Add converter for aten::_grouped_mm.default

[Sid-V5]

Implemented the converter for aten::_grouped_mm.default to address #2795.

Changes

• Added aten_grouped_mm function in onnxscript/function_libs/torch_lib/ops/core.py

Implementation Details

The aten::_grouped_mm operator performs grouped matrix multiplication. This implementation handles the batch/dense mode (when offs is None), where groups are implicit in the batch dimension:

• self: (G, M, K), mat2: (G, K, N) → result: (G, M, N)
• Uses op.MatMul for the core computation
• Supports optional bias addition via op.Add
• Supports optional out_dtype casting via op.Cast

The offset-based mode (when offs is provided) raises NotImplementedError, as it requires segment-level matrix multiplications that are not directly expressible with standard ONNX operators.

Testing

The function follows the same patterns as other converters in core.py (e.g., aten_bmm, aten_mm) and uses the @torch_op decorator for automatic registration.

Fixes #2795

[Sid-V5]

@microsoft-github-policy-service agree

[codecov]

Codecov Report

❌ Patch coverage is 20.00000% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.42%. Comparing base (e6f79e1) to head (c540859).

Files with missing lines	Patch %	Lines
onnxscript/function_libs/torch_lib/ops/core.py	20.00%	8 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (e6f79e1) and HEAD (c540859). Click for more details.

HEAD has 21 uploads less than BASE

Flag	BASE (e6f79e1)	HEAD (c540859)
	40	19

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2805       +/-   ##
===========================================
- Coverage   70.52%   60.42%   -10.10%     
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  Files         228      219        -9     
  Lines       27135    25620     -1515     
  Branches     2727     2633       -94     
===========================================
- Hits        19137    15481     -3656     
- Misses       7065     9355     +2290     
+ Partials      933      784      -149     

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