Initialize pre-allocated fields of JSObject with undefined.

src/objects-inl.h

 // Copyright 2011 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 1576 matching lines @@
   index -= map()->inobject_properties();
   ASSERT(index < 0);
   int offset = map()->instance_size() + (index * kPointerSize);
   WRITE_FIELD(this, offset, value);
   CONDITIONAL_WRITE_BARRIER(GetHeap(), this, offset, mode);
   return value;
 }
 
 
 
-void JSObject::InitializeBody(int object_size, Object* value) {
-  ASSERT(!value->IsHeapObject() || !GetHeap()->InNewSpace(value));
-  for (int offset = kHeaderSize; offset < object_size; offset += kPointerSize) {
-    WRITE_FIELD(this, offset, value);
+void JSObject::InitializeBody(Map* map,
+                              Object* pre_allocated_value,
+                              Object* filler_value) {
+  ASSERT(!filler_value->IsHeapObject() ||
+         !GetHeap()->InNewSpace(filler_value));
+  ASSERT(!pre_allocated_value->IsHeapObject() ||
+         !GetHeap()->InNewSpace(pre_allocated_value));
+  int size = map->instance_size();
+  int offset = kHeaderSize;
+  if (filler_value != pre_allocated_value) {
+    int pre_allocated = map->pre_allocated_property_fields();
+    ASSERT(pre_allocated * kPointerSize + kHeaderSize <= size);
+    for (int i = 0; i < pre_allocated; i++) {
+      WRITE_FIELD(this, offset, pre_allocated_value);
+      offset += kPointerSize;
+    }
+  }
+  while (offset < size) {
+    WRITE_FIELD(this, offset, filler_value);
+    offset += kPointerSize;
   }
 }
 
 
 bool JSObject::HasFastProperties() {
   return !properties()->IsDictionary();
 }
 
 
 int JSObject::MaxFastProperties() {
@@ skipping 3032 matching lines @@
 #undef WRITE_INT_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_