[Bug libgomp/124737] New: Undeferred task with detach clause should not wait for the allow-completion event to be fulfilled

[protze at itc dot rwth-aachen.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124737

            Bug ID: 124737
           Summary: Undeferred task with detach clause should not wait for
                    the allow-completion event to be fulfilled
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgomp
          Assignee: unassigned at gcc dot gnu.org
          Reporter: protze at itc dot rwth-aachen.de
                CC: jakub at gcc dot gnu.org
  Target Milestone: ---

Created attachment 64107
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=64107&action=edit
OpenMP program that deadlocks when executed with libgomp

The attached test comes from the libomp OMPT tests
(https://github.com/llvm/llvm-project/blob/main/openmp/runtime/test/ompt/tasks/task_late_fulfill.c). 

The execution is blocked in GOMP_task for `gomp_sem_wait (&completion_sem);`.

>From the OpenMP spec:
> undeferred task: A task for which execution is not deferred with respect to 
> its generating task region. That is, its generating task region is suspended 
> until execution of the structured block associated with the undeferred task is 
> completed.

The generating task is only suspended for executing the structured block of the
task, but not until the allow-completion event is fulfilled.
As a side-effect, out-dependences for undeferred tasks actually need to be
handled and cannot be ignored.