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

[Dingli Zhang]

> 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

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26719/files
  - new: https://git.openjdk.org/jdk/pull/26719/files/cdae1d05..703205d3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26719&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26719&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/26719.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26719/head:pull/26719

PR: https://git.openjdk.org/jdk/pull/26719