[cfe-dev] What's the rationale to continue declare compatibility with GCC 4.2.1?

[James Y Knight via cfe-dev]

I think it was not a good idea to remove __VERSION__, but only because it
actually breaks software (and not just Python). I don't think it's terribly
important to preserve theoretically-pure compatibility at this point, but
it is rather useful to keep practical compatibility.

I note a couple other changes in this area which might also be problematic.
- "4.2.1 Compatible" was removed from the beginning of __VERSION__.
- clang -dumpversion reports clang's version (e.g. "9.0.0", rather than
always saying "4.2.1")

My inclination is that the former is very unlikely to break something (why
would anyone use that string for anything other than human readable output,
for which the new value is better?).

The latter, though, seems more risky, and I'm not sure there's much value
to that change. Possibly it should be put back.


On Fri, Jul 19, 2019 at 7:53 AM JF Bastien <jfbastien at apple.com> wrote:

>
>
> On Jul 19, 2019, at 1:50 PM, JF Bastien via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
>
> On Jul 17, 2019, at 2:13 PM, James Y Knight via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
> The reason has always been that changing it would undoubtedly break some
> software which uses features of newer GCCs that aren't implemented in
> Clang. And there are indeed some of those features, even if they are weird
> edge cases.
>
>
> What you’re saying leads me to believe that
> https://reviews.llvm.org/rL365962 shouldn’t have been committed. Unless
> we now decide it’s OK to break code which check GCC quirks?
>
>
> To be clear, it was reverted, but we don’t really seem to have a standing
> policy. It was more “Python broke” that caused a revert.
>
>
> Also, by this point, Clang is a widely-enough used compiler, that I'd
> expect most maintained software to be attempting to support it explicitly
> -- best via __has_builtin/__has_feature/__has_attribute/etc tests as
> applicable, falling back to the GCC version check if those macros don't
> exist.
>
> On Wed, Jul 17, 2019 at 7:22 AM Simon Atanasyan via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
>> Hi,
>>
>> Recently I get a request to implement in Clang a MIPS-related feature
>> which exists in GCC pre 4.4 and removed in later versions. There is a
>> rationale behind such strange request -- third-party software checks a
>> compiler's compatibility using __GNUC__,__GNUC_MINOR__ macros and
>> selects code dedicated for obsoleted version of GCC.
>>
>> As to me I would use for __GNUC__,__GNUC_MINOR__,__GNUC_PATCHLEVEL__
>> macros defined in the InitializePredefinedMacros function the same
>> values as a minimal GCC version required for building LLVM/Clang [1].
>> Now it's 5.1.0.
>>
>> Is there any rationale to continue declare compatibility with old GCC
>> 4.2.1?
>>
>> [1] https://llvm.org/docs/GettingStarted.html#software
>>
>> --
>> Simon Atanasyan
>> _______________________________________________
>> cfe-dev mailing list
>> cfe-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>
>
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20190719/e8f30de4/attachment.html>