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Fix scratch local when optimizing cmpxchg in Heap2Local #8496

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Merged
tlively merged 5 commits into from
Mar 21, 2026
+147 −4
Merged

Fix scratch local when optimizing cmpxchg in Heap2Local #8496

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a31e628
[WIP] Handle StructCmpxchg::expected in Heap2Local
tlively Mar 19, 2026
698251d
Fix staleness by updating parents
tlively Mar 19, 2026
f1cdca4
do less
tlively Mar 19, 2026
bf9d3b0
Fix scratch local when optimizing cmpxchg in Heap2Local
tlively Mar 19, 2026
36ca2f4
Merge branch 'main' into heap2local-nullable-expected-scratch
tlively Mar 21, 2026
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12 changes: 9 additions & 3 deletions src/passes/Heap2Local.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1175,9 +1175,15 @@ struct Struct2Local : PostWalker<Struct2Local> {
assert(!field.isPacked());

// Hold everything in scratch locals, just like for other RMW ops and
// struct.new.
// struct.new. Use a nullable (shared) eqref local for `expected` to
// accommodate any allowed optimized or unoptimized value there.
auto expectedType = type;
if (type.isRef()) {
expectedType =
Type(HeapTypes::eq.getBasic(type.getHeapType().getShared()), Nullable);
}
auto oldScratch = builder.addVar(func, type);
auto expectedScratch = builder.addVar(func, type);
auto expectedScratch = builder.addVar(func, expectedType);
auto replacementScratch = builder.addVar(func, type);
auto local = localIndexes[curr->index];

Expand All @@ -1189,7 +1195,7 @@ struct Struct2Local : PostWalker<Struct2Local> {

// Create the check for whether we should do the exchange.
auto* lhs = builder.makeLocalGet(local, type);
auto* rhs = builder.makeLocalGet(expectedScratch, type);
auto* rhs = builder.makeLocalGet(expectedScratch, expectedType);
Expression* pred;
if (type.isRef()) {
pred = builder.makeRefEq(lhs, rhs);
Expand Down
139 changes: 138 additions & 1 deletion test/lit/passes/heap2local-rmw.wast
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Expand Up @@ -590,7 +590,7 @@
;; CHECK: (func $rmw-cmpxchg-ref (type $4) (param $0 (ref null $struct)) (param $1 (ref null $struct)) (result (ref null $struct))
;; CHECK-NEXT: (local $2 (ref null $struct))
;; CHECK-NEXT: (local $3 (ref null $struct))
;; CHECK-NEXT: (local $4 (ref null $struct))
;; CHECK-NEXT: (local $4 eqref)
;; CHECK-NEXT: (local $5 (ref null $struct))
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (block (result nullref)
Expand Down Expand Up @@ -1146,3 +1146,140 @@
(unreachable)
)
)

(module
(rec
;; CHECK: (rec
;; CHECK-NEXT: (type $outer (struct (field (mut (ref $inner)))))
(type $outer (struct (field (mut (ref $inner)))))
;; CHECK: (type $inner (struct))
(type $inner (struct))

;; CHECK: (type $shared-outer (shared (struct (field (mut (ref $shared-inner))))))
(type $shared-outer (shared (struct (field (mut (ref $shared-inner))))))
;; CHECK: (type $shared-inner (shared (struct)))
(type $shared-inner (shared (struct)))
)

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

;; CHECK: (func $cmpxchg-non-nullable-field (type $4)
;; CHECK-NEXT: (local $0 (ref $inner))
;; CHECK-NEXT: (local $1 (ref $inner))
;; CHECK-NEXT: (local $2 (ref $inner))
;; CHECK-NEXT: (local $3 eqref)
;; CHECK-NEXT: (local $4 (ref $inner))
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (block (result (ref $inner))
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (block (result nullref)
;; CHECK-NEXT: (local.set $1
;; CHECK-NEXT: (struct.new_default $inner)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $0
;; CHECK-NEXT: (local.get $1)
;; CHECK-NEXT: )
;; CHECK-NEXT: (ref.null none)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $3
;; CHECK-NEXT: (block (result nullref)
;; CHECK-NEXT: (ref.null none)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $4
;; CHECK-NEXT: (struct.new_default $inner)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $2
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: (if
;; CHECK-NEXT: (ref.eq
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: (local.get $3)
;; CHECK-NEXT: )
;; CHECK-NEXT: (then
;; CHECK-NEXT: (local.set $0
;; CHECK-NEXT: (local.get $4)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.get $2)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $cmpxchg-non-nullable-field
(drop
(struct.atomic.rmw.cmpxchg $outer 0
;; When `ref` gets optimized, we need to make sure the scratch local for
;; `expected` is nullable, even though the operand and field are both
;; non-nullable. This avoids type errors when we later optimize the
;; `expected` field and make it a nullref.
(struct.new $outer
(struct.new_default $inner)
)
(struct.new_default $inner)
(struct.new_default $inner)
)
)
)

;; CHECK: (func $cmpxchg-non-nullable-field-shared (type $4)
;; CHECK-NEXT: (local $0 (ref $shared-inner))
;; CHECK-NEXT: (local $1 (ref $shared-inner))
;; CHECK-NEXT: (local $2 (ref $shared-inner))
;; CHECK-NEXT: (local $3 (ref null (shared eq)))
;; CHECK-NEXT: (local $4 (ref $shared-inner))
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (block (result (ref $shared-inner))
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (block (result (ref null (shared none)))
;; CHECK-NEXT: (local.set $1
;; CHECK-NEXT: (struct.new_default $shared-inner)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $0
;; CHECK-NEXT: (local.get $1)
;; CHECK-NEXT: )
;; CHECK-NEXT: (ref.null (shared none))
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $3
;; CHECK-NEXT: (block (result (ref null (shared none)))
;; CHECK-NEXT: (ref.null (shared none))
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $4
;; CHECK-NEXT: (struct.new_default $shared-inner)
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.set $2
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: (if
;; CHECK-NEXT: (ref.eq
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: (local.get $3)
;; CHECK-NEXT: )
;; CHECK-NEXT: (then
;; CHECK-NEXT: (local.set $0
;; CHECK-NEXT: (local.get $4)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (local.get $2)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $cmpxchg-non-nullable-field-shared
(drop
(struct.atomic.rmw.cmpxchg $shared-outer 0
;; Same, but now with shared types. The scratch local must be a shared
;; eqref.
(struct.new $shared-outer
(struct.new_default $shared-inner)
)
(struct.new_default $shared-inner)
(struct.new_default $shared-inner)
)
)
)
)
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