https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71559
--- Comment #13 from Carlos Tripiana Montes <tripiana at gmail dot com> --- The code you are referring to (ix86_fp_compare_mode) is an old, well-stablish, one: https://gcc.gnu.org/viewcvs/gcc/trunk/gcc/config/i386/i386.c?r1=38978&r2=38979&pathrev=38979& (line 4653 enum machine_mode) The actual code comes from a 2001's commit. Just to point out that, most probably, there's a lot of code depending on it.