RFR: 8355563: VectorAPI: Refactor current implementation of subword gather load API [v2]

[Emanuel Peter]

On Tue, 1 Jul 2025 06:07:03 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

>> Xiaohong Gong has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:
>> 
>>  - Address review comments
>>  - Merge 'jdk:master' into JDK-8355563
>>  - 8355563: VectorAPI: Refactor current implementation of subword gather load API
>
> Ping again! Thanks in advance!

@XiaohongGong I'm a little busy at the moment, and soon going on a summer vacation, so I cannot promise a full review soon. Feel free to ask someone else to have a look.

I quickly looked through your new benchmark results you published after integration of https://github.com/openjdk/jdk/pull/25539. There seem to still be a few cases where `Gain < 1`. Especially:

GatherOperationsBenchmark.microShortGather512_MASK         256 thrpt  30  ops/ms 11587.465  10674.598  0.92
GatherOperationsBenchmark.microShortGather512_MASK        1024 thrpt  30  ops/ms  2902.731   2629.739  0.90
GatherOperationsBenchmark.microShortGather512_MASK        4096 thrpt  30  ops/ms   741.546    671.124  0.90

and

GatherOperationsBenchmark.microShortGather256_MASK         256 thrpt  30  ops/ms 11339.217  10951.141  0.96
GatherOperationsBenchmark.microShortGather256_MASK        1024 thrpt  30  ops/ms  2840.081   2718.823  0.95
GatherOperationsBenchmark.microShortGather256_MASK        4096 thrpt  30  ops/ms   725.334    696.343  0.96

and

GatherOperationsBenchmark.microByteGather512_MASK           64 thrpt  30  ops/ms 50588.210  48220.741  0.95


Do you know what happens in those cases?

That said: https://github.com/openjdk/jdk/pull/25539 seems to have been quite the sucess, there are way fewer regressions now than before 😊

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PR Comment: https://git.openjdk.org/jdk/pull/25138#issuecomment-3022057434