Implemented lazy sweeping of new space.

src/mark-compact.cc

 // 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 2912 matching lines @@
         }
         allocation = new_space->AllocateRaw(size);
         ASSERT(!allocation->IsFailure());
       }
       Object* target = allocation->ToObjectUnchecked();
 
       MigrateObject(HeapObject::cast(target)->address(),
                     object->address(),
                     size,
                     NEW_SPACE);
-    } else {
-      // Mark dead objects in the new space with null in their map field.
-      Memory::Address_at(object->address()) = NULL;
     }
   }
 
   heap_->IncrementYoungSurvivorsCounter(survivors_size);
   new_space->set_age_mark(new_space->top());
 }
 
 
 void MarkCompactCollector::EvacuateLiveObjectsFromPage(Page* p) {
   AlwaysAllocateScope always_allocate;
@@ skipping 401 matching lines @@
                              GCTracer::Scope::MC_UPDATE_ROOT_TO_NEW_POINTERS);
     // Update roots.
     heap_->IterateRoots(&updating_visitor, VISIT_ALL_IN_SWEEP_NEWSPACE);
   }
 
   { GCTracer::Scope gc_scope(tracer_,
                              GCTracer::Scope::MC_UPDATE_OLD_TO_NEW_POINTERS);
     StoreBufferRebuildScope scope(heap_,
                                   heap_->store_buffer(),
                                   &Heap::ScavengeStoreBufferCallback);
-    heap_->store_buffer()->IteratePointersToNewSpace(&UpdatePointer);
+    heap_->store_buffer()->IteratePointersToNewSpaceAndClearMaps(
+        &UpdatePointer);
   }
 
   { GCTracer::Scope gc_scope(tracer_,
                              GCTracer::Scope::MC_UPDATE_POINTERS_TO_EVACUATED);
     SlotsBuffer::UpdateSlotsRecordedIn(heap_,
                                        migration_slots_buffer_,
                                        code_slots_filtering_required);
     if (FLAG_trace_fragmentation) {
       PrintF("  migration slots buffer: %d\n",
              SlotsBuffer::SizeOfChain(migration_slots_buffer_));
@@ skipping 963 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal