RFR: 8290892: C2: Intrinsify Reference.reachabilityFence [v2]

Wed Sep 17 21:32:06 UTC 2025

On Fri, 12 Sep 2025 14:09:52 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

> Extra compile-time due to extra loop-opts round. https://github.com/openjdk/jdk/pull/25315#discussion_r2330176841 . It used to be a 20% increase, now you managed to make it only 10%. Still considerable. 

FTR 10% increase in loop opts time is observed with `-XX:+StressReachabiltyFences`.

> All of it just to call get_ctrl(referent) in enumerate_interfering_sfpts.

Well, I wouldn't frame it in such a way. RF elimination transformation relies on dominance information computed by `PhaseIdealLoop` to produce control input for each referent. And there are many other transformations under `PhaseIdealLoop` which "just" rely on dominance info it produces.

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PR Comment: https://git.openjdk.org/jdk/pull/25315#issuecomment-3304621503