[LCG] Add the other simple edge insertion API to the call graph. This

just connects an SCC to one of its descendants directly. Not much of an
impact. The last one is the hard one -- connecting an SCC to one of its
ancestors, and thereby forming a cycle such that we have to merge all
the SCCs participating in the cycle.

llvm-svn: 207751

llvm/include/llvm/Analysis/LazyCallGraph.h

@@ -267,6 +267,14 @@ public:
     /// of any SCCs.
     void insertIntraSCCEdge(Node &CallerN, Node &CalleeN);
 
+    /// \brief Insert an edge whose tail is in this SCC and head is in some
+    /// child SCC.
+    ///
+    /// There must be an existing path from the caller to the callee. This
+    /// operation is inexpensive and does not change the set of SCCs in the
+    /// graph.
+    void insertOutgoingEdge(Node &CallerN, Node &CalleeN);
+
     /// \brief Remove an edge whose source is in this SCC and target is *not*.
     ///
     /// This removes an inter-SCC edge. All inter-SCC edges originating from

llvm/lib/Analysis/LazyCallGraph.cpp

@@ -187,6 +187,21 @@ void LazyCallGraph::SCC::insertIntraSCCEdge(Node &CallerN, Node &CalleeN) {
   // Nothing changes about this SCC or any other.
 }
 
+void LazyCallGraph::SCC::insertOutgoingEdge(Node &CallerN, Node &CalleeN) {
+  // First insert it into the caller.
+  CallerN.insertEdgeInternal(CalleeN);
+
+  assert(G->SCCMap.lookup(&CallerN) == this && "Caller must be in this SCC.");
+
+  SCC &CalleeC = *G->SCCMap.lookup(&CalleeN);
+  assert(&CalleeC != this && "Callee must not be in this SCC.");
+  assert(CalleeC.isDescendantOf(*this) &&
+         "Callee must be a descendant of the Caller.");
+
+  // The only change required is to add this SCC to the parent set of the callee.
+  CalleeC.ParentSCCs.insert(this);
+}
+
 void LazyCallGraph::SCC::removeInterSCCEdge(Node &CallerN, Node &CalleeN) {
   // First remove it from the node.
   CallerN.removeEdgeInternal(CalleeN.getFunction());

llvm/unittests/Analysis/LazyCallGraphTest.cpp

@@ -452,6 +452,59 @@ TEST(LazyCallGraphTest, IntraSCCEdgeInsertion) {
   EXPECT_EQ(&SCC, CG1.lookupSCC(C));
 }
 
+TEST(LazyCallGraphTest, OutgoingSCCEdgeInsertion) {
+  std::unique_ptr<Module> M = parseAssembly(
+      "define void @a() {\n"
+      "entry:\n"
+      "  call void @b()\n"
+      "  call void @c()\n"
+      "  ret void\n"
+      "}\n"
+      "define void @b() {\n"
+      "entry:\n"
+      "  call void @d()\n"
+      "  ret void\n"
+      "}\n"
+      "define void @c() {\n"
+      "entry:\n"
+      "  call void @d()\n"
+      "  ret void\n"
+      "}\n"
+      "define void @d() {\n"
+      "entry:\n"
+      "  ret void\n"
+      "}\n");
+  LazyCallGraph CG(*M);
+
+  // Force the graph to be fully expanded.
+  for (LazyCallGraph::SCC &C : CG.postorder_sccs())
+    (void)C;
+
+  LazyCallGraph::Node &A = *CG.lookup(lookupFunction(*M, "a"));
+  LazyCallGraph::Node &B = *CG.lookup(lookupFunction(*M, "b"));
+  LazyCallGraph::Node &C = *CG.lookup(lookupFunction(*M, "c"));
+  LazyCallGraph::Node &D = *CG.lookup(lookupFunction(*M, "d"));
+  LazyCallGraph::SCC &AC = *CG.lookupSCC(A);
+  LazyCallGraph::SCC &BC = *CG.lookupSCC(B);
+  LazyCallGraph::SCC &CC = *CG.lookupSCC(C);
+  LazyCallGraph::SCC &DC = *CG.lookupSCC(D);
+  EXPECT_TRUE(AC.isAncestorOf(BC));
+  EXPECT_TRUE(AC.isAncestorOf(CC));
+  EXPECT_TRUE(AC.isAncestorOf(DC));
+  EXPECT_TRUE(DC.isDescendantOf(AC));
+  EXPECT_TRUE(DC.isDescendantOf(BC));
+  EXPECT_TRUE(DC.isDescendantOf(CC));
+
+  EXPECT_EQ(2, std::distance(A.begin(), A.end()));
+  AC.insertOutgoingEdge(A, D);
+  EXPECT_EQ(3, std::distance(A.begin(), A.end()));
+  EXPECT_TRUE(AC.isParentOf(DC));
+  EXPECT_EQ(&AC, CG.lookupSCC(A));
+  EXPECT_EQ(&BC, CG.lookupSCC(B));
+  EXPECT_EQ(&CC, CG.lookupSCC(C));
+  EXPECT_EQ(&DC, CG.lookupSCC(D));
+}
+
 TEST(LazyCallGraphTest, IntraSCCEdgeRemoval) {
   // A nice fully connected (including self-edges) SCC.
   std::unique_ptr<Module> M1 = parseAssembly(