[Bug tree-optimization/52904] -Wstrict-overflow false alarm with bounded loop

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52904

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-04-10
                 CC|                            |rguenth at gcc dot gnu.org
     Ever Confirmed|0                           |1

--- Comment #4 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-04-10 12:16:54 UTC ---
It's the

  if (nfds < 0)

conditional that we warn on.  We cannot currently derive an upper bound
for nfds based on the number of iterations of the loop as it is not
an induction variable we can analyze.

int
wait_reading_process_output (void)
{
  int nfds = 0;
  int channel;
  for (channel = 0; channel < 1024; ++channel)
    {
      if (foo (channel))
    nfds++;
    }
  if (nfds < 0)
    return 1;

This is in some way a missed optimization in value-range analysis as well.