[Wasm GC] Handle uses of default values in LocalSubtyping (#4024)

It is ok to use the default value of a reference even if we refine the type,
as it would be a more specifically-typed null, and all nulls compare the
same. However, if the default is used then we *cannot* alter the type to
be non-nullable, as then we'd use a null where that is not allowed.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/tools/execution-results.h b/src/tools/execution-results.h
index aabbb4819..8fc4c2eed 100644
--- a/src/tools/execution-results.h
+++ b/src/tools/execution-results.h
@@ -144,7 +144,9 @@ struct ExecutionResults {
   }
 
   bool areEqual(Literal a, Literal b) {
-    if (a.type != b.type) {
+    // We allow nulls to have different types (as they compare equal regardless)
+    // but anything else must have an identical type.
+    if (a.type != b.type && !(a.isNull() && b.isNull())) {
       std::cout << "types not identical! " << a << " != " << b << '\n';
       return false;
     }