https://twitter.com/aetos382/status/1050820473875877888

GetAttributeInstanceCreator.cs

static Func<CustomAttributeData, TAttribute> GetAttributeInstanceCreator<TAttribute>(
	CustomAttributeData customAttributeData)
{
	var customAttributeDataParameter = Expression.Parameter(typeof(CustomAttributeData));

	var constructorArgumentsExpression = Expression.Property(
		customAttributeDataParameter,
		nameof(CustomAttributeData.ConstructorArguments));

	var listOfConstructorArgumentIndexer = (PropertyInfo)typeof(IList<CustomAttributeTypedArgument>).GetDefaultMembers()[0];

	var constructorArgumentExpressions = new List<Expression>(customAttributeData.ConstructorArguments.Count);

	for (int i = 0; i < customAttributeData.ConstructorArguments.Count; ++i)
	{
		var constructorArgumentItemExpression = Expression.Property(
			constructorArgumentsExpression,
			listOfConstructorArgumentIndexer,
			Expression.Constant(i));

		var constructorArgumentValueExpression = Expression.Property(
			constructorArgumentItemExpression,
			nameof(CustomAttributeTypedArgument.Value));

		var constructorArgumentTypedValueExpression = Expression.Convert(
			constructorArgumentValueExpression,
			customAttributeData.ConstructorArguments[i].ArgumentType);

		constructorArgumentExpressions.Add(constructorArgumentTypedValueExpression);
	}

	var newExpression = Expression.New(
		customAttributeData.Constructor,
		constructorArgumentExpressions);

	var namedArgumentsExpression = Expression.Property(
		customAttributeDataParameter,
		nameof(CustomAttributeData.NamedArguments));

	var memberAssignments = new List<MemberAssignment>();

	var listOfNamedArgumentIndexer = (PropertyInfo)typeof(IList<CustomAttributeNamedArgument>).GetDefaultMembers()[0];

	for (int i = 0; i < customAttributeData.NamedArguments.Count; ++i)
	{
		var namedArgument = customAttributeData.NamedArguments[i];

		var namedArgumentItemExpression = Expression.Property(
			namedArgumentsExpression,
			listOfNamedArgumentIndexer,
			Expression.Constant(i));

		var namedArgumentTypedValueExpression = Expression.Property(
			namedArgumentItemExpression,
			nameof(CustomAttributeNamedArgument.TypedValue));

		var namedArgumentValueExpression = Expression.Property(
			namedArgumentTypedValueExpression,
			nameof(CustomAttributeTypedArgument.Value));

		var bindExpression = Expression.Bind(
			namedArgument.MemberInfo,
			Expression.Convert(
				namedArgumentValueExpression,
				namedArgument.TypedValue.ArgumentType));

		memberAssignments.Add(bindExpression);
	}
	
	var newAndInitExpression = Expression.MemberInit(
		newExpression,
		memberAssignments);

	var lambdaExpression = Expression.Lambda<Func<CustomAttributeData, TAttribute>>(
		newAndInitExpression,
		customAttributeDataParameter);

	return lambdaExpression.Compile();
}

static void Main()
{
	var hogeAttributeData = typeof(Hoge).GetCustomAttributesData().First(b => b.AttributeType == typeof(HogeAttribute));

	var createHogeAttributeDelegate = GetAttributeInstanceCreator<HogeAttribute>(hogeAttributeData);

	var hogeAttribute = createHogeAttributeDelegate(hogeAttributeData);

	hogeAttribute.Dump();
}

[Hoge(1, 2, P = 3, Q = 4, F = 5, G = 6)]
public class Hoge
{
}

public class HogeAttribute : Attribute
{
	public HogeAttribute(int x, int y)
	{
		this.X = x;
		this.Y = y;
	}
	
	public int X { get; }
	
	public int Y { get; }
	
	public int P { get; set; }
	
	public int Q { get; set; }
	
	public int F;
	
	public int G;
}