RE: new liveness pass

> The liveness pass looks really impressive. I don't quite follow your
> description though -- when you say that a variable is at the head of
> the liveness list or not there at all, you're certainly not implying that
> the list is a singleton, are you?

No. Since we are working on one variable at a time, and a variable is always
added to the front of the list, we can check for it only there.