RFR: 8318776: Require supports_cx8 to always be true [v5]

[David Holmes]

On Wed, 22 Nov 2023 15:50:17 GMT, Doug Lea <dl at openjdk.org> wrote:

>> David Holmes 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 seven additional commits since the last revision:
>> 
>>  - Merge with master and update Zero code accordingly
>>  - Merge branch 'master' into 8318776-supports_cx8
>>  - Remove unnecessary includes of vm_version.hpp.
>>    Fix copyright years.
>>  - Remove cx8 comment as no longer relevant (the spinlock is used regardless of cx8)
>>  - Remove suports_cx8() checks from gtest
>>  - Remove test for VMSupportsCX8
>>  - 8318776: Require supports_cx8 to always be true
>
> The deletion of backup code and the check for it in java.util.concurrent.AtomicLongFieldUpdater are clearly OK. We always thought the need for it was transient.

Thanks for looking at this @DougLea !

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PR Comment: https://git.openjdk.org/jdk/pull/16625#issuecomment-1823770525