RFR: 8290892: C2: Intrinsify Reference.reachabilityFence [v8]

[Vladimir Ivanov]

On Fri, 12 Sep 2025 13:18:33 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>>> Is this rf guaranteed to belong to the Allocation somehow?
>> 
>> I don't get your question. The code iterates over users of an allocation which is being eliminated.  Semantically, RF is a no-op on a scalarizable referent and has to be removed in order to let the scalarization happen.
>> 
>>> Ah, you could mention that later ReachabilityFenceNode::Identity removes the rf.
>> 
>> Done.
>
> @iwanowww

The code in `PhaseMacroExpand::process_users_of_allocation` iterates over direct users of result cast from Allocation nodes. And RF is not special there. Any other case in `PhaseMacroExpand::process_users_of_allocation()` would be affected.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25315#discussion_r2356922289