RFR: 8321688: Build on linux with GCC 7.5.0 fails after 8319577

[Kim Barrett]

On Mon, 11 Dec 2023 02:36:30 GMT, Guoxiong Li <gli at openjdk.org> wrote:

> Hi all,
> 
> This patch fixes the building failure introduced by [JDK-8319577](https://bugs.openjdk.org/browse/JDK-8319577) in old GCC version (linux & GCC 7.5.0 locally).
> 
> Thanks for the review.
> 
>  Best Regards,
> -- Guoxiong

The files being proposed for change are cloned copies of a 3rd-party library.
We may want to take updates from that library in the future. Having local
modifications makes that more difficult.

Also, this library uses C++17.  GCC support for C++17 was experimental until
GCC 9.  As such, it shouldn't be entirely surprising if an earlier version of
GCC might run into problems with it.

We've been discussing switching to using C++17 JDK-wide for some time, and I
think that may happen soon.  At that point the minimum supported version of
GCC will be changed to at least GCC 9.

So I think the answer here is that building this lbrary with GCC 7.5 is not
supported and a newer version should be used. So the change should be here:
https://github.com/openjdk/jdk/blob/b31454e36234091c3827c3b4d07f62345cb0cee4/src/java.base/linux/native/libsimdsort/simdsort-support.hpp#L34-L37
to require a later GCC version. That way, if building with an older version of
GCC then the code in the library won't be built and the library won't be used
by the JDK (because the relevant symbols won't be found).

But GCC 7.5 will probably not be supported for building the JDK for much longer.

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PR Comment: https://git.openjdk.org/jdk/pull/17047#issuecomment-1857502174