[jdk22] RFR: 8324688: C2: Disable ReduceAllocationMerges by default

[Vladimir Kozlov]

On Thu, 25 Jan 2024 10:27:37 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

> Due to several recent bug reports after the integration of [JDK-8287061](https://bugs.openjdk.org/browse/JDK-8287061) in JDK 22 (latest one being [JDK-8322854](https://bugs.openjdk.org/browse/JDK-8322854)), we've decided together with @JohnTortugo that we want to minimize the risk and that it's best to disable `ReduceAllocationMerges` by default for JDK 22 which disables the optimizations of [JDK-8287061](https://bugs.openjdk.org/browse/JDK-8287061). 
> 
> Thanks,
> Christian

Good. I approved this fix request for JDK 22.

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Marked as reviewed by kvn (Reviewer).

PR Review: https://git.openjdk.org/jdk22/pull/97#pullrequestreview-1844206989