[Relax] Add layout inference support for repeat operator

[guan404ming]

How

• Implemented InferLayoutRepeat function that:
  • Preserves layout when axis is specified (with axis transformation)
  • Returns 1D layout when axis is not specified (flatten mode)
  • Transforms the axis parameter based on layout changes (e.g., NCHW axis=1 → NHWC axis=3)

[gemini-code-assist]

Summary of Changes

Hello @guan404ming, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the Relax framework by implementing layout inference for the repeat operator. This ensures that repeat operations correctly adapt to existing tensor layouts, either by preserving the layout and adjusting the specified axis or by producing a flattened 1D output when no axis is provided, thereby improving the robustness of layout transformations.

Highlights

• Layout Inference for relax.repeat: Added FRelaxInferLayout for the relax.repeat operator to enable proper layout handling within the Relax framework.
• Axis-aware Layout Preservation: When an axis is specified for the repeat operation, the existing tensor layout is preserved, and the axis parameter is automatically transformed to align with the new layout (e.g., NCHW axis=1 becomes NHWC axis=3).
• Flattened Output for No Axis: If no axis is specified for the repeat operation, the system now correctly infers a 1D (flattened) output layout.
• New Test Cases: Introduced two new test cases, test_conv2d_repeat and test_conv2d_repeat_flatten, to validate the layout inference behavior for repeat in scenarios involving both axis-specified and flattened outputs.

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[gemini-code-assist]

Code Review

This pull request adds layout inference support for the relax.repeat operator. The implementation correctly handles two cases: when an axis is specified, it preserves the layout and transforms the axis accordingly; when no axis is specified, it correctly infers a 1D layout for the flattened output. The changes are well-tested with new unit tests covering both scenarios. My review includes a minor suggestion to improve code conciseness in the C++ implementation.

[gemini-code-assist]

This loop to find the index of '1' can be simplified by using ffi::String::find, which is more idiomatic and concise.

  size_t pos = new_axis_str.find('1');
  ICHECK(pos != std::string::npos) << "Failed to find transformed axis";
  int64_t new_axis = static_cast<int64_t>(pos);

[guan404ming]

cc @tlopex @mshr-h

[tlopex]

LGTM Thanks