While loop in IL - why stloc.0 and ldloc.0?
- by Michael Stum
I'm trying to understand how a while loop looks in IL. I have written this C# function:
static void Brackets()
{
while (memory[pointer] > 0)
{
// Snipped body of the while loop, as it's not important
}
}
The IL looks like this:
.method private hidebysig static void Brackets() cil managed
{
// Code size 37 (0x25)
.maxstack 2
.locals init ([0] bool CS$4$0000)
IL_0000: nop
IL_0001: br.s IL_0012
IL_0003: nop
// Snipped body of the while loop, as it's not important
IL_0011: nop
IL_0012: ldsfld uint8[] BFHelloWorldCSharp.Program::memory
IL_0017: ldsfld int16 BFHelloWorldCSharp.Program::pointer
IL_001c: ldelem.u1
IL_001d: ldc.i4.0
IL_001e: cgt
IL_0020: stloc.0
IL_0021: ldloc.0
IL_0022: brtrue.s IL_0003
IL_0024: ret
} // end of method Program::Brackets
For the most part this is really simple, except for the part after cgt.
What I don't understand is the local [0] and the stloc.0/ldloc.0. As far as I see it, cgt pushes the result to the stack, stloc.0 gets the result from the stack into the local variable, ldloc.0 pushes the result to the stack again and brtrue.s reads from the stack.
What is the purpose of doing this? Couldn't this be shortened to just cgt followed by brtrue.s?
