Shadow returns

I need to return i128 and f128 via a ptr passed in as the first
argument to a function. I am not seeing something in llvm-abi.h to
let me do this. How do I make a scalar (not an aggregate) use a
shadow return? Similarly I need to pass those types by pointer,
(byval arguments?) and don't see an obvious way to do that.



I don't think any calling convention has needed to do that before, so it won't be supported. It shouldn't be too bad to implement by adding some new macros similar to the existing LLVM_SHOULD*. Good luck and test thoroughly; it's easy to break other targets when you touch this stuff.