Avoid map transitions and multiple backing arrays for builtin prototypes...

src/runtime.cc

 // Copyright 2006-2009 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 1004 matching lines @@
         ASSERT(Top::has_pending_exception());
         return Failure::Exception();
       }
     }
   }
 
   return *value;
 }
 
 
+static Object* Runtime_OptimizeObjectForAddingMultipleProperties(
+    Arguments args) {
+  HandleScope scope;
+  ASSERT(args.length() == 2);
+  CONVERT_ARG_CHECKED(JSObject, object, 0);
+  CONVERT_SMI_CHECKED(properties, args[1]);
+  if (object->HasFastProperties()) {
+    NormalizeProperties(object, KEEP_INOBJECT_PROPERTIES, properties);
+  }
+  return *object;
+}
+
+
+static Object* Runtime_TransformToFastProperties(Arguments args) {
+  HandleScope scope;
+  ASSERT(args.length() == 1);
+  CONVERT_ARG_CHECKED(JSObject, object, 0);
+  if (!object->HasFastProperties() && !object->IsGlobalObject()) {
+    TransformToFastProperties(object, 0);
+  }
+  return *object;
+}
+
+
 static Object* Runtime_RegExpExec(Arguments args) {
   HandleScope scope;
   ASSERT(args.length() == 4);
   CONVERT_ARG_CHECKED(JSRegExp, regexp, 0);
   CONVERT_ARG_CHECKED(String, subject, 1);
   // Due to the way the JS calls are constructed this must be less than the
   // length of a string, i.e. it is always a Smi.  We check anyway for security.
   CONVERT_SMI_CHECKED(index, args[2]);
   CONVERT_ARG_CHECKED(JSArray, last_match_info, 3);
   RUNTIME_ASSERT(last_match_info->HasFastElements());
@@ skipping 6566 matching lines @@
   } else {
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     Counters::gc_last_resort_from_js.Increment();
     Heap::CollectAllGarbage();
   }
 }
 
 
 } }  // namespace v8::internal