{"record":{"id":"9401cf9f5f75e0d5","repo":"jax-ml/jax","slug":"unsupported-a-register-array-layout","errorCode":null,"errorMessage":"Unsupported A register array layout","messagePattern":"Unsupported A register array layout","errorType":"validation","errorClass":"ValueError","httpStatus":null,"severity":"error","filePath":"jax/experimental/mosaic/gpu/wgmma.py","lineNumber":164,"sourceCode":"  f8e5m2 = ir.Float8E5M2Type.get()\n  f8e4m3fn = ir.Float8E4M3FNType.get()\n  if b_k_stride % 16:\n    raise ValueError\n  assert bytewidth(a_element_type) == bytewidth(b_element_type)\n  # Only 16-bit types support transposes\n  supports_transpose = bytewidth(b_element_type) == 2\n  if not supports_transpose and (a_transpose or b_transpose):\n    raise ValueError(\"Only f16 WGMMA supports transposes\")\n  if a_in_regs := isinstance(a, fa.FragmentedArray):\n    if a.mlir_dtype not in {bf16, f16, i8, f8e5m2, f8e4m3fn}:\n      raise ValueError(f\"Unsupported A register array dtype: {a.mlir_dtype}\")\n    # Column count must be equal to swizzle // bytewidth.\n    elt_bytewidth = utils.bytewidth(a_element_type)\n    swizzle_elems = swizzle // elt_bytewidth\n    if a.shape != (64, swizzle_elems):\n      raise ValueError(\"Unsupported A register array shape\")\n    if a.layout not in {fa.WGMMA_LAYOUT, fa.WGMMA_LAYOUT_8BIT}:\n      raise ValueError(\"Unsupported A register array layout\")\n    if a_k_stride is not None or a_transpose is not None:\n      raise ValueError(\"Unsupported WGMMA features with A in registers\")\n  else:\n    if a_k_stride is None or a_k_stride % 16:\n      raise ValueError\n    if a_transpose is None:\n      raise ValueError\n\n  if isinstance(out_ty, ir.F32Type) or out_ty == i32:\n    num_acc_regs = n // 2\n    out_ty_field = ir.VectorType.get((1,), out_ty)\n    acc_regs = list(acc.flat)\n    assert acc_regs[0].type == ir.VectorType.get((1,), out_ty)\n    to_acc_vec_regs = lambda regs: np.array(regs).reshape(acc.shape)\n    acc_constraint = \"r\" if isinstance(out_ty, ir.IntegerType) else \"f\"\n  elif isinstance(out_ty, ir.F16Type):\n    num_acc_regs = n // 4\n    out_ty_field = i32","sourceCodeStart":146,"sourceCodeEnd":182,"githubUrl":"https://github.com/jax-ml/jax/blob/1e1c6a8fc06dfcd1247076ec5cae4640cea5d7bb/jax/experimental/mosaic/gpu/wgmma.py#L146-L182","documentation":"At wgmma.py:164, an in-register A FragmentedArray must be laid out as fa.WGMMA_LAYOUT (or fa.WGMMA_LAYOUT_8BIT for byte types) so registers match the wgmma A-operand fragment layout.","triggerScenarios":"Passing a as a FragmentedArray in a row-major or blocked layout when using the A-in-registers form of wgmma.","commonSituations":"Reusing a register tensor produced by earlier elementwise ops or a previous wgmma result without relayout; layout constant renames across JAX versions.","solutions":["Convert: a = a.to_layout(fa.WGMMA_LAYOUT_8BIT if 8-bit else fa.WGMMA_LAYOUT)","Pass A from SMEM instead of registers when the layout cannot be preserved","Verify layout constants exist in your installed JAX/mosaic version"],"exampleFix":"# before\nacc = wgmma.wgmma(a_rowmajor, b, acc, ...)\n# after\na = a_rowmajor.to_layout(fa.WGMMA_LAYOUT)\nacc = wgmma.wgmma(a, b, acc, ...)","handlingStrategy":"validation","validationCode":"assert a.layout in {fa.WGMMA_LAYOUT, fa.WGMMA_LAYOUT_8BIT}, 'convert A layout first'","typeGuard":"def wgmma_a_layout_ok(a): return a.layout in {fa.WGMMA_LAYOUT, fa.WGMMA_LAYOUT_8BIT}","tryCatchPattern":null,"preventionTips":["Call a.to_layout(fa.WGMMA_LAYOUT) right before wgmma","Avoid elementwise ops between layout conversion and wgmma"],"tags":["jax","mosaic-gpu","wgmma","layout","fragmented-array"],"backgroundTag":"unsupported-layout-conversion","analyzedSha":"1e1c6a8fc06dfcd1247076ec5cae4640cea5d7bb","analyzedAt":"2026-08-27T09:53:25.647Z","schemaVersion":2},"datasetVersion":"2026-08-27T13:17:12.746Z"}