[turbofan] Properly delete nodes in the GraphReducer.

test/cctest/compiler/test-graph-reducer.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 "graph-tester.h"
 #include "src/compiler/generic-node-inl.h"
 #include "src/compiler/graph-reducer.h"
 
@@ skipping 452 matching lines @@
   B1Forwarder f;
   reducer.AddReducer(&r);
   reducer.AddReducer(&f);
 
   // Tests first reducing A => B, then B1(x) => x.
   for (int i = 0; i < 3; i++) {
     int before = graph.NodeCount();
     reducer.ReduceGraph();
     CHECK_EQ(before, graph.NodeCount());
     CHECK_EQ(&OPB0, n1->op());
-    CHECK_EQ(&OPB1, n2->op());
+    CHECK_EQ(NULL, n2->op());
     CHECK_EQ(n1, end->InputAt(0));
-    CHECK_EQ(&OPB1, n3->op());
+    CHECK_EQ(NULL, n3->op());
     CHECK_EQ(n1, end->InputAt(0));
     CHECK_EQ(&OPB2, end->op());
     CHECK_EQ(0, n2->UseCount());
     CHECK_EQ(0, n3->UseCount());
   }
 }
 
 
 TEST(Sorter1) {
   HandleAndZoneScope scope;
@@ skipping 166 matching lines @@
   reducer.AddReducer(&once);
 
   // Tests A* => B* with in-place updates. Should only be applied once.
   int before = graph.NodeCount();
   reducer.ReduceGraph();
   CHECK_EQ(before, graph.NodeCount());
   CHECK_EQ(&OPB0, n1->op());
   CHECK_EQ(&OPB1, end->op());
   CHECK_EQ(n1, end->InputAt(0));
 }