RFR: 8365200: RISC-V: compiler/loopopts/superword/TestGeneralizedReductions.java fails with Zvbb and vlen=128 [v2]

[Fei Yang]

On Tue, 12 Aug 2025 01:09:53 GMT, Dingli Zhang <dzhang at openjdk.org> wrote:

>> Hi all,
>> Please take a look and review this PR, thanks!
>> 
>> [JDK-8352529](https://bugs.openjdk.org/browse/JDK-8352529) enables this IR verification test for riscv. This test pass with zvbb when vlen=256, but fail when vlen=128.
>> 
>> The reason for the error is the same as [JDK-8357694](https://bugs.openjdk.org/browse/JDK-8357694). 2-element reductions for INT/LONG are not profitable, so the compiler won't generate the corresponding reductions IR.
>> 
>> This issue was not addressed together with [JDK-8357694](https://bugs.openjdk.org/browse/JDK-8357694) because the testMapReductionOnGlobalAccumulator case where the error is reported has a different applyif method from other cases: zvbb needs to be enabled.
>> 
>> ### Test (fastdebug)
>> - [x] Run compiler/loopopts/superword/TestGeneralizedReductions.java on qemu-system w/ and w/o zvbb when vlen=256
>> - [x] Run compiler/loopopts/superword/TestGeneralizedReductions.java on qemu-system w/ and w/o zvbb when vlen=128
>
> Dingli Zhang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add missing whitespace

Marked as reviewed by fyang (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/26719#pullrequestreview-3108200157