Compiler generated IL overrides wrong method

[gafter]

The following program prints "1" instead of "2" as required. That is because the override in Derived is viewed by the runtime as overriding the wrong method (the C# compiler fails to produce the required methodimpl/.override data in the generated assembly).

A similar program with Base.M being abstract generates a type load exception at runtime.

using System;
class Base
{
    public virtual void M(out int x) { x = 1; }
}
abstract class Base2 : Base
{
    public virtual void M(ref int x) { }
}
class Derived : Base2
{
    public override void M(out int x) { x = 3; }
}
class Program
{
    static void Main()
    {
        var b = new Derived();
        b.M(out int x);
        Console.WriteLine(x);
    }
}

[gafter]

Fixed in #44025