[Bug tree-optimization/94187] [10 Regression] valgrind error in count_nonzero_bytes since r10-2101

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94187

--- Comment #11 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:741ff2a263fe0ddc343288331c0047c1a32af8b2

commit r10-7207-g741ff2a263fe0ddc343288331c0047c1a32af8b2
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Mar 17 10:43:46 2020 +0100

    strlen: Punt on UB reads past end of string literal [PR94187]

    The gcc.dg/pr68785.c test which contains:
    int
    foo (void)
    {
      return *(int *) "";
    }
    has UB in the program if it is ever called, but causes UB in the compiler
    as well as at least in theory non-reproduceable code generation.
    The problem is that nbytes is in this case 4, prep is the
    TREE_STRING_POINTER of a "" string literal with TREE_STRING_LENGTH of 1 and
    we do:
    4890              for (const char *p = prep; p != prep + nbytes; ++p)
    4891                if (*p)
    4892                  {
    4893                    *allnul = false;
    4894                    break;
    4895                  }
    and so read the bytes after the STRING_CST payload, which can be random.
    I think we should just punt in this case.

    2020-03-17  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/94187
            * tree-ssa-strlen.c (count_nonzero_bytes): Punt if
            nchars - offset < nbytes.