RFR: 8342382: Implement JEP 522: G1 GC: Improve Throughput by Reducing Synchronization [v54]

[Christian Hagedorn]

On Wed, 10 Sep 2025 08:28:26 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> With the decreased complexity of the barrier, C2 started unrolling that loop. I do not know how to determine a bound here.
>
> Is this going to be GC independent? What if the VM swaps to another GC ergonomically?

The test runs with `vm.flagless`. But I suggest to just go with `>= 1` instead to be on the safe side. The purpose of this IR rule in the context of this test is really just that it does not fail and not about catching real issues/verifying the IR.

If we still want to test the improved loop unrolling opportunities, I suggest to create a separate IR test for it, possibly in a separate RFE.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23739#discussion_r2336052099