Avoid streaming of stray referneces

[Jan Hubicka]

Hi,
this patch avoids stremaing completely useless stray references to gobal decl
stream.  I am re-testing the patch (rebased to current tree) on x86_64-linux
and intend to commit once testing finishes.

Honza

gcc/ChangeLog:

2020-05-22  Jan Hubicka  <hubi...@ucw.cz>

        * lto-streamer-out.c (lto_output_tree): Do not stream final ref if
        it is not needed.

gcc/lto/ChangeLog:

2020-05-22  Jan Hubicka  <hubi...@ucw.cz>

        * lto-common.c (lto_read_decls): Do not skip stray refs.

diff --git a/gcc/lto-streamer-out.c b/gcc/lto-streamer-out.c
index f5daadc657b..5ff7f33bfb1 100644
--- a/gcc/lto-streamer-out.c
+++ b/gcc/lto-streamer-out.c
@@ -1780,7 +1780,7 @@ lto_output_tree (struct output_block *ob, tree expr,
         it.  */
       if (!existed_p)
        lto_output_tree_1 (ob, expr, 0, ref_p, this_ref_p);
-      else
+      else if (this_ref_p)
        {
          if (streamer_dump_file)
            {
diff --git a/gcc/lto/lto-common.c b/gcc/lto/lto-common.c
index d04b1c9ca7b..3ea1894ce96 100644
--- a/gcc/lto/lto-common.c
+++ b/gcc/lto/lto-common.c
@@ -1955,25 +1955,19 @@ lto_read_decls (struct lto_file_decl_data *decl_data, 
const void *data,
       else
        {
          t = lto_input_tree_1 (&ib_main, data_in, tag, 0);
-         /* We streamed in new tree.  Add it to cache and process dref.  */
-         if (data_in->reader_cache->nodes.length () == from + 1)
+         gcc_assert (data_in->reader_cache->nodes.length () == from + 1);
+         num_unshared_trees_read++;
+         data_in->location_cache.accept_location_cache ();
+         process_dref (data_in, t, from);
+         if (TREE_CODE (t) == IDENTIFIER_NODE
+             || (TREE_CODE (t) == INTEGER_CST
+                 && !TREE_OVERFLOW (t)))
+           ;
+         else
            {
-             num_unshared_trees_read++;
-             data_in->location_cache.accept_location_cache ();
-             process_dref (data_in, t, from);
-             if (TREE_CODE (t) == IDENTIFIER_NODE
-                 || (TREE_CODE (t) == INTEGER_CST
-                     && !TREE_OVERFLOW (t)))
-               ;
-             else
-               {
-                 lto_maybe_register_decl (data_in, t, from);
-                 process_new_tree (t, &hm, from, &total, data_in);
-               }
+             lto_maybe_register_decl (data_in, t, from);
+             process_new_tree (t, &hm, from, &total, data_in);
            }
-         else
-           /* FIXME: It seems useless to pickle stray references.  */
-           gcc_assert (data_in->reader_cache->nodes.length () == from);
        }
     }