PR c++/73456 - ICE with constrained parameter pack.

	* logic.cc (non_atomic_constraint_p): Handle EXPR_PACK_EXPANSION.

From-SVN: r239376

gcc/cp/ChangeLog

+2016-08-11  Jason Merrill  <jason@redhat.com>
+
+	PR c++/73456
+	* logic.cc (non_atomic_constraint_p): Handle EXPR_PACK_EXPANSION.
+
 2016-08-10  Jason Merrill  <jason@redhat.com>
 
 	Implement C++17 constexpr if.

gcc/cp/logic.cc

@@ -305,6 +305,9 @@ non_atomic_constraint_p (tree t)
     case ICONV_CONSTR:
     case DEDUCT_CONSTR:
     case EXCEPT_CONSTR:
+      /* A pack expansion isn't atomic, but it can't decompose to prove an
+	 atom, so it shouldn't cause analyze_atom to return undecided.  */
+    case EXPR_PACK_EXPANSION:
       return false;
     case CHECK_CONSTR:
     case PARM_CONSTR:

gcc/testsuite/g++.dg/concepts/variadic4.C

+// PR c++/73456
+// { dg-options "-std=c++1z -fconcepts" }
+
+template<typename...> struct list {};
+
+template<typename Seq>
+concept bool Sequence = true;
+
+template<Sequence... Seqs>
+struct zip;
+
+template<Sequence... Seqs>
+    requires requires { typename list<Seqs...>; }
+// main.cpp:12:8: internal compiler error: in non_atomic_constraint_p, at cp/logic.cc:315
+struct zip<Seqs...> {};
+
+int main()
+{
+    zip<list<>, list<int>> {};
+}