Implement DoWhile.

runtime/vm/flow_graph_builder.h

Index: runtime/vm/flow_graph_builder.h
===================================================================
--- runtime/vm/flow_graph_builder.h	(revision 5046)
+++ runtime/vm/flow_graph_builder.h	(working copy)
@@ -209,11 +209,11 @@
     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_;
   }
@@ -231,8 +231,8 @@
   }
 
   // Output parameters.
-  TargetEntryInstr** true_successor_address_;
-  TargetEntryInstr** false_successor_address_;
+  BlockEntryInstr** true_successor_address_;
+  BlockEntryInstr** false_successor_address_;
 };
 
 }  // namespace dart