RFR: 8353572: x86: AMD platforms miss the check for CLWB feature flag [v3]

[Aleksey Shipilev]

On Wed, 9 Apr 2025 18:34:30 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Noticed this when doing [JDK-8353558](https://bugs.openjdk.org/browse/JDK-8353558). We only check for CLWB feature flag for Intel platforms. But AMD APM (Rev. 3.36—March 2024) tells me there is a CLWB flag in CPUID Fn0000_0007_EBX_x0 leaf as well. It is in the same place as the flag for Intel.
>> 
>> Additional testing:
>>  - [x] Ad-hoc tests on Ryzen 5950X
>
> Aleksey Shipilev 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 five additional commits since the last revision:
> 
>  - Add assert
>  - Merge branch 'master' into JDK-8353572-amd-clwb
>  - More feature flag commonning
>  - Merge branch 'master' into JDK-8353572-amd-clwb
>  - Fix

Or @vnkozlov?

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PR Comment: https://git.openjdk.org/jdk/pull/24385#issuecomment-2802682639