a CLASS IS guard of SELECT TYPE in device code fails at the link

Legality: independently confirmed. 2 independent readings find the program legal and the result required. How this is checked

SELECT TYPE with a CLASS IS guard in a declare target subroutine called in a target region fails at the device link on CCE 19, 20 and 21 (undefined _EXTENDS_TYPE_OF). AFAR runs it correctly.

Affected variants

Compiler	MI300A gfx942 unified memory (XNACK 1)	MI300A gfx942 copy (XNACK 0)	MI250X gfx90a copy (XNACK 0)	MI300X gfx942 copy (XNACK 0)	MI350X gfx950 copy (XNACK 0)	A100 sm_80 separate memory	A100 sm_80 managed memory
AFAR 24.3.0	correct	correct	unknown not run	correct	correct	n/a	n/a
CCE 19.0.0	not supported	not supported	unknown not run	unknown not run	unknown not run	n/a	n/a
CCE 20.0.2	not supported	not supported	unknown not run	unknown not run	unknown not run	n/a	n/a
CCE 21.0.3	not supported	not supported	unknown not run	unknown not run	unknown not run	n/a	n/a
CCE 21.0.4	not supported	not supported	unknown not run	unknown not run	unknown not run	n/a	n/a
NVHPC 25.11	n/a	n/a	n/a	n/a	n/a	fails another way	fails another way
NVHPC 26.9	n/a	n/a	n/a	n/a	n/a	fails another way	fails another way
GCC 16.2.0	fails another way	fails another way	fails another way	fails another way	fails another way	fails another way	n/a

"behaves incorrectly" / "not supported": this issue, confirmed in up to four environments (another build directory, another node, a repeat). "fails another way": a different failure, not counted as this issue. "unknown": not run there, or the runs disagree.

Messages

Result	Compiler and GPU	Message
not supported	CCE 19.0.0, MI300A unified CCE 19.0.0, MI300A copy	show Warning: Headers and libraries from cray-libsci/25.03.0 will be ignored because depends on PE_MPICH which is unavailable.. lld: error: undefined symbol: _EXTENDS_TYPE_OF >>> referenced by <dir>:(oop_$ck_L61_2) >>> referenced by <dir>:(oop_$ck_L61_2) >>> referenced by <dir>:(oop_$ck_L61_2) >>> referenced 3 more times
not supported	CCE 20.0.2, MI300A unified CCE 20.0.2, MI300A copy	show Warning: Headers and libraries from cray-libsci/25.09.0 will be ignored because depends on PE_MPICH which is unavailable.. lld: error: undefined symbol: _EXTENDS_TYPE_OF >>> referenced by <dir>:(oop_$ck_L61_2) >>> referenced by <dir>:(oop_$ck_L61_2) >>> referenced by <dir>:(oop_$ck_L61_2) >>> referenced 3 more times
not supported	CCE 21.0.3, MI300A unified CCE 21.0.3, MI300A copy	show Warning: Headers and libraries from cray-libsci/26.03.0 will be ignored because depends on PE_MPICH which is unavailable.. lld: error: undefined symbol: _EXTENDS_TYPE_OF >>> referenced by <dir>//cooltmpdir-y9hUzu/repro-cce-openmppost_lld.amdgpu.lto.o:(oop_$ck_L61_2) >>> referenced by <dir>//cooltmpdir-y9hUzu/repro-cce-openmppost_lld.amdgpu.lto.o:(oop_$ck_L61_2) >>> referenced by <dir>//cooltmpdir-y9hUzu/repro-cce-openmppost_lld.amdgpu.lto.o:(oop_$ck_L61_2) >>> referenced 3 more times
not supported	CCE 21.0.4, MI300A unified CCE 21.0.4, MI300A copy	show Warning: Headers and libraries from cray-libsci/26.03.0 will be ignored because depends on PE_MPICH which is unavailable.. lld: error: undefined symbol: _EXTENDS_TYPE_OF >>> referenced by <dir>//cooltmpdir-oSh743/repro-cce-openmppost_lld.amdgpu.lto.o:(oop_$ck_L61_2) >>> referenced by <dir>//cooltmpdir-oSh743/repro-cce-openmppost_lld.amdgpu.lto.o:(oop_$ck_L61_2) >>> referenced by <dir>//cooltmpdir-oSh743/repro-cce-openmppost_lld.amdgpu.lto.o:(oop_$ck_L61_2) >>> referenced 3 more times
fails another way	NVHPC 25.11, A100 separate NVHPC 25.11, A100 managed NVHPC 26.9, A100 separate NVHPC 26.9, A100 managed	show NVFORTRAN-S-1058-Call to Compiler runtime function not supported - pgf90_same_type_as_i8 (site-oop--cce-class-is-device-link.f90: 37) 0 inform, 0 warnings, 1 severes, 0 fatal for tag
fails another way	GCC 16.2.0, MI300A unified GCC 16.2.0, MI300A copy GCC 16.2.0, MI250X	show site-oop--cce-class-is-device-link.f90:44:16: error: variable ‘__vtab_oop_m_Ext2’ has been referenced in offloaded code but hasn’t been marked to be included in the offloaded code 44 \| end module oop_m \| ^ site-oop--cce-class-is-device-link.f90:44:16: error: variable ‘__vtab_oop_m_Base_t’ has been referenced in offloaded code but hasn’t been marked to be included in the offloaded code lto1: fatal error: errors during merging of translation units compilation terminated. gcn mkoffload: fatal error: <home>/gcc-16.2/bin/x86_64-pc-linux-gnu-accel-amdgcn-amdhsa-gcc returned 1 exit status compilation terminated.
fails another way	GCC 16.2.0, MI300X GCC 16.2.0, MI350X	show site-oop--cce-class-is-device-link.f90:44:16: error: variable ‘__vtab_oop_m_Ext2’ has been referenced in offloaded code but hasn’t been marked to be included in the offloaded code 44 \| end module oop_m \| ^ site-oop--cce-class-is-device-link.f90:44:16: error: variable ‘__vtab_oop_m_Base_t’ has been referenced in offloaded code but hasn’t been marked to be included in the offloaded code lto1: fatal error: errors during merging of translation units compilation terminated. gcn mkoffload: fatal error: <home>/<user>/gcc-16.2/bin/x86_64-pc-linux-gnu-accel-amdgcn-amdhsa-gcc returned 1 exit status compilation terminated.
fails another way	GCC 16.2.0, A100 separate	show site-oop--cce-class-is-device-link.f90:44:16: error: variable ‘__vtab_oop_m_Ext2’ has been referenced in offloaded code but hasn’t been marked to be included in the offloaded code 44 \| end module oop_m \| ^ site-oop--cce-class-is-device-link.f90:44:16: error: variable ‘__vtab_oop_m_Base_t’ has been referenced in offloaded code but hasn’t been marked to be included in the offloaded code lto1: fatal error: errors during merging of translation units compilation terminated. nvptx mkoffload: fatal error: <home>/gcc-16.2/bin/x86_64-pc-linux-gnu-accel-nvptx-none-gcc returned 1 exit status compilation terminated.

