[GC] Ignore public types in SignatureRefining (WebAssembly#7022)

Similar to WebAssembly#7017 and WebAssembly#7018

Author: kripken

src/passes/SignatureRefining.cpp

@@ -147,18 +147,11 @@ struct SignatureRefining : public Pass {
       }
     }
 
-    // We cannot alter the signature of an exported function, as the outside may
-    // notice us doing so. For example, if we turn a parameter from nullable
-    // into non-nullable then callers sending a null will break. Put another
-    // way, we need to see all callers to refine types, and for exports we
-    // cannot do so.
-    // TODO If a function type is passed we should also mark the types used
-    //      there, etc., recursively. For now this code just handles the top-
-    //      level type, which is enough to keep the fuzzer from erroring. More
-    //      generally, we need to decide about adding a "closed-world" flag of
-    //      some kind.
-    for (auto* exportedFunc : ExportUtils::getExportedFunctions(*module)) {
-      allInfo[exportedFunc->type].canModify = false;
+    // Find the public types, which we must not modify.
+    for (auto type : ModuleUtils::getPublicHeapTypes(*module)) {
+      if (type.isFunction()) {
+        allInfo[type].canModify = false;
+      }
     }
 
     // For now, do not optimize types that have subtypes. When we modify such a

test/lit/passes/signature-refining.wast

@@ -1119,3 +1119,43 @@
   ;; (see tests above for how we handle refining of return values).
  )
 )
+
+;; Visibility: The type we'd like to refine, $sig, is in a rec group with a
+;; public type, so do not optimize.
+(module
+ (rec
+  ;; CHECK:      (rec
+  ;; CHECK-NEXT:  (type $sig (sub (func (param anyref))))
+  (type $sig (sub (func (param anyref))))
+
+  ;; CHECK:       (type $struct (struct))
+  (type $struct (struct))
+ )
+
+ ;; Export a global with $struct to make it public.
+ ;; CHECK:      (type $2 (func))
+
+ ;; CHECK:      (global $struct (ref $struct) (struct.new_default $struct))
+ (global $struct (ref $struct) (struct.new $struct))
+
+ ;; CHECK:      (export "struct" (global $struct))
+ (export "struct" (global $struct))
+
+ ;; CHECK:      (func $func (type $sig) (param $x anyref)
+ ;; CHECK-NEXT:  (nop)
+ ;; CHECK-NEXT: )
+ (func $func (type $sig) (param $x anyref)
+ )
+
+ ;; CHECK:      (func $caller (type $2)
+ ;; CHECK-NEXT:  (call $func
+ ;; CHECK-NEXT:   (struct.new_default $struct)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $caller
+  (call $func
+   (struct.new $struct)
+  )
+ )
+)
+