Carter Burwell confirmed that Rob will perform "Renesmee's Lullaby" in BD 2

@CarterBuwell tweeted:

"Just wrote "Renesmee's Lullaby" for Twilight Breaking Dawn. Rob Pattinson will play it on camera this week."


Confirmation on his official website:

"And he just wrote "Renesmee's Lullaby" for Twilight Breaking Dawn 2, which Rob Pattinson will play on camera. The film will be released in November 2012."

Source