On Wed, 30 Nov 2022 08:43:54 GMT, Aleksey Shipilev <sh...@openjdk.org> wrote:
>> [JDK-8271820](https://bugs.openjdk.org/browse/JDK-8271820) introduced the >> `@Stable private Boolean callerSensitive;` cache in `Method`. That field is >> essentially a tri-state `Boolean` that relies on its `null` value to serve >> as "not initialized" value for `@Stable`. >> >> This works well when the holder `Method` instance is constant: JIT compilers >> fold `@Stable` well. But if such folding fails, we always dereference the >> full-blown reference to "boxed" `Boolean` from the field on every access. We >> can instead do a more lean tri-state primitive field to improve that >> non-optimized case without sacrificing optimized case. >> >> I chose `byte` and `-1`, `0`, `1` to let the fastpath encode well on most >> (all?) architectures. >> >> On adhoc benchmark like: >> >> >> @State(Scope.Thread) >> public class WrapperConstness { >> static final Method CONST; >> static Method NON_CONST; >> >> static { >> try { >> CONST = WrapperConstness.class.getDeclaredMethod("target"); >> NON_CONST = CONST; >> } catch (NoSuchMethodException e) { >> throw new RuntimeException(e); >> } >> } >> >> public void target() {} >> >> @Benchmark >> public void nonConstant() throws Exception { >> NON_CONST.invoke(this); >> } >> >> @Benchmark >> public void constant() throws Exception { >> CONST.invoke(this); >> } >> } >> >> >> We have a minor improvement for non-const case, confirmed due to better >> `isCallerSensitive` access: >> >> >> Benchmark Mode Cnt Score Error Units >> >> # Baseline >> WrapperConstness.constant avgt 25 0.410 ± 0.010 ns/op >> WrapperConstness.nonConstant avgt 25 7.283 ± 0.025 ns/op >> >> # Patched >> WrapperConstness.constant avgt 5 0.407 ± 0.008 ns/op >> WrapperConstness.nonConstant avgt 5 7.054 ± 0.027 ns/op ; -3% >> >> >> Additional testing: >> - [x] Ad-hoc benchmarks >> - [x] Linux x86_64 fastdebug `java/lang/reflect` >> - [x] Linux x86_64 fastdebug `tier1`, `tier2` > > Aleksey Shipilev has updated the pull request incrementally with one > additional commit since the last revision: > > Add a newline Marked as reviewed by alanb (Reviewer). ------------- PR: https://git.openjdk.org/jdk/pull/11422
