The object is provided by the objc runtime and is never visible in the
module itself, but even so, the address point we compute points into it,
and "+16" is guaranteed not to overflow.
This matches the c++ vtable IRGen.
Note that I'm not entirely convinced the 'i8*' type is correct here: at
the IR level, we're accessing memory that's outside the global object.
But we don't control the allocation, so it's not obviously wrong either.
But either way, this is only in a global initializer, so I don't think
it's going to be mucked with. Filed PR35352 to discuss that.
llvm-svn: 318545
Ahmed Bougacha