[llvm-dev] [RFC] Increase minimum supported GCC version for building LLVM to 4.8

[Teresa Johnson via llvm-dev]

Hi Justin,

Wanted to follow up to see if Danny's response or the other responses
addressed your concerns.

Rather than specific new features in gcc 4.8+, it is more an issue of 4.7
being stale, as evidenced by some of the issues reported here and in the
thread I pointed to, and 4.8 being the version shipped with Linux distros.
Gcc is currently at 6.X, so 4.7 is quite a few major releases ago (even
taking into account the change in Gcc major release version numbering).

Thanks,
Teresa

On Wed, Oct 12, 2016 at 9:42 PM, Daniel Berlin via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

>
>
> On Wed, Oct 12, 2016 at 9:14 PM, Justin Bogner via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Teresa Johnson via llvm-dev <llvm-dev at lists.llvm.org> writes:
>> > According to the documentation at
>> > http://llvm.org/docs/GettingStarted.html#software, compiling LLVM with
>> GCC
>> > requires at least version 4.7.0. However, there are apparently several
>> > problems building current LLVM/Clang with gcc 4.7.X. This proposal is to
>> > increase the minimum required GCC to 4.8.
>>
>> -1 unless it's particularly hard to fix the incompatibilities that have
>> been introduced or there are strong pain points in supporting 4.7.4. We
>> should only increase the minimum version of our host compilers if we
>> have strong motivation to do so.
>>
>
> We do: Everyone we care about has already done so, including not just all
> developers, but all users anyone can find.
>
> Nobody is testing or ensuring it builds with 4.7, nor is there any
> compelling reason anyone can give to do so
>
> Testing with 4.7 would actually require people go and install non-default
> compilers for their long term supported distros in the buildbots, etc
> (that's a pain point right there).
>
> Last i looked, 3.9 did  not even build with gcc 4.7, and not a single
> complaint, bug filed, etc.
>
> (note: I haven't double checked this, it was definitely true at one point).
>
> Even the case where someone noticed that Teresa points out is an odd case,
> and not a normal usage.
>
> I think the above is a pretty strong motivation, even if it's not the
> typical motivation of "it adds x feature we want".
>
> We can certainly offer support for 4.7  if we want to, but if we are
> offering 4.7 just because 4.8 doesn't have magical new features that we
> would upgrade to, that seems wrong.
> We should offer support for 4.7 because someone actually wants it, and we
> care about that someone.
> Otherwise, it fails the very trivial test of "who cares if we support 4.7
> or not"
>
>
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>


-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |  408-460-2413
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