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

[Magnus Ihse Bursie]

On Tue, 12 Dec 2023 02:31:58 GMT, Kim Barrett <kbarrett 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
>
> Please hold off on this change while I follow up on JDK-8319577.  This code
> requires C++17, which was turned on for a relevant small subset of the JDK by
> that change.  There was some discussion there about version limiting that
> change, but that doesn't seem to have been done, with this breakage being a
> consequence.

@kimbarrett There were a long discussion about the C++17 support. The end result, which led me to approve the build changes, was the claims made beginning with https://github.com/openjdk/jdk/pull/16534#discussion_r1414570644:

>  [...] the updated code which added guards to check for GCC version >= 7.5 in src/java.base/linux/native/libsimdsort/{avx2-linux-qsort.cpp, avx512-linux-qsort.cpp}. GCC >= 7.5 is needed to compile libsimdsort using C++17 features. Made sure that OpenJDK builds without errors using both GCC 7.5 and GCC 6.4.

> The GCC complier for versions 6 (and even 5) silently ignores the flag -std=c++17

Somehow the JDK compiled with 7.5 for the author of that patch, but fails for the author of this patch. I don't understand how this both can be true.

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PR Comment: https://git.openjdk.org/jdk/pull/17047#issuecomment-1852290498