[jdk17u-dev] RFR: 8309254: Implement fast-path for ASCII-compatible CharsetEncoders on RISC-V [v3]

[Dingli Zhang]

> I would like to backport [JDK-8309254](https://bugs.openjdk.org/browse/JDK-8309254). 
> The backport is not clean because 17u has no  [JDK-8302908](https://bugs.openjdk.org/browse/JDK-8302908), which use v0 as mask register.
> The test `test/hotspot/jtreg/compiler/intrinsics/string/TestEncodeIntrinsics.java` passed and command log with "-XX:+PrintOptoAssembly" output is similar to the mainline:
> 
> ...
> 240     Encode ISO array R12, R11, R13 -> R10 # KILL R12, R11, R13, R28, V1-V3
> ...
> 0118    Encode ASCII array R12, R11, R13 -> R10 # KILL R12, R11, R13, R25, V1-V3
> ...

Dingli Zhang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge remote-tracking branch 'origin/master' into backport-8309254
 - Merge remote-tracking branch 'origin/master' into backport-8309254
 - 8309254: Implement fast-path for ASCII-compatible CharsetEncoders on RISC-V

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

Changes:
  - all: https://git.openjdk.org/jdk17u-dev/pull/1567/files
  - new: https://git.openjdk.org/jdk17u-dev/pull/1567/files/bd1c4506..539e39fe

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1567&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1567&range=01-02

  Stats: 1592 lines in 31 files changed: 944 ins; 283 del; 365 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1567.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1567/head:pull/1567

PR: https://git.openjdk.org/jdk17u-dev/pull/1567