On Fri, Jan 05, 2018 at 09:52:36AM +0100, Richard Biener wrote:
> On Wed, Jan 3, 2018 at 5:31 PM, Marek Polacek <pola...@redhat.com> wrote:
> > Here we are crashing because cxx_fold_indirect_ref got a POINTER_PLUS_EXPR
> > with offset > signed HOST_WIDE_INT and we tried to convert it to sHWI.
> >
> > The matching code in fold_indirect_ref_1 uses uHWIs so I've followed suit.
> > But that code now also uses poly_uint64 and I'm not sure if any of the
> > constexpr.c code should use it, too. But this patch fixes the ICE.
>
> POINTER_PLUS_EXPR offets are to be interpreted as signed (ptrdiff_t)
> so using uhwi and then performing an unsigned division is wrong code.
> See mem_ref_offset how to deal with this (ugh - poly-ints...). Basically
> you have to force the thing to signed. Like just use
>
> HOST_WIDE_INT offset = TREE_INT_CST_LOW (op01);
Does it really matter here though? Any negative offsets there are UB, we
should punt on them rather than try to optimize them.
As we known op01 is unsigned, if we check that it fits into shwi_p, it means
it will be 0 to shwi max and then we can handle it in uhwi too.
/* ((foo*)&vectorfoo)[1] => BIT_FIELD_REF<vectorfoo,...> */
if (VECTOR_TYPE_P (op00type)
&& (same_type_ignoring_top_level_qualifiers_p
- (type, TREE_TYPE (op00type))))
+ (type, TREE_TYPE (op00type)))
+ && tree_fits_shwi_p (op01))
{
- HOST_WIDE_INT offset = tree_to_shwi (op01);
+ unsigned HOST_WIDE_INT offset = tree_to_uhwi (op01);
tree part_width = TYPE_SIZE (type);
- unsigned HOST_WIDE_INT part_widthi = tree_to_shwi
(part_width)/BITS_PER_UNIT;
+ unsigned HOST_WIDE_INT part_widthi
+ = tree_to_uhwi (part_width) / BITS_PER_UNIT;
unsigned HOST_WIDE_INT indexi = offset * BITS_PER_UNIT;
tree index = bitsize_int (indexi);
if (known_lt (offset / part_widthi,
TYPE_VECTOR_SUBPARTS (op00type)))
return fold_build3_loc (loc,
BIT_FIELD_REF, type, op00,
part_width, index);
}
Jakub
