GNU bug report logs - #38322
GCC optimize levels makes huge impact on performance

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Package: grep;

Reported by: Balázs Vinarz <vinibali1 <at> gmail.com>

Date: Fri, 22 Nov 2019 17:05:02 UTC

Severity: normal

Done: Paul Eggert <eggert <at> cs.ucla.edu>

Bug is archived. No further changes may be made.

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Message #8 received at 38322 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Balázs Vinarz <vinibali1 <at> gmail.com>
Cc: 38322 <at> debbugs.gnu.org
Subject: Re: bug#38322: GCC optimize levels makes huge impact on performance
Date: Fri, 22 Nov 2019 17:52:53 -0800

On 11/22/19 8:00 AM, Balázs Vinarz wrote:
> Would you mind change the default optimize level on the make
> configuration? Did somebody ever measured the benefits using different
> GCC optimalization levels?

Lots of measurements have been done. They often disagree. Even if grep 
changed the default optimization level (which I'm not sure is a good 
idea), distros like Ubuntu often override the default and if so, changes 
to the default wouldn't help you.

> I know that this is a special use case, but the improvement is huge.
> I'm looking forward for your feedback.

It sounds like you're using grep to do set subtraction; is this a 
common-enough usage to be worth special-casing grep for? (One could 
argue that it's easy enough to do set subtraction with Awk or Python or 
whatever....) If we do want to tune grep for set-like operations, that 
suggests doing some surgery to its internals rather than merely fiddling 
with -O flags.
This bug report was last modified 5 years and 136 days ago.

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