RFR: 8300109: RISC-V: Improve code generation for MinI/MaxI nodes [v3]

[Fei Yang]

> As described by the issue, code generation for MinI/MaxI nodes on RISC-V could be improved when one of the source register is the same as the destination register. Also the code could be further simplified when that source register is constant 0 making use of the dedicated zero register of the architecture. This adds new match rules for those cases. 
> 
> Testing:
> - [x] Run the new jtreg test added by: https://github.com/openjdk/jdk/pull/11570
> - [x] Tier1-3 tested with release build on HiFive Unmatched board.
> - [x] Run non-trivial benchmark workloads (dacapo, specjvm, renaissance, etc) with fastdebug build on HiFive Unmatched board.

Fei Yang 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 four additional commits since the last revision:

 - Comment
 - Merge branch 'master' into JDK-8300109
 - Comment
 - 8300109: RISC-V: Improve code generation for MinI/MaxI nodes

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/11988/files
  - new: https://git.openjdk.org/jdk/pull/11988/files/a17a391c..1264837c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11988&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11988&range=01-02

  Stats: 1418 lines in 60 files changed: 492 ins; 360 del; 566 mod
  Patch: https://git.openjdk.org/jdk/pull/11988.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11988/head:pull/11988

PR: https://git.openjdk.org/jdk/pull/11988