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);
Richard.
> Bootstrapped/regtested on x86_64-linux, ok for trunk/7?
>
> 2018-01-03 Marek Polacek <pola...@redhat.com>
>
> PR c++/83659
> * constexpr.c (cxx_fold_indirect_ref): Use unsigned HOST_WIDE_INT
> when computing offsets.
>
> * g++.dg/torture/pr83659.C: New test.
>
> diff --git gcc/cp/constexpr.c gcc/cp/constexpr.c
> index 1aeacd51810..cf7c994b381 100644
> --- gcc/cp/constexpr.c
> +++ gcc/cp/constexpr.c
> @@ -3109,9 +3109,10 @@ cxx_fold_indirect_ref (location_t loc, tree type, tree
> op0, bool *empty_base)
> && (same_type_ignoring_top_level_qualifiers_p
> (type, TREE_TYPE (op00type))))
> {
> - 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);
>
> diff --git gcc/testsuite/g++.dg/torture/pr83659.C
> gcc/testsuite/g++.dg/torture/pr83659.C
> index e69de29bb2d..d9f709bb520 100644
> --- gcc/testsuite/g++.dg/torture/pr83659.C
> +++ gcc/testsuite/g++.dg/torture/pr83659.C
> @@ -0,0 +1,11 @@
> +// PR c++/83659
> +// { dg-do compile }
> +
> +typedef int V __attribute__ ((__vector_size__ (16)));
> +V a;
> +
> +int
> +main ()
> +{
> + reinterpret_cast <int *> (&a)[-1] += 1;
> +}
>
> Marek
