UESTIONS about interpretation of LLVM IR

Hello, everybody!

I am new to LLVM and currently I am doing some research on how to execute LLVM IR on M5 modular platform.
I have read the Language reference and bitcode format manual of LLVM, but I don’t quite know how it is encoded and executed.
Unlike normal assembly code, LLVM IR is more type-fixed and high-level programed. Therefore, I don’t quite understand:
1, How the instruction fields mapped into the virtual registers.
2, How does it complete the calling of functions and how they pass the parameters.
3, And, whether it call libraries’ functions is also not clear to me.
Problems are not limited to these and I beg for your help sincerely.
If someone knows, please contact with me.

Thanks very much!