From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-patches-return-402190-listarch-gcc-patches=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 20473 invoked by alias); 7 Jul 2015 09:12:57 -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 20462 invoked by uid 89); 7 Jul 2015 09:12:56 -0000
Authentication-Results: sourceware.org; auth=none
X-Virus-Found: No
X-Spam-SWARE-Status: No, score=-0.6 required=5.0 tests=AWL,BAYES_50,FREEMAIL_FROM,RCVD_IN_DNSWL_LOW,SPF_PASS autolearn=ham version=3.3.2
X-HELO: mail-ob0-f172.google.com
Received: from mail-ob0-f172.google.com (HELO mail-ob0-f172.google.com) (209.85.214.172) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES128-GCM-SHA256 encrypted) ESMTPS; Tue, 07 Jul 2015 09:12:55 +0000
Received: by obbkm3 with SMTP id km3so124329211obb.1        for <gcc-patches@gcc.gnu.org>; Tue, 07 Jul 2015 02:12:53 -0700 (PDT)
MIME-Version: 1.0
X-Received: by 10.202.79.209 with SMTP id d200mr2971908oib.46.1436260373459; Tue, 07 Jul 2015 02:12:53 -0700 (PDT)
Received: by 10.76.115.167 with HTTP; Tue, 7 Jul 2015 02:12:53 -0700 (PDT)
In-Reply-To: <alpine.DEB.2.20.1507070800550.1693@laptop-mg.saclay.inria.fr>
References: <SN2PR0701MB1024267AF107C82E4F2F8A6C8E920@SN2PR0701MB1024.namprd07.prod.outlook.com>	<alpine.DEB.2.20.1507070800550.1693@laptop-mg.saclay.inria.fr>
Date: Tue, 07 Jul 2015 09:12:00 -0000
Message-ID: <CAFiYyc1c_NVr1eKVg3v5xv4829aMDbp0QnrmeB-BEYCmg6uQ+A@mail.gmail.com>
Subject: Re: [PR25529] Convert (unsigned t * 2)/2 into unsigned (t & 0x7FFFFFFF)
From: Richard Biener <richard.guenther@gmail.com>
To: "gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>
Cc: "Hurugalawadi, Naveen" <Naveen.Hurugalawadi@caviumnetworks.com>
Content-Type: text/plain; charset=UTF-8
X-IsSubscribed: yes
X-SW-Source: 2015-07/txt/msg00451.txt.bz2

On Tue, Jul 7, 2015 at 8:06 AM, Marc Glisse <marc.glisse@inria.fr> wrote:
> On Tue, 7 Jul 2015, Hurugalawadi, Naveen wrote:
>
>> Please find attached the patch "PR25529.patch" that converts the pattern:-
>> (unsigned * 2)/2 is into unsigned &0x7FFFFFFF
>
>
> +/* Simplify (unsigned t * 2)/2 -> unsigned t & 0x7FFFFFFF.  */
> +(for div (trunc_div ceil_div floor_div round_div exact_div)
> + (simplify
> +  (div (mult @0 INTEGER_CST@1) INTEGER_CST@1)
>
> You don't need to repeat INTEGER_CST, the second time @1 is enough.
>
> +  (with { tree n2 = build_int_cst (TREE_TYPE (@0),
> +                                  wi::exact_log2 (@1)); }
> +  (if (TYPE_UNSIGNED (TREE_TYPE (@0)))
> +   (bit_and @0 (rshift (lshift { build_minus_one_cst (TREE_TYPE (@0)); }
> +                              { n2; }) { n2; }))))))
>
> What happens if you write t*3/3?

Huh, and you posted this patch twice?  See my reply to the other copy
for the correctness issues and better handling of exact_div

Richard.

> --
> Marc Glisse