You can do tail call optimisation when the last thing you do before you return is a call. That tail call is not necessarily recursive, let alone a call to yours

You can do tail call optimisation when the last thing you do before you return is a call. That tail call is not necessarily recursive, let alone a call to yourself. Whatever it is, its position means your current stack-frame can be reclaimed before you jump. If you can only optimise calls to yourself, you have a very limited form of tail call optimisation. It's an important point in the context of Scheme, where they made a big deal out of experimenting with continuation passing style. In CPS, all function calls are tail calls, and you want to optimise them all, even though most are not recursive.