[WIP] Reworking implementation of operation masking sanitizer

[elazaro-riverside]

Fill this PR in when ready.

[elazaro-riverside]

The current operation masking sanitizer creates wrappers that return the first argument as a stub for the original operation. The problem is that the compiler instrumentation replaces all uses with the stub meaning that arguments that are "normal" are replaced as well.

The new approach will focus on transforming the wrappers from stubs into compiler-generated contract enforcement. The key idea is that the compiler won't know about the operation specifically (ex. strcpy). It will know about the preconditions that must hold before allowing the operation to be executed.

[elazaro-riverside]

One of the challenges is generating the correct preconditions for the corresponding predicate.

[elazaro-riverside]

I want to introduce this new abstraction in RESOLVE to represent predicates and contracts.

enum class PredicateKind {
    InBounds,
    NotEqual,
    NotNull,
    Nonzero,
};

// Predicates tell the compiler what
// must be true before executing 
// operation
struct Predicate {
   PredicateKind kind;
   unsigned arg0;
   unsigned arg1;
};

struct Contract {
   std::string fnName;
   std::vector<Predicate> predicates;
};