Why reflection lookup on Java 8 is much slower than on Java 13?

[igabaydulin]

• Benchmark results on Java 8

Benchmark                                                 Mode  Cnt    Score    Error  Units
c.g.i.r.j.b.compile.Instance.newInstance                  avgt    5    5.399 ±  2.618  ns/op
c.g.i.r.j.b.compile.PublicMethodDirectAccess.invoke       avgt    5    3.412 ±  1.776  ns/op
c.g.i.r.j.b.other.HashMapBenchmark.put                    avgt    5   59.235 ± 17.800  ns/op
c.g.i.r.j.b.other.JacksonBenchmark.jacksonMapping         avgt    5  262.843 ± 22.358  ns/op
c.g.i.r.j.b.runtime.PrivateMethodReflectionAccess.invoke  avgt    5    9.890 ±  6.709  ns/op
c.g.i.r.j.b.runtime.PrivateMethodReflectionAccess.lookup  avgt    5  413.902 ± 52.149  ns/op
c.g.i.r.j.b.runtime.PublicMethodReflectionAccess.invoke   avgt    5    9.881 ±  4.878  ns/op
c.g.i.r.j.b.runtime.PublicMethodReflectionAccess.lookup   avgt    5  412.168 ± 66.915  ns/op
c.g.i.r.j.b.runtime.ReflectionInstance.newInstance        avgt    5   46.380 ±  4.468  ns/op

• Benchmark results on Java 13 (pull request)

Benchmark                                                 Mode  Cnt    Score    Error  Units
c.g.i.r.j.b.compile.Instance.newInstance                  avgt    5    5.618 ±  2.549  ns/op
c.g.i.r.j.b.compile.PublicMethodDirectAccess.invoke       avgt    5    3.682 ±  0.701  ns/op
c.g.i.r.j.b.other.HashMapBenchmark.put                    avgt    5   52.031 ± 13.063  ns/op
c.g.i.r.j.b.other.JacksonBenchmark.jacksonMapping         avgt    5  314.913 ± 20.882  ns/op
c.g.i.r.j.b.runtime.PrivateMethodReflectionAccess.invoke  avgt    5    7.161 ±  4.484  ns/op
c.g.i.r.j.b.runtime.PrivateMethodReflectionAccess.lookup  avgt    5   51.903 ±  9.042  ns/op
c.g.i.r.j.b.runtime.PublicMethodReflectionAccess.invoke   avgt    5    7.301 ±  4.643  ns/op
c.g.i.r.j.b.runtime.PublicMethodReflectionAccess.lookup   avgt    5   50.762 ±  4.371  ns/op
c.g.i.r.j.b.runtime.ReflectionInstance.newInstance        avgt    5   69.863 ± 18.715  ns/op

On local machine results are pretty the same no matter which Java version is used. Maybe default JVM args differ or some optimisations are not enabled for unknown reason yet :)

It would be interesting to solve it 🤓