A CIL Tutorial - Department of Computer Science - ETH Zürich

CHAPTER 9. TYPE QUALIFIER INFERENCE 74
OCaml Pitfall: In graphCreate you might be tempted to say:
A.make n {ncolors = [ ]; ...}. However this would be problematic. The array
would be initialized, not with copies of the given node record, but rather
with references to a single node because the record literal would be evaluated
before being passed to A.make. On the other hand, the newNode function is
called for each array element, allocating a fresh node for each one.
The function typesAddEdge places an edge in the graph from the node for type from type to the
node for type to type.
let rec typesAddEdge (g : graph) (from type : typ) (to type : typ) : unit =
let from id = node of type from type in
let to id = node of type to type in
graphAddEdge g from id to id
Before dening the visitor that will build the graph, we dene a couple of functions that will make
handling function calls a bit easier. The function addEdgesForCallArgs adds edges arising from
the assignment of actuals to formals at function call sites.
let addEdgesForCallArgs (g : graph) (fe : exp) (aes : exp list) : unit =
let fts = fe | > function elements | > snd | > L.map snd3 in
let ats = aes | > list take (L.length fts) | > L.map typeOf in
L.iter2 (typesAddEdge g) ats fts
The function addEdgesForCallRet adds edges for the assignment of return values at call sites.
let addEdgesForCallRet (g : graph) (fe : exp) (rlvo : lval option) : unit =
match rlvo with
| None → ()
| Some rlv →
let rt, = function elements fe in
typesAddEdge g rt (typeOfLval rlv)
The visitor graphBuilder adds edges to the graph. Edges encode constraints on type qualiers.
We place an edge from node A to node B when the type of A must be included in the type of
B. Thus, if we have an assignment lv = e the type of lv has to be big enough to handle the
type of e. That is, the type of e must be included in the type of lv. Then, we can just think of
casts, parameter passing, and the return statements as dierent ways of doing assignments, and
add edges for them the same way.