Summary:
Non-backwards-compatible change introduced in https://github.com/pytorch/pytorch/pull/53843 is tripping up a lot of code. Better to set it to False initially and then potentially flip to True in the later version to give people time to adapt.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55169
Reviewed By: mruberry
Differential Revision: D27511150
Pulled By: jbschlosser
fbshipit-source-id: 1ac018557c0900b31995c29f04aea060a27bc525
Summary:
*Context:* https://github.com/pytorch/pytorch/issues/53406 added a lint for trailing whitespace at the ends of lines. However, in order to pass FB-internal lints, that PR also had to normalize the trailing newlines in four of the files it touched. This PR adds an OSS lint to normalize trailing newlines.
The changes to the following files (made in 54847d0adb9be71be4979cead3d9d4c02160e4cd) are the only manually-written parts of this PR:
- `.github/workflows/lint.yml`
- `mypy-strict.ini`
- `tools/README.md`
- `tools/test/test_trailing_newlines.py`
- `tools/trailing_newlines.py`
I would have liked to make this just a shell one-liner like the other three similar lints, but nothing I could find quite fit the bill. Specifically, all the answers I tried from the following Stack Overflow questions were far too slow (at least a minute and a half to run on this entire repository):
- [How to detect file ends in newline?](https://stackoverflow.com/q/38746)
- [How do I find files that do not end with a newline/linefeed?](https://stackoverflow.com/q/4631068)
- [How to list all files in the Git index without newline at end of file](https://stackoverflow.com/q/27624800)
- [Linux - check if there is an empty line at the end of a file [duplicate]](https://stackoverflow.com/q/34943632)
- [git ensure newline at end of each file](https://stackoverflow.com/q/57770972)
To avoid giving false positives during the few days after this PR is merged, we should probably only merge it after https://github.com/pytorch/pytorch/issues/54967.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/54737
Test Plan:
Running the shell script from the "Ensure correct trailing newlines" step in the `quick-checks` job of `.github/workflows/lint.yml` should print no output and exit in a fraction of a second with a status of 0. That was not the case prior to this PR, as shown by this failing GHA workflow run on an earlier draft of this PR:
- https://github.com/pytorch/pytorch/runs/2197446987?check_suite_focus=true
In contrast, this run (after correcting the trailing newlines in this PR) succeeded:
- https://github.com/pytorch/pytorch/pull/54737/checks?check_run_id=2197553241
To unit-test `tools/trailing_newlines.py` itself (this is run as part of our "Test tools" GitHub Actions workflow):
```
python tools/test/test_trailing_newlines.py
```
Reviewed By: malfet
Differential Revision: D27409736
Pulled By: samestep
fbshipit-source-id: 46f565227046b39f68349bbd5633105b2d2e9b19
Summary:
**BC-breaking note**: This change throws errors for cases that used to silently pass. The old behavior can be obtained by setting `error_if_nonfinite=False`
Fixes https://github.com/pytorch/pytorch/issues/46849
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53843
Reviewed By: malfet
Differential Revision: D27291838
Pulled By: jbschlosser
fbshipit-source-id: 216d191b26e1b5919a44a3af5cde6f35baf825c4
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45667
First part of #3867 (Pooling operators still to do)
This adds a `padding='same'` mode to the interface of `conv{n}d`and `nn.Conv{n}d`. This should match the behaviour of `tensorflow`. I couldn't find it explicitly documented but through experimentation I found `tensorflow` returns the shape `ceil(len/stride)` and always adds any extra asymmetric padding onto the right side of the input.
Since the `native_functions.yaml` schema doesn't seem to support strings or enums, I've moved the function interface into python and it now dispatches between the numerically padded `conv{n}d` and the `_conv{n}d_same` variant. Underscores because I couldn't see any way to avoid exporting a function into the `torch` namespace.
A note on asymmetric padding. The total padding required can be odd if both the kernel-length is even and the dilation is odd. mkldnn has native support for asymmetric padding, so there is no overhead there, but for other backends I resort to padding the input tensor by 1 on the right hand side to make the remaining padding symmetrical. In these cases, I use `TORCH_WARN_ONCE` to notify the user of the performance implications.
