Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752724AbbEAQpk (ORCPT ); Fri, 1 May 2015 12:45:40 -0400 Received: from mail-ig0-f174.google.com ([209.85.213.174]:35076 "EHLO mail-ig0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751878AbbEAQpg (ORCPT ); Fri, 1 May 2015 12:45:36 -0400 MIME-Version: 1.0 In-Reply-To: <20150501163329.GU1751@tucnak.redhat.com> References: <20150501151630.GH5029@twins.programming.kicks-ass.net> <20150501163329.GU1751@tucnak.redhat.com> Date: Fri, 1 May 2015 09:45:35 -0700 X-Google-Sender-Auth: zyBajZQw9InJMlNLJ2LZI-0Rxdw Message-ID: Subject: Re: [PATCH] x86: Optimize variable_test_bit() From: Linus Torvalds To: Jakub Jelinek Cc: Richard Henderson , Vladimir Makarov , Peter Zijlstra , Ingo Molnar , "H. Peter Anvin" , Thomas Gleixner , Linux Kernel Mailing List , Borislav Petkov Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1002 Lines: 21 On Fri, May 1, 2015 at 9:33 AM, Jakub Jelinek wrote: > > CCing Richard as author of asm goto and Vlad as register allocator > maintainer. There are a few enhancement requests to support this, like > http://gcc.gnu.org/PR59615 and http://gcc.gnu.org/PR52381 , but indeed the > reason why no outputs are allowed is the register allocation issue. So would it help if it was documented that output registers would only be valid for the "fallthrough" case of an asm goto, and would be considered undefined for any jump targets? It wouldn't be the perfect situation, but it would be better than not having any outputs at all, and as mentioned, it would probably be sufficient for a fair number of cases. Linus -- 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/