[turbofan] Use reference equal to zero instead of a smi check.

[turbofan] Use reference equal to zero instead of a smi check.

In typed lowering we can use the ReferenceEqual simplified operator
instead of ObjectIsSmi to check for context extensions. This generates
the desired code.

R=mstarzinger@chromium.org

Committed: https://crrev.com/e0fa8758584e9aaedebe22fd1ee3c82b3867c14a
Cr-Commit-Position: refs/heads/master@{#28776}

[Benedikt Meurer, 2015-06-03 03:46:08]

Hey Michi,

The ObjectIsSmi hack was actually only necessary if we do it before typed
lowering. In typed lowering, ReferenceEqual will do the right thing. Please take
a look.

Thanks,
Benedikt

[Jakob Kummerow, 2015-06-03 05:08:44]

jkummerow@chromium.org changed reviewers:
+ jkummerow@chromium.org

[Jakob Kummerow, 2015-06-03 05:08:45]

lgtm

[Benedikt Meurer, 2015-06-03 05:09:14]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-06-03 05:09:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1163963003/1

[commit-bot: I haz the power, 2015-06-03 05:10:51]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-03 05:11:04]

Patchset 1 (id:??) landed as
https://crrev.com/e0fa8758584e9aaedebe22fd1ee3c82b3867c14a
Cr-Commit-Position: refs/heads/master@{#28776}