[arm64] Improve some new builtins.

[arm64] Improve some new builtins.

- Simplify the variable-length pop sequence on entry. (It now uses
  smaller code with no branches.)
- Use conditional compare to merge branches where appropriate.
- Make use of Ldrsw + UntagSmiFieldMemOperand to load smis more
  efficiently.
- Only load 'undefined' and 'null' once per builtin.
- A few other small improvements.

BUG=

Committed: https://crrev.com/efc641a7be54978cd85a4dcdf1950cd97725917d
Cr-Commit-Position: refs/heads/master@{#32975}

[jbramley, 2015-12-18 15:58:00]

jacob.bramley@arm.com changed reviewers:
+ bmeurer@chromium.org, yangguo@chromium.org

[jbramley, 2015-12-18 15:58:01]

This merges our implementation of issue 1523753002 with yours, hopefully getting
the best of both.

[jbramley, 2015-12-18 15:59:02]

By the way, I'll be on holiday for a couple of weeks, so in my absence feel free
to commit, modify or just wait until I get back, as you wish.

[Benedikt Meurer, 2015-12-18 20:16:21]

Nice. LGTM.

[Benedikt Meurer, 2015-12-18 20:16:25]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-12-18 20:16:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1537903004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1537903004/1

[commit-bot: I haz the power, 2015-12-18 20:52:12]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-12-18 20:52:53]

Description was changed from

==========
[arm64] Improve some new builtins.

- Simplify the variable-length pop sequence on entry. (It now uses
  smaller code with no branches.)
- Use conditional compare to merge branches where appropriate.
- Make use of Ldrsw + UntagSmiFieldMemOperand to load smis more
  efficiently.
- Only load 'undefined' and 'null' once per builtin.
- A few other small improvements.

BUG=
==========

to

==========
[arm64] Improve some new builtins.

- Simplify the variable-length pop sequence on entry. (It now uses
  smaller code with no branches.)
- Use conditional compare to merge branches where appropriate.
- Make use of Ldrsw + UntagSmiFieldMemOperand to load smis more
  efficiently.
- Only load 'undefined' and 'null' once per builtin.
- A few other small improvements.

BUG=

Committed: https://crrev.com/efc641a7be54978cd85a4dcdf1950cd97725917d
Cr-Commit-Position: refs/heads/master@{#32975}
==========

[commit-bot: I haz the power, 2015-12-18 20:52:54]

Patchset 1 (id:??) landed as
https://crrev.com/efc641a7be54978cd85a4dcdf1950cd97725917d
Cr-Commit-Position: refs/heads/master@{#32975}

[Michael Achenbach, 2015-12-19 07:54:47]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1539073002/ by machenbach@chromium.org.

The reason for reverting is: [Sheriff] Breaks arm64 nosnap debug:
https://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20arm64%20-%20....

[jbramley, 2016-01-05 11:31:23]

Sorry, we'd assumed that we'd never see more than 2 arguments, but these
functions seem to use kDontAdaptArgumentsSentinel so they don't get adapted.

I'll look into it and make a new CL.