From 947bbe11df57c70085578f381d952e84347dd286 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Fri, 9 Mar 2018 22:35:25 -0500
Subject: [PATCH] PR c++/84785 - ICE with alias template and default targs.

	* pt.c (type_unification_real): Set processing_template_decl if
	saw_undeduced == 1.

From-SVN: r258410
---
 gcc/cp/ChangeLog                           |  6 ++++++
 gcc/cp/pt.c                                |  6 ++++++
 gcc/testsuite/g++.dg/cpp0x/alias-decl-63.C | 18 ++++++++++++++++++
 3 files changed, 30 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/alias-decl-63.C

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 763a6947ec25..527ed0e4aded 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2018-03-09  Jason Merrill  <jason@redhat.com>
+
+	PR c++/84785 - ICE with alias template and default targs.
+	* pt.c (type_unification_real): Set processing_template_decl if
+	saw_undeduced == 1.
+
 2018-03-03  Jason Merrill  <jason@redhat.com>
 
 	PR c++/84686 - missing volatile loads.
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 27e4c84ac799..423d92c66f46 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -18602,7 +18602,13 @@ type_unification_real (tree tparms,
 	  location_t save_loc = input_location;
 	  if (DECL_P (parm))
 	    input_location = DECL_SOURCE_LOCATION (parm);
+
+	  if (saw_undeduced == 1)
+	    ++processing_template_decl;
 	  arg = tsubst_template_arg (arg, targs, complain, NULL_TREE);
+	  if (saw_undeduced == 1)
+	    --processing_template_decl;
+
 	  if (arg != error_mark_node && !uses_template_parms (arg))
 	    arg = convert_template_argument (parm, arg, targs, complain,
 					     i, NULL_TREE);
diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-63.C b/gcc/testsuite/g++.dg/cpp0x/alias-decl-63.C
new file mode 100644
index 000000000000..04fb42d9e091
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-63.C
@@ -0,0 +1,18 @@
+// PR c++/84785
+// { dg-do compile { target c++11 } }
+
+template <typename> struct A;
+template <bool> struct B;
+template <bool B, typename> using enable_if_t = typename B<B>::type;
+template <long> using type_pack_element = int;
+struct variant {
+  variant() {}
+  template <typename Arg, long I = Arg::type::value,
+            typename = type_pack_element<I>, enable_if_t<A<Arg>::value, int>>
+  variant(Arg &&);
+};
+
+struct S {
+  variant var;
+};
+int main() { S s; }
-- 
2.47.2