On PASM and PIR registers

[Klaas-Jan Stol]

hello,

Parrot has 2 categories of registers: PASM registers, which are of the 
form [S|N|I|P]<digit><digit> (which is kinda odd, if only regs 0-31 are 
available) and PIR registers, which are formed like: $[S|N|I|P]<digit>+

In the old days, this distinction was necessary for the register 
allocator to translate PIR registers to PASM registers, because there 
were only 32 regs of each type (S/N/I/P).

IIUC, the number of registers is now equal to "the necessary number of 
registers"; that is, each sub has as many registers as it needs to do 
its job.

So, my question is now, why do we still need the PASM registers (except 
for backward compatibility) if we have PIR registers (which, after a 
possible "we don't need them", brings the question, why we need the "$", 
but that's a different topic). In other words, why not stick to 1 category:
either $[SNIP]<digit>+ (or maybe skip the $ altogether, but again, 
that's not the point here)?

regards,
klaas-jan