Date: Sat, 12 Jul 2003 22:27:24 -0500 From: David Leimbach <leimy2k@mac.com> To: Craig Rodrigues <rodrigc@crodrigues.org> Cc: freebsd-current@freebsd.org Subject: Re: GCC 3.3.1, new warnings with <limits> Message-ID: <EBB653B2-B4E1-11D7-BE3B-0003937E39E0@mac.com> In-Reply-To: <20030713031312.GA89014@crodrigues.org> References: <20030712155333.GA79322@crodrigues.org> <BEDC8C48-B4DC-11D7-BE3B-0003937E39E0@mac.com> <20030713031312.GA89014@crodrigues.org>
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> Hi, > > I think that this is a FreeBSD issue. I compiled > the same file under Linux, with a GCC 3.3.1 checked out on 7/11 > and did not encounter this warning. > I think you hit it on the head. > I looked in the source code of gcc and found this: > /usr/src/contrib/gcc/c-common.c > > 2597 case LT_EXPR: > 2598 if (extra_warnings && !in_system_header > 2599 && ! (TREE_CODE (primop0) == INTEGER_CST > 2600 && ! TREE_OVERFLOW (convert > (c_common_signed_typ > e (type), > 2601 > primop0)))) > 2602 warning ("comparison of unsigned expression < > 0 is alway > s false"); > 2603 value = boolean_false_node; > 2604 break; > > > > > I am guessing that the C preprocessor does not think that it is > in a system header, and thus prints out the warning. > > If I take the following preprocessed source (test.ii) and compile it > under FreeBSD with g++ -W -c test.ii: > > ======================================================================= > ======== > # 1 "test.cc" > # 1 "<built-in>" > # 1 "<command line>" > # 1 "test.cc" > # 1 "/usr/include/c++/3.3/iostream" 1 3 > # 43 "/usr/include/c++/3.3/iostream" 3 > > static const int digits = (sizeof(unsigned int) * 8 - ((unsigned > int)(-1) < 0)); > > ======================================================================= > ======== > > I get: > > In file included from test.cc:1: > /usr/include/c++/3.3/iostream:44: warning: comparison of unsigned > expression < > 0 is always false > > > > > > If I compile the same file on my Linux box, with a gcc checked out > from the FSF CVS repository (gcc version 3.3.1 20030711 (prerelease)), > I do not get the warning. > > I am not an expert on the GNU C preprocessor format, but I changed > two of the lines in the above file to: > > # 1 "/usr/include/c++/3.3/iostream" 1 > # 43 "/usr/include/c++/3.3/iostream" > > and when I recompiled it under Linux, I also got the warning: > > In file included from test.cc:1: > /usr/include/c++/3.3/iostream:44: warning: comparison of unsigned > expression < > 0 is always false > > > > Any GCC/FreeBSD expert care to comment? ;) > > -- > Craig Rodrigues > http://crodrigues.org > rodrigc@crodrigues.org
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