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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
It would be probably better to just turn off the individual
optimizations with -fprofile-use (for optimizations that are implied by
this flag there should be no need to re-profile each time).
If you can find particular optimization that gets out of control, it
would be lot easier to fix it...
Honza
> 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
> >