How do I get debug information from a function?

Question

I've used Clang to compile a function with debug information enabled. For Instructions there's the handy getDebugLoc(), but there's no such thing for Functions. Given a Function instance, how can I get the debug information (I'm guessing in DISubProgram form) for it?

I've seen the guide entry explaining how that debug information is represented, and the metadata does contain a link back to the function, but there's apparently no link back. Am I supposed to iterate over all the metadata in the module?

Answer 1

I think you need to use the DebugInfoFinder. Here is a sample code:

DebugInfoFinder Finder;
Finder.processModule(M);
for (DebugInfoFinder::iterator i = Finder.subprogram_begin(),
                    e = Finder.subprogram_end();
                    i != e; ++i) {
                DISubprogram S(*i);

                if (S.getFunction() == F) {
                    errs() << S.getLineNumber(); << "\n";
                }
            }

where F is the function you are looking for.

Answer 2

you can use getSubprogram() as describled in doxygen: Function class

Answer 3

I don't think there's currently an easier way. There used to be a global metadata node that collected all function metadata entries (llvm.dbg.sp) but it was removed a while ago in favor of llvm.dbg.cu which reflects the DWARF structure more closely.

I suppose that the common uses of debug metadata don't require by-function lookup, and any extra information that could be removed, was removed, because saving space is important and metadata in IR is already way too big.