RFR: JDK-8216437 : PPC64: Add intrinsic for GHASH algorithm [v29]

[Martin Doerr]

On Wed, 19 Mar 2025 08:26:55 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 three additional commits since the last revision:
> 
>  - comments
>  - comments
>  -  comments

src/hotspot/cpu/ppc/stubGenerator_ppc.cpp line 640:

> 638:     __ vsldoi(vTmp8, vZero, vReducedLow, 1);            // 0x1
> 639:     __ vor(vTmp8, vConstC2, vTmp8);                     // 0xC2...1
> 640:     __ vsplt(vTmp9, 0, vH);                             // MSB of H

I think the instruction name should be vspltb, but we should better clean this up in a separate RFE. Seems like the immediate value should be the last argument. Maybe we can find more to clean up and document that in a new RFE.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20235#discussion_r2032016756