Support slots recording for compaction during incremental marking.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 6e0bb5556e975e6367939a1fbd30a7aefea59c5a..d5aaac4e40e24016d8669b044c7f01d34166d394 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -4304,13 +4304,20 @@ void Heap::IterateAndMarkPointersToFromSpace(Address start,
     // the store buffer.  These pages are scanned to find pointers that point
     // to the new space.  In that case we may hit newly promoted objects and
     // fix the pointers before the promotion queue gets to them.  Thus the 'if'.
-    if (Heap::InFromSpace(object)) {
-      callback(reinterpret_cast<HeapObject**>(slot), HeapObject::cast(object));
-      if (InNewSpace(*slot)) {
-        ASSERT(Heap::InToSpace(*slot));
-        ASSERT((*slot)->IsHeapObject());
-        store_buffer_.EnterDirectlyIntoStoreBuffer(
-            reinterpret_cast<Address>(slot));
+    if (object->IsHeapObject()) {
+      if (Heap::InFromSpace(object)) {
+        callback(reinterpret_cast<HeapObject**>(slot),
+                 HeapObject::cast(object));
+        Object* new_object = *slot;
+        if (InNewSpace(new_object)) {
+          ASSERT(Heap::InToSpace(new_object));
+          ASSERT(new_object->IsHeapObject());
+          store_buffer_.EnterDirectlyIntoStoreBuffer(
+              reinterpret_cast<Address>(slot));
+        }
+        ASSERT(!MarkCompactCollector::IsOnEvacuationCandidate(new_object));
+      } else if (MarkCompactCollector::IsOnEvacuationCandidate(object)) {
+        mark_compact_collector()->RecordSlot(slot, slot, object);

[Erik Corry, 2011/07/04 11:04:11]

Does this happen?  The pointer can't suddenly start pointing into the evacuation
candidate unless we are allocating in the evacuation candidate while promoting
from new space.  It seems wrong to allocate in an evacuation candidate once we
have decided it is an evacuation candidate.

[Vyacheslav Egorov (Chromium), 2011/08/05 12:50:28]

This else if belongs to the first if. So yes this can happen. Added a comment.

       }
     }
     slot_address += kPointerSize;