RFR: 8351666: [PPC64] Make non-volatile VectorRegisters available for C2 register allocation [v4]

[Richard Reingruber]

On Thu, 10 Apr 2025 23:28:07 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

> Better instructions are now used on Power9/10.
👍

> VSR0-31 removal has caused issues like "fatal error: Not compilable at tier 4: unsupported outgoing calling sequence". I've added them back. I'll take another look.

I see. Thanks for trying. I'd be ok with creating a separate RFE for that task.
You should investigate though the number of spill slots used for a vector register. Reading the comments (see link in previous comment) my understanding is that with `Op_VecX` and `SlotsPerVecX = 4` it might be 4 x 4 slots (16 x 4 = 64 bytes) but only 4 slots (16 bytes) are needed.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23987#discussion_r2039009614