RFR: 8359965: Enable paired pushp and popp instruction usage for APX enabled CPUs [v2]

[Jatin Bhateja]

On Mon, 21 Jul 2025 15:44:47 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Hi Jatin (@jatin-bhateja), for the first iteration, would it be ok to get the push_paired/pop_paired changes integrated and then make the push2p/pop2p related optimizations in a separate PR?
>> 
>> Thanks,
>> Vamsi
>
> Hi @vamsi-parasa , I think it's ok not to expose pop_ppx / push_ppx as separate interfaces, and let processor forward the values b/w push and matching pop if balancing constraints are satisfied.
> 
> <img width="1055" height="151" alt="image" src="https://github.com/user-attachments/assets/6923ca1b-11eb-4fae-8d51-14f1bfe27cea" />

> Hi Jatin (@jatin-bhateja), the reason to make the push_ppx/pop_ppx usage explicit is because an unbalanced push_ppx operation has a performance penalty.

Thanks @vamsi-parasa , as per APX specification PPX is an optimization hint and should only improve performance if balancing contraintins are met. so I don't think it will have any performance penalty.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25889#discussion_r2227032048