cgraphunit: Avoid code generation differences based on -w/TREE_NO_WARNING [PR94277]

The following testcase FAILs with -fcompare-debug, but not because -g vs.
-g0 would make a difference, but because the second compilation is done with
-w in order not to emit warnings twice and -w seems to affect the *.gkd dump
content.
This is because TREE_NO_WARNING flag, or warn_unused_function does affect
not just whether a warning/pedwarn is printed, but also whether we set
TREE_PUBLIC on such decls.
The following patch makes sure we set it regardless of anything warning
related (TREE_NO_WARNING or warn_unused_function).

2020-03-24  Jakub Jelinek  <jakub@redhat.com>

	PR debug/94277
	* cgraphunit.c (check_global_declaration): For DECL_EXTERNAL and
	non-TREE_PUBLIC non-DECL_ARTIFICIAL FUNCTION_DECLs, set TREE_PUBLIC
	regardless of whether TREE_NO_WARNING is set on it or whether
	warn_unused_function is true or not.

	* gcc.dg/pr94277.c: New test.

1 files changed, 6 insertions, 6 deletions

diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
index d7ed405bf2c..3415660440e 100644
--- a/gcc/cgraphunit.c
+++ b/gcc/cgraphunit.c
@@ -1068,15 +1068,15 @@ check_global_declaration (symtab_node *snode)
       && DECL_INITIAL (decl) == 0
       && DECL_EXTERNAL (decl)
       && ! DECL_ARTIFICIAL (decl)
-      && ! TREE_NO_WARNING (decl)
-      && ! TREE_PUBLIC (decl)
-      && (warn_unused_function
-	  || snode->referred_to_p (/*include_self=*/false)))
+      && ! TREE_PUBLIC (decl))
     {
-      if (snode->referred_to_p (/*include_self=*/false))
+      if (TREE_NO_WARNING (decl))
+	;
+      else if (snode->referred_to_p (/*include_self=*/false))
 	pedwarn (input_location, 0, "%q+F used but never defined", decl);
       else
-	warning (OPT_Wunused_function, "%q+F declared %<static%> but never defined", decl);
+	warning (OPT_Wunused_function, "%q+F declared %<static%> but never "
+				       "defined", decl);
       /* This symbol is effectively an "extern" declaration now.  */
       TREE_PUBLIC (decl) = 1;
     }