Re: Benchmarking temporary Lisp objects [Was: Re: [RFC] temporary Lisp_Strings]

[Paul Eggert]

Dmitry Antipov wrote:
> I'm talking about the case when we can't us __attribute__ ((aligned (X))).

How about something like this?

typedef unsigned long uintptr_t;

typedef uintptr_t Lisp_Object;

struct Lisp_Cons
{
  Lisp_Object car;
  Lisp_Object cdr;
};

static Lisp_Object
cons_init (void *result, Lisp_Object a, Lisp_Object b)
{
  struct Lisp_Cons *p = (struct Lisp_Cons *) (((uintptr_t) result + 7) 
& -8);
  p->car = a;
  p->cdr = b;
  return (Lisp_Object) p + 3;
}

#define BCONS(a, b) cons_init ((char[sizeof (struct Lisp_Cons) + 7]){}, 
a, b)
#define untag(x) ((struct Lisp_Cons *) (uintptr_t) ((x) - 3))

int
foo (void)
{
  Lisp_Object a = BCONS (0, 0);
  Lisp_Object b = BCONS (0, a);
  return untag (untag(b) -> cdr) -> car;
}