A CIL Tutorial - Department of Computer Science - ETH Zürich

CHAPTER 8. DEPENDANT TYPE QUALIFIERS 67
let colors of exp (c : ctxt) (loc : location) (e : exp) : colors =
match e with
| Lval lv → colors of lval c loc lv
| → colors of type c loc (typeOf e)
colorCheckVisitor visits a function with a context c that contains mappings for the local variables
and formal parameters. At assignments and function calls, it inserts function calls that the type
of the destination lvalue or formal parameter includes the type of the right-hand-side or actual
parameter.
These instructions are inserted using self#queueInstr. This is yet another mechanism with
which one can modify the AST. self#queueInstr can be called from any visitor method. Instructions
queued up with self#queueInstr are dequeued (i.e. inserted) at the latest possible point
before the AST node currently being visited. So, if we queue up an instruction while visiting an
instruction, the new instruction will be inserted immediately before the one currently being visited.
The case for checking function calls is ommitted because of its length, but it is a very useful
pattern, and might help with one of the exercises from a previous chapter.
class colorCheckVisitor (c : ctxt) = object(self)
inherit nopCilVisitor
method vinst (i : instr) =
match i with
| Set(lv, e, loc) →
let lvc = colors of lval c loc lv in
let ec = colors of exp c loc e in
self#queueInstr (colors includes loc ec lvc);
DoChildren
| → DoChildren
end
The function checkColorTypes invokes the visitor colorCHeckVisitor on function fd using context
c.
let checkColorTypes (c : ctxt) (fd : fundec) (loc : location) : unit =
let c = context for locals c fd in
let vis = new colorCheckVisitor c in
ignore(visitCilFunction vis fd)
The function tut8 is the entry point to the code in this tutorial. It rst initializes our dynamic
type-checking functions (tut8 init), then builds a global context for compiling type attributes
(context for globals), performs the type-check, and nally erases the color attributes.