[Developers] g++ warning: operation on *bla* may be undefined

[Jonathan Thornburg]

Hi,

On Thu, 26 Oct 2006, Erik Schnetter wrote:
> gcc has __attribute__((unused)) to mark variables that are intentionally
> unused.  This suppresses this warning.  Other compilers may have similar ways
> for annotating variables.
> 
> I have implemented a bit of generic infrastructure to declare variables, which
> makes it easier to experiment with these things.  I have also implemented
> autodetecting whether __attribute__((unused)) is supported, so that it is used
> when present, and an old-style mechanism is used otherwise.  A similar thing
> is done for Fortran code.
> 
> The changes are straightforward, but touch quite a number of files.  I would
> need to isolate them from other changes, and then they need to be tested
> thoroughly.  I can do the first part if you are interested.
> 
> We discussed this before, and then the consensus was that using
> __attribute__((unused)) was not worth the effort because the existing
> mechanisms were sufficient.  Maybe this has changed with gcc 4 having become
> too clever.

IMHO Erik's suggestion of using  __attribute__((unused))  is the right
way to solve this problem, while our current approach of trying to fool
compilers is a chronic hassle which is gradually getting less effective
as compilers get smarter.

Erik, I would be happy to test your __attributre__((unused)) patches
with gcc in my Cactus compiles...

ciao,

-- 
-- Jonathan Thornburg <jthorn at aei.mpg.de>      
   Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut),
   Golm, Germany, "Old Europe"     http://www.aei.mpg.de/~jthorn/home.html      
   "Washing one's hands of the conflict between the powerful and the
    powerless means to side with the powerful, not to be neutral."
                                      -- quote by Freire / poster by Oxfam