https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94962
--- Comment #6 from Hongtao.liu <crazylht at gmail dot com> --- (In reply to Nemo from comment #5) > (In reply to Jakub Jelinek from comment #2) > > I would be happy if GCC could just emit optimal code (single vcmpeqd > instruction) for this useful constant: > > _mm256_set_m128i(_mm_setzero_si128(), _mm_set1_epi8(-1)) > > aka. > > _mm256_inserti128_si256(_mm256_setzero_si256(), _mm_set1_epi8(-1), 0) > > > (The latter is just what GCC uses to implement _mm256_zextsi128_si256, if I > am reading the headers correctly.) > > It's a minor thing, but I was a little surprised to find that none of the > compilers I know of are able to do this. At least, not with any input I > tried. vmovdqa xmm0, xmm0 is not redundant here, it would clear up 128-256 bit which is the meaning of `zext`.
