A while back, I was poking around LLVM bugs, and discovered, to my surprise, that LLVM doesn’t support the va_arg intrinsic, used by functions to accept multiple arguments, at all on amd64. It turns out that clang and llvm-gcc, the compilers that backend to LLVM, have their own implementations in the frontend, so this isn’t as big a deal as it might sound, but it was still a surprise to me.
