From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 3472 invoked by alias); 16 Mar 2004 17:11:31 -0000 Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Archive: List-Post: List-Help: Sender: gcc-owner@gcc.gnu.org Received: (qmail 3458 invoked from network); 16 Mar 2004 17:11:29 -0000 Received: from unknown (HELO yosemite.airs.com) (209.128.65.135) by sources.redhat.com with SMTP; 16 Mar 2004 17:11:29 -0000 Received: (qmail 23491 invoked by uid 10); 16 Mar 2004 17:11:26 -0000 Received: (qmail 13883 invoked by uid 500); 16 Mar 2004 17:11:07 -0000 From: Ian Lance Taylor To: Paul Koning Cc: gcc@gcc.gnu.org Subject: Re: GCC Status Report (2004-03-09) References: <200403091809.i29I9P04020607@sirius.codesourcery.com> <200403111030.14616.ebotcazou@act-europe.fr> <40573108.4080602@codesourcery.com> <16471.12911.55000.733792@gargle.gargle.HOWL> Date: Tue, 16 Mar 2004 17:11:00 -0000 In-Reply-To: <16471.12911.55000.733792@gargle.gargle.HOWL> Message-ID: User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-SW-Source: 2004-03/txt/msg00827.txt.bz2 Paul Koning writes: > >>>>> "Mark" == Mark Mitchell writes: > > Mark> The other alternative I can think of is to introduce a > Mark> scheduling barrier (e.g., a dummy vaolatile asm) after the > Mark> clearing operation. > > It would be nice if there were a clearly documented way to do that. > > I've found two: > > asm("") > asm("":::"memory") > > The former does what I want but isn't documented and (according to > what I was told) should NOT be counted on to be a barrier. > > The latter is documented and does a superset of what I needed at the > time. I say "superset" because it causes registers to be reloaded > with data from variables (due to the memory clobber). That's a > performance hit if I didn't have any real memory clobbers in the > system. > > Perhaps we need asm("":::"barrier")? Seconded. For high performance device manipulation, it would be good to have a way to say "do not schedule instructions across this point" without also saying "clobber everything". Ian