[virtmach] parrot VM?

[Chris Lattner]

> > One very significant drawback of stack-based VMs is that they are almost 
> > impossible to do meaningful optimizations on.  If your VM performs any 
> > substation optimization, you will often find that you have to translate 
> > from a stack-based rep to a register based representation anyway, losing 
> > any advantages the stack based VM gives you.

> 	But aren't there some portability issues with a register VM?
> 	Wouldn't you want to map the VM registers to real registers
> 	(since you want performance in the first place)? That
> 	might make it difficult to have a register VM that runs fast

The idea is not to emit a certain number of registers (GNU lightning uses 
6 always for example [I believe]), but to use an infinite number of 
registers, then run a register allocation pass as part of code generation, 
to convert it into the optimal number of registers for the actual 
machine...

-Chris

http://llvm.cs.uiuc.edu/
http://www.nondot.org/~sabre/Projects/