[wasm] Improve pimpl implementation in WasmInterpreter::Thread

[wasm] Improve pimpl implementation in WasmInterpreter::Thread

As no one will ever try to allocate a Thread directly, we can just make
Thread a proxy of ThreadImpl by reinterpret_casting between both types.
This allows to not mention ThreadImpl in the header at all, and to
define it in an anonymous namespace in the implementation, allowing for
more optimizations.
It also saves runtime, as no memory load is needed to forward from
Thread to ThreadImpl, and we do not need to allocate ThreadImpl objects
on the heap.

R=titzer@chromium.org

Review-Url: https://codereview.chromium.org/2643443002
Cr-Commit-Position: refs/heads/master@{#42450}
Committed: https://chromium.googlesource.com/v8/v8/+/4f91cee32153211b4bf60856cf8068d00ece2b6e

[Clemens Hammacher, 2017-01-17 20:00:46]

The CQ bit was checked by clemensh@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-01-17 20:00:49]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-01-17 20:06:51]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-01-17 20:06:52]

Dry run: Try jobs failed on following builders:
  v8_android_arm_compile_rel on master.tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_android_arm_compile_rel/...)

[Clemens Hammacher, 2017-01-18 09:44:09]

The CQ bit was checked by clemensh@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-01-18 09:44:16]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-01-18 10:10:05]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-01-18 10:10:06]

Dry run: This issue passed the CQ dry run.

[titzer, 2017-01-18 10:19:50]

LGTM.

Can you leave a comment somewhere that this might be risky behavior?

[Clemens Hammacher, 2017-01-18 10:49:57]

On 2017/01/18 at 10:19:50, titzer wrote:
> LGTM.
> 
> Can you leave a comment somewhere that this might be risky behavior?

Done.

[Clemens Hammacher, 2017-01-18 10:50:07]

The CQ bit was checked by clemensh@chromium.org

[Clemens Hammacher, 2017-01-18 10:50:07]

The patchset sent to the CQ was uploaded after l-g-t-m from titzer@chromium.org
Link to the patchset: https://codereview.chromium.org/2643443002/#ps40001
(title: "Add comment about risky reinterpret_cast")

[commit-bot: I haz the power, 2017-01-18 10:50:14]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[Clemens Hammacher, 2017-01-18 10:51:10]

The CQ bit was unchecked by clemensh@chromium.org

[Clemens Hammacher, 2017-01-18 11:38:45]

The CQ bit was checked by clemensh@chromium.org

[commit-bot: I haz the power, 2017-01-18 11:38:53]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-01-18 11:40:30]

CQ is committing da patch.

Bot data: {"patchset_id": 40001, "attempt_start_ts": 1484739525224930,
"parent_rev": "977038516bbdd0427eacf8be4496e63b451f3ffe", "commit_rev":
"4f91cee32153211b4bf60856cf8068d00ece2b6e"}

[commit-bot: I haz the power, 2017-01-18 11:40:33]

Description was changed from

==========
[wasm] Improve pimpl implementation in WasmInterpreter::Thread

As no one will ever try to allocate a Thread directly, we can just make
Thread a proxy of ThreadImpl by reinterpret_casting between both types.
This allows to not mention ThreadImpl in the header at all, and to
define it in an anonymous namespace in the implementation, allowing for
more optimizations.
It also saves runtime, as no memory load is needed to forward from
Thread to ThreadImpl, and we do not need to allocate ThreadImpl objects
on the heap.

R=titzer@chromium.org
==========

to

==========
[wasm] Improve pimpl implementation in WasmInterpreter::Thread

As no one will ever try to allocate a Thread directly, we can just make
Thread a proxy of ThreadImpl by reinterpret_casting between both types.
This allows to not mention ThreadImpl in the header at all, and to
define it in an anonymous namespace in the implementation, allowing for
more optimizations.
It also saves runtime, as no memory load is needed to forward from
Thread to ThreadImpl, and we do not need to allocate ThreadImpl objects
on the heap.

R=titzer@chromium.org

Review-Url: https://codereview.chromium.org/2643443002
Cr-Commit-Position: refs/heads/master@{#42450}
Committed:
https://chromium.googlesource.com/v8/v8/+/4f91cee32153211b4bf60856cf8068d00ec...
==========

[commit-bot: I haz the power, 2017-01-18 11:40:34]

Committed patchset #3 (id:40001) as
https://chromium.googlesource.com/v8/v8/+/4f91cee32153211b4bf60856cf8068d00ec...