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

[Bhavana Kilambi]

On Tue, 15 Jul 2025 12:16:42 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> `dst, src1, src2` and `tmp` need to be different registers. Only `dst` and `index` can match depending on the type of the input. The reason why I didn't add `index` to the assertion.
>> for the `src2 == src1 + 1` case, this is being checked in the definition of the `tbl` instruction for SVE in `src/hotspot/cpu/aarch64/assembler_aarch64.hpp` (but I realized it's not for Neon). Do you think it's enough if I make the Neon `tbl` instruction definition compatible with the SVE one? Or it's better to add a separate assertion here as well?
>
> Just assert at the start of every function whatever that function needs.

I'll add the `src2 == src1 + 1` assertion in my next PS. Thanks!

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PR Review Comment: https://git.openjdk.org/jdk/pull/23570#discussion_r2207350457