Test Plan: Imported from OSS
Reviewed By: ejguan
Differential Revision: D27170744
Pulled By: jbschlosser
fbshipit-source-id: b3d8a0380e0787ae781f2e5d8ee365a7bfd49f22
Summary:
Fixes https://github.com/pytorch/pytorch/issues/50577
Learning rate schedulers had not yet been implemented for the C++ API.
This pull request introduces the learning rate scheduler base class and the StepLR subclass. Furthermore, it modifies the existing OptimizerOptions such that the learning rate scheduler can modify the learning rate.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/52268
Reviewed By: mrshenli
Differential Revision: D26818387
Pulled By: glaringlee
fbshipit-source-id: 2b28024a8ea7081947c77374d6d643fdaa7174c1
Summary:
Context: https://github.com/pytorch/pytorch/pull/53299#discussion_r587882857
These are the only hand-written parts of this diff:
- the addition to `.github/workflows/lint.yml`
- the file endings changed in these four files (to appease FB-internal land-blocking lints):
- `GLOSSARY.md`
- `aten/src/ATen/core/op_registration/README.md`
- `scripts/README.md`
- `torch/csrc/jit/codegen/fuser/README.md`
The rest was generated by running this command (on macOS):
```
git grep -I -l ' $' -- . ':(exclude)**/contrib/**' ':(exclude)third_party' | xargs gsed -i 's/ *$//'
```
I looked over the auto-generated changes and didn't see anything that looked problematic.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53406
Test Plan:
This run (after adding the lint but before removing existing trailing spaces) failed:
- https://github.com/pytorch/pytorch/runs/2043032377
This run (on the tip of this PR) succeeded:
- https://github.com/pytorch/pytorch/runs/2043296348
Reviewed By: walterddr, seemethere
Differential Revision: D26856620
Pulled By: samestep
fbshipit-source-id: 3f0de7f7c2e4b0f1c089eac9b5085a58dd7e0d97
Summary:
Fixes https://github.com/pytorch/pytorch/issues/39784
At the time the issue was filed, there was only issue (1) below.
There are actually now two issues here:
1. We always set all inputs passed in through `inputs` arg as `needed = True` in exec_info. So if we pass in an input that has a grad_fn that is not materialized, we create an entry of exec_info with nullptr as key with `needed = True`. Coincidentally, when we perform simple arithmetic operations, such as "2 * x", one of the next edges of mul is an invalid edge, meaning that its grad_fn is also nullptr. This causes the discovery algorithm to set all grad_fns that have a path to this invalid_edge as `needed = True`.
2. Before the commit that enabled the engine skipped the dummy node, we knew that root node is always needed, i.e., we hardcode `exec_info[&graph_root]=true`. The issue was that this logic wasn't updated after the code was updated to skip the graph root.
To address (1), instead of passing in an invalid edge if an input in `inputs` has no grad_fn, we create a dummy grad_fn. This is done in both python and cpp entry points. The alternative is to add logic for both backward() and grad() cases to check whether the grad_fn is nullptr and set needed=false in that case (the .grad() case would be slightly more complicated than the .backward() case here).
For (2), we perform one final iteration of the discovery algorithm so that we really know whether we need to execute the graph root.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51940
Reviewed By: VitalyFedyunin
Differential Revision: D26369529
Pulled By: soulitzer
fbshipit-source-id: 14a01ae7988a8de621b967a31564ce1d7a00084e
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50321
Quantization team reported that when there are two empty tensors are replicated among ranks, the two empty tensors start to share storage after resizing.
The root cause is unflatten_dense_tensor unflattened the empty tensor as view of flat tensor and thus share storage with other tensors.
This PR is trying to avoid unflatten the empty tensor as view of flat tensor so that empty tensor will not share storage with other tensors.
Test Plan: unit test
Reviewed By: pritamdamania87
Differential Revision: D25859503
fbshipit-source-id: 5b760b31af6ed2b66bb22954cba8d1514f389cca
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49348
This is a redux of #45666 post refactor, based off of
d534f7d4c5
Credit goes to peterbell10 for the implementation.
