Revert "[ValueTracking] Teach computeKnownBits for PHI nodes to compute sign bit for a recurrence with a NSW addition."

This is breaking an optimizaton remark test in clang. I've identified a couple fixes for that, but want to understand it better before I commit to anything.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@274102 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed