No -march (Generic x86_64)
[jamarial@chie build]$ time tools/ffhash sha512 ../etv5k-x264-b10000.mkv
real    0m1.134s
user    0m1.100s
sys     0m0.030s

march=haswell (implicit -mbmi2)
[jamarial@chie build]$ time tools/ffhash sha512 ../etv5k-x264-b10000.mkv
real    0m0.869s
user    0m0.830s
sys     0m0.037s