Processor peak performance includes the speed-up provided by the vector instructions, but in order to exploit it you need specific programming techniques.

Auto-vectorization is the easiest and more portable way to get vectorization , but not all loops can be vectorized.

Some examples:

• Loop with dependencies between iterations can not be vectorized.

for (i=1; i<MAX; i++) {
   d[i] = e[i] – a[i-1];
   a[i] = b[i] + c[i];
}