[Bug rtl-optimization/29797] Miscompiles bit test / set in OpenOffice

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2006-11-10 14:35 -------
/* Optimize away "if (x & C) x |= C" and similar bit manipulation
   transformations.  */

static int
noce_try_bitop (struct noce_if_info *if_info)
{
...
  /* ??? We could also handle AND here.  */
  if (GET_CODE (cond) == ZERO_EXTRACT)
    {
      if (XEXP (cond, 1) != const1_rtx
          || GET_CODE (XEXP (cond, 2)) != CONST_INT
          || ! rtx_equal_p (x, XEXP (cond, 0)))
        return FALSE;
      bitnum = INTVAL (XEXP (cond, 2));
      mode = GET_MODE (x);
      if (bitnum >= HOST_BITS_PER_WIDE_INT) 
        return FALSE;
... which is wrong for little-endian bitfieds ...
      /* if ((x & C) == 0) x |= C; is transformed to x |= C.   */
      /* if ((x & C) != 0) x |= C; is transformed to nothing.  */
      if (GET_CODE (a) == IOR)
        result = (code == NE) ? a : NULL_RTX;
      else if (code == NE)
        {
          /* if ((x & C) == 0) x ^= C; is transformed to x |= C.   */
          result = gen_int_mode ((HOST_WIDE_INT) 1 << bitnum, mode);
          result = simplify_gen_binary (IOR, mode, x, result);
        }
      else
        {
          /* if ((x & C) != 0) x ^= C; is transformed to x &= ~C.  */
          result = gen_int_mode (~((HOST_WIDE_INT) 1 << bitnum), mode);
          result = simplify_gen_binary (AND, mode, x, result);
        }


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29797