[Python-Dev] Compiler warnings

Wed Feb 1 08:15:41 CET 2006

Tim Peters wrote:
>>I noticed a few compiler warnings, when I compile Python on my amd64 with
>>gcc 4.0.3:
>>>>Objects/longobject.c: In function 'PyLong_AsDouble':
>>Objects/longobject.c:655: warning: 'e' may be used uninitialized in this function
>>> Well, that's pretty bizarre. There's _obviously_ no way to get to a
> reference to `e` without going through
>> 	x = _PyLong_AsScaledDouble(vv, &e);
>> first. That isn't a useful warning.

It inlines the function to make this determination. Now, it's not true
that e can be uninitialized then, but there the gcc logic fails:
If you take the
 if (vv == NULL || !PyLong_Check(vv)) {
 PyErr_BadInternalCall();
 return -1;
 }
case in _PyLong_AsScaledDouble, *exponent won't be initialized. Then,
in PyLong_AsDouble, with
 x = _PyLong_AsScaledDouble(vv, &e);
 if (x == -1.0 && PyErr_Occurred())
 return -1.0;
it looks like the return would not be taken if PyErr_Occurred returns
false. Of course, it won't, but that is difficult to analyse.
> I don't know. Is this version of gcc broken in some way relative to
> other gcc versions, or newer, or ... ? We certainly don't want to see
> warnings under gcc, since it's heavily used, but I'm not clear on why
> other versions of gcc aren't producing these warnings (or are they,
> and people have been ignoring that?).

gcc 4 does inlining in far more cases now.
Regards,
Martin