RFR: 8352218: RISC-V: Zvfh requires RVV [v2]

[Robbin Ehn]

On Thu, 20 Mar 2025 13:44:36 GMT, Hamlin Li <mli at openjdk.org> wrote:

> I'm fine with either way, maybe we should put the change of Fei's suggestion into another PR?

As this additional change do not change the behavior of UseFlags.
It only changes that ext_Zv?? will not be enable if there is no ext_V.

Another options is to set this directly in hwprobe query:
`if (VM_Version::ext_V.enable_feature() && is_set(RISCV_HWPROBE_KEY_IMA_EXT_0, RISCV_HWPROBE_EXT_ZVFH)) {`

So the issue you describe 3 is already there. Which is essentialy the cpu string will contain cpu features that are disabled.
(as none reads the RVFeature's after boot)
And as I said the issue is building feature string from RVFeatureValue instead of the UseFlags.

I think this should go in as is, and a follow up to address the cpu string.
So the cpu string, as the other platforms, reflect 'active ISA'.

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PR Comment: https://git.openjdk.org/jdk/pull/24094#issuecomment-2740578758