// are updated when necessary, to propagate tokens. The function may either be
// rewritten to create a token or take in and return a token, depending on its
// visibility and if there are any callers.
LogicalResult RewriteFunction(
    OpBuilder& builder, ModuleOp module, FuncOp func,
    const llvm::SmallDenseMap<StringRef, FuncToRewrite>& funcs,
    const llvm::SmallPtrSetImpl<Operation*>& control_flow_ops,