[runtime] Use "the hole" instead of smi 0 as sentinel for context extension.

[runtime] Use "the hole" instead of smi 0 as sentinel for context extension.

This way we avoid the %_IsSmi magic that is required in TurboFan to
(efficiently) check abitrary context slots for smi 0. Checking against
"the hole" is common in the AstGraphBuilder and "the hole" is also used
to mark other context slots as not initialized.

R=mstarzinger@chromium.org

Committed: https://crrev.com/9e6448813d41858c3f879ecde41b13bda0770673
Cr-Commit-Position: refs/heads/master@{#32407}

[Benedikt Meurer, 2015-11-30 12:47:50]

Hey Michi,

Here's the cleanup for the extension slot.
Please take a look.

Thanks,
Benedikt

[Michael Starzinger, 2015-11-30 13:02:48]

LGTM.

https://codereview.chromium.org/1484723003/diff/1/src/runtime/runtime-scopes.cc
File src/runtime/runtime-scopes.cc (right):

https://codereview.chromium.org/1484723003/diff/1/src/runtime/runtime-scopes....
src/runtime/runtime-scopes.cc:309:
context->set_extension(HeapObject::cast(*object));
nit: Explicit cast should not be necessary, as it is an up-cast.

[Benedikt Meurer, 2015-11-30 13:04:20]

https://codereview.chromium.org/1484723003/diff/1/src/runtime/runtime-scopes.cc
File src/runtime/runtime-scopes.cc (right):

https://codereview.chromium.org/1484723003/diff/1/src/runtime/runtime-scopes....
src/runtime/runtime-scopes.cc:309:
context->set_extension(HeapObject::cast(*object));
On 2015/11/30 13:02:48, Michael Starzinger wrote:
> nit: Explicit cast should not be necessary, as it is an up-cast.

Done.

[Benedikt Meurer, 2015-11-30 13:04:24]

The CQ bit was checked by bmeurer@chromium.org

[Benedikt Meurer, 2015-11-30 13:04:24]

The patchset sent to the CQ was uploaded after l-g-t-m from
mstarzinger@chromium.org
Link to the patchset: https://codereview.chromium.org/1484723003/#ps20001
(title: "Address comment.")

[commit-bot: I haz the power, 2015-11-30 13:04:36]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1484723003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1484723003/20001

[commit-bot: I haz the power, 2015-11-30 13:23:08]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-11-30 13:23:35]

Description was changed from

==========
[runtime] Use "the hole" instead of smi 0 as sentinel for context extension.

This way we avoid the %_IsSmi magic that is required in TurboFan to
(efficiently) check abitrary context slots for smi 0. Checking against
"the hole" is common in the AstGraphBuilder and "the hole" is also used
to mark other context slots as not initialized.

R=mstarzinger@chromium.org
==========

to

==========
[runtime] Use "the hole" instead of smi 0 as sentinel for context extension.

This way we avoid the %_IsSmi magic that is required in TurboFan to
(efficiently) check abitrary context slots for smi 0. Checking against
"the hole" is common in the AstGraphBuilder and "the hole" is also used
to mark other context slots as not initialized.

R=mstarzinger@chromium.org

Committed: https://crrev.com/9e6448813d41858c3f879ecde41b13bda0770673
Cr-Commit-Position: refs/heads/master@{#32407}
==========

[commit-bot: I haz the power, 2015-11-30 13:23:36]

Patchset 2 (id:??) landed as
https://crrev.com/9e6448813d41858c3f879ecde41b13bda0770673
Cr-Commit-Position: refs/heads/master@{#32407}