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Re: Live range shrinkage in pre-reload scheduling
- From: Maxim Kuvyrkov <maxim dot kuvyrkov at linaro dot org>
- To: ramrad01 at arm dot com, Charles Baylis <charles dot baylis at linaro dot org>
- Cc: Vladimir Makarov <vmakarov at redhat dot com>, Kyrill Tkachov <kyrylo dot tkachov at arm dot com>, "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>, Richard Sandiford <rdsandiford at googlemail dot com>
- Date: Thu, 15 May 2014 19:36:09 +1200
- Subject: Re: Live range shrinkage in pre-reload scheduling
- Authentication-results: sourceware.org; auth=none
- References: <5371F395 dot 8050208 at arm dot com> <53736CFD dot 6030402 at redhat dot com> <87d2fgco2v dot fsf at talisman dot default> <CAJA7tRZyXSamdb_jbnX+-HywZEajB=+Y-SzCyHzyTJDyfnhQJw at mail dot gmail dot com>
On May 15, 2014, at 6:46 PM, Ramana Radhakrishnan <firstname.lastname@example.org> wrote:
>> I'm not claiming it's a great heuristic or anything. There's bound to
>> be room for improvement. But it was based on "reality" and real results.
>> Of course, if it turns out not be a win for ARM or s390x any more then it
>> should be disabled.
> The current situation that Kyrill is investigating is a case where we
> notice the first scheduler pass being a bit too aggressive with
> creating ILP opportunities with the A15 scheduler that causes
> performance differences with not turning on the first scheduler pass
> vs using the defaults.
Charles has a work-in-progress patch that fixes a bug in SCHED_PRESSURE_MODEL that causes the above symptoms. The bug causes 1st scheduler to unnecessarily increase live ranges of pseudo registers when there are a lot of instructions in the ready list.
Charles, can you finish your patch in the next several days and post it for review?