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

[Kareem Ergawy via flang-commits]

ergawy 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
> ``§
> ```

Thanks Tom, looking into it, and will handle before merging.

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