https://reviews.llvm.org/D102996 changes the operand of bundle "clang.arc.attachedcall". This patch makes changes to llvm that are needed to handle the new IR.
This should make it easier to understand what the IR is doing and also simplify some of the passes as they no longer have to translate the integer values to the runtime functions.
This "null operand" sentence seems new in LangRef, but I'm not seeing tests / code changes for it. Is this just fixing a documentation bug, or are you intending this for a different patch?