[Python-Dev] Compiler warnings (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
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 'PyLongAsDouble': 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 = PyLongAsScaledDouble(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

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