RFR: 8336635: Add IR test for Reference.refersTo intrinsic [v2]

[Tobias Hartmann]

On Wed, 17 Jul 2024 11:01:08 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> As the follow-up for [JDK-8256999](https://bugs.openjdk.org/browse/JDK-8256999), we can directly test for the (absence of) GC barriers in C2 `Reference.refersTo` intrinsic. This would be come less relevant for G1 after Late Barrier expansion lands, but would still be relevant for Shenandoah for a while. It would also be good for backports.
>> 
>> Additional testing:
>>  - [x] Test fails when I deliberately remove `AS_NO_KEEPALIVE` from the C2 intrinsic
>>  - [x] Test passes with GC explicitly passed as `TEST_VM_OPTS`
>
> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Ditch Epsilon test that might run out of memory

Looks good to me otherwise. I submitted this through our testing and will report back once it passed.

test/hotspot/jtreg/compiler/c2/irTests/gc/ReferenceRefersToTests.java line 33:

> 31: /*
> 32:  * @test
> 33:  * @bug 8336635

Should this refer to `8256999` instead?

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Marked as reviewed by thartmann (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20215#pullrequestreview-2185555347
PR Review Comment: https://git.openjdk.org/jdk/pull/20215#discussion_r1682681133