Make the GN build flag 'use_lld' usable on Linux.

Make the GN build flag 'use_lld' usable on Linux.

We are testing a new linker, LLD, for use within Chromium. This CL adds the
necessary machinery to allow us to use LLD on Linux by enabling the existing
GN build flag 'use_lld'.

This CL teaches the LLVM package build script to build LLD on non-Windows
platforms (for top-of-tree builds only), moves the 'use_lld' build flag from
the Windows toolchain configuration to the generic GN compiler configuration,
and gates the required linker flags for LLD on Linux on that flag.

BUG=607968
R=thakis@chromium.org,brettw@chromium.org,krasin@chromium.org

Committed: https://crrev.com/22afe741dcbb7bca0b792349f07fcac175716692
Cr-Commit-Position: refs/heads/master@{#390733}

[brettw, 2016-04-27 22:55:46]

https://codereview.chromium.org/1925843002/diff/1/build/config/compiler/BUILD.gn
File build/config/compiler/BUILD.gn (right):

https://codereview.chromium.org/1925843002/diff/1/build/config/compiler/BUILD...
build/config/compiler/BUILD.gn:48: # Set to true to use lld, the LLVM linker.
It seems this is Posixonly. If so, can you wrap this in an is_posix block so
it's not listed as available for other platforms? Put the comment inside the
block (the args help looks at the comment immediately above the variable and an
if statement in between will confuse it). If not or if this is going to change,
the comment should talk about when this flag is applicable.

https://codereview.chromium.org/1925843002/diff/1/build/config/compiler/BUILD...
build/config/compiler/BUILD.gn:55: is_linux && (current_cpu == "x64" ||
current_cpu == "arm") && !use_lld
This won't actually do what you want. The build overrides are applied at the end
of the declare_args block so this won't see any user overrides of the use_lld
variable.

To fix this, make a new declare_args block after the current one and move
use_gold into it.

https://codereview.chromium.org/1925843002/diff/1/build/config/compiler/BUILD...
build/config/compiler/BUILD.gn:339: # TODO(brettw) common.gypi has this only for
target toolset.
I think you can delete this comment.

[pcc1, 2016-04-27 23:21:05]

https://codereview.chromium.org/1925843002/diff/1/build/config/compiler/BUILD.gn
File build/config/compiler/BUILD.gn (right):

https://codereview.chromium.org/1925843002/diff/1/build/config/compiler/BUILD...
build/config/compiler/BUILD.gn:48: # Set to true to use lld, the LLVM linker.
On 2016/04/27 22:55:46, brettw wrote:
> It seems this is Posixonly. If so, can you wrap this in an is_posix block so
> it's not listed as available for other platforms? Put the comment inside the
> block (the args help looks at the comment immediately above the variable and
an
> if statement in between will confuse it). If not or if this is going to
change,
> the comment should talk about when this flag is applicable.

It's also available on Windows. I've added more information to the comment.

https://codereview.chromium.org/1925843002/diff/1/build/config/compiler/BUILD...
build/config/compiler/BUILD.gn:55: is_linux && (current_cpu == "x64" ||
current_cpu == "arm") && !use_lld
On 2016/04/27 22:55:46, brettw wrote:
> This won't actually do what you want. The build overrides are applied at the
end
> of the declare_args block so this won't see any user overrides of the use_lld
> variable.
> 
> To fix this, make a new declare_args block after the current one and move
> use_gold into it.

Done.

https://codereview.chromium.org/1925843002/diff/1/build/config/compiler/BUILD...
build/config/compiler/BUILD.gn:339: # TODO(brettw) common.gypi has this only for
target toolset.
On 2016/04/27 22:55:46, brettw wrote:
> I think you can delete this comment.

Done.

[brettw, 2016-04-27 23:35:21]

lgtm

[Nico, 2016-04-29 17:02:03]

lgtm

Might want to file a tracking bug for this and link to it in the BUG= line.

[pcc1, 2016-04-29 17:52:02]

Description was changed from

==========
Make the GN build flag 'use_lld' usable on Linux.

We are testing a new linker, LLD, for use within Chromium. This CL adds the
necessary machinery to allow us to use LLD on Linux by enabling the existing
GN build flag 'use_lld'.

This CL teaches the LLVM package build script to build LLD on non-Windows
platforms (for top-of-tree builds only), moves the 'use_lld' build flag from
the Windows toolchain configuration to the generic GN compiler configuration,
and gates the required linker flags for LLD on Linux on that flag.

BUG=
R=thakis@chromium.org,brettw@chromium.org,krasin@chromium.org
==========

to

==========
Make the GN build flag 'use_lld' usable on Linux.

