Warn or Error if Trying to Read to ArgOut in Accel

[mattfel1]

Physically, we can do this. But shouldn't we throw an error since you should be using a HostIO and not an ArgOut? Currently it won't crash anywhere until chisel compilation

[dkoeplin]

I agree its a bit weird, but by convention so far, ArgOut is just a register that the host can access after Accel executes. HostIO is one that it can access during Accel execution. Effectively that means Accel can do whatever it wants for both ArgOut and HostIO, only the host is limited.

[mattfel1]

Ok I'll correct the codegen and check it inside one of the other unit tests

[mattfel1]

There may be an issue when you have a read and write to an argout that is unrolled into multiple parallel accesses. Look into this