This is a common operation, but ONNX doesn't give us a convenient way of expressing this

[justinchuby]

          This is a common operation, but ONNX doesn't give us a convenient way of expressing this. We could potentially extend either the [Flatten op](https://onnx.ai/onnx/operators/onnx__Flatten.html#l-onnx-doc-flatten) or [Reshape op](https://onnx.ai/onnx/operators/onnx__Reshape.html) to support this. This is a one-sided flatten. Alternatively, if reshape has an attribute to align the shape with existing shape starting from the end (instead of beginning), we could specify the new target shape as `[-1, 0, 0, 0]`. Just some idle thoughts ...

Originally posted by @gramalingam in #1514 (comment)

[titaiwangms]

Is this supposed to be changing ops in pixelshuffle? I think we should make it more clear to look actionable.