RFR: 8290892: C2: Intrinsify Reference.reachabilityFence [v19]

[Vladimir Ivanov]

On Thu, 30 Oct 2025 15:40:51 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Can you write a comment what `ctrl`? Is it the `referent_ctrl`?
>
> Ah no, in all cases I could see it was actually the `rf` itself, right? Why not give it a more specific name?

> But it seems you are using it from different places. Can you find a better name?

Both IGVN (`ReachabilityFenceNode::Identity()`) and `PhaseIdealLoop` perform redundant RF elimination, so `is_redundant_rf_helper` is there so they can share the same implementation. I could name it `is_redundant_rf`, but it doesn't look like an improvement to me. It's tailored specifically for those 2 particular use cases and it is not intended to be used outside `reachability.cpp`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25315#discussion_r2487894458