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

src/incremental-marking-inl.h

Index: src/incremental-marking-inl.h
diff --git a/src/incremental-marking-inl.h b/src/incremental-marking-inl.h
index 1e28e4a06b1cf1cf7ead93c810b17cf2134ebf4f..427a8f00ba177209c141bcf2af5e946c4da624c5 100644
--- a/src/incremental-marking-inl.h
+++ b/src/incremental-marking-inl.h
@@ -44,8 +44,13 @@ 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 (reinterpret_cast<Address>(slot) - reinterpret_cast<Address>(obj)

[Michael Starzinger, 2012/11/21 17:11:38]

We don't even need to record relocation slots when the slot is right of the bar,
so we can early return with false in this case.

Also, can we have the address computation trickery as a helper function in
MemoryChunk. All the assertions could also go in there. For example with the
following signature.

bool MemoryChunk::IsAheadOfProgressBar(Object** slot);

[Hannes Payer (out of office), 2012/11/21 18:03:57]

Done.

+            < chunk->progress_bar()) {
+          ASSERT(reinterpret_cast<Address>(slot)
+                 > reinterpret_cast<Address>(obj));
+          WhiteToGreyAndPush(value_heap_obj, value_bit);
+          RestartIfNotMarking();
+        }
       } else {
         BlackToGreyAndUnshift(obj, obj_bit);
         RestartIfNotMarking();