A CIL Tutorial - Department of Computer Science - ETH Zürich

CHAPTER 3. DATAFLOW ANALYSIS 28
let varmap list handle inst (i : instr) (vml : varmap list) : varmap list =
match i with
| Set((Var vi, NoOffset), e, loc) when ¬(vi.vglob) ∧ (isIntegralType vi.vtype) →
let k = oekind of exp vml e in
varmap list replace vml (vi.vid, (vi, k))
| Set((Mem , ), , )
| Call → varmap list kill vml (∗ Kill vars with vaddrof set ∗)
| → vml (∗ Not handling inline assembly. Ignoring writes to struct elds ∗)
The module OddEvenDF implements the ForwardsTransfer signature, and is the input module
to the DF.ForwardsDataFlow functor. The meanings of its members are documented in detail in
dataflow.mli. We include here only the interesting members. The function combinePredecessors
is used to determine when the analysis should terminate. If newly calculated incoming state fails to
change the old value, then it returns None, otherwise it calculates the join of the states and returns
the result. The function doInstr calls our transfer function varmap list handle inst to obtain
the state after an instruction given the incoming state ll.
module OddEvenDF = struct
(∗...∗)
let combinePredecessors (s : stmt) £(old : t) (ll : t) =
if varmap list equal old ll then None else
Some(varmap list combine old ll)
let doInstr (i : instr) (ll : t) =
let action = varmap list handle inst i in
DF.Post action
(∗...∗)
end
Other members of the ForwardsTransfer signature may also be implemented to implement a more
sophisticated analysis.
We nally invoke the functor to obtain the module OddEven, which contains the function
compute, which performs the dataow analysis.
module OddEven = DF.ForwardsDataFlow(OddEvenDF)
3.1.5 Running the analysis
The collectVars function determines the initial abstract state (Bottom) on entry to the rst statement
of a function.