[llvm-bugs] [Bug 141438] [Flang][OpenMP] Variable in parallel sections construct with default(private) clause is not treated as private

[LLVM Bugs via llvm-bugs]

Issue	141438
Summary	[Flang][OpenMP] Variable in parallel sections construct with default(private) clause is not treated as private
Labels	flang:openmp
Assignees
Reporter	ohno-fj

    ```
Version of flang : 21.0.0(fb86b3d96b73f4e628288b180ef4e038da8b7bc1)/AArch64
```

sngf_reduction71_222.f90:
```fortran
program main
  integer a
  a=10
!$omp parallel sections default(private)
 a=15
!$omp end parallel sections
  print *,'a = ', a
end program main
```

`Variable (a)` in `parallel sections construct` with `default (private) clause` is not treated as `private`.  
After `parallel sections construct` ends, the value of `variable (a)` is expected to be 10.

I found `variable (a)` is treated as `private` in the following cases:
- `default (private) clause` is changed to `private (a) clause`
   See sngf_reduction71_232.f90 below.
- `parallel sections construct` is changed to `parallel construct`
   See sngf_reduction71_223.f90 below.

The following are the test program, Flang, Gfortran and ifx compilation/execution result.


```
$ export OMP_NUM_THREADS=2; flang -fopenmp sngf_reduction71_222.f90; ./a.out
flang-21: warning: OpenMP support in flang is still experimental [-Wexperimental-option]
 a =  15
$
```

```
$ export OMP_NUM_THREADS=2; gfortran -fopenmp sngf_reduction71_222.f90; ./a.out
 a =           10
$
```

```
$ export OMP_NUM_THREADS=2; ifx -qopenmp sngf_reduction71_222.f90; ./a.out
 a = 10
$
```

sngf_reduction71_232.f90:
```fortran
program main
  integer a
  a=10
!$omp parallel sections private(a)
  a=15
!$omp end parallel sections
  print *,'a = ', a
end program main
```

```
$ export OMP_NUM_THREADS=2; flang -fopenmp sngf_reduction71_232.f90; ./a.out
flang-21: warning: OpenMP support in flang is still experimental [-Wexperimental-option]
 a = 10
$
```

sngf_reduction71_223.f90:
```fortran
program main
  integer a
  a=10
!$omp parallel default(private)
  a=15
!$omp end parallel
 print *,'a = ', a
end program main
```

```
$ export OMP_NUM_THREADS=2; flang -fopenmp sngf_reduction71_223.f90; ./a.out
flang-21: warning: OpenMP support in flang is still experimental [-Wexperimental-option]
 a = 10
$
```

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