https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78611
--- Comment #5 from Uroš Bizjak <ubizjak at gmail dot com> --- I can confirm the slowdown with -mavx on ivybridge-E: -msse4 real 0m0.278s user 0m0.276s sys 0m0.002s -mavx real 0m0.699s user 0m0.696s sys 0m0.003s in -msse4 case, perf report annotates mtz_ with: 1.33 │ → callq logf@plt │ addss 0x7acb(%rip),%xmm0 # 40b0cc <options.236.5085+0x4c> 6.87 │ mulss 0x7ac7(%rip),%xmm0 # 40b0d0 <options.236.5085+0x50> 9.53 │ addss 0x7aa7(%rip),%xmm0 # 40b0b8 <options.236.5085+0x38> 7.54 │ cvttss %xmm0,%eax 7.76 │ cmp %r12d,%eax and in -mavx case: 0.09 │ → callq logf@plt │ vaddss 0x7a85(%rip),%xmm0,%xmm0 # 40b16c <options.236.5085+0x4c> 59.65 │ vmulss 0x7a81(%rip),%xmm0,%xmm0 # 40b170 <options.236.5085+0x50> 2.92 │ vaddss 0x7a61(%rip),%xmm0,%xmm0 # 40b158 <options.236.5085+0x38> 2.04 │ vcvtts %xmm0,%eax 2.65 │ cmp %r12d,%eax Something happens with vmulss, but I doubt it is the compiler fault.