% cat repro.F90
module mod_my_model
  type :: my_model_t
    contains
#ifdef FAIL
      private
      procedure, public :: step    => step_my_model
#endif
  end type my_model_t
  type, extends(my_model_t) :: my_adj_t
    contains
      procedure, public :: step    => step_my_adj
  end type my_adj_t
  interface
    module subroutine step_my_adj( this, step_length, istat )
        implicit none
        class ( my_adj_t ), intent(inout)         :: this
        integer,            intent(in),  optional :: step_length
        integer,            intent(out), optional :: istat
    end subroutine step_my_adj
  end interface
contains
    subroutine step_my_model( this, step_length, istat )
      implicit none
      class ( my_model_t ), intent(inout)         :: this
      integer,              intent(in),  optional :: step_length
      integer,              intent(out), optional :: istat
    end subroutine step_my_model
end module mod_my_model
% pgf90 -c repro.F90
% pgf90 -c -DFAIL repro.F90
/opt/nvidia/hpc_sdk/Linux_x86_64/21.1/compilers/share/llvm/bin/llc: error: /opt/nvidia/hpc_sdk/Linux_x86_64/21.1/compilers/share/llvm/bin/llc: /tmp/nvfortrannU0BNWU9OQKd.ll:8:75: error: use of undefined value '@step_my_adj_'
@mod_my_model$$$my_adj_t$$$td$vft = global [1 x i8*] [i8* bitcast(void()* @step_my_adj_ to i8*)]
                                                                          ^
% ifort -c -DFAIL repro.F90
%