bug#12796: Optimize `ido-completing-read' for larger lists with flex matching enabled

[Leo <sdl.web@gmail.com>]

On 2012-11-08 12:14 +0800, Stefan Monnier wrote:
> Indeed.  This undesired behavior was introduced by the change to
> split-string introduced in Emacs-22, so the patch fixes a regression
> w.r.t Emacs-21.

Thanks for that information.

>
>> So do you mind installing the following small change for 24.3 that
>> greatly improves ido performance:
>
> I guess it's OK, yes.

Can I incorporate your suggestion on removing the backtracking issue? I
have found cases where flex matching perform badly but with your
suggestion, for example, cut the time from 4.8s to 0.3s.

The patch could look like this:

diff --git a/lisp/ido.el b/lisp/ido.el
index 31d5279d..0a740b2a 100644
--- a/lisp/ido.el
+++ b/lisp/ido.el
@@ -3783,7 +3783,11 @@ (defun ido-set-matches-1 (items &optional do-full)
 	       ido-enable-flex-matching
 	       (> (length ido-text) 1)
 	       (not ido-enable-regexp))
-      (setq re (mapconcat #'regexp-quote (split-string ido-text "") ".*"))
+      (setq re (concat (regexp-quote (string (aref ido-text 0)))
+		       (mapconcat (lambda (c)
+				    (concat "[^" (string c) "]*"
+					    (regexp-quote (string c))))
+				  (substring ido-text 1) "")))



Leo