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

[Bhavana Kilambi]

On Wed, 16 Jul 2025 11:31:53 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> @theRealAph Thanks for your comments. The Neon implementation would not fail if UseSVE == 1 (Does the comment imply something like this?). Only that we are making a choice of generating Neon instructions for UseSVE = 1 and vec_len = 16. 
>> 
>> The conditions that can reach this method are - UseSVE = 0, 1 with vec_len = 8 or 16 and UseSVE = 2 with any vec_len (based on the conditions in `Matcher::match_rule_supported_vector()`). We have already filtered out `UseSVE = 1` with `vec_len = 8` and `UseSVE = 2` at line #2904. So if the control reaches #2915 then it's either `UseSVE = 0` with any vec_len and `UseSVE = 1` with `vec_len = 16` and that's what the comment mentions.
>
> Then that's what your comment should say. It does not: it says "conditions must satisfy" which implies that this is something the following code needs for correct operation.
> 
> The language in your reply here is fine. Say that instead of "one of these conditions must satisfy".

Thanks for the suggestion. Will do that in my next PS.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23570#discussion_r2210111107