RFR: 8368732: RISC-V: Detect support for misaligned vector access via hwprobe [v2]

[Fei Yang]

On Fri, 26 Sep 2025 08:36:19 GMT, Hamlin Li <mli at openjdk.org> wrote:

>> Fei Yang has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains three new commits since the last revision:
>> 
>>  - More white spaces
>>  - White spaces
>>  - 8368732: RISC-V: Detect support for misaligned vector access via hwprobe
>
> src/hotspot/cpu/riscv/vm_version_riscv.cpp line 181:
> 
>> 179:   }
>> 180: 
>> 181:   if (FLAG_IS_DEFAULT(AlignVector) && unaligned_vector.enabled()) {
> 
> Seems this `unaligned_vector.enabled` is not necessary?

The purpose is to give a consistent view of how the these extensions should be used. That is we only use the value of the extension when it is enabled. Otherwise, we are relying on the default value -1, which doesn't seem safe to me. And it shouldn't be a issue in performance to have this check here. What do you think?

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PR Review Comment: https://git.openjdk.org/jdk/pull/27512#discussion_r2386558533