[Bug fortran/77505] Negative character length not treated as LEN=0

[elizebethp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77505

Elizebeth Punnoose <elizebethp at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |elizebethp at gmail dot com

--- Comment #3 from Elizebeth Punnoose <elizebethp at gmail dot com> ---
The segmentation fault is reproducible on x86 & ARM64, with the top of trunk.
I have now added a check in trans-array.c:trans_array_constructor()
to check for character lengths less than zero, for character arrays.
If the length is found to be negative, a warning message is printed that the
length will be considered as LEN=0, and the length is set to zero.

Index: trans-array.c
===================================================================
--- trans-array.c       (revision 241960)
+++ trans-array.c       (working copy)
@@ -2226,6 +2226,8 @@
   gfc_ss_info *ss_info;
   gfc_expr *expr;
   gfc_ss *s;
+  tree neg_len;
+  char *msg;

   /* Save the old values for nested checking.  */
   old_first_len = first_len;
@@ -2271,6 +2273,19 @@
          gfc_conv_expr_type (&length_se, expr->ts.u.cl->length,
                              gfc_charlen_type_node);
          ss_info->string_length = length_se.expr;
+
+          /* Check if the length is negative, if so print a warning
+             and consider the length as zero. */
+          neg_len = fold_build2_loc (input_location, LT_EXPR,
+                                     boolean_type_node,
+                                     ss_info->string_length, build_int_cst
(gfc_charlen_type_node, 0));
+          msg = xasprintf ("Negative character length will be treated as
LEN=0");
+          gfc_trans_runtime_check (false, true, neg_len, &length_se.pre,
where, msg);
+          free(msg);
+          ss_info->string_length = fold_build3_loc (input_location, COND_EXPR,
gfc_charlen_type_node,
+                                 neg_len, gfc_index_zero_node,
ss_info->string_length);
+          ss_info->string_length = gfc_evaluate_now (ss_info->string_length,
&length_se.pre);
+
          gfc_add_block_to_block (&outer_loop->pre, &length_se.pre);
          gfc_add_block_to_block (&outer_loop->post, &length_se.post);
        }

The test suite has run clean with the above changes merged on top of trunk.
Kindly review and provide your suggestions if any.
I will post the patch on the gcc-patches mail list, if there is no objection.