RFR: 8315338: RISC-V: Change flags for stable extensions to non-experimental

[Robbin Ehn]

On Wed, 6 Sep 2023 08:55:59 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

> Hi all, please consider.
> 
> These flags can be automatically turned on if you are using a 6.5 kernel with the proper hardware.
> So they are not considered experimental.
> 
> Running tier1

> There is still no hardware support for these extensions for now. IMHO, it's better to keep the experimental flags for them. We could add some checks to prevent enabling these experimental extensions by default:
> 
> ```c++
> if (!UnlockExperimentalVMOptions && UseRVV) {
>   FLAG_SET_DEFAULT(UseRVV, false);
> }
> ```
> ```

I think the nice thing auto enabling of these is that we get a lot of bake-time.
Manually adding the options for your hardware/qemu setup is often overlooked.
Just my 5 cent.

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PR Comment: https://git.openjdk.org/jdk/pull/15585#issuecomment-1717539663