[SCEV] Prove no-overflow via constant ranges

Exploit ScalarEvolution::getRange's newly acquired smartness (since
r262438) by using that to infer nsw and nuw when possible.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@262639 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed