RFR: 8329597: C2: Intrinsify Reference.clear [v9]

[Yudi Zheng]

On Wed, 9 Oct 2024 08:44:34 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`
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 18 commits:
> 
>  - Simplify: just do keep alive checks
>  - Merge branch 'master' into JDK-8329597-intrinsify-reference-clear
>  - More precise bit-unmasks
>  - Reconcile with late barrier expansion in G1
>  - Merge branch 'master' into JDK-8329597-intrinsify-reference-clear
>  - Review comments
>  - Merge branch 'master' into JDK-8329597-intrinsify-reference-clear
>  - Also dispatch to slow-path on other arches
>  - Fix other arches
>  - Tighten up comments in Reference javadoc
>  - ... and 8 more: https://git.openjdk.org/jdk/compare/580eb62d...9f7ad7ab

src/hotspot/share/gc/z/zBarrierSetRuntime.hpp line 43:

> 41:   static void store_barrier_on_oop_field_with_healing(oop* p);
> 42:   static void store_barrier_on_oop_field_without_healing(oop* p);
> 43:   static void no_keepalive_store_barrier_on_oop_field_without_healing(oop* p);

Could you please export this to JVMCI? I.e.,

diff --git a/src/hotspot/share/jvmci/vmStructs_jvmci.cpp b/src/hotspot/share/jvmci/vmStructs_jvmci.cpp
index 5452cca96b8..46aeb996c56 100644
--- a/src/hotspot/share/jvmci/vmStructs_jvmci.cpp
+++ b/src/hotspot/share/jvmci/vmStructs_jvmci.cpp
@@ -847,6 +847,7 @@
   ZGC_ONLY(DECLARE_FUNCTION_FROM_ADDR(declare_function_with_value, ZBarrierSetRuntime::load_barrier_on_oop_field_preloaded_store_good))           \
   ZGC_ONLY(DECLARE_FUNCTION_FROM_ADDR(declare_function_with_value, ZBarrierSetRuntime::no_keepalive_load_barrier_on_weak_oop_field_preloaded))    \
   ZGC_ONLY(DECLARE_FUNCTION_FROM_ADDR(declare_function_with_value, ZBarrierSetRuntime::no_keepalive_load_barrier_on_phantom_oop_field_preloaded)) \
+  ZGC_ONLY(DECLARE_FUNCTION_FROM_ADDR(declare_function_with_value, ZBarrierSetRuntime::no_keepalive_store_barrier_on_oop_field_without_healing)   \
   ZGC_ONLY(DECLARE_FUNCTION_FROM_ADDR(declare_function_with_value, ZBarrierSetRuntime::store_barrier_on_native_oop_field_without_healing))        \
   ZGC_ONLY(DECLARE_FUNCTION_FROM_ADDR(declare_function_with_value, ZBarrierSetRuntime::store_barrier_on_oop_field_with_healing))                  \
   ZGC_ONLY(DECLARE_FUNCTION_FROM_ADDR(declare_function_with_value, ZBarrierSetRuntime::store_barrier_on_oop_field_without_healing))               \

Thanks!

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PR Review Comment: https://git.openjdk.org/jdk/pull/20139#discussion_r1800848130