RFR: 8321003: RISC-V: C2 MulReductionVI [v2]

[Hamlin Li]

> Hi,
> Can you help to review this patch to implement MulReductionVI/MulReductionVL/MulReductionVF/MulReductionVD?
> On riscv, there is no straightforward instructions to do it, but we can do it with a reduction tree, which could reduce the time complexity to lg(N).
> Thanks
> 
> ## Performance
> TBD

Hamlin Li has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - merge master
 - fix issues
 - Initial commit

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

Changes: https://git.openjdk.org/jdk/pull/19015/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19015&range=01
  Stats: 147 lines in 8 files changed: 147 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19015.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19015/head:pull/19015

PR: https://git.openjdk.org/jdk/pull/19015