Swapped transition array and descriptor array.

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index ba7fcf0b32fde861d6bf94fc0e7d176aa98f19a2..83e2280c6b349a03c730b18f239a0fa1122889ae 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -1849,28 +1849,26 @@ template void Marker<MarkCompactCollector>::MarkMapContents(Map* map);
 template <class T>
 void Marker<T>::MarkMapContents(Map* map) {
   // Make sure that the back pointer stored either in the map itself or inside
-  // its prototype transitions array is marked. Treat pointers in the descriptor
-  // array as weak and also mark that array to prevent visiting it later.
+  // its transitions array is marked. Treat pointers in the transitions array as
+  // weak and also mark that array to prevent visiting it later.
   base_marker()->MarkObjectAndPush(HeapObject::cast(map->GetBackPointer()));
 
-  Object** descriptor_array_slot =
-      HeapObject::RawField(map, Map::kInstanceDescriptorsOrBackPointerOffset);
-  Object* descriptor_array = *descriptor_array_slot;
-  if (descriptor_array->IsDescriptorArray()) {
-    MarkDescriptorArray(reinterpret_cast<DescriptorArray*>(descriptor_array));
+  Object** transitions_slot =
+      HeapObject::RawField(map, Map::kTransitionsOrBackPointerOffset);
+  Object* transitions = *transitions_slot;
+  if (transitions->IsTransitionArray()) {
+    MarkTransitionArray(reinterpret_cast<TransitionArray*>(transitions));
   } else {
     // Already marked by marking map->GetBackPointer().
-    ASSERT(descriptor_array->IsMap() || descriptor_array->IsUndefined());
+    ASSERT(transitions->IsMap() || transitions->IsUndefined());
   }
 
-  // Mark the Object* fields of the Map. Since the descriptor array has been
-  // marked already, it is fine that one of these fields contains a pointer
-  // to it. But make sure to skip back pointer.
-  STATIC_ASSERT(Map::kPointerFieldsEndOffset ==
-                Map::kBitField3Offset + kPointerSize);
+  // Mark the Object* 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.
   Object** start_slot =
       HeapObject::RawField(map, Map::kPointerFieldsBeginOffset);
-  Object** end_slot = HeapObject::RawField(map, Map::kBitField3Offset);
+  Object** end_slot = HeapObject::RawField(map, Map::kPointerFieldsEndOffset);
   for (Object** slot = start_slot; slot < end_slot; slot++) {
     Object* obj = *slot;
     if (!obj->NonFailureIsHeapObject()) continue;
@@ -1881,77 +1879,15 @@ void Marker<T>::MarkMapContents(Map* map) {
 
 
 template <class T>
-void Marker<T>::MarkDescriptorArray(DescriptorArray* descriptors) {
-  // Empty descriptor array is marked as a root before any maps are marked.
-  ASSERT(descriptors != descriptors->GetHeap()->empty_descriptor_array());
-
-  if (!base_marker()->MarkObjectWithoutPush(descriptors)) return;
-  Object** descriptor_start = descriptors->data_start();
-
-  // Since the descriptor array itself is not pushed for scanning, all fields
-  // that point to objects manually have to be pushed, marked, and their slots
-  // recorded.
-  if (descriptors->HasEnumCache()) {
-    Object** enum_cache_slot = descriptors->GetEnumCacheSlot();
-    Object* enum_cache = *enum_cache_slot;
-    base_marker()->MarkObjectAndPush(
-        reinterpret_cast<HeapObject*>(enum_cache));
-    mark_compact_collector()->RecordSlot(descriptor_start,
-                                         enum_cache_slot,
-                                         enum_cache);
-  }
-
-  if (descriptors->HasTransitionArray()) {
-    Object** transitions_slot = descriptors->GetTransitionsSlot();
-    Object* transitions = *transitions_slot;
-    mark_compact_collector()->RecordSlot(descriptor_start,
-                                         transitions_slot,
-                                         transitions);
-    MarkTransitionArray(reinterpret_cast<TransitionArray*>(transitions));
-  }
-
-  // If the descriptor contains a transition (value is a Map), we don't mark the
-  // value as live. It might be removed by ClearNonLiveTransitions later.
-  for (int i = 0; i < descriptors->number_of_descriptors(); ++i) {
-    Object** key_slot = descriptors->GetKeySlot(i);
-    Object* key = *key_slot;
-    if (key->IsHeapObject()) {
-      base_marker()->MarkObjectAndPush(HeapObject::cast(key));
-      mark_compact_collector()->RecordSlot(descriptor_start, key_slot, key);
-    }
-
-    Object** value_slot = descriptors->GetValueSlot(i);
-    if (!(*value_slot)->IsHeapObject()) continue;
-    HeapObject* value = HeapObject::cast(*value_slot);
-
-    mark_compact_collector()->RecordSlot(descriptor_start,
-                                         value_slot,
-                                         value);
-
-    PropertyDetails details(descriptors->GetDetails(i));
-
-    switch (details.type()) {
-      case NORMAL:
-      case FIELD:
-      case CONSTANT_FUNCTION:
-      case HANDLER:
-      case INTERCEPTOR:
-      case CALLBACKS:
-        base_marker()->MarkObjectAndPush(value);
-        break;
-      case TRANSITION:
-      case NONEXISTENT:
-        UNREACHABLE();
-        break;
-    }
-  }
-}
-
-template <class T>
 void Marker<T>::MarkTransitionArray(TransitionArray* transitions) {
   if (!base_marker()->MarkObjectWithoutPush(transitions)) return;
   Object** transitions_start = transitions->data_start();
 
+  DescriptorArray* descriptors = transitions->descriptors();
+  base_marker()->MarkObjectAndPush(descriptors);
+  mark_compact_collector()->RecordSlot(
+      transitions_start, transitions->GetDescriptorsSlot(), descriptors);
+
   if (transitions->HasPrototypeTransitions()) {
     // Mark prototype transitions array but don't push it into marking stack.
     // This will make references from it weak. We will clean dead prototype