Re: gcc 3.2 makes slower code

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Article #423

#423

From: eMail2Me
Date: Mon, 25 Nov 2002 19:58

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Jeffrey Cunningham on Monday 25 November 2002 14:01 wrote:

> Okay, here's what I've come up with so far. There is a core of
> calculations my code must perform thousands of times. I benchmarked just
> this core with and without I/O, on gcc 2.95 and 3.2, using -O2 and -O3 on
> the latter. Here are the results:
> 
> gcc 2.95 with IO: .20 minutes
> gcc 2.95 w/o IO: .18 minutes
> gcc 3.2 -O3 with IO: .32 minutes
> gcc 3.2 -O3 w/o IO: .27 minutes
> gcc 3.2 -O2 w/o IO: .27 minutes
> 
> conclusions: (1) it isn't the I/O. The "slowdown factor" going to gcc 3.2
> is x1.6 with I/O and x1.5 without. And (2) it makes no difference to these
> calculations (intensive floating point vector operations) whether I use
> -O3 or -O2.
> 
> I haven't tried any of the more esoteric optimization tricks yet. But at
> this point I'm somewhat alarmed by the loss in performance.
> 
> -Jeff

I know this may sound too much of a work. However, you might want to grab 
and recompile with optimizations the source of gcc-3.2 from SusE 8.1 
distro. Then, recompile the glibc library as well might help.

-- 
eMail2Me

PS. Use REPLY to contact me!

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From: eMail2Me <SPAMMERS.eMail2Me@False.Alarmed.HomeLinux.net>
Subject: Re: gcc 3.2 makes slower code
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