Re: [PATCH] Fix some undefined behavior spots in gcc sources (PR c/53968)

[Richard Guenther <richard dot guenther at gmail dot com>]

On Mon, Aug 13, 2012 at 2:01 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> John Regehr discovered a couple of spots in GCC sources that invoke
> undefined behavior during bootstrap/regtest, the following patch fixes most
> of them.  I couldn't reproduce the diagnostic.c failure and would like to
> leave the ipa hunk to Honza, I think the probability/frequency code often
> might go out of the expected limits and then invoke undefined signed
> overflow.
>
> The double_int_mask change is because e.g. with -E, ptr_mode is VOIDmode and
> so double_int_mask is called with 0 precision during compiler
> initialization.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

Ok.

Thanks,
Richard.

> 2012-08-13  Jakub Jelinek  <jakub@redhat.com>
>
>         PR c/53968
>         * tree.c (integer_pow2p): Avoid undefined signed overflows.
>         * simplify-rtx.c (neg_const_int): Likewise.
>         * expr.c (fixup_args_size_notes): Likewise.
>         * stor-layout.c (set_min_and_max_values_for_integral_type): Likewise.
>         * double-int.c (mul_double_wide_with_sign): Likewise.
>         (double_int_mask): Likewise.
>         * tree-ssa-loop-ivopts.c (get_address_cost): Likewise.
>
> --- gcc/tree.c.jj       2012-08-10 15:48:53.000000000 +0200
> +++ gcc/tree.c  2012-08-13 10:25:46.610502929 +0200
> @@ -1849,7 +1849,7 @@ int
>  integer_pow2p (const_tree expr)
>  {
>    int prec;
> -  HOST_WIDE_INT high, low;
> +  unsigned HOST_WIDE_INT high, low;
>
>    STRIP_NOPS (expr);
>
> --- gcc/simplify-rtx.c.jj       2012-08-10 15:49:20.000000000 +0200
> +++ gcc/simplify-rtx.c  2012-08-13 09:51:43.628508537 +0200
> @@ -66,7 +66,7 @@ static rtx simplify_binary_operation_1 (
>  static rtx
>  neg_const_int (enum machine_mode mode, const_rtx i)
>  {
> -  return gen_int_mode (- INTVAL (i), mode);
> +  return gen_int_mode (-(unsigned HOST_WIDE_INT) INTVAL (i), mode);
>  }
>
>  /* Test whether expression, X, is an immediate constant that represents
> --- gcc/expr.c.jj       2012-08-10 15:49:07.000000000 +0200
> +++ gcc/expr.c  2012-08-13 10:40:01.182501639 +0200
> @@ -3828,7 +3828,7 @@ fixup_args_size_notes (rtx prev, rtx las
>
>        add_reg_note (insn, REG_ARGS_SIZE, GEN_INT (args_size));
>  #ifdef STACK_GROWS_DOWNWARD
> -      this_delta = -this_delta;
> +      this_delta = -(unsigned HOST_WIDE_INT) this_delta;
>  #endif
>        args_size -= this_delta;
>      }
> --- gcc/stor-layout.c.jj        2012-08-10 15:49:20.000000000 +0200
> +++ gcc/stor-layout.c   2012-08-13 10:14:14.388505253 +0200
> @@ -2568,10 +2568,14 @@ set_min_and_max_values_for_integral_type
>         = build_int_cst_wide (type,
>                               (precision - HOST_BITS_PER_WIDE_INT > 0
>                                ? -1
> -                              : ((HOST_WIDE_INT) 1 << (precision - 1)) - 1),
> +                              : (HOST_WIDE_INT)
> +                                (((unsigned HOST_WIDE_INT) 1
> +                                  << (precision - 1)) - 1)),
>                               (precision - HOST_BITS_PER_WIDE_INT - 1 > 0
> -                              ? (((HOST_WIDE_INT) 1
> -                                  << (precision - HOST_BITS_PER_WIDE_INT - 1))) - 1
> +                              ? (HOST_WIDE_INT)
> +                                ((((unsigned HOST_WIDE_INT) 1
> +                                   << (precision - HOST_BITS_PER_WIDE_INT
> +                                       - 1))) - 1)
>                                : 0));
>      }
>
> --- gcc/double-int.c.jj 2012-08-10 15:49:07.000000000 +0200
> +++ gcc/double-int.c    2012-08-13 11:24:17.816495757 +0200
> @@ -170,7 +170,7 @@ mul_double_wide_with_sign (unsigned HOST
>         {
>           k = i + j;
>           /* This product is <= 0xFFFE0001, the sum <= 0xFFFF0000.  */
> -         carry += arg1[i] * arg2[j];
> +         carry += (unsigned HOST_WIDE_INT) arg1[i] * arg2[j];
>           /* Since prod[p] < 0xFFFF, this sum <= 0xFFFFFFFF.  */
>           carry += prod[k];
>           prod[k] = LOWPART (carry);
> @@ -625,7 +625,7 @@ double_int_mask (unsigned prec)
>    else
>      {
>        mask.high = 0;
> -      mask.low = ((unsigned HOST_WIDE_INT) 2 << (prec - 1)) - 1;
> +      mask.low = prec ? ((unsigned HOST_WIDE_INT) 2 << (prec - 1)) - 1 : 0;
>      }
>
>    return mask;
> --- gcc/tree-ssa-loop-ivopts.c.jj       2012-08-10 15:49:07.000000000 +0200
> +++ gcc/tree-ssa-loop-ivopts.c  2012-08-13 10:17:51.227504425 +0200
> @@ -3173,7 +3173,7 @@ get_address_cost (bool symbol_present, b
>
>        for (i = width; i >= 0; i--)
>         {
> -         off = -((HOST_WIDE_INT) 1 << i);
> +         off = -((unsigned HOST_WIDE_INT) 1 << i);
>           XEXP (addr, 1) = gen_int_mode (off, address_mode);
>           if (memory_address_addr_space_p (mem_mode, addr, as))
>             break;
> @@ -3182,7 +3182,7 @@ get_address_cost (bool symbol_present, b
>
>        for (i = width; i >= 0; i--)
>         {
> -         off = ((HOST_WIDE_INT) 1 << i) - 1;
> +         off = ((unsigned HOST_WIDE_INT) 1 << i) - 1;
>           XEXP (addr, 1) = gen_int_mode (off, address_mode);
>           if (memory_address_addr_space_p (mem_mode, addr, as))
>             break;
>
>         Jakub