IPhone : Converting iPad app to iPhone - xib size issue

I'm trying to implement iPad app in iPhone, The steps i followed are

1. Copied the existing .xib of first view controller and renamed it to name_iPhone.xib


2. 
   

   Enabled size class and auto layouts for name_iPhone.xib

   
   


3. 
   

   Kept the size for view as Inferred

   
   

Now i am printing the screen width(self.view.frame) in log.

NSLog(@"View Frame : %@",NSStringFromCGRect(self.view.frame));

The result is

View frame : {{0, 0}, {600, 600}} //this is the results regardless of any device i run

Actually the log should print the device(in which i am running the app) dimensions, But it always prints 600*600 regardless of device in which app is running. How to automatically resize the root view of a controller according to device dimensions. Please help me finding the solution.