Benchmarks for #115746 (davidwrighton) #433

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

namespace PInvokeBenchmark
{
    public class PInvokeBenchmarks
    {
        // Define a delegate type for our managed function
        private delegate int ManagedDelegate(bool value);
        
        // Define a matching function pointer type for unmanaged calls
        private unsafe delegate int UnmanagedDelegate(bool value);
        
        // The managed implementation
        private static int ManagedImplementation(bool value)
        {
            return value ? 42 : 0;
        }
        
        // Our instance of the delegate
        private readonly ManagedDelegate _managedDelegate;
        
        // Marshaled function pointer
        private readonly unsafe delegate* unmanaged<bool, int> _nativeFunctionPointer;
        
        // Delegate wrapping the marshaled function pointer
        private readonly unsafe delegate* unmanaged<bool, int> _unmanagedDelegate;

        // P/Invoke declaration for the native method
        [DllImport(@"C:\temp\pinvokeBench\NativeDll\NativeDll.dll", CallingConvention = CallingConvention.Cdecl)]
        private static extern int Method(bool value);


        public unsafe PInvokeBenchmarks()
        {
            // Create the managed delegate
            _managedDelegate = ManagedImplementation;

            // Marshal it to a native function pointer
            _nativeFunctionPointer = (delegate* unmanaged<bool, int>)Marshal.GetFunctionPointerForDelegate(_managedDelegate);

        }

        [Benchmark]
        public unsafe int MarshaledDelegateCall()
        {
            return _nativeFunctionPointer(true);
        }
    }
}