RFR: 8329331: Intrinsify Unsafe::setMemory [v21]

[Sandhya Viswanathan]

On Tue, 16 Apr 2024 00:04:15 GMT, Scott Gibbons <sgibbons at openjdk.org> wrote:

>> This code makes an intrinsic stub for `Unsafe::setMemory` for x86_64.  See [this PR](https://github.com/openjdk/jdk/pull/16760) for discussion around this change.
>> 
>> Overall, making this an intrinsic improves overall performance of `Unsafe::setMemory` by up to 4x for all buffer sizes.
>> 
>> Tested with tier-1 (and full CI).  I've added a table of the before and after numbers for the JMH I ran (`MemorySegmentZeroUnsafe`).
>> 
>> [setMemoryBM.txt](https://github.com/openjdk/jdk/files/14808974/setMemoryBM.txt)
>
> Scott Gibbons has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add enter() and leave(); remove Windows-specific register stuff

@vnkozlov Could you please review this PR from @asgibbons? Looking forward to your inputs.

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PR Comment: https://git.openjdk.org/jdk/pull/18555#issuecomment-2064852401