[flang-commits] [flang] [flang][PFT-to-MLIR] Wrap unstructured Fortran constructs in scf.execute_region (PR #208635)

[Tom Eccles via flang-commits]

tblah wrote:

Codex found an issue here:

> branchesAreInternal checks only controlSuccessor, which
>    stores only the first multiway-branch target. Computed GOTO or arithmetic IF with a later external
>    target gets wrapped and produces an illegal cross-region branch. The exact-head reproducer fails FIR
>    verification; disabling wrapping succeeds.
  
It produced this reproducer, which I have verified does successfully lower to HLFIR with the new option disabled but fails with it enabled (as default)
```
subroutine computed_goto_exit(n, selector, a)
  integer :: n, selector, i
  real :: a(n)
  do i = 1, n
    go to (10, 99), selector
10  a(i) = real(i)
  end do
  a(1) = -1.0
99 continue
end subroutine

subroutine arithmetic_if_exit(n, x, a)
  integer :: n, i
  real :: x, a(n)
  do i = 1, n
    if (x) 10, 10, 99
10  a(i) = real(i)
  end do
  a(1) = -1.0
99 continue
end subroutine
``§

https://github.com/llvm/llvm-project/pull/208635