`Unsafe.storeStoreFence` currently delegates to stronger `Unsafe.storeFence`. We can teach compilers to map this directly to already existing rules that handle `MemBarStoreStore`. Like explicit `LoadFence`/`StoreFence`, we introduce the special node to differentiate explicit fence and implicit store-store barriers. This node is usually used to simulate safe `final`-field like constructions in special JDK classes, like `ConstantCallSite` and friends.
Motivational performance difference on benchmarks from JDK-8276054 on ARM32: Benchmark Mode Cnt Score Error Units Multiple.plain avgt 3 2.669 ± 0.004 ns/op Multiple.release avgt 3 16.688 ± 0.057 ns/op Multiple.storeStore avgt 3 14.021 ± 0.144 ns/op // Better MultipleWithLoads.plain avgt 3 4.672 ± 0.053 ns/op MultipleWithLoads.release avgt 3 16.689 ± 0.044 ns/op MultipleWithLoads.storeStore avgt 3 14.012 ± 0.010 ns/op // Better MultipleWithStores.plain avgt 3 14.687 ± 0.009 ns/op MultipleWithStores.release avgt 3 45.393 ± 0.192 ns/op MultipleWithStores.storeStore avgt 3 38.048 ± 0.033 ns/op // Better Publishing.plain avgt 3 27.079 ± 0.201 ns/op Publishing.release avgt 3 27.088 ± 0.241 ns/op Publishing.storeStore avgt 3 27.009 ± 0.259 ns/op // Within error, hidden by allocation Single.plain avgt 3 2.670 ± 0.002 ns/op Single.releaseFence avgt 3 6.675 ± 0.001 ns/op Single.storeStoreFence avgt 3 8.012 ± 0.027 ns/op // Worse, seems to be ARM32 implementation artifact As expected, this does not affect x86_64 at all, because both `release` and `storeStore` are effectively no-ops, only affecting compiler optimizations: Benchmark Mode Cnt Score Error Units Multiple.plain avgt 3 0.406 ± 0.002 ns/op Multiple.release avgt 3 0.409 ± 0.018 ns/op Multiple.storeStore avgt 3 0.406 ± 0.001 ns/op MultipleWithLoads.plain avgt 3 4.328 ± 0.006 ns/op MultipleWithLoads.release avgt 3 4.600 ± 0.014 ns/op MultipleWithLoads.storeStore avgt 3 4.602 ± 0.006 ns/op MultipleWithStores.plain avgt 3 0.812 ± 0.001 ns/op MultipleWithStores.release avgt 3 0.812 ± 0.002 ns/op MultipleWithStores.storeStore avgt 3 0.812 ± 0.002 ns/op Publishing.plain avgt 3 6.370 ± 0.059 ns/op Publishing.release avgt 3 6.358 ± 0.436 ns/op Publishing.storeStore avgt 3 6.367 ± 0.054 ns/op Single.plain avgt 3 0.407 ± 0.039 ns/op Single.releaseFence avgt 3 0.406 ± 0.001 ns/op Single.storeStoreFence avgt 3 0.406 ± 0.001 ns/op Additional testing: - [x] Linux x86_64 fastdebug `tier1` ------------- Commit messages: - Formatting - Little cleanup - 8252990: Intrinsify Unsafe.storeStoreFence Changes: https://git.openjdk.java.net/jdk/pull/6136/files Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6136&range=00 Issue: https://bugs.openjdk.java.net/browse/JDK-8252990 Stats: 39 lines in 16 files changed: 33 ins; 5 del; 1 mod Patch: https://git.openjdk.java.net/jdk/pull/6136.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/6136/head:pull/6136 PR: https://git.openjdk.java.net/jdk/pull/6136
