On Tue, Mar 19, 2024 at 03:47:37PM +0100, Richard Biener wrote:
> The following fixes bogus truncation of a value-range for an int128
> array index when computing the maximum extent for a variable array
> reference. Instead of possibly slowing things down by using
> widest_int the following makes sure the range bounds fit within
> the constraints offset_int were designed for.
Perhaps you could use wide_int/poly_wide_int with precision
of offset_int if it is at most 64-bit precision and twice that precision
otherwise.
I think large BITINT_TYPEs shouldn't be a problem since r14-7200,
so another fix might to truncate at gimplification time
ARRAY_REF indexes wider than sizetype to sizetype. Maybe GCC 15-ish
material though.
Anyway, guess your patch is ok as is too.
> PR middle-end/113396
> * tree-dfa.cc (get_ref_base_and_extent): Use index range
> bounds only if they fit within the address-range constraints
> of offset_int.
>
> * gcc.dg/torture/pr113396.c: New testcase.
> ---
> gcc/testsuite/gcc.dg/torture/pr113396.c | 19 +++++++++++++++++++
> gcc/tree-dfa.cc | 6 ++++--
> 2 files changed, 23 insertions(+), 2 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/torture/pr113396.c
>
> diff --git a/gcc/testsuite/gcc.dg/torture/pr113396.c
> b/gcc/testsuite/gcc.dg/torture/pr113396.c
> new file mode 100644
> index 00000000000..585f717bdda
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/torture/pr113396.c
> @@ -0,0 +1,19 @@
> +/* { dg-do run } */
> +/* { dg-require-effective-target int128 } */
> +
> +unsigned char m[] = {5, 79, 79, 79, 79};
> +__int128 p;
> +int main()
> +{
> + int g1 = 0;
> + p = 0;
> + for (int aj = 0; aj < 256; aj++)
> + {
> + m[0] = -4;
> + for (; p >= 0; p -= 1) {
> + g1 = m[p];
> + }
> + }
> + if (g1 != 0xfc)
> + __builtin_abort();
> +}
> diff --git a/gcc/tree-dfa.cc b/gcc/tree-dfa.cc
> index cbd3774b21f..93e53b29a6d 100644
> --- a/gcc/tree-dfa.cc
> +++ b/gcc/tree-dfa.cc
> @@ -549,7 +549,8 @@ get_ref_base_and_extent (tree exp, poly_int64 *poffset,
> /* Try to constrain maxsize with range information. */
> offset_int omax
> = offset_int::from (max, TYPE_SIGN (TREE_TYPE (index)));
> - if (known_lt (lbound, omax))
> + if (wi::get_precision (max) <= ADDR_MAX_BITSIZE
> + && known_lt (lbound, omax))
> {
> poly_offset_int rmaxsize;
> rmaxsize = (omax - lbound + 1)
> @@ -567,7 +568,8 @@ get_ref_base_and_extent (tree exp, poly_int64 *poffset,
> /* Try to adjust bit_offset with range information. */
> offset_int omin
> = offset_int::from (min, TYPE_SIGN (TREE_TYPE (index)));
> - if (known_le (lbound, omin))
> + if (wi::get_precision (min) <= ADDR_MAX_BITSIZE
> + && known_le (lbound, omin))
> {
> poly_offset_int woffset
> = wi::sext (omin - lbound,
> --
> 2.35.3
Jakub
