RFR: JDK-8216437 : PPC64: Add intrinsic for GHASH algorithm [v26]

[Suchismith Roy]

On Fri, 21 Feb 2025 15:23:11 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> Suchismith Roy has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - change branch and remove not needed variables
>>  - change branch and remove not needed variables
>
> src/hotspot/cpu/ppc/stubGenerator_ppc.cpp line 703:
> 
>> 701:       __ vec_perm(vTmp4, vHigh, vHigh, loadOrder);
>> 702:       __ vec_perm(vTmp5, vLow, vLow, loadOrder);
>> 703:       __ vec_perm(vH, vTmp5, vTmp4, vPerm);
> 
> Can we compute a different vPerm such that we only need one `vec_perm` instruction in the loop?

As per the algorithm mentioned section 6.4 in Power ISA, we need 2 loads to access from nearest aligned address(to the unaligned address) and the next aligned address. 

Without the vec_perm, I faced the issue of wrong control vectors generated due to Endianness. Hence I had to include them.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20235#discussion_r1965777969