From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Booth Subject: Re: [PATCH 16/16] fix handling of integer constant expressions Date: Wed, 27 Jun 2007 21:26:28 +0900 Message-ID: <20070627122628.GR7590@daikokuya.co.uk> References: <1a25667a20e43a072f733a3ec2b8e79d@kernel.crashing.org> <20070624203837.GE21478@ftp.linux.org.uk> <467F531A.3030702@freedesktop.org> <20070626221040.GI21478@ftp.linux.org.uk> <20070626221134.GA21350@ftp.linux.org.uk> <20070626233226.GO7590@daikokuya.co.uk> <20070627001803.GJ21478@ftp.linux.org.uk> <20070627115245.GP7590@daikokuya.co.uk> <20070627121948.GN21478@ftp.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from v035086.ppp.asahi-net.or.jp ([124.155.35.86]:7516 "HELO daikokuya.co.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with SMTP id S1756342AbXF0M0W (ORCPT ); Wed, 27 Jun 2007 08:26:22 -0400 Content-Disposition: inline In-Reply-To: <20070627121948.GN21478@ftp.linux.org.uk> Sender: linux-sparse-owner@vger.kernel.org List-Id: linux-sparse@vger.kernel.org To: Al Viro Cc: Josh Triplett , Segher Boessenkool , Linus Torvalds , linux-kernel@vger.kernel.org, linux-sparse@vger.kernel.org Al Viro wrote:- > Egads... After rereading that... What a mess. > > int foo(void) > { > static int a[1][0,2]; > } > > is, AFAICS, allowed. Reason: > int a[0,2] > is a VLA due to 6.7.5.2[4] (0,2 is not an ICE). However, due to the language > in the same section, > int a[1][0,2] > is *not* a VLA, since (a) 2 is an ICE and (b) its element type "has a known > constant size" (it does - the value of 0,2 is certainly guaranteed to be 2). > I.e., it's VM type, but not a VLA. I.e. only the first part of 6.7.5.2[2] > applies and we are actually fine. > > So we can have a static single-element array of int [0,2], but > not a plain static int [0,2]. Lovely, that... DR 312 clarified the meaning of "known constant size" http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_312.htm in the sensible way, thankfully, so your example is actually invalid. Neil.