longest common suffix of two strings

gistfile1.el

;; awful hack, get the common suffix from two strings using regexp-quote

(let* ((a "foo/bar") 
       (b "baz/bar") 
       (ro (regexp-opt (list a b))))
  (string-match "\\\\)\\(.*?\\)\\\\)$" ro)
  (match-string 1 ro))
;; "/bar"

;; what trickery be this?!
;; (regexp-opt '("foooooooobaz" "barrrrrrrbaz")) ;; "\\(?:\\(?:barrrrrrr\\|foooooooo\\)baz\\)"
;; so we match the last \\)baz\\)$