[turbofan] Proper dead code elimination as regular reducer.

src/compiler/common-operator-reducer.h

 // 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.
 
 #ifndef V8_COMPILER_COMMON_OPERATOR_REDUCER_H_
 #define V8_COMPILER_COMMON_OPERATOR_REDUCER_H_
 
 #include "src/compiler/graph-reducer.h"
 
 namespace v8 {
@@ skipping 15 matching lines @@
                         MachineOperatorBuilder* machine)
       : AdvancedReducer(editor),
         graph_(graph),
         common_(common),
         machine_(machine) {}
   ~CommonOperatorReducer() final {}
 
   Reduction Reduce(Node* node) final;
 
  private:
+  Reduction ReduceBranch(Node* node);
+  Reduction ReduceMerge(Node* node);
   Reduction ReduceEffectPhi(Node* node);
   Reduction ReducePhi(Node* node);
   Reduction ReduceSelect(Node* node);
 
   Reduction Change(Node* node, Operator const* op, Node* a);
   Reduction Change(Node* node, Operator const* op, Node* a, Node* b);
 
   Graph* graph() const { return graph_; }
   CommonOperatorBuilder* common() const { return common_; }
   MachineOperatorBuilder* machine() const { return machine_; }
 
   Graph* const graph_;
   CommonOperatorBuilder* const common_;
   MachineOperatorBuilder* const machine_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_COMMON_OPERATOR_REDUCER_H_