RFR: 8277617: Optimize array copy and clear on x86_64

[Jie Fu]

On Tue, 23 Nov 2021 04:50:42 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> @dholmes-ora The Intel platforms that supports this ISA has improved implementation of 64-byte load/stores. I could not find any other better way to check in the absence of cupid bit.
>> If it helps, I could further restrict it to (is_intel_family_core() && supports_serialize()). Also, I can add a comment towards this to the avx3_threshold() method.
>
> @sviswa7 that further restriction and an explanatory comment would be appreciated. Thanks.

> @dholmes-ora We see about 25% gain on a micro on our latest platform. There is no cpuid bit for this, so the closest was to check for the new serialize ISA supported on this platform.

It would be better to add a jmh test for this opt.
Thanks.

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