As mentioned on PR30845, we were performing our vXi64 multiplication as:
AloBlo = pmuludq(a, b); AloBhi = pmuludq(a, psrlqi(b, 32)); AhiBlo = pmuludq(psrlqi(a, 32), b); return AloBlo + psllqi(AloBhi, 32)+ psllqi(AhiBlo, 32);
when we could avoid one of the upper shifts with:
AloBlo = pmuludq(a, b); AloBhi = pmuludq(a, psrlqi(b, 32)); AhiBlo = pmuludq(psrlqi(a, 32), b); return AloBlo + psllqi(AloBhi + AhiBlo, 32);
This matches the lowering on gcc/icc.