Linear(x: for, step(2)) sends the front end into an endless loop after "too many errors"

Affected variants

"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

clang-c-linear-directive-name-hang.c:3:38: error: expected expression
    3 |   #pragma omp parallel for linear(x: for, step(2))
      |                                      ^
clang-c-linear-directive-name-hang.c:3:38: error: expected expression
clang-c-linear-directive-name-hang.c:3:38: error: expected expression
clang-c-linear-directive-name-hang.c:3:38: error: expected expression
clang-c-linear-directive-name-hang.c:3:38: error: expected expression
clang-c-linear-directive-name-hang.c:3:38: error: expected expression

clang-c-linear-directive-name-hang.c: In function ‘main’:
clang-c-linear-directive-name-hang.c:3:38: error: expected expression before ‘for’
    3 |   #pragma omp parallel for linear(x: for, step(2))
      |                                      ^~~
clang-c-linear-directive-name-hang.c:3:34: error: ‘linear’ clause step expression must be integral
    3 |   #pragma omp parallel for linear(x: for, step(2))
      |                                  ^

Reproduce

AFAR 24.3.0, MI300A unified

$AFAR/bin/amdclang -fopenmp --offload-arch=gfx942 -fopenmp-version=60 -fopenmp-version=60 -O2 repro.c -o repro
HSA_XNACK=1 OMP_TARGET_OFFLOAD=mandatory ./repro

CCE 19.0.0, MI300A unified

module load cce/19.0.0 craype-accel-amd-gfx942 rocm/6.4.3
module unload cray-mpich
craycc -fopenmp -fopenmp-targets=amdgcn-amd-amdhsa -Xopenmp-target=amdgcn-amd-amdhsa -march=gfx942 -fopenmp-version=60 -O2 repro.c -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
craycc -fopenmp -fopenmp-targets=amdgcn-amd-amdhsa -Xopenmp-target=amdgcn-amd-amdhsa -march=gfx942 -fopenmp-version=60 -O2 repro.c -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
craycc -fopenmp -fopenmp-targets=amdgcn-amd-amdhsa -Xopenmp-target=amdgcn-amd-amdhsa -march=gfx942 -fopenmp-version=60 -O2 repro.c -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
craycc -fopenmp -fopenmp-targets=amdgcn-amd-amdhsa -Xopenmp-target=amdgcn-amd-amdhsa -march=gfx942 -fopenmp-version=60 -O2 repro.c -o repro
HSA_XNACK=1 OMP_TARGET_OFFLOAD=mandatory ./repro

NVHPC 25.11, A100 separate (runs correctly)

export LD_LIBRARY_PATH=$NVHPC_25_11/compilers/lib
nvc -mp=gpu -gpu=cc80 -gpu=mem:separate -O2 repro.c -o repro
OMP_TARGET_OFFLOAD=mandatory ./repro

/* Finding (C): a directive-name modifier in a linear clause sends
   the clang front end into an endless loop.

   Legal OpenMP 6.0 C: linear(x: for, step(2)) names the directive the
   clause applies to (6.0 §5.4, p.174: "The directive-name-modifier is a
   universal modifier that can be used on any clause"; linear, 6.0
   §7.5.6, p.232). Expected: compiles
   (or, for a compiler without the 6.0 modifier, one diagnostic).

   Observed (2026-10-19): AFAR amdclang 24.0.0git and CCE craycc 19.0.0
   (the omp60-c-clause-linear-directive_name program: also 20.0.2 and
   21.0.3) print "error: expected expression" at the `for` twenty times,
   then "fatal error: too many errors emitted, stopping now", and do not
   exit: killed after 40 s with -fsyntax-only (the matrix: compile
   timeout on all four toolchains). Without `for,` it compiles at once.

   amdclang -fopenmp -fopenmp-version=60 -fsyntax-only
   craycc -fopenmp -fopenmp-version=60 -fsyntax-only */
int main(void) {
  int x = 0, b[8];
  #pragma omp parallel for linear(x: for, step(2))
  for (int i = 0; i < 8; i++) { b[i] = x; x += 2; }
  return b[1];
}

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

clang-c-linear-directive-name-hang.c:3:38: error: expected expression
    3 |   #pragma omp parallel for linear(x: for, step(2))
      |                                      ^
clang-c-linear-directive-name-hang.c:3:38: error: expected expression
clang-c-linear-directive-name-hang.c:3:38: error: expected expression
clang-c-linear-directive-name-hang.c:3:38: error: expected expression
clang-c-linear-directive-name-hang.c:3:38: error: expected expression
clang-c-linear-directive-name-hang.c:3:38: error: expected expression

What the specification requires

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

Evidence