Do not cache functions until we know they are fully constructed.

src/execution.cc

 // Copyright 2006-2008 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 421 matching lines @@
   return result;
 }
 
 
 Handle<JSFunction> Execution::InstantiateFunction(
     Handle<FunctionTemplateInfo> data, bool* exc) {
   // Fast case: see if the function has already been instantiated
   int serial_number = Smi::cast(data->serial_number())->value();
   Object* elm =
       Top::global_context()->function_cache()->GetElement(serial_number);
-  if (!elm->IsUndefined()) return Handle<JSFunction>(JSFunction::cast(elm));
+  if (elm->IsJSFunction()) return Handle<JSFunction>(JSFunction::cast(elm));
   // The function has not yet been instantiated in this context; do it.
   Object** args[1] = { Handle<Object>::cast(data).location() };
   Handle<Object> result =
       Call(Top::instantiate_fun(), Top::builtins(), 1, args, exc);
   if (*exc) return Handle<JSFunction>::null();
   return Handle<JSFunction>::cast(result);
 }
 
 
 Handle<JSObject> Execution::InstantiateObject(Handle<ObjectTemplateInfo> data,
@@ skipping 128 matching lines @@
   // All allocation spaces other than NEW_SPACE have the same effect.
   Heap::CollectGarbage(0, OLD_DATA_SPACE);
   return v8::Undefined();
 }
 
 
 static GCExtension kGCExtension;
 v8::DeclareExtension kGCExtensionDeclaration(&kGCExtension);
 
 } }  // namespace v8::internal