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

[Hamlin Li]

On Wed, 19 Mar 2025 06:50:25 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> Hi please consider.
>> 
>> Added case to turn off UseZvfh when no RVV. 
>> Which is the cause of the test issues, zvfh on but no rvv.
>> 
>> Also made all case identical and added no warning when default.
>> Move them to the common init, as the "UseExtension" is not C2 specific.
>> 
>> Manual tested and some random compiler tests.
>> 
>> Thanks, Robbin
>
> Robbin Ehn has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:
> 
>  - hwprobe deps
>  - Merge branch 'master' into maxvector_0
>  - Moved to common
>  - Disable UseZvfh when no RVV

src/hotspot/cpu/riscv/vm_version_riscv.hpp line 92:

> 90:   void update_flag() {                     \
> 91:       assert(enabled(), "Must be.");       \
> 92:       if (FLAG_IS_DEFAULT(flag)) {         \

As this patch introduces a way to automatically disable a flag based on its dependant flag, this could introduce potential issue if the expected order is not guarantee when writing the code. It's better to have an assert there, this could be acheive by just using the existing `_value`, e.g. 
`assert(dep.value() != -1);`
Or maybe it's better to introduce a new field like `initialized`?

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PR Review Comment: https://git.openjdk.org/jdk/pull/24094#discussion_r2005832663