[cfe-dev] libc++ supporting older compilers

Eric Fiselier via cfe-dev cfe-dev at lists.llvm.org
Mon Dec 21 17:32:04 PST 2015

I think we have found consensus, or at least mild agreement, that nobody
needs libc++ to support GCC 4.6, 4.7 or 4.8.
Unless there are any late objections I'm going to proceed with

* Requiring GCC 4.9+ to use libc++ in C++11 mode.

While GCC 4.9 may not be optimal for everybody it is a compiler we can
meaningfully support.
Users of GCC 4.9+ should expect no test failures in C++11 mode and I will
set up a buildbot to enforce this.

This new requirement also has an exciting implication: Libc++ no longer has
to configure for incomplete C++11 implementations.**
This means that libc++ no longer has to restrict its use of C++11 features
such as "constexpr" and alias templates in C++11 mode.

However I still don't know what to do about GCC in C++03 mode, which still
has over 600 test failures. But that is a separate
question and deserves it's separate thread. Expect to see a new thread in
cfe-dev tonight.


** I'll triple check this before I act on it.

On Mon, Dec 21, 2015 at 4:49 PM, Eric Fiselier <eric at efcs.ca> wrote:

> On Mon, Dec 21, 2015 at 8:19 AM, Craig, Ben via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>> On 12/19/2015 2:44 PM, Renato Golin wrote:
>>> On 18 December 2015 at 14:30, Craig, Ben via cfe-dev
>>> <cfe-dev at lists.llvm.org> wrote:
>>>> Ubuntu 12.04 LTS (precise), released Apr-26-2012: GCC 4.6.3
>>>> Ubuntu 14.04 LTS (trusty), released Apr-17-2014: GCC 4.8.2
>>> Previous LTS is deprecated when a new LTS comes along, so no one
>>> should have to worry about 12.04 in this day and age.
>>> Is there any one that this is important?
> These configurations break enough that I doubt anybody is depending on
> them. I think I would have seen more bug reports if people were trying to
> use it.
> This is also the entirely wrong question to ask. What's important is that
> Libc++ is allowed to required C++11, and C++11 implementation should work.
> People who insist on using a ToT STL with an old compiler puzzle me. You
> can't expect new library features without additional language support.
> /Eric
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