[Bug fortran/86945] BUG with optimisation of select case statement in gfortran v8.x

[anlauf at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86945

--- Comment #3 from Harald Anlauf <anlauf at gmx dot de> ---
Self contained alternative testcase:

program test
  implicit none
  integer, volatile :: id,ierr
  id = 1
  print*,'id=',id
  call foo1 ()
  print*,'ierr1, OK = ',ierr, ierr == 0
  call foo2 ()
  print*,'ierr2, OK = ',ierr, ierr == 0
contains
  subroutine foo1 ()
    select case(id)
    case(-HUGE(0):-1)
       ierr = id
    case default
       ierr = 0
    end select
  end subroutine foo1
  subroutine foo2 ()
    select case(id)
!   case(-HUGE(0)-1:-1)
    case(          :-1)
       ierr = id
    case default
       ierr = 0
    end select
  end subroutine foo2
end program test

With -O0:

 id=           1
 ierr1, OK =            0 T
 ierr2, OK =            0 T

With -Og, -O1 and higher:

 id=           1
 ierr1, OK =            0 T
 ierr2, OK =            1 F