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

[Emanuel Peter]

On Mon, 16 Jun 2025 09:39:23 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> src/hotspot/share/opto/compile.cpp line 2526:
>> 
>>> 2524:     print_method(PHASE_ELIMINATE_REACHABILITY_FENCES, 2);
>>> 2525:     if (failing())  return;
>>> 2526:   }
>> 
>> You will have to check the impact on compile time here. Running an extra round of loop opts might be significant.
>> 
>> Do you really need to use a loop opts phase for this? Or would something like `process_for_post_loop_opts_igvn` work for it?
>
> Might be helpful if you write in a comment if this eliminates all or just some of the reachability fences.

Can we limit it to cases where we actually have reachability fences?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25315#discussion_r2149509147