Changing an index comment unnecessarily rebuilds index

CREATE TABLE t1(a INT, b INT);

CREATE INDEX i1 ON t1(a) COMMENT 'comment1';  

ALTER TABLE t1 DROP INDEX i1, ADD INDEX i1(a) COMMENT 'comment2';

SHOW CREATE TABLE t1;

diff --git a/sql/sql_table.cc b/sql/sql_table.cc

index c4b07ad2035..5986e8201c4 100644

--- a/sql/sql_table.cc

+++ b/sql/sql_table.cc

@@ -6368,6 +6368,13 @@ static bool fill_alter_inplace_info(THD *thd,

           new_field->field->field_index != key_part->fieldnr - 1)

         goto index_changed;

     }

+

+    /* Check that key comment is not changed. */

+    if (table_key->comment.length != new_key->comment.length ||

+        (table_key->comment.length &&

+         strcmp(table_key->comment.str, new_key->comment.str) != 0))

+        goto index_changed;

+

     continue;

   index_changed: