RFR: 8348868: AArch64: Add backend support for SelectFromTwoVector [v3]

[Xiaohong Gong]

On Tue, 17 Jun 2025 08:23:32 GMT, Bhavana Kilambi <bkilambi at openjdk.org> wrote:

>> src/hotspot/cpu/aarch64/aarch64.ad line 4990:
>> 
>>> 4988: %{
>>> 4989:   constraint(ALLOC_IN_RC(v17_veca_reg));
>>> 4990:   match(vReg);
>> 
>> Not sure whether it's better to use `match(VecA)` here.
>
> `VecA` is also matched in `vReg`. I thought we want to also match `VecD` (for 64bit) and `VecX` (for 128-bit) as well and `vReg` matches all the three of them. What do you think?

I'm fine with both. I pointed out this just because I noticed the reg is limited to `veca` in line-4989.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23570#discussion_r2151651950