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Subject: [Bug middle-end/95903] gcc 10: wrong code with -fwrapv
Date: Sat, 27 Jun 2020 10:42:34 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95903

--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:37995960984ea2222346dd9d168d332cd6f7adf0

commit r11-1685-g37995960984ea2222346dd9d168d332cd6f7adf0
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Sat Jun 27 12:38:23 2020 +0200

    c-family: Use TYPE_OVERFLOW_UNDEFINED instead of !TYPE_UNSIGNED in
pointer_sum [PR95903]

    For lp64 targets and int off ... ptr[off + 1]
    is lowered in pointer_sum to *(ptr + ((sizetype) off + (sizetype) 1)).
    That is fine when signed integer wrapping is undefined (and is not done
    already if off has unsigned type), but changes behavior for -fwrapv, wh=
ere
    overflow is well defined.  Runtime test could be:
    int
    main ()
    {
      char *p =3D __builtin_malloc (0x100000000UL);
      if (!p) return 0;
      char *q =3D p + 0x80000000UL;
      int o =3D __INT_MAX__;
      q[o + 1] =3D 1;
      if (q[-__INT_MAX__ - 1] !=3D 1) __builtin_abort ();
      return 0;
    }
    with -fwrapv or so, not included in the testsuite because it requires 4=
GB
    allocation (with some other test it would be enough to have something
    slightly above 2GB, but still...).

    2020-06-27  Jakub Jelinek  <jakub@redhat.com>

            PR middle-end/95903
    gcc/c-family/
            * c-common.c (pointer_int_sum): Use TYPE_OVERFLOW_UNDEFINED ins=
tead
of
            !TYPE_UNSIGNED check to see if we can apply distributive law and
handle
            smaller precision intop operands separately.
    gcc/testsuite/
            * c-c++-common/pr95903.c: New test.=