Add error check on return value of build_co_await

gcc/cp/ChangeLog
	* coroutines.cc (finish_co_await_expr): Add error check on return
	value of build_co_await.
	(finish_co_yield_expr): Ditto.

gcc/cp/ChangeLog

 2020-01-22  Jun Ma <JunMa@linux.alibaba.com>
 
+	* coroutines.cc (finish_co_await_expr): Add error check on return
+	value of build_co_await.
+	(finish_co_yield_expr,): Ditto.
+
+2020-01-22  Jun Ma <JunMa@linux.alibaba.com>
+
 	* coroutines.cc (lookup_awaitable_member): Lookup an awaitable member.
 	(lookup_promise_method): Emit diagnostic when get NULL_TREE back only.
 	(build_co_await): Use lookup_awaitable_member instead of lookup_member.

gcc/cp/coroutines.cc

@@ -819,8 +819,11 @@ finish_co_await_expr (location_t kw, tree expr)
 
   /* Now we want to build co_await a.  */
   tree op = build_co_await (kw, a, CO_AWAIT_SUSPEND_POINT);
+  if (op != error_mark_node)
+    {
       TREE_SIDE_EFFECTS (op) = 1;
       SET_EXPR_LOCATION (op, kw);
+    }
 
   return op;
 }
@@ -885,9 +888,11 @@ finish_co_yield_expr (location_t kw, tree expr)
      promise transform_await().  */
 
   tree op = build_co_await (kw, yield_call, CO_YIELD_SUSPEND_POINT);
-
+  if (op != error_mark_node)
+    {
       op = build2_loc (kw, CO_YIELD_EXPR, TREE_TYPE (op), expr, op);
       TREE_SIDE_EFFECTS (op) = 1;
+    }
 
   return op;
 }