gcc/cp/ChangeLog:

	* cp-tree.h (cp_operator_id, cp_assignment_operator_id): Document.

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index da45d95..234441b 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -1731,9 +1731,16 @@ struct GTY(()) language_function {
    || (NAME) == cp_operator_id (DELETE_EXPR)	\
    || (NAME) == cp_operator_id (VEC_DELETE_EXPR))
 
+/* Evaluates to an id matching operator CODE.  Used to obtain the set
+   of operator overloads for the specified CODE.  */
 #define cp_operator_id(CODE) \
   (operator_name_info[(int) (CODE)].identifier)
-#define cp_assignment_operator_id(CODE) \
+
+/* An id matching a member assignment operator CODE, both simple (with
+   CODE == NOP_EXPR) and compound (e.g., with CODE == PLUS_EXPR for +=).
+   Includes copy assignment.  Use copy_fn_p() to test specifically for
+   copy assignment.  */
+#define cp_assignment_operator_id(CODE)				\
   (assignment_operator_name_info[(int) (CODE)].identifier)
 /* In parser.c.  */
 extern tree cp_literal_operator_id (const char *);