Apparently this guy came up with some pretty goofy optimizations like switching in and out of thumb mode to reuse the extra register file along with more "norma

Apparently this guy came up with some pretty goofy optimizations like switching in and out of thumb mode to reuse the extra register file along with more "normal" stuff like self modifying code. I don't think there are any compilers that do that (and I think most people wouldn't want that.) You can totally write GBA games in just C though. In fact I learned C writing GBA homebrew in my teens.