[turbofan] Fix control reducer for dead loops.

src/compiler/control-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/compiler/common-operator.h"
 #include "src/compiler/control-reducer.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/node-marker.h"
 #include "src/compiler/node-matchers.h"
@@ skipping 366 matching lines @@
     EnsureStateSize(id);
     state_[id] = kVisited;
   }
 
   Node* dead() { return jsgraph_->DeadControl(); }
 
   //===========================================================================
   // Reducer implementation: perform reductions on a node.
   //===========================================================================
   Node* ReduceNode(Node* node) {
-    if (node->op()->ControlInputCount() == 1) {
+    if (node->op()->ControlInputCount() == 1 ||
+        node->opcode() == IrOpcode::kLoop) {
       // If a node has only one control input and it is dead, replace with dead.
       Node* control = NodeProperties::GetControlInput(node);
       if (control->opcode() == IrOpcode::kDead) {
         TRACE(("ControlDead: #%d:%s\n", node->id(), node->op()->mnemonic()));
         return control;
       }
     }
 
     // Reduce branches, phis, and merges.
     switch (node->opcode()) {
@@ skipping 206 matching lines @@
   impl.Reduce();
 }
 
 
 void ControlReducer::TrimGraph(Zone* zone, JSGraph* jsgraph) {
   ControlReducerImpl impl(zone, jsgraph, NULL);
   impl.Trim();
 }
 
 
+Node* ControlReducer::ReduceMerge(JSGraph* jsgraph,
+                                  CommonOperatorBuilder* common, Node* node) {
+  Zone zone;
+  ControlReducerImpl impl(&zone, jsgraph, common);
+  return impl.ReduceMerge(node);
+}
+
+
 Node* ControlReducer::ReducePhiForTesting(JSGraph* jsgraph,
                                           CommonOperatorBuilder* common,
                                           Node* node) {
   Zone zone;
   ControlReducerImpl impl(&zone, jsgraph, common);
   return impl.ReducePhi(node);
 }
 
 
-Node* ControlReducer::ReduceMergeForTesting(JSGraph* jsgraph,
-                                            CommonOperatorBuilder* common,
-                                            Node* node) {
-  Zone zone;
-  ControlReducerImpl impl(&zone, jsgraph, common);
-  return impl.ReduceMerge(node);
-}
-
-
 Node* ControlReducer::ReduceIfNodeForTesting(JSGraph* jsgraph,
                                              CommonOperatorBuilder* common,
                                              Node* node) {
   Zone zone;
   ControlReducerImpl impl(&zone, jsgraph, common);
   switch (node->opcode()) {
     case IrOpcode::kIfTrue:
       return impl.ReduceIfTrue(node);
     case IrOpcode::kIfFalse:
       return impl.ReduceIfFalse(node);
     default:
       return node;
   }
 }
 }
 }
 }  // namespace v8::internal::compiler