Re: [tree-ssa] Computed gotos

[Jamie Lokier <jamie at shareable dot org>]

Segher Boessenkool wrote:
> Robert Dewar wrote:
> >OK, my confusion then sorry. Why on earth is the C version called a 
> >computed
> >goto, that sure is a confused terminology, but I guess one that is familiar
> >in the GNU C world. I will take off my Fortran hat :-)
> 
> The manual says:
> 
> 	"The analogous feature in Fortran is called an assigned goto,
> 	but that name seems inappropriate in C, where one can do more
> 	than simply store label addresses in label variables."
> 
> Not that I can see what more that could be (unless undefined
> behaviour is allowed).

Dubious, but works:

#include <stdint.h>
#include <stdio.h>

int main ()
{
  uintptr_t label = (uintptr_t) &&label1;
  uintptr_t flip = (uintptr_t) &&label1 ^ (uintptr_t) &&label2;

  for (int i = 0; i < 10; i++, label ^= flip)
    {
      goto *(void *) label;
    label1:
      printf ("red\n");
      continue;
    label2:
      printf ("green\n");
    }

  return 0;
}