Warns when TensorIterator would resize its output (#42079)
Summary:
See https://github.com/pytorch/pytorch/issues/41027.
This adds a helper to resize output to ATen/native/Resize.* and updates TensorIterator to use it. The helper throws a warning if a tensor with one or more elements needs to be resized. This warning indicates that these resizes will become an error in a future PyTorch release.
There are many functions in PyTorch that will resize their outputs and don't use TensorIterator. For example,
https://github.com/pytorch/pytorch/blob/985fd970aad85799a568b76c2a1b75a1c422fe53/aten/src/ATen/native/cuda/NaiveConvolutionTranspose2d.cu#L243
And these functions will need to be updated to use this helper, too. This PR avoids their inclusion since the work is separable, and this should let us focus on the function and its behavior in review. A TODO appears in the code to reflect this.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42079
Reviewed By: VitalyFedyunin
Differential Revision: D22846851
Pulled By: mruberry
fbshipit-source-id: d1a413efb97e30853923bce828513ba76e5a495d
