RFR: 8347981: RISC-V: Add Zfa zli imm loads [v3]

[Fei Yang]

On Thu, 23 Jan 2025 07:10:25 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> src/hotspot/cpu/riscv/vm_version_riscv.hpp line 160:
>> 
>>> 158:   decl(ext_Zbs         , "Zbs"         , RV_NO_FLAG_BIT, true , UPDATE_DEFAULT(UseZbs))         \
>>> 159:   decl(ext_Zcb         , "Zcb"         , RV_NO_FLAG_BIT, true , UPDATE_DEFAULT(UseZcb))         \
>>> 160:   decl(ext_Zfa         , "Zfa"         , RV_NO_FLAG_BIT, true , UPDATE_DEFAULT(UseZfa))         \
>> 
>> Are we auto-enabling an experimental feature?
>
> No, as Zfa is not mapped in RiscvHwprobe::add_features_from_query_result() I don't see how it would auto enbled?
> 
>  UPDATE_DEFAULT only updates "Use flag" after the extension, if it is default, i.e. not set by user, no?
> 
> As we have a two step mechanism hwprobe -> extensions flag -> Use flag.
> 
> But if you want I can do it the other way around, add it to hwprobe but do not update the Use flag?

Ah, I see. Thanks. Let's keep the current shape. We can auto-enable it when we have the hardware for testing.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23171#discussion_r1926486760