Desugar async/await to create the resulting Promise upfront

src/accessors.cc

 // Copyright 2012 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/accessors.h"
 
 #include "src/api.h"
 #include "src/contexts.h"
 #include "src/deoptimizer.h"
 #include "src/execution.h"
@@ skipping 719 matching lines @@
 
 
 void Accessors::FunctionLengthGetter(
     v8::Local<v8::Name> name,
     const v8::PropertyCallbackInfo<v8::Value>& info) {
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(info.GetIsolate());
   HandleScope scope(isolate);
   Handle<JSFunction> function =
       Handle<JSFunction>::cast(Utils::OpenHandle(*info.Holder()));
   Handle<Object> result;
-  if (!JSFunction::GetLength(isolate, function).ToHandle(&result)) {
+  // This may invoke the compiler, so check for stack overflow like other
+  // compiler entrypoints, and return 0 on failure (as on an exception).
+  StackLimitCheck check(isolate);
+  if (check.JsHasOverflowed(1 * KB)) {
+    result = handle(Smi::FromInt(0), isolate);

[caitp, 2016/08/12 01:57:10]

thinking about this, we only want to return 0 if compiling is actually needed,
right? Are we not able to move this to JSFunction::GetLength()?

[Dan Ehrenberg, 2016/08/12 02:20:47]

I backed out this change in the most recent version. Now, it'll throw an
exception and go down the exception path because of the stack overflow from
within fullcodegen.

+  } else if (!JSFunction::GetLength(isolate, function).ToHandle(&result)) {
     result = handle(Smi::FromInt(0), isolate);
     isolate->OptionalRescheduleException(false);
   }
 
   info.GetReturnValue().Set(Utils::ToLocal(result));
 }
 
 Handle<AccessorInfo> Accessors::FunctionLengthInfo(
       Isolate* isolate, PropertyAttributes attributes) {
   return MakeAccessor(isolate, isolate->factory()->length_string(),
@@ skipping 476 matching lines @@
 Handle<AccessorInfo> Accessors::ErrorStackInfo(Isolate* isolate,
                                                PropertyAttributes attributes) {
   Handle<AccessorInfo> info =
       MakeAccessor(isolate, isolate->factory()->stack_string(),
                    &ErrorStackGetter, &ErrorStackSetter, attributes);
   return info;
 }
 
 }  // namespace internal
 }  // namespace v8