llvm dev - Dec 2015 - MISched: latency of function-live-in registers?

I use the machine scheduler with my out-of-tree backend. 

Is it possible to tell the machine scheduler that certain function-live-in
physical registers (i.e., function arguments) have a non-zero latency?

Said another way, I want to indicate to the scheduler that certain physical
registers are not available at the beginning of the function's entry block
and that attempting to access those registers will incur a stall.

Thanks,
Nick Johnson
D. E. Shaw Research