[LLVMdev] How to insert metadata in llvm IR?

[Kevin Fang]

As title.
I try to write a pass to covert the bitcode with no debug info to the bitcode 
with 
debug info. I use DIBuilder as a LLVM API so that I can generate DI(Debug info). 
Now I have some DIDescriptor , e.g. DIVariable ,DICompileUnit, DISubprogram , I 
can use some function to insert metadata.

1. LLVM::Instruction::SetDebugLoc(...) => insert the debug info location like 
DILexicalBlock ,and insert !dbg appending an instruction.
2. LLVM::Instruction::setMetadata(...) => insert the metadta and !dbg appending 
an 
instruction.
3. DIBuilder::insertDeclare(...) =>  insert variable declare (like 
@llvm.dbg.declare) and metadata.
4. llvm::NamedMDNode::addOperand(...) => insert and Named Metadata. Like 

I can use above four function to insert metadata into bitcode. But I can't just 
insert a metadata. 
This problem is occur when I want to create an DISubprogram 
metadata into bc. 
I can't use above four function because this descriptor not 
append any instruction and I can't use declare to generate it. 
This descriptor is 
not a NamedMDNode too. I have try many way to insert it, but I failed...

Can you tell me a right way to insert this MD? 
thanks

--
Kevin FangA