>>It's the register size of the underlying ISA, on top of which the ABI is 
>>> implemented.  I think I'll rename mips_regsize and mips_saved_regsize to 
>>> clarify this.
> 
> 
> Please.

I've committed the attached - mips_isa_regsize and mips_abi_regsize. 
Hopefully this will help people spot the bugs.

Andrew