;;; compute the kill set when there are any vars killed. We bum this a
;;; bit by special-casing when only one var is killed, and just using
;;; that var's constraints as the kill set. This set could possibly be
;;; compute the kill set when there are any vars killed. We bum this a
;;; bit by special-casing when only one var is killed, and just using
;;; that var's constraints as the kill set. This set could possibly be