Re: Static Chain Argument in call_expr

["Paulo J. Matos" <pocm at soton dot ac dot uk>]

On 3/8/07, Duncan Sands <baldrick@free.fr> wrote:
> > in tree.def, in DEFTREECODE for call_expr, it says operand 2 is the
> > static chain argument, or NULL. Can someone tell me or reference me to
> > what static chain argument is?
>
> It's for nested functions, eg
>
> int parent (int n)
> {
>   int child (int m) { return m * n; }
>
>   return child (2);
> }
>
> Notice how child using a variable of parent, namely
> the parameter n.  This gets lowered to something like:
>
> struct frame { int n; };
>
> int child (struct frame *static_chain, int m) { return m * static_chain->n; }
>
> int parent (int n)
> {
>   struct frame FRAME;
>   FRAME.n = n;
>   return child (&FRAME, 2);
> }

Ah, nice, didn't know that was possible in C. Is that new in C99 or
it's a GCC extension?

Cheers,

Paulo Matos

> Ciao,
>
> Duncan.


--
Paulo Jorge Matos - pocm at soton.ac.uk
http://www.personal.soton.ac.uk/pocm
PhD Student @ ECS
University of Southampton, UK