FixUpSquares.cs

public class FixUpSquares : ExpressionVisitor
{
	protected override Expression VisitBinary(BinaryExpression node)
	{
		if(node.NodeType == ExpressionType.Add)
		{
			if(addNode.Left.NodeType == ExpressionType.Constant && addNode.Right.NodeType == ExpressionType.Constant)
			{
				var left = (ConstantExpression) addNode.Left;
				var right = (ConstantExpression) addNode.Right;

				if(EqualityComparer<object>.Default.Equals(left.Value, right.Value))
				{
					node = Expression.Multiply(left, Expression.Constant(2));
				}
			}
		}

		return node;
	}
}