Revert "Revert "Add intrinsic for Reference.get()""

This reverts commit a9b870b73a155ce70c867d5b3f9758fab0b45f07.

Change-Id: Ic2a9b47f2b911bef4b764d10bc33cf000e4b4211
diff --git a/runtime/mirror/reference.cc b/runtime/mirror/reference.cc
new file mode 100644
index 0000000..533aaca
--- /dev/null
+++ b/runtime/mirror/reference.cc
@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2011 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "reference.h"
+
+namespace art {
+namespace mirror {
+
+ReferenceClass* Reference::java_lang_ref_Reference_ = nullptr;
+
+void Reference::SetClass(ReferenceClass* java_lang_ref_Reference) {
+  CHECK(java_lang_ref_Reference_ == nullptr);
+  CHECK(java_lang_ref_Reference != nullptr);
+  java_lang_ref_Reference_ = java_lang_ref_Reference;
+}
+
+void Reference::ResetClass() {
+  CHECK(java_lang_ref_Reference_ != nullptr);
+  java_lang_ref_Reference_ = nullptr;
+}
+
+void Reference::VisitRoots(RootCallback* callback, void* arg) {
+  if (java_lang_ref_Reference_ != nullptr) {
+    callback(reinterpret_cast<mirror::Object**>(&java_lang_ref_Reference_),
+             arg, 0, kRootStickyClass);
+  }
+}
+
+}  // namespace mirror
+}  // namespace art
diff --git a/runtime/mirror/reference.h b/runtime/mirror/reference.h
index 9c9d87b..15e0145 100644
--- a/runtime/mirror/reference.h
+++ b/runtime/mirror/reference.h
@@ -17,7 +17,10 @@
 #ifndef ART_RUNTIME_MIRROR_REFERENCE_H_
 #define ART_RUNTIME_MIRROR_REFERENCE_H_
 
+#include "class.h"
 #include "object.h"
+#include "object_callbacks.h"
+#include "thread.h"
 
 namespace art {
 
@@ -29,9 +32,11 @@
 }  // namespace gc
 
 struct ReferenceOffsets;
+struct ReferenceClassOffsets;
 struct FinalizerReferenceOffsets;
 
 namespace mirror {
+class ReferenceClass;
 
 // C++ mirror of java.lang.ref.Reference
 class MANAGED Reference : public Object {
@@ -80,6 +85,15 @@
 
   bool IsEnqueuable() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
+  static ReferenceClass* GetJavaLangRefReference() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
+    CHECK(java_lang_ref_Reference_ != nullptr);
+    return ReadBarrier::BarrierForRoot<mirror::ReferenceClass, kWithReadBarrier>(
+        &java_lang_ref_Reference_);
+  }
+  static void SetClass(ReferenceClass* klass);
+  static void ResetClass(void);
+  static void VisitRoots(RootCallback* callback, void* arg);
+
  private:
   // Note: This avoids a read barrier, it should only be used by the GC.
   HeapReference<Object>* GetReferentReferenceAddr() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
@@ -92,12 +106,46 @@
   HeapReference<Reference> queue_next_;  // Note this is Java volatile:
   HeapReference<Object> referent_;  // Note this is Java volatile:
 
+  static ReferenceClass* java_lang_ref_Reference_;
+
   friend struct art::ReferenceOffsets;  // for verifying offset information
   friend class gc::ReferenceProcessor;
   friend class gc::ReferenceQueue;
   DISALLOW_IMPLICIT_CONSTRUCTORS(Reference);
 };
 
+// Tightly coupled with the ReferenceProcessor to provide switch for slow/fast path. Consistency
+// is maintained by ReferenceProcessor.
+class MANAGED ReferenceClass : public Class {
+ public:
+  static MemberOffset DisableIntrinsicOffset() {
+    return OFFSET_OF_OBJECT_MEMBER(ReferenceClass, disable_intrinsic_);
+  }
+  static MemberOffset SlowPathEnabledOffset() {
+    return OFFSET_OF_OBJECT_MEMBER(ReferenceClass, slow_path_enabled_);
+  }
+
+  void Init() {
+    disable_intrinsic_ = false;
+    slow_path_enabled_ = false;
+  }
+
+  bool GetSlowPathEnabled() const {
+    return slow_path_enabled_;
+  }
+  void SetSlowPathEnabled(bool enabled) {
+    slow_path_enabled_ = enabled;
+  }
+
+ private:
+  int32_t disable_intrinsic_;
+  int32_t slow_path_enabled_;
+  // allows runtime to safely enable/disable intrinsics fast path for benchmarking
+
+  friend struct art::ReferenceClassOffsets;  // for verifying offset information
+  DISALLOW_IMPLICIT_CONSTRUCTORS(ReferenceClass);
+};
+
 // C++ mirror of java.lang.ref.FinalizerReference
 class MANAGED FinalizerReference : public Reference {
  public: