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From: Zdenek Dvorak <rakdver@kam.mff.cuni.cz>
To: Tom de Vries <vries@codesourcery.com>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: [PATCH PR45098] Disallow NULL pointer in pointer arithmetic
Date: Thu, 16 Jun 2011 15:33:00 -0000	[thread overview]
Message-ID: <20110616152451.GA12880@kam.mff.cuni.cz> (raw)
In-Reply-To: <4DF9F1DC.8080306@codesourcery.com>

Hi,

> diff -u gcc/tree-ssa-loop-niter.c (working copy) gcc/tree-ssa-loop-niter.c (working copy)
> --- gcc/tree-ssa-loop-niter.c (working copy)
> +++ gcc/tree-ssa-loop-niter.c (working copy)
> @@ -2875,6 +2875,16 @@
>    low = lower_bound_in_type (type, type);
>    high = upper_bound_in_type (type, type);
>  
> +  /* In C, pointer arithmetic p + 1 cannot use a NULL pointer, and p - 1 cannot
> +     produce a NULL pointer.  The contrary would mean NULL points to an object,
> +     while NULL is supposed to compare unequal with the address of all objects.
> +     Furthermore, p + 1 cannot produce a NULL pointer and p - 1 cannot use a
> +     NULL pointer since that would mean wrapping, which we assume here not to
> +     happen.  So, we can exclude NULL from the valid range of pointer
> +     arithmetic.  */
> +  if (int_cst_value (low) == 0)
> +    low = build_int_cstu (TREE_TYPE (low), TYPE_ALIGN_UNIT (TREE_TYPE (type)));
> +
>    record_nonwrapping_iv (loop, base, step, stmt, low, high, false, true);
>  }

OK,

Zdenek

  reply	other threads:[~2011-06-16 15:25 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-06-16  6:42 Tom de Vries
2011-06-16  6:51 ` Tom de Vries
2011-06-16  7:34 ` Zdenek Dvorak
2011-06-16 12:22   ` Tom de Vries
2011-06-16 15:33     ` Zdenek Dvorak [this message]
2011-06-16 15:42       ` Richard Guenther
2011-06-16 15:54         ` Zdenek Dvorak
2011-06-16 18:10           ` Tom de Vries
2011-06-16 22:03 ` Jeff Law
2011-06-17 10:44   ` Tom de Vries
2011-06-17 10:56     ` Richard Guenther
2011-06-17 10:57       ` Zdenek Dvorak
2011-06-17 11:13         ` Richard Guenther
2011-06-17 11:22           ` Zdenek Dvorak
2011-06-17 13:01             ` Richard Guenther
2011-06-17 14:57               ` Zdenek Dvorak
2011-06-17 18:24                 ` Jeff Law
2011-06-20 11:06                   ` Richard Guenther
2011-06-20 12:26                     ` Zdenek Dvorak
2011-06-20 12:41                       ` Zdenek Dvorak
2011-06-20 13:29                         ` Richard Guenther
2011-06-20 13:35                           ` Michael Matz

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