[LCG] Remove the use of the parent sets to compute connectivity when

merging RefSCCs.

The logic to directly use the reference edges is simpler and not
substantially slower (despite the comments to the contrary) because this
is not actually an especially hot part of LCG in practice.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310161 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/LazyCallGraph.cpp

@@ -957,22 +957,20 @@ LazyCallGraph::RefSCC::insertIncomingRefEdge(Node &SourceN, Node &TargetN) {
   // RefSCCs (and their edges) are visited here.
   auto ComputeSourceConnectedSet = [&](SmallPtrSetImpl<RefSCC *> &Set) {
     Set.insert(&SourceC);
-    SmallVector<RefSCC *, 4> Worklist;
-    Worklist.push_back(&SourceC);
-    do {
-      RefSCC &RC = *Worklist.pop_back_val();
-      for (RefSCC &ParentRC : RC.parents()) {
-        // Skip any RefSCCs outside the range of source to target in the
-        // postorder sequence.
-        int ParentIdx = G->getRefSCCIndex(ParentRC);
-        assert(ParentIdx > SourceIdx && "Parent cannot precede source in postorder!");
-        if (ParentIdx > TargetIdx)
-          continue;
-        if (Set.insert(&ParentRC).second)
-          // First edge connecting to this parent, add it to our worklist.
-          Worklist.push_back(&ParentRC);
-      }
-    } while (!Worklist.empty());
+    auto IsConnected = [&](RefSCC &RC) {
+      for (SCC &C : RC)
+        for (Node &N : C)
+          for (Edge &E : *N)
+            if (Set.count(G->lookupRefSCC(E.getNode())))
+              return true;
+
+      return false;
+    };
+
+    for (RefSCC *C : make_range(G->PostOrderRefSCCs.begin() + SourceIdx + 1,
+                                G->PostOrderRefSCCs.begin() + TargetIdx + 1))
+      if (IsConnected(*C))
+        Set.insert(C);
   };
 
   // Use a normal worklist to find which SCCs the target connects to. We still