From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Howells Subject: Re: [PATCH] asm-generic: fix -Wtype-limits compiler warnings Date: Wed, 24 Jul 2019 08:49:31 +0100 Message-ID: <31573.1563954571@warthog.procyon.org.uk> References: <1563914986-26502-1-git-send-email-cai@lca.pw> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Return-path: In-Reply-To: <1563914986-26502-1-git-send-email-cai@lca.pw> Content-ID: <31572.1563954571.1@warthog.procyon.org.uk> Sender: linux-kernel-owner@vger.kernel.org To: Qian Cai Cc: dhowells@redhat.com, akpm@linux-foundation.org, davem@davemloft.net, arnd@arndb.de, jakub@redhat.com, ndesaulniers@google.com, morbo@google.com, jyknight@google.com, natechancellor@gmail.com, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-arch.vger.kernel.org Qian Cai wrote: > Fix it by moving almost all of this multi-line macro into a proper > function __get_order(), and leave get_order() as a single-line macro in > order to avoid compilation errors. The idea was that you could compile-time initialise a global variable with get_order(): int a = get_order(SOME_MACRO); This is the same reason that ilog2() is a macro: int a = ilog2(SOME_MACRO); See the banner comment on get_order(): * This function may be used to initialise variables with compile time * evaluations of constants. If you're moving the constant branch into __get_order(), an inline function, then we'll no longer be able to do this and you need to modify the comment too. In fact, would there still be a point in having the get_order() macro? Also, IIRC, older versions of gcc see __builtin_constant_p(n) == 0 inside an function, inline or otherwise, even if the passed-in argument *is* constant. David From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:49420 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725776AbfGXHte (ORCPT ); Wed, 24 Jul 2019 03:49:34 -0400 From: David Howells In-Reply-To: <1563914986-26502-1-git-send-email-cai@lca.pw> References: <1563914986-26502-1-git-send-email-cai@lca.pw> Subject: Re: [PATCH] asm-generic: fix -Wtype-limits compiler warnings MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <31572.1563954571.1@warthog.procyon.org.uk> Date: Wed, 24 Jul 2019 08:49:31 +0100 Message-ID: <31573.1563954571@warthog.procyon.org.uk> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Qian Cai Cc: dhowells@redhat.com, akpm@linux-foundation.org, davem@davemloft.net, arnd@arndb.de, jakub@redhat.com, ndesaulniers@google.com, morbo@google.com, jyknight@google.com, natechancellor@gmail.com, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org Message-ID: <20190724074931.Q4JaAxHRos2pCaah4tjarnh0Y1Yjz-VoNmpy4-T3F2o@z> Qian Cai wrote: > Fix it by moving almost all of this multi-line macro into a proper > function __get_order(), and leave get_order() as a single-line macro in > order to avoid compilation errors. The idea was that you could compile-time initialise a global variable with get_order(): int a = get_order(SOME_MACRO); This is the same reason that ilog2() is a macro: int a = ilog2(SOME_MACRO); See the banner comment on get_order(): * This function may be used to initialise variables with compile time * evaluations of constants. If you're moving the constant branch into __get_order(), an inline function, then we'll no longer be able to do this and you need to modify the comment too. In fact, would there still be a point in having the get_order() macro? Also, IIRC, older versions of gcc see __builtin_constant_p(n) == 0 inside an function, inline or otherwise, even if the passed-in argument *is* constant. David