[riscv-port] RFR: 8278994: riscv: RVC: basic instruction set

[Xiaolin Zheng]

On Mon, 20 Dec 2021 08:10:10 GMT, Xiaolin Zheng <xlinzheng at openjdk.org> wrote:

> Hi team,
> 
> This patch includes the basic definition of the RVC instruction set and some cleanups. Tested a simple `test/hotspot/jtreg/compiler/` folder on qemu.
> 
> Thanks,
> Xiaolin

I have discussed with Yadong and we may hold the optional `RVC_Assembler` implementation temporarily. This will not affect the `CompressibleRegion` implementation so please feel safe. Now this patch might be ready to review because it seems less possible to change in design, and thank you for your patience.

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PR: https://git.openjdk.java.net/riscv-port/pull/34