Add OutputFixPass to fix invalid graph outputs

[justinchuby]

This pull request introduces a new pass, OutputFixPass, to the ONNX IR transformation pipeline. The main purpose of this pass is to ensure that the model's outputs conform to ONNX specifications by inserting Identity nodes where necessary. This helps to fix cases where graph inputs are directly used as outputs or where the same value is used multiple times as an output, both of which are not allowed by ONNX.

The most important changes include:

New Pass Implementation

• Added a new file, output_fix.py, implementing OutputFixPass. This pass automatically inserts Identity nodes in two scenarios: when a graph input is directly used as an output, and when a value is used multiple times as an output. The pass applies to both the main graph and all subgraphs/functions.

AI use

I used copilot to create the tests and some of the logic.

[Copilot]

Pull request overview

This PR introduces OutputFixPass, a new transformation pass that ensures ONNX model validity by inserting Identity nodes when graph inputs are directly used as graph outputs. This addresses an ONNX specification requirement where direct input-to-output connections are not permitted.

Key Changes:

• Implements OutputFixPass to detect and fix direct input-to-output connections by inserting Identity nodes
• Handles main graphs, subgraphs, and function bodies recursively
• Preserves output metadata (name, shape, type, doc_string, and metadata_props) when inserting Identity nodes

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

File	Description
src/onnx_ir/passes/common/output_fix.py	Implements the new OutputFixPass with logic to insert Identity nodes between direct input-output connections
src/onnx_ir/passes/common/output_fix_test.py	Comprehensive test suite covering various scenarios including subgraphs, functions, and edge cases
src/onnx_ir/passes/common/__init__.py	Registers and exports OutputFixPass in the common passes module

[codecov]

Codecov Report

❌ Patch coverage is 95.08197% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.66%. Comparing base (7283e95) to head (b73f540).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/onnx_ir/passes/common/output_fix.py	94.91%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #269      +/-   ##
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+ Coverage   77.28%   77.66%   +0.38%     
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  Files          40       41       +1     
  Lines        5097     5157      +60     
  Branches     1027     1039      +12     
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+ Hits         3939     4005      +66     
+ Misses        860      851       -9     
- Partials      298      301       +3     

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.