[llvm-bugs] [Bug 51258] New: Assertion triggered when a serialized parallel region is after a detached task

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=51258

            Bug ID: 51258
           Summary: Assertion triggered when a serialized parallel region
                    is after a detached task
           Product: OpenMP
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Runtime Library
          Assignee: unassignedbugs at nondot.org
          Reporter: tianshilei1992 at gmail.com
                CC: llvm-bugs at lists.llvm.org

The reproducer is every simple:
```
#include <omp.h>

int main(int argc, char *argv[]) {
#pragma omp parallel
  {
    omp_event_handle_t event;
    int a = 0;

#pragma omp task shared(a) detach(event)
    { a = 1; }

#pragma omp parallel
    { a = 2; }

#pragma omp taskwait
  }
  return 0;
}
```
Please ignore that the detached task is never fulfilled, because it is not the
point. If it is executed with env `OMP_NUM_THREADS=1`, then an assertion is
triggered.
```
Assertion failure at kmp_runtime.cpp(1114):
serial_team->t.t_task_team[this_thr->th.th_task_state] == __null.
OMP: Error #13: Assertion failure at kmp_runtime.cpp(1114).
OMP: Hint Please submit a bug report with this message, compile and run
commands used, and machine configuration info including native compiler and
operating system versions. Faster response will be obtained by including all
program sources. For information on submitting this issue, please see
https://bugs.llvm.org/.
```
Basically, `__kmp_serialized_parallel` assumes that the corresponding task team
should be nullptr. However, if a detached task is encountered before, the task
team will be setup in `__kmp_task_alloc`.

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