Avoid ICE on unsupported use of __integer_pack.

	* pt.c (tsubst_pack_expansion): Sorry rather than abort
	on __integer_pack as subexpression of pattern.

From-SVN: r260404

gcc/cp/ChangeLog

+2018-05-19  Jason Merrill  <jason@redhat.com>
+
+	* pt.c (tsubst_pack_expansion): Sorry rather than abort
+	on __integer_pack as subexpression of pattern.
+
 2018-05-18  Jason Merrill  <jason@redhat.com>
 
 	PR c++/58407 - deprecated implicit copy ops.

gcc/cp/pt.c

@@ -12067,8 +12067,13 @@ tsubst_pack_expansion (tree t, tree args, tsubst_flags_t complain,
 	}
       else if (builtin_pack_call_p (parm_pack))
 	{
-	  /* ??? Support use in other patterns.  */
-	  gcc_assert (parm_pack == pattern);
+	  if (parm_pack != pattern)
+	    {
+	      if (complain & tf_error)
+		sorry ("%qE is not the entire pattern of the pack expansion",
+		       parm_pack);
+	      return error_mark_node;
+	    }
 	  return expand_builtin_pack_call (parm_pack, args,
 					   complain, in_decl);
 	}

gcc/testsuite/g++.dg/ext/integer-pack4.C

+// { dg-additional-options -std=c++17 }
+
+template<int ... Ns> int f() { return (Ns + ...); }
+template<int N> int g() {
+  return f<__integer_pack(N)...>(); // Fine.
+}
+template<int N> int h() {
+  return f<(2*__integer_pack(N))...>(); // { dg-bogus "sorry" "" { xfail *-*-* } }
+}
+int main() { return g<3>()+h<3>(); }