compiler options were for VC++ 6.0 compiler: 
/nologo /G3 /ML /W3 /GX /Zd /O2 /Ob0 /D "WIN32" /D "NDEBUG" /D "_CONSOLE" /D "_MBCS" Fp"Release/test2.pch" /YX /Fo"Release/" 


Comparing both versions, the pass by reference code requires one "push GPR" instruction less. 


passing by reference:
// saving 1. mov  ecx,dword ptr [esp]
//        2. push ecx,
// compared to the by value version
//
28:   void main()
29:   {
00401040   sub         esp,8
30:       Point  v, v2;
31:
32:      v2=moveRef(v, 1, 2);   
00401043   push        2
00401045   lea         eax,[esp+4]
00401049   push        1
0040104B   push        eax
0040104C   call        moveRef (00401000)
33:       //v2=moveValue(v, 1, 2);
34:
35:       dummy(v2);
00401051   lea         ecx,[esp+0Ch]
00401055   mov         dword ptr [esp+0Ch],eax
00401059   push        ecx
0040105A   mov         dword ptr [esp+14h],edx
0040105E   call        00400000
36:   }
00401063   xor         eax,eax
00401065   add         esp,18h
00401068   ret


passing by value
  void main()
29:   {
00401040   sub         esp,8
30:       Point  v, v2;
31:
32:      //v2=moveRef(v, 1, 2);
33:       v2=moveValue(v, 1, 2);
00401043   mov         eax,dword ptr [esp+4]
00401047   mov         ecx,dword ptr [esp]
0040104B   push        2
0040104D   push        1
0040104F   push        eax
00401050   push        ecx
00401051   call        moveValue (00401020)
00401056   mov         dword ptr [esp+14h],edx
34:
35:       dummy(v2);
0040105A   lea         edx,[esp+10h]
0040105E   push        edx
0040105F   mov         dword ptr [esp+14h],eax
00401063   call        00400000
36:   }
00401068   xor         eax,eax
0040106A   add         esp,1Ch
0040106D   ret


// passing by reference
// costs:
// 1. mov         ecx,dword ptr [esp+4]
// compared to the by reference version
//
10:   struct Point moveRef(const Point& a, int x, int y)
11:   {
12:       Point result = a;
00401000   mov         ecx,dword ptr [esp+4]
00401004   mov         eax,dword ptr [ecx]
00401006   mov         edx,dword ptr [ecx+4]
13:       result.x += x;
00401009   mov         ecx,dword ptr [esp+8]
0040100D   add         eax,ecx
14:       result.y += y;
0040100F   mov         ecx,dword ptr [esp+0Ch]
00401013   add         edx,ecx
15:       return result;
16:   }
00401015   ret


// passing by value
19:   Point moveValue(Point a, int x, int y)
20:   {
21:
22:     a.x += x;
00401020   mov         eax,dword ptr [esp+4]
00401024   mov         edx,dword ptr [esp+0Ch]
23:     a.y += y;
00401028   mov         ecx,dword ptr [esp+10h]
0040102C   add         eax,edx
0040102E   mov         edx,dword ptr [esp+8]
00401032   add         edx,ecx
24:     return a;
25:   }
00401034   ret