[flang] Incorrect array bound after remapping of zero-sized array pointer

[DanielCChen]

Consider the following reducer:

   program main

        double precision, target :: tar2(100)
        double precision, pointer :: ptr(:,:,:)

        i = -2
        call sub (i)

        contains
            function set_bd(i)
                integer i, set_bd
                allocatable set_bd
                allocate(set_bd, source = i)
            end function

            subroutine sub(i)
                integer i
                ptr(i:i-1, 1:set_bd(0), int(3.2):i) => tar2
                print*, lbound(ptr)
                print*, ubound(ptr)
            end subroutine
        End program

Flang outpus

> a.out
 1 1 3
 0 0 -2

The expected output should be

> a.out
 1 1 1
 0 0 0

All ifort, gfortran and XLF produces the correct result.

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: Daniel Chen (DanielCChen)

Consider the following reducer: ``` program main

    double precision, target :: tar2(100)
    double precision, pointer :: ptr(:,:,:)

    i = -2
    call sub (i)

    contains
        function set_bd(i)
            integer i, set_bd
            allocatable set_bd
            allocate(set_bd, source = i)
        end function

        subroutine sub(i)
            integer i
            ptr(i:i-1, 1:set_bd(0), int(3.2):i) => tar2
            print*, lbound(ptr)
            print*, ubound(ptr)
        end subroutine
    End program

Flang outpus

> a.out
1 1 3
0 0 -2

The expected output should be

> a.out
1 1 1
0 0 0

All ifort, gfortran and XLF produces the correct result.
</details>

[kkwli]

The further reduced case:

program main
  double precision, target :: tar2(100)
  double precision, pointer :: ptr(:)
  i = -2
  call sub(i)
contains
  subroutine sub(i)
    integer i
    ptr(3:i) => tar2
    print*, lbound(ptr) , ubound(ptr)
  end subroutine
End program

Output:

 3 -2

This behavior is inconsistent to the following case where the upper and lower bound are reset to 1 and 0 respectively:

  i = -2
  call sub(i)
contains
  subroutine sub(i)
    integer arr(3:i)
    print *, lbound(arr), ubound(arr)
  end
end

[klausler]

This is a lowering bug -- the pointer remapping here doesn't use the runtime.