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Re: -fprofile-generate and -fprofile-use
- From: Peter Steinmetz <steinmtz at us dot ibm dot com>
- To: gcc at gcc dot gnu dot org
- Cc: janis187 <janis187 at us dot ibm dot com>, girish_vaithees at yahoo dot com, hubicka at ucw dot cz
- Date: Tue, 30 Aug 2005 10:53:07 -0500
- Subject: Re: -fprofile-generate and -fprofile-use
There was some discussion a few weeks ago about some apps running slower
with FDO enabled.
I've recently investigated a similar situation using mainline. In my case,
the fact that the loop_optimize pass is disabled during FDO was the cause
of the slowdown. It appears that was recently disabled as part of Jan
Hubicka's patch to eliminate RTL based profiling. The commentary indicates
that the old loop optimizer is incompatible with tree profiling.
While this doesn't explain all of the degradations discussed (some were
showing up on older versions of the compiler), it may explain some.
Pete