RFR: 8283307: Vectorize unsigned shift right on signed subword types [v3]

[Jie Fu]

On Thu, 2 Jun 2022 22:12:40 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> @merykitty @sviswa7 Could you help confirm if byte/short shift operations are vectorizable with all AVX versions of x86?
>
> @pfustc They are available either directly or through a series of instructions for majority of the architectures. All implemented in x86.ad. The match_rule_supported and match_rule_supported_vector will appropriately return true/false.

RShiftVB would fail with `UseSSE < 4`.
But is there a x86 machine running jtreg tests with `UseSSE < 4`?

For `RShiftV{B,S}`, neither `match_rule_supported ` nor `match_rule_supported_vector ` would return false on x86 with AVX=1.
So the test seems fine on x86, right? @sviswa7 @pfustc

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PR: https://git.openjdk.java.net/jdk/pull/7979