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Re: -fprofile-generate and -fprofile-use
- From: girish vaitheeswaran <girish_vaithees at yahoo dot com>
- To: Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>, Peter Steinmetz <steinmtz at us dot ibm dot com>
- Cc: Steven Bosscher <stevenb at suse dot de>, gcc at gcc dot gnu dot org, girish_vaithees at yahoo dot com, hubicka at ucw dot cz, janis187 at us dot ibm dot com
- Date: Wed, 31 Aug 2005 15:40:22 -0700 (PDT)
- Subject: Re: -fprofile-generate and -fprofile-use
I do not see this flag in gcc3.4.4.
perflab2% gcc -o conftest -O3 -march=pentium4
-fmove-loop-invariants conftest.c
cc1: error: unrecognized command line option
"-fmove-loop-invariants"
Am I missing something?
-girish
--- Zdenek Dvorak <rakdver@atrey.karlin.mff.cuni.cz>
wrote:
> Hello,
>
> > >A more likely source of performance degradation
> is that loop unrolling
> > >is enabled when profiling, and loop unrolling is
> almost always a bad
> > >pessimization on 32 bits x86 targets.
> >
> > To clarify, I was compiling with -funroll-loops
> and -fpeel-loops
> > enabled in both cases.
> >
> > The FDO slowdown in my case was caused by the
> presence of some loop
> > invariant code that was getting removed from the
> loop by the loop
> > optimizer pass in the non-FDO case.
>
> you may try adding -fmove-loop-invariants flag,
> which enables new
> invariant motion pass.
>
> Zdenek
>