[Bug debug/97599] [8/9/10/11 Regression] missing unspecified_parameters DIE in DWARF for functions with variable arguments

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97599

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Another version of the patch:
--- gcc/dwarf2out.c.jj  2020-10-27 18:38:00.001979404 +0100
+++ gcc/dwarf2out.c     2020-10-28 10:52:29.618796758 +0100
@@ -22756,6 +22756,7 @@ gen_subprogram_die (tree decl, dw_die_re
   tree origin = decl_ultimate_origin (decl);
   dw_die_ref subr_die;
   dw_die_ref old_die = lookup_decl_die (decl);
+  bool old_die_had_no_children = false;

   /* This function gets called multiple times for different stages of
      the debug process.  For example, for func() in this code:
@@ -22846,6 +22847,9 @@ gen_subprogram_die (tree decl, dw_die_re
   if (old_die && declaration)
     return;

+  if (in_lto_p && old_die && old_die->die_child == NULL)
+    old_die_had_no_children = true;
+
   /* Now that the C++ front end lazily declares artificial member fns, we
      might need to retrofit the declaration into its class.  */
   if (!declaration && !origin && !old_die
@@ -23365,6 +23369,10 @@ gen_subprogram_die (tree decl, dw_die_re
          else if (DECL_INITIAL (decl) == NULL_TREE)
            gen_unspecified_parameters_die (decl, subr_die);
        }
+      else if ((subr_die != old_die || old_die_had_no_children)
+              && prototype_p (TREE_TYPE (decl))
+              && stdarg_p (TREE_TYPE (decl)))
+       gen_unspecified_parameters_die (decl, subr_die);
     }

   if (subr_die != old_die)