8293295: Add type check asserts to java_lang_ref_Reference accessors

Reviewed-by: stefank, kbarrett, coleenp

Author: xmas92

src/hotspot/share/classfile/javaClasses.hpp

@@ -988,6 +988,8 @@ class java_lang_ref_Reference: AllStatic {
   static bool is_referent_field(oop obj, ptrdiff_t offset);
   static inline bool is_final(oop ref);
   static inline bool is_phantom(oop ref);
+  static inline bool is_weak(oop ref);
+  static inline bool is_soft(oop ref);
 
   static int referent_offset()    { CHECK_INIT(_referent_offset); }
   static int queue_offset()       { CHECK_INIT(_queue_offset); }

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

@@ -27,6 +27,7 @@
 
 #include "classfile/javaClasses.hpp"
 
+#include "memory/referenceType.hpp"
 #include "oops/access.inline.hpp"
 #include "oops/instanceKlass.inline.hpp"
 #include "oops/method.hpp"
@@ -132,14 +133,17 @@ bool java_lang_String::is_instance(oop obj) {
 // Accessors
 
 oop java_lang_ref_Reference::weak_referent_no_keepalive(oop ref) {
+  assert(java_lang_ref_Reference::is_weak(ref) || java_lang_ref_Reference::is_soft(ref), "must be Weak or Soft Reference");
   return ref->obj_field_access<ON_WEAK_OOP_REF | AS_NO_KEEPALIVE>(_referent_offset);
 }
 
 oop java_lang_ref_Reference::weak_referent(oop ref) {
+  assert(java_lang_ref_Reference::is_weak(ref) || java_lang_ref_Reference::is_soft(ref), "must be Weak or Soft Reference");
   return ref->obj_field_access<ON_WEAK_OOP_REF>(_referent_offset);
 }
 
 oop java_lang_ref_Reference::phantom_referent_no_keepalive(oop ref) {
+  assert(java_lang_ref_Reference::is_phantom(ref), "must be Phantom Reference");
   return ref->obj_field_access<ON_PHANTOM_OOP_REF | AS_NO_KEEPALIVE>(_referent_offset);
 }
 
@@ -195,6 +199,14 @@ bool java_lang_ref_Reference::is_phantom(oop ref) {
   return InstanceKlass::cast(ref->klass())->reference_type() == REF_PHANTOM;
 }
 
+bool java_lang_ref_Reference::is_weak(oop ref) {
+  return InstanceKlass::cast(ref->klass())->reference_type() == REF_WEAK;
+}
+
+bool java_lang_ref_Reference::is_soft(oop ref) {
+  return InstanceKlass::cast(ref->klass())->reference_type() == REF_SOFT;
+}
+
 inline oop java_lang_Thread::continuation(oop java_thread) {
   return java_thread->obj_field(_continuation_offset);
 }