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Re: Partial PRE optimization causing slowdown
- From: Steve Ellcey <sellcey at mips dot com>
- To: Richard Biener <richard dot guenther at gmail dot com>
- Cc: GCC Development <gcc at gcc dot gnu dot org>
- Date: Fri, 13 Dec 2013 08:33:59 -0800
- Subject: Re: Partial PRE optimization causing slowdown
- Authentication-results: sourceware.org; auth=none
- References: <f8528a93-eca2-4727-a190-966cdd9ecc3f at BAMAIL02 dot ba dot imgtec dot org> <CAFiYyc0Ws_aT1eNkCEcyxeW7dTyVph1c04GsN2uGym4d9y3tvQ at mail dot gmail dot com>
On Fri, 2013-12-13 at 11:26 +0100, Richard Biener wrote:
> On Thu, Dec 12, 2013 at 8:19 PM, Steve Ellcey <sellcey@mips.com> wrote:
> > I have a question about the partial pre (-ftree-partial-pre) optimization
> > that was added in GCC 4.8. I have noticed that this optimization is slowing
> > down the bitmnp01 benchmark in the EEMBC1.1 suite on MIPS. I see this with
> > the 4.8 GCC and with ToT GCC. Comparing "-O3 -fno-tree-partial-pre" vs.
> > just "-O3" on the Tot GCC with MIPS, I see almost a 50% slowdown in the
> > benchmark due to the partial pre optimization.
>
> Note that partial PRE wasn't added in 4.8 but much earlier. But 4.8 got an
> option to disable it - which means you have a workaround at your hands now.
>
> Richard.
That is interesting because we saw this slowdown on MIPS between 4.7 and
4.8 and someone tracked it down to this patch:
2012-11-16 Jan Hubicka <jh@suse.cz>
PR tree-optimization/54717
* tree-ssa-pre.c (do_partial_partial_insertion): Consider also edges
with ANTIC_IN.
Steve Ellcey
sellcey@mips.com