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Postings from September 2001
(Firstly, I'd say trust Nick's expertise--he has spent a good-sized chunk
of his career doing software simulations of CPUs, and knows whereof he
speaks, both in terms of software running on hardware and software running
on software)
At 05:33 PM 9/6/2001 +0200, Paolo Molaro wrote:
>I believe that a stack-based machine will have roughly the same
>performance when interpreted as a register-based machine, but
>it easily allows to take a step further and JIT compile the bytecode
>to machine code. If we are going to execute low-level opcodes,
>no matter what architecture you choose for the interpreter,
>JIT code runs faster:-)
On x86 machines. Maybe. I think you both underestimate
> > is a pain.) Explicit stack ops are going to give them indigestion.
> > The P-III+ model is that most things are "on the C stack" i.e. offsets
> > from the few "base" registers. The hardware then "aliases" those offsets
> > into its real registers. I don't think Parrot's register files will give
> > it much trouble, but throwing away the right inc/dec-of-pointer ops that
> > a stack machine implies will (there are obviously HW special cases for
> x86's
>
>With the difference that the registers are malloc()ed while the eval
>stack in a stack machine is in the actual cpu stack.
Absolutely *not*. No way is the eval stack going to be the real CPU stack.
That puts nasty artificial limits, or massive memory requirements, on the
interpreter. It also makes GC a major pain in the neck, since it means
walking the stack and trying to extract real variable usage info. Bletch.
Even if perl 6 goes the stack route, we won't be using the system stack.
The registers will be from heap memory, but that's not a problem in and of
itself. Cache lines are cache lines.
Anyway, I think the point's moot for now. Parrot's register based unless
either performance is substandard and demonstrably because of the register
architecture, or because I get bussed and my successor's more comfortable
with stacks. (The first is certainly possible)
Dan
--------------------------------------"it's like this"-------------------
Dan Sugalski even samurai
dan@sidhe.org have teddy bears and even
teddy bears get drunk
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