cilk plus array notation not vectorized with gcc 4.9.0

Question

I'm trying to figure out why gcc 4.9.0 won't vectorize a simple array addition when using gcc 4.9.0, using -O -ftree-vectorize:

int a[256], b[256], c[256];
foo () {
  int i;
  a[:] = b[:] + c[:];
}

From looking at the assembler produced this loop hasn't been vectorized and with the -fopt-info-vec-all flag I get a lot of output telling me why vectorization failed, beginning with:

>testvec.c:5: note: ===== analyze_loop_nest ===== 
>testvec.c:5: note: === vect_analyze_loop_form === 
>testvec.c:5: note: not vectorized: control flow in loop. 
>testvec.c:5: note: bad loop form.

which is puzzling, since there's not control flow in the loop. Vectorization of the for loop using standard array notation for the same operation works fine.

Answer 1

It looks like only the latest version of GCC (6.1) can vectorize your example:

http://melpon.org/wandbox/permlink/LOIweYNRRLXeJsZf