[Bug libstdc++/22200] numeric_limits<signed>::is_modulo is inconsistent with gcc

["rguenth at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #34 from rguenth at gcc dot gnu dot org  2010-02-21 13:04 -------
(In reply to comment #33)
> (In reply to comment #32)
> > If this hazard is so prevalent shouldn't it deserve a separate PR?
> > If a method or function depend on a flag or macro then it can be handled
> > by overloading and specialization without ODR violation.
> 
> It would be closed immediately as WONTFIX, to be clear. There is nothing we can
> do in the foreseeable future, it's **everywhere** and totally unfixable without
> breaking ABI and much more than that.
> 
> > When this hazard is, like in this case, appears in a constant then things
> > are more difficult. An unexpected behavior may be observed when is_modulo
> > is passed by reference, and I don't see what can be done in this case,
> > not in 100% of the scenarios. Even if GCC annotates the two different 
> > variants of is_modulo differently, such that there will be two different
> > physical allocations of is_modulo, it will still be possible to get to
> > some misbehavior in weird cases. Oh well...
> 
> I see that I'm not going to work on it. Actually, I'll wait one month or so,
> and then if I will not get at least one concrete proposal, I will close this
> one as WONTFIX.

Or suspend it.  I think this warrants a defect report anyway since I think
is_modulo was intended to describe CPU behavior as otherwise defining
signed integer overflow as undefined in one piece of the standard and
then requiring a sane answer for is_modulo in another part sounds
like a conflict of interest.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22200