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Re: -fprofile-generate and -fprofile-use
- From: Jan Hubicka <jh at suse dot cz>
- To: Peter Steinmetz <steinmtz at us dot ibm dot com>
- Cc: gcc at gcc dot gnu dot org, janis187 <janis187 at us dot ibm dot com>,girish_vaithees at yahoo dot com, hubicka at ucw dot cz
- Date: Tue, 30 Aug 2005 18:24:01 +0200
- Subject: Re: -fprofile-generate and -fprofile-use
- References: <OF05184606.4EBE0844-ON8625706D.0055D24F-8625706D.00573FA5@us.ibm.com>
>
> 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.
Do you have specific testcase? It would be interesting to see if new
optimizer can catch up at least on kill-loop branch.
Thanks for investigating!
Honza
>
> Pete