(let ((old "old") (new "new")
      (target (get-buffer-create "*My Diff*"))
      (labels (and (diff-check-labels)
                   (mapcar 'shell-quote-argument
                           (list "--label"
                                 "*old revision*"
                                 "--label"
                                 "*new revision*")))))
  (if labels
      (let ((diff-use-labels nil)
            (sw (nconc labels
                       (if (listp diff-switches)
                           diff-switches
                         (list diff-switches)))))
        (diff-no-select old new switches nil target))
    (diff-no-select     old new nil      nil target)))