https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89475
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- x &= 0xaa55; x = __builtin_bswap16 (x); if (x & 0xaa55) I think that should be: x &= 0xaa55; x = __builtin_bswap16 (x); if (x & 0x55aa) instead.