[Bug tree-optimization/99101] optimization bug with -ffinite-loops

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99101

--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
The following reduced testcase fails in the described way at -O2 with the C++
FE and with the C FE if you specify -ffinite-loops in addition to -O2.  Already
CDDCE1 does the problematic transform which means the first breakpoint
hit on perform_tree_ssa_dce is the problematic one easing further
investigation.

volatile int xx;
int main()
{
  int read_finish_ = 1;
  int jobs_ = 1;
  int at_eof_ = 0;
  while (1)
    {
      int num_job = jobs_;
      for (int i = 0; i < jobs_; i++)
        {
          if (at_eof_) continue;
          if (read_finish_)
            {
              at_eof_ = 1;
              __builtin_printf ("1\n");
              if (xx)
                __builtin_abort ();
            }
        }
      jobs_ -= num_job;
    }
  return 0;
}