Re: [Lightning] Compiling C to Lightning

[Paolo Bonzini]

Ludovic Courtès wrote:

> Hi,
>
> Paolo Bonzini <address@hidden> writes:
>
>  
>
> > I think Ludovic does not want that, but rather something similar to `c 
> > (which was based on lcc).  Starting from TinyCC to get a working parser, 
> > could be an idea.
> >    
>
> What's `c?  Pointers?  Googling for it proved to be hard.  ;-)
>  
tick c gives this result: http://pdos.csail.mit.edu/tickc/

> How did you address similar issues in OCaml and GNU Smalltalk?
>  
By recoding everything.  Unfortunately you will need to do some recoding 
anyway, if you want to optimize register allocation for some common 
cases.  For example GST usually stores results in V0, but simple 
operands (no message sends) can be also loaded in V1.  So when adding 
two values I need something like

   compute operand 0 in V0
   save it
   compute operand 1 in V0
   load operand 0 into V1
   compute addition

But if operand 0 and 1 are both pretty simple, I can just do

   compute operand 0 in V1
   compute operand 1 in V0
   compute addition

And if operand 1 is simple, I can do

   compute operand 0 in V0
   move it to V1
   compute operand 1 in V0
   compute addition

Just a couple of this special cases may give a speed boost of 10-15%.  I 
don't remember `c, but I think that it could implement this kind of 
templating only because its backend supported an infinite number of 
registers (so it just created new temporaries for every expression it 
compiled).

Paolo