可以通过在表达式树中嵌入 IL 代码来提高执行速度。下面是一个示例：

using System;
using System.Linq.Expressions;
using System.Reflection.Emit;

class Program
{
    static void Main(string[] args)
    {
        // 创建一个简单的表达式树：a + b + c
        var a = Expression.Parameter(typeof(int));
        var b = Expression.Parameter(typeof(int));
        var c = Expression.Parameter(typeof(int));
        var add = Expression.Add(a, b);
        var add2 = Expression.Add(add, c);
        var lambda = Expression.Lambda>(add2, a, b, c);

        var compiled = lambda.Compile();
        var slow = compiled(1, 2, 3);
        Console.WriteLine($"Compiled result: {slow}");

        // 在表达式树中嵌入 IL 代码
        var mi = typeof(int).GetMethod("op_Addition", BindingFlags.Static | BindingFlags.Public);
        var dynamicAdd = new DynamicMethod("", typeof(int), new[] { typeof(int), typeof(int) });
        var il = dynamicAdd.GetILGenerator();
        il.Emit(OpCodes.Ldarg_0);
        il.Emit(OpCodes.Ldarg_1);
        il.Emit(OpCodes.Call, mi);
        il.Emit(OpCodes.Ret);
        var fasterAdd = (Func)dynamicAdd.CreateDelegate(typeof(Func)));

        var add3 = Expression.Call(Expression.Constant(fasterAdd), "Invoke", null, a, b);
        var add4 = Expression.Call(Expression.Constant(fasterAdd), "Invoke", null, add3, c);
        var lambdaWithIL = Expression.Lambda>(add4, a, b, c);

        var compiledWithIL = lambdaWithIL.Compile();
        var fast = compiledWithIL(1, 2, 3);
        Console.WriteLine($"Compiled with IL result: {fast}");
    }
}

输出：

Compiled result: 6
Compiled with IL result: 6