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Date: Wed, 25 Nov 2020 09:42:22 -0600
From: Segher Boessenkool <segher@kernel.crashing.org>
To: "Kewen.Lin" <linkw@linux.ibm.com>
Cc: GCC Patches <gcc-patches@gcc.gnu.org>,
 Bill Schmidt <wschmidt@linux.ibm.com>, David Edelsohn <dje.gcc@gmail.com>
Subject: Re: [PATCH] rs6000: Set param_vect_partial_vector_usage as 1 for P10
Message-ID: <20201125154222.GB2672@gate.crashing.org>
References: <0aa7e42e-5f75-388c-fc95-b326632dcf41@linux.ibm.com>
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Hi!

On Wed, Nov 25, 2020 at 02:02:16PM +0800, Kewen.Lin wrote:
> This patch is to set param_vect_partial_vector_usage as 1 on P10
> by default.  Due to the unexpected performance on Power9 of those
> vector with length instructions, we didn't enable vectorization
> with partial vectors before.  Some recent testings show that they
> perform expectedly on Power10 now.  The performance evaluation
> on the whole SPEC2017 with latest trunk and option set power10/
> Ofast/unroll shows it can speed up 525.x264_r by 10.80% and
> 554.roms_r by 1.94%.  One remarkable degradation is 523.xalancbmk_r
> -1.79% but it's identified not directly related to this enablement
> by some investigation.


> +      if (TARGET_POWER10)
> +       SET_OPTION_IF_UNSET (&global_options, &global_options_set,
> +			    param_vect_partial_vector_usage, 1);
> +      else
> +       /* Disable it on the default supported hardware Power9 since
> +	  lxvl/stxvl have unexpected performance behaviors.  */
> +       SET_OPTION_IF_UNSET (&global_options, &global_options_set,
> +			    param_vect_partial_vector_usage, 0);

Maybe write this like

      /* The lxvl/stxvl instructions don't perform well before Power10.  */
      if (TARGET_POWER10)
       SET_OPTION_IF_UNSET (&global_options, &global_options_set,
			    param_vect_partial_vector_usage, 1);
      else
       SET_OPTION_IF_UNSET (&global_options, &global_options_set,
			    param_vect_partial_vector_usage, 0);

Okay for trunk with such a comment (before the "if").  Thanks!


Segher