Revert part of 11727 as it sometimes tanked V8 benchmark (raytrace) performance

src/objects.cc

 // Copyright 2012 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 7545 matching lines @@
   return code->optimizable();
 }
 
 
 MaybeObject* JSObject::OptimizeAsPrototype() {
   if (IsGlobalObject()) return this;
 
   // Make sure prototypes are fast objects and their maps have the bit set
   // so they remain fast.
   Map* proto_map = map();
-  if (!proto_map->used_for_prototype()) {
-    if (!HasFastProperties()) {
-      MaybeObject* new_proto = TransformToFastProperties(0);
-      if (new_proto->IsFailure()) return new_proto;
-      ASSERT(new_proto == this);
-      proto_map = map();
-      if (!proto_map->is_shared()) {
-        proto_map->set_used_for_prototype(true);
-      }
-    } else {
-      Heap* heap = GetHeap();
-      // We use the hole value as a singleton key in the prototype transition
-      // map so that we don't multiply the number of maps unnecessarily.
-      Map* new_map =
-          proto_map->GetPrototypeTransition(heap->the_hole_value());
-      if (new_map == NULL) {
-        MaybeObject* maybe_new_map =
-            proto_map->CopyDropTransitions(DescriptorArray::MAY_BE_SHARED);
-        if (!maybe_new_map->To<Map>(&new_map)) return maybe_new_map;
-        new_map->set_used_for_prototype(true);
-        MaybeObject* ok =
-            proto_map->PutPrototypeTransition(heap->the_hole_value(),
-                                              new_map);
-        if (ok->IsFailure()) return ok;
-      }
-      ASSERT(!proto_map->is_shared() && !new_map->is_shared());
-      set_map(new_map);
-    }
+  if (!HasFastProperties()) {
+    MaybeObject* new_proto = TransformToFastProperties(0);
+    if (new_proto->IsFailure()) return new_proto;
+    ASSERT(new_proto == this);
+    proto_map = map();
   }
   return this;
 }
 
 
 MaybeObject* JSFunction::SetInstancePrototype(Object* value) {
   ASSERT(value->IsJSReceiver());
   Heap* heap = GetHeap();
 
-  // First some logic for the map of the prototype to make sure the
-  // used_for_prototype flag is set.
+  // First some logic for the map of the prototype to make sure it is in fast
+  // mode.
   if (value->IsJSObject()) {
     MaybeObject* ok = JSObject::cast(value)->OptimizeAsPrototype();
     if (ok->IsFailure()) return ok;
   }
 
   // Now some logic for the maps of the objects that are created by using this
   // function as a constructor.
   if (has_initial_map()) {
     // If the function has allocated the initial map
     // replace it with a copy containing the new prototype.
@@ skipping 5658 matching lines @@
   set_year(Smi::FromInt(year), SKIP_WRITE_BARRIER);
   set_month(Smi::FromInt(month), SKIP_WRITE_BARRIER);
   set_day(Smi::FromInt(day), SKIP_WRITE_BARRIER);
   set_weekday(Smi::FromInt(weekday), SKIP_WRITE_BARRIER);
   set_hour(Smi::FromInt(hour), SKIP_WRITE_BARRIER);
   set_min(Smi::FromInt(min), SKIP_WRITE_BARRIER);
   set_sec(Smi::FromInt(sec), SKIP_WRITE_BARRIER);
 }
 
 } }  // namespace v8::internal