Internals: Add orderPreRanked. No functional change.

src/V3Graph.h

@@ -102,8 +102,13 @@ public:
     /// Order all vertices by rank and fanout, lowest first
     /// Sort all vertices by rank and fanout, lowest first
     /// Sort all edges by weight, lowest first
+    /// Side-effect: assigns ranks to every node.
     void order();
 
+    // Similar to order() but does not assign ranks. Caller must
+    // ensure that the graph has been ranked ahead of the call.
+    void orderPreRanked();
+
     /// Make acyclical (into a tree) by breaking a minimal subset of cutable edges.
     void acyclic(V3EdgeFuncP edgeFuncp);
 

src/V3GraphAlg.cpp

@@ -507,7 +507,10 @@ void V3Graph::order() {
 
     // Compute rankings again
     rank(&V3GraphEdge::followAlwaysTrue);
+    orderPreRanked();
+}
 
+void V3Graph::orderPreRanked() {
     // Compute fanouts
     // Vertex::m_user begin: 1 indicates processing, 2 indicates completed
     userClearVertices();