How to get point-to set?

[yuffon]

Hi, I am using SVF to get point-to set. I see in

AliasResult BVDataPTAImpl::alias(const PointsTo& p1, const PointsTo& p2)
{

    PointsTo pts1;
    expandFIObjs(p1,pts1);
    PointsTo pts2;
    expandFIObjs(p2,pts2);

    if (containBlackHoleNode(pts1) || containBlackHoleNode(pts2) || pts1.intersects(pts2))
        return AliasResult::MayAlias;
    else
        return AliasResult::NoAlias;
}

It seems that I should use expandFIObjs to get the entire pt set, isn't it? Besides, what is the meaning of blackhole nodes?