[vectorIntrinsics] RFR: 8283749: AArch64: Add the backend support for vector bitcount

[Xiaohong Gong]

On Wed, 6 Apr 2022 03:31:45 GMT, Ningsheng Jian <njian at openjdk.org> wrote:

>> This patch adds the NEON and SVE backend match rules for the vector bitcount operations which both work for the vector api
>> and auto-vectorization.
>> 
>> Note that the "`PopCountVI`" node is used for vectors with "`byte/short/int`" basic types while "`PopCountVL`" is used for
>> vectors with long basic type. And also note that the output basic type of "`PopCountVL`" is "`T_LONG`" when it is generated
>> by vector api and it is "`T_INT`" when generated by SLP.
>> 
>> Also enables "`test/hotspot/jtreg/compiler/vectorization/TestPopCountVectorLong.java`" for SVE.
>
> Marked as reviewed by njian (Committer).

Thanks for the review @nsjian !

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PR: https://git.openjdk.java.net/panama-vector/pull/188