RFR: 8277617: Adjust AVX3Threshold for copy/fill stubs

[David Holmes]

On Wed, 1 Dec 2021 09:39:18 GMT, Jie Fu <jiefu 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.

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.

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