[Bug tree-optimization/50756] New: request to better handle non-constant distance vectors to avoid unnecessary alias check

["vincenzo.innocente at cern dot ch" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50756

             Bug #: 50756
           Summary: request to better handle non-constant distance vectors
                    to avoid unnecessary alias check
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: vincenzo.innocente@cern.ch


this is a follow up to PR50698
this snippet

void loop(float *  x, int n) {
  for (int i=0;i!=n; ++i)
    x[i]=x[i+n]+x[i+2*n];
}

generates aliasing checks even if memory regions are clearly disjoint
(see analysis in comments 6 and 7 of PR50698)

I'm now experimenting with "structure of arrays" in place of "array of
structures" to make better use of vectorization (and cpu-caches). Reducing
unecessary aliasing will further improve performance (and reduce code size).It
will also avoid the need to set --param vect-max-version-for-alias-checks=100
or so.