[turbofan] Introduce a dedicated StringCharAt operator.

[turbofan] Introduce a dedicated StringCharAt operator.

Previously String element access and String.prototype.charAt were
lowered to a subgraph StringFromCharCode(StringCharCodeAt(s, k)),
however that can be fairly expensive both runtime and compile time
wise. The dedicated StringCharAt operator is implemented via a call
to a builtin that does exactly this.

R=yangguo@chromium.org

Review-Url: https://codereview.chromium.org/2599683002
Cr-Commit-Position: refs/heads/master@{#41909}
Committed: https://chromium.googlesource.com/v8/v8/+/05f5ebce2f34753d0fb32fd2f3b6e652c8682e09

[Benedikt Meurer, 2016-12-22 06:04:40]

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

[commit-bot: I haz the power, 2016-12-22 06:04:46]

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

[Yang, 2016-12-22 06:06:49]

On 2016/12/22 06:04:39, Benedikt Meurer wrote:

lgtm.

[Benedikt Meurer, 2016-12-22 06:07:02]

The CQ bit was unchecked by bmeurer@chromium.org

[Benedikt Meurer, 2016-12-22 06:07:06]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2016-12-22 06:07:16]

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, 2016-12-22 06:49:08]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1482386826385320, "parent_rev":
"7430881471f1a75c25e1d5eeb67f211a9a377bf9", "commit_rev":
"05f5ebce2f34753d0fb32fd2f3b6e652c8682e09"}

[commit-bot: I haz the power, 2016-12-22 06:49:12]

Description was changed from

==========
[turbofan] Introduce a dedicated StringCharAt operator.

Previously String element access and String.prototype.charAt were
lowered to a subgraph StringFromCharCode(StringCharCodeAt(s, k)),
however that can be fairly expensive both runtime and compile time
wise. The dedicated StringCharAt operator is implemented via a call
to a builtin that does exactly this.

R=yangguo@chromium.org
==========

to

==========
[turbofan] Introduce a dedicated StringCharAt operator.

Previously String element access and String.prototype.charAt were
lowered to a subgraph StringFromCharCode(StringCharCodeAt(s, k)),
however that can be fairly expensive both runtime and compile time
wise. The dedicated StringCharAt operator is implemented via a call
to a builtin that does exactly this.

R=yangguo@chromium.org

Review-Url: https://codereview.chromium.org/2599683002
Cr-Commit-Position: refs/heads/master@{#41909}
Committed:
https://chromium.googlesource.com/v8/v8/+/05f5ebce2f34753d0fb32fd2f3b6e652c86...
==========

[commit-bot: I haz the power, 2016-12-22 06:49:13]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/v8/v8/+/05f5ebce2f34753d0fb32fd2f3b6e652c86...