RFR: 8259948: Aarch64: Add cast nodes for Aarch64 Neon backend [v2]

[Eric Liu]

On Fri, 6 Aug 2021 09:48:50 GMT, Wang Huang <whuang at openjdk.org> wrote:

>> * In this issue, we plan to complete all missing implementation for aarch64 neon backend. For example, cast from Byte to Long, cast from Long to Byte, and so on.
>> * It may be a solver of JDK-8269866, or part of it.
>
> Wang Huang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix code style

src/hotspot/cpu/aarch64/aarch64_neon.ad line 308:

> 306: %}
> 307: 
> 308: instruct vcvt2Sto2I(vecD dst, vecD src)

Do we really need this rule? There still have some mid-end issues remained[1] that some vector sizes could be marked as unsupported in advance.  

I suppose some rules are useless after that fix.

[1] https://github.com/openjdk/jdk/pull/3507/files#r623691031

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