[llvm-dev] A Short Policy Proposal Regarding Host Compilers

Keane, Erich via llvm-dev
Fri, 11 May 2018 13:37:22 -0000

Hi All-
As we all know, the C++14 discussion is flaring up again.  Chandler brought up
that he would like a concrete plan to switch.  In my opinion, this is
insufficient, as it will result in us simply having this discussion AGAIN next
release.  Instead, I would prefer us to have a concrete Policy on our host
compilers.  That way, changes like this are unsurprising to our users, and
advance our codebase sufficiently.  I believe the arguments for/against
upgrading have been made repeatedly, so I won't repeat them here.  My
proposal is thus:

Starting with the Clang 7.0 release, we will officially support any major
release of our host compilers (MSVC, GCC, Clang, ?ICC?) released in the past 3*
years from our previous branch date to give trunk-developers time to transition
(so for 7.0, 3 years before January 3, 2018).  This will be enforced via the
CMake CheckCompilerVersion script (ala https://reviews.llvm.org/D46723).
ADDITIONALLY, a CMake warning will be issued for any major release less than
1.5* years old to give our users sufficient time to transition/upgrade their
compilers.  Finally, our dependent C++ version will be the best released
standard officially supported by the collection of compilers (for example,
we'd support -C++20 if all compilers had std=c++20 or eqiv, but NOT
std=c++2a).

The 3-years/1.5 years would result in our minimum GCC/Clang becoming:
GCC5.1/Clang3.6.  We would WARN on anything older than GCC7.1/Clang3.8

/End Proposal


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