1 files changed, 27 insertions, 3 deletions
diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp
index 5f18beb73..9d50275b9 100644
--- a/src/passes/OptimizeInstructions.cpp
+++ b/src/passes/OptimizeInstructions.cpp
@@ -1494,11 +1494,35 @@ struct OptimizeInstructions
   }
 
   void visitRefEq(RefEq* curr) {
+    // The types may prove that the same reference cannot appear on both sides.
+    auto leftType = curr->left->type;
+    auto rightType = curr->right->type;
+    if (leftType == Type::unreachable || rightType == Type::unreachable) {
+      // Leave this for DCE.
+      return;
+    }
+    auto leftHeapType = leftType.getHeapType();
+    auto rightHeapType = rightType.getHeapType();
+    auto leftIsHeapSubtype = HeapType::isSubType(leftHeapType, rightHeapType);
+    auto rightIsHeapSubtype = HeapType::isSubType(rightHeapType, leftHeapType);
+    if (!leftIsHeapSubtype && !rightIsHeapSubtype &&
+        (leftType.isNonNullable() || rightType.isNonNullable())) {
+      // The heap types have no intersection, so the only thing that can
+      // possibly appear on both sides is null, but one of the two is non-
+      // nullable, which rules that out. So there is no way that the same
+      // reference can appear on both sides.
+      auto* result =
+        Builder(*getModule()).makeConst(Literal::makeZero(Type::i32));
+      replaceCurrent(getDroppedChildrenAndAppend(
+        curr, *getModule(), getPassOptions(), result));
+      return;
+    }
+
     // Equality does not depend on the type, so casts may be removable.
     //
-    // This is safe to do first because nothing else here cares about the type,
-    // and we consume the two input references, so removing a cast could not
-    // help our parents (see "notes on removing casts").
+    // This is safe to do first because nothing farther down cares about the
+    // type, and we consume the two input references, so removing a cast could
+    // not help our parents (see "notes on removing casts").
     skipCast(curr->left, Type::eqref);
     skipCast(curr->right, Type::eqref);