[PATCH] arm: Add ARM VFPv4 VFMA instruction support in fma/fmaf (BZ 15503)

[Wilco Dijkstra]

Hi Adhemerval,

(retry, hopefully it doesn't get messed up again...)

> It is enabled through math-use-builtins-fma.h if  glibc is built
> for VPFv4 (__ARM_FEATURE_FMA predefined by GCC), or through IFUNC
> (testing HWCAP_ARM_VFPv4) otherwise.

A decade late(!), but it looks good to me. I presume using ifunc to native fma still
has a 2x penalty vs inlining fma like your x86 results show?

What is the penalty if you don't have fma? It seems like the new Coremath functions
will cause significant regressions on older targets that we need to discuss in more...

Cheers,
Wilco