[flang-commits] [flang] [flang][openmp]Add UserReductionDetails and use in DECLARE REDUCTION (PR #131628)

[Kiran Chandramohan via flang-commits]

kiranchandramohan wrote:

There is a crash in `Fortran::semantics::IsReductionAllowedForType` for the following test.

```
module custom_reduce_mod
  type :: my_data
    real :: val
  end type my_data

  !$omp declare reduction(+:my_data:omp_out = omp_out + omp_in) &
  !$omp& initializer(omp_priv = my_data(0.0))

  interface operator(+)
    module procedure combine_values
  end interface
contains
  function combine_values(a, b) result(c)
    type(my_data), intent(in) :: a, b
    type(my_data) :: c
    c%val = a%val + b%val
  end function combine_values
end module custom_reduce_mod

subroutine compute_sum
  use custom_reduce_mod
  implicit none
  type(my_data) :: total
  integer :: idx

  total = my_data(0.0)

  !$omp parallel do reduction(+:total)
  do idx = 1, 100
    total = total + my_data(real(idx))
  end do
  !$omp end parallel do

  print *, 'Total sum: ', total%val
end subroutine compute_sum
```

The following test also crashes in some checks for pure functions.
```
pure logical function is_reduction_valid()
  !$omp declare reduction (bar : integer : red_out = red_out + red_in) initializer (red_priv = 0)
  is_reduction_valid = .false.
end function is_reduction_valid
```

https://github.com/llvm/llvm-project/pull/131628