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 Received: from mga09.intel.com ([134.134.136.24]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1qLPGt-004GBr-0w for linux-arm-kernel@lists.infradead.org; Mon, 17 Jul 2023 14:33:16 +0000 Date: Mon, 17 Jul 2023 17:31:44 +0300 From: Andy Shevchenko Subject: Re: [PATCH v3 1/5] lib/bitmap: add bitmap_{set,get}_value() Message-ID: References: <20230717113709.328671-1-glider@google.com> <20230717113709.328671-2-glider@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+lwn-linux-arm-kernel=archive.lwn.net@lists.infradead.org List-Archive: To: catalin.marinas@arm.com, will@kernel.org, pcc@google.com, andreyknvl@gmail.com, linux@rasmusvillemoes.dk, yury.norov@gmail.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, eugenis@google.com, syednwaris@gmail.com, william.gray@linaro.org, Arnd Bergmann On Mon, Jul 17, 2023 at 05:29:12PM +0300, Andy Shevchenko wrote: > On Mon, Jul 17, 2023 at 04:14:57PM +0200, Alexander Potapenko wrote: ... > > > > + map[index] &= ~(GENMASK(nbits + offset - 1, offset)); > > > > > > I remember that this construction may bring horrible code on some architectures > > > with some version(s) of the compiler (*). > > > > Wow, even the trunk Clang and GCC seem to generate better code for > > your version of this line: https://godbolt.org/z/36Kqxhe6j > > Wow, indeed! Perhaps time to report to clang and GCC people. I believe the root > cause is that in the original version compiler can't prove that l is constant > for GENMASK(). > > > > To fix that I found an easy refactoring: > > > > > > map[index] &= ~(GENMASK(nbits, 0) << offset)); nbits - 1 it should be, btw. In any case it seems the code is still better. > > I'll take this one. > > > > > (*) don't remember the actual versions, though, but anyway... -- With Best Regards, Andy Shevchenko _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel