Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261656AbVDZST0 (ORCPT ); Tue, 26 Apr 2005 14:19:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261608AbVDZSTZ (ORCPT ); Tue, 26 Apr 2005 14:19:25 -0400 Received: from mail-in-01.arcor-online.net ([151.189.21.41]:42453 "EHLO mail-in-01.arcor-online.net") by vger.kernel.org with ESMTP id S261670AbVDZSTM (ORCPT ); Tue, 26 Apr 2005 14:19:12 -0400 From: "Bodo Eggert " <7eggert@gmx.de> Subject: Re: [PATCH GIT 0.6] make use of register variables & size_t To: Matthias-Christian Ott , Linus Torvalds , git@vger.kernel.org, Linux Kernel Mailing List Reply-To: 7eggert@gmx.de Date: Tue, 26 Apr 2005 20:18:02 +0200 References: <3X9X6-5JP-27@gated-at.bofh.it> <3Xdel-8u2-43@gated-at.bofh.it> <3XfpD-21C-11@gated-at.bofh.it> User-Agent: KNode/0.7.2 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7Bit Message-Id: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1318 Lines: 23 Matthias-Christian Ott wrote: > And if you think "register" variables are outdated, please remove the > CONFIG_REGPARM option from the Kernel source. Register variables are outdated because they hinder the compiler from optimizing by taking away 1/7 of the usable registers on x86. Use six register variables and you're back to a accumulator-machine. Use -O2 or -Os instead, the compiler is smarter than you. The regparm calling convention will change the load value -> store value on stack -> call sequence into load value -> call -> store if needed Obviously the second form can be better optimized than the first one. Therefore it's a gain instead of a loss. If you really want to help the compiler, look for something like repeated pointer dereference or access to global variables and cache them in block- local variables (pointers, int and uint only, even for caching chars). Beware of volatile variables, and don't forget to look at the assembler code. -- The generation of random numbers is too important to be left to chance. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/