[Bug rtl-optimization/97092] [10/11 Regression] aarch64, SVE: ICE in ira-color.c since r10-4752-g2d56600c

["andrea.corallo at arm dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97092

--- Comment #7 from Andrea Corallo <andrea.corallo at arm dot com> ---
"rsandifo at gcc dot gnu.org via Gcc-bugs" <gcc-bugs@gcc.gnu.org>
writes:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97092
>
> --- Comment #6 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> ---
> (In reply to Andrea Corallo from comment #5)
>> "rsandifo at gcc dot gnu.org via Gcc-bugs" <gcc-bugs@gcc.gnu.org>
>> writes:
>> 
>> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97092
>> >
>> > --- Comment #4 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> ---
>> > (In reply to Andrea Corallo from comment #3)
>> >> Created attachment 49710 [details]
>> >> PR97092.patch
>> >> 
>> >> What is going on is that in 'update_costs_from_allocno' we try to
>> >> identify the smallest mode using narrower_subreg_mode to then update the
>> >> costs.
>> >> 
>> >> The two modes involved here are E_DImode and E_VNx2QImode, cause these
>> >> are not ordered we ICE in 'paradoxical_subreg_p'.
>> >> 
>> >> Now I don't know if the strategy we want is:
>> >> 
>> >> - In 'update_costs_from_allocno' when modes are not ordered instead of
>> >>   calling 'narrower_subreg_mode' just keep the current one.
>> >> 
>> >> - Always select the cheapest mode in terms of cost.
>> >> 
>> >> The attached I'm testing implements the second.
>> 
>> Hi Richard,
>> 
>> thanks for commenting.
>> 
>> > I think instead we should consider recomputing “mode” in each
>> > iteration of the loop, rather than carry over the result of
>> > previous iterations.  I.e. use:
>> >
>> >     mode = narrower_subreg_mode (ALLOCNO_MODE (cp->first),
>> >                                  ALLOCNO_MODE (cp->second));
>> 
>> Are we garanteed to have ALLOCNO_MODE (cp->first) and ALLOCNO_MODE
>> (cp->second) always satisfying 'ordered_p'?
> Yeah, I think so.  If the modes aren't ordered then we shouldn't
> create a copy between them.

Great, I'm going to test the suggested then.

Thanks

  Andrea