RFR: 8320995: RISC-V: C2 PopCountVI [v4]

[Hamlin Li]

> Hi,
> Can you help to review this patch?
> Both auto-vect and vector api depends on this intrinsic.
> Thanks!
> 
> ## Performance
> Not performance test was done, as this depends on vcpop.v instruction in zvbb extension and the code seqeunce is rather simple than non-intrinsic version.

Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:

  minor fix

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/19065/files
  - new: https://git.openjdk.org/jdk/pull/19065/files/f316f660..cbfde208

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19065&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19065&range=02-03

  Stats: 9 lines in 3 files changed: 0 ins; 3 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/19065.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19065/head:pull/19065

PR: https://git.openjdk.org/jdk/pull/19065