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Re: -fprofile-generate and -fprofile-use
- From: girish vaitheeswaran <girish_vaithees at yahoo dot com>
- To: Jan Hubicka <hubicka at ucw dot cz>, Janis Johnson <janis187 at us dot ibm dot com>
- Cc: girish vaitheeswaran <girish_vaithees at yahoo dot com>, gcc at gcc dot gnu dot org
- Date: Wed, 20 Jul 2005 16:38:34 -0700 (PDT)
- Subject: Re: -fprofile-generate and -fprofile-use
I started with a clean slate in my build environment
and did not have any residual files hanging around.
Are the steps I have indicated in my earlier email
correct. Is there a way I can break down the problem
into a smaller sub-set of flags and eliminate the flag
causing the performance problem. What I mean is since
-fprofile-generate and -fprofile-use enable a bunch of
flags, would it make sense to avoid profiling and try
out some of the individual flags on a trial and error
basis. If so what would be the flags to start the
trials with.
-girish
--- Jan Hubicka <hubicka@ucw.cz> wrote:
> > On Wed, Jul 20, 2005 at 10:45:01AM -0700, girish
> vaitheeswaran wrote:
> > > > --- Steven Bosscher <stevenb@suse.de> wrote:
> > > >
> > > > > On Wednesday 20 July 2005 18:53, girish
> vaitheeswaran wrote:
> > > > > > I am seeing a 20% slowdown with feedback
> optimization.
> > > > > > Does anyone have any thoughts on this.
> > > > >
> > > > > My first thought is that you should probably
> first
> > > > > tell what compiler
> > > > > you are using.
> > >
> > > I am using gcc 3.4.3
> > > -girish
> >
> > Which platform? I've seen slower code for
> profile-directed optimizations
> > on powerpc64-linux with GCC 4.0 and mainline.
> It's a bug, but I haven't
> > looked into it enough to provide a small test case
> for a problem report.
>
> Actually I would be very interested in seeing
> testcases such as those.
> (and the Girish' slowdown too if possible). In
> general some slowdowns
> in side corners are probably unavoidable but both
> 3.4.3 and 4.0 seems to
> have pretty consistent improvements with profiling
> at least for SPEC and
> i386 I am testing pretty regularly.
> Such slodowns usually indicate problems like
> incorrectly updated profile
> or incorrectly readed in profile because of
> missmatch in CFGs in between
> profile and feedback run that are rather dificult to
> notice and hunt
> down...
>
> Honza
> >
> > Janis
>