[jdk17u-dev] RFR: 8304976: Optimize DateTimeFormatterBuilder.ZoneTextPrinterParser.getTree()

[Oli Gillespie]

Hi all,

This pull request contains a backport of commit [438c969b](https://github.com/openjdk/jdk/commit/438c969b7b07eeef0158b089e5a168849e04bf56) from the [openjdk/jdk](https://git.openjdk.org/jdk) repository.

The commit being backported was authored by Sergey Tsypanov on 29 Mar 2023 and was reviewed by Naoto Sato.

Since the original uses the new `newHashMap` and `newHashSet` methods from https://bugs.openjdk.org/browse/JDK-8284780 which are not here in 17, I've not included those changes in the backport. They are not a significant part of the original fix, the main point of the change is kept which is avoiding the creation of 2 new hash sets on the cached path. Running the included benchmark confirms the performance improvement even with the omissions:

Base:

Benchmark                                                  Mode  Cnt      Score     Error   Units
ZonedDateTimeFormatterBenchmark.parse                      avgt   20  18248.082 ? 166.440   ns/op
ZonedDateTimeFormatterBenchmark.parse:?gc.alloc.rate       avgt   20   1274.964 ?  11.448  MB/sec
ZonedDateTimeFormatterBenchmark.parse:?gc.alloc.rate.norm  avgt   20  24400.418 ?   1.591    B/op
ZonedDateTimeFormatterBenchmark.parse:?gc.count            avgt   20     44.000            counts
ZonedDateTimeFormatterBenchmark.parse:?gc.time             avgt   20     35.000                ms


Patch:

Benchmark                                                  Mode  Cnt    Score   Error   Units
ZonedDateTimeFormatterBenchmark.parse                      avgt   20  923.943 ? 8.737   ns/op
ZonedDateTimeFormatterBenchmark.parse:?gc.alloc.rate       avgt   20  883.450 ? 8.163  MB/sec
ZonedDateTimeFormatterBenchmark.parse:?gc.alloc.rate.norm  avgt   20  856.021 ? 0.079    B/op
ZonedDateTimeFormatterBenchmark.parse:?gc.count            avgt   20   32.000          counts
ZonedDateTimeFormatterBenchmark.parse:?gc.time             avgt   20   27.000              ms

-------------

Commit messages:
 - Backport 438c969b7b07eeef0158b089e5a168849e04bf56

Changes: https://git.openjdk.org/jdk17u-dev/pull/1414/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1414&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304976
  Stats: 60 lines in 2 files changed: 57 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1414.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1414/head:pull/1414

PR: https://git.openjdk.org/jdk17u-dev/pull/1414