RFR: 8329331: Intrinsify Unsafe::setMemory [v2]

[Doug Simon]

On Mon, 1 Apr 2024 21:30:19 GMT, Scott Gibbons <sgibbons at openjdk.org> wrote:

>> This code makes an intrinsic stub for `Unsafe::setMemory`.  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:
> 
>   Use non-sse fill (old left in)

Wouldn't it be better to do this intrinsification directly in the JIT without calling out to a stub?

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PR Comment: https://git.openjdk.org/jdk/pull/18555#issuecomment-2031348841