A CIL Tutorial - Department of Computer Science - ETH Zürich

CHAPTER 3. DATAFLOW ANALYSIS 30
let instrOddEvens (il : instr list) (vml : varmap list) : varmap list list =
let proc one hil i =
match hil with
| [ ] → (varmap list handle inst i vml) :: hil
| vml' :: rst as l → (varmap list handle inst i vml') :: l
in
il | > L.fold left proc one [vml]
|> L.tl
|> L.rev
Now that we can get the state on entry to statements and instructions, we can make a special visitor
class such that when we inherit from it, the resulting visitor will have the current OddEven state
available in every method.
The vmlVisitorClass class inherits from nopCilVisitor. When visiting a statement, if the
statement is a list of instructions, it uses instrOddEvens to store the entry states into a mutable
instance eld state list. If the statement is not an instruction list, it uses getOddEvens to put
the state on entry to the statement into another mutable instance eld current state. When
an instruction is visited, it takes the head of state list, writes it to current state, and removes
the rst state of state list. The visitor also adds a method get cur vml(), which returns
current state.
Inheriting from this visitor will cause the state found by the analysis on entry to a statement or an
instruction to be available in the vstmt and vinst methods of the inheriting class. Classes inheriting
from vmlVisitorClass must call super#vstmt and super#vinst if they override vstmt or vinst
respectively. To get the current state, inheriting classes can call self#get cur vml. Additionally,
when passing an inheritor of vmlVisitorClass to a function requiring a nopCilVisitor, we must
do an up-cast because of the additional method get cur vml(). See the function evenOddAnalysis
below.
class vmlVisitorClass = object(self)
inherit nopCilVisitor
val mutable sid = − 1
val mutable state list = [ ]
val mutable current state = None
method vstmt stm =
sid ← stm.sid;
begin match getOddEvens sid with
| None → current state ← None
| Some vml → begin
match stm.skind with
| Instr il →
current state ← None;
state list ← instrOddEvens il vml
| → current state ← None
end end;