On Thu, Jan 25, 2018 at 3:45 PM, Jakub Jelinek <ja...@redhat.com> wrote:
> 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.
Ah, of course. Didn't look up enough context to see what this code
does in the end ;)
> /* ((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))
nevertheless this appearant "mismatch" deserves a comment (checking
shwi and using uhwi).
> {
> - 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
