[turbofan] Optimize string "length" property access based on types.

[turbofan] Optimize string "length" property access based on types.

Optimize string "length" property access based on static type
information if possible, but also optimistically optimize the access
based on type feedback from the LoadIC.

R=jarin@chromium.org

Committed: https://crrev.com/17add22ff4b9c5ca638502e7708f0d9d99baca40
Cr-Commit-Position: refs/heads/master@{#29543}

Committed: https://crrev.com/b19f118c1675d3f4db8b3b63c9f6d98bbee7b32f
Cr-Commit-Position: refs/heads/master@{#29588}

[Benedikt Meurer, 2015-07-08 09:35:00]

Hey Michi,

This is the first step towards optimistic (cross-context) lowering in TurboFan.
I put this into the separate JSTypeFeedbackLowering as you suggested. I limited
it to string.length for the first version, but will extend that to array.length
and keyed loads soonish.
Please take a look.

Thanks,
Benedikt

[Jarin, 2015-07-08 16:42:55]

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

[Jarin, 2015-07-08 16:42:55]

lgtm from my side.

[Benedikt Meurer, 2015-07-08 19:09:57]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-07-08 19:10:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1216593003/20001

[commit-bot: I haz the power, 2015-07-08 19:12:48]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-07-08 19:13:06]

Patchset 2 (id:??) landed as
https://crrev.com/17add22ff4b9c5ca638502e7708f0d9d99baca40
Cr-Commit-Position: refs/heads/master@{#29543}

[adamk, 2015-07-08 21:29:29]

A revert of this CL (patchset #2 id:20001) has been created in
https://codereview.chromium.org/1224083002/ by adamk@chromium.org.

The reason for reverting is: Causes crash when running
benchmarks/octane/regexp.js on ARM:
http://build.chromium.org/p/client.v8/builders/V8%20Arm/builds/2492/steps/Ben....

[Benedikt Meurer, 2015-07-09 12:40:39]

The CQ bit was checked by bmeurer@chromium.org

[Benedikt Meurer, 2015-07-09 12:40:40]

The patchset sent to the CQ was uploaded after l-g-t-m from jarin@chromium.org
Link to the patchset: https://codereview.chromium.org/1216593003/#ps40001
(title: "REBASE")

[commit-bot: I haz the power, 2015-07-09 12:40:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1216593003/40001

[Benedikt Meurer, 2015-07-09 12:41:31]

Patch triggered an existing bug on ARM debug. That should be resolved by now, so
relanding.

[Benedikt Meurer, 2015-07-09 12:45:03]

The CQ bit was unchecked by bmeurer@chromium.org

[Benedikt Meurer, 2015-07-09 13:46:05]

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

[commit-bot: I haz the power, 2015-07-09 13:46:23]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1216593003/40001

[commit-bot: I haz the power, 2015-07-09 13:47:46]

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

[commit-bot: I haz the power, 2015-07-09 13:47:47]

Dry run: This issue passed the CQ dry run.

[Benedikt Meurer, 2015-07-13 05:32:16]

The CQ bit was checked by bmeurer@chromium.org

[Benedikt Meurer, 2015-07-13 05:32:17]

The patchset sent to the CQ was uploaded after l-g-t-m from jarin@chromium.org
Link to the patchset: https://codereview.chromium.org/1216593003/#ps60001
(title: "REBASE")

[commit-bot: I haz the power, 2015-07-13 05:32:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1216593003/60001

[commit-bot: I haz the power, 2015-07-13 06:02:21]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2015-07-13 06:02:31]

Patchset 4 (id:??) landed as
https://crrev.com/b19f118c1675d3f4db8b3b63c9f6d98bbee7b32f
Cr-Commit-Position: refs/heads/master@{#29588}