On Tue, Aug 16, 2022 at 3:57 PM Eric Botcazou via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi,
>
> the following bogus warning:
>
> In function 'lto26',
> inlined from 'main' at /home/eric/gnat/bugs/V721-018/b~lto26.adb:237:7:
> lto26.adb:11:13: warning: writing 1 byte into a region of size 0 [-Wstringop-
> overflow=]
> 11 | Set (R, (7, 0, 84, Stream_Element (I), 0, 0, 0), 1);
> | ^
> lto26.adb: In function 'main':
> lto26.adb:11:50: note: at offset -9223372036854775808 into destination object
> 'A.0' of size 7
> 11 | Set (R, (7, 0, 84, Stream_Element (I), 0, 0, 0), 1);
> | ^
>
> comes from a discrepancy between get_offset_range, which uses a signed type,
> and handle_array_ref, which uses an unsigned one, to do offset computations.
>
> Tested on x86-64/Linux, OK for the mainline?
Hmm, can we instead do
if (!integer_zerop (lowbnd) && tree_fits_shwi_p (lowbnd))
{
const offset_int lb = offset_int::from (lowbnd, SIGNED);
...
? In particular interpreting the unsigned lowbnd as SIGNED when
not wlb.get_precision () < TYPE_PRECISION (sizetype), offset_int
should handle all positive and negative byte offsets since it can
also represent them measured in bits. Unfortunately the
wide_int classes do not provide the maximum precision they can
handle. That said, the check, if any, should guard the whole
orng adjustment, no? (in fact I wonder why we just ignore lowbnd
if it doesn't fit or is variable...)
>
>
> 2022-08-16 Eric Botcazou <ebotca...@adacore.com>
>
> * pointer-query.cc (handle_array_ref): Fix handling of low bound.
>
>
> 2022-08-16 Eric Botcazou <ebotca...@adacore.com>
>
> * gnat.dg/lto26.adb: New test.
> * gnat.dg/lto26_pkg1.ads, gnat.dg/lto26_pkg1.adb: New helper.
> * gnat.dg/lto26_pkg2.ads, gnat.dg/lto26_pkg2.adb: Likewise.
>
> --
> Eric Botcazou
