[Bug middle-end/95903] gcc 10: wrong code with -fwrapv

cvs-commit at gcc dot gnu.org gcc-bugzilla@gcc.gnu.org
Wed Sep 16 19:22:27 GMT 2020


--- Comment #12 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-9 branch has been updated by Jakub Jelinek


commit r9-8902-ga1eb6e41832816b671d3b945014f7e8255167470
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, where
    overflow is well defined.  Runtime test could be:
    main ()
      char *p = __builtin_malloc (0x100000000UL);
      if (!p) return 0;
      char *q = p + 0x80000000UL;
      int o = __INT_MAX__;
      q[o + 1] = 1;
      if (q[-__INT_MAX__ - 1] != 1) __builtin_abort ();
      return 0;
    with -fwrapv or so, not included in the testsuite because it requires 4GB
    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
            * c-common.c (pointer_int_sum): Use TYPE_OVERFLOW_UNDEFINED instead
            !TYPE_UNSIGNED check to see if we can apply distributive law and
            smaller precision intop operands separately.
            * c-c++-common/pr95903.c: New test.

    (cherry picked from commit 37995960984ea2222346dd9d168d332cd6f7adf0)

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