https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87133
--- Comment #5 from Martin Liška <marxin at gcc dot gnu.org> --- In calls.c I see: │4742 if (outmode != VOIDmode) │4743 { │4744 tfom = lang_hooks.types.type_for_mode (outmode, 0); >│4745 if (aggregate_value_p (tfom, 0)) (gdb) p tfom $2 = <tree 0x0> (gdb) p outmode $3 = E_KFmode Would it help?