Make is_win_fastlink imply -fstandalone-debug for clang

Make is_win_fastlink imply -fstandalone-debug for clang

Visual Studio can't find type information outside of the object file
currently being debugged with /DEBUG:FASTLINK. So, every object file
needs to have "standalone" debug information in this mode. However, that
generates a lot more debug info and slows down normal links, so only do
this when we know fastlink is in use.

While we're at it, explicitly pass -fno-standalone-debug to clang when
we're not using is_win_fastlink. This will make sure Chromium keeps using
limited debug info if clang switches the default for -fstandalone-debug.

R=thakis@chromium.org,brucedawson@chromium.org
BUG=657518
Committed: https://crrev.com/482876ffc87c08dcd8474001eec6d0717f41c4eb
Cr-Commit-Position: refs/heads/master@{#440163}

[Nico, 2016-12-16 23:32:19]

Doesn't this make fastlink slower? By how much? Since it has "fast" in the
name I'd guess that many people set this.

On Dec 16, 2016 6:25 PM, "rnk@chromium.org via codereview.chromium.org" <
reply@chromiumcodereview-hr.appspotmail.com> wrote:

> Reviewers: brucedawson, Nico (out Thu Dec 15)
> CL: https://codereview.chromium.org/2587603002/
>
> Description:
> Make is_win_fastlink imply -fstandalone-debug for clang
>
> Visual Studio can't find type information outside of the object file
> currently being debugged with /DEBUG:FASTLINK. So, every object file
> needs to have "standalone" debug information in this mode. However, that
> generates a lot more debug info and slows down normal links, so only do
> this when we know fastlink is in use.
>
> While we're at it, explicitly pass -fno-standalone-debug to clang when
> we're not using is_win_fastlink. This will make sure Chromium keeps using
> limited debug info if clang switches the default for -fstandalone-debug.
>
> R=thakis@chromium.org,brucedawson@chromium.org
> BUG=657518
>
> Affected files (+10, -0 lines):
> M build/config/compiler/BUILD.gn
>
>
> Index: build/config/compiler/BUILD.gn
> diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.
> gn
> index f3a69627b3b04726b55af755978481a6a7cd2ff7..
> b5231b1537587a51bdcf520f1adb0afc7eb91cda 100644
> --- a/build/config/compiler/BUILD.gn
> +++ b/build/config/compiler/BUILD.gn
> @@ -1560,6 +1560,16 @@ config("symbols") {
> } else {
> ldflags = [ "/DEBUG" ]
> }
> +
> + if (is_clang) {
> + # /DEBUG:FASTLINK requires every object file to have standalone debug
> + # information.
> + if (is_win_fastlink) {
> + cflags += [ "-fstandalone-debug" ]
> + } else {
> + cflags += [ "-fno-standalone-debug" ]
> + }
> + }
> } else {
> if (is_mac || is_ios) {
> cflags = [ "-gdwarf-2" ]
>
>
>

-- 
You received this message because you are subscribed to the Google Groups
"Chromium-reviews" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to chromium-reviews+unsubscribe@chromium.org.

[Reid Kleckner, 2016-12-16 23:50:07]

On 2016/12/16 23:32:19, Nico (out Thu Dec 15) wrote:
> Doesn't this make fastlink slower? By how much? Since it has "fast" in the
> name I'd guess that many people set this.

I haven't measured, but I would expect this to impact compile times, not link
times. fastlink just leaves the type information where it is.

I can measure, but regardless of the results, I think we should make this
change, because we're only faster now by virtual of dropping some fraction of
type information in this configuration.

[Reid Kleckner, 2016-12-17 00:19:59]

This moved fastlink time from 91.6s to 101.4s. I ran each link twice and took
the second result, hopefully warming up disk caches. Here's the actual timings:
http://pastebin.com/6Rc5Fcmr

[brucedawson, 2016-12-19 23:10:24]

On 2016/12/17 00:19:59, Reid Kleckner wrote:
> This moved fastlink time from 91.6s to 101.4s. I ran each link twice and took
> the second result, hopefully warming up disk caches. Here's the actual
timings:
> http://pastebin.com/6Rc5Fcmr

That seems like a very modest increase in fastlink times, and the result
(debugging works) seems quite worthwhile.

I must say that I am continually disappointed by how little fastlink really
helps, and how many extra problems it causes. It's worth it, but not *clearly*
worth it.

But hey, I know more about clang's debug information now.

