WIP [esnext] implement async iteration proposal

src/builtins/builtins-async.cc

Index: src/builtins/builtins-async.cc
diff --git a/src/builtins/builtins-async.cc b/src/builtins/builtins-async.cc
new file mode 100644
index 0000000000000000000000000000000000000000..520fc795de6a3ae85e0a22c3e15ffc02e3e7ece2
--- /dev/null
+++ b/src/builtins/builtins-async.cc
@@ -0,0 +1,91 @@
+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/builtins/builtins-async.h"
+#include "src/builtins/builtins-utils.h"
+#include "src/builtins/builtins.h"
+#include "src/code-factory.h"
+#include "src/code-stub-assembler.h"
+#include "src/frames-inl.h"
+
+namespace v8 {
+namespace internal {
+
+Node* AsyncBuiltinsAssembler::Await(
+    Node* context, Node* generator, Node* value, Node* outer_promise,
+    const NodeGenerator1& create_closure_context, int on_resolve_context_index,
+    int on_reject_context_index, bool is_catchable) {
+  // Let promiseCapability be ! NewPromiseCapability(%Promise%).
+  Node* const wrapped_value = AllocateAndInitJSPromise(context);
+
+  // Perform ! Call(promiseCapability.[[Resolve]], undefined, « promise »).
+  InternalResolvePromise(context, wrapped_value, value);
+
+  Node* const native_context = LoadNativeContext(context);
+
+  Node* const closure_context = create_closure_context(native_context);
+  Node* const map = LoadContextElement(
+      native_context, Context::STRICT_FUNCTION_WITHOUT_PROTOTYPE_MAP_INDEX);
+
+  Node* const on_reject_shared_fun =
+      LoadContextElement(native_context, on_reject_context_index);
+  CSA_SLOW_ASSERT(
+      this, HasInstanceType(on_reject_shared_fun, SHARED_FUNCTION_INFO_TYPE));
+  Node* const on_reject = AllocateFunctionWithMapAndContext(
+      map, on_reject_shared_fun, closure_context);
+
+  Node* const on_resolve_shared_fun =
+      LoadContextElement(native_context, on_resolve_context_index);
+  CSA_SLOW_ASSERT(
+      this, HasInstanceType(on_resolve_shared_fun, SHARED_FUNCTION_INFO_TYPE));
+  Node* const on_resolve = AllocateFunctionWithMapAndContext(
+      map, on_resolve_shared_fun, closure_context);
+
+  Node* const throwaway_promise =
+      AllocateAndInitJSPromise(context, wrapped_value);
+
+  // The Promise will be thrown away and not handled, but it shouldn't trigger
+  // unhandled reject events as its work is done
+  PromiseSetHasHandler(throwaway_promise);
+
+  Label do_perform_promise_then(this);
+  GotoUnless(IsDebugActive(), &do_perform_promise_then);
+  {
+    Label common(this);
+    GotoUnless(HasInstanceType(value, JS_PROMISE_TYPE), &common);
+    {
+      // Mark the reject handler callback to be a forwarding edge, rather
+      // than a meaningful catch handler
+      Node* const key =
+          HeapConstant(factory()->promise_forwarding_handler_symbol());
+      CallRuntime(Runtime::kSetProperty, on_reject, key, TrueConstant(),
+                  SmiConstant(STRICT));
+
+      if (!is_catchable) {
+        PromiseSetHasHandler(value);
+      }
+    }
+
+    Goto(&common);
+    Bind(&common);
+    // Mark the dependency to outer Promise in case the throwaway Promise is
+    // found on the Promise stack
+    CSA_SLOW_ASSERT(this, HasInstanceType(outer_promise, JS_PROMISE_TYPE));
+
+    Node* const key = HeapConstant(factory()->promise_handled_by_symbol());
+    CallRuntime(Runtime::kSetProperty, throwaway_promise, key, outer_promise,
+                SmiConstant(STRICT));
+  }
+
+  Goto(&do_perform_promise_then);
+  Bind(&do_perform_promise_then);
+  InternalPerformPromiseThen(context, wrapped_value, on_resolve, on_reject,
+                             throwaway_promise, UndefinedConstant(),
+                             UndefinedConstant());
+
+  return wrapped_value;
+}
+
+}  // namespace internal
+}  // namespace v8