Avoid relying on NVRO for HashMap

Avoid relying on NVRO for HashMap

The previous CL[1] relies on NRVO (Named Return Value Optimization)[2],
which is defined as "may" in C++ spec. This CL allows non-NRVO
compilers.

[1] https://codereview.chromium.org/2192703002
[2] http://en.cppreference.com/w/cpp/language/copy_elision

BUG=586517, 633943
Committed: https://crrev.com/23d537bfe5050e53dd965cc2805cbb8d0268630a
Cr-Commit-Position: refs/heads/master@{#410940}

[kojii, 2016-08-08 15:21:10]

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

[commit-bot: I haz the power, 2016-08-08 15:21:29]

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

[kojii, 2016-08-08 15:54:14]

Description was changed from

==========
nrvo

[1] http://en.cppreference.com/w/cpp/language/copy_elision

BUG=586517, 633943
==========

to

==========
Avoid relying on NVRO for HashMap

The previous CL[1] relies on NRVO (Named Return Value Optimization)[2],
which is defined as "may" in C++ spec. This CL allows non-NRVO
compilers.

[1] https://codereview.chromium.org/2192703002
[2] http://en.cppreference.com/w/cpp/language/copy_elision

BUG=586517, 633943
==========

[kojii, 2016-08-08 15:58:10]

kojii@chromium.org changed reviewers:
+ drott@chromium.org

[kojii, 2016-08-08 15:58:11]

PTAL. Another possibility. If this looks good to you, I'll land after a while so
that we can see the graph separately from the previous CL.

[commit-bot: I haz the power, 2016-08-08 16:46:21]

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

[commit-bot: I haz the power, 2016-08-08 16:46:22]

Dry run: This issue passed the CQ dry run.

[drott, 2016-08-08 17:22:00]

On 2016/08/08 at 15:58:11, kojii wrote:
> PTAL. Another possibility. If this looks good to you, I'll land after a while
so that we can see the graph separately from the previous CL.

Is there another way to see this more sharply, for example by looking at the
disassembly on Mac for temporary object creation or so? Or can you execute
measurements locally? This CL in itself LGTM, but I'd be surprised if this
change makes 16kb difference.

[kojii, 2016-08-08 17:40:47]

On 2016/08/08 at 17:22:00, drott wrote:
> On 2016/08/08 at 15:58:11, kojii wrote:
> > PTAL. Another possibility. If this looks good to you, I'll land after a
while so that we can see the graph separately from the previous CL.
> 
> Is there another way to see this more sharply, for example by looking at the
disassembly on Mac for temporary object creation or so? Or can you execute
measurements locally? This CL in itself LGTM, but I'd be surprised if this
change makes 16kb difference.

I don't know how to setup that test locally...I can ask kouhei@ tomorrow. I
heard it took him one day to setup Android memory test.

For this code, there are 400 entries of HashMap, 400*16=6.4kb. Since HashMap
should be sparse, it looks possible to me.

Relying on NRVO looked ok since MSVC supports it and I thought MSVC is the last
one to support new features in C++, but when I re-think now, there may be other
forks that use older/less capable compilers, so probably better not to rely on
it.

[kojii, 2016-08-10 01:40:06]

The CQ bit was checked by kojii@chromium.org

[commit-bot: I haz the power, 2016-08-10 01:40:57]

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, 2016-08-10 03:15:23]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-08-10 03:20:52]

Description was changed from

==========
Avoid relying on NVRO for HashMap

The previous CL[1] relies on NRVO (Named Return Value Optimization)[2],
which is defined as "may" in C++ spec. This CL allows non-NRVO
compilers.

[1] https://codereview.chromium.org/2192703002
[2] http://en.cppreference.com/w/cpp/language/copy_elision

BUG=586517, 633943
==========

to

==========
Avoid relying on NVRO for HashMap

The previous CL[1] relies on NRVO (Named Return Value Optimization)[2],
which is defined as "may" in C++ spec. This CL allows non-NRVO
compilers.

[1] https://codereview.chromium.org/2192703002
[2] http://en.cppreference.com/w/cpp/language/copy_elision

BUG=586517, 633943

Committed: https://crrev.com/23d537bfe5050e53dd965cc2805cbb8d0268630a
Cr-Commit-Position: refs/heads/master@{#410940}
==========

[commit-bot: I haz the power, 2016-08-10 03:20:53]

Patchset 1 (id:??) landed as
https://crrev.com/23d537bfe5050e53dd965cc2805cbb8d0268630a
Cr-Commit-Position: refs/heads/master@{#410940}