SimplifyGlobals: Do not switch a get to use a global of another type (#6605)

If we wanted to switch types in such cases we'd need to refinalize (which is likely
worth doing, though other passes should refine globals anyhow).

Author: kripken

src/passes/SimplifyGlobals.cpp

@@ -317,7 +317,14 @@ struct GlobalUseModifier : public WalkerPass<PostWalker<GlobalUseModifier>> {
   void visitGlobalGet(GlobalGet* curr) {
     auto iter = copiedParentMap->find(curr->name);
     if (iter != copiedParentMap->end()) {
-      curr->name = iter->second;
+      auto original = iter->second;
+      // Only apply this optimization if the global we are switching to has the
+      // right type for us.
+      // TODO: We could also allow it to be more refined, but would then need to
+      //       refinalize.
+      if (getModule()->getGlobal(original)->type == curr->type) {
+        curr->name = original;
+      }
     }
   }
 

test/lit/passes/simplify-globals-gc.wast

@@ -31,3 +31,27 @@
  )
 )
 
+(module
+ ;; CHECK:      (type $struct (struct ))
+ (type $struct (struct ))
+
+ ;; CHECK:      (type $1 (func (result anyref)))
+
+ ;; CHECK:      (global $a (ref $struct) (struct.new_default $struct))
+ (global $a (ref $struct) (struct.new_default $struct))
+ ;; CHECK:      (global $b (ref $struct) (global.get $a))
+ (global $b (ref $struct) (global.get $a))
+ ;; CHECK:      (global $c (ref null $struct) (global.get $a))
+ (global $c (ref null $struct) (global.get $a))
+
+ ;; CHECK:      (func $get-c (type $1) (result anyref)
+ ;; CHECK-NEXT:  (global.get $c)
+ ;; CHECK-NEXT: )
+ (func $get-c (result anyref)
+  ;; $c has a less-refined type than the other two. We do not switch this to
+  ;; get from either $a or $b because of that, but we could if we also
+  ;; refinalized TODO
+  (global.get $c)
+ )
+)
+