RFR: 8259948: Aarch64: Add cast nodes for Aarch64 Neon backend [v5]

[Eric Liu]

On Mon, 27 Sep 2021 01:30:20 GMT, Wu Yan <wuyan at openjdk.org> wrote:

>> I suggested to test this PR with the latest code. As some vector sizes which should not be supported for `VectorReinterpret` and `VectorCast*2X` have been fixed after https://github.com/openjdk/jdk/pull/5160. E.g. 128short => 64int.
>> 
>> For the case above, as the species are different, it
>> 1. reinterprets 8 short to 2 short
>> 2. casts 2 short to 2 int
>> 
>> Since we don't support short type with element size less than 4, this situation should be detected as unsupported when trying to generate `VectorReinterpret` node with 2 short, which in current branch is mistaken for 4 short.
>> 
>> I think those workaround code for jdk17(https://github.com/openjdk/jdk17/commit/52788702c11683fbf0e79dca07e75cf1fd8fc334) could be removed entirely in this work.
>
> You are right, I'll fix it.

Kindly remind that those workaround code should be removed after the latest merge.

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PR: https://git.openjdk.java.net/jdk/pull/4839