[PATCH] Fix c++/67337 (segfault in mangle.c)

[Markus Trippelsdorf <markus@trippelsdorf.de>]

decl_mangling_context() in mangle.c returns a NULL_TREE in case of
template type parameters. write_template_prefix() needs to handle this
situation.

Tested on ppc64le.

This is a regression from gcc=4.8.
OK for trunk, gcc-5 and gcc-4.9?

Thanks.

	PR c++/67337
	* mangle.c (write_template_prefix): Guard against context==NULL.

diff --git a/gcc/cp/mangle.c b/gcc/cp/mangle.c
index 342cb93e68b3..a9993f40b94d 100644
--- a/gcc/cp/mangle.c
+++ b/gcc/cp/mangle.c
@@ -1149,7 +1149,7 @@ write_template_prefix (const tree node)
      So, for the example above, `Outer<int>::Inner' is represented as a
      substitution candidate by a TREE_LIST whose purpose is `Outer<int>'
      and whose value is `Outer<T>::Inner<U>'.  */
-  if (TYPE_P (context))
+  if (context && TYPE_P (context))
     substitution = build_tree_list (context, templ);
   else
     substitution = templ;
diff --git a/gcc/testsuite/g++.dg/template/pr67337.C b/gcc/testsuite/g++.dg/template/pr67337.C
new file mode 100644
index 000000000000..df2651bc9a57
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/pr67337.C
@@ -0,0 +1,25 @@
+template <class> class A
+{
+  void m_fn1 (int *, int);
+};
+
+template <class> class B
+{
+public:
+  typedef int Type;
+};
+
+template <class> class C
+{
+public:
+  C (int);
+  template <template <class> class T> void m_fn2 (typename T<void>::Type);
+};
+
+template <>
+void
+A<int>::m_fn1 (int *, int)
+{
+  C<int> a (0);
+  a.m_fn2<B> (0);
+}
-- 
Markus