[Bug c/47418] warning: array subscript is above array bounds at O2 with sin6_addr

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47418

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.01.25 11:24:58
     Ever Confirmed|0                           |1

--- Comment #4 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-01-25 11:24:58 UTC ---
VRP sees

<bb 2>:
  D.2725_3 = u.sa_data[15];
  D.2726_4 = (int) D.2725_3;
  D.2728_6 = u.sa_data[14];
  D.2729_7 = (int) D.2728_6;
...
  D.2769_47 = u.sa_data[0];
  D.2770_48 = (int) D.2769_47;
  test_func (0, D.2770_48, D.2768_46, D.2765_43, D.2762_40, D.2759_37,
D.2756_34, D.2753_31, D.2750_28, D.2747_25, D.2744_22, D.2741_19, D.2738_16,
D.2735_13, D.2732_10, D.2729_7, D.2726_4);
  return 0;

because of our fancy way of re-building non-addressed components.

With 4.6 the warning is gone and we instead have (thanks to MEM-REF):

<bb 2>:
  D.2695_3 = MEM[(char *)&u + 15B];
  D.2696_4 = (int) D.2695_3;
  D.2698_6 = MEM[(char *)&u + 14B];
  D.2699_7 = (int) D.2698_6;
...
  D.2740_48 = (int) D.2739_47;
  test_func (0, D.2740_48, D.2738_46, D.2735_43, D.2732_40, D.2729_37,
D.2726_34, D.2723_31, D.2720_28, D.2717_25, D.2714_22, D.2711_19, D.2708_16,
D.2705_13, D.2702_10, D.2699_7, D.2696_4);
  return 0;

thus, no more array access and still non-address-taken u.  4.4 also warns
about

small-test.c: In function 'main':
small-test.c:18: warning: array subscript is above array bounds
small-test.c:18: warning: array subscript is above array bounds
small-test.c:18: warning: array subscript is above array bounds
small-test.c:18: warning: 'u' is used uninitialized in this function

4.3 doesn't warn at all.

Confirmed.  I'd close it as fixed in 4.6 and add a testcase (no time for
that right now).