Implement control reducer, which reduces branches and phis together in a single fixpoint.

src/compiler/control-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_CONTROL_REDUCER_H_
 #define V8_COMPILER_CONTROL_REDUCER_H_
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 class JSGraph;
 class CommonOperatorBuilder;
+class Node;
 
 class ControlReducer {
  public:
   // Perform branch folding and dead code elimination on the graph.
   static void ReduceGraph(Zone* zone, JSGraph* graph,
                           CommonOperatorBuilder* builder);
 
   // Trim nodes in the graph that are not reachable from end.
   static void TrimGraph(Zone* zone, JSGraph* graph);
+
+  // Testing interface.
+  static Node* ReducePhiForTesting(JSGraph* graph,
+                                   CommonOperatorBuilder* builder, Node* node);
+  static Node* ReduceBranchForTesting(JSGraph* graph,
+                                      CommonOperatorBuilder* builder,
+                                      Node* node);
+  static Node* ReduceMergeForTesting(JSGraph* graph,
+                                     CommonOperatorBuilder* builder,
+                                     Node* node);
 };
 }
 }
 }  // namespace v8::internal::compiler
 
 #endif  // V8_COMPILER_CONTROL_REDUCER_H_