+ /// \brief Insert an edge whose tail is in a descendant SCC and head is in
+ /// this SCC.
+ ///
+ /// There must be an existing path from the callee to the caller in this
+ /// case. NB! This is has the potential to be a very expensive function. It
+ /// inherently forms a cycle in the prior SCC DAG and we have to merge SCCs
+ /// to resolve that cycle. But finding all of the SCCs which participate in
+ /// the cycle can in the worst case require traversing every SCC in the
+ /// graph. Every attempt is made to avoid that, but passes must still
+ /// exercise caution calling this routine repeatedly.
+ ///
+ /// FIXME: We could possibly optimize this quite a bit for cases where the
+ /// caller and callee are very nearby in the graph. See comments in the
+ /// implementation for details, but that use case might impact users.
+ SmallVector<SCC *, 1> insertIncomingEdge(Node &CallerN, Node &CalleeN);
+