[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@gcc.gnu.org>]

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

--- Comment #11 from rguenther at suse dot de <rguenther at suse dot de> 2011-03-10 12:57:59 UTC ---
On Thu, 10 Mar 2011, ebotcazou at gcc dot gnu.org wrote:

> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48031
> 
> --- Comment #10 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2011-03-10 12:46:33 UTC ---
> > No it isn't.  But given that fold at this place doesn't even
> > fill in the array-ref element-size slot but provides NULL_TREE
> > it is probably a fix for the better anyway?
> 
> Why not explicitly test in_gimple_form like in other places in the folder?

That would work, too.  You see no problem with a NULL operand 3
of array-refs?  If you create an array with a variable lower bound,
take its address, convert it to pointer to element type and
dereference that, would it expand ok if it does not have the
element size set properly?  At least get_inner_reference seems to
unconditionally multiply with array_ref_element_size () * index,
and array_ref_element_size () does not work for variable-size types
if the array-ref doesn't have the gimplified value.

You can probably come up with an Ada testcase that gets miscompiled?
(C arrays always have a lower bound of zero, thus the index
will be zero thus the multiplication ensures that the garbage
returned by array_ref_element_size is thrown away).

Richard.