Add map-based read barrier to WeakCell

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 9e9bd591b112a3cee24c911cc8ec50bca0f21ec1..05155441d2db023f69ba787a9ef336197fbb87cc 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -1949,22 +1949,42 @@ void PropertyCell::set_type_raw(Object* val, WriteBarrierMode ignored) {
 }
 
 
-Object* WeakCell::value() const { return READ_FIELD(this, kValueOffset); }
+Object* WeakCell::value(Heap* heap) {
+  Object* pointer = READ_FIELD(this, kValueOffsetDontForgetTheReadBarrier);
+  NOBARRIER_WRITE_FIELD(this, kMapOffset, GetHeap()->used_weak_cell_map());
+  return pointer;
+}
+
+
+Object* WeakCell::ValueNoReadBarrier() {
+  return READ_FIELD(this, kValueOffsetDontForgetTheReadBarrier);
+}
+
+
+void WeakCell::TriggerReadBarrier(Object* possible_weak_cell) {
+  if (possible_weak_cell->IsWeakCell()) {
+    WeakCell* weak_cell = reinterpret_cast<WeakCell*>(possible_weak_cell);
+    weak_cell->value(weak_cell->GetHeap());
+  }
+}
 
 
 void WeakCell::clear() {
   DCHECK(GetHeap()->gc_state() == Heap::MARK_COMPACT);
-  WRITE_FIELD(this, kValueOffset, Smi::FromInt(0));
+  WRITE_FIELD(this, kValueOffsetDontForgetTheReadBarrier, Smi::FromInt(0));
 }
 
 
 void WeakCell::initialize(HeapObject* val) {
-  WRITE_FIELD(this, kValueOffset, val);
-  WRITE_BARRIER(GetHeap(), this, kValueOffset, val);
+  WRITE_FIELD(this, kValueOffsetDontForgetTheReadBarrier, val);
+  WRITE_BARRIER(GetHeap(), this, kValueOffsetDontForgetTheReadBarrier, val);
 }
 
 
-bool WeakCell::cleared() const { return value() == Smi::FromInt(0); }
+bool WeakCell::cleared() const {
+  Object* pointer = READ_FIELD(this, kValueOffsetDontForgetTheReadBarrier);
+  return pointer == Smi::FromInt(0);
+}
 
 
 Object* WeakCell::next() const { return READ_FIELD(this, kNextOffset); }
@@ -2368,16 +2388,26 @@ void FixedDoubleArray::FillWithHoles(int from, int to) {
 }
 
 
-Object* WeakFixedArray::Get(int index) const {
+Object* WeakFixedArray::Get(Heap* heap, int index) const {
   Object* raw = FixedArray::cast(this)->get(index + kFirstIndex);
   if (raw->IsSmi()) return raw;
-  return WeakCell::cast(raw)->value();
+  return WeakCell::cast(raw)->value(heap);
+}
+
+
+bool WeakFixedArray::EqualAt(int index, Object* object) const {
+  DCHECK(index < Length());
+  Object* raw = FixedArray::cast(this)->get(index + kFirstIndex);
+  if (raw->IsSmi()) return raw == object;
+  return WeakCell::cast(raw)->ValueNoReadBarrier() == object;
 }
 
 
 bool WeakFixedArray::IsEmptySlot(int index) const {
   DCHECK(index < Length());
-  return Get(index)->IsSmi();
+  Object* raw = FixedArray::cast(this)->get(index + kFirstIndex);
+  if (raw->IsSmi()) return true;
+  return WeakCell::cast(raw)->cleared();
 }
 
 
@@ -7605,7 +7635,6 @@ String::SubStringRange::iterator String::SubStringRange::end() {
 #undef FIELD_ADDR
 #undef FIELD_ADDR_CONST
 #undef READ_FIELD
-#undef NOBARRIER_READ_FIELD
 #undef WRITE_FIELD
 #undef NOBARRIER_WRITE_FIELD
 #undef WRITE_BARRIER