[string] Optimize ToDirectStringAssembler for sequential strings

[string] Optimize ToDirectStringAssembler for sequential strings

ToDirectStringAssembler is used in StringCharCodeAt and SubString
(which uses StringCharCodeAt internally). SubString is used all over the
place (e.g. RegExp result construction), and is critical for benchmark
performance.

The CL introducing ToDirectStringAssembler caused a couple of
regressions which this is intended to fix by adding a fast path for
sequential strings.

BUG=chromium:702246
Review-Url: https://codereview.chromium.org/2754933003
Cr-Commit-Position: refs/heads/master@{#43897}
Committed: https://chromium.googlesource.com/v8/v8/+/338257509d7f5ec8ea0a16ba3eb263265efa06f9

[jgruber, 2017-03-17 09:15:42]

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

[commit-bot: I haz the power, 2017-03-17 09:15:52]

Dry run: 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, 2017-03-17 09:37:41]

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

[commit-bot: I haz the power, 2017-03-17 09:37:42]

Dry run: This issue passed the CQ dry run.

[jgruber, 2017-03-17 09:45:09]

jgruber@chromium.org changed reviewers:
+ ishell@chromium.org

[jgruber, 2017-03-17 09:45:10]

Benched locally and this combination of deferred and a fast jump for sequential
strings improves performance on RegExp microbenchmarks and JetStream (probably
due to better block scheduling).

[jgruber, 2017-03-17 10:18:17]

Description was changed from

==========
[string] Performance improvements for ToDirectStringAssembler

ToDirectStringAssembler is used in StringCharCodeAt and SubString
(which uses StringCharCodeAt internally). SubString is used all over the
place (e.g. RegExp result construction), and is critical for benchmark
performance.

The CL introducing ToDirectStringAssembler caused a couple of
regressions which this is intended to fix by adding a fast path for
sequential strings.

BUG=chromium:702246
==========

to

==========
[string] Optimize ToDirectStringAssembler for sequential strings

ToDirectStringAssembler is used in StringCharCodeAt and SubString
(which uses StringCharCodeAt internally). SubString is used all over the
place (e.g. RegExp result construction), and is critical for benchmark
performance.

The CL introducing ToDirectStringAssembler caused a couple of
regressions which this is intended to fix by adding a fast path for
sequential strings.

BUG=chromium:702246
==========

[jgruber, 2017-03-17 12:02:01]

jgruber@chromium.org changed reviewers:
+ cbruni@chromium.org

[Camillo Bruni, 2017-03-17 12:14:00]

lgtm

[jgruber, 2017-03-17 12:15:23]

The CQ bit was checked by jgruber@chromium.org

[commit-bot: I haz the power, 2017-03-17 12:15:34]

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, 2017-03-17 12:19:30]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1489752923117420, "parent_rev":
"50e1019dce7405295ddb091a89fa6e2bfc04ceb9", "commit_rev":
"338257509d7f5ec8ea0a16ba3eb263265efa06f9"}

[commit-bot: I haz the power, 2017-03-17 12:19:34]

Description was changed from

==========
[string] Optimize ToDirectStringAssembler for sequential strings

ToDirectStringAssembler is used in StringCharCodeAt and SubString
(which uses StringCharCodeAt internally). SubString is used all over the
place (e.g. RegExp result construction), and is critical for benchmark
performance.

The CL introducing ToDirectStringAssembler caused a couple of
regressions which this is intended to fix by adding a fast path for
sequential strings.

BUG=chromium:702246
==========

to

==========
[string] Optimize ToDirectStringAssembler for sequential strings

ToDirectStringAssembler is used in StringCharCodeAt and SubString
(which uses StringCharCodeAt internally). SubString is used all over the
place (e.g. RegExp result construction), and is critical for benchmark
performance.

The CL introducing ToDirectStringAssembler caused a couple of
regressions which this is intended to fix by adding a fast path for
sequential strings.

BUG=chromium:702246

Review-Url: https://codereview.chromium.org/2754933003
Cr-Commit-Position: refs/heads/master@{#43897}
Committed:
https://chromium.googlesource.com/v8/v8/+/338257509d7f5ec8ea0a16ba3eb263265ef...
==========

[commit-bot: I haz the power, 2017-03-17 12:19:36]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/v8/v8/+/338257509d7f5ec8ea0a16ba3eb263265ef...