Make embedded maps in optimized code weak.

src/objects-visiting-inl.h

Index: src/objects-visiting-inl.h
diff --git a/src/objects-visiting-inl.h b/src/objects-visiting-inl.h
index 925b2562f292558687716cc6be8c0b618d1f7f04..c6299b57b3f53c0785bac0b3d6ca36162b454ed4 100644
--- a/src/objects-visiting-inl.h
+++ b/src/objects-visiting-inl.h
@@ -261,12 +261,9 @@ void StaticMarkingVisitor<StaticVisitor>::VisitMap(
     map_object->ClearCodeCache(heap);
   }
 
-  // When map collection is enabled we have to mark through map's
-  // transitions and back pointers in a special way to make these links
-  // weak.  Only maps for subclasses of JSReceiver can have transitions.
-  STATIC_ASSERT(LAST_TYPE == LAST_JS_RECEIVER_TYPE);
-  if (FLAG_collect_maps &&
-      map_object->instance_type() >= FIRST_JS_RECEIVER_TYPE) {
+  // When map collection is enabled we have to mark through map's transitions
+  // and back pointers in a special way to make these links weak.
+  if (FLAG_collect_maps && map_object->CanTransition()) {
     MarkMapContents(heap, map_object);
   } else {
     StaticVisitor::VisitPointers(heap,
@@ -394,6 +391,15 @@ void StaticMarkingVisitor<StaticVisitor>::MarkMapContents(
     ASSERT(transitions->IsMap() || transitions->IsUndefined());
   }
 
+  // Mark prototype dependent codes array but do not push it onto marking
+  // stack, this will make references from it weak. We will clean dead
+  // dead codes when we iterate over maps in ClearNonLiveTransitions.
+  Object** slot = HeapObject::RawField(reinterpret_cast<HeapObject*>(map),
+                                       Map::kDependentCodesOffset);
+  HeapObject* obj = HeapObject::cast(*slot);
+  heap->mark_compact_collector()->RecordSlot(slot, slot, obj);
+  StaticVisitor::MarkObjectWithoutPush(heap, obj);
+
   // Mark the pointer fields of the Map. Since the transitions array has
   // been marked already, it is fine that one of these fields contains a
   // pointer to it.
@@ -645,8 +651,20 @@ void Code::CodeIterateBody(ObjectVisitor* v) {
   IteratePointer(v, kTypeFeedbackInfoOffset);
 
   RelocIterator it(this, mode_mask);
-  for (; !it.done(); it.next()) {
-    it.rinfo()->Visit(v);
+  if (kind() == OPTIMIZED_FUNCTION) {
+    // Treat embedded maps in optimized code as weak.

[Michael Starzinger, 2012/12/14 14:15:26]

I think this is the wrong place to skip embedded maps because this visitor is
used in other places (e.g. HeapObject::IterateBody) as well. And there you don't
want to skip embedded maps. So this has to be specific to the
StaticMarkingVisitor. We already talked about this offline.

[ulan, 2013/01/17 09:35:10]

Done.

+    for (; !it.done(); it.next()) {
+      RelocInfo* info = it.rinfo();
+      if (!RelocInfo::IsEmbeddedObject(info->rmode()) ||
+          !info->target_object()->IsMap() ||
+          !Map::cast(info->target_object())->CanTransition()) {
+        info->Visit(v);
+      }
+    }
+  } else {
+    for (; !it.done(); it.next()) {
+      it.rinfo()->Visit(v);
+    }
   }
 }
 
@@ -677,8 +695,20 @@ void Code::CodeIterateBody(Heap* heap) {
       reinterpret_cast<Object**>(this->address() + kTypeFeedbackInfoOffset));
 
   RelocIterator it(this, mode_mask);
-  for (; !it.done(); it.next()) {
-    it.rinfo()->template Visit<StaticVisitor>(heap);
+  if (kind() == OPTIMIZED_FUNCTION) {
+    // Treat embedded maps in optimized code as weak.

[Michael Starzinger, 2012/12/14 14:15:26]

Likewise.

[ulan, 2013/01/17 09:35:10]

Done.

+    for (; !it.done(); it.next()) {
+      RelocInfo* info = it.rinfo();
+      if (!RelocInfo::IsEmbeddedObject(info->rmode()) ||
+          !info->target_object()->IsMap() ||
+          !Map::cast(info->target_object())->CanTransition()) {
+        it.rinfo()->template Visit<StaticVisitor>(heap);
+      }
+    }
+  } else {
+    for (; !it.done(); it.next()) {
+      it.rinfo()->template Visit<StaticVisitor>(heap);
+    }
   }
 }