Compilation 变量累加循环的矢量化

我用icc编译了以下循环

for (int i = 0; i < arrays_size; ++i) {
      total = total + C[i];
}

---

有人能解释一下这意味着什么以及如何将这个循环矢量化吗？

根据

total

和

C[i]

的类型，您可以利用加法和首和4或8（或更多）小计的关联性和交换性

int subtotal[4] = {0,0,0,0};
for (int i = 0; i < arrays_size; i+=4) {
    for(int k=0; k<4; ++k)
        subtotal[k] += C[i+k];
}
// handle remaining elements of C, if necessary ...
// sum-up sub-totals:
total = (subtotal[0]+subtotal[2]) + (subtotal[1]+subtotal[3]);

int小计[4]={0,0,0}；
对于（int i=0；iint subtotal[4] = {0,0,0,0};
for (int i = 0; i < arrays_size; i+=4) {
    for(int k=0; k<4; ++k)
        subtotal[k] += C[i+k];
}
// handle remaining elements of C, if necessary ...
// sum-up sub-totals:
total = (subtotal[0]+subtotal[2]) + (subtotal[1]+subtotal[3]);