Codegen for ModuleInitializer and static readonly fields

ModuleInitializer_static_readonly.cs

using System;
using System.Runtime.CompilerServices;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

BenchmarkRunner.Run<Bench>();

[ShortRunJob]
[DisassemblyDiagnoser]
public class Bench
{
    [Benchmark]
    public double GetConstValue_DefaultConst() => DefaultConst.Sqrt2;

    [Benchmark]
    public double GetConstValue_CCtorConst() => CCtorConst.Sqrt2;

    [Benchmark]
    public double GetConstValue_ModuleInitializerConst() => ModuleInitializerConst.Sqrt2;

    [Benchmark]
    public double UseValueInLoop_DefaultConst()
    {
        double s = 0;

        for (int i = 0; i < 1_000; ++i)
        {
            s += DefaultConst.Sqrt2;
        }

        return s;
    }

    [Benchmark]
    public double UseValueInLoop_CCtorConst()
    {
        double s = 0;

        for (int i = 0; i < 1_000; ++i)
        {
            s += CCtorConst.Sqrt2;
        }

        return s;
    }

    [Benchmark]
    public double UseValueInLoop_ModuleInitializerConst()
    {
        double s = 0;

        for (int i = 0; i < 1_000; ++i)
        {
            s += ModuleInitializerConst.Sqrt2;
        }

        return s;
    }
}

public static class DefaultConst
{
    public static readonly double Sqrt2 = Math.Sqrt(2);
}

public static class CCtorConst
{
    public static readonly double Sqrt2;

    static CCtorConst() => Sqrt2 = Math.Sqrt(2);
}

public static class ModuleInitializerConst
{
    public static readonly double Sqrt2 = Math.Sqrt(2);

    [ModuleInitializer]
    public static void DummyAccessToInit()
    {
        _ = Sqrt2;
    }
}

(At least for .NET 6) a cctor and module initializer yield good code too.

public static class CCtorConst1
{
    public static readonly double Sqrt2;

    static CCtorConst1() => Sqrt2 = Math.Sqrt(2);

    [ModuleInitializer]
    internal static void Init()
    {
        _ = Sqrt2;
    }
}

results in the same code as with ModuleInitializerConst.