How to add a Metadata String to an LLVM module with the C++ API?

Question

I'm trying to add a metadata string to my LLVM module. The stripped down version of what I'm trying is

#include <llvm/LLVMContext.h>
#include <llvm/Module.h>
#include <llvm/Metadata.h>

using namespace llvm;

int main() {
    Module* module = new Module("test", getGlobalContext());
    MDString::get(module->getContext(), "test");
    module->dump();
}

I can compile and run it:

Desktop% g++ llvm.cc -o llvm `llvm-config --cppflags --ldflags --libs all`
Desktop% ./llvm 
; ModuleID = 'test'

But as one can see, the metadata does not show up.

Can I somehow add the string to the module? The module itself only seems to offer access to named metadata. Now I don't know where else I could look. Any suggestions?

Supplement: I got the feeling that you can't just have a metadata string "floating around" in your module, it seems like you have to add it to a named metadata node. Is that right?

Answer 1

Try this:

#include <llvm/LLVMContext.h>
#include <llvm/Module.h>
#include <llvm/Metadata.h>

using namespace llvm;

int main() {
  Module* module = new Module("test", getGlobalContext());

  Value *Elts[] = {
    MDString::get(module->getContext(), "test1")
  };
  MDNode *Node = MDNode::get(getGlobalContext(), Elts);

  NamedMDNode *NMD = module->getOrInsertNamedMetadata("test2");
  NMD->addOperand(Node);

  module->dump();
}

I am not sure if you are able to have metadata "floating around" as you say. If it's not attached to any part of your program then what good is it doing? I've been looking into MD a bit lately... I found similar code in lib/Analysis/DIBuilder.cpp. Good luck.