RFR: 8357460: RISC-V: Optimize array fill stub for small size [v3]

[Fei Yang]

On Fri, 23 May 2025 15:38:36 GMT, Feilong Jiang <fjiang at openjdk.org> wrote:

>> Please consider.
>> As discussed in https://github.com/openjdk/jdk/pull/23890#discussion_r2094920943, we can also further optimize the array fill stub by unrolling the storage of values when the size is less than 8.
>> 
>> This PR also removes the **aligned tail part** with the consideration of code size and testing coverage. As the test reveals there are no significant regressions.
>> 
>> 
>> Before:
>> Benchmark                 (size)  Mode  Cnt   Score   Error  Units
>> ArrayFill.fillByteArray        7  avgt   12  27.215 ± 0.073  ns/op
>> ArrayFill.fillByteArray       15  avgt   12  32.687 ± 0.904  ns/op
>> ArrayFill.fillIntArray         7  avgt   12  28.629 ± 0.006  ns/op
>> ArrayFill.fillIntArray        15  avgt   12  29.351 ± 0.009  ns/op
>> ArrayFill.fillShortArray       7  avgt   12  30.776 ± 0.006  ns/op
>> ArrayFill.fillShortArray      15  avgt   12  31.724 ± 0.447  ns/op
>> ArrayFill.zeroByteArray        7  avgt   12  27.199 ± 0.006  ns/op
>> ArrayFill.zeroByteArray       15  avgt   12  32.685 ± 0.900  ns/op
>> ArrayFill.zeroIntArray         7  avgt   12  28.630 ± 0.007  ns/op
>> ArrayFill.zeroIntArray        15  avgt   12  29.352 ± 0.011  ns/op
>> ArrayFill.zeroShortArray       7  avgt   12  30.776 ± 0.006  ns/op
>> ArrayFill.zeroShortArray      15  avgt   12  31.497 ± 0.012  ns/op
>> 
>> After:
>> Benchmark                 (size)  Mode  Cnt   Score   Error  Units
>> ArrayFill.fillByteArray        7  avgt   12  20.137 ± 0.042  ns/op
>> ArrayFill.fillByteArray       15  avgt   12  32.928 ± 0.004  ns/op
>> ArrayFill.fillIntArray         7  avgt   12  28.630 ± 0.004  ns/op
>> ArrayFill.fillIntArray        15  avgt   12  29.344 ± 0.005  ns/op
>> ArrayFill.fillShortArray       7  avgt   12  31.494 ± 0.004  ns/op
>> ArrayFill.fillShortArray      15  avgt   12  31.492 ± 0.008  ns/op
>> ArrayFill.zeroByteArray        7  avgt   12  19.980 ± 0.164  ns/op
>> ArrayFill.zeroByteArray       15  avgt   12  32.927 ± 0.004  ns/op
>> ArrayFill.zeroIntArray         7  avgt   12  28.629 ± 0.005  ns/op
>> ArrayFill.zeroIntArray        15  avgt   12  29.346 ± 0.006  ns/op
>> ArrayFill.zeroShortArray       7  avgt   12  32.193 ± 0.027  ns/op
>> ArrayFill.zeroShortArray      15  avgt   12  31.495 ± 0.010  ns/op
>> 
>> 
>> Testing:
>> - [x] tier1
>
> Feilong Jiang 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 branch 'openjdk:master' into riscv-optimize-generate-fill
>  - Merge branch 'openjdk:master' into riscv-optimize-generate-fill
>  - Merge branch 'master' of https://github.com/openjdk/jdk into riscv-optimize-generate-fill
>  - optimize array fill stub for small size

Looks good. Thanks.

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Marked as reviewed by fyang (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/25350#pullrequestreview-2867010574