Changed scavenge GC to collect unmodified references

src/heap/heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/heap.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/base/bits.h"
 #include "src/base/once.h"
@@ skipping 1433 matching lines @@
   }
 }
 
 
 static bool IsUnscavengedHeapObject(Heap* heap, Object** p) {
   return heap->InNewSpace(*p) &&
          !HeapObject::cast(*p)->map_word().IsForwardingAddress();
 }
 
 
+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);
 }
 
 
 void PromotionQueue::Initialize() {
   // The last to-space page may be used for promotion queue. On promotion
   // conflict, we use the emergency stack.
   DCHECK((Page::kPageSize - MemoryChunk::kBodyOffset) % (2 * kPointerSize) ==
@@ skipping 136 matching lines @@
     if (collector->is_code_flushing_enabled()) {
       collector->code_flusher()->IteratePointersToFromSpace(&scavenge_visitor);
     }
   }
 
   {
     GCTracer::Scope gc_scope(tracer(), GCTracer::Scope::SCAVENGER_SEMISPACE);
     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(
         &scavenge_visitor, &IsUnscavengedHeapObject)) {
       new_space_front = DoScavenge(&scavenge_visitor, new_space_front);
     }
     isolate()->global_handles()->RemoveObjectGroups();
     isolate()->global_handles()->RemoveImplicitRefGroups();
   }
 
@@ skipping 4484 matching lines @@
 }
 
 
 // static
 int Heap::GetStaticVisitorIdForMap(Map* map) {
   return StaticVisitorBase::GetVisitorId(map);
 }
 
 }  // namespace internal
 }  // namespace v8