Merge changes 8634 and 8636 to trunk.

src/mark-compact.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1643 matching lines @@
 
     if (map->IsMarked() && map->attached_to_shared_function_info()) {
       // This map is used for inobject slack tracking and has been detached
       // from SharedFunctionInfo during the mark phase.
       // Since it survived the GC, reattach it now.
       map->unchecked_constructor()->unchecked_shared()->AttachInitialMap(map);
     }
 
     // Clear dead prototype transitions.
     int number_of_transitions = map->NumberOfProtoTransitions();
-    FixedArray* prototype_transitions = map->unchecked_prototype_transitions();
-    int new_number_of_transitions = 0;
-    const int header = Map::kProtoTransitionHeaderSize;
-    const int proto_offset =
-        header + Map::kProtoTransitionPrototypeOffset;
-    const int map_offset = header + Map::kProtoTransitionMapOffset;
-    const int step = Map::kProtoTransitionElementsPerEntry;
-    for (int i = 0; i < number_of_transitions; i++) {
-      Object* prototype = prototype_transitions->get(proto_offset + i * step);
-      Object* cached_map = prototype_transitions->get(map_offset + i * step);
-      if (HeapObject::cast(prototype)->IsMarked() &&
-          HeapObject::cast(cached_map)->IsMarked()) {
-        if (new_number_of_transitions != i) {
-          prototype_transitions->set_unchecked(
-              heap_,
-              proto_offset + new_number_of_transitions * step,
-              prototype,
-              UPDATE_WRITE_BARRIER);
-          prototype_transitions->set_unchecked(
-              heap_,
-              map_offset + new_number_of_transitions * step,
-              cached_map,
-              SKIP_WRITE_BARRIER);
+    if (number_of_transitions > 0) {
+      FixedArray* prototype_transitions =
+          map->unchecked_prototype_transitions();
+      int new_number_of_transitions = 0;
+      const int header = Map::kProtoTransitionHeaderSize;
+      const int proto_offset =
+          header + Map::kProtoTransitionPrototypeOffset;
+      const int map_offset = header + Map::kProtoTransitionMapOffset;
+      const int step = Map::kProtoTransitionElementsPerEntry;
+      for (int i = 0; i < number_of_transitions; i++) {
+        Object* prototype = prototype_transitions->get(proto_offset + i * step);
+        Object* cached_map = prototype_transitions->get(map_offset + i * step);
+        if (HeapObject::cast(prototype)->IsMarked() &&
+            HeapObject::cast(cached_map)->IsMarked()) {
+          if (new_number_of_transitions != i) {
+            prototype_transitions->set_unchecked(
+                heap_,
+                proto_offset + new_number_of_transitions * step,
+                prototype,
+                UPDATE_WRITE_BARRIER);
+            prototype_transitions->set_unchecked(
+                heap_,
+                map_offset + new_number_of_transitions * step,
+                cached_map,
+                SKIP_WRITE_BARRIER);
+          }
+          new_number_of_transitions++;
         }
-        new_number_of_transitions++;
       }
 
       // Fill slots that became free with undefined value.
       Object* undefined = heap()->raw_unchecked_undefined_value();
       for (int i = new_number_of_transitions * step;
            i < number_of_transitions * step;
            i++) {
         prototype_transitions->set_unchecked(heap_,
                                              header + i,
                                              undefined,
@@ skipping 1569 matching lines @@
 }
 
 
 void MarkCompactCollector::Initialize() {
   StaticPointersToNewGenUpdatingVisitor::Initialize();
   StaticMarkingVisitor::Initialize();
 }
 
 
 } }  // namespace v8::internal