[turbofan] Introduce explicit loop exits markers.

src/compiler/dead-code-elimination.h

 // Copyright 2015 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_DEAD_CODE_ELIMINATION_H_
 #define V8_COMPILER_DEAD_CODE_ELIMINATION_H_
 
 #include "src/compiler/graph-reducer.h"
 
 namespace v8 {
@@ skipping 12 matching lines @@
  public:
   DeadCodeElimination(Editor* editor, Graph* graph,
                       CommonOperatorBuilder* common);
   ~DeadCodeElimination() final {}
 
   Reduction Reduce(Node* node) final;
 
  private:
   Reduction ReduceEnd(Node* node);
   Reduction ReduceLoopOrMerge(Node* node);
+  Reduction ReduceLoopExit(Node* node);
   Reduction ReduceNode(Node* node);
 
+  Reduction RemoveLoopExit(Node* node);
+
   void TrimMergeOrPhi(Node* node, int size);
 
   Graph* graph() const { return graph_; }
   CommonOperatorBuilder* common() const { return common_; }
   Node* dead() const { return dead_; }
 
   Graph* const graph_;
   CommonOperatorBuilder* const common_;
   Node* const dead_;
 
   DISALLOW_COPY_AND_ASSIGN(DeadCodeElimination);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_DEAD_CODE_ELIMINATION_H_