Followup on a recent discussion on D59978: It seems that the current consensus is that LLVM has a forward-progress requirement and also intends to keep it in the future. llvm.sideeffect is not a temporary workaround, but the final solution. While this is pretty disappointing for non-C++ frontends, let's make sure this is at least documented in LangRef.
I haven't found a great place to put this, so I created a separate section