A CIL Tutorial - Department of Computer Science - ETH Zürich

CHAPTER 1. THE AST 12
1.1 tut1.ml
The function tut1FixInstr returns false if the instruction i is an assignment to a global variable
called deleted. Otherwise it returns true. We'll be using this function as an argument to
List.filter.
let tut1FixInstr (i : instr) : bool =
match i with
| Set((Var vi, NoOffset), , loc)
when vi.vname = "deleted" ∧ vi.vglob →
E.log "%a: Deleted assignment: %a\n" d loc loc d instr i;
false
| → true
The tut1FixStmt function inspects a statement. If the statement is a list of instructions, it overwrites
the mutable skind eld of the statement with a list of instructions ltered by tut1FixInstr.
Otherwise, it recursively descends into sub-statements.
let rec tut1FixStmt (s : stmt) : unit =
match s.skind with
| Instr il →
s.skind ← Instr(List.filter tut1FixInstr il)
| If( , tb, fb, ) →
tut1FixBlock tb;
tut1FixBlock fb
(∗ and so forth.∗)
| → ()
and tut1FixBlock (b : block) : unit = List.iter tut1FixStmt b.bstmts
let tut1FixFunction (fd : fundec) : unit = tut1FixBlock fd.sbody
Now that we have dened a set of functions for traversing the AST of a function denition, we can
write a function for the entry point into this module that iterates over all of the globals of a le.
When we nd the function called target we invoke tut1FixFunction.
let tut1 (f : file) : unit =
List.iter (fun g →
match g with
| GFun (fd, loc) when fd.svar.vname = "target" →
tut1FixFunction fd
| → ())
f.globals