[llvm-dev] Using C++14 code in LLVM

Mon Oct 3 09:28:32 PDT 2016

What concerns me the most is not “is this feature present?”, but rather “is it good enough to build trunk?”.
The fact that clang-3.4 shipped with support for a specific feature does not mean the compiler couldn’t crash or miscompile under some very specific conditions when using this feature.

So I don’t see much interested in a test that shows the feature “works” with (rather “is present in”) clang-3.4, I’m interested in continuously testing that clang-3.4 can build trunk, always.

Even today, we claim to support building with clang-3.1 but are we testing it? Is there a bot building trunk with 3.1?

— 
Mehdi

> On Oct 3, 2016, at 9:11 AM, C Bergström via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Oh it's "documented" - great.. well that doesn't give any weight to if
> it works and how robust. Is there tests for these features or not? I
> know if I wanted to add or change *anything* a test would be required.
> 
> On Mon, Oct 3, 2016 at 10:11 PM, Zachary Turner <zturner at google.com> wrote:
>> It's documented here
>> 
>> http://clang.llvm.org/cxx_status.html
>> 
>> On Mon, Oct 3, 2016 at 4:00 AM C Bergström <cbergstrom at pathscale.com> wrote:
>>> 
>>> I see a lot of people talking about c++14 and *maybe* clang-N.N.N will
>>> support it, but is there any tests which can be used to
>>> actually/tangibly verify this?
>>> 
>>> Is there tests for the features being proposed to take advantage of?
>>> It would be prudent to ensure there's tests available to verify on
>>> buildbots before any decision to switch is made.
>>> 
>>> Break this into steps and it becomes a plan instead of just tossing
>>> opinions around.
>>> 
>>> From what I read so far - I'd speculate that only old Linux and NetBSD
>>> will have an issue with the bump. Worst case those platforms need an
>>> extra step to bootstrap, but should that hold everything back? Either
>>> newer clang is good enough to replace the older version or it's not.
>>> However, testing as a pre-cursor and getting facts is important.
>>> 
>>> #1 Tests for the features
>>> #2 Bug tracker to identify any regressions blocking updating
>>> #3 Buildbots to verify
>>> 
>>> On Mon, Oct 3, 2016 at 6:49 PM, Dimitry Andric via llvm-dev
>>> <llvm-dev at lists.llvm.org> wrote:
>>>> I wasn't able to find that information on the distrowatch page you
>>>> linked, but I will assume that it is talking about the available ports, e.g.
>>>> packages external to the FreeBSD base system.  In the FreeBSD ports
>>>> collection, we have clang 3.3 through 3.9 available, and a 4.0 trunk
>>>> snapshot as of 2016-08-24.
>>>> 
>>>> On the other hand, the base system is a little different, in the sense
>>>> that we use clang to bootstrap the whole system, and use the FreeBSD build
>>>> system instead of llvm/clang's native build system.  Also, we don't have all
>>>> the additional tools like llc, opt, and so on, by default.
>>>> 
>>>> FreeBSD 10.3 currently has clang 3.4.1, with libc++ from around that
>>>> time, plus a bunch of patches.  I think it will be able to do most of C++14,
>>>> except maybe some corner cases.
>>>> 
>>>> FreeBSD 11.0 (which is going to ship any day now) has clang 3.8.0, with
>>>> libc++ 3.8.0.
>>>> 
>>>> I'm currently working on importing clang 3.9.0 into FreeBSD 12 (the
>>>> development version) together with libc++ 3.9.0, compiler-rt 3.9.0 and so
>>>> on.  These will hopefully land before the end of this month.  After about a
>>>> month, I will merge it all into FreeBSD 11, so it will end up in FreeBSD
>>>> 11.1.
>>>> 
>>>> -Dimitry
>>>> 
>>>>> On 03 Oct 2016, at 05:43, Zachary Turner via llvm-dev
>>>>> <llvm-dev at lists.llvm.org> wrote:
>>>>> 
>>>>> For anyone still on gcc 4.2.1, then I think this entire discussion is
>>>>> kind of irrelevant, because they are already having to build a new toolchain
>>>>> to compile LLVM, since the minimum is currently 4.7.  So for those people, I
>>>>> would imagine 4.7 vs. 4.9 makes no difference?
>>>>> 
>>>>> Maybe I'm misunderstanding the table of the distrowatch page, but if
>>>>> FreeBSD 11 has clang 3.8 as you say, why does distrowatch say FreeBSD 10 and
>>>>> 11 have clang 3.9?
>>>>> 
>>>>> On Sun, Oct 2, 2016 at 7:10 PM Krzysztof Parzyszek via llvm-dev
>>>>> <llvm-dev at lists.llvm.org> wrote:
>>>>> On 10/2/2016 6:09 PM, Zachary Turner via llvm-dev wrote:
>>>>>> The BSDs don't seem as much of an issue.  FreeBSD 10 and 11 both have
>>>>>> LLVM 3.9 and GCC 4.9.  NetBSD 6.1.5 and 7.0 both have GCC 5.3 and
>>>>>> LLVM
>>>>>> 3.8.  Open BSD has a very old GCC, but distrowatch claims that it
>>>>>> also
>>>>>> has LLVM 3.8.
>>>>> 
>>>>> FreeBSD 11 has clang 3.8.0.  There is gcc in the /usr/src/contrib, but
>>>>> that's 4.2.1.  There are still platforms that FreeBSD supports that
>>>>> have
>>>>> not finished moving to clang (from gcc 4.2.1).
>>>>> 
>>>>> -Krzysztof
>>>>> _______________________________________________
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>>>> 
>>>> 
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