RFR: JDK-8216437 : PPC64: Add intrinsic for GHASH algorithm [v27]

[Martin Doerr]

On Wed, 26 Feb 2025 12:21:39 GMT, Suchismith Roy <sroy at openjdk.org> wrote:

>> JBS Issue : [JDK-8216437](https://bugs.openjdk.org/browse/JDK-8216437)
>> 
>> Currently acceleration code for GHASH is missing for PPC64. 
>> 
>> The current implementation utlilises SIMD instructions on Power and uses Karatsuba multiplication for obtaining the final result.
>
> Suchismith Roy has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - change pattern for Linux, fix for AIX
>  - change pattern for Linux, fix for AIX

This looks much better! Thanks! I'll rerun tests.
Maybe you can find names for some of the temp registers? Especially vTmp4 and vTmp11 are expected to contain specific values before entering `computeGCMProduct`. This would improve readability.

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PR Review: https://git.openjdk.org/jdk/pull/20235#pullrequestreview-2645116179