[turbofan] Insert sigma nodes for loop variable backedge.

src/compiler/loop-variable-optimizer.h

 // Copyright 2016 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.
 
 #ifndef V8_COMPILER_LOOP_VARIABLE_OPTIMIZER_H_
 #define V8_COMPILER_LOOP_VARIABLE_OPTIMIZER_H_
 
 #include "src/zone-containers.h"
 
 namespace v8 {
@@ skipping 50 matching lines @@
   void Run();
 
   LoopVariableOptimizer(Graph* graph, CommonOperatorBuilder* common,
                         Zone* zone);
 
   const ZoneMap<int, InductionVariable*>& induction_variables() {
     return induction_vars_;
   }
 
   void ChangeToInductionVariablePhis();
-  void ChangeFromInductionVariablePhis();
+  void ChangeToPhisAndInsertSigmas();
 
  private:
   const int kAssumedLoopEntryIndex = 0;
   const int kFirstBackedge = 1;
 
   class Constraint;
   class VariableLimits;
 
   void VisitBackedge(Node* from, Node* loop);
   void VisitNode(Node* node);
@@ skipping 21 matching lines @@
   Zone* zone_;
   ZoneMap<int, const VariableLimits*> limits_;
   ZoneMap<int, InductionVariable*> induction_vars_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_LOOP_VARIABLE_OPTIMIZER_H_