As sayed in title.
The example as below (it is hard to be with repeat ... repeat while) :
@startuml
skinparam conditionStyle InsideDiamond
start
:foo as starting label; //same name 1
:read data; //same name 2
:generate diagrams;
if (more data?) then (yes)
:This is backward1;
:foo as starting label; //sanme name 1
else (no)
if (condition two?) then (no)
:This is backward2;
:read data; //same name 2
else (yes)
stop
endif
endif
stop
@enduml