Remove roll_node_t::partial

The field roll_node_t::partial holds if and only if
savept has been set. Make savept a pointer.

trx_rollback_start(): Use the semantic type undo_no_t for roll_limit.

storage/innobase/include/trx0roll.h

 /*****************************************************************************
 
 Copyright (c) 1996, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2015, 2018, MariaDB Corporation.
+Copyright (c) 2015, 2019, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -200,9 +200,7 @@ enum roll_node_state {
 struct roll_node_t{
 	que_common_t		common;	/*!< node type: QUE_NODE_ROLLBACK */
 	enum roll_node_state	state;	/*!< node execution state */
-	bool			partial;/*!< TRUE if we want a partial
-					rollback */
-	trx_savept_t		savept;	/*!< savepoint to which to
+	const trx_savept_t*	savept;	/*!< savepoint to which to
 					roll back, in the case of a
 					partial rollback */
 	que_thr_t*		undo_thr;/*!< undo query graph */

storage/innobase/trx/trx0roll.cc

@@ -83,8 +83,7 @@ trx_rollback_to_savepoint_low(
 	roll_node = roll_node_create(heap);
 
 	if (savept != NULL) {
-		roll_node->partial = TRUE;
-		roll_node->savept = *savept;
+		roll_node->savept = savept;
 		check_trx_state(trx);
 	} else {
 		assert_trx_nonlocking_or_in_list(trx);
@@ -1122,7 +1121,7 @@ que_thr_t*
 trx_rollback_start(
 /*===============*/
 	trx_t*		trx,		/*!< in: transaction */
-	ib_id_t		roll_limit)	/*!< in: rollback to undo no (for
+	undo_no_t	roll_limit)	/*!< in: rollback to undo no (for
 					partial undo), 0 if we are rolling back
 					the entire transaction */
 {
@@ -1215,7 +1214,7 @@ trx_rollback_step(
 
 		ut_a(node->undo_thr == NULL);
 
-		roll_limit = node->partial ? node->savept.least_undo_no : 0;
+		roll_limit = node->savept ? node->savept->least_undo_no : 0;
 
 		trx_commit_or_rollback_prepare(trx);