RFR: 8277617: Optimize array copy and clear on x86_64

[David Holmes]

On Tue, 23 Nov 2021 04:25:23 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> 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.

@sviswa7 that further restriction and an explanatory comment would be appreciated. Thanks.

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