Re: [PATCH] middle-end/113396 - int128 array index and value-ranges

[Jakub Jelinek <jakub@redhat.com>]

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