[Bug tree-optimization/53516] New: Vectorization and memset recognition miscompile bitfield stores

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53516

             Bug #: 53516
           Summary: Vectorization and memset recognition miscompile
                    bitfield stores
    Classification: Unclassified
           Product: gcc
           Version: 4.7.1
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: rguenth@gcc.gnu.org
        ReportedBy: rguenth@gcc.gnu.org


The following is miscompiled at -O3.

extern void abort (void);

struct Foo
{
  char a : 1;
  char b : 7;
};

struct Foo x[256];
int y[256];

void __attribute__((noinline,noclone)) bar (int n)
{
  int i;
  for (i = 0; i < n; ++i)
    {
      x[i].a = 0;
      y[i] = 3;
    }
}

int main()
{
  x[5].b = 7;
  bar (256);
  if (x[5].b != 7)
    abort ();
  return 0;
}