Subtensor lift: reason about advanced indices jointly when gating#2251
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ricardoV94 wants to merge 3 commits into
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Subtensor lift: reason about advanced indices jointly when gating#2251ricardoV94 wants to merge 3 commits into
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ricardoV94
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Jun 27, 2026
| and idx.type.ndim > 0 | ||
| and not inp.type.broadcastable[axis] | ||
| ] | ||
| if not _indices_provably_not_larger(adv_indices, fgraph): |
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shouldn't this take the variable for the static shape
ricardoV94
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| continue | ||
| if not _index_provably_not_larger(idx, inp.type.shape[axis], fgraph): | ||
| return None | ||
| adv_indices = [ |
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this should be called adv_indices and input_static_dim
Generalize the duplicate-free reasoning used to gate the advanced-index write rewrites from a per-axis check to a joint one over the whole advanced index group, sharing the logic across subtensor.py and subtensor_lift.py. - _index_provably_unique: per-axis uniqueness, now also proving single-signed aranges and views (Reshape/DimShuffle) that preserve the value multiset. - _indices_jointly_unique: distinct joint coordinate tuples via all-axes uniqueness, a single Nonzero (e.g. tril_indices), or jointly-unique constants where no single axis is unique on its own. - _indices_provably_not_larger: bound a gather by the indexed axes' size using static shapes, per-axis bounds, or joint uniqueness.
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We had heuristics that work per-axis, but we should reason about the advanced indices together since they interact. E.g., tril_indices, would fail the per-axis checks, as each index (row, col) is larger than the respective axis and contains duplicates. But jointly they index less than the full array and don't have duplicates, so we want to lift it through Elemwise and the like.
Shows up in pymc-devs/pymc#8297