diff -r e64e3cd120b7 -r 50c0d24d3971 src/hotspot/share/prims/jvm.cpp
--- a/src/hotspot/share/prims/jvm.cpp	Tue May 08 17:58:14 2018 -0700
+++ b/src/hotspot/share/prims/jvm.cpp	Tue May 08 20:59:58 2018 -0400
@@ -629,35 +629,6 @@
 JVM_END
 
 
-template<DecoratorSet decorators>
-static void fixup_clone_referent(oop src, oop new_obj) {
-  typedef HeapAccess<decorators> RefAccess;
-  const int ref_offset = java_lang_ref_Reference::referent_offset;
-  oop referent = RefAccess::oop_load_at(src, ref_offset);
-  RefAccess::oop_store_at(new_obj, ref_offset, referent);
-}
-
-static void fixup_cloned_reference(ReferenceType ref_type, oop src, oop clone) {
-  // Kludge: After unbarriered clone, re-copy the referent with
-  // correct barriers. This works for current collectors, but won't
-  // work for ZGC and maybe other future collectors or variants of
-  // existing ones (like G1 with concurrent reference processing).
-  if (ref_type == REF_PHANTOM) {
-    fixup_clone_referent<ON_PHANTOM_OOP_REF>(src, clone);
-  } else {
-    fixup_clone_referent<ON_WEAK_OOP_REF>(src, clone);
-  }
-  if ((java_lang_ref_Reference::next(clone) != NULL) ||
-      (java_lang_ref_Reference::queue(clone) == java_lang_ref_ReferenceQueue::ENQUEUED_queue())) {
-    // If the source has been enqueued or is being enqueued, don't
-    // register the clone with a queue.
-    java_lang_ref_Reference::set_queue(clone, java_lang_ref_ReferenceQueue::NULL_queue());
-  }
-  // discovered and next are list links; the clone is not in those lists.
-  java_lang_ref_Reference::set_discovered(clone, NULL);
-  java_lang_ref_Reference::set_next(clone, NULL);
-}
-
 JVM_ENTRY(jobject, JVM_Clone(JNIEnv* env, jobject handle))
   JVMWrapper("JVM_Clone");
   Handle obj(THREAD, JNIHandles::resolve_non_null(handle));
@@ -676,35 +647,27 @@
 #endif
 
   // Check if class of obj supports the Cloneable interface.
-  // All arrays are considered to be cloneable (See JLS 20.1.5)
-  if (!klass->is_cloneable()) {
+  // All arrays are considered to be cloneable (See JLS 20.1.5).
+  // All j.l.r.Reference classes are considered non-cloneable.
+  if (!klass->is_cloneable() ||
+      (klass->is_instance_klass() &&
+       InstanceKlass::cast(klass)->reference_type() != REF_NONE)) {
     ResourceMark rm(THREAD);
     THROW_MSG_0(vmSymbols::java_lang_CloneNotSupportedException(), klass->external_name());
   }
 
   // Make shallow object copy
-  ReferenceType ref_type = REF_NONE;
   const int size = obj->size();
   oop new_obj_oop = NULL;
   if (obj->is_array()) {
     const int length = ((arrayOop)obj())->length();
     new_obj_oop = CollectedHeap::array_allocate(klass, size, length, CHECK_NULL);
   } else {
-    ref_type = InstanceKlass::cast(klass)->reference_type();
-    assert((ref_type == REF_NONE) ==
-           !klass->is_subclass_of(SystemDictionary::Reference_klass()),
-           "invariant");
     new_obj_oop = CollectedHeap::obj_allocate(klass, size, CHECK_NULL);
   }
 
   HeapAccess<>::clone(obj(), new_obj_oop, size);
 
-  // If cloning a Reference, set Reference fields to a safe state.
-  // Fixup must be completed before any safepoint.
-  if (ref_type != REF_NONE) {
-    fixup_cloned_reference(ref_type, obj(), new_obj_oop);
-  }
-
   Handle new_obj(THREAD, new_obj_oop);
   // Caution: this involves a java upcall, so the clone should be
   // "gc-robust" by this stage.