Re: [Lightning] Order of function arguments on mips

[Paolo Bonzini]

On 10/20/2010 09:35 AM, Paulo César Pereira de Andrade wrote:
> Em 20 de outubro de 2010 04:32, Paolo Bonzini<address@hidden>  escreveu:
> > On 10/20/2010 02:32 AM, Paulo César Pereira de Andrade wrote:
> > >    What you suggest to avoid minimal problems with lightning?
> > >
> > > _jit_prepare("dfii")
> > > to be understood as:
> > > <unkown_return_type>    function(double, float, int, int);
> >
> > While it is a bit long, maybe
> >
> >   jit_prepare_d(1);
> >   jit_prepare_f(1);
> >   jit_prepare_i(2);
> >
> > would "just work"?
>
>    If there are no jit_pusharg calls in between, it could be an
> option.

Yes, however you need space in _jit to store the offsets, because these 
are computed from the first argument while the arguments are pushed 
starting from the last.

Suppose you have

       prepare_p 1
       prepare_d 1
       prepare_i 1
       prepare_d 1
       prepare_i 1

At this point you know that the space on the stack will be 40 bytes, and 
the "next offset" is 36.

Then...

>      prepare 3
>      prepare_d 2
>          movi_i %r0 4

... this decrements the next offset by 4, and places "4" at $sp[32-35].

>          pusharg_i %r0
>          movi_d %f0 3.0
>          pusharg_d %f0

... this decrements the next offset by 8, places "3.0" and $sp[24].

>         movi_i %r0 2
>         pusharg_i %r0

Now there's no way (without storing all the offsets) to know if the next 
argument should be at 20-23 or 16-19.

With the full list of arguments stored in _jit, it can work.  I prefer 
this to your proposal (a string like "pdidi"), because anyway the 
offsets have to be computed (you cannot just use the format stirng in 
pusharg_x).  The format string can be implemented in your assembler or 
in general at a higher layer than lightning.

Paolo