In testlib/qsignalspy.h, there is the following code:

                void *argv[] = { &tp, &i };
                QMetaObject::metacall(const_cast<QObject*>(obj),
                                      QMetaObject::RegisterMethodArgumentMetaType,
                                      member.methodIndex(), argv);

i is in this case the iterator of the for loop.

Since 0161f00e5043090f22b23de9822c09062b17d675 we generate the following code in moc:

    } else if (_c == QMetaObject::RegisterMethodArgumentMetaType) {
        if (_id < 2)
            *reinterpret_cast<QMetaType *>(_a[0]) = QMetaType();

This overwrites the loop iterator with 0 if sizeof(int) < sizeof(void*), and we enter an infinite loop.

I am assuming the code in QSignalSpy is wrong, but since it is the moc output that has changed and it causes memory corruption, I think it is better if someone who knows this code makes the call on what the right fix is.