intel 编译器的矢量化测试

其中有一段数据是存在依赖的，是不能矢量化的，注释掉看一下效果吧。

/*
*Name : vectorized.c
*Purpose: test the performance of intel compiler
*Author: Albert
*/
#include <stdio.h>
#include <sys/time.h>
#include <string.h>

const int MAX = 2000000;
const int ITERMAX = 20000;
int main(void) {
	
	int i, iter,arr[MAX];
	timeval start,end;
	long long tPassed = 0;
	memset(arr, 0, sizeof(arr));
	gettimeofday(&start,0);
	for (iter = 1; iter < ITERMAX; iter++) {
//		for(i = 1; i < MAX; i++){
//			arr[i] = arr[i-1] + 1;
//		}
		for(i = 1; i < MAX; i++){
                        arr[i] += 1;
                }
	}
	gettimeofday(&end,0);
	end.tv_sec -= start.tv_sec;
	end.tv_usec -= start.tv_usec;
	tPassed = 1000000LL * end.tv_sec + end.tv_usec; 
	tPassed /= 1000;
	printf("%lld ms\n",tPassed);
	return 0;
}

环境：

Linux v3901 2.6.18-53.el5 #1 SMP Wed Oct 10 16:34:19 EDT 2007 x86_64 x86_64 x86_64 GNU/Linux，32GB内存，Intel(R) Xeon(R) CPU           E5450  @ 3.00GHz，8核，L1-Cahce 6144 KB.

[scwangj@v3901 simple]$ icpc vectorized.c -o ivectorized 
vectorized.c(19): (col. 2) remark: PERMUTED LOOP WAS VECTORIZED.
[scwangj@v3901 simple]$ g++ vectorized.c -o vectorized
[scwangj@v3901 simple]$ ./ivectorized 
3696 ms
[scwangj@v3901 simple]$ ./vectorized 
114530 ms

时间上快了30倍还要多！个人觉得这个结果超过了预期的16倍，不太靠谱，原因在于测试程序不合适，表达式过于简单，等有功夫了再改吧