[Bug tree-optimization/55018] [4.7/4.8 Regression] CDDCE pass is too aggressive sometimes with infinite loops and with some functions

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55018

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> 2012-10-22 09:00:55 UTC ---
It's simple - you basically have

<bb 2>:
  if (Connect_5(D) != 0)
    goto <bb 4>;
  else
    goto <bb 5>;

<bb 3>:
  # occurrence_3 = PHI <0(5), occurrence_1(3)>
  # .MEM_17 = PHI <.MEM_9(D)(5), .MEM_2(3)>
  occurrence_1 = occurrence_3 + 1;
  # .MEM_2 = VDEF <.MEM_17>
  printf ("Sender_Signal  occurrence  %d \n", occurrence_1);
  goto <bb 3>;

and this invokes undefined behavior because occurrence_1 = occurrence_3 + 1
overflows.  Thus GCC is free to do anything.  Fixing the testcase doesn't
fix the code though:

void Sender_signal(int Connect)
{
  unsigned int occurrence = 0;
  int State = 3;
  if (Connect)
    State = 0;
start:
  if (Connect)
    goto start;
  occurrence++;
  if (State != 2)
    __builtin_printf("Sender_Signal occurrence %u\n", occurrence);
  goto start;
}