Teach InstCombine that (fmul X, -1.0) can be simplified to (fneg X), which LLVM expresses as (fsub -0.0, X).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199420 91177308-0d34-0410-b5e6-96231b3b80d8