[Bug tree-optimization/31715] [4.3 Regression] Array calculation done incorrectly

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2007-04-26 23:22 -------
That's probably exposed by Honzas struct/array_ref folding changes.

we have after inlining

p_4(D) = &arr;
 D.1631_5 = p_4(D) + -4B;
  n.0_6 = 4;
  D.1633_7 = n.0_6 * 4;
  D.1634_8 = (DWORD *) D.1633_7;
  D.1635_9 = D.1631_5 + D.1634_8;
  D.1636_10 = *D.1635_9;

and fold the reference to arr[1073741823] from within
maybe_fold_offset_to_array_ref.  In the index calculation

      if (TREE_CODE (elt_size) != INTEGER_CST
          || div_and_round_double (TRUNC_DIV_EXPR, 1,
                                   TREE_INT_CST_LOW (offset),
                                   TREE_INT_CST_HIGH (offset),
                                   TREE_INT_CST_LOW (elt_size),
                                   TREE_INT_CST_HIGH (elt_size),
                                   &lquo, &hquo, &lrem, &hrem)
          || lrem || hrem)
        return NULL_TREE;

      idx = build_int_cst_wide (TREE_TYPE (offset), lquo, hquo);

we need to treat offset as signed for the division.  For this we first
need to sign extend offset and then do the division.  Like with the
following

Index: tree-ssa-ccp.c
===================================================================
*** tree-ssa-ccp.c      (revision 124201)
--- tree-ssa-ccp.c      (working copy)
*************** maybe_fold_offset_to_array_ref (tree bas
*** 1593,1605 ****
      }
    else
      {
!       unsigned HOST_WIDE_INT lquo, lrem;
!       HOST_WIDE_INT hquo, hrem;

        if (TREE_CODE (elt_size) != INTEGER_CST
!         || div_and_round_double (TRUNC_DIV_EXPR, 1,
!                                  TREE_INT_CST_LOW (offset),
!                                  TREE_INT_CST_HIGH (offset),
                                   TREE_INT_CST_LOW (elt_size),
                                   TREE_INT_CST_HIGH (elt_size),
                                   &lquo, &hquo, &lrem, &hrem)
--- 1593,1606 ----
      }
    else
      {
!       unsigned HOST_WIDE_INT lquo, lrem, lsoff;
!       HOST_WIDE_INT hquo, hrem, hsoff;

+       fit_double_type (TREE_INT_CST_LOW (offset),
+                      TREE_INT_CST_HIGH (offset), &lsoff, &hsoff,
+                      signed_type_for (TREE_TYPE (offset)));
        if (TREE_CODE (elt_size) != INTEGER_CST
!         || div_and_round_double (TRUNC_DIV_EXPR, 0, lsoff, hsoff,
                                   TREE_INT_CST_LOW (elt_size),
                                   TREE_INT_CST_HIGH (elt_size),
                                   &lquo, &hquo, &lrem, &hrem)


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org, hubicka at gcc dot gnu
                   |                            |dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31715