[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`
- [ ] Linux x86_64 fastdebug `tier1`, `tier2`
-------------
Commit messages:
- Fix
Changes: https://git.openjdk.org/jdk/pull/11422/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11422&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8297784
Stats: 8 lines in 1 file changed: 3 ins; 0 del; 5 mod
Patch: https://git.openjdk.org/jdk/pull/11422.diff
Fetch: git fetch https://git.openjdk.org/jdk pull/11422/head:pull/11422
PR: https://git.openjdk.org/jdk/pull/11422
