RFR: 8371319: java.lang.reflect.Method#equals doesn't short-circuit with same instances

[Chen Liang]

There is currently no shortcut for fast equals for Method or Constructor. While the comparison for declaring class, name (interned strings' identity), and return type are very efficient with identity comparison, the comparison for parameter type is not so much: We always have to iterate through every parameter.

Luckily, even though we are burdened with the different method and constructor instance due to setAccessible, their parameter type arrays are shared most of the time; in particular, in the same root method/constructor hierarchy, all instances share the same method object. Thus, we can perform a `==` check on the incoming array to provide a fast path.

Benchmark numbers before and after:

Benchmark                                    Mode  Cnt  Score   Error  Units
ExecutableCompareBenchmark.distinctParams    avgt    5  1.189 ± 0.024  ns/op
ExecutableCompareBenchmark.equalMethods      avgt    5  2.449 ± 0.033  ns/op
ExecutableCompareBenchmark.sameMethodObject  avgt    5  0.541 ± 0.027  ns/op

Benchmark                                    Mode  Cnt  Score   Error  Units
ExecutableCompareBenchmark.distinctParams    avgt    5  1.186 ± 0.042  ns/op
ExecutableCompareBenchmark.equalMethods      avgt    5  1.078 ± 0.049  ns/op
ExecutableCompareBenchmark.sameMethodObject  avgt    5  0.395 ± 0.018  ns/op

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Commit messages:
 - Short-circuiting for equal methods

Changes: https://git.openjdk.org/jdk/pull/28221/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28221&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371319
  Stats: 88 lines in 2 files changed: 88 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28221.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28221/head:pull/28221

PR: https://git.openjdk.org/jdk/pull/28221