let defines_desc =
function
IL0stmtDefTemp(id,_,_) -> singleton id
| IL0stmtReadToTemp(id,_,_,_) -> singleton id
| IL0stmtSequence(l) -> union_list (List.map defines_il0 l)
| IL0stmtParallel(l) -> union_list (List.map defines_il0 l)
| _ -> empty