Integrated: 8329597: C2: Intrinsify Reference.clear

[Aleksey Shipilev]

On Thu, 11 Jul 2024 15:28:37 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> [JDK-8240696](https://bugs.openjdk.org/browse/JDK-8240696) added the native method for `Reference.clear`. The original patch skipped intrinsification of this method, because we thought `Reference.clear` is not on a performance sensitive path. However, it shows up prominently on simple benchmarks that touch e.g. `ThreadLocal` cleanups. See the bug for an example profile with `RRWL` benchmarks.
> 
> We need to know the actual oop strongness/weakness before we call into C2 Access API, this work models this after existing code for `refersTo0` intrinsics. C2 Access also need a support for `AS_NO_KEEPALIVE` for stores. 
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `all`
>  - [x] Linux AArch64 server fastdebug, `all`

This pull request has now been integrated.

Changeset: 7625b299
Author:    Aleksey Shipilev <shade at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/7625b29920e95f9b754057fe0a2c4ab0afa5cb0c
Stats:     362 lines in 26 files changed: 341 ins; 0 del; 21 mod

8329597: C2: Intrinsify Reference.clear

Reviewed-by: rcastanedalo, eosterlund, kvn

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PR: https://git.openjdk.org/jdk/pull/20139