From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 63277 invoked by alias); 7 Jul 2015 09:24:45 -0000 Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-patches-owner@gcc.gnu.org Received: (qmail 63263 invoked by uid 89); 7 Jul 2015 09:24:45 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.7 required=5.0 tests=BAYES_00,KAM_LAZY_DOMAIN_SECURITY,RP_MATCHES_RCVD autolearn=no version=3.3.2 X-HELO: mail2-relais-roc.national.inria.fr Received: from mail2-relais-roc.national.inria.fr (HELO mail2-relais-roc.national.inria.fr) (192.134.164.83) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (CAMELLIA256-SHA encrypted) ESMTPS; Tue, 07 Jul 2015 09:24:43 +0000 Received: from nat-eduroam-138-gw-01-sif.saclay.inria.fr (HELO 201-176.eduroam.saclay.inria.fr) ([195.83.213.138]) by mail2-relais-roc.national.inria.fr with ESMTP/TLS/DHE-RSA-AES256-SHA; 07 Jul 2015 11:24:40 +0200 Date: Tue, 07 Jul 2015 09:24:00 -0000 From: Marc Glisse Reply-To: gcc-patches@gcc.gnu.org To: Richard Biener cc: "gcc-patches@gcc.gnu.org" , "Hurugalawadi, Naveen" Subject: Re: [PR25529] Convert (unsigned t * 2)/2 into unsigned (t & 0x7FFFFFFF) In-Reply-To: Message-ID: References: User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed X-SW-Source: 2015-07/txt/msg00452.txt.bz2 On Tue, 7 Jul 2015, Richard Biener wrote: > On Tue, Jul 7, 2015 at 8:06 AM, Marc Glisse 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 They are not the same, one is for left shifts and the other one for right shifts. And that makes a big difference: in t*c/c, the division is always exact, so all divisions are equivalent. This is not the case for t/c*c. -- Marc Glisse