C语言优化ifelse,c语言ifelse的效率比较

闲着没事测试下if-else的执行效率

测试环境&＃xff1a;Mac pro i7 2.3Ghz 。。。编译器gcc 4.9&＃xff0c;代码没有进行优化-O0&＃xff1b;

测试代码&＃xff1a;c代码1&＃xff1a;

int main(){

int n&＃61;100000000;

int b&＃61;-1;

int a&＃61;0;

while(n-->0){

if(b<0) b--;else b--;

if(b<0) b--;else b--;

if(b<0) b--;else b--;

if(b<0) b--;else b--;

if(b<0) b--;else b--;

if(b<0) b--;else b--;

if(b<0) b--;else b--;

if(b<0) b--;else b--;

if(b<0) b--;else b--;

if(b<0) b--;else b--;

}

return 0;

}

汇编代码1&＃xff1a;

_main:

LFB0:

pushl%ebp

LCFI0:

movl%esp, %ebp

LCFI1:

subl$16, %esp

movl$100000000, -4(%ebp)

movl$-1, -8(%ebp)

movl$0, -12(%ebp)

jmpL2

L22:

cmpl$0, -8(%ebp)

jnsL3

subl$1, -8(%ebp)

jmpL4

L3:

subl$1, -8(%ebp)

L4:

cmpl$0, -8(%ebp)

jnsL5

subl$1, -8(%ebp)

jmpL6

L5:

subl$1, -8(%ebp)

L6:

cmpl$0, -8(%ebp)

jnsL7

subl$1, -8(%ebp)

jmpL8

L7:

subl$1, -8(%ebp)

L8:

cmpl$0, -8(%ebp)

jnsL9

subl$1, -8(%ebp)

jmpL10

L9:

subl$1, -8(%ebp)

L10:

cmpl$0, -8(%ebp)

jnsL11

subl$1, -8(%ebp)

jmpL12

L11:

subl$1, -8(%ebp)

L12:

cmpl$0, -8(%ebp)

jnsL13

subl$1, -8(%ebp)

jmpL14

L13:

subl$1, -8(%ebp)

L14:

cmpl$0, -8(%ebp)

jnsL15

subl$1, -8(%ebp)

jmpL16

L15:

subl$1, -8(%ebp)

L16:

cmpl$0, -8(%ebp)

jnsL17

subl$1, -8(%ebp)

jmpL18

L17:

subl$1, -8(%ebp)

L18:

cmpl$0, -8(%ebp)

jnsL19

subl$1, -8(%ebp)

jmpL20

L19:

subl$1, -8(%ebp)

L20:

cmpl$0, -8(%ebp)

jnsL21

subl$1, -8(%ebp)

jmpL2

L21:

subl$1, -8(%ebp)

L2:

movl-4(%ebp), %eax

leal-1(%eax), %edx

movl%edx, -4(%ebp)

testl%eax, %eax

jgL22

movl$0, %eax

leave

c代码2&＃xff1a;

int main(){

int n&＃61;100000000;

int b&＃61;-1;

int a&＃61;0;

while(n-->0){

if(b>0) b--;else b--;

if(b>0) b--;else b--;

if(b>0) b--;else b--;

if(b>0) b--;else b--;

if(b>0) b--;else b--;

if(b>0) b--;else b--;

if(b>0) b--;else b--;

if(b>0) b--;else b--;

if(b>0) b--;else b--;

if(b>0) b--;else b--;

}

return 0;

}

汇编代码2&＃xff1a;

_main:

LFB0:

pushl%ebp

LCFI0:

movl%esp, %ebp

LCFI1:

subl$16, %esp

movl$100000000, -4(%ebp)

movl$-1, -8(%ebp)

movl$0, -12(%ebp)

jmpL2

L22:

cmpl$0, -8(%ebp)

jleL3

subl$1, -8(%ebp)

jmpL4

L3:

subl$1, -8(%ebp)

L4:

cmpl$0, -8(%ebp)

jleL5

subl$1, -8(%ebp)

jmpL6

L5:

subl$1, -8(%ebp)

L6:

cmpl$0, -8(%ebp)

jleL7

subl$1, -8(%ebp)

jmpL8

L7:

subl$1, -8(%ebp)

L8:

cmpl$0, -8(%ebp)

jleL9

subl$1, -8(%ebp)

jmpL10

L9:

subl$1, -8(%ebp)

L10:

cmpl$0, -8(%ebp)

jleL11

subl$1, -8(%ebp)

jmpL12

L11:

subl$1, -8(%ebp)

L12:

cmpl$0, -8(%ebp)

jleL13

subl$1, -8(%ebp)

jmpL14

L13:

subl$1, -8(%ebp)

L14:

cmpl$0, -8(%ebp)

jleL15

subl$1, -8(%ebp)

jmpL16

L15:

subl$1, -8(%ebp)

L16:

cmpl$0, -8(%ebp)

jleL17

subl$1, -8(%ebp)

jmpL18

L17:

subl$1, -8(%ebp)

L18:

cmpl$0, -8(%ebp)

jleL19

subl$1, -8(%ebp)

jmpL20

L19:

subl$1, -8(%ebp)

L20:

cmpl$0, -8(%ebp)

jleL21

subl$1, -8(%ebp)

jmpL2

L21:

subl$1, -8(%ebp)

L2:

movl-4(%ebp), %eax

leal-1(%eax), %edx

movl%edx, -4(%ebp)

testl%eax, %eax

jgL22

movl$0, %eax

leave执行结果&＃xff1a;

看来else执行的效率高一些。。。。