;;; decides if it can use a shorter sequence, and if so, emits that
;;; sequence to the segment and returns T. If it can't do better than
;;; the worst case, it should return NIL (without emitting anything).
;;; decides if it can use a shorter sequence, and if so, emits that
;;; sequence to the segment and returns T. If it can't do better than
;;; the worst case, it should return NIL (without emitting anything).