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

[Richard Reingruber]

On Thu, 10 Apr 2025 15:08:18 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> src/hotspot/cpu/ppc/ppc.ad line 1934:
>> 
>>> 1932:   if (reg < 136+256) return rc_vs;
>>> 1933: 
>>> 1934:   assert(OptoReg::is_stack(reg), "what else is it?");
>> 
>> Maybe add
>> ```c++
>>   assert(_last_Mach_Reg == 398, "hardcoded register indices need to be updated from enum MachRegisterNumbers");
>
> Shouldn't the existing assertion catch all problematic cases?

No sure. If, for instance, we removed the definition of the unused R13, we could get wrong results.
And speaking of it, IMO, we should remove that definition and other unused too.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23987#discussion_r2037736417