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

JF Bastien via cfe-dev cfe-dev at lists.llvm.org
Fri Oct 19 11:02:08 PDT 2018

> On Oct 19, 2018, at 10:03 AM, Keane, Erich via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> Thanks for the update Zachary!
> I indeed missed the LLVM-Dev meeting, so this is a welcome bit of news for me! 
> I’m glad we decided to go with the cmake-warning mechanism.  Was there ever any discussion about a rolling warning system as I proposed here? https://reviews.llvm.org/D47073 <https://reviews.llvm.org/D47073>
> It had received positive feedback on the mailing list, though Chandler had/has some reservations.  IMO, it is a way of going about this that prevents this discussion from being so contentious in the future.

We talked about going with exactly your patch, modulo bikeshed on timeline and exact compiler versions. Chandler’s concerns (IIUC) are handled by Zachary.

> -Erich
>   <>
> From: cfe-dev [mailto:cfe-dev-bounces at lists.llvm.org <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 <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>>; Clang Dev <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>>
> 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)

As we discussed, going to 17 seems ambitious but I’m happy if we do it! We’ll need to ban a few library features from C++17 because they’re not fully supported in those versions.

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