[llvm-dev] [cfe-dev] LLVM C++14/C++17 BoF - Summary

[via llvm-dev]

Thanks, I'm glad we don't necessarily have to upgrade OS to get upgraded compilers. I've never been too clear on these Unix sys-admin sorts of things.

I'm happy this is going forward, I'm happy there is a plan, and I am *especially* happy that we have a reasonable amount of time to get ready for it.  If there's some place that someone is going to write down the general desire/policy for future advances in the minimum language standard used by the project, please make sure that statement includes reasonable advance notice to allow everyone time to go through acquisition, validation, and deployment steps.  Which has to include time for corporate procurement and IT engagement.  I'd say 3 months is definitely a minimum lead time, and some contributors might need more.

Are all the bot owners on board?
--paulr

From: jfbastien at apple.com [mailto:jfbastien at apple.com]
Sent: Friday, October 19, 2018 2:37 PM
To: Robinson, Paul
Cc: zturner at google.com; llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] [cfe-dev] LLVM C++14/C++17 BoF - Summary




On Oct 19, 2018, at 11:27 AM, via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:

So, there was agreement that the default gcc for recent-but-not-latest distros was not important? That is, it's okay to require people to upgrade their tools in order to work with LLVM?

In my team's case, a lot of us are on Ubuntu 16.04 which comes with gcc 5.4, which is not gcc 7.  And currently for Windows we're on MSVC 2015.
I suppose by March we can persuade our IT to upgrade all the people and bots to Ubuntu 18.04 (gcc 7.3?) and deploy MSVC 2017.  But it's something we need to plan for.
(I suppose I should thank the Google folks for being such slugs :) about being ready to switch, because it will give us time to get things organized for ourselves.)

The discussion from folks using Linux as well as from Linux vendors was that distros which come with older versions of GCC also provide easy ways to install newer versions of GCC, without upgrading the distro.

There was little discussion of MSVC, besides praising its C++17 support in the latest version.



--paulr

From: cfe-dev [mailto:cfe-dev-bounces at lists.llvm.org] On Behalf Of Zachary Turner via cfe-dev
Sent: Friday, October 19, 2018 9:58 AM
To: llvm-dev; Clang Dev
Subject: [cfe-dev] LLVM C++14/C++17 BoF - Summary

For those of you who were not able to attend the LLVM Developer Meeting (and as a recap for those who were), we had a productive BoF about enabling C++14 or C++17 in LLVM.  The outcome of this can be generally summarized as:

* There were no major objections to moving to C++14 / C++17 "as soon as possible"
* "As soon as possible" is not immediately, but we are currently targeting March of 2019 due to some downstream contributors' needing to resolve some blockages before it can be possible.
* There did not seem to be a strong sentiment that we should only move to C++14, so for the sake of this discussion we're assuming 17 unless someone presents a strong argument why 17 is *less* desirable than 14.

Minimum Compiler Versions for "Reasonable C++17 Support" (Mostly everything minus CTAD)
GCC - Version 7 [1]  (Version 8 for CTAD)
Clang - Version 4 [2]  (Version 5 for CTAD)
MSVC - 2017 Update 5 [3] (Update 7 for CTAD)

We plan to add a CMake warning if your compiler version is below these versions soon.  Around January, we will promote this to a CMake error which you must manually override by passing -DCMAKE_ALLLOW_DEPRECATED_COMPILER.

If I'm forgetting anything or misrepresenting anything that was said at the BoF please feel free to correct me.

[1] - https://www.gnu.org/software/gcc/projects/cxx-status.html
[2] - https://clang.llvm.org/cxx_status.html
[3] - https://docs.microsoft.com/en-us/cpp/visual-cpp-language-conformance?view=vs-2017
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