CCState.AllocateRegBlock from TargetCallingConv.td?

I see that the generated XGenCallingConv.inc includes this code for the CCAssignToReg action:

if (unsigned Reg = State.AllocateReg(RegList1)) {
State.addLoc(CCValAssign::getReg(ValNo, ValVT, Reg, LocVT, LocInfo));
return false;
}

Is there any action that will call State.AllocateRegBlock? Specifically, I have a bunch of i16 registers for return values. If a value is i16, I can allocate one, but if a value is i32, I need to allocate a block of 2. I wanted to use a tablegen file to specify this, since it would save me a lot of coding. Can I get a confirmation that this is just not supported in a .td file, and that I have to write the code myself?

Thanks,

–Rob