{"record":{"id":"0cff7d982153bb77","repo":"jax-ml/jax","slug":"rhs-must-be-an-smem-ref","errorCode":null,"errorMessage":"RHS must be an SMEM Ref.","messagePattern":"RHS must be an SMEM Ref\\.","errorType":"validation","errorClass":"ValueError","httpStatus":null,"severity":"error","filePath":"jax/_src/pallas/mosaic_gpu/primitives.py","lineNumber":2572,"sourceCode":"                               *barrier_scales_and_transforms_leaves,\n                               acc_transforms_tree, a_transforms_tree,\n                               b_transforms_tree,\n                               barrier_transforms_tree,\n                               a_scale_transforms_tree,\n                               b_scale_transforms_tree,\n                               a_sparse_metadata_transforms_tree,\n                               collective_axis,\n                               arrive,\n                               scaled,\n                               sparse):\n  del accumulate, acc_transforms_tree, a_transforms_tree, b_transforms_tree, barrier_transforms_tree\n\n  if acc.memory_space != gpu_core.TMEM:\n    raise ValueError(\"Accumulator must be a TMEM Ref.\")\n  if a.memory_space not in (gpu_core.SMEM, gpu_core.TMEM):\n    raise ValueError(\"LHS must be a TMEM/SMEM Ref.\")\n  if b.memory_space != gpu_core.SMEM:\n    raise ValueError(\"RHS must be an SMEM Ref.\")\n\n  if collective_axis is not None:\n    # TODO(justinfu): If under a core_map, the avals for acc/a\n    # become normal MemRefs so we cannot check if they are collective.\n    # Figure out a way to fix this.\n    if isinstance(acc, gpu_core.AbstractTMEMRef) and not acc.collective:\n      raise ValueError(\n          \"Accumulator Ref must be collective if collective_axis is set.\")\n    if isinstance(a, gpu_core.AbstractTMEMRef) and not a.collective:\n      raise ValueError(\n          \"LHS Ref must be collective if collective_axis is set.\")\n\n  scales_and_transforms_leaves = barrier_scales_and_transforms_leaves\n  if arrive:\n    barrier, *scales_and_transforms_leaves = barrier_scales_and_transforms_leaves\n    orders_tensor_core = getattr(\n        barrier.inner_aval.dtype, \"orders_tensor_core\", False)\n    if not orders_tensor_core:","sourceCodeStart":2554,"sourceCodeEnd":2590,"githubUrl":"https://github.com/jax-ml/jax/blob/1e1c6a8fc06dfcd1247076ec5cae4640cea5d7bb/jax/_src/pallas/mosaic_gpu/primitives.py#L2554-L2590","documentation":"The RHS operand of tcgen05.mma must be an SMEM ref. TMEM or GMEM RHS operands are rejected.","triggerScenarios":"Passing b as a TMEM ref or an unstaged GMEM input to tcgen05.mma.","commonSituations":"Symmetric allocation of A and B in TMEM when only A may live there; skipping the SMEM staging/swizzle for B when porting a kernel.","solutions":["Stage the B tile into SMEM with the required swizzle/tiling transforms","Do not allocate B in TMEM","Verify b.memory_space == SMEM before the call"],"exampleFix":"# before\nb_tmem = allocate(TMEM, (k, n), jnp.float8_e4m3fnuz)\ntcgen05.mma(a_smem, b_tmem, acc, k_dim=k)\n# after\nb_smem = load_to_smem(b_gmem, swizzle=128)\ntcgen05.mma(a_smem, b_smem, acc, k_dim=k)","handlingStrategy":"type-guard","validationCode":"assert b.memory_space == gpu_core.SMEM","typeGuard":"def is_smem(ref):\n    return getattr(ref, 'memory_space', None) == gpu_core.SMEM","tryCatchPattern":null,"preventionTips":["Never allocate B in TMEM","Check memory spaces in a shared pre-MMA assert block"],"tags":["jax","pallas","tcgen05","smem","memory-space"],"backgroundTag":"gpu-memory-space-validation","analyzedSha":"1e1c6a8fc06dfcd1247076ec5cae4640cea5d7bb","analyzedAt":"2026-08-27T09:53:25.647Z","schemaVersion":2},"datasetVersion":"2026-08-27T13:17:12.746Z"}