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Re: -fprofile-generate and -fprofile-use
- From: Peter Steinmetz <steinmtz at us dot ibm dot com>
- To: Steven Bosscher <stevenb at suse dot de>
- Cc: 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: Tue, 30 Aug 2005 11:11:38 -0500
- Subject: Re: -fprofile-generate and -fprofile-use
>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.
I'm running on powerpc-linux.