Avoid redundant work in scheduler loop header/depth calculation.

test/cctest/compiler/test-scheduler.cc

Index: test/cctest/compiler/test-scheduler.cc
diff --git a/test/cctest/compiler/test-scheduler.cc b/test/cctest/compiler/test-scheduler.cc
index 5f5c9d190a0899f145d8feee5aa28e59df3f50c3..aed8f8b96f68020e99cb64f996e266bb1887f9c1 100644
--- a/test/cctest/compiler/test-scheduler.cc
+++ b/test/cctest/compiler/test-scheduler.cc
@@ -1816,7 +1816,7 @@ TEST(NestedFloatingDiamonds) {
 }
 
 
-TEST(LoopedFloatingDiamond) {
+TEST(LoopedFloatingDiamond1) {
   HandleAndZoneScope scope;
   Graph graph(scope.main_zone());
   CommonOperatorBuilder common(scope.main_zone());
@@ -1855,6 +1855,46 @@ TEST(LoopedFloatingDiamond) {
 }
 
 
+TEST(LoopedFloatingDiamond2) {
+  HandleAndZoneScope scope;
+  Graph graph(scope.main_zone());
+  CommonOperatorBuilder common(scope.main_zone());
+  SimplifiedOperatorBuilder simplified(scope.main_zone());
+  MachineOperatorBuilder machine;
+
+  Node* start = graph.NewNode(common.Start(2));
+  graph.SetStart(start);
+
+  Node* p0 = graph.NewNode(common.Parameter(0), start);
+
+  Node* c = graph.NewNode(common.Int32Constant(7));
+  Node* loop = graph.NewNode(common.Loop(2), start, start);
+  Node* ind = graph.NewNode(common.Phi(kMachAnyTagged, 2), p0, p0, loop);
+
+  Node* br1 = graph.NewNode(common.Branch(), p0, graph.start());
+  Node* t1 = graph.NewNode(common.IfTrue(), br1);
+  Node* f1 = graph.NewNode(common.IfFalse(), br1);
+  Node* m1 = graph.NewNode(common.Merge(2), t1, f1);
+  Node* phi1 = graph.NewNode(common.Phi(kMachAnyTagged, 2), c, ind, m1);
+
+  Node* add = graph.NewNode(machine.IntAdd(), ind, phi1);
+
+  Node* br = graph.NewNode(common.Branch(), add, loop);
+  Node* t = graph.NewNode(common.IfTrue(), br);
+  Node* f = graph.NewNode(common.IfFalse(), br);
+
+  loop->ReplaceInput(1, t);   // close loop.
+  ind->ReplaceInput(1, add);  // close induction variable.
+
+  Node* ret = graph.NewNode(common.Return(), ind, start, f);
+  Node* end = graph.NewNode(common.End(), ret, f);
+
+  graph.SetEnd(end);
+
+  ComputeAndVerifySchedule(20, &graph);
+}
+
+
 TEST(PhisPushedDownToDifferentBranches) {
   HandleAndZoneScope scope;
   Graph graph(scope.main_zone());