RFR: 8316961: Fallback implementations for 64-bit Atomic::{add,xchg} on 32-bit platforms [v2]

[David Holmes]

On Fri, 20 Oct 2023 12:00:50 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> ...and on the other hand, it requires platforms to implement 8-byte CAS:

Surely the `supports_cx8` issue must have been raised when the template atomics were put in place. I need to go back and see what was said then, to see how we got in this mess.

I can accept the current proposal doesn't make the mess worse, it just shone a light on the fact there is a mess. If ARMv6 is broken then maybe it needs to be dropped? (Not in this PR of course.)

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PR Comment: https://git.openjdk.org/jdk/pull/16252#issuecomment-1774345744