[AArch64 NEON] Fixed fused multiply negate add/sub patterns

The correct pattern matching should be:

- fnmadd is (-Ra) + (-Rn)*Rm  which should be matched as:

  fma (fneg node:$Rn),  node:$Rm, (fneg node:$Ra) and as

  (f32 (fsub (f32 (fneg FPR32:$Ra)), (f32 (fmul FPR32:$Rn, FPR32:$Rm))))

- fnmsub is (-Ra) + Rn*Rm which should be matched as

  fma node:$Rn,  node:$Rm, (fneg node:$Ra) and as

  (f32 (fsub (f32 (fmul FPR32:$Rn, FPR32:$Rm)), FPR32:$Ra))))



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197928 91177308-0d34-0410-b5e6-96231b3b80d8
[AArch64] Check fmul node single use in fused multiply patterns

Check for single use of fmul node in fused multiply patterns
to allow generation of fused multiply add/sub instructions.
Otherwise fmul operation ends up being repeated more than
once which does not help peformance on targets with
only one MAC unit, as for example cortex-a53.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197929 91177308-0d34-0410-b5e6-96231b3b80d8