First, well done on a great product, to all those who
have worked on the compiler.
I have used Keil and HiTech compilers for an 8052, and
both use the registers to pass parameters to functions.
My project which compiles using the Keil compiler is 96
bytes short of data when compiled using SDCC because
most of the parameters are passed in data space.
Have you considered using the registers to pass
parameters as part of the optimisation of data space?
or allowing this as an option?