[Wasm GC] Generalize `skipCast` to work with all type hierarchies (#5422)

`skipCast` takes an optional parameter that bounds how general the resulting
type is allowed to be. That parameter previously had a default value of `anyref`
with the intention of allowing all casts to be skipped, but that default
inadvertently prevented any casts in the `func` or `extern` type hierarchies
from being skipped. Update `skipCast` so that the default parameter allows all
casts to be skipped in all hierarchies.

1 files changed, 5 insertions, 4 deletions

diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp
index 6d4b7b674..bbb497f39 100644
--- a/src/passes/OptimizeInstructions.cpp
+++ b/src/passes/OptimizeInstructions.cpp
@@ -1495,20 +1495,21 @@ struct OptimizeInstructions
   // |requiredType| is not provided we will accept any type there.
   //
   // See "notes on removing casts", above, for when this is safe to do.
-  void skipCast(Expression*& input,
-                Type requiredType = Type(HeapType::any, Nullable)) {
+  void skipCast(Expression*& input, Type requiredType = Type::none) {
     // Traps-never-happen mode is a requirement for us to optimize here.
     if (!getPassOptions().trapsNeverHappen) {
       return;
     }
     while (1) {
       if (auto* as = input->dynCast<RefAs>()) {
-        if (Type::isSubType(as->value->type, requiredType)) {
+        if (requiredType == Type::none ||
+            Type::isSubType(as->value->type, requiredType)) {
           input = as->value;
           continue;
         }
       } else if (auto* cast = input->dynCast<RefCast>()) {
-        if (Type::isSubType(cast->ref->type, requiredType)) {
+        if (requiredType == Type::none ||
+            Type::isSubType(cast->ref->type, requiredType)) {
           input = cast->ref;
           continue;
         }