[v8] Add LTO support for Android Chromium.

Add LTO support for Android Chromium.

This is to add support for a Link-Time Optimizations experiment in Android Chromium. As it is disabled by default, it won't change anything for most configurations.

R=ulan@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=23336

[ulan, 2014-08-22 13:47:48]

https://codereview.chromium.org/497713002/diff/1/build/toolchain.gypi
File build/toolchain.gypi (right):

https://codereview.chromium.org/497713002/diff/1/build/toolchain.gypi#newcode247
build/toolchain.gypi:247: # Disable LTO for v8
Could you please expand this commet explaining why we need to disable it and
when can we enable it? Maybe a link to a chromium issue?

[Fabrice (no longer in Chrome), 2014-08-22 14:13:25]

LTO merges all the flags at link time. v8 is built with -O2  (optimize for
speed) and that takes precedence over -Os (optimize for size), which we use in
the rest of Chromium.
So, essentially, the "-O2" option spills into the rest of the build. There's no
"fix" for that as it's not a bug.
I hope the explanation in the file is clear enough.

https://codereview.chromium.org/497713002/diff/1/build/toolchain.gypi
File build/toolchain.gypi (right):

https://codereview.chromium.org/497713002/diff/1/build/toolchain.gypi#newcode247
build/toolchain.gypi:247: # Disable LTO for v8
On 2014/08/22 13:47:48, ulan wrote:
> Could you please expand this commet explaining why we need to disable it and
> when can we enable it? Maybe a link to a chromium issue?

Done.

[ulan, 2014-08-22 14:28:12]

On 2014/08/22 14:13:25, Fabrice de Gans wrote:
> LTO merges all the flags at link time. v8 is built with -O2  (optimize for
> speed) and that takes precedence over -Os (optimize for size), which we use in
> the rest of Chromium.
> So, essentially, the "-O2" option spills into the rest of the build. There's
no
> "fix" for that as it's not a bug.
> I hope the explanation in the file is clear enough.
> 
> https://codereview.chromium.org/497713002/diff/1/build/toolchain.gypi
> File build/toolchain.gypi (right):
> 
>
https://codereview.chromium.org/497713002/diff/1/build/toolchain.gypi#newcode247
> build/toolchain.gypi:247: # Disable LTO for v8
> On 2014/08/22 13:47:48, ulan wrote:
> > Could you please expand this commet explaining why we need to disable it and
> > when can we enable it? Maybe a link to a chromium issue?
> 
> Done.

Thanks, lgtm.

[Fabrice (no longer in Chrome), 2014-08-22 14:49:49]

The CQ bit was checked by fdegans@chromium.org

[commit-bot: I haz the power, 2014-08-22 14:50:37]

CQ is trying da patch. Follow status at
 https://v8-status.appspot.com/cq/fdegans@chromium.org/497713002/20001

[commit-bot: I haz the power, 2014-08-22 14:50:37]

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

[commit-bot: I haz the power, 2014-08-22 14:50:38]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[Michael Achenbach, 2014-08-22 14:51:32]

FYI: v8 doesn't support a cq yet. Use 'git cl dcommit'.

[Fabrice (no longer in Chrome), 2014-08-22 15:13:42]

On 2014/08/22 14:51:32, Michael Achenbach wrote:
> FYI: v8 doesn't support a cq yet. Use 'git cl dcommit'.

Can one of you do it? I am not a committer so I don't think I can do it.
I'm getting this error:
URL access forbidden for unknown reason: MKACTIVITY of [...]: 403 Forbidden
(https://v8.googlecode.com)

[Yang, 2014-08-25 07:32:36]

Committed patchset #2 manually as 23336 (presubmit successful).