Reland "Precisely sweep scan on scavenge pages and use heap iterator to iterate over them."

src/objects-inl.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Review notes:
 //
 // - The use of macros in these inline functions may seem superfluous
 // but it is absolutely needed to make sure gcc generates optimal
 // code. gcc is not happy when attempting to inline too deep.
 //
@@ skipping 1462 matching lines @@
 Address HeapObject::address() {
   return reinterpret_cast<Address>(this) - kHeapObjectTag;
 }
 
 
 int HeapObject::Size() {
   return SizeFromMap(map());
 }
 
 
+bool HeapObject::ContainsPointers() {
+  InstanceType type = map()->instance_type();
+  if (type <= LAST_NAME_TYPE) {
+    if (type == SYMBOL_TYPE) {
+      return true;
+    }
+    ASSERT(type < FIRST_NONSTRING_TYPE);
+    // There are four string representations: sequential strings, external
+    // strings, cons strings, and sliced strings.
+    // Only the latter two contain non-map-word pointers to heap objects.
+    return ((type & kIsIndirectStringMask) == kIsIndirectStringTag);
+  }
+  return (type > LAST_DATA_TYPE);
+}
+
+
 void HeapObject::IteratePointers(ObjectVisitor* v, int start, int end) {
   v->VisitPointers(reinterpret_cast<Object**>(FIELD_ADDR(this, start)),
                    reinterpret_cast<Object**>(FIELD_ADDR(this, end)));
 }
 
 
 void HeapObject::IteratePointer(ObjectVisitor* v, int offset) {
   v->VisitPointer(reinterpret_cast<Object**>(FIELD_ADDR(this, offset)));
 }
 
@@ skipping 5632 matching lines @@
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 #undef NOBARRIER_READ_BYTE_FIELD
 #undef NOBARRIER_WRITE_BYTE_FIELD
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_