From e8ef9fdfb9fd4b16169377a7c65309bb110a0064 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Tue, 27 Feb 2018 12:26:47 -0500
Subject: [PATCH] PR c++/84489 - dependent default template argument

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

From-SVN: r258039
---
 gcc/cp/ChangeLog                          |  5 +++++
 gcc/cp/pt.c                               | 21 ++++++++++++++-------
 gcc/testsuite/g++.dg/cpp0x/fntmpdefarg7.C | 10 ++++++++++
 3 files changed, 29 insertions(+), 7 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/fntmpdefarg7.C

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index dd35f1bda52..b2973d1b301 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,8 @@
+2018-02-27  Jason Merrill  <jason@redhat.com>
+
+	PR c++/84489 - dependent default template argument
+	* pt.c (type_unification_real): Handle early substitution failure.
+
 2018-02-26  Jason Merrill  <jason@redhat.com>
 
 	PR c++/84560 - ICE capturing multi-dimensional VLA.
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 42fd872d6c0..a3da40912d6 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -19831,21 +19831,28 @@ type_unification_real (tree tparms,
 	    continue;
 	  tree parm = TREE_VALUE (tparm);
 
-	  if (TREE_CODE (parm) == PARM_DECL
-	      && uses_template_parms (TREE_TYPE (parm))
-	      && saw_undeduced < 2)
-	    continue;
+	  tsubst_flags_t fcomplain = complain;
+	  if (saw_undeduced == 1)
+	    {
+	      /* When saw_undeduced == 1, substitution into parm and arg might
+		 fail or not replace all template parameters, and that's
+		 fine.  */
+	      fcomplain = tf_none;
+	      if (TREE_CODE (parm) == PARM_DECL
+		  && uses_template_parms (TREE_TYPE (parm)))
+		continue;
+	    }
 
 	  tree arg = TREE_PURPOSE (tparm);
 	  reopen_deferring_access_checks (*checks);
 	  location_t save_loc = input_location;
 	  if (DECL_P (parm))
 	    input_location = DECL_SOURCE_LOCATION (parm);
-	  arg = tsubst_template_arg (arg, full_targs, complain, NULL_TREE);
-	  if (!uses_template_parms (arg))
+	  arg = tsubst_template_arg (arg, full_targs, fcomplain, NULL_TREE);
+	  if (arg != error_mark_node && !uses_template_parms (arg))
 	    arg = convert_template_argument (parm, arg, full_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 00000000000..636bf1afd88
--- /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
+}
-- 
2.30.2