Aside: VC++ 2017 is supposed to have a faster implementation of /debug:fastlink

lgtm

[Reid Kleckner, 2016-12-21 17:35:08]

The CQ bit was checked by rnk@chromium.org

[commit-bot: I haz the power, 2016-12-21 17:35:38]

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

[Nico, 2016-12-21 17:45:27]

(FWIW it doesn't seem like a modest increase to me -- over 10 %--
especially given that the base time is already very slow.)

On Wed, Dec 21, 2016 at 12:35 PM, commit-bot@chromium.org via
codereview.chromium.org <reply@chromiumcodereview-hr.appspotmail.com> wrote:

> CQ is trying da patch. Follow status at
>
> https://chromium-cq-status.appspot.com/v2/patch-status/
> codereview.chromium.org/2587603002/1
>
>
> https://codereview.chromium.org/2587603002/
>

-- 
You received this message because you are subscribed to the Google Groups
"Chromium-reviews" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to chromium-reviews+unsubscribe@chromium.org.

[commit-bot: I haz the power, 2016-12-21 18:40:01]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1482341708090190, "parent_rev":
"a6a13441f7e9e70bcb8ec329f78881c00f58c718", "commit_rev":
"3bec35b89736689e52eed4f0210c6c503082bd48"}

[commit-bot: I haz the power, 2016-12-21 18:40:32]

Description was changed from

==========
Make is_win_fastlink imply -fstandalone-debug for clang

Visual Studio can't find type information outside of the object file
currently being debugged with /DEBUG:FASTLINK. So, every object file
needs to have "standalone" debug information in this mode. However, that
generates a lot more debug info and slows down normal links, so only do
this when we know fastlink is in use.

While we're at it, explicitly pass -fno-standalone-debug to clang when
we're not using is_win_fastlink. This will make sure Chromium keeps using
limited debug info if clang switches the default for -fstandalone-debug.

R=thakis@chromium.org,brucedawson@chromium.org
BUG=657518
==========

to

==========
Make is_win_fastlink imply -fstandalone-debug for clang

Visual Studio can't find type information outside of the object file
currently being debugged with /DEBUG:FASTLINK. So, every object file
needs to have "standalone" debug information in this mode. However, that
generates a lot more debug info and slows down normal links, so only do
this when we know fastlink is in use.

While we're at it, explicitly pass -fno-standalone-debug to clang when
we're not using is_win_fastlink. This will make sure Chromium keeps using
limited debug info if clang switches the default for -fstandalone-debug.

R=thakis@chromium.org,brucedawson@chromium.org
BUG=657518

Review-Url: https://codereview.chromium.org/2587603002
==========

[commit-bot: I haz the power, 2016-12-21 18:40:33]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-12-21 18:44:42]

Description was changed from

==========
Make is_win_fastlink imply -fstandalone-debug for clang

Visual Studio can't find type information outside of the object file
currently being debugged with /DEBUG:FASTLINK. So, every object file
needs to have "standalone" debug information in this mode. However, that
generates a lot more debug info and slows down normal links, so only do
this when we know fastlink is in use.

While we're at it, explicitly pass -fno-standalone-debug to clang when
we're not using is_win_fastlink. This will make sure Chromium keeps using
limited debug info if clang switches the default for -fstandalone-debug.

R=thakis@chromium.org,brucedawson@chromium.org
BUG=657518

Review-Url: https://codereview.chromium.org/2587603002
==========

to

==========
Make is_win_fastlink imply -fstandalone-debug for clang

Visual Studio can't find type information outside of the object file
currently being debugged with /DEBUG:FASTLINK. So, every object file
needs to have "standalone" debug information in this mode. However, that
generates a lot more debug info and slows down normal links, so only do
this when we know fastlink is in use.

While we're at it, explicitly pass -fno-standalone-debug to clang when
we're not using is_win_fastlink. This will make sure Chromium keeps using
limited debug info if clang switches the default for -fstandalone-debug.

R=thakis@chromium.org,brucedawson@chromium.org
BUG=657518

Committed: https://crrev.com/482876ffc87c08dcd8474001eec6d0717f41c4eb
Cr-Commit-Position: refs/heads/master@{#440163}
==========

[commit-bot: I haz the power, 2016-12-21 18:44:43]

Patchset 1 (id:??) landed as
https://crrev.com/482876ffc87c08dcd8474001eec6d0717f41c4eb
Cr-Commit-Position: refs/heads/master@{#440163}