Await always waits

runtime/vm/ast.h

Index: runtime/vm/ast.h
===================================================================
--- runtime/vm/ast.h	(revision 41104)
+++ runtime/vm/ast.h	(working copy)
@@ -170,41 +170,26 @@
 
 
 // AwaitMarker nodes are used to generate markers that the FlowGraphBuilder
-// relies on. They can occur in two kinds:
-// 1) kNewContinuationState: A marker indicating that a new await state needs to
-//    be added to a function preamble. This type also triggers storing of the
-//    current context.
-// 2) kTargetForContinuation: A marker indicating an entry point for the most
-//    recent generated state.
+// relies on. A marker indicates that a new await state needs to be
+// added to a function preamble. This type also triggers storing of the
+// current context.
 //
-// In general it is expected (ASSERT) that the different kinds of markers reach
-// the FlowGraphBuilder in alternating order. That is:
-//   <new state> -> <other nodes> -> <target> -> <other nodes> ->
-//   <new state> -> ...
+// It is expected (ASSERT) that an AwaitMarker is followed by
+// a return node of kind kContinuationTarget. That is:
+//   <AwaitMarker> -> <other nodes> -> <kContinuationTarget> -> <other nodes> ->
+//   <AwaitMarker> -> ...
 class AwaitMarkerNode : public AstNode {
  public:
-  enum MarkerType {
-    kNewContinuationState,
-    kTargetForContinuation,
-  };
+  AwaitMarkerNode() : AstNode(Scanner::kNoSourcePos) { }
 
-  explicit AwaitMarkerNode(MarkerType marker_type)
-    : AstNode(Scanner::kNoSourcePos),
-      marker_type_(marker_type) { }
-
   void VisitChildren(AstNodeVisitor* visitor) const { }
 
-  MarkerType marker_type() const {
-    return marker_type_;
-  }
-
   LocalScope* scope() const { return scope_; }
   void set_scope(LocalScope* scope) { scope_ = scope; }
 
   DECLARE_COMMON_NODE_FUNCTIONS(AwaitMarkerNode);
 
  private:
-  MarkerType marker_type_;
   LocalScope* scope_;
 
   DISALLOW_COPY_AND_ASSIGN(AwaitMarkerNode);
@@ -579,16 +564,22 @@
   DISALLOW_IMPLICIT_CONSTRUCTORS(PrimaryNode);
 };
 
-// Return nodes can be of different types:
-// * A regular return node that in the case of async functions gets replaced
-//   with appropriate completer calls. This kind is generated by dart code.
-// * A continuation return that just returns from a function. This kind is
-//   generated by AST transformers.
+// In asynchronous code that gets suspeded and resumed, return nodes
+// can be of different types:
+// * A regular return node that in the case of async functions
+//    gets replaced with appropriate completer calls. (kRegular)
+// * A continuation return that just returns from a function, without
+//   completing the Future. (kContinuation)
+// * A continuation return followed by a continuation target, i.e. the
+//   location at which the closure resumes the next time it gets invoked.
+//   (kContinuationTarget).
+// In synchronous functions, return nodes are always of type'kRegular'
 class ReturnNode : public AstNode {
  public:
   enum ReturnType {
     kRegular,
     kContinuation,
+    kContinuationTarget
   };
 
   // Return from a void function returns the null object.