Reland "[turbofan] Fix select lowering" with fix.

src/compiler/select-lowering.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_SELECT_LOWERING_H_
 #define V8_COMPILER_SELECT_LOWERING_H_
 
 #include <map>
 
 #include "src/compiler/graph-reducer.h"
@@ skipping 10 matching lines @@
 
 // Lowers Select nodes to diamonds.
 class SelectLowering FINAL : public Reducer {
  public:
   SelectLowering(Graph* graph, CommonOperatorBuilder* common);
   ~SelectLowering();
 
   Reduction Reduce(Node* node) OVERRIDE;
 
  private:
-  typedef std::map<Node*, Node*, std::less<Node*>,
-                   zone_allocator<std::pair<Node* const, Node*>>> Merges;
+  typedef std::multimap<Node*, Node*, std::less<Node*>,
+                        zone_allocator<std::pair<Node* const, Node*>>> Merges;
+
+  bool ReachableFrom(Node* const sink, Node* const source);
 
   CommonOperatorBuilder* common() const { return common_; }
   Graph* graph() const { return graph_; }
 
   CommonOperatorBuilder* common_;
   Graph* graph_;
   Merges merges_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_SELECT_LOWERING_H_