From 27664bbdeab6f5ced2c0fa58555da5ae060feeb6 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Fri, 2 Mar 2018 13:24:40 -0500
Subject: [PATCH] PR c++/84489 - dependent default template argument

	* pt.c (type_unification_real): Handle early substitution failure.

From-SVN: r258152
---
 gcc/cp/ChangeLog                          |  5 +++++
 gcc/cp/pt.c                               |  4 ++--
 gcc/testsuite/g++.dg/cpp0x/fntmpdefarg7.C | 10 ++++++++++
 3 files changed, 17 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/fntmpdefarg7.C

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index d30784fbf156..ab5a911f44ff 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,8 @@
+2018-03-02  Jason Merrill  <jason@redhat.com>
+
+	PR c++/84489 - dependent default template argument
+	* pt.c (type_unification_real): Handle early substitution failure.
+
 2018-02-28  Jason Merrill  <jason@redhat.com>
 
 	PR c++/71784 - ICE with ref-qualifier and explicit specialization.
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 9dbf17ba4d88..27e4c84ac799 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -18603,10 +18603,10 @@ type_unification_real (tree tparms,
 	  if (DECL_P (parm))
 	    input_location = DECL_SOURCE_LOCATION (parm);
 	  arg = tsubst_template_arg (arg, targs, complain, NULL_TREE);
-	  if (!uses_template_parms (arg))
+	  if (arg != error_mark_node && !uses_template_parms (arg))
 	    arg = convert_template_argument (parm, arg, targs, complain,
 					     i, NULL_TREE);
-	  else if (saw_undeduced < 2)
+	  else if (saw_undeduced == 1)
 	    arg = NULL_TREE;
 	  else
 	    arg = error_mark_node;
diff --git a/gcc/testsuite/g++.dg/cpp0x/fntmpdefarg7.C b/gcc/testsuite/g++.dg/cpp0x/fntmpdefarg7.C
new file mode 100644
index 000000000000..636bf1afd883
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/fntmpdefarg7.C
@@ -0,0 +1,10 @@
+// PR c++/84489
+// { dg-do compile { target c++11 } }
+
+template <class T = int, T N = T(), bool B = (N >> 1)>
+T f1() {return 0;}
+
+int main()
+{
+  f1(); // Bug here
+}
-- 
2.47.2