Avoid array cloning in Path.Get*Chars

[stephentoub]

It's faster to just allocate a new array.
Per comment at #11293 (comment)
cc: @jkotas

[jkotas]

👍

[stephentoub]

Test Innerloop Windows_NT Debug Build and Test please (known AV in coreclr)

[drieseng]

Did you mean to remove this?

[stephentoub]

Yes. It's now in the other partial files.

[drieseng]

I'm waiting for someone from MS to treath this like it's a community contribution, and ask you to show the numbers ;-)

[stephentoub]

I'm waiting for someone from MS to treath this like its a community contribution, and ask you to show the numbers ;-)

Code:

using System;
using System.Diagnostics;
using System.Runtime.CompilerServices;

class Program
{
    static void Main()
    {
        const int Iters = 10000000;
        var sw = new Stopwatch();
        while (true)
        {
            sw.Restart();
            for (int i = 0; i < Iters; i++) GetClone();
            sw.Stop();
            Console.WriteLine($"Clone: {sw.Elapsed.TotalSeconds}");

            sw.Restart();
            for (int i = 0; i < Iters; i++) GetNew();
            sw.Stop();
            Console.WriteLine($"New  : {sw.Elapsed.TotalSeconds}");

            Console.WriteLine();
        }
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    static char[] GetClone() => (char[])Array.Clone();

    [MethodImpl(MethodImplOptions.NoInlining)]
    static char[] GetNew() => new char[]
    {
        '\"', '<', '>', '|', '\0',
        (char)1, (char)2, (char)3, (char)4, (char)5, (char)6, (char)7, (char)8, (char)9, (char)10,
        (char)11, (char)12, (char)13, (char)14, (char)15, (char)16, (char)17, (char)18, (char)19, (char)20,
        (char)21, (char)22, (char)23, (char)24, (char)25, (char)26, (char)27, (char)28, (char)29, (char)30,
        (char)31
    };

    static readonly char[] Array = GetNew();
}

64-bit Results:

Clone: 0.8212021
New  : 0.1450638

Clone: 0.7894494
New  : 0.1448052

Clone: 0.8033437
New  : 0.1470242

Clone: 0.8033267
New  : 0.1465283

32-bit Results:

Clone: 1.0977963
New  : 0.1940705

Clone: 1.0942017
New  : 0.1991546

Clone: 1.0645428
New  : 0.1985613