Reproduce

CCE 19.0.0, MI300A unified

module load cce/19.0.0 craype-accel-amd-gfx942 rocm/6.4.3
module unload cray-mpich
ftn -fopenmp -O2 repro.f90 -o repro
HSA_XNACK=1 OMP_TARGET_OFFLOAD=mandatory ./repro

CCE 20.0.2, MI300A unified

module load cce/20.0.2 craype-accel-amd-gfx942 rocm/6.4.3
module unload cray-mpich
ftn -fopenmp -O2 repro.f90 -o repro
HSA_XNACK=1 OMP_TARGET_OFFLOAD=mandatory ./repro

CCE 21.0.3, MI300A unified

module load cce/21.0.3 craype-accel-amd-gfx942 rocm/7.2.0
module unload cray-mpich
ftn -fopenmp -O2 repro.f90 -o repro
HSA_XNACK=1 OMP_TARGET_OFFLOAD=mandatory ./repro

CCE 21.0.4, MI300A unified

module load cce/21.0.4 craype-accel-amd-gfx942 rocm/7.2.0
module unload cray-mpich
ftn -fopenmp -O2 repro.f90 -o repro
HSA_XNACK=1 OMP_TARGET_OFFLOAD=mandatory ./repro

AFAR 24.3.0, MI300A unified (runs correctly)

$AFAR/bin/amdflang -fopenmp --offload-arch=gfx942 -O2 repro.f90 -o repro
HSA_XNACK=1 OMP_TARGET_OFFLOAD=mandatory ./repro

Program (81 lines)

