[async-iteration] implement AsyncGenerator

- Introduce new struct AsyncGeneratorRequest, which holds
  information pertinent to resuming execution of an
  AsyncGenerator, such as the Promise associated with the async
  generator request. It is intended to be used as a singly
  linked list, and holds a pointer to the next item in te queue.

- Introduce JSAsyncGeneratorObject (subclass of
  JSGeneratorObject), which includes several new internal fields
  (`queue` which contains a singly linked list of
  AsyncGeneratorRequest objects, and `await_input` which
  contains the sent value from an Await expression (This is
  necessary to prevent function.sent (used by yield*) from
  having the sent value observably overwritten during
  execution).

- Modify SuspendGenerator to accept a set of Flags, which
  indicate whether the suspend is for a Yield or Await, and
  whether it takes place on an async generator or ES6
  generator.

- Introduce interpreter intrinsics and TF intrinsic lowering for
  accessing the await input of an async generator

- Modify the JSGeneratorStore operator to understand whether or
  not it's suspending for a normal yield, or an AsyncGenerator
  Await. This ensures appropriate registers are stored.

- Add versions of ResumeGeneratorTrampoline which store the
  input value in a different field depending on wether it's an
  AsyncGenerator Await resume, or an ordinary resume. Also modifies
  whether debug code will assert that the generator object is a
  JSGeneratorObject or a JSAsyncGeneratorObject depending on the
  resume type.

BUG=v8:5855
R=bmeurer@chromium.org, rmcilroy@chromium.org, jgruber@chromium.org,
littledan@chromium.org, neis@chromium.org
TBR=marja@chromium.org

Change-Id: I9d58df1d344465fc937fe7eed322424204497187
Reviewed-on: https://chromium-review.googlesource.com/446961
Commit-Queue: Caitlin Potter <caitp@igalia.com>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44240}
78 files changed
tree: d676516e76f8afbf7dbac31cc0670ff436523c9a
  1. benchmarks/
  2. build_overrides/
  3. docs/
  4. gni/
  5. gypfiles/
  6. include/
  7. infra/
  8. samples/
  9. src/
  10. test/
  11. testing/
  12. third_party/
  13. tools/
  14. .clang-format
  15. .gitignore
  16. .gn
  17. .ycm_extra_conf.py
  18. AUTHORS
  19. BUILD.gn
  20. ChangeLog
  21. CODE_OF_CONDUCT.md
  22. codereview.settings
  23. DEPS
  24. LICENSE
  25. LICENSE.fdlibm
  26. LICENSE.strongtalk
  27. LICENSE.v8
  28. LICENSE.valgrind
  29. Makefile
  30. Makefile.android
  31. OWNERS
  32. PRESUBMIT.py
  33. README.md
  34. snapshot_toolchain.gni
  35. WATCHLISTS
README.md

V8 JavaScript Engine

V8 is Google's open source JavaScript engine.

V8 implements ECMAScript as specified in ECMA-262.

V8 is written in C++ and is used in Google Chrome, the open source browser from Google.

V8 can run standalone, or can be embedded into any C++ application.

V8 Project page: https://github.com/v8/v8/wiki

Getting the Code

Checkout depot tools, and run

    fetch v8

This will checkout V8 into the directory v8 and fetch all of its dependencies. To stay up to date, run

    git pull origin
    gclient sync

For fetching all branches, add the following into your remote configuration in .git/config:

    fetch = +refs/branch-heads/*:refs/remotes/branch-heads/*
    fetch = +refs/tags/*:refs/tags/*

Contributing

Please follow the instructions mentioned on the V8 wiki.