Use existing Range vectorized fill in Enumerable.OrderBy

[stephentoub]

We already have a method that vectorizes the fill in Enumerable.Range. We can use the same helper in OrderBy when filling the integer map used to enable stability.

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

BenchmarkSwitcher.FromAssembly(typeof(Tests).Assembly).Run(args);

[HideColumns("Job", "Error", "StdDev", "Median", "RatioSD")]
public class Tests
{
    private IEnumerable<int> _data;

    [Params(4, 40, 400)]
    public int Count { get; set; }

    [GlobalSetup]
    public void Setup() => _data = Enumerable.Range(0, Count).ToArray();

    [Benchmark]
    public int OrderBy()
    {
        int sum = 0;
        foreach (int value in _data.OrderBy(i => i))
            sum += value;
        return sum;
    }
}

Method	Toolchain	Count	Mean	Ratio
OrderBy	\main\corerun.exe	4	98.84 ns	1.00
OrderBy	\pr\corerun.exe	4	99.85 ns	1.01
OrderBy	\main\corerun.exe	40	515.74 ns	1.00
OrderBy	\pr\corerun.exe	40	490.10 ns	0.95
OrderBy	\main\corerun.exe	400	6,716.60 ns	1.00
OrderBy	\pr\corerun.exe	400	6,200.64 ns	0.93