SplitToSequence layer with unequal split generates incorrect onnx model

[bas-aarts]

converting the attached ONNX model

with the following script:

from onnxscript import ir
from onnxscript.optimizer import optimize

ir_model = ir.load("input.onnx")
optimized_model = optimize(ir_model)
ir.save(optimized_model, "output.onnx")

results in the following output model:

The uneven split in the SplitToSequence layer has been converted to an even split Split layer.

input.onnx.zip

versions of relevant packages:

ml_dtypes         0.5.4
onnx              1.20.1
onnx-ir           0.2.0
onnxscript        0.6.2