As I've said before, m32c is probably a "worst case" scenario for gcc as it has not one, not two, not even three, but FOUR different types of registers (8/16 bit general, 16 bit only general, 24 bit address registers, and control (incl $fp) registers), and only a small number (2) of each.
I think our mxp is more 'interesting'. It got several hundred register classes, auto-generated, and some important ones have only a single member. We got a number of vector registers, a flags register, and an accumulator. All of them are 128 bit wide and an 8-bit mask selects which 16-bit wide lanes of the 128 bit word are operated on - i.e. 255 different combinations. A lot of instructions clobber the accumulator and/or the flags and to make sure that the registers are lined up, I have to make flags and accumulator allocated registers. Then the first few of the vector registers are also special because they can also be used as 16 and 32 bit scalar registers. A truely complete register class set would have 2^32 register classes even before getting into such niceties as call used / clobered regs and sibcalls, but I considered this slightly impractical considering the amount of memory that would cost.
