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Re: Do not imply -fweb with -fpeel-loops
- From: Bill Schmidt <wschmidt at linux dot vnet dot ibm dot com>
- To: Richard Biener <richard dot guenther at gmail dot com>
- Cc: Jan Hubicka <hubicka at ucw dot cz>, GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Tue, 31 May 2016 10:02:51 -0500
- Subject: Re: Do not imply -fweb with -fpeel-loops
- Authentication-results: sourceware.org; auth=none
- References: <20160531104919 dot GA95630 at kam dot mff dot cuni dot cz> <CAFiYyc2=aUGpK3QjG=4t8mGtVOFVb6yqzJJ=n36j0fvv5-UjOw at mail dot gmail dot com> <20160531114207 dot GB35041 at kam dot mff dot cuni dot cz> <CAFiYyc1a6s5ZT=snOGTA+4prUDqptN6R+6s3d_a9LRTVV5qSuA at mail dot gmail dot com>
If the decision is taken to remove -fweb, please give me a heads-up as I have a target-specific pass that shares infrastructure with it. I can factor that out to facilitate the removal; just let me know.
Thanks!
-- Bill
Bill Schmidt, Ph.D.
GCC for LInux on Power
Linux on Power Toolchain
IBM Linux Technology Center
wschmidt@linux.vnet.ibm.com
> On May 31, 2016, at 8:50 AM, Richard Biener <richard.guenther@gmail.com> wrote:
>
> On Tue, May 31, 2016 at 1:42 PM, Jan Hubicka <hubicka@ucw.cz> wrote:
>>>> I would say we should handle -frename-registers same way as we do -fschedule-insns.
>>>> I.e. enable/disable it on target basis rather than budnle it to loop unrolling.
>>>> But that is for future patch. I will commit this and propose patch making -fpeel-loops
>>>> independent of rename-registers next
>>>
>>> Ok. Does -fweb still do what its documentation says (enable register
>>> allocation to
>>> work on pseudos directly)? Given its downside and strong GIMPLE
>>> optimizations maybe
>>> it is time to remove it?
>>
>> I will wait with comitting the renaming patch and we will see the effect with
>> -fno-unroll-loops on ia64 tester (it probably pays back more on in-order
>> target) and we can test effect with -funroll-loops by patching it tomorrow.
>>
>> I guess IRA does live range pslitting by itself. Register allocator is not the
>> only pass which does not like reuse of pseudo. Web originally also made
>> -fschedule-insns (not -fschedule-insns2) and CSE to work harder.
>>
>> In tree-SSA world most of reuse is avoided by out-of-ssa pass. Random reuse
>> these days is limited to loop unrolling and RTL expansion I think. Without
>> unroling webizer renames 204 pseudos on tramp3d that seems close to 0. I can
>> try to dig into that. With -funroll-all-loops it renames 17309 registers.
>> Of course it would be possible to write unroller specific renamer, but it would
>> hardly be any wasier than webizer.
>
> And we have things like -fsplit-ivs-in-unroller that does part of it...
>
> Richard.
>
>> Honza
>