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

[Martin Doerr]

On Fri, 21 Feb 2025 16:08:09 GMT, Suchismith Roy <sroy at openjdk.org> wrote:

>> 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.

Please understand my question correctly. I didn't propose to remove all `ver_perm`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20235#discussion_r1965808162