Make sure when we shrink an object that we store a filler first into the free memory before updatin…

src/objects-inl.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 107 matching lines @@
 // Getter that returns a Smi as an int and writes an int as a Smi.
 #define SMI_ACCESSORS(holder, name, offset)             \
   int holder::name() {                                  \
     Object* value = READ_FIELD(this, offset);           \
     return Smi::cast(value)->value();                   \
   }                                                     \
   void holder::set_##name(int value) {                  \
     WRITE_FIELD(this, offset, Smi::FromInt(value));     \
   }
 
+#define SYNCHRONIZED_SMI_ACCESSORS(holder, name, offset)    \
+  int holder::synchronized_##name() {                       \
+    Object* value = ACQUIRE_READ_FIELD(this, offset);       \
+    return Smi::cast(value)->value();                       \
+  }                                                         \
+  void holder::synchronized_set_##name(int value) {         \
+    RELEASE_WRITE_FIELD(this, offset, Smi::FromInt(value)); \
+  }
+
 
 #define BOOL_GETTER(holder, field, name, offset)           \
   bool holder::name() {                                    \
     return BooleanBit::get(field(), offset);               \
   }                                                        \
 
 
 #define BOOL_ACCESSORS(holder, field, name, offset)        \
   bool holder::name() {                                    \
     return BooleanBit::get(field(), offset);               \
@@ skipping 950 matching lines @@
   return GetPropertyWithReceiver(this, key, attributes);
 }
 
 
 #define FIELD_ADDR(p, offset) \
   (reinterpret_cast<byte*>(p) + offset - kHeapObjectTag)
 
 #define READ_FIELD(p, offset) \
   (*reinterpret_cast<Object**>(FIELD_ADDR(p, offset)))
 
+#define ACQUIRE_READ_FIELD(p, offset)                                    \
+  reinterpret_cast<Object*>(                                             \
+      Acquire_Load(reinterpret_cast<AtomicWord*>(FIELD_ADDR(p, offset))))
+
+#define NO_BARRIER_READ_FIELD(p, offset)                                    \
+  reinterpret_cast<Object*>(                                                \
+      NoBarrier_Load(reinterpret_cast<AtomicWord*>(FIELD_ADDR(p, offset))))
+
 #define WRITE_FIELD(p, offset, value) \
   (*reinterpret_cast<Object**>(FIELD_ADDR(p, offset)) = value)
 
+#define RELEASE_WRITE_FIELD(p, offset, value)                           \
+  Release_Store(reinterpret_cast<AtomicWord*>(FIELD_ADDR(p, offset)),   \
+                reinterpret_cast<AtomicWord>(value));
+
+#define NO_BARRIER_WRITE_FIELD(p, offset, value)                           \
+  NoBarrier_Store(reinterpret_cast<AtomicWord*>(FIELD_ADDR(p, offset)),    \
+                  reinterpret_cast<AtomicWord>(value));
+
 #define WRITE_BARRIER(heap, object, offset, value)                      \
   heap->incremental_marking()->RecordWrite(                             \
       object, HeapObject::RawField(object, offset), value);             \
   if (heap->InNewSpace(value)) {                                        \
     heap->RecordWrite(object->address(), offset);                       \
   }
 
 #define CONDITIONAL_WRITE_BARRIER(heap, object, offset, value, mode)    \
   if (mode == UPDATE_WRITE_BARRIER) {                                   \
     heap->incremental_marking()->RecordWrite(                           \
@@ skipping 230 matching lines @@
 void HeapObject::set_map(Map* value) {
   set_map_word(MapWord::FromMap(value));
   if (value != NULL) {
     // TODO(1600) We are passing NULL as a slot because maps can never be on
     // evacuation candidate.
     value->GetHeap()->incremental_marking()->RecordWrite(this, NULL, value);
   }
 }
 
 
+Map* HeapObject::synchronized_map() {
+  return synchronized_map_word().ToMap();
+}
+
+
+void HeapObject::synchronized_set_map(Map* value) {
+  synchronized_set_map_word(MapWord::FromMap(value));
+  if (value != NULL) {
+    // TODO(1600) We are passing NULL as a slot because maps can never be on
+    // evacuation candidate.
+    value->GetHeap()->incremental_marking()->RecordWrite(this, NULL, value);
+  }
+}
+
+
 // Unsafe accessor omitting write barrier.
 void HeapObject::set_map_no_write_barrier(Map* value) {
   set_map_word(MapWord::FromMap(value));
 }
 
 
 MapWord HeapObject::map_word() {
-  return MapWord(reinterpret_cast<uintptr_t>(READ_FIELD(this, kMapOffset)));
+  return MapWord(
+      reinterpret_cast<uintptr_t>(NO_BARRIER_READ_FIELD(this, kMapOffset)));
 }
 
 
 void HeapObject::set_map_word(MapWord map_word) {
-  // WRITE_FIELD does not invoke write barrier, but there is no need
-  // here.
-  WRITE_FIELD(this, kMapOffset, reinterpret_cast<Object*>(map_word.value_));
+  NO_BARRIER_WRITE_FIELD(
+      this, kMapOffset, reinterpret_cast<Object*>(map_word.value_));
 }
 
 
+MapWord HeapObject::synchronized_map_word() {
+  return MapWord(
+      reinterpret_cast<uintptr_t>(ACQUIRE_READ_FIELD(this, kMapOffset)));
+}
+
+
+void HeapObject::synchronized_set_map_word(MapWord map_word) {
+  RELEASE_WRITE_FIELD(
+      this, kMapOffset, reinterpret_cast<Object*>(map_word.value_));
+}
+
+
 HeapObject* HeapObject::FromAddress(Address address) {
   ASSERT_TAG_ALIGNED(address);
   return reinterpret_cast<HeapObject*>(address + kHeapObjectTag);
 }
 
 
 Address HeapObject::address() {
   return reinterpret_cast<Address>(this) - kHeapObjectTag;
 }
 
@@ skipping 1528 matching lines @@
 
 
 template <typename Shape, typename Key>
 HashTable<Shape, Key>* HashTable<Shape, Key>::cast(Object* obj) {
   ASSERT(obj->IsHashTable());
   return reinterpret_cast<HashTable*>(obj);
 }
 
 
 SMI_ACCESSORS(FixedArrayBase, length, kLengthOffset)
+SYNCHRONIZED_SMI_ACCESSORS(FixedArrayBase, length, kLengthOffset)
+
 SMI_ACCESSORS(FreeSpace, size, kSizeOffset)
 
 SMI_ACCESSORS(String, length, kLengthOffset)
+SYNCHRONIZED_SMI_ACCESSORS(String, length, kLengthOffset)
 
 
 uint32_t Name::hash_field() {
   return READ_UINT32_FIELD(this, kHashFieldOffset);
 }
 
 
 void Name::set_hash_field(uint32_t value) {
   WRITE_UINT32_FIELD(this, kHashFieldOffset, value);
 #if V8_HOST_ARCH_64_BIT
@@ skipping 3859 matching lines @@
 #undef READ_UINT32_FIELD
 #undef WRITE_UINT32_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_