jax-ml/jax · error · ValueError

Can only concatenate 1D vectors

Error message

Can only concatenate 1D vectors

What it means

Beyond the first element, vector_concat also verifies each operand is itself rank-1; a later operand of rank>=2 raises this ValueError (note: a ValueError, unlike the NotImplementedError used for the first operand).

Source

Thrown at jax/experimental/mosaic/gpu/utils.py:2137

  )


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]:
      [v_len] = ir.VectorType(v.type).shape
      [w_len] = ir.VectorType(w.type).shape
      mask = ir.DenseI64ArrayAttr.get(list(range(v_len + w_len)))
      return vector.shuffle(*vectors, mask=mask)
    case _:
      assert vectors
      l = _vector_concat_rec(vectors[: len(vectors) // 2])
      r = _vector_concat_rec(vectors[len(vectors) // 2 :])

View on GitHub (pinned to 1e1c6a8fc0)

Solutions

1. Flatten every operand to rank-1 before concatenating (vector.shape_cast)
2. Validate all operands in a loop: assert ir.VectorType(v.type).rank == 1
3. Fix the producer emitting the multi-dimensional vector

Example fix

# before
v = vector_concat([flat_a, tile_2d])
# after
flat_tile = vector.shape_cast(ir.VectorType.get((tile_2d.type.num_elements,), tile_2d.type.element_type), tile_2d)
v = vector_concat([flat_a, flat_tile])

assert all(ir.VectorType(v.type).rank == 1 for v in vectors), 'all operands must be 1D'

def all_rank1(vals) -> bool:
    return all(isinstance(v.type, ir.VectorType) and ir.VectorType(v.type).rank == 1 for v in vals)

When it happens

Trigger: Calling vector_concat where vectors[0] is 1D but a subsequent element is e.g. vector<2x4xf32>.

Common situations: Heterogeneous fragment lists where one producer changed shape; appending a reshaped tile to a list of flat vectors.

Related errors

• Expected metadata to be 3-dimensional (M, K // 4, 2), but it
• Only 2D gathers/scatters for async load/store are supported.
• Only 1D vectors are supported {v_ty}
• Cannot concatenate an empty list of vectors
• Cannot concatenate non-vector values

AI-assisted analysis of jax-ml/jax@1e1c6a8fc0 (2026-08-27). Data as JSON: /api/errors/45ab98e528423f68. Report an issue: GitHub.