GNU bug report logs - #17229
[PATCH 2/2] grep: speed-up by using memchr() in Boyer-Moore searching

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Message #58 received at 17229 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Norihiro Tanaka <noritnk <at> kcn.ne.jp>
Cc: 17229 <at> debbugs.gnu.org
Subject: Re: bug#17229: [PATCH 2/2] grep: speed-up by using memchr() in
 Boyer-Moore searching
Date: Sun, 27 Apr 2014 13:32:57 -0700

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

Norihiro Tanaka wrote:
> Could you try above cases?

Thanks, you're observing a 2.7x performance speedup with macros on your 
platform and your benchmark.  With the same patch, I observed only a 
1.18x speedup on the same benchmark.  As usual, I'm testing with AMD 
Phenom II X4 910e + GCC 4.9.0 + Fedora 20 + default (-O2) optimization. 
 I'm curious about why you're observing a much bigger performance 
difference with macros.  What platform are you using?

Anyway, an 18% speedup is still a speedup, so I looked into it.  GCC 
4.9.0 misses a non-obvious opportunity for function inlining.  I 
installed a tweak (attached) that should make the inlining opportunity 
obvious to compilers nowadays.  On my platform this gave a 28% speedup, 
i.e., a bit better than the macro-using patch would have.

[0001-kwset-improve-performance-by-inlining-more.patch (text/plain, attachment)]

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