RFR: 8277617: Optimize array copy and clear on x86_64

[Sandhya Viswanathan]

On Tue, 23 Nov 2021 02:54:51 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Currently 32-byte instructions are used for small array copy and clear. 
>> This can be optimized by using 64-byte instructions.
>> 
>> Please review.
>> 
>> Best Regards,
>> Sandhya
>
> But what exactly is it that you are checking for? What is the connection between the ISA version and the decision to effectively zero out AVX3Threshold?

@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.

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