RFR: 8350126: Regression ~3% on Crypto-ChaCha20Poly1305.encrypt for MacOSX aarch64 [v4]

[Andrew Haley]

On Mon, 21 Apr 2025 21:53:33 GMT, Jamil Nimeh <jnimeh at openjdk.org> wrote:

>> This fix addresses a performance regression found on some aarch64 processors, namely the Apple M1, when we moved to a quarter round parallel implementation in JDK-8349106.  After making some improvements in the ordering of the instructions in the 20-round loop we found that going back to a block-parallel implementation was faster, but it definitely needed the ordering changes for that to be the case.  More importantly, the block parallel implementation with the interleaving turns out to be faster on even those processors that showed improvements when moving to the quarter round parallel implementation.
>> 
>> There is a spreadsheet attached to the JBS bug that shows 3 different implementations relative to the current (QR-parallel with no interleaving) implementation on 3 different ARM64 processors.  Comparative benchmarks can also be found below.
>
> Jamil Nimeh has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:
> 
>  - Merge with main
>  - Regroup CRC32 stub generators together
>  - Place columnar/diagonal alignment code into separate method
>  - 8350126: Regression ~3% on Crypto-ChaCha20Poly1305.encrypt for MacOSX aarch64

Marked as reviewed by aph (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/24420#pullrequestreview-2784665815