PR c++/80916 - spurious "static but not defined" warning.

Nothing can refer to an internal decl with no definition, so we shouldn't
treat such a decl as a possible devirtualization target.

	* gimple-fold.c (can_refer_decl_in_current_unit_p): Return false
	for an internal symbol with DECL_EXTERNAL.

From-SVN: r269459

gcc/ChangeLog

+2019-01-25  Jason Merrill  <jason@redhat.com>
+
+	PR c++/80916 - spurious "static but not defined" warning.
+	* gimple-fold.c (can_refer_decl_in_current_unit_p): Return false
+	for an internal symbol with DECL_EXTERNAL.
+
 2019-04-07  Richard Biener  <rguenther@suse.de>
 
 	PR middle-end/89618

gcc/gimple-fold.c

@@ -121,9 +121,12 @@ can_refer_decl_in_current_unit_p (tree decl, tree from_decl)
       || !VAR_OR_FUNCTION_DECL_P (decl))
     return true;
 
-  /* Static objects can be referred only if they was not optimized out yet.  */
-  if (!TREE_PUBLIC (decl) && !DECL_EXTERNAL (decl))
+  /* Static objects can be referred only if they are defined and not optimized
+     out yet.  */
+  if (!TREE_PUBLIC (decl))
     {
+      if (DECL_EXTERNAL (decl))
+	return false;
       /* Before we start optimizing unreachable code we can be sure all
 	 static objects are defined.  */
       if (symtab->function_flags_ready)

gcc/testsuite/g++.dg/warn/unused-fn1.C

+// PR c++/80916
+// { dg-options "-Os -Wunused" }
+
+struct j {
+  virtual void dispatch(void *) {}
+};
+template <typename>
+struct i : j {
+  void dispatch(void *) {} // warning: 'void i< <template-parameter-1-1> >::dispatch(void*) [with <template-parameter-1-1> = {anonymous}::l]' declared 'static' but never defined [-Wunused-function]
+};
+namespace {
+  struct l : i<l> {};
+}
+void f(j *k) {
+  k->dispatch(0);
+}