GNU bug report logs - #43862
[PATCH] grep: set RE_NO_SUB for calling regex only to check syntax

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From: Norihiro Tanaka <noritnk <at> kcn.ne.jp>
To: 43862 <at> debbugs.gnu.org
Subject: bug#43862: [PATCH] grep: set RE_NO_SUB for calling regex only to check syntax
Date: Thu, 08 Oct 2020 18:40:36 +0900

[Message part 1 (text/plain, inline)]

We can set RE_NO_SUB for calling regex only to check syntax.  It brings
performance gains in cases to have a lot of enormous epsilon nodes.


$ printf '(%020000d)\n' | sed 's/0/|/g' >pat

(before)
$ time -p env LC_ALL=C src/grep -Ef pat /dev/null
real 6.15
user 4.62
sys 1.52

(after)
$ time -p env LC_ALL=C src/grep -Ef pat /dev/null
real 0.66
user 0.19
sys 0.46

[0001-grep-set-RE_NO_SUB-for-calling-regex-only-to-check-s.patch (text/plain, attachment)]

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