https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114657
--- Comment #3 from Joseph S. Myers <jsm28 at gcc dot gnu.org> --- https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2958.htm has my analysis of the various notions of "type" used in relation to bit-fields and the questions of what expressions are considered to have special properties associated with referring to a bit-field.