[5455919] Fix Q/DQ/Cast placement in 'FP32 required' custom ops

[gcunhase]

What does this PR do?

Type of change: Bug fix

Overview: Fix incorrect quantization of custom ops when some input tensors are required to be in INT8 and some in FP32.

Before fix	After fix

Usage

$ python -m modelopt.onnx.quantization --onnx_path=$MODEL_PATH.onnx \
    --trt_plugins $PLUGIN_PATH.so \
    --trt_plugins_precision $CUSTOM_OP_NAME:$PRECISION

Testing

1. BEVFormer model

• Follow step 1 in README.
• In the quantization step, do:

$ python -m modelopt.onnx.quantization --onnx_path=/mnt/models/bevformer_tiny_epoch_24_cp2_op13.onnx \
      --trt_plugins=$PLUGIN_PATH \
      --trt_plugins_precision MultiScaleDeformableAttnTRT:[int8,int32,fp32,int8,int8]:[int8] \
      --high_precision_dtype fp16

See table in "Overview" for expected graph structure.

2. 5455919 model

Validated model in bug 5455919.

Before your PR is "Ready for review"

• Make sure you read and follow Contributor guidelines and your commits are signed.
• Is this change backward compatible?: Yes
• Did you write any new necessary tests?: No
• Did you add or update any necessary documentation?: No
• Did you update Changelog?: Yes

Additional Information

• [5455919] Insert cast nodes for 'FP32 required' ops #363: Feature expansion.
• [5620660][ONNX] Remove toposort after quantization #524: The graph cleanup is actually needed after Q/DQ trimming around custom ops. Moved the cleanup lines to inside that function.

[ajrasane]

LGTM. Can we add a test case for this?

[codecov]

Codecov Report

❌ Patch coverage is 32.25806% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.43%. Comparing base (9cd0824) to head (49a4513).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
modelopt/onnx/quantization/qdq_utils.py	0.00%	17 Missing ⚠️
modelopt/onnx/autocast/precisionconverter.py	71.42%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #554      +/-   ##
==========================================
- Coverage   74.47%   74.43%   -0.04%     
==========================================
  Files         182      182              
  Lines       18225    18238      +13     
==========================================
+ Hits        13573    13576       +3     
- Misses       4652     4662      +10     

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