Forward white to grey transition only if slot is before the progress bar of a given object.

BUG=

Review URL: https://codereview.chromium.org/11415070

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13063 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/incremental-marking-inl.h

@@ -44,8 +44,12 @@ bool IncrementalMarking::BaseRecordWrite(HeapObject* obj,
     if (Marking::IsBlack(obj_bit)) {
       MemoryChunk* chunk = MemoryChunk::FromAddress(obj->address());
       if (chunk->IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR)) {
-        WhiteToGreyAndPush(value_heap_obj, value_bit);
-        RestartIfNotMarking();
+        if (chunk->IsLeftOfProgressBar(slot)) {
+          WhiteToGreyAndPush(value_heap_obj, value_bit);
+          RestartIfNotMarking();
+        } else {
+          return false;
+        }
       } else {
         BlackToGreyAndUnshift(obj, obj_bit);
         RestartIfNotMarking();

src/spaces.h

@@ -503,6 +503,12 @@ class MemoryChunk {
     }
   }
 
+  bool IsLeftOfProgressBar(Object** slot) {
+    Address slot_address = reinterpret_cast<Address>(slot);
+    ASSERT(slot_address > this->address());
+    return (slot_address - this->address() + kObjectStartOffset) <
+           progress_bar();
+  }
 
   static void IncrementLiveBytesFromGC(Address address, int by) {
     MemoryChunk::FromAddress(address)->IncrementLiveBytes(by);