--------------------------------------------
--------------------------------------------
Case 1
-------------------------------------------
main()
{
  int i;

  for(i=1;i<=2;i++){printf("test out\n"); }
  printf("end\n");
}

------------------------------------------
-O0 No Optimization
------------------------------------------
        .section        .rodata
.LC0:
        .byte    0x74,0x65,0x73,0x74,0x20,0x6f,0x75,0x74,0xa,0x0
.LC1:
        .byte    0x65,0x6e,0x64,0xa,0x0
.text
        .p2align 2,0x90
.globl main
                .type            main,@function
main:
        pushl %ebp
        movl %esp,%ebp
        subl $24,%esp
        nop
        movl $1,-4(%ebp)
        .p2align 2,0x90
.L3:
        cmpl $2,-4(%ebp)
        jle .L6
        jmp .L4
        .p2align 2,0x90
.L6:
        addl $-12,%esp
        pushl $.LC0
        call printf
        addl $16,%esp
.L5:
        incl -4(%ebp)
        jmp .L3
        .p2align 2,0x90
.L4:
        addl $-12,%esp
        pushl $.LC1
        call printf
        addl $16,%esp
.L2:
        leave
        ret
.Lfe1:
                .size            main,.Lfe1-main
        .ident  "GCC: (GNU) c 2.95.4 20020320 [FreeBSD]"

------------------------------------------
  cc -O3 Max Optimization
------------------------------------------
        .file   "test-opt1.c"
        .version        "01.01"
gcc2_compiled.:
        .section        .rodata
.LC0:
        .byte    0x74,0x65,0x73,0x74,0x20,0x6f,0x75,0x74,0xa,0x0
.LC1:
        .byte    0x65,0x6e,0x64,0xa,0x0
.text
        .p2align 2,0x90
.globl main
                .type            main,@function
main:
        pushl %ebp
        movl %esp,%ebp
        subl $20,%esp
        pushl %ebx
        movl $1,%ebx
        .p2align 2,0x90
.L6:
        addl $-12,%esp
        pushl $.LC0
        call printf
        addl $16,%esp
        decl %ebx
        jns .L6
        addl $-12,%esp
        pushl $.LC1
        call printf
        movl -24(%ebp),%ebx
        leave
        ret
.Lfe1:
                .size            main,.Lfe1-main
        .ident  "GCC: (GNU) c 2.95.4 20020320 [FreeBSD]"

--------------------------------------------
--------------------------------------------
Case 2
--------------------------------------------
--------------------------------------------

main()
{
  int i,x;

  i=2;
  x=1+i;
  printf("result=%d\n",x);
}
--------------------------------------------
No Optimization
--------------------------------------------
        .file   "test-opt2.c"
        .version        "01.01"
gcc2_compiled.:
        .section        .rodata
.LC0:
        .byte    0x72,0x65,0x73,0x75,0x6c,0x74,0x3d,0x25,0x64,0xa
        .byte    0x0
.text
        .p2align 2,0x90
.globl main
                .type            main,@function
main:
        pushl %ebp
        movl %esp,%ebp
        subl $24,%esp
        movl $2,-4(%ebp)
        movl -4(%ebp),%eax
        incl %eax
        movl %eax,-8(%ebp)
        addl $-8,%esp
        movl -8(%ebp),%eax
        pushl %eax
        pushl $.LC0
        call printf
        addl $16,%esp
.L2:
        leave
        ret
.Lfe1:
                .size            main,.Lfe1-main
        .ident  "GCC: (GNU) c 2.95.4 20020320 [FreeBSD]"

--------------------------------------------
Max Optimization
--------------------------------------------

        .file   "test-opt2.c"
        .version        "01.01"
gcc2_compiled.:
        .section        .rodata
.LC0:
        .byte    0x72,0x65,0x73,0x75,0x6c,0x74,0x3d,0x25,0x64,0xa
        .byte    0x0
.text
        .p2align 2,0x90
.globl main
                .type            main,@function
main:
        pushl %ebp
        movl %esp,%ebp
        subl $8,%esp
        addl $-8,%esp
        pushl $3
        pushl $.LC0
        call printf
        leave
        ret
.Lfe1:
                .size            main,.Lfe1-main
        .ident  "GCC: (GNU) c 2.95.4 20020320 [FreeBSD]"
------------------------------------------------
Case 3
-------------------------------------------------

main()
{
  long i,x;
  x=0;
  for(i=1;i<100000000;i++){x=x+i; }
  printf("result=%d\n",x);
}
------------------------------------------------
% cc -O0 test-opt1.c

% time a.out

result=887459712
0.301u 0.000s 0:00.31 96.7%     5+167k 0+0io 0pf+0w

% cc -O3 test-opt1.c

% time a.out

result=887459712
0.114u 0.000s 0:00.11 100.0%    5+192k 0+0io 0pf+0w