[Bug fortran/31203] Character length should never be negative

["fxcoudert at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #5 from fxcoudert at gcc dot gnu dot org  2007-03-18 23:03 -------
When creating a testcase for this one, I found we have a similar problem with
character functions:

$ cat a.f90
program test
  print *, len(bar(-1))
contains
  function bar(i)
    integer, intent(in) :: i
    character(len=i) :: bar
    bar = ""
  end function bar
end program test
$ gfortran a.f90 && ./a.out
Fortran runtime error: Attempt to allocate a negative amount of memory.


Complete patch is:

Index: trans-expr.c
===================================================================
--- trans-expr.c        (revision 123028)
+++ trans-expr.c        (working copy)
@@ -227,6 +227,8 @@

   gfc_init_se (&se, NULL);
   gfc_conv_expr_type (&se, cl->length, gfc_charlen_type_node);
+  se.expr = fold_build2 (MAX_EXPR, gfc_charlen_type_node, se.expr,
+                        build_int_cst (gfc_charlen_type_node, 0));
   gfc_add_block_to_block (pblock, &se.pre);

   tmp = cl->backend_decl;
@@ -2256,6 +2258,8 @@
         }
         else
         {
+         tree tmp;
+
          /* Calculate the length of the returned string.  */
          gfc_init_se (&parmse, NULL);
          if (need_interface_mapping)
@@ -2264,7 +2268,11 @@
            gfc_conv_expr (&parmse, sym->ts.cl->length);
          gfc_add_block_to_block (&se->pre, &parmse.pre);
          gfc_add_block_to_block (&se->post, &parmse.post);
-         cl.backend_decl = fold_convert (gfc_charlen_type_node, parmse.expr);
+         
+         tmp = fold_convert (gfc_charlen_type_node, parmse.expr);
+         tmp = fold_build2 (MAX_EXPR, gfc_charlen_type_node, tmp,
+                            build_int_cst (gfc_charlen_type_node, 0));
+         cl.backend_decl = tmp;
        }

       /* Set up a charlen structure for it.  */


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31203