We are testing a new linker, LLD, for use within Chromium. This CL adds the
necessary machinery to allow us to use LLD on Linux by enabling the existing
GN build flag 'use_lld'.

This CL teaches the LLVM package build script to build LLD on non-Windows
platforms (for top-of-tree builds only), moves the 'use_lld' build flag from
the Windows toolchain configuration to the generic GN compiler configuration,
and gates the required linker flags for LLD on Linux on that flag.

BUG=607968
R=thakis@chromium.org,brettw@chromium.org,krasin@chromium.org
==========

[pcc1, 2016-04-29 17:52:07]

The CQ bit was checked by pcc@chromium.org

[commit-bot: I haz the power, 2016-04-29 17:52:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1925843002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1925843002/20001

[commit-bot: I haz the power, 2016-04-29 18:32:28]

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

[commit-bot: I haz the power, 2016-04-29 18:32:29]

Try jobs failed on following builders:
  win_clang on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_clang/builds/...)

[pcc1, 2016-04-29 18:55:03]

The CQ bit was checked by pcc@chromium.org

[pcc1, 2016-04-29 18:55:04]

The patchset sent to the CQ was uploaded after l-g-t-m from brettw@chromium.org,
thakis@chromium.org
Link to the patchset: https://codereview.chromium.org/1925843002/#ps40001
(title: "Move use_lld flag to build/toolchain/toolchain.gni")

[commit-bot: I haz the power, 2016-04-29 18:55:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1925843002/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1925843002/40001

[commit-bot: I haz the power, 2016-04-29 20:15:22]

Description was changed from

==========
Make the GN build flag 'use_lld' usable on Linux.

We are testing a new linker, LLD, for use within Chromium. This CL adds the
necessary machinery to allow us to use LLD on Linux by enabling the existing
GN build flag 'use_lld'.

This CL teaches the LLVM package build script to build LLD on non-Windows
platforms (for top-of-tree builds only), moves the 'use_lld' build flag from
the Windows toolchain configuration to the generic GN compiler configuration,
and gates the required linker flags for LLD on Linux on that flag.

BUG=607968
R=thakis@chromium.org,brettw@chromium.org,krasin@chromium.org
==========

to

==========
Make the GN build flag 'use_lld' usable on Linux.

We are testing a new linker, LLD, for use within Chromium. This CL adds the
necessary machinery to allow us to use LLD on Linux by enabling the existing
GN build flag 'use_lld'.

This CL teaches the LLVM package build script to build LLD on non-Windows
platforms (for top-of-tree builds only), moves the 'use_lld' build flag from
the Windows toolchain configuration to the generic GN compiler configuration,
and gates the required linker flags for LLD on Linux on that flag.

BUG=607968
R=thakis@chromium.org,brettw@chromium.org,krasin@chromium.org
==========

[commit-bot: I haz the power, 2016-04-29 20:15:24]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2016-04-30 17:28:14]

Patchset 3 (id:??) landed as
https://crrev.com/22afe741dcbb7bca0b792349f07fcac175716692
Cr-Commit-Position: refs/heads/master@{#390733}

[commit-bot: I haz the power, 2016-04-30 18:02:04]

Description was changed from

==========
Make the GN build flag 'use_lld' usable on Linux.

We are testing a new linker, LLD, for use within Chromium. This CL adds the
necessary machinery to allow us to use LLD on Linux by enabling the existing
GN build flag 'use_lld'.

This CL teaches the LLVM package build script to build LLD on non-Windows
platforms (for top-of-tree builds only), moves the 'use_lld' build flag from
the Windows toolchain configuration to the generic GN compiler configuration,
and gates the required linker flags for LLD on Linux on that flag.

BUG=607968
R=thakis@chromium.org,brettw@chromium.org,krasin@chromium.org
==========

to

==========
Make the GN build flag 'use_lld' usable on Linux.

We are testing a new linker, LLD, for use within Chromium. This CL adds the
necessary machinery to allow us to use LLD on Linux by enabling the existing
GN build flag 'use_lld'.

This CL teaches the LLVM package build script to build LLD on non-Windows
platforms (for top-of-tree builds only), moves the 'use_lld' build flag from
the Windows toolchain configuration to the generic GN compiler configuration,
and gates the required linker flags for LLD on Linux on that flag.

BUG=607968
R=thakis@chromium.org,brettw@chromium.org,krasin@chromium.org

Committed: https://crrev.com/22afe741dcbb7bca0b792349f07fcac175716692
Cr-Commit-Position: refs/heads/master@{#390733}
==========