http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49700 --- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-07-11 09:33:36 UTC --- Oh, so it's a sum ... Well, the I suppose you run into the usual array-prefetching compile-time hog. Try -fno-prefetch-loop-arrays.