gccのprefetch

Example from here

#geshi(c++){{ for (i = 0; i < n; i++) {

   a[i] = a[i] + b[i];
   __builtin_prefetch (&a[i+j], 1, 1);
   __builtin_prefetch (&b[i+j], 0, 1);
   /* ... */

} }}

__builtin_prefetch takes 3 parameters, which later 2 are optional
the first parameter is the data to be prefetched
the second parameter is 0 or 1, compile time constant
- 0 is to read the data (which is default)
- 1 is to write
the third parameter is locality 0,1,2 or 3 and has to be compile time constant
- 0 is no temporal locality. it will be purged after access
- 3 is strong temporal locality. It'll try to keep the data in cache as much as possible(default)