Re: [PATCH 2/2] ivopts: Consider number of invariants when calculating register pressure.

[Dimitrije Milosevic <Dimitrije.Milosevic@Syrmia.com>]

Hi Richard,

> don't you add n_invs twice now given
>
>  unsigned n_old = data->regs_used, n_new = n_invs + n_cands;
>  unsigned regs_needed = n_new + n_old, available_regs = target_avail_regs;
>
> ?

If you are referring to the "If we have enough registers." case, correct. After c18101f,
for that case, the returned cost is equal to 2 * n_invs + n_cands. Before c18101f, for 
that case, the returned cost is equal to n_invs + n_cands. Another solution would be
to just return n_invs + n_cands if we have enough registers.

Regards,
Dimitrije


From: Richard Biener <richard.guenther@gmail.com>
Sent: Tuesday, October 25, 2022 1:07 PM
To: Dimitrije Milosevic <Dimitrije.Milosevic@Syrmia.com>
Cc: gcc-patches@gcc.gnu.org <gcc-patches@gcc.gnu.org>; Djordje Todorovic <Djordje.Todorovic@syrmia.com>
Subject: Re: [PATCH 2/2] ivopts: Consider number of invariants when calculating register pressure. 
 
On Fri, Oct 21, 2022 at 3:57 PM Dimitrije Milosevic
<dimitrije.milosevic@syrmia.com> wrote:
>
> From: Dimitrije Milošević <dimitrije.milosevic@syrmia.com>
>
> This patch slightly modifies register pressure model function to consider
> both the number of invariants and the number of candidates, rather than
> just the number of candidates. This used to be the case before c18101f.

don't you add n_invs twice now given

  unsigned n_old = data->regs_used, n_new = n_invs + n_cands;
  unsigned regs_needed = n_new + n_old, available_regs = target_avail_regs;

?

> gcc/ChangeLog:
>
>         * tree-ssa-loop-ivopts.cc (ivopts_estimate_reg_pressure): Adjust.
>
> Signed-off-by: Dimitrije Milosevic <dimitrije.milosevic@syrmia.com>
> ---
>  gcc/tree-ssa-loop-ivopts.cc | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/gcc/tree-ssa-loop-ivopts.cc b/gcc/tree-ssa-loop-ivopts.cc
> index d53ba05a4f6..9d0b669d671 100644
> --- a/gcc/tree-ssa-loop-ivopts.cc
> +++ b/gcc/tree-ssa-loop-ivopts.cc
> @@ -6409,9 +6409,9 @@ ivopts_estimate_reg_pressure (struct ivopts_data *data, unsigned n_invs,
>            + target_spill_cost [speed] * (n_cands - available_regs) * 2
>            + target_spill_cost [speed] * (regs_needed - n_cands);
>
> -  /* Finally, add the number of candidates, so that we prefer eliminating
> -     induction variables if possible.  */
> -  return cost + n_cands;
> +  /* Finally, add the number of invariants and the number of candidates,
> +     so that we prefer eliminating induction variables if possible.  */
> +  return cost + n_invs + n_cands;
>  }
>
>  /* For each size of the induction variable set determine the penalty.  */
> --
> 2.25.1
>