From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 60006 invoked by alias); 26 Jul 2016 15:26:40 -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 59995 invoked by uid 89); 26 Jul 2016 15:26:40 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-3.2 required=5.0 tests=BAYES_00,RP_MATCHES_RCVD,SPF_HELO_PASS autolearn=ham version=3.3.2 spammy=opportunity X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES256-GCM-SHA384 encrypted) ESMTPS; Tue, 26 Jul 2016 15:26:39 +0000 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id F026F7F6A8; Tue, 26 Jul 2016 15:26:37 +0000 (UTC) Received: from localhost.localdomain (ovpn-116-144.phx2.redhat.com [10.3.116.144]) by int-mx10.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u6QFQbFL020225; Tue, 26 Jul 2016 11:26:37 -0400 Subject: Re: [PATCH, vec-tails 07/10] Support loop epilogue combining To: Ilya Enkovich References: <20160519194450.GH40563@msticlxl57.ims.intel.com> <18ccae1a-30c3-c23c-e28f-287f9d41eaa0@redhat.com> <20160628122439.GB4143@msticlxl57.ims.intel.com> <20160720143705.GA2605@msticlxl57.ims.intel.com> <4bb744cb-92df-ca29-54e2-82162216e88c@redhat.com> <5cacdc29-e916-f460-3c44-5fa6450a24a9@redhat.com> Cc: Richard Biener , gcc-patches From: Jeff Law Message-ID: <37fbe5e6-6e44-ffff-5467-21e162919586@redhat.com> Date: Tue, 26 Jul 2016 15:26:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-IsSubscribed: yes X-SW-Source: 2016-07/txt/msg01725.txt.bz2 On 07/26/2016 03:57 AM, Ilya Enkovich wrote: >> >> Ilya, what's the fundamental reason why we need to run >> if-conversion again? Yes, I know you want to if-convert the >> epilogue, but why? >> >> What are the consequences of not doing if-conversion on the >> epilogue? Presumably we miss a vectorization opportunity on the >> tail. But that may be a reasonable limitation to allow the >> existing work to move forward while you go back and revamp things a >> little. > > If we have some control-flow in a loop then we have to if-convert it > for vectorizer. We need to preserve both versions: if-converted one > for vectorizer and the original one to be used if vectorization > fails. For epilogues we have similar situation and need two > versions. I do it by running if-conversion on a copy of original > loop. Note that it doesn't run full if-conversion pass. If-conversion > is called for epilogue loop only. Right. So what I think Richi wants you to try is to use the if-converted loop to construct the if-converted epilogue. It seems conceptually simple and low cost -- the question is on the implementation side. I have no clue how painful that would be. jeff