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..dda79ce24ea08e4bc5606b6cbdae5ec0f1b8f6a6 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -1451,6 +1451,21 @@ 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 (!object->IsJSObject()) {
+    return false;
+  }
+  Object* obj_constructor = (JSObject::cast(object))->map()->GetConstructor();
+  JSFunction* constructor = JSFunction::cast(obj_constructor);
+  if (constructor == NULL) return false;
+  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);
@@ -1569,6 +1584,13 @@ void Heap::Scavenge() {
   promotion_queue_.Initialize();
 
   ScavengeVisitor scavenge_visitor(this);
+
+  if (FLAG_scavenge_remove_unmodified_objects) {
+    isolate()->global_handles()->IdentifyWeakUnmodifiedObjects(

[mythria, 2015/09/25 17:23:51]

Before, we process anything we park the unmodified objects as partially
dependent. This allows the later passes to discard these objects. In the earlier
patches, we used to do this when we processed object groups. However, by that
time all weak nodes have been moved to to_space and that causes problems if we
want to discard them

+        &IsUnModifiedNewSpaceObject);
+  }
+
+
   {
     // Copy roots.
     GCTracer::Scope gc_scope(tracer(), GCTracer::Scope::SCAVENGER_ROOTS);
@@ -1607,7 +1629,7 @@ void Heap::Scavenge() {
     new_space_front = DoScavenge(&scavenge_visitor, new_space_front);
   }
 
-  {
+  if (!FLAG_scavenge_remove_unmodified_objects) {
     GCTracer::Scope gc_scope(tracer(),
                              GCTracer::Scope::SCAVENGER_OBJECT_GROUPS);
     while (isolate()->global_handles()->IterateObjectGroups(
@@ -2852,8 +2874,8 @@ void Heap::AddAllocationSiteToScratchpad(AllocationSite* site,
       // candidates are not part of the global list of old space pages and
       // releasing an evacuation candidate due to a slots buffer overflow
       // results in lost pages.
-      mark_compact_collector()->ForceRecordSlot(allocation_sites_scratchpad(),
-                                                slot, *slot);
+      mark_compact_collector()->RecordSlot(allocation_sites_scratchpad(), slot,
+                                           *slot);
     }
     allocation_sites_scratchpad_length_++;
   }