http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60300
--- Comment #3 from Matthijs Kooijman <matthijs at stdin dot nl> --- Hmm, I don't think the gcc sources support that. AFAICT, they attempt to just find the shortest approach, without caring for speed. For example, look at avr.c, around line 1265, where it says: /************ Use shortest method ************/ emit_insn (get_sequence_length (sp_plus_insns) < get_sequence_length (fp_plus_insns) ? sp_plus_insns : fp_plus_insns); https://github.com/mirrors/gcc/blob/c2e306f5efb32b7eed856a1844487cff09aa86ac/gcc/config/avr/avr.c#L1265-L1270