Re: c/10143: Post increment doesn work more than once per statement

["Nick Macdonald" <macdonn@nortelnetworks.com>]

The following reply was made to PR c/10143; it has been noted by GNATS.

From: "Nick Macdonald" <macdonn@nortelnetworks.com>
To: "Joseph S. Myers" <jsm28@cam.ac.uk>
Cc: Falk Hueffner <falk.hueffner@student.uni-tuebingen.de>,
   gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org
Subject: Re: c/10143: Post increment doesn work more than once per statement
Date: Wed, 19 Mar 2003 14:54:29 -0500

 Good point... I did not see that recommendation, however, even if I
 had.... check this:
 
 
 {macdonn}85: which gcc
 /opt/unsupported/gcc-2.95.2/bin/gcc
 {macdonn}86: gcc -Wall shift.c
 shift.c: In function `main':
 shift.c:67: warning: unsigned int format, long unsigned int arg (arg 4)
 shift.c:68: warning: unsigned int format, long unsigned int arg (arg 4)
 shift.c:70: warning: unsigned int format, long unsigned int arg (arg 4)
 shift.c:71: warning: unsigned int format, long unsigned int arg (arg 3)
 shift.c:72: warning: unsigned int format, long unsigned int arg (arg 4)
 {macdonn}87: gcc -Wsequence-point shift.c
 cc1: Invalid option `-Wsequence-point'
 
 
 {macdonn}193: gcc -Wall WeirdForLoop.c        
 {macdonn}194: gcc -v
 Reading specs from
 /tmp/gcc_install/lib/gcc-lib/sparc-sun-solaris2.8/3.2.2/specs
 Configured with: ../configure --with-as=/usr/ccs/bin/as
 --with-ld=/usr/ccs/bin/ld --disable-nls --prefix=/tmp/gcc_install
 Thread model: posix
 gcc version 3.2.2
 {macdonn}195: gcc -Wsequence-point WeirdForLoop.c
 
 There is no sequence point warning when compiling either program... 
 using either 2.95.2 or 3.2.2
 
 
 As for your questions... I submitted by bug by starting from this URL:
 http://www.gnu.org/directory/gcc.html which led to this URL:
 http://www.gnu.org/software/gcc/gnats.html which led to this URL: 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl  and no where along that path did
 I see the recommendationabout warnings (even though in this case that
 would not have helped.)
 
 
 A person comment on all this:
 I was just trying to make the product better...  I feel the answer of
 "not a bug" to be a bit pedantic...  sure, technically it may not be a
 bug...  however, logically, the current behaviour is less than stellar
 and it should be addressed to make post and pre increment behave more or
 less similarly...  I have learned a valuable lesson from all this, and I
 will now write better code because of it... but I still think that the
 choice of implementing this behaviour in the chosen manner is highly
 likely to make a bad problem much more seriously wrong than it should
 be.  (If the evil empire can do something meaningful with it...  we
 should be able to learn from that...)
 
 If this bizarre code generating behaviour is to stand as is then I'd
 rather the compiler default to warning on this behaviour than to make it
 my requirement to know that I should request a sequence point
 warning...  i.e. default the warning on and make it a requirement to
 supress it.
 
 Nick
 
 
 "Joseph S. Myers" wrote:
 > 
 > On 19 Mar 2003, Falk Hueffner wrote:
 > 
 > > > (Is there a FAQ entry somewhere that deals with this issue?)
 > >
 > > See the documentation of -Wsequence-point. (We should probably add
 > > this to the list of C non-bugs...)
 > 
 > The bug reporting instructions <http://gcc.gnu.org/bugs.html> say:
 > 
 >    Before reporting that GCC compiles your code incorrectly, please
 >    compile it with gcc -Wall and see whether this shows anything wrong
 >    with your code that could be the cause instead of a bug in GCC.
 > 
 > To the submitter: did you see this part of the instructions and try
 > compiling your code with -Wall (which includes -Wsequence-point, which
 > would have shown up the problem with the code)?  If not, how could we
 > improve the documentation of how to submit bugs so that you would have
 > seen and followed these instructions?  If you did use -Wall, how could we
 > clarify the warning message?
 > 
 > --
 > Joseph S. Myers
 > jsm28@cam.ac.uk
 
 -- 
 Nick MacDonald
 Nortel Networks, Belleville
 macdonn@nortelnetworks.com
 (613) 966-0100 Ext. 8755  ESN: 343-8755