Re: [PATCH] Adjust memory_move_cost for MASK_REGS when MODE_SIZE > 8.

[Uros Bizjak <ubizjak@gmail.com>]

On Fri, Mar 31, 2023 at 7:11 AM liuhongt <hongtao.liu@intel.com> wrote:
>
> RA sometimes will use lowest the cost of the mode with all different regclasses
> w/o check if it's hard_regno_mode_ok.
> It's impossible to put modes whose size > 8 into MASK_REGS, ajdust the cost to
> avoid potential performance issue.

I was going to ask to open a PR in order to fix RA instead of the
proposed workaround, but the patch just prevents a theoretical issue
and follows the established practice with other regclasses. Perhaps
these workarounds are not needed with the current RA, but this is a
tangential issue which should be fixed for all regclasses.

> Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
> Ok for trunk?

OK.

Thanks,
Uros.

>
> gcc/ChangeLog:
>
>         * config/i386/i386.cc (inline_memory_move_cost): Return 100
>         for MASK_REGS when MODE_SIZE > 8.
> ---
>  gcc/config/i386/i386.cc | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
> index 2cc8e9548a9..2581b800a06 100644
> --- a/gcc/config/i386/i386.cc
> +++ b/gcc/config/i386/i386.cc
> @@ -19847,9 +19847,12 @@ inline_memory_move_cost (machine_mode mode, enum reg_class regclass, int in)
>           index = 1;
>           break;
>         /* DImode loads and stores assumed to cost the same as SImode.  */
> -       default:
> +       case 4:
> +       case 8:
>           index = 2;
>           break;
> +       default:
> +         return 100;
>         }
>
>        if (in == 2)
> --
> 2.39.1.388.g2fc9e9ca3c
>