RFR: 8340189: 8339531 incorrect for Big Endian platforms

[Per Minborg]

On Tue, 15 Oct 2024 13:33:16 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>>> This version uses little endian accesses on big endian machines. This may defeat the purpose of [JDK-8339531](https://bugs.openjdk.org/browse/JDK-8339531) for those platforms. Accesses are typically slower when using them with endianness mismatch. But it looks at least correct. Thanks for providing a fix.
>> 
>> Are you able to run the `SegmentBulkMismatch` benchmark on the various BE platforms? This will provide us with clear figures if there is an improvement or not.  (The benchmark runs both the old and new code path)
>> 
>> When we have the figures, we could (if necessary) open up a new issue targeting improved performance for BE platforms. I could help in such an effort but I can't drive it because I don't have access to a BE platform.
>
>> Are you able to run the `SegmentBulkMismatch` benchmark on the various BE platforms?
> 
> Thanks for the hint. I've run it with the old implementation before [JDK-8339531](https://bugs.openjdk.org/browse/JDK-8339531) but with the new micro benchmark and the current implementation with your fix on Power8 Big Endian. Some benchmarks are faster now, some a little slower, but I couldn't see any significant regression. So, I guess we can live with it.

Thanks, @TheRealMDoerr and @offamitkumar for helping me out with this one!

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PR Comment: https://git.openjdk.org/jdk/pull/21258#issuecomment-2414003523