re PR c++/71528 (multiple extern reference declarations produce uninitialized access)

	PR c++/71528
	* decl.c (duplicate_decls): For DECL_INITIALIZED_P non-external
	olddecl vars, preserve their TREE_READONLY bit.

	* g++.dg/opt/pr71528.C: New test.

From-SVN: r237458

gcc/cp/ChangeLog

 2016-06-14  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/71528
+	* decl.c (duplicate_decls): For DECL_INITIALIZED_P non-external
+	olddecl vars, preserve their TREE_READONLY bit.
+
 	PR c++/71516
 	* decl.c (complete_vars): Handle gracefully type == error_mark_node.
 

gcc/cp/decl.c

@@ -2066,6 +2066,14 @@ duplicate_decls (tree newdecl, tree olddecl, bool newdecl_is_friend)
       if (VAR_P (newdecl))
 	{
 	  DECL_THIS_EXTERN (newdecl) |= DECL_THIS_EXTERN (olddecl);
+	  /* For already initialized vars, TREE_READONLY could have been
+	     cleared in cp_finish_decl, because the var needs runtime
+	     initialization or destruction.  Make sure not to set
+	     TREE_READONLY on it again.  */
+	  if (DECL_INITIALIZED_P (olddecl)
+	      && !DECL_EXTERNAL (olddecl)
+	      && !TREE_READONLY (olddecl))
+	    TREE_READONLY (newdecl) = 0;
 	  DECL_INITIALIZED_P (newdecl) |= DECL_INITIALIZED_P (olddecl);
 	  DECL_NONTRIVIALLY_INITIALIZED_P (newdecl)
 	    |= DECL_NONTRIVIALLY_INITIALIZED_P (olddecl);

gcc/testsuite/ChangeLog

 2016-06-14  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/71528
+	* g++.dg/opt/pr71528.C: New test.
+
 	PR c++/71516
 	* g++.dg/init/pr71516.C: New test.
 

gcc/testsuite/g++.dg/opt/pr71528.C

+// PR c++/71528
+// { dg-do run }
+// { dg-options "-O2" }
+
+extern int &x;
+int y;
+
+int &
+foo ()
+{
+  return y;
+}
+
+int &x = foo ();
+
+int
+main ()
+{
+  if (&x != &y)
+    __builtin_abort ();
+}
+
+extern int &x;