From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 11734 invoked by alias); 21 Jun 2010 20:19:03 -0000 Received: (qmail 11720 invoked by uid 22791); 21 Jun 2010 20:19:02 -0000 X-SWARE-Spam-Status: No, hits=-6.9 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_HI,SPF_HELO_PASS,T_RP_MATCHES_RCVD X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 21 Jun 2010 20:18:57 +0000 Received: from int-mx03.intmail.prod.int.phx2.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.16]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o5LKIeZC000764 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Mon, 21 Jun 2010 16:18:40 -0400 Received: from ns3.rdu.redhat.com (ns3.rdu.redhat.com [10.11.255.199]) by int-mx03.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id o5LKIdKs001136; Mon, 21 Jun 2010 16:18:39 -0400 Received: from [172.17.80.6] (ovpn01.gateway.prod.ext.phx2.redhat.com [10.5.9.1]) by ns3.rdu.redhat.com (8.13.8/8.13.8) with ESMTP id o5LKIcRG031849; Mon, 21 Jun 2010 16:18:38 -0400 Message-ID: <4C1FC91D.401@redhat.com> Date: Mon, 21 Jun 2010 21:35:00 -0000 From: Jeff Law User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100430 Fedora/3.0.4-3.fc13 Thunderbird/3.0.4 MIME-Version: 1.0 To: Steven Bosscher CC: Maxim Kuvyrkov , gcc-patches Subject: Re: 0005-Search-all-dominated-blocks-for-expressions-to-hoist.patch References: <4C18F225.2040509@codesourcery.com> <4C18F491.2000406@codesourcery.com> <4C1FB369.4080006@redhat.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-IsSubscribed: yes 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 X-SW-Source: 2010-06/txt/msg02084.txt.bz2 On 06/21/10 13:28, Steven Bosscher wrote: > > I experimented with a patch similar to Maxim's already 2.5 years ago > (and offered to work on it for CS, but there was no interest in this > work at the time :-/) See these three Bugzilla comments: > > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33828#c2 > Right. This is precisely the problem with using immediate dominators. This doesn't argue that Maxim's approach is wrong or bad for compile time performance or anything like that. It merely raises the same issue. > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33828#c8 > Clearly something should be done about this. If you have a testcase for Maxim that would be a help. One could argue that adding the REG_EQUAL note created by hoisting to the hash table is a waste of time, fixing that would eliminate this problem. > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33828#c13 > > Note especially the pessimization in comment #13 of PR33828. > Therefore I maintain my objection to this patch. > Clearly you don't want to hoist any higher than the lowest common dominator. Otherwise you unreasonably lengthen lifetimes. Maxim will need to address this problem as well. Jeff