Is there a way to see the native code produced by theJITter for given C# / CIL?

Question

In a comment on this answer (which suggests using bit-shift operators over integer multiplication / division, for performance), I queried whether this would actually be fast

Answer 1

While you're debugging (and only while you're debugging) just click at Debug - Windows - Disassembly or press the corresponding shortcut Ctrl+Alt+D.

Answer 2

You won't get meaningful results until you configure the debugger. Tools + Options, Debugging, General, turn off "Suppress JIT optimization on module load". Switch to the Release mode configuration. A sample snippet:

static void Main(string[] args) {
  int value = 4;
  int result = divideby2(value);
}

You are doing it right if the disassembly looks like this:

00000000  ret  

You'll have to fool the JIT optimizer to force the expression to be evaluated. Using Console.WriteLine(variable) can help. Then you ought to see something like this:

0000000a  mov         edx,2 
0000000f  mov         eax,dword ptr [ecx] 
00000011  call        dword ptr [eax+000000BCh] 

Yup, it evaluated the result at compile time. Works pretty well, doesn't it.

Answer 3

Yes. Visual Studio has a built in disassembler to do that. You have to add the command to your menu bar though. Go to Extras/Customize/Commands (I don't know if they are really called that way in the english version though) and add the command Dissassembly, which is unter Debugging, somewhere to your menu bar.

Then, set a breakpoint in your program and when it breaks, click on this Disassembly command. VS will show you the disassembled machine code.

Example output for a Divider-method:

public static int Divider(int intArg)
    {
00000000  push        ebp  
00000001  mov         ebp,esp 
00000003  push        edi  
00000004  push        esi  
00000005  push        ebx  
00000006  sub         esp,34h 
00000009  mov         esi,ecx 
0000000b  lea         edi,[ebp-38h] 
0000000e  mov         ecx,0Bh 
00000013  xor         eax,eax 
00000015  rep stos    dword ptr es:[edi] 
00000017  mov         ecx,esi 
00000019  xor         eax,eax 
0000001b  mov         dword ptr [ebp-1Ch],eax 
0000001e  mov         dword ptr [ebp-3Ch],ecx 
00000021  cmp         dword ptr ds:[00469240h],0 
00000028  je          0000002F 
0000002a  call        6BA09D91 
0000002f  xor         edx,edx 
00000031  mov         dword ptr [ebp-40h],edx 
00000034  nop              
    return intArg / 2;
00000035  mov         eax,dword ptr [ebp-3Ch] 
00000038  sar         eax,1 
0000003a  jns         0000003F 
0000003c  adc         eax,0 
0000003f  mov         dword ptr [ebp-40h],eax 
00000042  nop              
00000043  jmp         00000045 
    }