[Bug tree-optimization/53805] combine_comparisons changes trapping behavior

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53805

--- Comment #7 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-06-29 14:54:21 UTC ---
(In reply to comment #6)
> On Fri, 29 Jun 2012, rguenth at gcc dot gnu.org wrote:
> 
> > We happily remove dead trapping statements:
> > 
> > void foo(double x, int y)
> > {
> >   1 / x;
> 
> Bug with -ftrapping-math.  Maybe a known bug - there are plenty of open 
> bugs for ways in which -ftrapping-math -frounding-math fail to implement 
> standard C semantics - but a bug.
> 
> >   1 / y;
> 
> Arguably a bug with -ftrapv (again, the option could reasonably be split 
> into different cases), but not otherwise.

All CPUs I know trap for 1 / 0, even in the integer division case.  -ftrapv
is a completely different story - for it we'd even have to preserve

void foo (int x, int y)
{
  x + y;
}