[riscv-port] RFR: 8277440: riscv: Move UseVExt from product to experimental [v2]

[Fei Yang]

On Fri, 19 Nov 2021 09:43:32 GMT, Yanhong Zhu <yzhu at openjdk.org> wrote:

>> Currently, riscv port supports vector operations which is fully compatible with vector extension 1.0 spec. And we have passed tier 1-4 tests with option "-XX:+UseVExt" with QEMU.
>> 
>> Due to lack of native environment which supports vector extension 1.0, we cannot carry out tests for vector operations on real hardware. So we decided to move port-specific option UseVExt from product to experimental for now, and rename UseVExt to UseRVV.
>> 
>> This also fixes some typos in comments, and  removes unused v extension instructions.
>> 
>> The test results on HiFive Unleashed board (rv64imafdc) and NeZha D1 board (rv64imafdcvu) are in line with expectations.
>
> Yanhong Zhu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Set UseRVV EXPERIMENTAL

Thanks for cleanup. Looks good.

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Marked as reviewed by fyang (Lead).

PR: https://git.openjdk.java.net/riscv-port/pull/11