[optimizer] Collapse Slices

[justinchuby]

The optimizer currently does not collapse these slices, but there has to be a way to remove them I think?

[gramalingam]

Yes, it can be optimized.

Do you know where it is coming from? Just wondering if some change in source onnxscript function is also possible.

[justinchuby]

This is coming from the aten slice ops when there are indexed assignments I believe. So they are from pytorch.

[titaiwangms]

Found this in a timm model called ghostnet_100, which in onnx_dynamo, it generates 3 slices, while in torchscript, we only use 1. This can be repro on benchmark. cc @xadupre

[titaiwangms]

The right side is dynamo, and the other side is torchscript.

[titaiwangms]

It also happens to slice_scatter as well.

[titaiwangms]

Investigated more and found these op.Slice should probably be no op, since it's not slicing anything based on the output shape..