[Pyrex] bad del code generation

[Eric Huss]

I'm having a hard time figuring out how to fix this problem in the
compiler.  It seems that temporarily allocated objects in a del statement
generate the wrong deletion code.  The following is an example:

def foo():
    bar = [47]
    del bar[0]
    return

The snippet of C code it generates is:

  /* del bar[0]
  */
  __pyx_1 = PyInt_FromLong(0); if (!__pyx_1) {__pyx_filename = __pyx_f[0]; __pyx_lineno = 3; goto __pyx_L1;}
  if (PyObject_DelItem(__pyx_v_bar, __pyx_1) < 0) {__pyx_filename = __pyx_f[0]; __pyx_lineno = 3; goto __pyx_L1;}
  Py_DECREF(__pyx_1); __pyx_1 = 0;

  /* return
  */
  Py_DECREF(__pyx_1); __pyx_1 = 0;
  __pyx_r = Py_None; Py_INCREF(Py_None);
  goto __pyx_L0;

You can see that it allocates the number 0 as __pyx_1, calls delitem, then
decref's it and sets it to zero.  Unfortunately a return statement will
attempt to call DECREF on __pyx_1 even though it is NULL.

I'll work around it for now by putting the index value into a local
variable, but it would be nice to fix the problem.

-Eric