RFR: 8290892: C2: Intrinsify Reference.reachabilityFence [v11]

[Dean Long]

On Fri, 12 Sep 2025 14:00:53 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Vladimir Ivanov has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Minor fix
>
> src/hotspot/share/opto/reachability.cpp line 81:
> 
>> 79:  * (c) Unfortunately, it's not straightforward to stay with safepoint-attached representation till the very end,
>> 80:  * because information about derived oops is attached to safepoints in a similar way. So, for now RFs are
>> 81:  * rematerialized at safepoints before RA (phase #3).
> 
> I still don't understand this. What is similar to what? And why is that a problem?

Why don't we put RF edges somewhere else, so they don't look like derived oops?  I was thinking they could go in the monitor area, or if that causes problems, we introduce a new area.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25315#discussion_r2353965620