jax-ml/jax · error · ValueError

All arrays must have the same signedness, got

Error message

All arrays must have the same signedness, got {arr.is_signed} at index {i} (expected {arr0.is_signed})

What it means

For integer fragment types, Mosaic tracks signedness separately from bit width, and register concatenation cannot mix signed and unsigned interpretations of the same type. concatenate therefore verifies arr.is_signed matches arrays[0] and raises ValueError otherwise.

Solutions

Re-load the mismatched fragments with a consistent is_signed value matching arrays[0].is_signed.
Centralize load configuration (is_signed, dtype) in one helper so all fragments in a concat group agree.
Pre-check: assert all(a.is_signed == arrays[0].is_signed for a in arrays).

Example fix

# before
regs_a = FragmentedArray.load_untiled(src_a, is_signed=True)
regs_b = FragmentedArray.load_untiled(src_b, is_signed=False)
out = FragmentedArray.concatenate([regs_a, regs_b])  # error
# after
regs_b = FragmentedArray.load_untiled(src_b, is_signed=True)
out = FragmentedArray.concatenate([regs_a, regs_b])

Defensive patterns

Strategy: validation

Validate before calling

s = arrays[0].is_signed
assert all(a.is_signed == s for a in arrays), [
    (i, a.is_signed) for i, a in enumerate(arrays)
]
out = FragmentedArray.concatenate(arrays, axis=axis)

Prevention

Pass is_signed explicitly at every load site; never rely on defaults.
Centralize load configuration in one helper.
Remember signedness is tracked independently of mlir dtype.

When it happens

Trigger: Concatenating an i8-as-signed fragment with an i8-as-unsigned fragment (same mlir dtype, different is_signed flag), typically after loads that specified different is_signed values.

Common situations: Loading some tiles with is_signed=True and others with is_signed=False (e.g., signed activations vs unsigned indices/quantized weights); refactoring loads and dropping the is_signed argument so it defaults differently across call sites.

Related errors

AI-assisted analysis of jax-ml/jax@1e1c6a8fc0 (2026-08-27). Data as JSON: /api/errors/7d5bf0fe2c57d6ee. Report an issue: GitHub.

Appendix: source

Thrown at jax/experimental/mosaic/gpu/fragmented_array.py:5364

    axis += rank

  if len(arrays) == 1:
    return arr0

  new_shape = list(arr0.shape)
  for i, arr in enumerate(arrays[1:], start=1):
    if len(arr.shape) != rank:
      raise ValueError(
          f"All arrays must have the same rank, got {len(arr.shape)} at index"
          f" {i} (expected {rank})"
      )
    if arr.mlir_dtype != arr0.mlir_dtype:
      raise ValueError(
          f"All arrays must have the same dtype, got {arr.mlir_dtype} at"
          f" index {i} (expected {arr0.mlir_dtype})"
      )
    if arr.is_signed != arr0.is_signed:
      raise ValueError(
          f"All arrays must have the same signedness, got {arr.is_signed} at"
          f" index {i} (expected {arr0.is_signed})"
      )
    for d in range(rank):
      if d != axis and arr.shape[d] != arr0.shape[d]:
        raise ValueError(
            "All arrays must have matching shapes along non-concatenated"
            f" dimensions, got shape {arr.shape} at index {i} (expected dim"
            f" {d} to be {arr0.shape[d]})"
        )
    new_shape[axis] += arr.shape[axis]
  new_shape = tuple(new_shape)

  match arr0.layout:
    case TiledLayout():
      for i, arr in enumerate(arrays[1:], start=1):
        if arr.layout != arr0.layout:
          raise ValueError(

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