He's not a diver.
Alves, Busquets - yes, Messi - no. If you watch Barcelona regularly you will know he gets kicked up and down the pitch basically every match and most of the time will try and stay on his feet.
Even on that one occasion last night when people were calling him a diver, it wasn't a dive. It was a fair tackle that made Messi fall to the ground and the ref gave a free kick. It was a bad decision from the referee, not a dive.
If we're talking about the one that got Denilson booked, it appeared to me he had a sneeky look at the ref whilst rolling around.