RFR: 8277617: Adjust AVX3Threshold for copy/fill stubs

Wed Dec 1 09:42:30 UTC 2021

On Wed, 1 Dec 2021 09:20:48 GMT, Nils Eliasson <neliasso 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.

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