[Bug tree-optimization/57385] [tree-ssa] Possible segfault in fully_constant_vn_reference_p

[aivchenk at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57385

--- Comment #1 from Alexander Ivchenko <aivchenk at gmail dot com> ---
Following fix could solve the problem:

diff --git a/gcc-4.6/gcc/tree-ssa-sccvn.c b/gcc-4.6/gcc/tree-ssa-sccvn.c
index eb88969..704a86c 100644
--- a/gcc-4.6/gcc/tree-ssa-sccvn.c
+++ b/gcc-4.6/gcc/tree-ssa-sccvn.c
@@ -1115,6 +1115,7 @@ fully_constant_vn_reference_p (vn_reference_t ref)
              == TYPE_MODE (TREE_TYPE (TREE_TYPE (arg0->op0))))
          && GET_MODE_CLASS (TYPE_MODE (op->type)) == MODE_INT
          && GET_MODE_SIZE (TYPE_MODE (op->type)) == 1
+         && tree_int_cst_sgn (op->op0) >= 0
          && compare_tree_int (op->op0, TREE_STRING_LENGTH (arg0->op0)) < 0)
        return build_int_cst_type (op->type,
                                   (TREE_STRING_POINTER (arg0->op0)