[flang-commits] [flang] [flang][OpenMP][Semantics] Don't allow reduction of derived type components (PR #125480)

[Kiran Chandramohan via flang-commits]

kiranchandramohan wrote:

> > How does it work for array elements? Isn't there a similar issue?
> 
> It seems we just do reduction on the whole array, ignoring the indexing.

The following program seemed to work correctly with ifx. 
I see that flang currently generates a combiner that does the reduction on the whole array but the final answer it computes is also correct.
```
program mn
  integer :: i
  integer :: arr(10)
  arr = 0
  !$omp parallel do reduction(+:arr(3))
  do i=1,10
    arr(3) = arr(3) + i
  end do
  !$omp end parallel do
  print *, arr
end program
```
> 
> > Does this exclude array elements also?
> 
> I imagine it should do. gfortran and classic-flang don't allow it.
> 
> So does this sound okay to you:
> 
> 1. I change this patch to deny derived type components for all standard versions
> 2. I do a followup patch denying array indexing

I am not 100% sure about this since previous versions explicitly allowed array elements. It might be worth asking a question to the OpenMP committee.

https://github.com/llvm/llvm-project/pull/125480