! # Finding (fortran-oop): SELECT TYPE with a CLASS IS guard in device code fails to link (_EXTENDS_TYPE_OF)
!
! - toolchains and modes that fail: cce19 (CCE 19.0.0: copy, unified), cce20 (CCE 20.0.2: copy, unified), cce21 (CCE 21.0.3: copy,
!   unified), cce21_4 (CCE 21.0.4: copy, unified); -O2
! - build: ftn -fopenmp -O2 (module load cce/<v> craype-accel-amd-gfx942 rocm/<r>; OpenACC: ftn -h acc)
! - failure: rejected (link_undefined_symbol, the program's own object); OMP_TARGET_OFFLOAD=mandatory
! - observed: `lld: error: undefined symbol: _EXTENDS_TYPE_OF`, every CCE release, both modes
! - expected: compiles; `r1= 121`
! - rule: Fortran 2018 11.1.11 (CLASS IS guards); no OpenMP restriction on SELECT TYPE in device procedures
! (section 6)
! - same-compiler control: TYPE IS guards only (oop-poly-select-type) link (and then take the wrong branch:
!   cce-select-type-guard-not-taken.f90)
! - other families: AFAR correct; GCC 16.2 rejects it (gcc-vtab-not-marked-for-offload.f90)
! - gate and confirmer: 8 cells, 8 confirmed in the gate's four environments (a-d; results/oop/main/gate_reruns*.jsonl); confirmer
!   (results/oop/main/confirm.jsonl): compiler_bug (R10b-own-link-or-hang) 8
! - programs (1): oop-poly-class-is (offload/engine/oop_gen.py; this file is the first one)
! - legality: for the cce cells: the rules (offload.engine.rules, with the fortran-oop restrictions) and AFAR's flang front end
!   (-fsyntax-only) (tools/campaigns/oop.py legality, results/oop/main/legality.json)
module oop_m
  implicit none
  integer, parameter :: n = 64
  type base_t
    integer :: a = 0
  end type base_t
  type, extends(base_t) :: ext1
    integer :: u = 0
  end type ext1
  type, extends(base_t) :: ext2
    integer :: v = 0
  end type ext2
contains
  subroutine tag(s, t)
    !$omp declare target
    class(base_t), intent(in) :: s
    integer, intent(out) :: t
    t = 0
    select type (s)
      class is (base_t)
        t = 1
      type is (ext2)
        t = 2
    end select
  end subroutine tag
end module oop_m

program oop
  use omp_lib
  use oop_m
  implicit none
  integer :: host_flag
  logical :: ok
  integer :: r1
  type(ext1) :: e1
  type(ext2) :: e2
  type(base_t) :: b0
  integer :: t1, t2, t3
  host_flag = 1
  !$omp target map(from: host_flag)
  host_flag = merge(1, 0, omp_is_initial_device())
  !$omp end target
  !$omp target map(tofrom: e1, e2, b0) map(from: t1, t2, t3)
  call tag(e1, t1)
  call tag(e2, t2)
  call tag(b0, t3)
  !$omp end target
  r1 = 100 * t1 + 10 * t2 + t3
  ok = .true.
  ok = ok .and. (r1 == 121)
  print '(a,i0)', 'r1= ', r1
  print '(a,i0,a,a)', 'RESULT ran_on_host=', host_flag, ' check=', merge('pass', 'fail', ok)
end program oop
! spec (requirement): the base language is Fortran 2003, 2008 and 2018, and only the few Fortran features listed in the
!   base-language section have unspecified behavior (SELECT TYPE with a CLASS IS guard is not one of them; its semantics are the
!   Fortran standard's, with no OpenMP text of its own); a declare target procedure must be executable on a device.
! "While future versions of the OpenMP specification are expected to address the following features, currently their use may
!   result in unspecified behavior." (5.2 §1.7 p.36 l.6-8)
! "Declare target directives apply to procedures and/or variables to ensure that they can be executed or accessed on a device."
!   (5.2 §7.8 p.204 l.16-17)
! spec (this program): the declare target subroutine tag uses SELECT TYPE with a CLASS IS guard and is called in a target
!   region; CCE 19, 20 and 21 build it but fail at the link (undefined symbol _EXTENDS_TYPE_OF), so the procedure cannot be
!   executed on the device.

Source in the repository

Something to add? Dispute its legality · Report it fixed in a newer release · Report a mistake on this page

Expected and observed

Observed where it behaves incorrectly

Warning:
 Headers and libraries from cray-libsci/25.03.0 will be ignored because depends on PE_MPICH which is unavailable..
lld: error: undefined symbol: _EXTENDS_TYPE_OF
>>> referenced by <dir>:(oop_$ck_L61_2)
>>> referenced by <dir>:(oop_$ck_L61_2)
>>> referenced by <dir>:(oop_$ck_L61_2)
>>> referenced 3 more times

What the specification requires

The specification text this program relies on and the compiler is expected to support.

OpenMP 5.2 §1.7 p.36 l.6-8

While future versions of the OpenMP specification are expected to address the following features, currently their use may result in unspecified behavior.

OpenMP 5.2 §7.8 p.204 l.16-17

Declare target directives apply to procedures and/or variables to ensure that they can be executed or accessed on a device.

Evidence

Other compilers run it correctly

AFAR 24.3.0