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..60fbec657afce100a8865a00f1d5e2edb2b9eef5 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -1451,6 +1451,24 @@ static bool IsUnscavengedHeapObject(Heap* heap, Object** p) {
 }
 
 
+static bool IsUnModifiedNewSpaceObject(Object** p) {
+  Object* object = *p;
+  DCHECK(object->IsHeapObject());
+  HeapObject* heap_object = HeapObject::cast(object);
+  if (!heap_object->GetIsolate()->heap()->InFromSpace(heap_object)) return true;
+  if (heap_object->map_word().IsForwardingAddress()) return true;
+  if (!object->IsJSObject()) {
+    DCHECK(object->IsName());
+    return false;
+  }
+  // if (heap_object->map()->GetBackPointer()->IsUndefined()) return true;
+  JSFunction* constructor =
+      JSFunction::cast((JSObject::cast(object))->map()->GetConstructor());
+  if (constructor->initial_map() == heap_object->map()) return true;
+  return false;
+}
+
+
 void Heap::ScavengeStoreBufferCallback(Heap* heap, MemoryChunk* page,
                                        StoreBufferEvent event) {
   heap->store_buffer_rebuilder_.Callback(page, event);
@@ -1607,7 +1625,11 @@ void Heap::Scavenge() {
     new_space_front = DoScavenge(&scavenge_visitor, new_space_front);
   }
 
-  {
+  if (false) {
+    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(