[Bug default/25439] namespace DIE added to duplicate chain list (--odr-mode=basic)

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

https://sourceware.org/bugzilla/show_bug.cgi?id=25439

--- Comment #2 from Tom de Vries <vries at gcc dot gnu.org> ---
Tentative patch:
...
index 08e3df4..e2a4ec4 100644
--- a/dwz.c
+++ b/dwz.c
@@ -3370,24 +3370,31 @@ checksum_ref_die (dw_cu_ref cu, dw_die_ref top_die,
dw_die_ref die,
        }
     }

-  if (!only_hash_name_p
-      && (top_die == NULL || top_die->die_ck_state != CK_BAD))
-    for (child = die->die_child; child; child = child->die_sib)
-      {
-       unsigned int r
-         = checksum_ref_die (cu,
-                             top_die ? top_die
-                             : child->die_named_namespace
-                             ? NULL : child, child,
-                             second_idx, second_hash);
-       if (top_die == NULL)
-         assert (r == 0 && obstack_object_size (&ob) == 0);
-
-       if (ret == 0 || (r && r < ret))
-         ret = r;
-       if (top_die && top_die->die_ck_state == CK_BAD)
-         break;
-      }
+  if (top_die == NULL || top_die->die_ck_state != CK_BAD)
+    {
+      hashval_t save_checksum;
+      if (top_die)
+       save_checksum = top_die->u.p1.die_ref_hash;
+      for (child = die->die_child; child; child = child->die_sib)
+       {
+         unsigned int r
+           = checksum_ref_die (cu,
+                               top_die ? top_die
+                               : child->die_named_namespace
+                               ? NULL : child, child,
+                               second_idx, second_hash);
+         if (top_die == NULL)
+           assert (r == 0 && obstack_object_size (&ob) == 0);
+
+         if (ret == 0 || (r && r < ret))
+           ret = r;
+         if (top_die && top_die->die_ck_state == CK_BAD)
+           break;
+       }
+      if (top_die
+         && top_die->die_ck_state != CK_BAD && only_hash_name_p)
+       top_die->u.p1.die_ref_hash = save_checksum;
+    }--

   if (top_die == die)
     {
...

However, that also drops effectiveness to less than 1%:
...
$ rm -f 1; ./dwz -Lnone -lnone -o 1 cc1 --no-odr
$ rm -f 2; ./dwz -Lnone -lnone -o 2 cc1 --odr-mode=basic
$ diff.sh cc1 1
.debug_info      red: 44.84%    111527248  61527733
.debug_abbrev    red: 40.28%    1722726  1028968
.debug_str       red: 0%        6609355  6609355
total            red: 42.30%    119859329 69166056
$ diff.sh cc1 2
.debug_info      red: 45.44%    111527248  60860046
.debug_abbrev    red: 42.87%    1722726  984340
.debug_str       red: 0%        6609355  6609355
total            red: 42.89%    119859329 68453741
...

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