http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49760
--- Comment #3 from rguenther at suse dot de <rguenther at suse dot de> 2011-07-18 09:44:23 UTC --- On Mon, 18 Jul 2011, vincenzo.innocente at cern dot ch wrote: > 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. Probably the same issue - the out array may point to in.size and thus clobber it (yes - only if the loop runs exactly once, but we don't use that information yet). > > 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 I suppose we can't vectorize the k iterator (or rather we don't apply store motion). You should avoid using induction variables that live in memory.
