microsoft/onnxscript

[Optimizer] Fold Shape -> {Slice, Gather} -> Concat -> Reshape

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#2,736 opened on Dec 17, 2025

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contribution welcomegood first issuemodule: rewriter

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Description

In Shape -> {Slice, Gather} -> Concat -> Reshape, when the dynamic axis coming from Shape is a single axis and the rest of the dimensions are not -1, we can replace the shape for Reshape to have a static -1 axis, and eliminate the nodes for dynamic shape evaluation.

Contributor guide

Research direction
Identify the pattern in the ONNX graph where a Shape node is followed by Slice/Gather, then Concat, then Reshape. Implement a pass to replace the Reshape shape with a static 1 for the dynamic axis, eliminating the dynamic shape computation.
Tech stack
python
Domain
ai
Issue type
Performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
PythonGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70