RFR: JDK-8216437 : PPC64: Add intrinsic for GHASH algorithm [v6]

[Martin Doerr]

On Thu, 9 Jan 2025 09:07:21 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 one additional commit since the last revision:
> 
>   restore

src/hotspot/cpu/ppc/vm_version_ppc.cpp line 310:

> 308: 
> 309:   if (FLAG_IS_DEFAULT(UseGHASHIntrinsics) && VM_Version::has_vsx()) {
> 310:     FLAG_SET_DEFAULT(UseGHASHIntrinsics, true);

An attempt to enable `UseGHASHIntrinsics` should be rejected if `!VM_Version::has_vsx()` and a warning printed. See handling of other flags.
Alternatively, we could require Power8 by doing [JDK-8331859](https://bugs.openjdk.org/browse/JDK-8331859) first (or at least a part of it).

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PR Review Comment: https://git.openjdk.org/jdk/pull/20235#discussion_r1908953536