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

[Ningsheng Jian]

On Thu, 31 Mar 2022 08:55:05 GMT, Xiaohong Gong <xgong 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).

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