[llvm-dev] [RFC] migrating past C++11

[via llvm-dev]

It seems the CMake changes have landed; but the docs are still a bit out of date?
CMake.html talks about LLVM_FORCE_USE_OLD_TOOLCHAIN but not LLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN.

Also, it looks like LLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN is not propagated down to the NATIVE configuration when you set LLVM_OPTIMIZED_TABLEGEN.  If that's going to be a permanent deficiency, it should be mentioned in the docs as well.
Thanks,
--paulr

From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of JF Bastien via llvm-dev
Sent: Saturday, February 02, 2019 1:04 AM
To: via llvm-dev
Subject: Re: [llvm-dev] [RFC] migrating past C++11

After a few attempts I think we’re in sight of success: we only have the two following bots remaining with old versions of libstdc++ and new versions of clang:

polly-amd64-linux
polly-arm-linux

Once fixed the toolchain bump should stick.


On Jan 31, 2019, at 2:07 PM, JF Bastien via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:




On Jan 31, 2019, at 2:03 PM, Alex Bradbury <asb at asbradbury.org<mailto:asb at asbradbury.org>> wrote:

On Tue, 29 Jan 2019 at 21:05, JF Bastien via llvm-dev
<llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:


The patch is about ready to land, which means any older compiler will soft-error (which you can turn off with LLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN). I think we should then cherry-pick the patch to the LLVM 8 branch.

The last remaining issue are the buildbots. I audited *all* bots in http://lab.llvm.org:8011/buildslaves (there's so many!). Some of them are down, I therefore have no idea what they run. Here are the bots that will definitely break, with their maintainers:

Galina Kistanova <gkistanova at gmail.com<mailto:gkistanova at gmail.com>>
am1i-slv1 -- gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4
as-bldslv4 -- Microsoft (R) Visual Studio (R) 2015 (14.0)
ps4-buildslave2 -- Microsoft (R) Visual Studio (R) 2015 (14.0)

Hexagon QA <llvm.buildmaster at quicinc.com<mailto:llvm.buildmaster at quicinc.com>>
hexagon-build-02 -- gcc (Ubuntu 4.9.2-10ubuntu13) 4.9.2
hexagon-build-03 -- gcc (Ubuntu 4.9.2-10ubuntu13) 4.9.2

Vitaly Buka <vitalybuka at google.com<mailto:vitalybuka at google.com>>
sanitizer-buildbot6 -- gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4

Reid Kleckner <rnk at google.com<mailto:rnk at google.com>>
sanitizer-windows -- Microsoft (R) Visual Studio (R) 2015 (14.0)

Ilia Taraban <mstester.llvm at gmail.com<mailto:mstester.llvm at gmail.com>>
windows7-buildbot -- Microsoft (R) Visual Studio (R) 2015 (14.0)


The maintainers have 3 options:

1. Pass LLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN to their bot, suffer breakage later.
2. Update the bot to a newer compiler version.
3. Entirely turn down the bot.

I’ve emailed the maintainers and some have already responded. Once all bots are in a good state I’ll commit the patch (unless someone else chimes in with new information).

Did anyone pick option 1)? If I understand correctly, we probably want
to ensure that at least some bots do this, so we can ensure an old
compiler + LLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN build actually remains
functional up until the point support for the old compiler is actually
removed.

Reid asked me to do so for sanitizer-windows:
https://reviews.llvm.org/D57525

Ideally yes we’d have bots covering all eventualities, but this is but one of many holes in our coverage. On the upside, that hole is disappearing in a few months :)



Best,

Alex

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