[jdk16] RFR: 8260585: AArch64: Wrong code generated for shifting right and accumulating four unsigned short integers [v4]

[Dong Bo]

> This is a typo introduced by JDK-8255949.
> Compiler will generate `ushr` for shifting right and accumulating four short integers.
> It produces wrong results for specific case. The instruction should be `usra`.

Dong Bo has updated the pull request incrementally with two additional commits since the last revision:

 - fix trailing whitespace
 - add tests for shifting counts

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

Changes:
  - all: https://git.openjdk.java.net/jdk16/pull/136/files
  - new: https://git.openjdk.java.net/jdk16/pull/136/files/b7ef8fb8..f2e490a3

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk16&pr=136&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk16&pr=136&range=02-03

  Stats: 286 lines in 1 file changed: 245 ins; 6 del; 35 mod
  Patch: https://git.openjdk.java.net/jdk16/pull/136.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16 pull/136/head:pull/136

PR: https://git.openjdk.java.net/jdk16/pull/136