Some tests depends on conditional RISCV extension support. Like ReverseBytes requires Zbb extension. See review comments in https://github.com/openjdk/jdk/pull/23030
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all the ReverseBytes variants will be available on riscv64 if we have the Zbb extension [1]. And I see the newly added IR tests in this file also works on such platforms. I wonder if there is an easy way to enable these IR tests for these platforms.

[1] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/riscv/riscv_b.ad#L181
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We can enhance IR framework to include extension in cpu feature string. And these tests can be enabled depends on it.