RFR: 8336856: Optimize String Concat [v23]

[Shaojin Wen]

On Fri, 2 Aug 2024 00:59:06 GMT, Shaojin Wen <duke at openjdk.org> wrote:

>> The current implementation of StringConcat is to mix the coder and length into a long. This operation will have some overhead for int/long/boolean types. We can separate the calculation of the coder from the calculation of the length, which can improve the performance in the scenario of concat int/long/boolean.
>> 
>> This idea comes from the suggestion of @l4es in the discussion of PR https://github.com/openjdk/jdk/pull/20253#issuecomment-2240412866
>
> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix performance regression caused by args.erase()

The following test will see the performance regression


git checkout d573c297219115976ad03f70fbd7777aedc3d4b8
make test TEST="micro:java.lang.StringConcat.concatConst6Object" MICRO="VM_OPTIONS=-Djava.lang.invoke.StringConcat.highArityThreshold=0"

git checkout e2b30b3f5f74ba8881e3674f3e0beef12883b138
make test TEST="micro:java.lang.StringConcat.concatConst6Object" MICRO="VM_OPTIONS=-Djava.lang.invoke.StringConcat.highArityThreshold=0"



# d573c29
Benchmark                        (intValue)  Mode  Cnt   Score   Error  Units
StringConcat.concatConst6Object        4711  avgt   15  74.717 ? 8.146  ns/op

# e2b30b3
Benchmark                        (intValue)  Mode  Cnt   Score   Error  Units
StringConcat.concatConst6Object        4711  avgt   15  51.573 ? 0.385  ns/op

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PR Comment: https://git.openjdk.org/jdk/pull/20273#issuecomment-2264308978