RFR: 8277617: Adjust AVX3Threshold for copy/fill stubs

[Sandhya Viswanathan]

On Wed, 1 Dec 2021 12:41:14 GMT, David Holmes <dholmes at openjdk.org> wrote:

>>> As I understand it - old AVX512 platforms will continue to work as before.
>> 
>> According to @sviswa7 's comments (no cupid bit for the latest ISA), `is_intel_family_core() && supports_serialize()` can't distinguish all the old AVX512 platforms from the latest ones.
>> So I think it may be possible some old AVX512 machines will behave differently after this opt.
>> 
>> @sviswa7 , can you further explain what's the difference of the 64-byte instructions between Intel's old and latest AVX512 platforms?
>> Why can't we enable them as default on old platforms?
>> Thanks.
>
>> > As I understand it - old AVX512 platforms will continue to work as before.
>> 
>> According to @sviswa7 's comments (no cupid bit for the latest ISA), `is_intel_family_core() && supports_serialize()` can't distinguish all the old AVX512 platforms from the latest ones. So I think it may be possible some old AVX512 machines will behave differently after this opt.
> 
> I do not see such comments. From my previous questions on this it was indicated that any CPU that supports `serialize` has the improved performance.

@dholmes-ora @DamonFool @jatin-bhateja @neliasso Thanks a lot for the review. If no further objections, I plan to integrate this PR tomorrow (Friday 12/3).

-------------

PR: https://git.openjdk.java.net/jdk/pull/6512