Merge 183060: Prevent loop-unroll from making assumptions about undefined behavior.

    Fixes rdar:14036816, PR16130.

    There is an opportunity to compute precise trip counts for 'or'
    expressions and multi-exit loops.
    rdar:14038809: Optimize trip count computation for multi-exit loops.

    To do this we need to record the fact that ExitLimit assumes NSW. When
    it does not we can safely assume that the loop trip count is the
    minimum ExitLimt across all subexpressions and loop exits.

    git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183060 91177308-0d34-0410-b5e6-96231b3b80d8


git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_33@183066 91177308-0d34-0410-b5e6-96231b3b80d8