Performance problem

Łukasz Lew lukasz.lew@gmail.com
Sun Sep 21 21:42:00 GMT 2008


Thanks for a fast answer,
I use -O3 -march=native -fomit-frame-pointer -DDEBUG -ffast-math
-frename-registers -ggdb3  -Wall -Wextra -Wswitch-enum
but I have the same effect with only -O3

Versions:
g++-4.2 (GCC) 4.2.4 (Ubuntu 4.2.4-1ubuntu1)
g++-4.3 (Ubuntu 4.3.2-1ubuntu7) 4.3.2

The original library is here:
http://www.mimuw.edu.pl/~lew/hg/libego/?shortlog
I extracted only the benchmark part:
http://www.mimuw.edu.pl/~lew/libego_benchmark.tgz

I also found strange one-line difference that degrades performance
of g++-4.2 compiled binary to the level of g++-4.3.

I don't get it at all ..
If you have any insights please let me know, it is very important to me.
Lukasz

On Sun, Sep 21, 2008 at 23:24, Brian D. McGrew <brian@visionpro.com> wrote:
> Source code would be a good start???  Optimization flags???  Architecture flags???  How was gcc-4.3 vs. gcc-4.2 built???  (g++ --version will show this).
>
> -brian
>
> -----Original Message-----
> From: gcc-help-owner@gcc.gnu.org [mailto:gcc-help-owner@gcc.gnu.org] On Behalf Of Lukasz Lew
> Sent: Sunday, September 21, 2008 2:20 PM
> To: gcc-help@gcc.gnu.org
> Subject: Performance problem
>
> Hi
>
> I have a program that when compiled with g++-4.3 is 10% slower than with g++-4.2
> I tried to look at the asm output, but its way too different.
> How should I proceed to get my 10% back?
>
> Thanks
> Lukasz
>



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