Clang: error accessing vector

Hi to everybody.
I'm getting the following error while working on a Clang plugin:

error: call to a function

::operator[](unsigned long)' that is not present in the target

The interesting code is the following:

attributes, string name) {
    for(int i = 0; i < attributes.size(); i++) {
        if(>getDirectCallee()->getName().str() ==
"call_this_opencl_buffer_size") {
            Expr* param = attributes[i]->getArg(0);
            // Attribute first arg must be a call (buffer) arg name
            if(param->isEvaluatable(context)) {
                string param_name;
                llvm::raw_string_ostream stream(param_name);
                param->printPretty(stream, NULL,
                if(param_name == name) {
                    int arg =>getNumArgs();
                    Expr* size_arg =>getArg(1);
                    printf(" OK\n");
                    return size_arg;
    return NULL;

The problem is that I'm getting erroneous values for some of the variables
in the code, such as size_arg. I argue the error reported affects the
correctness of the entire function body.

I tried to google the error with ne results.
Can you help me?
Thank you very much!

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