[cfe-dev] Troubles tracking a function parameter with the static analyzer

[Ivan Reche]

Hey all,

Suppose I'm working with the following C snippet:

void inc(int *num) {*num++;}
void dec(int *num) {*num--;}

void f(int var) {
    inc(&var);
    dec(&var);
}

By using a static analyzer, I want to be able to tell if the value of var
didn't change during the function's execution. I know I have to keep its
state on my own (that's the point of writing a Clang checker), but I'm
having troubles getting a unique reference of this variable.

For example: if I use the following API

void MySimpleChecker::checkPostCall(const CallEvent &Call,
                                    CheckerContext &C) const {
    SymbolRef MyArg = Call.getArgSVal(0).getAsSymbol();
}

I'd expect it to return a pointer to this symbol's representation in my
checker's context. However, I always get 0 into MyArg by using it this way.
This happens for both inc and dec functions in the pre and post callbacks.

What am I missing here? What concepts did I get wrong?

Note: I'm currently reading the Clang CFE Internals Manual and I've read
the excellent How to Write a Checker in 24 Hours material. I still couldn't
find my answer so far.

Thanks in advance!

Best regards,

Ivan
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