https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120456
Alexander Monakov <amonakov at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |amonakov at gcc dot gnu.org --- Comment #1 from Alexander Monakov <amonakov at gcc dot gnu.org> --- GCC would have to figure out that 128-bit halves of the first argument to __builtin_shuffle are identical (256-bit pshufb works on 128-bit halves separately, i.e. index 0 in the second half picks the 16'th byte of the input).