Await always waits

runtime/vm/flow_graph_builder.cc

Index: runtime/vm/flow_graph_builder.cc
===================================================================
--- runtime/vm/flow_graph_builder.cc	(revision 40935)
+++ runtime/vm/flow_graph_builder.cc	(working copy)
@@ -258,10 +258,7 @@
         temp_count_(0),
         args_pushed_(0),
         nesting_stack_(NULL),
-        osr_id_(osr_id),
-        jump_cnt_(0),
-        await_joins_(new(I) ZoneGrowableArray<JoinEntryInstr*>()),
-        await_levels_(new(I) ZoneGrowableArray<intptr_t>()) { }
+        osr_id_(osr_id) { }
 
 
 void FlowGraphBuilder::AddCatchEntry(CatchBlockEntryInstr* entry) {
@@ -1095,6 +1092,14 @@
 
 
   AddReturnExit(node->token_pos(), return_value);
+
+  if (function.is_async_closure() &&
+      (node->return_type() == ReturnNode::kContinuationTarget)) {
+    JoinEntryInstr* const join = new(I) JoinEntryInstr(
+        owner()->AllocateBlockId(), owner()->try_index());
+    owner()->await_joins().Add(join);
+    exit_ = join;
+  }
 }
 
 
@@ -2229,26 +2234,18 @@
     ASSERT(jump_cnt >= 0);
     // Sanity check that we always add a JoinEntryInstr before adding a new
     // state.
-    ASSERT(jump_cnt == owner()->await_joins()->length());
+    ASSERT(jump_cnt == owner()->await_joins().length());
     // Store the counter in :await_jump_var.
     Value* jump_val = Bind(new (I) ConstantInstr(
         Smi::ZoneHandle(I, Smi::New(jump_cnt))));
     Do(BuildStoreLocal(*jump_var, jump_val));
     // Save the current context for resuming.
     BuildSaveContext(*ctx_var);
-    owner()->await_levels()->Add(owner()->context_level());
+    owner()->await_levels().Add(owner()->context_level());
     return;
   }
   if (node->marker_type() == AwaitMarkerNode::kTargetForContinuation) {
-    // We need to create a new await target which involves:
-    // * Append a join that is also added to the list that will later result in
-    //   a preamble.
-    JoinEntryInstr* const join = new(I) JoinEntryInstr(
-        owner()->AllocateBlockId(), owner()->try_index());
-    owner()->await_joins()->Add(join);
-    Goto(join);
-    exit_ = join;
-    return;
+    UNREACHABLE();  //XXX
   }
   UNREACHABLE();
 }
@@ -3881,7 +3878,7 @@
     LoadLocalNode* load_jump_cnt = new(I) LoadLocalNode(
         Scanner::kNoSourcePos, jump_var);
     ComparisonNode* check_jump_cnt;
-    const intptr_t num_await_states = owner()->await_joins()->length();
+    const intptr_t num_await_states = owner()->await_joins().length();
     for (intptr_t i = 0; i < num_await_states; i++) {
       check_jump_cnt = new(I) ComparisonNode(
           Scanner::kNoSourcePos,
@@ -3895,8 +3892,8 @@
       EffectGraphVisitor for_false(owner());
 
       for_true.BuildAwaitJump(top_scope,
-                              (*owner()->await_levels())[i],
-                              (*owner()->await_joins())[i]);
+                              owner()->await_levels()[i],
+                              owner()->await_joins()[i]);
       Join(for_test, for_true, for_false);
 
       if (i == 0) {