[Bug c/67629] bogus -Wreturn-type in a function with tautological if-else

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67629

--- Comment #5 from Martin Liška <marxin at gcc dot gnu.org> ---
That's for CC. However as the warning is triggered early, we don't have
optimized IL:

(gdb) p debug_function(cfun->decl, 0)
foo (_Bool a)
{
  int D.1836;

  <bb 2> [0.00%] [count: INV]:
  if (a != 0)
    goto <bb 3>; [INV] [count: INV]
  else
    goto <bb 4>; [INV] [count: INV]

  <bb 3> [0.00%] [count: INV]:
  D.1836 = 0;
  // predicted unlikely by early return (on trees) predictor.
  goto <bb 7>; [INV] [count: INV]

  <bb 4> [0.00%] [count: INV]:
  _1 = ~a;
  if (_1 != 0)
    goto <bb 5>; [INV] [count: INV]
  else
    goto <bb 6>; [INV] [count: INV]

  <bb 5> [0.00%] [count: INV]:
  D.1836 = 1;
  // predicted unlikely by early return (on trees) predictor.
  goto <bb 7>; [INV] [count: INV]

  <bb 6> [0.00%] [count: INV]:
  return;

  <bb 7> [0.00%] [count: INV]:
<L4>:
  return D.1836;

}