As recently discussed on llvm-dev [1], this patch makes it illegal for two Functions to point to the same DISubprogram and updates FunctionCloner to also clone the debug info of a function to conform to the new requirement. To simplify the implementation it also factors out the creation of inlineAt locations from the Inliner into a general-purpose utility in DILocation.
[1] http://lists.llvm.org/pipermail/llvm-dev/2017-May/112661.html