From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-patches-return-493333-listarch-gcc-patches=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 51553 invoked by alias); 3 Jan 2019 13:06:15 -0000
Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-patches.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-patches/>
List-Post: <mailto:gcc-patches@gcc.gnu.org>
List-Help: <mailto:gcc-patches-help@gcc.gnu.org>
Sender: gcc-patches-owner@gcc.gnu.org
Received: (qmail 51542 invoked by uid 89); 3 Jan 2019 13:06:14 -0000
Authentication-Results: sourceware.org; auth=none
X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=BAYES_00,SPF_PASS autolearn=ham version=3.3.2 spammy=Hx-languages-length:1521
X-HELO: foss.arm.com
Received: from usa-sjc-mx-foss1.foss.arm.com (HELO foss.arm.com) (217.140.101.70) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Thu, 03 Jan 2019 13:06:13 +0000
Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249])	by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 10A07EBD;	Thu,  3 Jan 2019 05:06:12 -0800 (PST)
Received: from localhost (unknown [10.32.98.35])	by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C37813F5D4;	Thu,  3 Jan 2019 05:06:10 -0800 (PST)
From: Richard Sandiford <richard.sandiford@arm.com>
To: Jakub Jelinek <jakub@redhat.com>
Mail-Followup-To: Jakub Jelinek <jakub@redhat.com>,Richard Biener <rguenther@suse.de>,  Jason Merrill <jason@redhat.com>,  "Joseph S. Myers" <joseph@codesourcery.com>,  Jan Hubicka <jh@suse.cz>,  gcc-patches@gcc.gnu.org, richard.sandiford@arm.com
Cc: Richard Biener <rguenther@suse.de>,  Jason Merrill <jason@redhat.com>,  "Joseph S. Myers" <joseph@codesourcery.com>,  Jan Hubicka <jh@suse.cz>,  gcc-patches@gcc.gnu.org
Subject: Re: [PATCH] Add __builtin_convertvector support (PR c++/85052)
References: <20190103100640.GM30353@tucnak>
Date: Thu, 03 Jan 2019 13:06:00 -0000
In-Reply-To: <20190103100640.GM30353@tucnak> (Jakub Jelinek's message of "Thu,	3 Jan 2019 11:06:40 +0100")
Message-ID: <875zv5sxfi.fsf@arm.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain
X-SW-Source: 2019-01/txt/msg00102.txt.bz2

Jakub Jelinek <jakub@redhat.com> writes:
> +      /* Can't use get_compute_type here, as supportable_convert_operation
> +	 doesn't necessarily use an optab and needs two arguments.  */
> +      tree vector_compute_type
> +	= type_for_widest_vector_mode (TREE_TYPE (arg_type), mov_optab);
> +      unsigned HOST_WIDE_INT nelts;
> +      if (vector_compute_type
> +	  && VECTOR_MODE_P (TYPE_MODE (vector_compute_type))
> +	  && subparts_gt (arg_type, vector_compute_type)
> +	  && TYPE_VECTOR_SUBPARTS (vector_compute_type).is_constant (&nelts))
> +	{
> +	  while (nelts > 1)
> +	    {
> +	      tree ret1_type = build_vector_type (TREE_TYPE (ret_type), nelts);
> +	      tree arg1_type = build_vector_type (TREE_TYPE (arg_type), nelts);
> +	      if (supportable_convert_operation (code, ret1_type, arg1_type,
> +						 &decl, &code1))
> +		{
> +		  new_rhs = expand_vector_piecewise (gsi, do_vec_conversion,
> +						     ret_type, arg1_type, arg,
> +						     decl, code1);
> +		  g = gimple_build_assign (lhs, new_rhs);
> +		  gsi_replace (gsi, g, false);
> +		  return;
> +		}
> +	      nelts = nelts / 2;
> +	    }
> +	}

I think for this it would be better to use:

      if (vector_compute_type
	  && VECTOR_MODE_P (TYPE_MODE (vector_compute_type))
	  && subparts_gt (arg_type, vector_compute_type))
	{
	  unsigned HOST_WIDE_INT nelts = constant_lower_bound
	    (TYPE_VECTOR_SUBPARTS (vector_compute_type));

since the loop is self-checking.

E.g. this will make the Advanced SIMD handling on AArch64 the same
regardless of whether SVE is also enabled.

Thanks,
Richard