RE: MSIL Inquiry involving boxing
- From: jetan@xxxxxxxxxxxxxxxxxxxx ("Jeffrey Tan[MSFT]")
- Date: Thu, 24 Aug 2006 10:10:10 GMT
Hi Ben,
Based on my test, I will get the similar result as you, below is what I got
from Reflector:
method private hidebysig static void Main() cil managed
{
.entrypoint
.maxstack 3
.locals init (
[0] object[] objArray1,
[1] object obj1,
[2] object[] objArray2)
L_0000: ldc.i4.3
L_0001: newarr object
L_0006: stloc.2
L_0007: ldloc.2
L_0008: ldc.i4.0
L_0009: ldc.i4.1
L_000a: box int32
L_000f: stelem.ref
L_0010: ldloc.2
L_0011: ldc.i4.1
L_0012: ldstr "Hello"
L_0017: stelem.ref
L_0018: ldloc.2
L_0019: ldc.i4.2
L_001a: ldc.i4.s 123
L_001c: box int32
L_0021: stelem.ref
...
}
I can not find the usage of retrieving the address of local variable with
*ldloca.s* instruction. The decision of IL output is controlled by the C#
compiler. This means the offical Microsoft provided C# compiler will try to
generate a redundant local variable for holding the about-to-be-box value.
I am not sure of what C# compiler the author used. I will try to test this
on Rotor.
I think the output provided by the tutorial author may not be a pratical C#
compiler generation, since it event does not generate *init* keyword for
locals. The keyword *init* means that the local variables must be
initialized before the method executes. I think this is an important
keyword for a commercial C# compiler, since it can leverage CLR's
verification process to detect the security hole/programming error for the
developer.
Anyway, I think you'd better contact the author of the tutorial for which
compiler he used to generate his sample output. Thanks.
Regarding the boxing for local variable address issue, this is handled by
JIT compiler in CLR. I think JIT compiler will take care of getting the
value data from the address and do boxing with this value data. If you are
curious with the boxing process, the most clear way of understanding it is
looking the Rotor source code for boxing. This souce code is defined in
Jitinterface.cpp JIT_Box() function(Rotor1.0). <Shared Source CLI
Essentials> gives box/unbox an explanation with source code in chapter3.
You may comiple the IL code provided by the IL tutorial and set a
breakpoint in JIT_Box function, then you will see the call stack of the
CLR, which you may find out how box instruction is doing under the cover.
Hope this helps.
Best regards,
Jeffrey Tan
Microsoft Online Community Support
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