[turbofan] Rework handling of loop exits in loop peeling.

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"
 #include "src/zone-containers.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
+// TODO(titzer): don't assume entry edges have a particular index.
+static const int kAssumedLoopEntryIndex = 0;  // assume loops are entered here.
+
 class LoopFinderImpl;
 
 typedef base::iterator_range<Node**> NodeRange;
 
 // Represents a tree of loops in a graph.
 class LoopTree : public ZoneObject {
  public:
   LoopTree(size_t num_nodes, Zone* zone)
       : zone_(zone),
         outer_loops_(zone),
@@ skipping 106 matching lines @@
     }
   }
 
   Zone* zone_;
   ZoneVector<Loop*> outer_loops_;
   ZoneVector<Loop> all_loops_;
   ZoneVector<int> node_to_loop_num_;
   ZoneVector<Node*> loop_nodes_;
 };
 
-
 class LoopFinder {
  public:
   // 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_