http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50698
--- Comment #7 from rguenther at suse dot de <rguenther at suse dot de> 2011-10-17 09:26:05 UTC --- On Sat, 15 Oct 2011, vincenzo.innocente at cern dot ch wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50698 > > --- Comment #6 from vincenzo Innocente <vincenzo.innocente at cern dot ch> > 2011-10-15 13:40:31 UTC --- > I now moved to a more realistic case that can be reduced to this: > > void loop(float * x, int n) { > for (int i=0;i!=n; ++i) > x[i]=x[i+n]+x[i+2*n]; > } > > > and it creates aliases even if the memory region are clearly disjoint: > (used gcc version 4.7.0 20111015 (experimental) (GCC) ) > keep here or open an other "enhancement request"? The problem is that x[i] and x[i+n] may alias for n == 0. So this is a completely different issue - that we miss to account for the fact that n is the loop bound for the induction variable i and that because i is signed, n has to be >= 0. Still we won't be able to compute a meaningful distance vector, as it depends on n, thus we have to version the loop anyway (the distance vector is n and 2 * n). Thus I'd say open a separate enhancement request stating that we need to handle non-constant distance vectors in a better way (do not hold your breath).
