https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125780
--- Comment #2 from Georg-Johann Lay <gjl at gcc dot gnu.org> --- Actually, this ICE also happens on avrs with plenty of registers (30) available, like: $ avr-gcc -mmcu=avr4 -Os -S -v Plus, no callee-saved register are used for argument passing. Is seems there are some hard-reg constraints bits missing?
