From a09c81b4ba40aac99fd4c37654e1231f4836f891 Mon Sep 17 00:00:00 2001
From: Jakub Jelinek <jakub@redhat.com>
Date: Tue, 14 Jun 2016 21:55:08 +0200
Subject: [PATCH] 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                   |  4 ++++
 gcc/cp/decl.c                      |  8 ++++++++
 gcc/testsuite/ChangeLog            |  3 +++
 gcc/testsuite/g++.dg/opt/pr71528.C | 23 +++++++++++++++++++++++
 4 files changed, 38 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/opt/pr71528.C

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index d006305bdc0..cd5996bdd1d 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,5 +1,9 @@
 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.
 
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 20e7307ddad..a03e48ff618 100644
--- a/gcc/cp/decl.c
+++ b/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);
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 0e3c9cd7738..4a55801352e 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,8 @@
 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.
 
diff --git a/gcc/testsuite/g++.dg/opt/pr71528.C b/gcc/testsuite/g++.dg/opt/pr71528.C
new file mode 100644
index 00000000000..bfe06220472
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/pr71528.C
@@ -0,0 +1,23 @@
+// 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;
-- 
2.30.2