RFR: 8349908: RISC-V: C2 SelectFromTwoVector

[Hamlin Li]

Hi,
Can you help to review the patch?
This optimization is mainly for the vector API.

Thanks

## Test

### jtreg
test/jdk/jdk/incubator/vector/

### Performance
run on bananapi

master vs patch
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Benchmark | (size) | Mode | Cnt | Score -master | Error - master | Score - patch | Error - patch | Units | Improvement (master / patch)
-- | -- | -- | -- | -- | -- | -- | -- | -- | --
SelectFromBenchmark.selectFromByteVector | 1024 | avgt | 10 | 26422.495 | 674.565 | 721.604 | 1.036 | ns/op | 36.616
SelectFromBenchmark.selectFromByteVector | 2048 | avgt | 10 | 53964.411 | 1751.618 | 1385.24 | 0.956 | ns/op | 38.957
SelectFromBenchmark.selectFromDoubleVector | 1024 | avgt | 10 | 218430.616 | 1369.409 | 7739.774 | 14.408 | ns/op | 28.222
SelectFromBenchmark.selectFromDoubleVector | 2048 | avgt | 10 | 387889.456 | 7889.791 | 16197.77 | 66.775 | ns/op | 23.947
SelectFromBenchmark.selectFromFloatVector | 1024 | avgt | 10 | 103483.717 | 492.525 | 3580.358 | 29.127 | ns/op | 28.903
SelectFromBenchmark.selectFromFloatVector | 2048 | avgt | 10 | 226125.02 | 3118.836 | 7797.025 | 4.346 | ns/op | 29.001
SelectFromBenchmark.selectFromIntVector | 1024 | avgt | 10 | 97007.999 | 2607.711 | 2898.38 | 0.833 | ns/op | 33.47
SelectFromBenchmark.selectFromIntVector | 2048 | avgt | 10 | 222303.308 | 3096.615 | 6398.214 | 30.345 | ns/op | 34.745
SelectFromBenchmark.selectFromLongVector | 1024 | avgt | 10 | 245033.436 | 1652.527 | 6307.773 | 24.597 | ns/op | 38.846
SelectFromBenchmark.selectFromLongVector | 2048 | avgt | 10 | 438503.547 | 5972.265 | 17215.996 | 167.442 | ns/op | 25.471
SelectFromBenchmark.selectFromShortVector | 1024 | avgt | 10 | 53632.502 | 2159.433 | 1418.215 | 2.953 | ns/op | 37.817
SelectFromBenchmark.selectFromShortVector | 2048 | avgt | 10 | 111764.327 | 1220.509 | 3061.386 | 14.716 | ns/op | 36.508

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-------------

Commit messages:
 - comments
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/23614/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23614&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8349908
  Stats: 38 lines in 1 file changed: 37 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/23614.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23614/head:pull/23614

PR: https://git.openjdk.org/jdk/pull/23614