RFR: 8327652: S390x: Implements SLP support [v7]

[Lutz Schmidt]

On Tue, 26 Mar 2024 15:10:37 GMT, Sidraya Jayagond <sjayagond at openjdk.org> wrote:

>> This PR Adds SIMD support on s390x.
>
> Sidraya Jayagond has updated the pull request incrementally with one additional commit since the last revision:
> 
>   PopCountVI supported by z14 onwards.

Decision pending how to handle string_compress and string_expand implementations. 
**I suggest using KILL** effects for the used vector registers. Default register allocation does not work because the code depends on registers with subsequent numbers.

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Changes requested by lucy (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/18162#pullrequestreview-1962975031