[Flang][OpenMP] Incorrect execution result of a do-variable defined as shared in parallel construct

[ohno-fj]

Version of flang-new : 18.0.0(0fe86f9c518fb1296bba8d66ce495f9dfff2c435)

A do-variable defined as shared in parallel construct has an incorrect value after executing parallel construct.
A do-variable is executing by private, not shared.

The following are the test program, Flang-new, Gfortran and ifort compilation/execution result.

snggz567_22.f90:

subroutine s1
  ip=100
  ip2=-100
!$omp parallel shared(ip) private(ip2)
  DO ip = 0, 1
  END DO
  DO ip2 = 0, 1
  END DO
!$omp end parallel
  print *,'ip  shared  :',ip
  print *,'ip2 private :',ip2
end subroutine s1

program main
  call s1
end program main

$ export OMP_NUM_THREADS=2; flang-new -fopenmp snggz567_22.f90; ./a.out
 ip  shared  : 100
 ip2 private : -100
$

$ export OMP_NUM_THREADS=2; gfortran -fopenmp snggz567_22.f90; ./a.out
 ip  shared  :           2
 ip2 private :        -100
$

$ export OMP_NUM_THREADS=2; ifort -qopenmp snggz567_22.f90; ./a.out
 ip  shared  :           2
 ip2 private :        -100
$

[llvmbot]

@llvm/issue-subscribers-openmp

Author: None (ohno-fj)

``` Version of flang-new : 18.0.0(0fe86f9)

A `do-variable` defined as `shared` in `parallel` construct  has an incorrect value after executing `parallel` construct.  
A `do-variable` is executing by `private`, not `shared`.

The following are the test program, Flang-new, Gfortran and ifort compilation/execution result.

snggz567_22.f90:
```fortran
subroutine s1
  ip=100
  ip2=-100
!$omp parallel shared(ip) private(ip2)
  DO ip = 0, 1
  END DO
  DO ip2 = 0, 1
  END DO
!$omp end parallel
  print *,'ip  shared  :',ip
  print *,'ip2 private :',ip2
end subroutine s1

program main
  call s1
end program main

$ export OMP_NUM_THREADS=2; flang-new -fopenmp snggz567_22.f90; ./a.out
 ip  shared  : 100
 ip2 private : -100
$

$ export OMP_NUM_THREADS=2; gfortran -fopenmp snggz567_22.f90; ./a.out
 ip  shared  :           2
 ip2 private :        -100
$

$ export OMP_NUM_THREADS=2; ifort -qopenmp snggz567_22.f90; ./a.out
 ip  shared  :           2
 ip2 private :        -100
$

[mjklemm]

The code is non-confirming OpenMP code. There is a race condition on the ip variable.

[luporl]

Even removing the race condition, there is still an issue with flang, as the program below still prints ip shared : 100.

subroutine s1
  ip=100
!$omp parallel shared(ip)
!$omp single
  DO ip = 0, 1
  END DO
!$omp end single
!$omp end parallel
  print *,'ip  shared  :',ip
end subroutine s1

program main
  call s1
end program main

It seems the problem is that flang is treating ip as predetermined, even with the shared clause which seems to be allowed by OpenMP 5.2 5.1.1 in this case:

Loop iteration variables of loops that are not associated with any OpenMP directive may be listed in data-sharing attribute clauses on the surrounding teams, parallel or task generating construct, and on enclosed constructs, subject to other restrictions.

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: None (ohno-fj)

``` Version of flang-new : 18.0.0(0fe86f9)

A `do-variable` defined as `shared` in `parallel` construct  has an incorrect value after executing `parallel` construct.  
A `do-variable` is executing by `private`, not `shared`.

The following are the test program, Flang-new, Gfortran and ifort compilation/execution result.

snggz567_22.f90:
```fortran
subroutine s1
  ip=100
  ip2=-100
!$omp parallel shared(ip) private(ip2)
  DO ip = 0, 1
  END DO
  DO ip2 = 0, 1
  END DO
!$omp end parallel
  print *,'ip  shared  :',ip
  print *,'ip2 private :',ip2
end subroutine s1

program main
  call s1
end program main

$ export OMP_NUM_THREADS=2; flang-new -fopenmp snggz567_22.f90; ./a.out
 ip  shared  : 100
 ip2 private : -100
$

$ export OMP_NUM_THREADS=2; gfortran -fopenmp snggz567_22.f90; ./a.out
 ip  shared  :           2
 ip2 private :        -100
$

$ export OMP_NUM_THREADS=2; ifort -qopenmp snggz567_22.f90; ./a.out
 ip  shared  :           2
 ip2 private :        -100
$