Apply Kevin's suggestions, make branch-compare generation more robust

runtime/vm/flow_graph_builder.h

 // Copyright (c) 2012, 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_BUILDER_H_
 #define VM_FLOW_GRAPH_BUILDER_H_
 
 #include "vm/allocation.h"
 #include "vm/ast.h"
 #include "vm/growable_array.h"
@@ skipping 297 matching lines @@
 // The cis and token_pos are used in checked mode to verify that the
 // condition of the test is of type bool.
 class TestGraphVisitor : public ValueGraphVisitor {
  public:
   TestGraphVisitor(FlowGraphBuilder* owner,
                    intptr_t temp_index,
                    intptr_t condition_token_pos)
       : ValueGraphVisitor(owner, temp_index),
         true_successor_address_(NULL),
         false_successor_address_(NULL),
-        condition_token_pos_(condition_token_pos) {
-  }
+        condition_token_pos_(condition_token_pos) { }
 
   TargetEntryInstr** true_successor_address() const {
     ASSERT(true_successor_address_ != NULL);
     return true_successor_address_;
   }
   TargetEntryInstr** false_successor_address() const {
     ASSERT(false_successor_address_ != NULL);
     return false_successor_address_;
   }
 
   intptr_t condition_token_pos() const { return condition_token_pos_; }
 
  private:
   // Construct and concatenate a Branch instruction to this graph fragment.
   // Closes the fragment and sets the output parameters.
   virtual void ReturnValue(Value* value);
 
+  // Either merges the computation into BranchInstr (Comparison, BooleanNegate)
+  // or adds a Bind instruction to the graph and returns its temporary value.
+  virtual void ReturnComputation(Computation* computation);
+
+  void MergeBranchWithComparison(ComparisonComp* comp);
+  void MergeBranchWithNegate(BooleanNegateComp* comp);
+
   // Output parameters.
   TargetEntryInstr** true_successor_address_;
   TargetEntryInstr** false_successor_address_;
 
   intptr_t condition_token_pos_;
 };
 
 }  // namespace dart
 
 #endif  // VM_FLOW_GRAPH_BUILDER_H_