[K/JS] KT-68860 Optimize listOf(element)

[lppedd]

See https://youtrack.jetbrains.com/issue/KT-68860

Note that the better approach (I was unsure if I could do it) would be to make arrayListOf(vararg) and mutableListOf(vararg) expect functions, so that on the JS actual side we can leverage the fact we can pass in an Array<T> to the constructor. That optimization would cover a much wider range of usages. This could be done afterwards tho.

@JSMonk

[fzhinkin]

Does the change actually optimize listOf's performance in any way?

[lppedd]

@fzhinkin with the following kotlinx-benchmark class

@State(Scope.Benchmark)
class ListOfBenchmark {
    val element = "abc"

    @Benchmark
    fun arrayListOfBenchmark(bh: Blackhole) {
        val l = arrayListOf(element)
        bh.consume(l)
    }

    @Benchmark
    fun arrayListBenchmark(bh: Blackhole) {
        val a = ArrayList<String>(arrayOf(element))
        bh.consume(a)
    }
}

I see

Benchmark                              Mode  Cnt         Score         Error    Units
ListOfBenchmark.arrayListBenchmark    thrpt    5  43439677.834 ± 2379846.100  ops/sec
ListOfBenchmark.arrayListOfBenchmark  thrpt    5  25355418.456 ±  923573.170  ops/sec

A straightforward ArrayList(array) call seems to win consistently on my machine.