RFR: 8354572: Turn off AlwaysMergeDMB for Ampere CPU by default

Tue Apr 15 10:00:45 UTC 2025

On Tue, 15 Apr 2025 09:02:36 GMT, Andrew Haley <aph at openjdk.org> wrote:

> Please post the numbers here.

Hi @theRealAph, I ran the benchmark from [JDK-8354572](https://bugs.openjdk.org/browse/JDK-8354572) with `-UseStoreStoreForCtor`, and the thoughput is ~51.1k ops/ms for `-AlwaysMergeDMB` on Ampere1, while it is ~23.8k ops/ms for `+AlwaysMergeDMB`.

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PR Comment: https://git.openjdk.org/jdk/pull/24652#issuecomment-2804499135