https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94359
--- Comment #6 from Iain Sandoe <iains at gcc dot gnu.org> ---
(In reply to Iain Sandoe from comment #5)
> (In reply to Iain Sandoe from comment #4)
> I'm going to discuss this with the coroutines paper authors - as to whether
> any constraints had been considered. Note, once again, that failure to
> implement this does not make us non-conforming.
coro paper author hadn't tested this configuration.
==
basically, the intent is that one can continue an arbitrary number
of coroutines, without overflowing the stack. Maybe there's an alternate
pattern that we could construct that would allow this; modulo the caller-
save of the TOC. Coroutine actor functions are marked with a flag, so we
do have a mechanism for handling them differently.
In the meantime, I guess this isn't going to work for PPC (AIX/powerpc64)
:( and we have to XFAIL or switch it off.
/* A C equivalent of what's being done. */
extern void actor (void *p);
/* This is how the public part of the coroutine frame ABI looks. */
typedef struct __frame {
void (*a) (void *);
void (*d) (void *);
float _other_things;
} generic_frame_t;
/* This is what a coroutine handle looks like. */
typedef struct __handle {
generic_frame_t *fp;
} generic_handle_t;
/* A fake call to get a handle... */
__attribute__((__noinline__))
generic_handle_t get_handle (void)
{
generic_frame_t *f = (generic_frame_t *)__builtin_malloc (sizeof
(generic_frame_t));
f->a = actor;
f->d = actor;
f->_other_things = 0.0F;
generic_handle_t h = {f};
return h;
}
/* .. and part of coroutine state machine that wants to continue
by executing another coroutine.
X86 tail-calls this for O2+ (even for PIC) m32/m64
PPC tail-calls for m32 (even for PIC), but not for ELFv2 m64.
with the TOC reg caller-saved, perhaps there's no sequence that can
work.
*/
void actor2 (void *p2)
{
generic_handle_t h = get_handle ();
generic_frame_t *t = h.fp;
/* Use the TOC. */
t->other_things = 1.1F;
(*t->a) ((void *)t);
}
