反匯編的時候帶上C代碼便于觀察

?

比較三元表達式和if else的差異

a1.c

#include <stdio.h>  int main(void)  
{  
int a=1;
int b=2;
int c=0;
a = (b>c)?1:0;
return 0;
}

a2.c

#include <stdio.h>  int main(void)  
{  
int a=1;
int b=2;
int c=0;
if(b>c)
{
a=1;
}
else
{
a=0;
}
return 0;
} 

?

編譯

#gcc -g a1.c

反匯編

#objdump -dS a.out

#include <stdio.h>  int main(void)  
{  8048394:       55                      push   %ebp8048395:       89 e5                   mov    %esp,%ebp8048397:       83 ec 10                sub    $0x10,%esp
int a=1;804839a:       c7 45 f4 01 00 00 00    movl   $0x1,-0xc(%ebp)
int b=2;80483a1:       c7 45 f8 02 00 00 00    movl   $0x2,-0x8(%ebp)
int c=0;80483a8:       c7 45 fc 00 00 00 00    movl   $0x0,-0x4(%ebp)
a = (b>c)?1:0;80483af:       8b 45 f8                mov    -0x8(%ebp),%eax80483b2:       3b 45 fc                cmp    -0x4(%ebp),%eax80483b5:       0f 9f c0                setg   %al80483b8:       0f b6 c0                movzbl %al,%eax80483bb:       89 45 f4                mov    %eax,-0xc(%ebp)
return 0;80483be:       b8 00 00 00 00          mov    $0x0,%eax
}  80483c3:       c9                      leave  80483c4:       c3                      ret    80483c5:       90                      nop

?

編譯

#gcc -g a2.c
反匯編

#objdump -dS a.out

#include <stdio.h>  int main(void)  
{  8048394:       55                      push   %ebp8048395:       89 e5                   mov    %esp,%ebp8048397:       83 ec 10                sub    $0x10,%esp
int a=1;804839a:       c7 45 f4 01 00 00 00    movl   $0x1,-0xc(%ebp)
int b=2;80483a1:       c7 45 f8 02 00 00 00    movl   $0x2,-0x8(%ebp)
int c=0;80483a8:       c7 45 fc 00 00 00 00    movl   $0x0,-0x4(%ebp)
if(b>c)80483af:       8b 45 f8                mov    -0x8(%ebp),%eax80483b2:       3b 45 fc                cmp    -0x4(%ebp),%eax80483b5:       7e 09                   jle    80483c0 <main+0x2c>
{
a=1;80483b7:       c7 45 f4 01 00 00 00    movl   $0x1,-0xc(%ebp)80483be:       eb 07                   jmp    80483c7 <main+0x33>
}
else
{
a=0;80483c0:       c7 45 f4 00 00 00 00    movl   $0x0,-0xc(%ebp)
}
return 0;80483c7:       b8 00 00 00 00          mov    $0x0,%eax
}  80483cc:       c9                      leave  80483cd:       c3                      ret    80483ce:       90                      nop

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