[Bug c++/43555] wrong address calculation of multidimensional variable-length array element

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2010-03-28 16:33 -------
Confirmed.  The problem seems to be gimplification of type sizes where
we end up putting the size calculation stmts into the conditional block,
a place not dominating the 2nd stmt where we re-use it:

  x2d = (double[0:(unsigned int) (SAVE_EXPR <(<unnamed-signed:32>) nx +
-1>)][0:(unsigned int) SAVE_EXPR <D.2820>] *) x1d;
  if (choice != 0) goto <D.2817>; else goto <D.2818>;
  <D.2817>:
  ny.2 = ny;
  D.2820 = ny.2 + -1;
  D.2821 = (unsigned int) D.2820;
  D.2822 = D.2821 + 1;
  D.2823 = &(*x2d)[1]{lb: 0 sz: D.2822 * 8}[0];
  D.2824 = (int) D.2823;
  x1d.3 = (int) x1d;
  D.2826 = D.2824 - x1d.3;
  D.2827 = D.2826 /[ex] 8;
  delta = (long unsigned int) D.2827;
  goto <D.2828>;
  <D.2818>:
  D.2829 = (unsigned int) D.2820;
  D.2830 = D.2829 + 1;
  D.2831 = &(*x2d)[1]{lb: 0 sz: D.2830 * 8}[0];
  D.2832 = (int) D.2831;
  x1d.4 = (int) x1d;
  D.2834 = D.2832 - x1d.4;
  D.2835 = D.2834 /[ex] 8;
  delta = (long unsigned int) D.2835;
  <D.2828>:
  printf (&"Choice: %d, Delta: %ld\n"[0], choice, delta);

also see how the type-sizes in the cast are not gimplified.  Thus, if
we'd have gimplified type-sizes when gimplifying

  <<cleanup_point <<< Unknown tree: expr_stmt
  (void) (x2d = (double[0:(unsigned int) (SAVE_EXPR <(<unnamed-signed:32>) nx +
-1>)][0:(unsigned int) (SAVE_EXPR <(<unnamed-signed:32>) ny + -1>)] *) x1d) >>>
>>;

it all would have worked out.  The C frontend seems to be lucky because
it decomposes the address difference internally:

  if (choice != 0)
    {
      delta = (long unsigned int) (((int) ((double *) x2d + (unsigned int)
SAVE_EXPR <ny> * 8) - (int) x1d) /[ex] 8);
    }
  else
    {
      delta = (long unsigned int) (((int) ((double *) x2d + (unsigned int)
SAVE_EXPR <ny> * 8) - (int) x1d) /[ex] 8);
    }

but even changing the testcase to sth different shows that for C we
properly gimplify type-sizes of casts.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |wrong-code
      Known to fail|                            |4.3.4 4.4.2 4.5.0
   Last reconfirmed|0000-00-00 00:00:00         |2010-03-28 16:33:10
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43555