How Do I Make This Hard to Misuse?

See?  I knew I was missing something.  Thanks to you and felixfix both, since you are both
describing the same particular optimization.  Cute, in an ugly, quaint way.  :-D

I'm certain I'm guilty of far worse horrors in my 2 decades of assembly programming.  This
optimization never occurred to me since I've always managed to pass arguments in registers.

(An odd fluke of history, that.  I've written whole-program assembly where I control all the
conventions, C with inline-asm only (no function calls from asm) on machines with stack-based
calling conventions, and C callable asm on machines with register based calling conventions.)