That works fine until you have things like branches and function calls. Most call conventions specify which registers arguments are in, and with what you're pro

That works fine until you have things like branches and function calls. Most call conventions specify which registers arguments are in, and with what you're proposing each function call needs to know where it is up to in the rotation at the beginning of the call. If the ahrdware looks after it (either through a index register that stores the position of the next write), then it becomes easier; but no one's doing that, and afaik, the mill is the first machine to do anything close. Stack machines are sort of similar, but word differently because they need to remember all values on the stack untill they're popped. The mill just forgets old results and the compiler must make sure they're still available when they're needed later.