+(when (and (not (featurep 'xemacs))
+ (= emacs-major-version 21)
+ (= emacs-minor-version 3)
+ (condition-case code
+ (let ((byte-compile-error-on-warn t))
+ (byte-optimize-form (quote (pop x)) t)
+ nil)
+ (error (string-match "called for effect"
+ (error-message-string code)))))
+ (defadvice byte-optimize-form-code-walker (around silence-warn-for-pop
+ (form for-effect)
+ activate)
+ "Silence the warning \"...called for effect\" for the `pop' form.
+It is effective only when the `pop' macro is defined by cl.el rather
+than subr.el."
+ (let (tmp)
+ (if (and (eq (car-safe form) 'car)
+ for-effect
+ (setq tmp (get 'car 'side-effect-free))
+ (not byte-compile-delete-errors)
+ (not (eq tmp 'error-free))
+ (eq (car-safe (cadr form)) 'prog1)
+ (let ((var (cadr (cadr form)))
+ (last (nth 2 (cadr form))))
+ (and (symbolp var)
+ (null (nthcdr 3 (cadr form)))
+ (eq (car-safe last) 'setq)
+ (eq (cadr last) var)
+ (eq (car-safe (nth 2 last)) 'cdr)
+ (eq (cadr (nth 2 last)) var))))
+ (progn
+ (put 'car 'side-effect-free 'error-free)
+ (unwind-protect
+ ad-do-it
+ (put 'car 'side-effect-free tmp)))
+ ad-do-it))))
+