[InstSimplify] Add self-fdiv identities for -ffinite-math-only.

When NaNs and Infs are ignored we can fold
 X /  X -> 1.0
-X /  X -> -1.0
 X / -X -> -1.0

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239701 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed