> Is -ftree-vectorize enabled by default at any -On? No, it is not. > Or it has to be turned on manually? Why? Yes, with -ftree-vectorize, and -maltivec for PowerPC or -msse (or -msse2) for x86. For more information see http://gcc.gnu.org/projects/tree-ssa/vectorization.html#using. Ira > -- > Zuxy