QList::reserve unconditionally copies elements

void QList<T>::reserve(qsizetype asize)
{
    // capacity() == 0 for immutable data, so this will force a detaching below
    if (asize <= capacity() - d.freeSpaceAtBegin()) {
        if (d->flags() & Data::CapacityReserved)
            return;  // already reserved, don't shrink
        if (!d->isShared()) {
            // accept current allocation, don't shrink
            d->setFlag(Data::CapacityReserved);
            return;
        }
    }

    DataPointer detached(qMax(asize, size()));
    detached->copyAppend(d->begin(), d->end());
    if (detached.d_ptr())
        detached->setFlag(Data::CapacityReserved);
    d.swap(detached);
}