Re: [PATCH] Check hard_regno_mode_ok before setting lowest memory move cost for the mode with different reg classes.

[Hongtao Liu <crazylht@gmail.com>]

On Thu, Apr 6, 2023 at 1:07 PM Liu, Hongtao via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
>
>
> > -----Original Message-----
> > From: Vladimir Makarov <vmakarov@redhat.com>
> > Sent: Wednesday, April 5, 2023 8:59 PM
> > To: Jeff Law <jeffreyalaw@gmail.com>; Liu, Hongtao
> > <hongtao.liu@intel.com>; gcc-patches@gcc.gnu.org
> > Subject: Re: [PATCH] Check hard_regno_mode_ok before setting lowest
> > memory move cost for the mode with different reg classes.
> >
> >
> > On 4/4/23 21:29, Jeff Law wrote:
> > >
> > >
> > > On 4/3/23 23:13, liuhongt via Gcc-patches wrote:
> > >> There's a potential performance issue when backend returns some
> > >> unreasonable value for the mode which can be never be allocate with
> > >> reg class.
> > >>
> > >> Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
> > >> Ok for trunk(or GCC14 stage1)?
> > >>
> > >> gcc/ChangeLog:
> > >>
> > >>     PR rtl-optimization/109351
> > >>     * ira.cc (setup_class_subset_and_memory_move_costs): Check
> > >>     hard_regno_mode_ok before setting lowest memory move cost for
> > >>     the mode with different reg classes.
> > > Not a regression *and* changing register allocation.  This seems like
> > > it should defer to gcc-14.
> > >
> > Yes, I am agree.  It should wait for gcc-14, especially when we are close to the
> > release. Also the testing x86-64 is not enough for such changes (although I
> > tried ppc64le and did not find any problem).
> >
> > Cost related patches for RA frequently result in new testsuite failures on
> > some targets.  Even if the change seems obvious and expected to improve
> > the generated code.
> >
> > Target dependent code sometimes defines correctly the costs only for some
> > possible cases and making less dependent from this pitfall is good.  So I think
> > the patch moves us to the right direction.
> >
> > The patch is ok for me to commit it to the trunk after the gcc-13 release and if
> > arm64 testing shows no GCC testsuite regression.
> Bootstrapped and regtested on aarch64-unknown-linux-gnu.
> Waiting for GCC14.
Committed.
> >
> > Thank you for working on this issue.
> >
>


-- 
BR,
Hongtao