8240324: Improve is_boot_class_loader_data() by adding simple check

Check if cld is the null_cld before looking at the class loader oop

Reviewed-by: coleenp

src/hotspot/share/classfile/classLoaderData.inline.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -39,8 +39,8 @@ inline oop ClassLoaderData::class_loader() const {
 }
 
 inline bool ClassLoaderData::is_boot_class_loader_data() const {
-    return class_loader() == NULL;
-  }
+  return this == _the_null_class_loader_data || class_loader() == NULL;
+}
 
 inline ClassLoaderData* ClassLoaderData::class_loader_data_or_null(oop loader) {
   if (loader == NULL) {