Adding hidden values always turned the object slow case because the...

src/objects.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 1111 matching lines @@
     set_properties(FixedArray::cast(values));
   }
   set_map(new_map);
   return FastPropertyAtPut(index, value);
 }
 
 
 Object* JSObject::AddFastProperty(String* name,
                                   Object* value,
                                   PropertyAttributes attributes) {
-  // Normalize the object if the name is not a real identifier.
+  // Normalize the object if the name is an actual string (not the
+  // hidden symbols) and is not a real identifier.
   StringInputBuffer buffer(name);
-  if (!Scanner::IsIdentifier(&buffer)) {
+  if (!Scanner::IsIdentifier(&buffer) && name != Heap::hidden_symbol()) {
     Object* obj = NormalizeProperties(CLEAR_INOBJECT_PROPERTIES);
     if (obj->IsFailure()) return obj;
     return AddSlowProperty(name, value, attributes);
   }
 
   DescriptorArray* old_descriptors = map()->instance_descriptors();
   // Compute the new index for new field.
   int index = map()->NextFreePropertyIndex();
 
   // Allocate new instance descriptors with (name, index) added
@@ skipping 4020 matching lines @@
            !FixedArray::cast(elements())->get(index)->IsTheHole();
   } else {
     return element_dictionary()->FindNumberEntry(index) != -1;
   }
 }
 
 
 Object* JSObject::GetHiddenProperties(bool create_if_needed) {
   String* key = Heap::hidden_symbol();
   if (this->HasFastProperties()) {
-    // If the object has fast properties, check whether the first slot in the
-    // descriptor array matches the hidden symbol. Since the hidden symbols
-    // hash code is zero it will always occupy the first entry if present.
+    // If the object has fast properties, check whether the first slot
+    // in the descriptor array matches the hidden symbol. Since the
+    // hidden symbols hash code is zero (and no other string has hash
+    // code zero) it will always occupy the first entry if present.
     DescriptorArray* descriptors = this->map()->instance_descriptors();
-    if (descriptors->number_of_descriptors() > 0) {
-      if (descriptors->GetKey(0) == key) {
-#ifdef DEBUG
-        PropertyDetails details(descriptors->GetDetails(0));
-        ASSERT(details.type() == FIELD);
-#endif  // DEBUG
-        Object* value = descriptors->GetValue(0);
-        return FastPropertyAt(Descriptor::IndexFromValue(value));
-      }
+    DescriptorReader r(descriptors);
+    if (!r.eos() && (r.GetKey() == key) && r.IsProperty()) {
+      ASSERT(r.type() == FIELD);
+      return FastPropertyAt(r.GetFieldIndex());
     }
   }
 
   // Only attempt to find the hidden properties in the local object and not
   // in the prototype chain.
   if (!this->HasLocalProperty(key)) {
     // Hidden properties object not found. Allocate a new hidden properties
     // object if requested. Otherwise return the undefined value.
     if (create_if_needed) {
       Object* obj = Heap::AllocateJSObject(
@@ skipping 2217 matching lines @@
   // No break point.
   if (break_point_objects()->IsUndefined()) return 0;
   // Single beak point.
   if (!break_point_objects()->IsFixedArray()) return 1;
   // Multiple break points.
   return FixedArray::cast(break_point_objects())->length();
 }
 #endif
 
 } }  // namespace v8::internal