RFR: 8319883: Zero: Use atomic built-ins for 64-bit accesses

[Aleksey Shipilev]

On Sun, 12 Nov 2023 22:11:46 GMT, David Holmes <dholmes at openjdk.org> wrote:

> Seems reasonable. Can I assume that the correct volatile access memory semantics are handled at a higher-level?

Yes, `Platform(Load|Store)` is about the relaxed accesses. The generic atomic code wraps these in `ScopedFence` that emits `OrderAccess` fences around the access, if stronger semantics is needed. As the follow-up, we might consider specializing `PlatformOrdered(Load|Store)` for Zero to avoid using fences, but it does not look necessary at the moment.

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PR Comment: https://git.openjdk.org/jdk/pull/16600#issuecomment-1807264821