From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 3796 invoked by alias); 30 Aug 2005 01:17:21 -0000 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 Received: (qmail 3625 invoked by uid 48); 30 Aug 2005 01:17:10 -0000 Date: Tue, 30 Aug 2005 02:09:00 -0000 Message-ID: <20050830011710.3624.qmail@sourceware.org> From: "greenrd at greenrd dot org" To: gcc-bugs@gcc.gnu.org In-Reply-To: <20050820162349.23495.greenrd@greenrd.org> References: <20050820162349.23495.greenrd@greenrd.org> Reply-To: gcc-bugzilla@gcc.gnu.org Subject: [Bug libgcj/23495] java.lang.String.equals is suboptimal X-Bugzilla-Reason: CC X-SW-Source: 2005-08/txt/msg03402.txt.bz2 List-Id: ------- Additional Comments From greenrd at greenrd dot org 2005-08-30 01:17 ------- (In reply to comment #7) > This seems like something glibc's memcmp should be doing also, could > you report a bug to glibc about this comparison? Actually I was wrong - it's not glibc's memcmp that's being used here, it's the gcc inlined memcmp (see http://sources.redhat.com/bugzilla/show_bug.cgi?id=1262 ), which uses the "CISC-style" instructions REP MOVSB. This performs badly in _every_ case on athlon-xp compared to a "RISC-style" loop. (Indeed this is documented - it's surprising that gcc has been using the wrong substitution for so long!) So I will submit a more conservative bug about changing the inlined memcmp into a loop, against gcc. And will test it on pentium 4 as well. The block-compare is harder to argue for at the gcc level because it is quite complicated for the case of memcmp on big-endian (see the glibc implementation) and therefore probably isn't a good case for inlining, at least not on x86. However, the block-compare makes perfect sense for the simpler case of java.lang.String.equals, as my results show. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23495