Implement DoWhile.

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 191 matching lines @@
            (false_successor_address_ == NULL));
     return true_successor_address_ != NULL;
   }
   bool can_be_false() const {
     // Either both successors are set or neither is set.
     ASSERT((true_successor_address_ == NULL) ==
            (false_successor_address_ == NULL));
     return false_successor_address_ != NULL;
   }
 
-  TargetEntryInstr** true_successor_address() const {
+  BlockEntryInstr** true_successor_address() const {

[Kevin Millikin (Google), 2012/03/07 09:15:44]

The reason this was TargetEntry is to statically enforce that the graph contains
no critical edges.  That's a useful property to have (for dataflow analysis and
for translation out of SSA).

Of course, that means that you have to eagerly split the back edge for the
do/while loop; but then you eliminate the need a pass to convert and code to do
runtime verification in debug builds.

OK to keep it like this for do/while, and add it to the list of issues to
settle.

     ASSERT(can_be_true());
     return true_successor_address_;
   }
-  TargetEntryInstr** false_successor_address() const {
+  BlockEntryInstr** false_successor_address() const {
     ASSERT(can_be_false());
     return false_successor_address_;
   }
 
  private:
   // Construct and concatenate a Branch instruction to this graph fragment.
   // Closes the fragment and sets the output parameters.
   void ReturnValue(Value* value);
 
   // Specify a computation as the final result.  Adds a Bind instruction to
   // the graph and branches on its value.
   virtual void ReturnComputation(Computation* computation) {
     AddInstruction(new BindInstr(temp_index(), computation));
     ReturnValue(new TempVal(temp_index()));
   }
 
   // Output parameters.
-  TargetEntryInstr** true_successor_address_;
-  TargetEntryInstr** false_successor_address_;
+  BlockEntryInstr** true_successor_address_;
+  BlockEntryInstr** false_successor_address_;
 };
 
 }  // namespace dart
 
 #endif  // VM_FLOW_GRAPH_BUILDER_H_