From 6284a979dba8e74efe6c36b33311f1b4bac10f44 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Thu, 25 Feb 2016 09:09:18 -0500
Subject: [PATCH] re PR c++/68049 (template instantiation involving may_alias
 defines symbol twice)

	PR c++/68049
	* tree.c (strip_typedefs): Use DECL_ORIGINAL_TYPE.

From-SVN: r233715
---
 gcc/cp/ChangeLog                              |  5 +++++
 gcc/cp/tree.c                                 | 10 ++++++++-
 .../g++.dg/ext/attribute-may-alias-3.C        | 22 +++++++++++++++++++
 3 files changed, 36 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/ext/attribute-may-alias-3.C

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 3ae4daf8612..eb5cfe6b566 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,8 @@
+2016-02-25  Jason Merrill  <jason@redhat.com>
+
+	PR c++/68049
+	* tree.c (strip_typedefs): Use DECL_ORIGINAL_TYPE.
+
 2016-02-25  Patrick Palka  <ppalka@gcc.gnu.org>
 
 	PR c++/69736
diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
index 0f7287ab0d7..ac38ce3fe11 100644
--- a/gcc/cp/tree.c
+++ b/gcc/cp/tree.c
@@ -1447,7 +1447,15 @@ strip_typedefs (tree t, bool *remove_attributes)
     }
 
   if (!result)
-      result = TYPE_MAIN_VARIANT (t);
+    {
+      if (typedef_variant_p (t))
+	/* Explicitly get the underlying type, as TYPE_MAIN_VARIANT doesn't
+	   strip typedefs with attributes.  */
+	result = TYPE_MAIN_VARIANT (DECL_ORIGINAL_TYPE (TYPE_NAME (t)));
+      else
+	result = TYPE_MAIN_VARIANT (t);
+    }
+  gcc_assert (!typedef_variant_p (result));
   if (TYPE_USER_ALIGN (t) != TYPE_USER_ALIGN (result)
       || TYPE_ALIGN (t) != TYPE_ALIGN (result))
     {
diff --git a/gcc/testsuite/g++.dg/ext/attribute-may-alias-3.C b/gcc/testsuite/g++.dg/ext/attribute-may-alias-3.C
new file mode 100644
index 00000000000..ba6091b6d72
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/attribute-may-alias-3.C
@@ -0,0 +1,22 @@
+// PR c++/68049
+// { dg-do compile { target c++11 } }
+
+template <typename T> struct Bar
+{
+    using type = T;
+};
+template <typename T> struct Foo
+{
+    typedef typename Bar<T>::type alias_type [[gnu::may_alias]];
+
+    alias_type operator()() { return {}; }
+};
+
+template <typename T> void print(T) {}
+
+int main()
+{
+    print(Foo<int>()());
+    print(0);
+    return 0;
+}