split_predict pass generates an invalid ONNX model (missing tensor elem_type) — fails onnx.checker and cannot be loaded by ONNX Runtime

Describe the bug
Hi ONNX Optimizer maintainers, thanks for the project!

When optimizing a valid ONNX model named model.onnx using only the split_predict pass, the resulting model.opt.onnx becomes invalid ONNX. It fails onnx.checker.check_model() with:

onnx.onnx_cpp2py_export.checker.ValidationError: Field 'elem_type' of 'type' is required but missing.

and ONNX Runtime fails to load it:

onnxruntime.capi.onnxruntime_pybind11_state.Fail: ... failed: Invalid tensor data type 0.

This suggests the pass may be producing incomplete/incorrect type information (elem_type) for some tensor(s) in the optimized graph.

Environment

OS: Ubuntu 20.04 LTS
Python: 3.9.6
onnx: 1.19.0
onnxruntime: 1.19.2
onnxoptimizer: 0.3.13

To Reproduce

1. Download and unzip the attached archive, then cd into the extracted directory

split_predict_repro.tar.gz

tar -xzvf split_predict_repro.tar.gz
cd split_predict_repro

2. Create a Python environment (Python 3.9.6) and install dependencies:

python3.9 -m venv .venv
source .venv/bin/activate
pip install -U pip
pip install -r requirements.txt

3. Run the split_predict pass on the case model and save model.opt.onnx:

python optimize_model.py --case ./case_00051_seed20654888

This script loads model.onnx and runs optimizer.optimize(model, ["split_predict"]), then saves model.opt.onnx.

3. Validate the optimized model with ONNX checker:

python ./check_model.py

check_model.py loads ./case_00051_seed20654888/model.opt.onnx and runs checker.check_model(m).

4. Try to run the optimized model with ONNX Runtime using stored oracle inputs:

python ./run_optimized_model.py

This script creates an InferenceSession from ./case_00051_seed20654888/model.opt.onnx and feeds inputs from oracle.pkl.

Expected behavior

• model.opt.onnx should remain a valid ONNX model after split_predict optimization.
• onnx.checker.check_model() should pass.
• ONNX Runtime should be able to create an InferenceSession for model.opt.onnx.

Actual behavior

ONNX checker fails:

onnx.onnx_cpp2py_export.checker.ValidationError: Field 'elem_type' of 'type' is required but missing.

ONNX Runtime fails to load:

onnxruntime.capi.onnxruntime_pybind11_state.Fail: [ONNXRuntimeError] : 1 : FAIL : Load model ... failed: Invalid tensor data type 0.

Attachments

I’m attaching:

• requirements.txt (dependency versions)
• optimize_model.py (runs split_predict and saves model.opt.onnx)
• check_model.py (runs ONNX checker on model.opt.onnx)
• run_optimized_model.py (loads model.opt.onnx via ORT and runs with oracle.pkl)
• the minimal failing folder ./case_00051_seed20654888 containing model.onnx, oracle.pkl, and the generated model.opt.onnx.

Thanks for your help!