[PATCH] Enable unrolling of multi-exit loops

[Andrew Trick]

I though getUDivExpr was less general. Looking at it now it seems to recurse in roughly the same situations as SCEVDivision, with no memoization. So I think it's ok to bring in SCEVDivision. I can't argue that will create a new problem.

http://reviews.llvm.org/D5550