[GC] Refinalize after selectify in RemoveUnusedBrs

src/passes/RemoveUnusedBrs.cpp

@@ -1146,6 +1146,7 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
       PassOptions& passOptions;
 
       bool needUniqify = false;
+      bool refinalize = false;
 
       FinalOptimizer(PassOptions& passOptions) : passOptions(passOptions) {}
 
@@ -1419,8 +1420,14 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
         if (condition.invalidates(ifTrue) || condition.invalidates(ifFalse)) {
           return nullptr;
         }
-        return Builder(*getModule())
-          .makeSelect(iff->condition, iff->ifTrue, iff->ifFalse);
+        auto* select = Builder(*getModule())
+                         .makeSelect(iff->condition, iff->ifTrue, iff->ifFalse);
+        if (select->type != iff->type) {
+          // If the select is more refined than the if it replaces, we must
+          // propagate that outwards.
+          refinalize = true;
+        }
+        return select;
       }
 
       void visitLocalSet(LocalSet* curr) {
@@ -1793,6 +1800,9 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
     if (finalOptimizer.needUniqify) {
       wasm::UniqueNameMapper::uniquify(func->body);
     }
+    if (finalOptimizer.refinalize) {
+      ReFinalize().walkFunctionInModule(func, getModule());
+    }
   }
 };
 

test/lit/passes/remove-unused-brs-gc.wast

@@ -864,4 +864,33 @@
    )
   )
  )
+
+ ;; CHECK:      (func $select-refinalize (type $13) (param $param (ref $struct)) (result (ref struct))
+ ;; CHECK-NEXT:  (select (result (ref $struct))
+ ;; CHECK-NEXT:   (select (result (ref $struct))
+ ;; CHECK-NEXT:    (struct.new_default $struct)
+ ;; CHECK-NEXT:    (struct.new_default $struct)
+ ;; CHECK-NEXT:    (i32.const 0)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:   (local.get $param)
+ ;; CHECK-NEXT:   (i32.const 0)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $select-refinalize (param $param (ref $struct)) (result (ref struct))
+  ;; The inner if can turn into a select. The type then changes, allowing the
+  ;; outer select to be refined, which will error if we do not refinalize.
+  (select (result (ref struct))
+   (if (result (ref struct))
+    (i32.const 0)
+    (then
+     (struct.new_default $struct)
+    )
+    (else
+     (struct.new_default $struct)
+    )
+   )
+   (local.get $param)
+   (i32.const 0)
+  )
+ )
 )