[Wasm GC] RefEq(x, null) => RefIsNull(x) (#4066)

1 files changed, 12 insertions, 0 deletions

diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp
index 7d9111e0b..51a2095ea 100644
--- a/src/passes/OptimizeInstructions.cpp
+++ b/src/passes/OptimizeInstructions.cpp
@@ -1121,6 +1121,18 @@ struct OptimizeInstructions
     if (areConsecutiveInputsEqual(curr->left, curr->right)) {
       replaceCurrent(
         Builder(*getModule()).makeConst(Literal::makeOne(Type::i32)));
+      return;
+    }
+
+    // Canonicalize to the pattern of a null on the right-hand side, if there is
+    // one. This makes pattern matching simpler.
+    if (curr->left->is<RefNull>()) {
+      std::swap(curr->left, curr->right);
+    }
+
+    // RefEq of a value to Null can be replaced with RefIsNull.
+    if (curr->right->is<RefNull>()) {
+      replaceCurrent(Builder(*getModule()).makeRefIs(RefIsNull, curr->left));
     }
   }