Optimized FMA intrinsic + FNEG , like
and FNEG + FMA, like
a*b-c or (-a)*b+c
Legalization of ISD::FNEG is delayed to give a chance to combine it with X86ISD::FMADD/MSUB/NMADD/NMSUB.
7 out of 8 test cases are optimized. The last test case requires additional investigation and, probably, changes in the clang header.