RFR: 8290892: C2: Intrinsify Reference.reachabilityFence [v3]

[Vladimir Ivanov]

On Mon, 26 May 2025 11:45:21 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> `ReachabilityFence` accepts only OOPs as a referent and `DecodeNKlass` produces `Klass` pointer.
>> 
>> I suspect it may be the case for safepoints as well (and `is_DecodeNarrowPtr()` is a a leftover from PermGen world), but I didn't check.
>
> Right, nevermind about `DecodeNKlass` then. My question on heap loads still stands: do we actually get `reachabilityFence(someField)` from anywhere?

Are you asking specifically about `ReachabilityFence -> DecodeN -> LoadN` shape? Yes, it's common, especially after inlining.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25315#discussion_r2112616254