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c#performanceinitializationjitil

Does initialization of local variable with null impacts performance?

Lets compare two pieces of code:

String str = null;
//Possibly do something...
str = "Test";
Console.WriteLine(str);

and 

String str;
//Possibly do something...
str = "Test";
Console.WriteLine(str);

I was always thinking that these pieces of code are equal. But after I have build these code (Release mode with optimization checked) and compared IL methods generated I have noticed that there are two more IL instructions in the first sample:

1st sample code IL:

.maxstack 1
.locals init ([0] string str)
IL_0000: ldnull
IL_0001: stloc.0
 IL_0002: ldstr "Test"
IL_0007: stloc.0
IL_0008: ldloc.0
IL_0009: call void [mscorlib]System.Console::WriteLine(string)
IL_000e: ret

2nd sample code IL:

.maxstack 1
.locals init ([0] string str)
IL_0000: ldstr "Test"
IL_0005: stloc.0
IL_0006: ldloc.0
IL_0007: call void [mscorlib]System.Console::WriteLine(string)
IL_000c: ret

Possibly this code is optimized by JIT compiller? So does the initialization of local bethod variable with null impacts the performence (I understand that it is very simple operation but any case) and we should avoid it? Thanks beforehand.

Solution

  • http://www.codinghorror.com/blog/2005/07/for-best-results-dont-initialize-variables.html

    To summarize from the article, after running various benchmarks, initializing an object to a value (either as part of a definition, in the class' constructor, or as part of an initialization method) can be anywhere from roughly 10-35% slower on .NET 1.1 and 2.0. Newer compilers may optimize away initialization on definition. The article closes by recommending to avoid initialization as a general rule.