I am trying to avoid the frequency throttling associated with using wide vector instructions. But I guess AVX should be safe ? Not sure about AVX512 though, won't it cause frequency drops if I use that instead?
XF86FixupBWInsts.cpp:208 checks whether the super reg %eax is live after movw D0(%rip), %ax. In the original code it is not live, but in our case it is because movd is reading from %eax. So it bails and does not replace the register.