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 0144262863b161ae31557b183370a13d0eca1ce1..335a3a755b47f331ae52b220f73b8ba7aa9465e2 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -1240,7 +1240,9 @@ bool Heap::PerformGarbageCollection(
       GCTracer::Scope scope(tracer(), GCTracer::Scope::EXTERNAL);
       VMState<EXTERNAL> state(isolate_);
       HandleScope handle_scope(isolate_);
-      CallGCPrologueCallbacks(gc_type, kNoGCCallbackFlags);
+      if (!(gc_type == kGCTypeScavenge &&
+            FLAG_scavenge_reclaim_unmodified_objects))

[rmcilroy, 2015/10/02 18:09:46]

Nit - swap flag and GC_type check order.

[mythria, 2015/10/05 10:55:34]

Done.

+        CallGCPrologueCallbacks(gc_type, kNoGCCallbackFlags);
     }
   }
 
@@ -1325,7 +1327,9 @@ bool Heap::PerformGarbageCollection(
       GCTracer::Scope scope(tracer(), GCTracer::Scope::EXTERNAL);
       VMState<EXTERNAL> state(isolate_);
       HandleScope handle_scope(isolate_);
-      CallGCEpilogueCallbacks(gc_type, gc_callback_flags);
+      if (!(gc_type == kGCTypeScavenge &&
+            FLAG_scavenge_reclaim_unmodified_objects))

[rmcilroy, 2015/10/02 18:09:46]

Ditto

[mythria, 2015/10/05 10:55:34]

Done.

+        CallGCEpilogueCallbacks(gc_type, gc_callback_flags);
     }
   }
 
@@ -1485,6 +1489,22 @@ static bool IsUnscavengedHeapObject(Heap* heap, Object** p) {
 }
 
 
+static bool IsUnModifiedNewSpaceObject(Object** p) {

[rmcilroy, 2015/10/02 18:09:46]

This function doesn't seem to check if the object is in the new space. Just call
it IsUnmodifiedHeapObject() ?

[mythria, 2015/10/05 10:55:34]

Done.

+  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();
+  if (!obj_constructor->IsJSFunction()) return false;
+  JSFunction* constructor = JSFunction::cast(obj_constructor);
+  if (constructor == NULL) return false;
+  if (constructor->initial_map() == heap_object->map()) return true;
+  return false;

[rmcilroy, 2015/10/02 18:09:46]

Nit - just:

return constructor != nullptr && constructor->initial_map() ==
heap_object->map()

(Also replace all NULL with nullptr throughout CL).

[mythria, 2015/10/05 10:55:34]

Done.

+}
+
+
 void Heap::ScavengeStoreBufferCallback(Heap* heap, MemoryChunk* page,
                                        StoreBufferEvent event) {
   heap->store_buffer_rebuilder_.Callback(page, event);
@@ -1603,6 +1623,12 @@ void Heap::Scavenge() {
   promotion_queue_.Initialize();
 
   ScavengeVisitor scavenge_visitor(this);
+
+  if (FLAG_scavenge_reclaim_unmodified_objects) {
+    isolate()->global_handles()->IdentifyWeakUnmodifiedObjects(
+        &IsUnModifiedNewSpaceObject);
+  }
+
   {
     // Copy roots.
     GCTracer::Scope gc_scope(tracer(), GCTracer::Scope::SCAVENGER_ROOTS);
@@ -1641,7 +1667,14 @@ void Heap::Scavenge() {
     new_space_front = DoScavenge(&scavenge_visitor, new_space_front);
   }
 
-  {
+  if (FLAG_scavenge_reclaim_unmodified_objects) {
+    isolate()->global_handles()->MarkNewSpaceWeakUnModifiedObjectsPending(
+        &IsUnscavengedHeapObject);
+
+    isolate()->global_handles()->IterateNewSpaceWeakUnModifiedRoots(
+        &scavenge_visitor);
+    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(
@@ -1650,14 +1683,14 @@ void Heap::Scavenge() {
     }
     isolate()->global_handles()->RemoveObjectGroups();
     isolate()->global_handles()->RemoveImplicitRefGroups();
-  }
 
-  isolate()->global_handles()->IdentifyNewSpaceWeakIndependentHandles(
-      &IsUnscavengedHeapObject);
+    isolate()->global_handles()->IdentifyNewSpaceWeakIndependentHandles(
+        &IsUnscavengedHeapObject);
 
-  isolate()->global_handles()->IterateNewSpaceWeakIndependentRoots(
-      &scavenge_visitor);
-  new_space_front = DoScavenge(&scavenge_visitor, new_space_front);
+    isolate()->global_handles()->IterateNewSpaceWeakIndependentRoots(
+        &scavenge_visitor);
+    new_space_front = DoScavenge(&scavenge_visitor, new_space_front);
+  }
 
   UpdateNewSpaceReferencesInExternalStringTable(
       &UpdateNewSpaceReferenceInExternalStringTableEntry);