Saving changes to LLVM BasicBlock Pass - llvm

Question

I successfully added some Metadata to a Basic Block in LLVM. Then I used Mod->dump() to display it on the screen.
The data is added successfully to my byte code, i.e. metadata is displayed on the screen.
My problem is that these changes are not updated in my original file.
How can I solve this problem?
class BasicBlock1 : public BasicBlockPass {
public:
BasicBlock1()
: BasicBlockPass(ID)
{}
virtual bool runOnBasicBlock(BasicBlock &BB) {
Value *A[] = {MDString::get(getGlobalContext(), "mymetadata")};
MDNode *Node = MDNode::get(getGlobalContext(), A);
for (BasicBlock::iterator ii = BB.begin(), ii_e = BB.end();
ii != ii_e; ++ii) {
ii->setMetadata("XXX", Node);
}
return true;
}
static char ID;
};
char FunctionPrint::ID = 0;
char BasicBlock1::ID =0;
int main(int argc, char **argv) {
Module *Mod = ParseIRFile(argv[1], Err, getGlobalContext());
PM.add(new BasicBlock1());
PM.run(*Mod);
Mod->dump();
return 0;
}

Answer 1

You write:
The data is added successfully to my byte code, i.e. metadata is displayed on the screen.
My problem is that these changes are not updated in my original file.
In your code snippet, you do not write your modified module anywhere, you just print it to the output. You can write it using:
std::string ErrorInfo;
raw_fd_ostream OS(argv[1], ErrorInfo, sys::fs::F_Binary);
if (ErrorInfo.empty()) WriteBitcodeToFile(*Mod, OS);