Global handles: Remove independent handle infrastructure

Bug: chromium:780749
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I4c993e2147494795402f141049eed30801dfb913
Reviewed-on: https://chromium-review.googlesource.com/782519Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49568}

include/v8.h

@@ -9113,7 +9113,6 @@ class Internals {
   static const int kNodeStateIsWeakValue = 2;
   static const int kNodeStateIsPendingValue = 3;
   static const int kNodeStateIsNearDeathValue = 4;
-  static const int kNodeIsIndependentShift = 3;
   static const int kNodeIsActiveShift = 4;
 
   static const int kFirstNonstringType = 0x80;
@@ -9312,16 +9311,11 @@ void Persistent<T, M>::Copy(const Persistent<S, M2>& that) {
   M::Copy(that, this);
 }
 
-
 template <class T>
 bool PersistentBase<T>::IsIndependent() const {
-  typedef internal::Internals I;
-  if (this->IsEmpty()) return false;
-  return I::GetNodeFlag(reinterpret_cast<internal::Object**>(this->val_),
-                        I::kNodeIsIndependentShift);
+  return true;
 }
 
-
 template <class T>
 bool PersistentBase<T>::IsNearDeath() const {
   typedef internal::Internals I;
@@ -9402,13 +9396,7 @@ void PersistentBase<T>::RegisterExternalReference(Isolate* isolate) const {
 }
 
 template <class T>
-void PersistentBase<T>::MarkIndependent() {
-  typedef internal::Internals I;
-  if (this->IsEmpty()) return;
-  I::UpdateNodeFlag(reinterpret_cast<internal::Object**>(this->val_),
-                    true,
-                    I::kNodeIsIndependentShift);
-}
+void PersistentBase<T>::MarkIndependent() {}
 
 template <class T>
 void PersistentBase<T>::MarkActive() {

src/global-handles.cc

@@ -41,8 +41,6 @@ class GlobalHandles::Node {
     STATIC_ASSERT(WEAK == Internals::kNodeStateIsWeakValue);
     STATIC_ASSERT(PENDING == Internals::kNodeStateIsPendingValue);
     STATIC_ASSERT(NEAR_DEATH == Internals::kNodeStateIsNearDeathValue);
-    STATIC_ASSERT(static_cast<int>(IsIndependent::kShift) ==
-                  Internals::kNodeIsIndependentShift);
     STATIC_ASSERT(static_cast<int>(IsActive::kShift) ==
                   Internals::kNodeIsActiveShift);
   }
@@ -54,7 +52,6 @@ class GlobalHandles::Node {
     object_ = reinterpret_cast<Object*>(kGlobalHandleZapValue);
     class_id_ = v8::HeapProfiler::kPersistentHandleNoClassId;
     index_ = 0;
-    set_independent(false);
     set_active(false);
     set_in_new_space_list(false);
     parameter_or_next_free_.next_free = nullptr;
@@ -76,7 +73,6 @@ class GlobalHandles::Node {
     DCHECK(state() == FREE);
     object_ = object;
     class_id_ = v8::HeapProfiler::kPersistentHandleNoClassId;
-    set_independent(false);
     set_active(false);
     set_state(NORMAL);
     parameter_or_next_free_.parameter = nullptr;
@@ -96,7 +92,6 @@ class GlobalHandles::Node {
     // Zap the values for eager trapping.
     object_ = reinterpret_cast<Object*>(kGlobalHandleZapValue);
     class_id_ = v8::HeapProfiler::kPersistentHandleNoClassId;
-    set_independent(false);
     set_active(false);
     weak_callback_ = nullptr;
     DecreaseBlockUses();
@@ -123,13 +118,6 @@ class GlobalHandles::Node {
     flags_ = NodeState::update(flags_, state);
   }
 
-  bool is_independent() {
-    return IsIndependent::decode(flags_);
-  }
-  void set_independent(bool v) {
-    flags_ = IsIndependent::update(flags_, v);
-  }
-
   bool is_active() {
     return IsActive::decode(flags_);
   }
@@ -194,12 +182,6 @@ class GlobalHandles::Node {
     set_state(PENDING);
   }
 
-  // Independent flag accessors.
-  void MarkIndependent() {
-    DCHECK(IsInUse());
-    set_independent(true);
-  }
-
   // Callback parameter accessors.
   void set_parameter(void* parameter) {
     DCHECK(IsInUse());
@@ -344,7 +326,7 @@ class GlobalHandles::Node {
   // Placed first to avoid offset computation.
   Object* object_;
 
-  // Next word stores class_id, index, state, and independent.
+  // Next word stores class_id, index, and state.
   // Note: the most aligned fields should go first.
 
   // Wrapper class ID.
@@ -353,10 +335,7 @@ class GlobalHandles::Node {
   // Index in the containing handle block.
   uint8_t index_;
 
-  // This stores three flags (independent, partially_dependent and
-  // in_new_space_list) and a State.
   class NodeState : public BitField<State, 0, 3> {};
-  class IsIndependent : public BitField<bool, 3, 1> {};
   // The following two fields are mutually exclusive
   class IsActive : public BitField<bool, 4, 1> {};
   class IsInNewSpaceList : public BitField<bool, 5, 1> {};
@@ -600,16 +579,6 @@ void* GlobalHandles::ClearWeakness(Object** location) {
   return Node::FromLocation(location)->ClearWeakness();
 }
 
-
-void GlobalHandles::MarkIndependent(Object** location) {
-  Node::FromLocation(location)->MarkIndependent();
-}
-
-bool GlobalHandles::IsIndependent(Object** location) {
-  return Node::FromLocation(location)->is_independent();
-}
-
-
 bool GlobalHandles::IsNearDeath(Object** location) {
   return Node::FromLocation(location)->IsNearDeath();
 }

src/global-handles.h

@@ -97,11 +97,6 @@ class GlobalHandles {
   // Clear the weakness of a global handle.
   static void* ClearWeakness(Object** location);
 
-  // Mark the reference to this object independent.
-  static void MarkIndependent(Object** location);
-
-  static bool IsIndependent(Object** location);
-
   // Tells whether global handle is near death.
   static bool IsNearDeath(Object** location);
 
@@ -158,8 +153,7 @@ class GlobalHandles {
   void MarkNewSpaceWeakUnmodifiedObjectsPending(
       WeakSlotCallbackWithHeap is_dead);
 
-  // Iterates over weak independent or unmodified handles.
-  // See the note above.
+  // Iterates over weak unmodified handles. See the note above.
   void IterateNewSpaceWeakUnmodifiedRootsForFinalizers(RootVisitor* v);
   void IterateNewSpaceWeakUnmodifiedRootsForPhantomHandles(
       RootVisitor* v, WeakSlotCallbackWithHeap should_reset_handle);