[Bug tree-optimization/101145] New: niter analysis fails for until-wrap condition

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101145

            Bug ID: 101145
           Summary: niter analysis fails for until-wrap condition
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

unsigned foo(unsigned val, unsigned start)
{
  unsigned cnt = 0;
  for (unsigned i = start; i > val; ++i)
    cnt++;
  return cnt;
}

fails niter analysis.  At least for the following variant
the number of iterations should be about UINT_MAX - start.

unsigned foo(unsigned val, unsigned start)
{
  unsigned cnt = 0;
  if (start > val)
    {
      unsigned i = start;
      do
        {
          cnt++;
        }
      while (++i > val);
    }
  return cnt;
}