MDEV-21495: Conditional jump or move depends on uninitialised value in sel_arg_range_seq_next

Initialize the parameter PARAM::max_key_part when we iterate over the ranges to get estimates
from EITS.

mysql-test/r/selectivity.result

@@ -1866,4 +1866,19 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 set optimizer_switch= @save_optimizer_switch;
 set optimizer_use_condition_selectivity= @save_optimizer_use_condition_selectivity;
 drop table t1,t2;
+#
+# MDEV-21495: Conditional jump or move depends on uninitialised value in sel_arg_range_seq_next
+#
+CREATE TABLE t1(a INT, b INT);
+INSERT INTO t1 SELECT seq, seq from seq_1_to_100;
+set optimizer_use_condition_selectivity=4;
+ANALYZE TABLE t1 PERSISTENT FOR ALL;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	Engine-independent statistics collected
+test.t1	analyze	status	OK
+SELECT * from t1 WHERE a = 5 and b = 5;
+a	b
+5	5
+set optimizer_use_condition_selectivity= @save_optimizer_use_condition_selectivity;
+drop table t1;
 # End of 10.1 tests

mysql-test/r/selectivity_innodb.result

@@ -1876,6 +1876,21 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 set optimizer_switch= @save_optimizer_switch;
 set optimizer_use_condition_selectivity= @save_optimizer_use_condition_selectivity;
 drop table t1,t2;
+#
+# MDEV-21495: Conditional jump or move depends on uninitialised value in sel_arg_range_seq_next
+#
+CREATE TABLE t1(a INT, b INT);
+INSERT INTO t1 SELECT seq, seq from seq_1_to_100;
+set optimizer_use_condition_selectivity=4;
+ANALYZE TABLE t1 PERSISTENT FOR ALL;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	Engine-independent statistics collected
+test.t1	analyze	status	OK
+SELECT * from t1 WHERE a = 5 and b = 5;
+a	b
+5	5
+set optimizer_use_condition_selectivity= @save_optimizer_use_condition_selectivity;
+drop table t1;
 # End of 10.1 tests
 set optimizer_switch=@save_optimizer_switch_for_selectivity_test;
 set @tmp_ust= @@use_stat_tables;

mysql-test/t/selectivity.test

@@ -1266,5 +1266,17 @@ set optimizer_switch= @save_optimizer_switch;
 set optimizer_use_condition_selectivity= @save_optimizer_use_condition_selectivity;
 drop table t1,t2;
 
+--echo #
+--echo # MDEV-21495: Conditional jump or move depends on uninitialised value in sel_arg_range_seq_next
+--echo #
+
+CREATE TABLE t1(a INT, b INT);
+INSERT INTO t1 SELECT seq, seq from seq_1_to_100;
+set optimizer_use_condition_selectivity=4;
+ANALYZE TABLE t1 PERSISTENT FOR ALL;
+SELECT * from t1 WHERE a = 5 and b = 5;
+set optimizer_use_condition_selectivity= @save_optimizer_use_condition_selectivity;
+drop table t1;
+
 --echo # End of 10.1 tests
 

sql/opt_range_mrr.cc

@@ -73,6 +73,7 @@ range_seq_t sel_arg_range_seq_init(void *init_param, uint n_ranges, uint flags)
 {
   SEL_ARG_RANGE_SEQ *seq= (SEL_ARG_RANGE_SEQ*)init_param;
   seq->at_start= TRUE;
+  seq->param->max_key_part= 0;
   seq->stack[0].key_tree= NULL;
   seq->stack[0].min_key= seq->param->min_key;
   seq->stack[0].min_key_flag= 0;