compiler note annotation dismality on sbcl

[Tobias C. Rittweiler]

This might be a purely sbcl-related issue.

(defmethod foo (x y)
  (let ((last (slot-value x 'last)))
    (cond (last
           (call-next-method x y)
           (call-next-method y x))
          ((read)
           (setf (slot-value x 'last y)))
          (t
           (call-next-method)))))

C-c C-c annotates the (DEFMETHOD which is quite a bit detached from the actual
offending code form (SETF (SLOT-VALUE X 'LAST Y)).