llvm dev - Mar 2016 - [cfe-dev] New buildbot with -Werror

My thought was that its reasonable to expect no warnings when building from
bootstrap (as you say) and the last release of Clang. Generally, I think we
should work around warnings in the last release of Clang if only for the
convenience of folks using that release to build stage1 and using Werror.

Certainly, we tend to fix warnings even from earlier Clang versions and
from GCC in order to keep Werror clean.

On Tue, Mar 22, 2016 at 5:06 PM Hal Finkel via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> ----- Original Message -----
> > From: "David Jones via cfe-dev" <cfe-dev at
lists.llvm.org>
> > To: cfe-dev at lists.llvm.org, llvm-dev at lists.llvm.org
> > Cc: gkistanova at gmail.com
> > Sent: Tuesday, March 22, 2016 7:00:28 PM
> > Subject: [cfe-dev] New buildbot with -Werror
> >
> > Greetings,
> >
> >
> > I would like to propose adding a buildbot which builds with -Werror.
> > The reason for a new buildbot in this configuration is twofold:
> >
> >
> > 1. It helps users who track and release from ToT, because they
> > (generally) seem to build with -Werror. Speaking from experience
> > :-), new warnings tend to crop up in a large range of commits, and
> > end up blocking one or more of these downstream users. These users
> > also seem to span several organizations, which makes coordination
> > difficult.
> >
> >
> > 1a. The current buildbots do not build with -Werror so that they will
> > run tests even if warnings are generated. It may or may not be
> > reasonable to enable -Werror by default for buildbots at some point
> > in the future, but I don't think it's quite reasonable to do
so yet
> > (judging based on the rate at which new warnings seem to get added,
> > that would leave too many buildbots broken). Adding a buildbot in
> > the -Werror configuration should help to inform any such future
> > changes.
> >
> >
> > 2. It helps users who develop without -Werror (either by conscious
> > choice or by oversight). Commits which inadvertently add warnings
> > often seem to get reverted; however, if a buildbot can deliver
> > warnings quickly, the committer can submit a small fix right away.
> >
> >
> > I have uploaded a diff to Phabricator, however I ask to please keep
> > high-level comments on this thread:
> > http://reviews.llvm.org/D18382
> >
> >
> >
> > This build would be owned and monitored by Google.
> >
> >
> > If there are no strong objections in the next few days, I will go
> > ahead with this plan.
> >
>
> I think having -Werror bots is a good idea, at least when self hosting.
> Non-self-hosting -Werror (i.e. with older versions of Clang, or with GCC,
> etc.) might also be useful, but I'm less sure (since we can't fix
those
> warnings if the warning is the problem).
>
>  -Hal
>
> >
> > Thanks,
> > dlj
> >
> >
> > _______________________________________________
> > cfe-dev mailing list
> > cfe-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
> >
>
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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On Tue, Mar 22, 2016 at 5:06 PM Hal Finkel via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> I think having -Werror bots is a good idea, at least when self hosting.
> Non-self-hosting -Werror (i.e. with older versions of Clang, or with GCC,
> etc.) might also be useful, but I'm less sure (since we can't fix
those
> warnings if the warning is the problem).

On Tue, Mar 22, 2016 at 5:12 PM, Chandler Carruth <chandlerc at
google.com>
wrote:
> My thought was that its reasonable to expect no warnings when building
> from bootstrap (as you say) and the last release of Clang. Generally, I
> think we should work around warnings in the last release of Clang if only
> for the convenience of folks using that release to build stage1 and using
> Werror.
>
> Certainly, we tend to fix warnings even from earlier Clang versions and
> from GCC in order to keep Werror clean.
>
I've dug around a bit, and it looks to me like separating phase1 and phase2
behavior is going to be a bit tricky (looking at zorg [*]) as long as we
want -Wno-error as the default for buildbots.

So, the first thing I would propose is to add this buildbot and run it for
a while, just to see what the current background rate of breakages will be.
I think getting a feel for the baseline is going to be a solid first step.

If that signal is good enough, and folks are happy getting nag mail when
they cause regressions :-) , then it probably makes sense to change the
zorg build commands to use -Wno-error on phase1 and -Werror on phase 2 by
default. That insulates against host compiler issues, but remains strict
when self-hosting.

For Chandler's suggestion to use -Werror on a phase 1 build with the
current release, that seems perfectly reasonable; but again, it's probably
best encoded with a zorg change specifically for that case. (I don't want
to add too many magical layers of CMake option overrides for two-phase
builds...)

[*] I'm specifically looking at _getClangCMakeBuildFactory here:
http://llvm.org/svn/llvm-project/zorg/trunk/zorg/buildbot/builders/ClangBuilder.py
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I just changed this build on green dragon to warn and email if warnings are
found in the console log:

http://lab.llvm.org:8080/green/job/clang-stage1-cmake-RA_build/
> On Mar 22, 2016, at 6:24 PM, David Jones via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> On Tue, Mar 22, 2016 at 5:06 PM Hal Finkel via llvm-dev <llvm-dev at
lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
> I think having -Werror bots is a good idea, at least when self hosting.
Non-self-hosting -Werror (i.e. with older versions of Clang, or with GCC, etc.)
might also be useful, but I'm less sure (since we can't fix those
warnings if the warning is the problem).
> 
> On Tue, Mar 22, 2016 at 5:12 PM, Chandler Carruth <chandlerc at
google.com <mailto:chandlerc at google.com>> wrote:
> My thought was that its reasonable to expect no warnings when building from
bootstrap (as you say) and the last release of Clang. Generally, I think we
should work around warnings in the last release of Clang if only for the
convenience of folks using that release to build stage1 and using Werror.
> 
> Certainly, we tend to fix warnings even from earlier Clang versions and
from GCC in order to keep Werror clean.
> 
> I've dug around a bit, and it looks to me like separating phase1 and
phase2 behavior is going to be a bit tricky (looking at zorg [*]) as long as we
want -Wno-error as the default for buildbots.
> 
> So, the first thing I would propose is to add this buildbot and run it for
a while, just to see what the current background rate of breakages will be. I
think getting a feel for the baseline is going to be a solid first step.
> 
> If that signal is good enough, and folks are happy getting nag mail when
they cause regressions :-) , then it probably makes sense to change the zorg
build commands to use -Wno-error on phase1 and -Werror on phase 2 by default.
That insulates against host compiler issues, but remains strict when
self-hosting.
> 
> For Chandler's suggestion to use -Werror on a phase 1 build with the
current release, that seems perfectly reasonable; but again, it's probably
best encoded with a zorg change specifically for that case. (I don't want to
add too many magical layers of CMake option overrides for two-phase builds...)
> 
> [*] I'm specifically looking at _getClangCMakeBuildFactory here:
>
http://llvm.org/svn/llvm-project/zorg/trunk/zorg/buildbot/builders/ClangBuilder.py
<http://llvm.org/svn/llvm-project/zorg/trunk/zorg/buildbot/builders/ClangBuilder.py>_______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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On 23 March 2016 at 00:12, Chandler Carruth via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> My thought was that its reasonable to expect no warnings when building from
> bootstrap (as you say) and the last release of Clang. Generally, I think we
> should work around warnings in the last release of Clang if only for the
> convenience of folks using that release to build stage1 and using Werror.
I agree. Since the environment is controllable, and if the bot starts
green while self-hosting, it's reasonable to assume -Werror can break
without problems.

The only problem is if both GCC and Clang have the same warning, and
fixing stage1 fixes stage2, we'd never know if Clang would have hit
the same assert.

But since this is regarding the build process, not Clang's warnings, I
think it's not a problem.

cheers,
--renato