When building ModemManager with -O3, you get the following failure:

mm-modem-messaging.c: In function 'mm_modem_messaging_get_supported_storages':
mm-modem-messaging.c:168:24: error: 'array' may be used uninitialized in this function [-Werror=maybe-uninitialized]
     *n_storages = array->len;
                        ^
cc1: all warnings being treated as errors
make[3]: *** [libmm_glib_la-mm-modem-messaging.lo] Error 1

That function does:

    GArray *array;
    [...]
    ensure_internal_supported_storages (self, &array);
    if (!array)
        return FALSE;
    *n_storages = array->len;

and ensure_internal_supported_storages() does

        if (dup && self->priv->supported_storages)
            *dup = g_array_ref (self->priv->supported_storages);

So nowhere array gets initialized to NULL. So this is indeed a potential crasher if it gets init'ed to some garbage and then ensure_internal_supported_storages() tries to write into it.