[flang-commits] [flang] [flang][OpenMP] Support ALLOCATABLE list items in LINEAR (PR #228827)

[Tom Eccles via flang-commits]

https://github.com/tblah commented:

This is great progress.

I think we need the more complete integration discussed in your plan (with dialect changes) to avoid these extra copies. Other than performance concerns, the copy changes results for a program like this (written by AI):

```
program p
  implicit none
  integer, allocatable :: i
  integer :: seen(3), k

  allocate(i)
  i = 42
  seen = -1
  k = 1

  !$omp simd linear(i:2) linear(k)
  do i = 1, 5, 2
    seen(k) = i
    k = k + 1
  end do
  !$omp end simd

  print *, seen, i
  if (any(seen /= [1, 3, 5])) stop 1
  if (i /= 7) stop 2 
end
```

The new copy in means that i gets values starting at 42 instead of being initialized to 1. This is because the copy happens inside the loop body instead of before it. So I think this should be handled in translation.

That also makes things simpler for other users of the dialect: the linear clause should stand on its own without also requiring separate privatization.

https://github.com/llvm/llvm-project/pull/228827