WebAssembly · tlively · Mar 31, 2026 · Mar 31, 2026
@@ -3574,6 +3574,10 @@ void FunctionValidator::visitStructCmpxchg(StructCmpxchg* curr) {
  } else if (field.type.isRef()) {
    expectedExpectedType = Type(
      HeapTypes::eq.getBasic(field.type.getHeapType().getShared()), Nullable);
+    shouldBeSubType(field.type,
+                    expectedExpectedType,
+                    curr,
+                    "struct.atomic.rmw field type invalid for operation");
  } else {
    shouldBeTrue(
      false, curr, "struct.atomic.rmw field type invalid for operation");
@@ -4127,6 +4131,10 @@ void FunctionValidator::visitArrayCmpxchg(ArrayCmpxchg* curr) {
  } else if (element.type.isRef()) {
    expectedExpectedType = Type(
      HeapTypes::eq.getBasic(element.type.getHeapType().getShared()), Nullable);
+    shouldBeSubType(element.type,
+                    expectedExpectedType,
+                    curr,
+                    "array.atomic.rmw element type invalid for operation");
  } else {
    shouldBeTrue(
      false, curr, "array.atomic.rmw element type invalid for operation");

@@ -0,0 +1,59 @@
+;; RUN: not wasm-opt %s -all 2>&1 | filecheck %s
+
+(module
+  ;; Shared types
+  (type $struct-any (shared (struct (field (mut (ref null (shared any)))))))
+  (type $array-any (shared (array (mut (ref null (shared any))))))
+
+  ;; Negative cases for struct.atomic.rmw.cmpxchg
+  ;; Use eqref for expected and replacement to isolate the error to the field type.
+  (func $struct-cmpxchg-anyref (param $ref (ref $struct-any)) (param $eq (ref null (shared eq)))
+    (drop
+      (struct.atomic.rmw.cmpxchg $struct-any 0
+        (local.get $ref)
+        (local.get $eq)
+        (local.get $eq)
+      )
+    )
+  )
+  ;; CHECK: [wasm-validator error in function struct-cmpxchg-anyref] struct.atomic.rmw field type invalid for operation
+
+  ;; Negative case for array.atomic.rmw.cmpxchg
+  (func $array-cmpxchg-anyref (param $ref (ref $array-any)) (param $eq (ref null (shared eq)))
+    (drop
+      (array.atomic.rmw.cmpxchg $array-any
+        (local.get $ref)
+        (i32.const 0)
+        (local.get $eq)
+        (local.get $eq)
+      )
+    )
+  )
+  ;; CHECK: [wasm-validator error in function array-cmpxchg-anyref] array.atomic.rmw element type invalid for operation
+
+  ;; Unshared types
+  (type $struct-unshared-any (struct (field (mut anyref))))
+  (func $struct-cmpxchg-unshared-anyref (param $ref (ref $struct-unshared-any)) (param $eq eqref)
+    (drop
+      (struct.atomic.rmw.cmpxchg $struct-unshared-any 0
+        (local.get $ref)
+        (local.get $eq)
+        (local.get $eq)
+      )
+    )
+  )
+  ;; CHECK: [wasm-validator error in function struct-cmpxchg-unshared-anyref] struct.atomic.rmw field type invalid for operation
+
+  ;; Check that it still fails for non-i32/i64/reference types.
+  (type $struct-v128 (struct (field (mut v128))))
+  (func $struct-cmpxchg-v128 (param $ref (ref $struct-v128)) (param $eq v128)
+    (drop
+      (struct.atomic.rmw.cmpxchg $struct-v128 0
+        (local.get $ref)
+        (local.get $eq)
+        (local.get $eq)
+      )
+    )
+  )
+  ;; CHECK: [wasm-validator error in function struct-cmpxchg-v128] unexpected false: struct.atomic.rmw field type invalid for operation
+)