https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108427
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- -mms-bitfields is enabled by default. See TARGET_MS_BITFIELD_LAYOUT_P and https://gcc.gnu.org/onlinedocs/gcc-12.2.0/gcc/x86-Options.html#index-mms-bitfields The layout of bitfields are different here ...