(defun fresh-vector (s)
  (etypecase s
    (list (coerce s 'vector))
    (vector (copy-seq s))))

(defun foo (s)
  (declare (optimize speed (debug 1) (safety 1)))
  (map 'vector 'identity s))

(defun bar (s)
  (declare (optimize speed (debug 1) (safety 1)))
  (fresh-vector s))


(defparameter *s* (alexandria:iota 10))

(time (loop :repeat 40000000 :do (foo *s*)))
;; Evaluation took:
;;   5.539 seconds of real time
;;   5.537333 seconds of total run time (5.536821 user, 0.000512 system)
;;   [ Run times consist of 0.008 seconds GC time, and 5.530 seconds non-GC time. ]
;;   99.96% CPU
;;   18,795,470,572 processor cycles
;;   5,119,999,824 bytes consed


(time (loop :repeat 40000000 :do (bar *s*)))
;; Evaluation took:
;;   4.089 seconds of real time
;;   4.087682 seconds of total run time (4.075785 user, 0.011897 system)
;;   [ Run times consist of 0.004 seconds GC time, and 4.084 seconds non-GC time. ]
;;   99.98% CPU
;;   13,877,019,964 processor cycles
;;   3,839,998,288 bytes consed