Separate markbits from heap object map words into bitmaps.

src/spaces.cc

Index: src/spaces.cc
diff --git a/src/spaces.cc b/src/spaces.cc
index 739154ca55c23474685ad77457b336df08d1e774..c541a65666244152a20a96893f3df1c8c002ad93 100644
--- a/src/spaces.cc
+++ b/src/spaces.cc
@@ -1559,6 +1559,7 @@ MaybeObject* OldSpaceFreeList::Allocate(int size_in_bytes, int* wasted_bytes) {
 
 
 void OldSpaceFreeList::MarkNodes() {
+#if 0
   for (int i = 0; i < kFreeListsLength; i++) {
     Address cur_addr = free_[i].head_node_;
     while (cur_addr != NULL) {
@@ -1567,6 +1568,8 @@ void OldSpaceFreeList::MarkNodes() {
       cur_node->SetMark();
     }
   }
+#endif
+  UNREACHABLE();
 }
 
 
@@ -1630,12 +1633,15 @@ MaybeObject* FixedSizeFreeList::Allocate() {
 
 
 void FixedSizeFreeList::MarkNodes() {
+#if 0
   Address cur_addr = head_;
   while (cur_addr != NULL && cur_addr != tail_) {
     FreeListNode* cur_node = FreeListNode::FromAddress(cur_addr);
     cur_addr = cur_node->next();
     cur_node->SetMark();
   }
+#endif
+  UNREACHABLE();
 }
 
 
@@ -1697,6 +1703,7 @@ void PagedSpace::FreePages(Page* prev, Page* last) {
     first->SetAllocationWatermark(first->ObjectAreaStart());
     first->SetCachedAllocationWatermark(first->ObjectAreaStart());
     first->SetRegionMarks(Page::kAllRegionsCleanMarks);
+    first->markbits()->Clear();
     first = first->next_page();
   } while (first != NULL);
 }
@@ -2328,8 +2335,8 @@ void LargeObjectSpace::FreeUnmarkedObjects() {
   LargePage* current = first_page_;
   while (current != NULL) {
     HeapObject* object = current->GetObject();
-    if (object->IsMarked()) {
-      object->ClearMark();
+    if (Marking::IsMarked(object)) {
+      Marking::ClearMark(object);
       MarkCompactCollector::tracer()->decrement_marked_count();
       previous = current;
       current = current->next_page();