// infinite loops). In these cases an artificial exit node is required.
MultipleRoots |= (DT.isPostDominator() && N != F.size());
+ // When naively implemented, the Lengauer-Tarjan algorithm requires a separate
+ // bucket for each vertex. However, this is unnecessary, because each vertex
+ // is only placed into a single bucket (that of its semidominator), and each
+ // vertex's bucket is processed before it is added to any bucket itself.
+ //
+ // Instead of using a bucket per vertex, we use a single array Buckets that
+ // has two purposes. Before the vertex V with preorder number i is processed,
+ // Buckets[i] stores the index of the first element in V's bucket. After V's
+ // bucket is processed, Buckets[i] stores the index of the next element in the
+ // bucket containing V, if any.
std::vector<unsigned> Buckets;
Buckets.resize(N + 1);
for (unsigned i = 1; i <= N; ++i)