Allocate arguments object on-demand instead of at function entry....

src/accessors.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 493 matching lines @@
 
   // Find the top invocation of the function by traversing frames.
   for (JavaScriptFrameIterator it; !it.done(); it.Advance()) {
     // Skip all frames that aren't invocations of the given function.
     JavaScriptFrame* frame = it.frame();
     if (frame->function() != *function) continue;
 
     // If there is an arguments variable in the stack, we return that.
     int index = ScopeInfo<>::StackSlotIndex(frame->code(),
                                             Heap::arguments_symbol());
-    if (index >= 0) return frame->GetExpression(index);
+    if (index >= 0) {
+      Handle<Object> arguments = Handle<Object>(frame->GetExpression(index));
+      if (!arguments->IsTheHole()) return *arguments;
+    }
 
     // If there isn't an arguments variable in the stack, we need to
     // find the frame that holds the actual arguments passed to the
     // function on the stack.
     it.AdvanceToArgumentsFrame();
     frame = it.frame();
 
     // Get the number of arguments and construct an arguments object
     // mirror for the right frame.
     const int length = frame->GetProvidedParametersCount();
@@ skipping 117 matching lines @@
 }
 
 
 const AccessorDescriptor Accessors::ObjectPrototype = {
   ObjectGetPrototype,
   ObjectSetPrototype,
   0
 };
 
 } }  // namespace v8::internal