RFR: 8348868: AArch64: Add backend support for SelectFromTwoVector [v15]

[Andrew Haley]

On Mon, 14 Jul 2025 11:30:01 GMT, Bhavana Kilambi <bkilambi at openjdk.org> wrote:

>> src/hotspot/cpu/aarch64/c2_MacroAssembler_aarch64.cpp line 2858:
>> 
>>> 2856: 
>>> 2857: // Implement selecting from two vectors using Neon instructions
>>> 2858: void C2_MacroAssembler::select_from_two_vectors_neon(FloatRegister dst, FloatRegister src1,
>> 
>> Need a comment here saying what this does.
>
> Thanks for the comment. I did mention on line #2857 that this implements selecting from two vectors using Neon instructions. Do you think I should add more description here? I have also added the conditions on which this function gets called in `C2_MacroAssembler::select_from_two_vectors()`.

Yes, you should. "Select items (on what basis?) from register(s) x and y and place them (in what order?) in dest.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23570#discussion_r2204857589