Re: Do not imply -fweb with -fpeel-loops

[Richard Biener <richard dot guenther at gmail dot com>]

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