MSAN use-of-uninitialized-value in decode_bytes()

main.myisampack                          w1 [ fail ]

        Test ended at 2020-05-25 11:16:20

CURRENT_TEST: main.myisampack

==401784==WARNING: MemorySanitizer: use-of-uninitialized-value

    #0 0x55df34ad8500 in decode_bytes /mariadb/10.5m/storage/myisam/mi_packrec.c:1236:14

    #1 0x55df34ad783e in uf_zerofill_normal /mariadb/10.5m/storage/myisam/mi_packrec.c:1011:3

    #2 0x55df34acdae6 in _mi_pack_rec_unpack /mariadb/10.5m/storage/myisam/mi_packrec.c:754:5

    #3 0x55df34a23e33 in sort_get_next_record /mariadb/10.5m/storage/myisam/mi_check.c:3629:11

    #4 0x55df34a3aee2 in sort_key_read /mariadb/10.5m/storage/myisam/mi_check.c:3124:14

    #5 0x55df34b40252 in find_all_keys /mariadb/10.5m/storage/myisam/sort.c:311:18

    #6 0x55df34b40252 in _create_index_by_sort /mariadb/10.5m/storage/myisam/sort.c:227:17

    #7 0x55df34a35d48 in mi_repair_by_sort /mariadb/10.5m/storage/myisam/mi_check.c:2403:9

    #8 0x55df349fb9b9 in myisamchk /mariadb/10.5m/storage/myisam/myisamchk.c:1024:19

    #9 0x55df349f400d in main /mariadb/10.5m/storage/myisam/myisamchk.c:87:19

    #10 0x7f6381967e0a in __libc_start_main csu/../csu/libc-start.c:308:16

    #11 0x55df34978649 in _start (/dev/shm/10.5-msan/storage/myisam/myisamchk+0x49649)

  Memory was marked as uninitialized

    #0 0x55df3498493e in __msan_allocated_memory (/dev/shm/10.5-msan/storage/myisam/myisamchk+0x5593e)

    #1 0x55df34c4bcc7 in my_malloc /mariadb/10.5m/mysys/my_malloc.c:111:7

SUMMARY: MemorySanitizer: use-of-uninitialized-value /mariadb/10.5m/storage/myisam/mi_packrec.c:1236:14 in decode_bytes

Exiting

mysqltest: At line 34: exec of '/dev/shm/10.5-msan/storage/myisam/myisamchk -srq /dev/shm/10.5-msan/mysql-test/var/1/mysqld.1/data//test/t1' failed, error: 19712, status: 77, errno: 11

Output from before failure:

FLUSH TABLES;

	/* First use info in quick_table */

    low_byte=(bit_buff->current_byte >> (bits - table_bits)) & table_and;

    low_byte=decode_tree->table[low_byte];

    if (low_byte & IS_CHAR)