Avoid redundant work in scheduler loop header/depth calculation.

test/cctest/compiler/test-scheduler.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 #include "test/cctest/cctest.h"
 
 #include "src/compiler/access-builder.h"
 #include "src/compiler/common-operator.h"
 #include "src/compiler/generic-node-inl.h"
@@ skipping 1798 matching lines @@
 
   Node* ret = graph.NewNode(common.Return(), phi, ephi1, start);
   Node* end = graph.NewNode(common.End(), ret, start);
 
   graph.SetEnd(end);
 
   ComputeAndVerifySchedule(23, &graph);
 }
 
 
-TEST(LoopedFloatingDiamond) {
+TEST(LoopedFloatingDiamond1) {
   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);
@@ skipping 18 matching lines @@
 
   Node* ret = graph.NewNode(common.Return(), ind, start, f);
   Node* end = graph.NewNode(common.End(), ret, f);
 
   graph.SetEnd(end);
 
   ComputeAndVerifySchedule(20, &graph);
 }
 
 
+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());
   CommonOperatorBuilder common(scope.main_zone());
   SimplifiedOperatorBuilder simplified(scope.main_zone());
   MachineOperatorBuilder machine;
 
   Node* start = graph.NewNode(common.Start(2));
   graph.SetStart(start);
 
@@ skipping 102 matching lines @@
   graph.SetEnd(end);
 
   Schedule* schedule = ComputeAndVerifySchedule(6, &graph);
   BasicBlock* block = schedule->block(loop);
   CHECK_NE(NULL, loop);
   CHECK_EQ(block, schedule->block(effect));
   CHECK_GE(block->rpo_number(), 0);
 }
 
 #endif