MDEV-11640 gcol.gcol_select_myisam fails in buildbot on Power

JOIN_CACHE's were initialized in  check_join_cache_usage()
from make_join_readinfo(). After that make_join_readinfo() was looking
whether it's possible to use keyread. Later, after make_join_readinfo(),
optimizer decided whether to use filesort. And even later, at the
execution time, from join_read_first(), keyread was actually enabled.

The problem is, that if a query uses a vcol, base columns that it
depends on are automatically added to the read_set - because they're
needed to calculate the vcol. But if we're doing keyread, vcol is taken
from the index, not calculated, and base columns do not need to  be
in the read set (even should not be - as they aren't getting values).

The bug was that JOIN_CACHE used read_set with base columns,
they were not read because of keyread, so it was caching garbage.

So read_set is only known after the keyread was decided. And after the
filesort was decided, as filesort doesn't use keyread. But
check_join_cache_usage() needs to be done in make_join_readinfo(),
as the code below depends on these checks,

Fix: keep JOIN_CACHE checks where they were, but move initialization
down to the very end of JOIN::optimize_inner. If keyread was enabled,
update the read_set to include only columns that are part of the index.
Copy the keyread logic from join_read_first() to happen at optimize time.

1 files changed, 1 insertions, 1 deletions

diff --git a/mysql-test/r/join_outer.result b/mysql-test/r/join_outer.result
index 7fb3517ecb7..ffeddc989ec 100644
--- a/mysql-test/r/join_outer.result
+++ b/mysql-test/r/join_outer.result
@@ -2006,7 +2006,7 @@ SELECT * FROM (t2 LEFT JOIN t1 ON t1.b = t2.b) JOIN t3 ON t1.b = t3.b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	
 1	SIMPLE	t3	hash_ALL	PRIMARY	#hash#PRIMARY	4	test.t1.b	10	10.00	Using join buffer (flat, BNLH join)
-1	SIMPLE	t2	hash_index	PRIMARY	#hash#PRIMARY:PRIMARY	4:4	test.t1.b	27	3.70	Using join buffer (incremental, BNLH join)
+1	SIMPLE	t2	hash_index	PRIMARY	#hash#PRIMARY:PRIMARY	4:4	test.t1.b	27	3.70	Using index; Using join buffer (incremental, BNLH join)
 Warnings:
 Note	1003	select `test`.`t2`.`b` AS `b`,`test`.`t1`.`b` AS `b`,`test`.`t3`.`a` AS `a`,`test`.`t3`.`b` AS `b` from `test`.`t2` join `test`.`t1` join `test`.`t3` where `test`.`t3`.`b` = `test`.`t1`.`b` and `test`.`t2`.`b` = `test`.`t1`.`b`
 PREPARE stmt FROM