amdflang: an unnamed critical in a target parallel do does not exclude other threads (lost updates)

Legality: not independently confirmed. no independent review yet How this is checked

Same issue as catalog/afar-flang-critical-target-parallel-wrong; this program is another reproducer of it.

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	behaves incorrectly	behaves incorrectly	unknown not run	behaves incorrectly	behaves incorrectly	n/a	n/a
CCE 19.0.0	fails another way	fails another way	unknown not run	unknown not run	unknown not run	n/a	n/a
CCE 20.0.2	fails another way	fails another way	unknown not run	unknown not run	unknown not run	n/a	n/a
CCE 21.0.3	fails another way	fails another way	unknown not run	unknown not run	unknown not run	n/a	n/a
CCE 21.0.4	fails another way	fails another way	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	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
behaves incorrectly	AFAR 24.3.0, MI300A unified AFAR 24.3.0, MI300A copy AFAR 24.3.0, MI300X AFAR 24.3.0, MI350X	show RESULT checksum=129
fails another way	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.. MT_CONTEXT_CRITICAL_SECTION Error message :: unhandled construct type Error detected :: File '/workspace/crayftn/pdgcs/v_openmp.c', line 7617 Initiated from :: Line 660 (v_main.c) Optimizer built :: 2025-02-07 (production) File :: fuzz-1936-afar.f90
fails another way	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.. MT_CONTEXT_CRITICAL_SECTION Error message :: unhandled construct type Error detected :: File '/workspace/crayftn/pdgcs/v_openmp.c', line 7814 Initiated from :: Line 660 (v_main.c) Optimizer built :: 2025-11-17 (production) File :: fuzz-1936-afar.f90
fails another way	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.. MT_CONTEXT_CRITICAL_SECTION Error message :: unhandled construct type Error detected :: File '/workspace/crayftn/pdgcs/v_openmp.c', line 8197 Initiated from :: Line 732 (v_main.c) Optimizer built :: 2026-07-14 (production) File :: fuzz-1936-afar.f90
fails another way	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.. MT_CONTEXT_CRITICAL_SECTION Error message :: unhandled construct type Error detected :: File '/workspace/crayftn/pdgcs/v_openmp.c', line 8197 Initiated from :: Line 732 (v_main.c) Optimizer built :: 2026-09-24 (production) File :: fuzz-1936-afar.f90
fails another way	NVHPC 25.11, A100 separate NVHPC 25.11, A100 managed	show NVFORTRAN-F-1196-OpenMP - omp critical is not supported in GPU region (fuzz-1936-afar.f90: 34) NVFORTRAN/x86-64 Linux 25.11-0: compilation aborted
fails another way	NVHPC 26.9, A100 separate NVHPC 26.9, A100 managed	show NVFORTRAN-F-1196-OpenMP - omp critical is not supported in GPU region (fuzz-1936-afar.f90: 34) NVFORTRAN/x86-64 Linux 26.9-0: compilation aborted

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

GCC 16.2.0, MI300A unified (runs correctly)

export LD_LIBRARY_PATH=$GCC_16_2/lib64:/opt/rocm-7.2.1/lib
$GCC_16_2/bin/gfortran -fopenmp -foffload=amdgcn-amdhsa -foffload-options=amdgcn-amdhsa=-march=gfx942 -O2 repro.f90 -o repro
HSA_XNACK=1 OMP_TARGET_OFFLOAD=mandatory ./repro

Program (57 lines)

! Minimized by compliance.fuzz_min from fuzz seed 1936 (fuzz-1).
! toolchain: afar (-O2, HSA_XNACK=1, OMP_TARGET_OFFLOAD=mandatory)
! failure: wrong_code
! expected: the host reference checksum (host reference (afar) checksum=2147483504)
! observed: device checksum=129 ran_on_host=0
! Legal OpenMP 5.2: offload.engine.rules accepts it (offload.engine.prerun.check, rerun: with the
!   race rule and the restriction checks); NVHPC is no witness: it does not implement a feature the
!   program uses (NVFORTRAN-F-1196-OpenMP - omp critical is not supported in GPU
!   region); the check's other witness, the AFAR flang front end, is the compiler under test and is
!   not counted; no gfortran or gcc is a legality witness.
module fuzz_mod
  implicit none
contains
  integer function g1(x)
    !$omp declare target
    integer, intent(in) :: x
    g1 = mod(ior(merge(4, x, x /= 4), 4), 97)
  end function g1
end module fuzz_mod
program fuzz_prog
  use omp_lib, only: omp_is_initial_device
  use fuzz_mod, only: g1
  implicit none
  integer, parameter :: n = 100, m = 8
  integer, allocatable :: ia(:)
  integer :: ib(n)
  integer :: i, j, r1a
  logical :: lt
  integer(8) :: cs
  allocate(ia(n))
  do i = 1, n
    ia(i) = mod(i * 4 + 30, 211) - 80
  end do
  do i = 1, n
    ib(i) = mod(i * 58 + 12, 97) - 31
  end do
  r1a = 15
  lt = .true.
  ! fuzz: kernels
  !$omp target map(tofrom: r1a)
    !$omp parallel
      !$omp do
      do i = 1, n
        do j = m, 1, -1
          !$omp critical
          r1a = ieor(r1a, ((ib((mod(((j * 1) + 2), n) + 1)) + ib(32)) - ia(i)))
          !$omp end critical
        end do
      end do
      !$omp end do
    !$omp end parallel
  !$omp end target
  ! fuzz: checksum
  cs = 0
  cs = modulo(cs * 31_8 + int(r1a, 8), 2147483629_8)
  print '(a,i0,a,i0)', 'RESULT checksum=', cs, ' ran_on_host=', 0
end program fuzz_prog

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

RESULT checksum=129

What the specification requires

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

The same requirement as the issue catalog/afar-flang-critical-target-parallel-wrong.

OpenMP 5.2 §15.2 p.299

Evidence

Other compilers run it correctly

GCC 16.2.0