[turbofan] Eliminate empty string addition.

[turbofan] Eliminate empty string addition.

For additions like a+'' or ''+a where we have String feedback on the
JSAdd, we can drop the concatenation and just check that a is a valid
String already (via CheckString).

BUG=v8:6259
R=petermarshall@chromium.org

Review-Url: https://codereview.chromium.org/2894563002
Cr-Commit-Position: refs/heads/master@{#45395}
Committed: https://chromium.googlesource.com/v8/v8/+/cd1325a890b36ff715d95fcdd845cba43569ce29

[Benedikt Meurer, 2017-05-18 10:55:16]

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

[commit-bot: I haz the power, 2017-05-18 10:55:22]

Dry run: CQ is trying da patch.

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

[petermarshall, 2017-05-18 11:07:29]

LGTM! Thanks

[Benedikt Meurer, 2017-05-18 11:14:03]

The CQ bit was unchecked by bmeurer@chromium.org

[Benedikt Meurer, 2017-05-18 11:14:06]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2017-05-18 11:14:15]

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, 2017-05-18 11:31:51]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1495106046863600, "parent_rev":
"de4a4095cf22bc3c9cfa13eb5f8be28eb7a5f031", "commit_rev":
"cd1325a890b36ff715d95fcdd845cba43569ce29"}

[commit-bot: I haz the power, 2017-05-18 11:32:00]

Description was changed from

==========
[turbofan] Eliminate empty string addition.

For additions like a+'' or ''+a where we have String feedback on the
JSAdd, we can drop the concatenation and just check that a is a valid
String already (via CheckString).

BUG=v8:6259
R=petermarshall@chromium.org
==========

to

==========
[turbofan] Eliminate empty string addition.

For additions like a+'' or ''+a where we have String feedback on the
JSAdd, we can drop the concatenation and just check that a is a valid
String already (via CheckString).

BUG=v8:6259
R=petermarshall@chromium.org

Review-Url: https://codereview.chromium.org/2894563002
Cr-Commit-Position: refs/heads/master@{#45395}
Committed:
https://chromium.googlesource.com/v8/v8/+/cd1325a890b36ff715d95fcdd845cba4356...
==========

[commit-bot: I haz the power, 2017-05-18 11:32:01]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/v8/v8/+/cd1325a890b36ff715d95fcdd845cba4356...