RFR: 8309254: Implement fast-path for ASCII-compatible CharsetEncoders on RISC-V [v2]

[Dingli Zhang]

> [JDK-8274242](https://bugs.openjdk.org/browse/JDK-8274242) propose to extend the x86 ISO-8859-1 encoding intrinsic to work 
> also for ASCII-compatible encodings, which helps speeding up various 
> CharsetEncoders. Implementing a similar intrinsic should be considered on 
> RISC-V as well.
> 
> The instruct log with -XX:+PrintOptoAssembly output looks like:
> 
> 06e +   Encode ISO array R12, R11, R13 -> R10 # KILL R12, R11, R13, R7, V0-V3
> 
> 
> ## Testing:
> qemu w/ UseRVV:
> - [x] Tier1 tests (release)
> - [x] Tier2 tests (release)
> - [x] Tier3 tests (release)
> - [x] test/hotspot/jtreg/compiler/intrinsics/string/TestEncodeIntrinsics.java

Dingli Zhang has updated the pull request incrementally with one additional commit since the last revision:

  Add missing space

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/14256/files
  - new: https://git.openjdk.org/jdk/pull/14256/files/00eb80b6..a42fa50b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14256&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14256&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/14256.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14256/head:pull/14256

PR: https://git.openjdk.org/jdk/pull/14256