[Bug middle-end/14784] New: Tree-ssa alias analysis deficiency

["rakdver at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

Tree-ssa alias analysis does not take information about structure
fields into account.  Consequently head->using_obstack and bitmap_free
accesses in the following testcase are believed to alias, which prevents
further optimizations (load motion, unswitching) on tree level.

typedef struct bitmap_element_def
{
  unsigned int indx;
} bitmap_element;

typedef struct bitmap_head_def {
  bitmap_element *first;
  int using_obstack;
} bitmap_head;
typedef struct bitmap_head_def *bitmap;

bitmap_element *bitmap_free;

void foo (bitmap head, bitmap_element *elt)
{
  while (1)
    {
      if (head->using_obstack)
        bitmap_free = elt;
    }
}

-- 
           Summary: Tree-ssa alias analysis deficiency
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rakdver at gcc dot gnu dot org
                CC: dnovillo at redhat dot com,gcc-bugs at gcc dot gnu dot
                    org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14784