RFR: 8371711: AArch64: SVE intrinsics for Arrays.sort methods (int, float)

[Ruben]

On Tue, 9 Dec 2025 00:01:26 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> This patch adds an SVE implementation of primitive array sorting (Arrays.sort()) on AArch64 systems that support SVE. On non-SVE machines, we fall back to the existing Java implementation.
>> 
>> For smaller arrays (length <= 64), we use insertion sort; for larger arrays we use an SVE-vectorized quicksort partitioner followed by an odd-even transposition cleanup pass.
>> 
>> The SVE path is enabled by default for int type. For float type, it is available through the experimental flag :
>> 
>> `-XX:+UnlockExperimentalVMOptions -XX:+UseSVELibSimdSortForFP
>> `
>> Without this flag being enabled, the default Java implementation would be executed for floats (the flag is disabled by default).
>> 
>> Float is gated due to observed regressions on some small/medium sizes. On larger arrays, the SVE float path shows upto 1.47x speedup on Neoverse V2 and 2.12x on Neoverse V1.
>> 
>> Following are the performance numbers for **ArraysSort JMH benchmark** -
>> 
>> **Case A:** Ratio between the scores of master branch and `UseSVELibSimdSortForFP` flag disabled (which is the default).
>> **Case B:** Ratio between the scores of master branch and `UseSVELibSimdSortForFP` flag enabled (the int numbers will be the same but this now enables SVE vectorized sorting for floats).
>> **We would want the ratios to be >= 1 to be at par or better than the default Java implementation (master branch).**
>> 
>> On Neoverse V1:
>> 
>> 
>> Benchmark                       (size)   Mode    Cnt    A       B
>> ArraysSort.floatParallelSort    10       avgt    3      0.98    0.98
>> ArraysSort.floatParallelSort    25       avgt    3      1.01    0.83
>> ArraysSort.floatParallelSort    50       avgt    3      0.99    0.55
>> ArraysSort.floatParallelSort    75       avgt    3      0.99    0.66
>> ArraysSort.floatParallelSort    100      avgt    3      0.98    0.66
>> ArraysSort.floatParallelSort    1000     avgt    3      1.00    0.84
>> ArraysSort.floatParallelSort    10000    avgt    3      1.03    1.52
>> ArraysSort.floatParallelSort    100000   avgt    3      1.03    1.46
>> ArraysSort.floatParallelSort    1000000  avgt    3      0.98    1.81
>> ArraysSort.floatSort            10       avgt    3      1.00    0.98
>> ArraysSort.floatSort            25       avgt    3      1.00    0.81
>> ArraysSort.floatSort            50       avgt    3      0.99    0.56
>> ArraysSort.floatSort            75       avgt    3      0.99    0.65
>> ArraysSort.floatSort            100      avgt    3      0.98    0.70
>> ArraysSort.floatSort       ...
>
> Good work, Bhavana!
> 
> I reminds me of an effort I started a year ago to migrate native libraries to FFM.
> `vectormath` got integrated, but `libsimdsort` is still a draft:
>    https://github.com/iwanowww/jdk/tree/libsimdsort.1
> 
> Since you do profound refactorings in the libsimdsort library code, I suggest to introduce SVE variant on top of FFM from the beginning. Let me finalize the PR and post it for review. What do you think?

Hi @iwanowww,

Bhavana will be unavailable for some time, so I am coordinating the next steps and someone from our team will be taking over this PR. 

Thanks again for offering to finalize the libsimdsort FFM PR and post it for review. 

Do you have an estimate for when you expect to open it? We would like to plan the next update of the SVE Arrays.sort PR on top of it, so knowing an approximate timeline (and whether there is anything you would suggest we prepare in the meantime) would help.

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PR Comment: https://git.openjdk.org/jdk/pull/28675#issuecomment-3745085496