Convert diamond shaped control flow into a single conditional instruction.

runtime/vm/flow_graph.h

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_FLOW_GRAPH_H_
 #define VM_FLOW_GRAPH_H_
 
 #include "vm/growable_array.h"
 #include "vm/intermediate_language.h"
 #include "vm/parser.h"
@@ skipping 124 matching lines @@
   void Bailout(const char* reason) const;
 
   void InvalidateDominatorTree() { invalid_dominator_tree_ = true; }
 
 #ifdef DEBUG
   // Verification methods for debugging.
   bool VerifyUseLists();
 #endif  // DEBUG
 
  private:
+  friend class IfConverter;
   friend class BranchSimplifier;
   friend class ConstantPropagator;
 
   void DiscoverBlocks();
 
   // SSA transformation methods and fields.
   void ComputeDominators(GrowableArray<BitVector*>* dominance_frontier);
 
   void CompressPath(
       intptr_t start_index,
@@ skipping 35 matching lines @@
   GrowableArray<BlockEntryInstr*> preorder_;
   GrowableArray<BlockEntryInstr*> postorder_;
   GrowableArray<BlockEntryInstr*> reverse_postorder_;
   bool invalid_dominator_tree_;
   ConstantInstr* constant_null_;
 };
 
 }  // namespace dart
 
 #endif  // VM_FLOW_GRAPH_H_