[Bug target/94359] new test case g++.dg/coroutines/torture/symmetric-transfer-00-basic.C fails

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94359

Iain Sandoe <iains at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2020-03-27
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Iain Sandoe <iains at gcc dot gnu.org> ---
There are two cases here.

1) When the optimisation level is < 2 (where GCC does not normally tail-call).

 - in that case, the specific call [ which is in the tail position, and AFAIU
should be tail-callable ] is marked as TAIL_CALL, MUST_TAIL_CALL (hence the
complaint error: cannot tail-call: target is not able to optimize the call into
a sibling call, I suppose).

2) for O >= 2 where GCC would normally tail call anyway
 - for this, the coroutine code does not mark the cll specially, so for these
cases it indicates that the tail-call is not being made in "normal"
circumstance.

the function signature is

 void actor (void *)

and the codgen should be emitting an indirect call, followed by a void return 

(the indirect call is expanding __builtin_coro_resume() [expansion happens very
early in the ME].