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Re: -fprofile-generate and -fprofile-use
- From: Steven Bosscher <stevenb at suse dot de>
- To: gcc at gcc dot gnu dot org
- Cc: Peter Steinmetz <steinmtz at us dot ibm dot com>, janis187 <janis187 at us dot ibm dot com>, girish_vaithees at yahoo dot com, hubicka at ucw dot cz
- Date: Tue, 30 Aug 2005 17:58:20 +0200
- Subject: Re: -fprofile-generate and -fprofile-use
- References: <OF05184606.4EBE0844-ON8625706D.0055D24F-8625706D.00573FA5@us.ibm.com>
On Tuesday 30 August 2005 17:53, Peter Steinmetz wrote:
> While this doesn't explain all of the degradations discussed (some were
> showing up on older versions of the compiler), it may explain some.
There is a lot of empirical evidence that the loop optimizer already
doesn't do many useful things anymore, so this "some" is likely a
negligible some.
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.
Gr.
Steven