RFR: 8325821: [REDO] use "dmb.ishst+dmb.ishld" for release barrier [v5]

[Andrew Haley]

On Thu, 23 May 2024 05:59:03 GMT, kuaiwei <duke at openjdk.org> wrote:

>> Yes, usually they can be merged in macroAssembler. but  it can help to reduce the possibility of unmerged case. Thanks to point it.
>
> I checked code again. They will be merged if enable AlwaysMergeDMB. So we can skip the check.

Add a comment:

`// These will be merged if AlwaysMergeDMB is enabled.`

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PR Review Comment: https://git.openjdk.org/jdk/pull/19278#discussion_r1618693680