[Bug tree-optimization/80641] missed optimization with with std::vector resize in loop

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80641

--- Comment #18 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
With -O3 we now get:
int main ()
{
  <bb 2> [local count: 114863531]:
  return 0;

}

-O2 offlines destructors which prevents us from optimizing away new()

int main ()
{
  void * D.27676;
  int * c$_M_finish;
  int * __result;
  struct vector c;
  int _1;
  void * _10;
  long int _14;
  long unsigned int _30;
  long unsigned int _31;
  int * _40;
  int * _50;

  <bb 2> [local count: 114863530]:
  MEM[(struct _Vector_impl_data *)&c] ={v} {CLOBBER(bob)};
  MEM[(struct _Vector_impl_data *)&c]._M_end_of_storage = 0B;
  _40 = operator new (16);

  <bb 3> [local count: 114863530]:
  MEM <uint128_t> [(char * {ref-all})_40] = 0x30000000200000001;
  __result_33 = _40 + 16;
  c.D.25570._M_impl.D.24881._M_end_of_storage = __result_33;
  goto <bb 5>; [100.00%]

  <bb 4> [count: 0]:
<L14>:
  MEM <vector(2) long unsigned int> [(struct vector *)&c] = { 0, 0 };
  std::_Vector_base<int, std::allocator<int> >::~_Vector_base (&c.D.25570);
  _10 = __builtin_eh_pointer (9);
  __builtin_unwind_resume (_10);

  <bb 5> [local count: 339720492]:
  # c$_M_finish_32 = PHI <_50(8), __result_33(3)>
  _14 = c$_M_finish_32 - _40;

  <bb 6> [local count: 1073741824]:
  if (_14 != 0)
    goto <bb 7>; [94.50%]
  else
    goto <bb 9>; [5.50%]

  <bb 7> [local count: 1014686025]:
  _1 = MEM[(value_type &)c$_M_finish_32 + 18446744073709551612];
  if (_1 == 0)
    goto <bb 8>; [94.50%]
  else
    goto <bb 9>; [5.50%]

  <bb 8> [local count: 958878294]:
  _31 = (long unsigned int) _14;
  _30 = _31 + 18446744073709551612;
  _50 = _40 + _30;
  if (c$_M_finish_32 != _50)
    goto <bb 5>; [70.00%]
  else
    goto <bb 6>; [30.00%]

  <bb 9> [local count: 114863531]:
  MEM <int *> [(struct vector *)&c] = _40;
  MEM <int *> [(struct vector *)&c + 8B] = c$_M_finish_32;
  std::_Vector_base<int, std::allocator<int> >::~_Vector_base (&c.D.25570);
  c ={v} {CLOBBER(eob)};
  c ={v} {CLOBBER(eos)};
  return 0;

}