[PATCH] ranger: Fix up fold_using_range::range_of_address [PR103255]

Aldy Hernandez aldyh@redhat.com
Wed Nov 17 10:06:38 GMT 2021


On Wed, Nov 17, 2021 at 10:32 AM Jakub Jelinek <jakub@redhat.com> wrote:
>
> Hi!
>
> If on &base->member the offset isn't constant or isn't zero and
> -fdelete-null-pointer-checks and not -fwrapv-pointer and base has a range
> that doesn't include NULL, we return the range of the base.
> Usually it isn't a big deal, because for most pointers we just use
> varying, range_zero and range_nonzero ranges and nothing beyond that,
> but if a pointer is initialized from a constant, we actually track the
> exact range and in that case this causes miscompilation.
> As discussed on IRC, I think doing something like:
>               offset_int off2;
>               if (off_cst && off.is_constant (&off2))
>                 {
>                   tree cst = wide_int_to_tree (sizetype, off2 / BITS_PER_UNIT);
>                   // adjust range r with POINTER_PLUS_EXPR cst
>                   if (!range_includes_zero_p (&r))
>                     return true;
>                 }
>               // Fallback
>               r = range_nonzero (TREE_TYPE (gimple_assign_rhs1 (stmt)));
>               return true;
> could work, given that most of the pointer ranges are just the simple ones
> perhaps it is too much for little benefit.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK.  Thanks for the formatting fixes btw.

Unrelated, but we could remove the return value for range_of_address
since it always returns true.  I suppose it's consistent with
range_of_*, but unlike range_of_address, the other ones can receive
statements they can't process.

Aldy

>
> 2021-11-17  Jakub Jelinek  <jakub@redhat.com>
>
>         PR tree-optimization/103255
>         * gimple-range-fold.cc (fold_using_range::range_of_address): Return
>         range_nonzero rather than unadjusted base's range.  Formatting fixes.
>
>         * gcc.c-torture/execute/pr103255.c: New test.
>
> --- gcc/gimple-range-fold.cc.jj 2021-11-04 12:27:02.341298923 +0100
> +++ gcc/gimple-range-fold.cc    2021-11-16 22:10:44.453974329 +0100
> @@ -720,14 +720,20 @@ fold_using_range::range_of_address (iran
>         }
>        /* If &X->a is equal to X, the range of X is the result.  */
>        if (off_cst && known_eq (off, 0))
> -         return true;
> +       return true;
>        else if (flag_delete_null_pointer_checks
>                && !TYPE_OVERFLOW_WRAPS (TREE_TYPE (expr)))
>         {
> -        /* For -fdelete-null-pointer-checks -fno-wrapv-pointer we don't
> -        allow going from non-NULL pointer to NULL.  */
> -          if(!range_includes_zero_p (&r))
> -           return true;
> +         /* For -fdelete-null-pointer-checks -fno-wrapv-pointer we don't
> +            allow going from non-NULL pointer to NULL.  */
> +         if (!range_includes_zero_p (&r))
> +           {
> +             /* We could here instead adjust r by off >> LOG2_BITS_PER_UNIT
> +                using POINTER_PLUS_EXPR if off_cst and just fall back to
> +                this.  */
> +             r = range_nonzero (TREE_TYPE (gimple_assign_rhs1 (stmt)));
> +             return true;
> +           }
>         }
>        /* If MEM_REF has a "positive" offset, consider it non-NULL
>          always, for -fdelete-null-pointer-checks also "negative"
> --- gcc/testsuite/gcc.c-torture/execute/pr103255.c.jj   2021-11-16 22:14:10.660118225 +0100
> +++ gcc/testsuite/gcc.c-torture/execute/pr103255.c      2021-11-16 22:13:56.506314265 +0100
> @@ -0,0 +1,41 @@
> +/* PR tree-optimization/103255 */
> +
> +struct H
> +{
> +  unsigned a;
> +  unsigned b;
> +  unsigned c;
> +};
> +
> +#if __SIZEOF_POINTER__ >= 4
> +#define ADDR 0x400000
> +#else
> +#define ADDR 0x4000
> +#endif
> +#define OFF 0x20
> +
> +int
> +main ()
> +{
> +  struct H *h = 0;
> +  unsigned long o;
> +  volatile int t = 1;
> +
> +  for (o = OFF; o <= OFF; o += 0x1000)
> +    {
> +      struct H *u;
> +      u = (struct H *) (ADDR + o);
> +      if (t)
> +       {
> +         h = u;
> +         break;
> +       }
> +    }
> +
> +  if (h == 0)
> +    return 0;
> +  unsigned *tt = &h->b;
> +  if ((__SIZE_TYPE__) tt != (ADDR + OFF + __builtin_offsetof (struct H, b)))
> +    __builtin_abort ();
> +  return 0;
> +}
>
>         Jakub
>



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