A CIL Tutorial - Department of Computer Science - ETH Zürich

CHAPTER 3. DATAFLOW ANALYSIS 29
let collectVars (fd : fundec) : varmap list =
(fd.sformals @ fd.slocals)
|> L.filter (fun vi → isIntegralType vi.vtype)
|> L.map (fun vi → (vi.vid, (vi, Bottom)))
Here, the function computeOddEven calls the compute function of the OddEven module. First though,
use CIL's Cfg module to compute the control-ow graph for the function. Then, we grab the rst
statement of the function and add it to the stmtStartData hash with a state indicating that on
entry to the function the state for every variable is Bottom, which we get from the collectVars
function. In practice, this code should be placed in a try...with block, to handle cases where, e.g.
the function is empty.
let computeOddEven (fd : fundec) : unit =
Cfg.clearCFGinfo fd;
ignore(Cfg.cfgFun fd);
let first stmt = L.hd fd.sbody.bstmts in
let vml = collectVars fd in
IH.clear OddEvenDF.stmtStartData;
IH.add OddEvenDF.stmtStartData first stmt.sid vml;
OddEven.compute [first stmt]
3.1.6 Using the results
The function getOddEvens returns the state on entry to a statement by looking it up in the hash
table OddEvenDF.stmtStartData, which is lled in by OddEven.compute.
let getOddEvens (sid : int) : varmap list option =
try Some(IH.find OddEvenDF.stmtStartData sid)
with Not found → None
The function instrOddEvens calculates the states that exist on entry to each of a list of instructions.
In addition to the list of instructions, it takes as input the state on entry to the rst instruction in
the list.