PR c++/78489 - wrong SFINAE behavior.

	PR c++/84489
	* pt.c (type_unification_real): Don't defer substitution failure.

From-SVN: r258824

gcc/cp/ChangeLog

+2018-03-23  Jason Merrill  <jason@redhat.com>
+
+	PR c++/78489 - wrong SFINAE behavior.
+
+	PR c++/84489
+	* pt.c (type_unification_real): Don't defer substitution failure.
+
 2018-03-23  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/85015

gcc/cp/pt.c

@@ -19995,41 +19995,49 @@ type_unification_real (tree tparms,
 	  if (targ || tparm == error_mark_node)
 	    continue;
 	  tree parm = TREE_VALUE (tparm);
-
-	  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);
-
 	  if (saw_undeduced == 1)
 	    ++processing_template_decl;
-	  arg = tsubst_template_arg (arg, full_targs, fcomplain, NULL_TREE);
-	  if (saw_undeduced == 1)
-	    --processing_template_decl;
 
-	  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 == 1)
-	    arg = NULL_TREE;
+	  if (saw_undeduced == 1
+	      && TREE_CODE (parm) == PARM_DECL
+	      && uses_template_parms (TREE_TYPE (parm)))
+	    {
+	      /* The type of this non-type parameter depends on undeduced
+		 parameters.  Don't try to use its default argument yet,
+		 but do check whether the arguments we already have cause
+		 substitution failure, so that that happens before we try
+		 later default arguments (78489).  */
+	      tree type = tsubst (TREE_TYPE (parm), full_targs, complain,
+				  NULL_TREE);
+	      if (type == error_mark_node)
+		arg = error_mark_node;
+	      else
+		arg = NULL_TREE;
+	    }
 	  else
-	    arg = error_mark_node;
+	    {
+	      arg = tsubst_template_arg (arg, full_targs, complain, NULL_TREE);
+
+	      if (!uses_template_parms (arg))
+		arg = convert_template_argument (parm, arg, full_targs,
+						 complain, i, NULL_TREE);
+	      else if (saw_undeduced == 1)
+		arg = NULL_TREE;
+	      else
+		arg = error_mark_node;
+	    }
+
+	  if (saw_undeduced == 1)
+	    --processing_template_decl;
 	  input_location = save_loc;
 	  *checks = get_deferred_access_checks ();
 	  pop_deferring_access_checks ();
+
 	  if (arg == error_mark_node)
 	    return 1;
 	  else if (arg)

gcc/testsuite/g++.dg/cpp0x/fntmpdefarg4a.C

+// PR c++/55724
+// { dg-do compile { target c++11 } }
+
+template<int N> struct S {};
+template<typename T = int, T N = 42> void f(S<N>) {}
+int main() { S<1> s; f(s); }

gcc/testsuite/g++.dg/cpp0x/sfinae60.C

+// PR c++/78489
+// { dg-do compile { target c++11 } }
+
+template <bool P, class T = void> struct enable_if { using type = T; };
+template <class T> struct enable_if<false, T> {};
+
+template <class Dummy> struct use_type { using type = int; };
+
+template <bool Pred>
+struct get_type {
+    static_assert(Pred, "");
+    using type = int;
+};
+
+template <bool Val,
+              class      = typename enable_if<Val>::type, // Evaluation/Substitution should end here
+              class ValT = typename get_type<Val>::type,  // This should not be instantiated
+              typename use_type<ValT>::type = 0           // This NTTP causes ValT to be required
+            >
+constexpr bool test(int) { return false; }
+
+template <bool>
+constexpr bool test(long) { return true; }
+
+static_assert(test<false>(0), ""); // should call test(long)

gcc/testsuite/g++.dg/cpp0x/sfinae61.C

+// PR c++/78489
+// { dg-do compile { target c++11 } }
+
+template <bool Pred, class T> struct enable_if { typedef T type; };
+template <class T> struct enable_if<false, T> {};
+
+template <int Idx> struct blows_up { static_assert(Idx != Idx, ""); };
+
+template <int Idx,
+           // substitution should fail here
+          typename enable_if<Idx != Idx, int>::type = 0,
+          // GCC evaluates this statement
+          class = typename blows_up<Idx>::type 
+>
+void Foo() {}
+
+// Check the constructor in as SFINAE context
+template <int I> constexpr auto test(int) -> decltype((Foo<I>(), true)) { return true; }
+template <int>   constexpr bool test(long) { return false; }
+
+static_assert(!test<3>(0), ""); // Blows up