RFR: 8327652: S390x: Implements SLP support [v3]

[Martin Doerr]

On Mon, 18 Mar 2024 12:01:54 GMT, Sidraya Jayagond <sjayagond at openjdk.org> wrote:

>> This PR Adds SIMD support on s390x.
>
> Sidraya Jayagond has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add proper comments and cosmetic changes.

src/hotspot/cpu/s390/globals_s390.hpp line 115:

> 113:           "Use Z15 Vector instructions for superword optimization.")          \
> 114:   product(bool, UseSFPV, false,                                               \
> 115:           "Use SFPV Vector instructions for superword optimization.")         \

I'd probably make `UseSFPV` a diagnostic flag. Or do you think it needs to be an official flag which customers should set in production?
(I think making `SuperwordUseVX` a regular product switch is fine as it is the fundamental switch for turning vectorization on or off.)

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PR Review Comment: https://git.openjdk.org/jdk/pull/18162#discussion_r1528488541