c语言if-else的效率比较

闲着没事测试下if-else的执行效率

测试环境：Mac pro i7 2.3Ghz 。。。编译器gcc 4.9，代码没有进行优化-O0；

测试代码：c代码1：

int main(){

	int n=100000000;

	int b=-1;

	int a=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：

_main:

LFB0:

	pushl	%ebp

LCFI0:

	movl	%esp, %ebp

LCFI1:

	subl	$16, %esp

	movl	$100000000, -4(%ebp)

	movl	$-1, -8(%ebp)

	movl	$0, -12(%ebp)

	jmp	L2

L22:

	cmpl	$0, -8(%ebp)

	jns	L3

	subl	$1, -8(%ebp)

	jmp	L4

L3:

	subl	$1, -8(%ebp)

L4:

	cmpl	$0, -8(%ebp)

	jns	L5

	subl	$1, -8(%ebp)

	jmp	L6

L5:

	subl	$1, -8(%ebp)

L6:

	cmpl	$0, -8(%ebp)

	jns	L7

	subl	$1, -8(%ebp)

	jmp	L8

L7:

	subl	$1, -8(%ebp)

L8:

	cmpl	$0, -8(%ebp)

	jns	L9

	subl	$1, -8(%ebp)

	jmp	L10

L9:

	subl	$1, -8(%ebp)

L10:

	cmpl	$0, -8(%ebp)

	jns	L11

	subl	$1, -8(%ebp)

	jmp	L12

L11:

	subl	$1, -8(%ebp)

L12:

	cmpl	$0, -8(%ebp)

	jns	L13

	subl	$1, -8(%ebp)

	jmp	L14

L13:

	subl	$1, -8(%ebp)

L14:

	cmpl	$0, -8(%ebp)

	jns	L15

	subl	$1, -8(%ebp)

	jmp	L16

L15:

	subl	$1, -8(%ebp)

L16:

	cmpl	$0, -8(%ebp)

	jns	L17

	subl	$1, -8(%ebp)

	jmp	L18

L17:

	subl	$1, -8(%ebp)

L18:

	cmpl	$0, -8(%ebp)

	jns	L19

	subl	$1, -8(%ebp)

	jmp	L20

L19:

	subl	$1, -8(%ebp)

L20:

	cmpl	$0, -8(%ebp)

	jns	L21

	subl	$1, -8(%ebp)

	jmp	L2

L21:

	subl	$1, -8(%ebp)

L2:

	movl	-4(%ebp), %eax

	leal	-1(%eax), %edx

	movl	%edx, -4(%ebp)

	testl	%eax, %eax

	jg	L22

	movl	$0, %eax

	leave

c代码2：

int main(){

	int n=100000000;

	int b=-1;

	int a=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：

_main:

LFB0:

	pushl	%ebp

LCFI0:

	movl	%esp, %ebp

LCFI1:

	subl	$16, %esp

	movl	$100000000, -4(%ebp)

	movl	$-1, -8(%ebp)

	movl	$0, -12(%ebp)

	jmp	L2

L22:

	cmpl	$0, -8(%ebp)

	jle	L3

	subl	$1, -8(%ebp)

	jmp	L4

L3:

	subl	$1, -8(%ebp)

L4:

	cmpl	$0, -8(%ebp)

	jle	L5

	subl	$1, -8(%ebp)

	jmp	L6

L5:

	subl	$1, -8(%ebp)

L6:

	cmpl	$0, -8(%ebp)

	jle	L7

	subl	$1, -8(%ebp)

	jmp	L8

L7:

	subl	$1, -8(%ebp)

L8:

	cmpl	$0, -8(%ebp)

	jle	L9

	subl	$1, -8(%ebp)

	jmp	L10

L9:

	subl	$1, -8(%ebp)

L10:

	cmpl	$0, -8(%ebp)

	jle	L11

	subl	$1, -8(%ebp)

	jmp	L12

L11:

	subl	$1, -8(%ebp)

L12:

	cmpl	$0, -8(%ebp)

	jle	L13

	subl	$1, -8(%ebp)

	jmp	L14

L13:

	subl	$1, -8(%ebp)

L14:

	cmpl	$0, -8(%ebp)

	jle	L15

	subl	$1, -8(%ebp)

	jmp	L16

L15:

	subl	$1, -8(%ebp)

L16:

	cmpl	$0, -8(%ebp)

	jle	L17

	subl	$1, -8(%ebp)

	jmp	L18

L17:

	subl	$1, -8(%ebp)

L18:

	cmpl	$0, -8(%ebp)

	jle	L19

	subl	$1, -8(%ebp)

	jmp	L20

L19:

	subl	$1, -8(%ebp)

L20:

	cmpl	$0, -8(%ebp)

	jle	L21

	subl	$1, -8(%ebp)

	jmp	L2

L21:

	subl	$1, -8(%ebp)

L2:

	movl	-4(%ebp), %eax

	leal	-1(%eax), %edx

	movl	%edx, -4(%ebp)

	testl	%eax, %eax

	jg	L22

	movl	$0, %eax

	leave

执行结果：

看来else执行的效率高一些。。。。