Changed scavenge GC to collect unmodified references

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 31b93e71991e219b5c6050bd0f17bd890f6018ec..a34c57da0a8dc8c186260bd5b1ad3289442aeed3 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -1451,6 +1451,19 @@ static bool IsUnscavengedHeapObject(Heap* heap, Object** p) {
 }
 
 
+static bool IsUnModifiedNewSpaceObject(Object** p) {
+  Object* object = *p;
+  if (object->IsHeapObject()) {
+    HeapObject* heap_object = reinterpret_cast<HeapObject*>(object);
+    if (!heap_object->GetIsolate()->heap()->InFromSpace(heap_object))

[jochen (gone - plz use gerrit), 2015/09/21 11:33:25]

if (!IsUnscavengedHeapObject(..)) return true;

+      return true;
+    if (heap_object->map()->GetBackPointer()->IsUndefined()) return true;

[jochen (gone - plz use gerrit), 2015/09/21 11:54:19]

maybe this is the wrong check? Try
heap_object->map()->GetConstructor()->initial_map() == heap_object->map()?

+    return false;
+  }
+  return true;
+}
+
+
 void Heap::ScavengeStoreBufferCallback(Heap* heap, MemoryChunk* page,
                                        StoreBufferEvent event) {
   heap->store_buffer_rebuilder_.Callback(page, event);
@@ -1607,7 +1620,11 @@ void Heap::Scavenge() {
     new_space_front = DoScavenge(&scavenge_visitor, new_space_front);
   }
 
-  {
+  if (FLAG_scavenge_remove_unmodified_objects) {
+    isolate()->global_handles()->IterateNewSpaceWeakRoots(
+        &scavenge_visitor, &IsUnModifiedNewSpaceObject);
+    new_space_front = DoScavenge(&scavenge_visitor, new_space_front);
+  } else {
     GCTracer::Scope gc_scope(tracer(),
                              GCTracer::Scope::SCAVENGER_OBJECT_GROUPS);
     while (isolate()->global_handles()->IterateObjectGroups(