK-NEXT: )
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (block (result nullref)
;; CHECK-NEXT: (local.set $1
;; CHECK-NEXT: (ref.null none)
;; CHECK-NEXT: )
;; CHECK-NEXT: (ref.null none)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (call $effect-eq)
;; CHECK-NEXT: )
;; CHECK-NEXT: (array.atomic.get $array
;; CHECK-NEXT: (local.get $2)
;; CHECK-NEXT: (local.get $3)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $array-cmpxchg-expected-index-effect (param $array (ref $array))
(drop
;; The index is non-constant, but we can still optimize the expected
;; field. We must preserve the index and the order of its effects.
(array.atomic.rmw.cmpxchg $array
(local.get $array)
(call $effect-i32)
(array.new_default $array (i32.const 1))
(call $effect-eq)
)
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@kripken kripken Apr 2, 2026

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Is there a test for array.atomic.rmw.cmpxchg where we optimize the expected field but the index is out of bounds?

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@tlively tlively Apr 2, 2026

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The output will look the same, but I will add a test where the index is an OOB constant.

)
)

;; CHECK: (func $array-cmpxchg-expected-index-oob (type $1) (param $array (ref $array))
;; CHECK-NEXT: (local $1 eqref)
;; CHECK-NEXT: (local $2 (ref null $array))
;; CHECK-NEXT: (local $3 i32)
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (block (result eqref)
;; CHECK-NEXT: (local.set $2
;; CHECK-NEXT: (local.get $array)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $3
;; CHECK-NEXT: (i32.const -1)
;; CHECK-NEXT: )
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (block (result nullref)
;; CHECK-NEXT: (local.set $1
;; CHECK-NEXT: (ref.null none)
;; CHECK-NEXT: )
;; CHECK-NEXT: (ref.null none)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (call $effect-eq)
;; CHECK-NEXT: )
;; CHECK-NEXT: (array.atomic.get $array
;; CHECK-NEXT: (local.get $2)
;; CHECK-NEXT: (local.get $3)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $array-cmpxchg-expected-index-oob (param $array (ref $array))
(drop
;; Now the index is constant but surely out-of-bounds. We still optimize
;; the same, way leaving the array.atomic.get to trap.
(array.atomic.rmw.cmpxchg $array
(local.get $array)
(i32.const -1)
(array.new_default $array (i32.const 1))
(call $effect-eq)
)
)
)
)
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