From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 26190 invoked by alias); 3 Jun 2006 02:50:09 -0000 Received: (qmail 26028 invoked by uid 48); 3 Jun 2006 02:49:58 -0000 Date: Sat, 03 Jun 2006 02:50:00 -0000 Message-ID: <20060603024958.26027.qmail@sourceware.org> X-Bugzilla-Reason: CC References: Subject: [Bug target/27855] reassociation pass produces ~30% slower matrix multiplication code In-Reply-To: Reply-To: gcc-bugzilla@gcc.gnu.org To: gcc-bugs@gcc.gnu.org From: "pinskia at gcc dot gnu dot org" Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org X-SW-Source: 2006-06/txt/msg00160.txt.bz2 List-Id: ------- Comment #7 from pinskia at gcc dot gnu dot org 2006-06-03 02:49 ------- If you change the code to be integers, this also cause the drop too with reassociation even without -ffast-math so it is unrelated to the fact -ffast-math turns on reassociate for floating points for fast math. So what is happening is that the add to rC[0-4]_0 is being further down which causes variable's life to be extended. Yes there should be a pass at the tree level which optimizes variable's life time but I don't know how much use that is without a better register allocator in the first place. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27855