RFR: 8290892: C2: Intrinsify Reference.reachabilityFence [v14]

[Vladimir Ivanov]

On Wed, 24 Sep 2025 02:50:13 GMT, Dean Long <dlong at openjdk.org> wrote:

>> Vladimir Ivanov has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   scalarization support
>
> src/hotspot/share/opto/escape.cpp line 1230:
> 
>> 1228:     SafePointNode* sfpt = safepoints.at(spi)->as_SafePoint();
>> 1229:     JVMState *jvms      = sfpt->jvms();
>> 1230:     uint merge_idx      = (sfpt->req() - jvms->scloff());
> 
> The use of `sfpt->req()` looks wrong here, if `sfpt` still has non-debug edges.

Good catch, Dean! Will be fixed in the next update.

> Is it changing the behavior?

It doesn't. The sole purpose of the change is to please the assert in `create_scalarized_object_description()`.

At the end of successful call, `create_scalarized_object_description()` extends debug info to cover all newly added inputs. And the failure is non-recoverable. So, the very first iteration of the loop extends debug info beyond those 2 edges.  

I'll add a comment.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25315#discussion_r2377036545
PR Review Comment: https://git.openjdk.org/jdk/pull/25315#discussion_r2377068613