jax-ml/jax · error · ValueError

Cannot concatenate non-vector values

Error message

Cannot concatenate non-vector values

What it means

vector_concat only concatenates ir.VectorType values. If vectors[0].type is a scalar (or any non-vector type) the helper cannot determine element type/shape semantics and raises ValueError.

Source

Thrown at jax/experimental/mosaic/gpu/utils.py:2129

  [v_len] = v_ty.shape
  slice_length = len(range(v_len)[s])
  return vector.extract_strided_slice(
      ir.VectorType.get((slice_length,), v_ty.element_type),
      v,
      [s.start or 0],
      [slice_length],
      [1],
  )


def vector_concat(
    vectors: Sequence[ir.Value[ir.VectorType]],
) -> ir.Value[ir.VectorType]:
  if not vectors:
    raise ValueError("Cannot concatenate an empty list of vectors")
  vty = vectors[0].type
  if not isinstance(vty, ir.VectorType):
    raise ValueError("Cannot concatenate non-vector values")
  vty = ir.VectorType(vty)
  if vty.rank != 1:
    raise NotImplementedError("Only 1D vectors are supported")
  for v in vectors:
    if v.type.element_type != vty.element_type:
      raise ValueError("Cannot concatenate vectors of different element types")
    if v.type.rank != 1:
      raise ValueError("Can only concatenate 1D vectors")
  return _vector_concat_rec(vectors)


def _vector_concat_rec(
    vectors: Sequence[ir.Value[ir.VectorType]],
) -> ir.Value[ir.VectorType]:
  match vectors:
    case [v]:
      return v
    case [v, w]:

View on GitHub (pinned to 1e1c6a8fc0)

Solutions

1. Wrap scalars as vector<1xT> with vector.broadcast before concatenating
2. Verify each element's .type is ir.VectorType before the call
3. Trace where the list was built and fix producers to emit vectors

Example fix

# before
v = vector_concat([a_scalar, b_scalar])
# after
one = ir.VectorType.get((1,), a_scalar.type)
v = vector_concat([vector.broadcast(one, a_scalar), vector.broadcast(one, b_scalar)])

assert isinstance(vectors[0].type, ir.VectorType), 'vector_concat needs vectors'

def all_vectors(vals) -> bool:
    return all(isinstance(v.type, ir.VectorType) for v in vals)

When it happens

Trigger: Calling vector_concat where the first element is a scalar i32/f32, a memref value, or a tensor — e.g. accidentally passing extracted scalars instead of vector<1xT> values.

Common situations: Refactoring that replaced broadcast/scalar insert with raw scalars; passing results of extractelement (scalars) where extract_subvector outputs were expected.

Understand the failure class

Background: Invalid argument type errors: "must be of type string", "expected X, got Y", and ERR_INVALID_ARG_TYPE explained — this error's family across 15 libraries.

Related errors

• Unsupported mesh type: {type(mesh)}
• Expected an `NDIndexer`, but got {transforms[0]}
• inline_mgpu_p only supports plgpu.ShapeDtypeStruct return ty
• inline_mgpu_p only supports only SomeLayout and RefType arg
• Cannot concatenate an empty list of vectors

AI-assisted analysis of jax-ml/jax@1e1c6a8fc0 (2026-08-27). Data as JSON: /api/errors/c12469ce63af634c. Report an issue: GitHub.