Given the following code:

ctypedef bint mybool

cdef f():
        cdef mybool c
        cdef mybool x
        c = True
        x = True
        x = not x if c else x
        print(x)

Results in this C code:

/* "test.pyx":3
 * ctypedef bint mybool
 * 
 * cdef f():             # <<<<<<<<<<<<<<
 * 	cdef mybool c
 * 	cdef mybool x
 */

static PyObject *__pyx_f_4test_f(void) {
  __pyx_t_4test_mybool __pyx_v_c;
  __pyx_t_4test_mybool __pyx_v_x;
  PyObject *__pyx_r = NULL;
  __Pyx_RefNannyDeclarations
  PyObject *__pyx_t_1 = NULL;
  PyObject *__pyx_t_2 = NULL;
  __Pyx_RefNannySetupContext("f", 0);

  /* "test.pyx":6
 * 	cdef mybool c
 * 	cdef mybool x
 * 	c = True             # <<<<<<<<<<<<<<
 * 	x = True
 * 	x = not x if c else x
 */
  __pyx_v_c = 1;

  /* "test.pyx":7
 * 	cdef mybool x
 * 	c = True
 * 	x = True             # <<<<<<<<<<<<<<
 * 	x = not x if c else x
 * 	print(x)
 */
  __pyx_v_x = 1;

  /* "test.pyx":8
 * 	c = True
 * 	x = True
 * 	x = not x if c else x             # <<<<<<<<<<<<<<
 * 	print(x)
 */
  if ((__pyx_v_c != 0)) {
    __pyx_t_1 = ((PyObject *)(!(__pyx_v_x != 0)));
  } else {
    __pyx_t_1 = ((PyObject *)__pyx_v_x);
  }
  __pyx_v_x = ((__pyx_t_4test_mybool)__pyx_t_1);
  __pyx_t_1 = 0;

  /* "test.pyx":9
 * 	x = True
 * 	x = not x if c else x
 * 	print(x)             # <<<<<<<<<<<<<<
 */
  __pyx_t_1 = __Pyx_PyBool_FromLong(__pyx_v_x); if (unlikely(!__pyx_t_1)) __PYX_ERR(0, 9, __pyx_L1_error)
  __Pyx_GOTREF(__pyx_t_1);
  __pyx_t_2 = __Pyx_PyObject_CallOneArg(__pyx_builtin_print, __pyx_t_1); if (unlikely(!__pyx_t_2)) __PYX_ERR(0, 9, __pyx_L1_error)
  __Pyx_GOTREF(__pyx_t_2);
  __Pyx_DECREF(__pyx_t_1); __pyx_t_1 = 0;
  __Pyx_DECREF(__pyx_t_2); __pyx_t_2 = 0;

  /* "test.pyx":3
 * ctypedef bint mybool
 * 
 * cdef f():             # <<<<<<<<<<<<<<
 * 	cdef mybool c
 * 	cdef mybool x
 */

  /* function exit code */
  __pyx_r = Py_None; __Pyx_INCREF(Py_None);
  goto __pyx_L0;
  __pyx_L1_error:;
  __Pyx_XDECREF(__pyx_t_1);
  __Pyx_XDECREF(__pyx_t_2);
  __Pyx_AddTraceback("test.f", __pyx_clineno, __pyx_lineno, __pyx_filename);
  __pyx_r = 0;
  __pyx_L0:;
  __Pyx_XGIVEREF(__pyx_r);
  __Pyx_RefNannyFinishContext();
  return __pyx_r;
}

Which throws these compiler warnings:

$ gcc -shared -pthread -fPIC -fwrapv -O2 -Wall -fno-strict-aliasing -I/usr/include/python3.7 -o test test.c 
test.c: In function ‘__pyx_f_4test_f’:
test.c:1136:18: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
     __pyx_t_1 = ((PyObject *)(!(__pyx_v_x != 0)));
                  ^
test.c:1138:18: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
     __pyx_t_1 = ((PyObject *)__pyx_v_x);
                  ^
test.c:1140:16: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
   __pyx_v_x = ((__pyx_t_4test_mybool)__pyx_t_1);

The C boolean variable __pyx_v_x is incorrectly casted to PyObject * and back to bool.

This does not happen, if bint is used directly in the cdefs.