[turbofan] Use heavy-handed graph duplication to do loop peeling for OSR.

src/compiler/loop-analysis.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_LOOP_ANALYSIS_H_
 #define V8_COMPILER_LOOP_ANALYSIS_H_
 
 #include "src/base/iterator.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/node.h"
@@ skipping 71 matching lines @@
   int LoopNum(Loop* loop) const {
     return 1 + static_cast<int>(loop - &all_loops_[0]);
   }
 
   // Return a range which can iterate over the header nodes of {loop}.
   NodeRange HeaderNodes(Loop* loop) {
     return NodeRange(&loop_nodes_[0] + loop->header_start_,
                      &loop_nodes_[0] + loop->body_start_);
   }
 
+  // Return the header control node for a loop.
+  Node* HeaderNode(Loop* loop);
+
   // Return a range which can iterate over the body nodes of {loop}.
   NodeRange BodyNodes(Loop* loop) {
     return NodeRange(&loop_nodes_[0] + loop->body_start_,
                      &loop_nodes_[0] + loop->body_end_);
   }
 
   // Return a range which can iterate over the nodes of {loop}.
   NodeRange LoopNodes(Loop* loop) {
     return NodeRange(&loop_nodes_[0] + loop->header_start_,
                      &loop_nodes_[0] + loop->body_end_);
@@ skipping 41 matching lines @@
   // Build a loop tree for the entire graph.
   static LoopTree* BuildLoopTree(Graph* graph, Zone* temp_zone);
 };
 
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_LOOP_ANALYSIS_H_