Interesting post, thanks. It certainly seems like llvm-mos' codegen is improving markedly modulo some concerns brought up over bloat. But I also note that a number of the performance recommendations (prefer using more globals, avoid passing structures presumably due to the limited hardware stack) aren't exactly current programming convention - and for that matter, they're exactly what you would do writing assembly by hand. These recommendations would be true for cc65 too of course, but it still makes the point that using C to develop on 6502 is just making the dog walk, not the dog walking well.