c# – 在循环期间保持静态的属性的编译器优化

If you use data that is static for the duration of the loop,obtain it
before the loop instead of repeatedly accessing a field or property.

以下代码作为示例给出：

for (int item = 0; item < Customer.Orders.Count; item++)
{
   CalculateTax(Customer.State,Customer.Zip,Customer.Orders[item]);
}

变

string state = Customer.State;
string zip = Customer.Zip;
int count = Customers.Orders.Count;
for (int item = 0; item < count; item++)
{
   CalculateTax(state,zip,Customer.Orders[item]);
}

文章指出：

Note that if these are fields,it may be possible for the compiler to
do this optimization automatically. If they are properties,it is much
less likely. If the properties are virtual,it cannot be done
automatically.

为什么编译器以这种方式优化属性“更不可能”,何时可以预期特定属性是否被优化？我假设在访问器中执行附加操作的属性对于编译器来说更难以优化,并且那些仅修改后备字段的属性更可能被优化,但是需要一些更具体的规则.自动实现的属性是否始终优化？