[pytorchbot]

What is wrong today

torch.cat accepts tensors of different dtypes and promotes them:

torch.cat([torch.ones(2, dtype=torch.bfloat16), torch.ones(2)]).dtype  # torch.float32

to_edge rejects the same program:

SpecViolationError: These operators are taking Tensor inputs with mismatched dtypes:
... aten.cat.default ... {'tensors': torch.bfloat16, '__ret_0': torch.float32}

torch.stack, torch.concat and torch.hstack fail too, since they become cat.

cat([float32, int32]) is worse: it lowers without an error and gives wrong values. The portable cat kernel fix behind those values is in #24401.

What this change does

1. to_edge casts the inputs of cat and stack to the dtype eager promoted to. The RemoveMixedTypeOperators pass already did this for binary ops like add. For cat and stack it takes that dtype from the op's output, so an empty input dropped by an earlier pass still counts.
2. The edge dtype check (EdgeOpArgValidator) now checks every tensor of an input list, not only the first. That gap let cat([float32, int32]) pass.
3. ConvertDtypePass (used as I64toI32) left int64 topk indices in a cat it made int32, which the check in item 2 now rejects. It now casts the tensor-list inputs of ops it rewrites. Other inputs, like a gather index, get no new cast.

Compatibility:

• A pass after to_edge that changes only some cat or stack inputs to another dtype now fails the edge check. The Arm int64 passes, such as ConvertInt64OutputOpsToInt32Pass, can do this when passed as transform passes, as the Arm README shows. The Arm tester, scripts and recipes lower with _check_ir_validity=False, so they are not affected, and the README now says to do the same. An Arm test now expects this graph.
• A dropped empty input with a wider dtype now widens the output, as in eager.
• Mixed cat programs that already ran, like cat([float32, int64]), now carry a _to_dim_order_copy for each input of another dtype when re-exported. A selective build needs that operator to load them.

What was tested

• New tests, each failing without its fix: exir/program/test/test_program.py (float, integer, empty and repeated inputs), exir/tests/test_arg_validator.py and backends/transforms/test/test_convert_dtype_pass.py.
• On the portable runtime, cat with mixed float, integer, bool and empty inputs, stack, concat and hstack match eager.
• Apart from the new tests and the Arm test, exir and XNNPACK tests and the Arm, Cadence, Qualcomm, Vulkan and backends/transforms pass tests give the same results with and without this change. NXP and some Cadence pass tests could not run here.

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils @Sebastian-Larsson @robell @rascani

[pytorch-bot]

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⏳ 1 Pending, 1 Unrelated Failure

As of commit 84ce510 with merge base 4db778e ():

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / nxp-mcuxpresso-test / linux-job (gh) (trunk failure)
  RuntimeError: Command bash /__w/_temp/exec_script failed with exit code 1

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