Why didn't the compiler use the same object reference for the static expression tree?

Question

As I know, expression trees are immutable , so why didn't the compiler use the same object reference for a static expression as string literals?

To clarify the issue, see an example:

static void Main(string[] args)
{
    Test(p => true);//2637164
    Test(p => true);//3888474
    Test("true");//-292522067
    Test("true");//-292522067
    Console.ReadKey();
}

public static void Test(Expression<Func<string,bool>> exp)
{
    Console.WriteLine(exp.GetHashCode());
}

public static void Test(string str)
{
    Console.WriteLine(str.GetHashCode());
}

Answer 1

As I know, expression trees are immutable, so why did the compiler not use the same object reference for a static expression, such as string literals?

The spectrum says that the compiler is allowed but not required to set identical lambdas.

String literals are interned at run time for free; There is no cost to the compiler developer.

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Answer 2

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