Added TODO comments

sql/opt_subselect.cc

@@ -4217,6 +4217,8 @@ bool JOIN::optimize_unflattened_subqueries()
     both here inside if (...) branches. In future we could switch to function
     pointers.
 
+  TODO: consider moving this together with JOIN_TAB::preread_init
+  
   RETURN 
     NESTED_LOOP_OK - OK
     NESTED_LOOP_ERROR| NESTED_LOOP_KILLED - Error, abort the join execution

sql/sql_select.cc

@@ -9479,6 +9479,8 @@ double JOIN_TAB::scan_time()
 /**
   Initialize the join_tab before reading.
   Currently only derived table/view materialization is done here.
+
+  TODO: consider moving this together with join_tab_execution_startup
 */
 bool JOIN_TAB::preread_init()
 {