RFR: 8329331: Intrinsify Unsafe::setMemory [v26]

[Tobias Hartmann]

On Sat, 20 Apr 2024 22:31:48 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 with a new target base due to a merge or a rebase. The pull request now contains 37 commits:
> 
>  - Merge branch 'openjdk:master' into setMemory
>  - Fix UnsafeCopyMemoryMark scope issue
>  - Long to short jmp; other cleanup
>  - Review comments
>  - Address review comments; update copyright years
>  - Add enter() and leave(); remove Windows-specific register stuff
>  - Fix memory mark after sync to upstream
>  - Merge branch 'openjdk:master' into setMemory
>  - Set memory test (#23)
>    
>    * Even more review comments
>    
>    * Re-write of atomic copy loops
>    
>    * Change name of UnsafeCopyMemory{,Mark} to UnsafeMemory{Access,Mark}
>    
>    * Only add a memory mark for byte unaligned fill
>    
>    * Remove MUSL_LIBC ifdef
>    
>    * Remove MUSL_LIBC ifdef
>  - Set memory test (#22)
>    
>    * Even more review comments
>    
>    * Re-write of atomic copy loops
>    
>    * Change name of UnsafeCopyMemory{,Mark} to UnsafeMemory{Access,Mark}
>    
>    * Only add a memory mark for byte unaligned fill
>  - ... and 27 more: https://git.openjdk.org/jdk/compare/6d569961...1122b500

This introduced a regression, see [JDK-8331033](https://bugs.openjdk.org/browse/JDK-8331033).

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PR Comment: https://git.openjdk.org/jdk/pull/18555#issuecomment-2074459781