GNU bug report logs - #19306
[PATCH 1/2] dfa: avoid execution for a pattern including an unsupported expression

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From: arnold <at> skeeve.com
To: noritnk <at> kcn.ne.jp, jim <at> meyering.net
Cc: 19306 <at> debbugs.gnu.org
Subject: bug#19306: [PATCH 1/2] dfa: avoid execution for a pattern including an unsupported expression
Date: Sun, 19 Jul 2015 05:24:01 -0600

Hi.

This looks like a nice patch that gawk would beneifit from.

I have a minor suggestion, which is to make dfabackref into a
static function.

Thanks,

Arnold
----------------------
Norihiro Tanaka <noritnk <at> kcn.ne.jp> wrote:

> On Sat, 18 Jul 2015 22:15:33 -0700
> Jim Meyering <jim <at> meyering.net> wrote:
>
> > Hello,
> > Thank you for the patches in this report:
> > 
> >   http://bugs.gnu.org/19306
> > 
> > Please excuse my delay in getting back to you on this.
> > Would you revise each of those to include a test case
> > that demonstrates the problem/fix?
>
> Thanks for your reviewing of this report.
>
> This is not bug fix.  It avoids that BACKREF is found in the process of
> DFAEXEC and passed to regex in multibyte locale.  In other words, if a
> pattern includes BACKREF, grep does not try to use DFA from the
> beginning.
>
> I confirmed about 10% speed-up for a test case in attachment.
>
>   Before patching: real 7.29  user 7.26  sys 0.02
>   After patching : real 6.57  user 6.55  sys 0.01
>
> KWset and DFA superset succeeds for all rows in the test case, and DFA
> for multibyte succeeds, too.  However, all rows are rejected in regex.
>
> After patching, grep does not try DFA for multibyte, as pattern includes
> BACKREF.
>
> In addtion, I believe that DFA is simplified by removal of handling for
> BACKREF from dfaanalyze(), dfassbuild() and dfaexec().

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