Examining code generated by the Visual Studio C++ compiler, part 1 [duplicate]

Answer 1

This doesn't really answer the question, but is a helpful hint. Instead of mucking around with the OllyDbg.exe thing, you can make Visual Studio generate the asm file for you, which has the added bonus that it can put in the original source code as comments. This isn't a big deal for your current small project, but as your project grows, you may end up spending a fair amount of time figuring out which assembly code matches which source code.

From the command line, you want the /FAs and /Fa options (MSDN).

Here's part of the output for your example code (I compiled debug code, so the .asm is longer, but you can do the same thing for your optimized code):

_wmain  PROC                        ; COMDAT

; 8    : {

    push    ebp
    mov ebp, esp
    sub esp, 216                ; 000000d8H
    push    ebx
    push    esi
    push    edi
    lea edi, DWORD PTR [ebp-216]
    mov ecx, 54                 ; 00000036H
    mov eax, -858993460             ; ccccccccH
    rep stosd

; 9    :     int x=5; int y=1024;

    mov DWORD PTR _x$[ebp], 5
    mov DWORD PTR _y$[ebp], 1024        ; 00000400H
$LN2@wmain:

; 10   :     while(x) { x--; y/=2; }

    cmp DWORD PTR _x$[ebp], 0
    je  SHORT $LN1@wmain
    mov eax, DWORD PTR _x$[ebp]
    sub eax, 1
    mov DWORD PTR _x$[ebp], eax
    mov eax, DWORD PTR _y$[ebp]
    cdq
    sub eax, edx
    sar eax, 1
    mov DWORD PTR _y$[ebp], eax
    jmp SHORT $LN2@wmain
$LN1@wmain:

; 11   :     return x+y;

    mov eax, DWORD PTR _x$[ebp]
    add eax, DWORD PTR _y$[ebp]

; 12   : }

    pop edi
    pop esi
    pop ebx
    mov esp, ebp
    pop ebp
    ret 0
_wmain  ENDP

Hope that helps!