[base] Probe hashmap using indices rather than pointers

[base] Probe hashmap using indices rather than pointers

Using indices rather than pointers to probe the hashmap lets us
unconditionally mask the index to ensure it wraps around, rather than
branching on the pointer value. This produces slightly more optimal
code.

Committed: https://crrev.com/3abfc3370938a430f318153f843f42d98eef56e1
Cr-Commit-Position: refs/heads/master@{#40967}

[Leszek Swirski, 2016-11-11 17:11:21]

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

[commit-bot: I haz the power, 2016-11-11 17:11:33]

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

[Leszek Swirski, 2016-11-11 17:12:45]

leszeks@chromium.org changed reviewers:
+ rmcilroy@chromium.org

[Leszek Swirski, 2016-11-11 17:12:46]

I wasn't expecting this to make much of a difference, but funnily enough I see a
solid 1% improvement locally on Octane/CodeLoad with this change.

[commit-bot: I haz the power, 2016-11-11 17:39:28]

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

[commit-bot: I haz the power, 2016-11-11 17:39:29]

Dry run: This issue passed the CQ dry run.

[rmcilroy, 2016-11-14 13:09:28]

Interesting, I wouldn't have expected this to make much of a difference either.
LGTM.

[Leszek Swirski, 2016-11-14 14:09:00]

The CQ bit was checked by leszeks@chromium.org

[commit-bot: I haz the power, 2016-11-14 14:09:09]

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, 2016-11-14 15:01:25]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-11-17 22:32:44]

Description was changed from

==========
[base] Probe hashmap using indices rather than pointers

Using indices rather than pointers to probe the hashmap lets us
unconditionally mask the index to ensure it wraps around, rather than
branching on the pointer value. This produces slightly more optimal
code.
==========

to

==========
[base] Probe hashmap using indices rather than pointers

Using indices rather than pointers to probe the hashmap lets us
unconditionally mask the index to ensure it wraps around, rather than
branching on the pointer value. This produces slightly more optimal
code.

Committed: https://crrev.com/3abfc3370938a430f318153f843f42d98eef56e1
Cr-Commit-Position: refs/heads/master@{#40967}
==========

[commit-bot: I haz the power, 2016-11-17 22:32:45]

Patchset 1 (id:??) landed as
https://crrev.com/3abfc3370938a430f318153f843f42d98eef56e1
Cr-Commit-Position: refs/heads/master@{#40967}