RFR: 8296975: RISC-V: Enable UseRVA20U64 profile by default [v3]

[Xiaolin Zheng]

On Wed, 16 Nov 2022 05:21:52 GMT, Xiaolin Zheng <xlinzheng at openjdk.org> wrote:

>> The main purpose is to turn the option `UseRVC` on by default before JDK20 RDP 1. As per discussions [1], we can enable `UseRVA20U64`[2] by default to fulfill this.
>> 
>> 
>>> build/linux-riscv64-server-fastdebug/images/jdk/bin/java -XX:+PrintFlagsFinal -version | grep -E "UseRVC|UseRVA20U64"
>>      bool UseRVA20U64                              = true                                 {ARCH product} {default}
>>      bool UseRVC                                   = true                                 {ARCH product} {default}
>> openjdk version "20-internal" 2023-03-21
>> OpenJDK Runtime Environment (fastdebug build 20-internal-adhoc..jdk)
>> OpenJDK 64-Bit Server VM (fastdebug build 20-internal-adhoc..jdk, mixed mode)
>> 
>> 
>> [1] https://mail.openjdk.org/pipermail/riscv-port-dev/2022-November/000668.html
>> [2] https://github.com/openjdk/jdk/blob/873eccde01895de06e2216f6838d52d07188addd/src/hotspot/cpu/riscv/vm_version_riscv.cpp#L39-L44
>> 
>> Thanks,
>> Xiaolin
>
> Xiaolin Zheng has updated the pull request incrementally with one additional commit since the last revision:
> 
>   minor issue if users specify command line -XX:+UseRVA20U64 and RVC is not supported

> I mean something like [d75b565](https://github.com/openjdk/jdk/commit/d75b565dabc1dab3c508d2b4b83d34af5a1c7a35) (it hasn't been built or tested).

Thanks for the explanation :-)  I see, and your solution looks far better than mine. But making `UseRVA20U64` as default true is an opinion from @VladimirKempik discussed in the mailing list, so I would also like to ask if he is okay with this.

(I guess the `vm_exit_during_initialization` would make `UseRVA20U64` hard to become a default option though, for Java should start normally anywhere.)

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PR: https://git.openjdk.org/jdk/pull/11155