attribute. It is a variation of the x86_64 ABI:
* A struct returned indirectly uses the first register argument to pass the
pointer.
* Floats, Doubles and structs containing only one of them are not passed in
registers.
* Other structs are split into registers if they fit on the remaining ones.
Otherwise they are passed in memory.
* When a struct doesn't fit it still consumes the registers.
llvm-svn: 161022
Rafael Espindola