[LCG] Add a previously missing assert about the relationship of RefSCCs.

No intended change, everything seems to be in working order already.

llvm-svn: 287705

llvm/lib/Analysis/LazyCallGraph.cpp

@@ -1435,6 +1435,13 @@ void LazyCallGraph::RefSCC::insertTrivialRefEdge(Node &SourceN, Node &TargetN) {
 #ifndef NDEBUG
   // Check that the RefSCC is still valid when we finish.
   auto ExitVerifier = make_scope_exit([this] { verify(); });
+
+  // Check that we aren't breaking some invariants of the RefSCC graph.
+  RefSCC &SourceRC = *G->lookupRefSCC(SourceN);
+  RefSCC &TargetRC = *G->lookupRefSCC(TargetN);
+  if (&SourceRC != &TargetRC)
+    assert(SourceRC.isAncestorOf(TargetRC) &&
+           "Ref edge is not trivial in the RefSCC graph!");
 #endif
   // First insert it into the source or find the existing edge.
   auto InsertResult = SourceN.EdgeIndexMap.insert(