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Date: Mon, 19 May 2003 20:51:00 -0000
From: Richard Guenther <rguenth@tat.physik.uni-tuebingen.de>
To: Matt Austern <austern@apple.com>
cc: gcc@gcc.gnu.org
Subject: Re: Huge compile time & run time performance regression 3.3 -> HEAD
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On Mon, 19 May 2003, Matt Austern wrote:

> On Sunday, May 18, 2003, at 08:45  AM, Richard Guenther wrote:
>
> > Hi!
> >
> > As 3.3 is now out, I start comparing 3.3 to HEAD wrt compile time
> > performance and performance of the resulting code. As always these
> > comparisons are for a POOMA based scientific application.
> >
> > I experience a 100% compile time regression (673.50s -> 1284.48s) and
> > a 12% runtime performance regression (150s -> 171s) when comparing
> > gcc3.3 to HEAD.
> >
> > Time reports follow, the most prominent regressions are expand, global
> > CSE
> > (>300%!), loop analysis and branch prediction.
> >
> > Compile options are -ftemplate-depth-80 -fno-exceptions -O2
> > -march=athlon
> > -funroll-loops -fomit-frame-pointer
>
> Do you see any compile time regressions at -O0?
>
> (I'm asking for the obvious reason: trying to find out how much work we
> need to do in the front end as opposed to the back end.)

After killing all forced inlining, I get almost the same timings from 3.3
and 3.4, namely 42.50 and 44.89 seconds.

Slowdown comes from

3.3: name lookup           :   6.92 (17%) usr   0.90 (43%) sys   7.50
(18%) wall
3.4: name lookup           :   9.06 (22%) usr   0.81 (39%) sys  10.29
(23%) wall

Richard.