I wonder why you ask. As long as you are using no optimizations,
the other registers probably wont be used much, but no one is guaranteeing that, so I would never count on such observations.
Note that the libraries are built with optimizations enabled, even if your code is not.
Another thing, there is an option not to use A6 for the frame, so this makes one register more available. Using the register calling convention (that's advanced), uses improves the register usage too.
Daniel