(defun helm-smex-items ()
  (smex-rebuild-cache)
  (smex-convert-for-ido smex-cache))

(defun helm-smex-execute-command (command)
  (when (commandp command)
    (setq this-command command)
    (setq real-this-command command)
    (let ((prefix-arg current-prefix-arg))
      (command-execute command 'record)
      (smex-rank command))))

(setq helm-smex-source
  '((name . "M-x")
    (candidates . helm-smex-items)
    (coerce . intern)
    (action ("smex" . helm-smex-execute-command))))

(defun helm-smex ()
  (interactive)
  (helm :sources 'helm-smex-source :buffer "*helm-smex*"))

(provide 'helm-smex)