[Bug tree-optimization/48031] [4.4/4.5 Regression] gcc.c-torture/compile/pr42956.c ICEs gcc on m68k-linux, ivopts related?

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48031

--- Comment #6 from rguenther at suse dot de <rguenther at suse dot de> 2011-03-10 09:33:49 UTC ---
On Thu, 10 Mar 2011, mikpe at it dot uu.se wrote:

> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48031
> 
> --- Comment #5 from Mikael Pettersson <mikpe at it dot uu.se> 2011-03-10 09:22:04 UTC ---
> If I revert this part of r139061 then things work again:
> 
>     * gimplify.c (gimplify_conversion): Use maybe_fold_offset_to_address.
> 
> --- gcc/gimplify.c      (revision 139060)
> +++ gcc/gimplify.c      (revision 139061)
> @@ -1842,17 +1842,13 @@ gimplify_conversion (tree *expr_p)
>    /* Attempt to avoid NOP_EXPR by producing reference to a subtype.
>       For example this fold (subclass *)&A into &A->subclass avoiding
>       a need for statement.  */
> -  if (TREE_CODE (*expr_p) == NOP_EXPR
> +  if (CONVERT_EXPR_P (*expr_p)
>        && POINTER_TYPE_P (TREE_TYPE (*expr_p))
>        && POINTER_TYPE_P (TREE_TYPE (TREE_OPERAND (*expr_p, 0)))
> -      && (tem = maybe_fold_offset_to_reference
> +      && (tem = maybe_fold_offset_to_address
>                   (TREE_OPERAND (*expr_p, 0),
> -                  integer_zero_node, TREE_TYPE (TREE_TYPE (*expr_p)))))
> -    {
> -      tree ptr_type = build_pointer_type (TREE_TYPE (tem));
> -      if (useless_type_conversion_p (TREE_TYPE (*expr_p), ptr_type))
> -        *expr_p = build_fold_addr_expr_with_type (tem, ptr_type);
> -    }
> +                  integer_zero_node, TREE_TYPE (*expr_p))) != NULL_TREE)
> +    *expr_p = tem;
> 
>    /* If we still have a conversion at the toplevel,
>       then canonicalize some constructs.  */
> 
> The first condition change is Ok, it's the change to call m_f_o_t_address
> instead of m_f_o_t_reference and the then-clause change that matter.
> 
> Reverting this from trunk @ r139061 + r151559 backport, or trunk @ r151559,
> eliminates the ICE.

I think this is all just the right circumstances for triggering the bug.