[frlai]

After mutation functionalization, Python slices become ATen slices and enter LEAPP's slice-to-narrow rewrite. The rewrite currently uses raw bounds: on six elements, x[-3:], x[2:100], and x[4:2] produce invalid narrow lengths instead of the expected suffix, clipped slice, and empty result.

Normalize unit-step bounds against the runtime dimension size before calling torch.narrow: translate negative bounds, clip to [0, size], and make the length nonnegative. Preserve slice_copy allocation independence, including whole-axis copies. A scripted helper retains runtime size arithmetic under legacy tracing. Functionalization, the slice helpers, and the ATen rewrite pass live in leapp/leapp_graph/aten_rewrites.py; TracedTensorNode controls when the passes run. The separate functionalization.py module is removed. rewrite_aten_ops owns traversal, operator identification, applicability checks, and dispatch; module-level helpers perform the selected graph edits. Adding a rewrite means adding its helper and an explicit dispatch branch.

This is a stacked draft targeting feature/view-mutation-functionalization (PR #33), addressing #33 (comment). The independent-buffer copy_ aliasing issue remains separate.

Validation:

• PyTorch 2.14: affected Torch, NumPy, view-mutation, and conversion suites — 408 tests and 1,742 subtests passed.
• Minimum PyTorch 2.7.0: complete view-mutation suite — 49 tests passed.
• Torch and NumPy mutation/slice capture replayed on changed inputs through reloaded TorchScript, PT2, and ONNX artifacts.
• Internal graph unit checks execute slice/slice_copy rewrites directly, plus scripting and tracing at dimension sizes 0, 1, 3, 6, 11, and 101; copied outputs remain independent. Direct FX graph execution is unit coverage, not a supported LEAPP export backend.
• Variable-width PT2 and ONNX artifacts reloaded and checked at widths 8, 11, 12, 20, and 32 within the declared 8–32 range. Symbolic export still requires a shape range accepted by PyTorch; this does not introduce LEAPP dynamic-shape annotations.
• Before/after dispatch probes matched graph structure across 27 cases, with executable results also compared for 24 cases; the remaining three check copy-option guards and Warp skip behavior.
• Ruff 0.17.1 formatting and git diff --check passed.