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From: "michael at scivision dot dev" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug fortran/104391] New: Gfortran 9 regression with bind(C) and
 allocatable or pointer attribute
Date: Fri, 04 Feb 2022 20:45:31 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104391

            Bug ID: 104391
           Summary: Gfortran 9 regression with bind(C) and allocatable or
                    pointer attribute
           Product: gcc
           Version: 9.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: michael at scivision dot dev
  Target Milestone: ---

The `bind(C)` on a procedure appears to break `pointer` and `allocatable`
attributes of a variable with regard to index start. Specifically, on exiti=
ng a
procedure with `bind(c)`, the variable(s) have their indices shifted to
zero-based.

example that works with GCC <=3D 8.5 and GCC 12 (broken for GCC 9, 10, 11).

```
program test_bounds
use iso_fortran_env, only : error_unit
implicit none

real, allocatable :: a(:)
integer :: L1,L2, U1,U2
allocate(a(1:2))

L1 =3D lbound(a,1)
U1 =3D ubound(a,1)
call c_bounder(a)
L2 =3D lbound(a,1)
U2 =3D ubound(a,1)

if (L1 /=3D L2 .or. U1 /=3D U2) then
  write(error_unit, '(a,2i2,a,2i2)') 'FAIL: bounds changed before/after
lower:', L1,L2, " upper: ", U1,U2
  error stop
endif

print '(a)', "bounds check OK"

contains

subroutine c_bounder(a) bind(c)
real,  intent(inout) :: a(:)
end subroutine c_bounder

end program
```=