http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49760
--- Comment #2 from vincenzo Innocente <vincenzo.innocente at cern dot ch> 2011-07-18 09:39:49 UTC --- Thanks for the detailed explanation. In the real life code, "out" is filled calling "foo" multiple times (a sort of nested loop), "k" was used to track the current size of it. It is true that in this particular case I can just k+=N; at the end of the loop. The issue is more with "for (int i=0; i!=in.size; ++i)" as in foo2 because of "not vectorized: number of iterations cannot be computed" while copying it locally in N works. b.t.w. void foo(SoA const & __restrict__ in, SoB & __restrict__ out, int & __restrict__ k) { int N=in.size; for (int i=0; i!=N; ++i) { out.b[k] = in.c[i]+in.b[i]; out.a[k] = in.a[i]; ++k; } } does not vectorize either