Await always waits

runtime/vm/flow_graph_builder.cc

 // 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.
 
 #include "vm/flow_graph_builder.h"
 
 #include "lib/invocation_mirror.h"
 #include "vm/ast_printer.h"
 #include "vm/bit_vector.h"
 #include "vm/class_finalizer.h"
@@ skipping 1075 matching lines @@
 
   intptr_t current_context_level = owner()->context_level();
   ASSERT(current_context_level >= 0);
   if (owner()->parsed_function()->saved_entry_context_var() != NULL) {
     // CTX on entry was saved, but not linked as context parent.
     BuildRestoreContext(*owner()->parsed_function()->saved_entry_context_var());
   } else {
     UnchainContexts(current_context_level);
   }
 
-
-  AddReturnExit(node->token_pos(), return_value);
+  if (function.is_async_closure() &&
+      (node->return_type() == ReturnNode::kContinuation)) {
+    // This return instruction may be followed by instructions
+    // that get called when the async closure is resumed, so
+    // do not add an exit and close the fragment.
+    ReturnInstr* return_instr =
+        new(I) ReturnInstr(node->token_pos(), return_value);
+    AddInstruction(return_instr);
+  } else {
+    AddReturnExit(node->token_pos(), return_value);
+  }

[Florian Schneider, 2014/10/06 17:32:54]

I'd imagine this looking like this:

AddReturnExit(node->token_pos(), return_value);

if (function.is_async_closure() &&
    (node->return_type() == ReturnNode::kContinuation)) {
  JoinEntryInstr* join = new(I) JoinEntryInstr(
      owner()->AllocateBlockId(), owner()->try_index());
  owner()->AddAwaitJoin(join);
  exit_ = join;
}

where AddAwaitJoin is like AddCatchEntry and the await-joins blocks are added to
the successors of GraphEntryInstr like catch-blocks.

 }
 
 
 // <Expression> ::= Literal { literal: Instance }
 void EffectGraphVisitor::VisitLiteralNode(LiteralNode* node) {
   ReturnDefinition(new(I) ConstantInstr(node->literal()));
 }
 
 
 // Type nodes are used when a type is referenced as a literal. Type nodes
@@ skipping 1124 matching lines @@
     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());
     return;
   }
   if (node->marker_type() == AwaitMarkerNode::kTargetForContinuation) {

[Florian Schneider, 2014/10/06 17:32:55]

This always follows immediatly after a continuation-return, so we do all of this
as part of ReturnInstr if the type if ReturnType::kContinuation.

Then, there is no need for this type of AwaitMarkerNode anymore.

     // 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);

[Florian Schneider, 2014/10/06 17:32:55]

These targets should be added to the successors of the graph entry block (see
how we handle CatchBlockEntryInstr).

     Goto(join);

[Florian Schneider, 2014/10/06 17:32:54]

Remove this Goto. It is dead code and should not be needed.

     exit_ = join;
     return;
   }
   UNREACHABLE();
 }
 
 
 intptr_t EffectGraphVisitor::GetCurrentTempLocalIndex() const {
   return kFirstLocalSlotFromFp
       - owner()->num_stack_locals()
@@ skipping 2025 matching lines @@
   Report::MessageF(Report::kBailout,
                    Script::Handle(function.script()),
                    function.token_pos(),
                    "FlowGraphBuilder Bailout: %s %s",
                    String::Handle(function.name()).ToCString(),
                    reason);
   UNREACHABLE();
 }
 
 }  // namespace dart