Conjugate View (#54987)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/54987
Based off of ezyang (https://github.com/pytorch/pytorch/pull/44799) and bdhirsh (https://github.com/pytorch/pytorch/pull/43702) 's prototype:
Here's a summary of the changes in this PR:
This PR adds a new dispatch key called Conjugate. This enables us to make conjugate operation a view and leverage the specialized library functions that fast path with the hermitian operation (conj + transpose).
1. Conjugate operation will now return a view with conj bit (1) for complex tensors and returns self for non-complex tensors as before. This also means `torch.view_as_real` will no longer be a view on conjugated complex tensors and is hence disabled. To fill the gap, we have added `torch.view_as_real_physical` which would return the real tensor agnostic of the conjugate bit on the input complex tensor. The information about conjugation on the old tensor can be obtained by calling `.is_conj()` on the new tensor.
2. NEW API:
a) `.conj()` -- now returning a view.
b) `.conj_physical()` -- does the physical conjugate operation. If the conj bit for input was set, you'd get `self.clone()`, else you'll get a new tensor with conjugated value in its memory.
c) `.conj_physical_()`, and `out=` variant
d) `.resolve_conj()` -- materializes the conjugation. returns self if the conj bit is unset, else returns a new tensor with conjugated values and conj bit set to 0.
e) `.resolve_conj_()` in-place version of (d)
f) `view_as_real_physical` -- as described in (1), it's functionally same as `view_as_real`, just that it doesn't error out on conjugated tensors.
g) `view_as_real` -- existing function, but now errors out on conjugated tensors.
3. Conjugate Fallback
a) Vast majority of PyTorch functions would currently use this fallback when they are called on a conjugated tensor.
b) This fallback is well equipped to handle the following cases:
- functional operation e.g., `torch.sin(input)`
- Mutable inputs and in-place operations e.g., `tensor.add_(2)`
- out-of-place operation e.g., `torch.sin(input, out=out)`
- Tensorlist input args
- NOTE: Meta tensors don't work with conjugate fallback.
4. Autograd
a) `resolve_conj()` is an identity function w.r.t. autograd
b) Everything else works as expected.
5. Testing:
a) All method_tests run with conjugate view tensors.
b) OpInfo tests that run with conjugate views
- test_variant_consistency_eager/jit
- gradcheck, gradgradcheck
- test_conj_views (that only run for `torch.cfloat` dtype)
NOTE: functions like `empty_like`, `zero_like`, `randn_like`, `clone` don't propagate the conjugate bit.
Follow up work:
1. conjugate view RFC
2. Add neg bit to re-enable view operation on conjugated tensors
3. Update linalg functions to call into specialized functions that fast path with the hermitian operation.
Test Plan: Imported from OSS
Reviewed By: VitalyFedyunin
Differential Revision: D28227315
Pulled By: anjali411
fbshipit-source-id: acab9402b9d6a970c6d512809b627a290c8def5f
