From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DB392C4742C for ; Thu, 12 Nov 2020 01:45:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9F9AA2076E for ; Thu, 12 Nov 2020 01:45:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728149AbgKLBeG (ORCPT ); Wed, 11 Nov 2020 20:34:06 -0500 Received: from gate.crashing.org ([63.228.1.57]:47423 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728167AbgKLA4P (ORCPT ); Wed, 11 Nov 2020 19:56:15 -0500 Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 0AC0m0M3024953; Wed, 11 Nov 2020 18:48:00 -0600 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 0AC0lxOU024952; Wed, 11 Nov 2020 18:47:59 -0600 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Wed, 11 Nov 2020 18:47:59 -0600 From: Segher Boessenkool To: Peter Zijlstra Cc: Nick Desaulniers , Uros Bizjak , GCC Development , X86 ML , Jakub Jelinek , Andy Lutomirski , linux-toolchains@vger.kernel.org, Christian Borntraeger , Will Deacon , Linus Torvalds , Michael Ellerman Subject: Re: typeof and operands in named address spaces Message-ID: <20201112004759.GO2672@gate.crashing.org> References: <20201109124713.GP2594@hirez.programming.kicks-ass.net> <20201109193851.GI2672@gate.crashing.org> <20201110075742.GT2594@hirez.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201110075742.GT2594@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.4.2.3i Precedence: bulk List-ID: X-Mailing-List: linux-toolchains@vger.kernel.org On Tue, Nov 10, 2020 at 08:57:42AM +0100, Peter Zijlstra wrote: > On Mon, Nov 09, 2020 at 11:50:15AM -0800, Nick Desaulniers wrote: > > On Mon, Nov 9, 2020 at 11:46 AM Segher Boessenkool > > wrote: > > > On Mon, Nov 09, 2020 at 01:47:13PM +0100, Peter Zijlstra wrote: > > > > C in general does not provide means to strip qualifiers. > > > > > > Most ways you can try to use the result are undefined behaviour, even. > > > > Yes, removing `const` from a `const` declared variable (via cast) then > > expecting to use the result is a great way to have clang omit the use > > from the final program. This has bitten us in the past getting MIPS > > support up and running, and one of the MTK gfx drivers. > > Stripping const to delcare another variable is useful though. Sure C has > sharp edges, esp. if you cast stuff, but since when did that stop anyone > ;-) My point is that removing most qualifiers usually is a problem, so before doing this, we should think if it is such a good plan, whether there is a safer / saner solution, etc. Segher