RFR: 8316654: remove edundant dmb after casal instruction

[Stuart Monteith]

On Thu, 21 Sep 2023 09:33:59 GMT, Sun Jianye <jianyesun at openjdk.org> wrote:

> Hi,all.
> The `casal` means a CAS operate with both load-acquire and store-release semantics.It looks like the subsequent dmb is redundant. Can we remove it?

I don't think this is correct. The DMB is necessary for when the CASAL fails, the release semantics only applies for that instruction when the write is successful.

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PR Comment: https://git.openjdk.org/jdk/pull/15856#issuecomment-1729329265