amdflang: reduction on loop bind(teams) nested in a target teams region rejected

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

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	not supported	not supported	not supported	not supported	not supported	n/a	n/a
CCE 19.0.0	correct	correct	correct	unknown not run	unknown not run	n/a	n/a
CCE 20.0.2	correct	correct	correct	unknown not run	unknown not run	n/a	n/a
CCE 21.0.3	correct	correct	correct	unknown not run	unknown not run	n/a	n/a
CCE 21.0.4	correct	correct	correct	unknown not run	unknown not run	n/a	n/a
NVHPC 25.11	n/a	n/a	n/a	n/a	n/a	correct	correct
NVHPC 26.9	n/a	n/a	n/a	n/a	n/a	correct	correct
GCC 16.2.0	correct	correct	correct	correct	correct	correct	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	AFAR 24.3.0, MI300A unified AFAR 24.3.0, MI300A copy AFAR 24.3.0, MI250X AFAR 24.3.0, MI300X AFAR 24.3.0, MI350X	show error: Semantic errors in afar-flang-loop-bind-teams-reduction.f90 afar-flang-loop-bind-teams-reduction.f90:6:28: error: 'REDUCTION' clause not allowed with '!$OMP LOOP BIND(TEAMS)'. !$omp loop bind(teams) reduction(+: r) ^^^^^^^^^^^^^^^

Result

Compiler and GPU

Message

not supported

AFAR 24.3.0, MI300A unified
AFAR 24.3.0, MI300A copy
AFAR 24.3.0, MI250X
AFAR 24.3.0, MI300X
AFAR 24.3.0, MI350X

show

error: Semantic errors in afar-flang-loop-bind-teams-reduction.f90
afar-flang-loop-bind-teams-reduction.f90:6:28: error: 'REDUCTION' clause not allowed with '!$OMP LOOP BIND(TEAMS)'.
      !$omp loop bind(teams) reduction(+: r)
                             ^^^^^^^^^^^^^^^

Reproduce

AFAR 24.3.0, MI300A unified

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

CCE 19.0.0, MI300A unified (runs correctly)

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

Program (20 lines)

program p
  implicit none
  integer :: r, i
  r = 0
  !$omp target teams map(tofrom: r)
    !$omp loop bind(teams) reduction(+: r)
    do i = 1, 10
      r = r + i
    end do
  !$omp end target teams
  print *, 'r =', r
end program p
! spec (requirement): The reduction clause is permitted on the loop construct.
! "bind, collapse, lastprivate, order, private, reduction" (5.2 §11.7 p.257 l.4)
! spec (requirement): The behavior of a reduction clause on a loop with bind(teams) is unspecified only when the loop
!   is not nested inside a teams construct (and executes on a non-host device); nested inside teams it is specified.
! "then the behavior of a reduction clause that appears on the corresponding loop construct is unspecified if the
!   construct is not nested inside a teams construct." (5.2 §11.7.1 p.259 l.5-7)
! spec (this program): The loop bind(teams) reduction(+: r) is strictly nested in the teams region of target teams,
!   the case the restriction leaves specified, so r must be 55; amdflang rejects the reduction.

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

error: Semantic errors in afar-flang-loop-bind-teams-reduction.f90
afar-flang-loop-bind-teams-reduction.f90:6:28: error: 'REDUCTION' clause not allowed with '!$OMP LOOP BIND(TEAMS)'.
      !$omp loop bind(teams) reduction(+: r)
                             ^^^^^^^^^^^^^^^

What the specification requires

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

OpenMP 5.2 §11.7 p.257 l.4

bind, collapse, lastprivate, order, private, reduction

OpenMP 5.2 §11.7.1 p.259 l.5-7

then the behavior of a reduction clause that appears on the corresponding loop construct is unspecified if the construct is not nested inside a teams construct.

Evidence

Same compiler, one change

bind(teams) removed (the loop binds to the teams region by default): AFAR 24.3.0: correct; CCE 19.0.0: correct; CCE 20.0.2: correct; CCE 21.0.3: correct; CCE 21.0.4: correct

Control program

program p
  implicit none
  integer :: r, i
  r = 0
  !$omp target teams map(tofrom: r)
    !$omp loop reduction(+: r)
    do i = 1, 10
      r = r + i
    end do
  !$omp end target teams
  print *, 'r =', r
end program p

Other compilers run it correctly

CCE 19.0.0, CCE 20.0.2, CCE 21.0.3, CCE 21.0.4, NVHPC 25.11, NVHPC 26.9, GCC 16.2.0