function calls

[Peter da Silva]

(for comp.arch folks, Jim is basically saying that the more registers you
 have, the better, because it lets you put more variables in registers)

But, Jim, registers aren't free. The more registers you have the more bits
you have to hide in your carefully crafted instruction set to specify
registers. Modern RISC processors have up to 4 arguments to a given
instruction, so even if they're all registers (no mixed-mode instructions)
and you only have 16 registers, that's 16 bits gone right there.

Now, let's add some more bits to specify constants and maybe some addressing
modes, and you can run out of bits pretty quickly. With 64 registers (about
the most I'd expect you to be happy with), and immediate operands that
would leave you with about 5 bits to specify the instruction. Now suppose
you have room on the chip for 512 registers... why *not* use register
windows, or a stack cache, or something similar instead of just making
the instruction wider?
-- 
 _--_|\  `-_-' Peter da Silva. +1 713 274 5180. <peter at ficc.uu.net>.
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