Is there any performance increase by changing this .NET string to a const? Does the IL automatically do that?

Question

Given the following simple .NET code, is there any difference between these two, under the hood with respect to the string \"xml\"?

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Answer 1

Even more awesome, is that if there's another "xml" string used in another place, the compiler will only make one const creation and both of those references will refer to that single string reference/memory alloc.

This is normal behavior since .NET make "string interning" by default so many variables will references the same memory allocation

So .NET automatically performs string interning for all string literals. This is done by means of an intern pool – a special table that stores references to all unique strings.

Only explicitly declared string literals are interned on the compile stage. The strings created at runtime are not checked for being already added to the pool. For example:

Interning example

string s="AB";   //will be interned  
string s1 ="C";    
string s2 = s1+s2  //will not be interned 

For your first question no there is no differences since at compilation time the compiler can make a smart decision of replacing the variable by the content since const is hardcoded which make a better performance so you will not see any performance increase.