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

[Eric Liu]

On Thu, 12 Aug 2021 14:12:28 GMT, Wu Yan <wuyan at openjdk.org> wrote:

>> 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
>
> This rule has fixed the problem you mentioned. As for other problems, I'm not sure whether they still exist.

Currently, we are *not* going to support small vector lane count which less than 64bits[1][2]. I prefer to fix the mid-end problem first and remove this kind of rules in this patch.
 
[1] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/matcher.hpp#L341
[2] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/aarch64/aarch64.ad#L2491

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