RVC by default (cont'd)

[Xiaolin Zheng]

Hi team,
As RVC's proposed patches have been merged into the mainline, in response to the former thread[1] I would like to turn it on by default before the December RDP 1 deadline, for currently the hardware feature C extension has been ratified and implemented by mainstream RISC-V hardware like boards produced by Hifive, meaning we can test and verify our implementation on physical boards.
Opening another thread to refresh the content.
We can turn RVC on for now by using `-XX:+UnlockExperimentalVMOptions -XX:+UseRVC`. In addition we can examine the generated code by using options `-XX:+UnlockExperimentalVMOptions -XX:+UseRVC -XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly -XX:PrintAssemblyOptions=no-aliases,numeric,show-bytes` combined.
I have pushed a simple proposed patch[2] to turn it as default true.
The only thing I shall mention here is as we know there is a known issue that may relate to the opensbi lib. Please see previous discussions[3][4]. The pattern of that issue is very easy to be distinguished, which is an uncommon case and which turns out to be bugs hidden in underlying libraries at last. I think it should be users' responsibility to update their outdated libs, and such issue shall not stop our pace.
I have opened an JBS issue[5] to record this, marking it as "Won't fix".
If there's any suggestion or objection, please let me know. If not, I will file a patch around Nov 15 (may be next week since the deadline is looming) if everything looks okay.
Best Regards,
Xiaolin
[1] https://mail.openjdk.org/pipermail/riscv-port-dev/2022-September/000609.html <https://mail.openjdk.org/pipermail/riscv-port-dev/2022-September/000609.html >
[2] https://github.com/zhengxiaolinX/jdk/commit/b5b9c64529c27c40542f8cda720652fabf70682d <https://github.com/zhengxiaolinX/jdk/commit/b5b9c64529c27c40542f8cda720652fabf70682d >
[3] https://mail.openjdk.org/pipermail/riscv-port-dev/2022-September/000618.html <https://mail.openjdk.org/pipermail/riscv-port-dev/2022-September/000618.html >
[4] https://github.com/riscv-collab/riscv-openjdk/issues/23 <https://github.com/riscv-collab/riscv-openjdk/issues/23 >
[5] https://bugs.openjdk.org/browse/JDK-8296350 <https://bugs.openjdk.org/browse/JDK-8296350 >
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