Fixes#43945.
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Test Plan: Imported from OSS
Reviewed By: smessmer
Differential Revision: D25594004
Pulled By: ezyang
fbshipit-source-id: c8eb876bb3348308d6dc8ba7bf091a2a3389450f
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49138
See for details: https://fb.quip.com/QRtJAin66lPN
We need to model optional types explicitly, mostly for schema inference. So we cannot pass a `Tensor?[]` as `ArrayRef<Tensor>`, instead we need to pass it as an optional type. This PR changes it to `torch::List<c10::optional<Tensor>>`. It also makes the ops c10-full that were blocked by this.
## Backwards Compatibility
- This should not break the Python API because the representation in Python is the same and python_arg_parser just transforms the python list into a `List<optional<Tensor>>` instead of into a `List<Tensor>`.
- This should not break serialized models because there's some logic that allows loading a serialized `List<Tensor>` as `List<optional<Tensor>>`, see https://github.com/pytorch/pytorch/pull/49138/files#diff-9315f5dd045f47114c677174dcaa2f982721233eee1aa19068a42ff3ef775315R57
- This will break backwards compatibility for the C++ API. There is no implicit conversion from `ArrayRef<Tensor>` (which was the old argument type) to `List<optional<Tensor>>`. One common call pattern is `tensor.index({indices_tensor})`, where indices_tensor is another `Tensor`, and that will continue working because the `{}` initializer_list constructor for `List<optional<Tensor>>` can take `Tensor` elements that are implicitly converted to `optional<Tensor>`, but another common call pattern was `tensor.index(indices_tensor)`, where previously, the `Tensor` got implicitly converted to an `ArrayRef<Tensor>`, and to implicitly convert `Tensor -> optional<Tensor> -> List<optional<Tensor>>` would be two implicit conversions. C++ doesn't allow chaining. two implicit conversions. So those call sites have to be rewritten to `tensor.index({indices_tensor})`.
ghstack-source-id: 119269131
Test Plan:
## Benchmarks (C++ instruction counts):
### Forward
#### Script
```py
from torch.utils.benchmark import Timer
counts = Timer(
stmt="""
auto t = {{op call to measure}};
""",
setup="""
using namespace torch::indexing;
auto x = torch::ones({4, 4, 4});
""",
language="cpp",
).collect_callgrind(number=1_000)
print(counts)
```
#### Results
| Op call |before |after |delta | |
|------------------------------------------------------------------------|---------|--------|-------|------|
|x[0] = 1 |11566015 |11566015|0 |0.00% |
|x.index({0}) |6807019 |6801019 |-6000 |-0.09%|
|x.index({0, 0}) |13529019 |13557019|28000 |0.21% |
|x.index({0, 0, 0}) |10677004 |10692004|15000 |0.14% |
|x.index({"..."}) |5512015 |5506015 |-6000 |-0.11%|
|x.index({Slice(None, None, None)}) |6866016 |6936016 |70000 |1.02% |
|x.index({None}) |8554015 |8548015 |-6000 |-0.07%|
|x.index({false}) |22400000 |22744000|344000 |1.54% |
|x.index({true}) |27624088 |27264393|-359695|-1.30%|
|x.index({"...", 0, true, Slice(1, None, 2), torch::tensor({1, 2})})|123472000|123463306|-8694|-0.01%|
### Autograd
#### Script
```py
from torch.utils.benchmark import Timer
counts = Timer(
stmt="""
auto t = {{op call to measure}};
""",
setup="""
using namespace torch::indexing;
auto x = torch::ones({4, 4, 4}, torch::requires_grad());
""",
language="cpp",
).collect_callgrind(number=1_000)
print(counts)
```
Note: the script measures the **forward** path of an op call with autograd enabled (i.e. calls into VariableType). It does not measure the backward path.
#### Results
| Op call |before |after |delta | |
|------------------------------------------------------------------------|---------|--------|-------|------|
|x.index({0}) |14839019|14833019|-6000| 0.00% |
|x.index({0, 0}) |28342019|28370019|28000| 0.00% |
|x.index({0, 0, 0}) |24434004|24449004|15000| 0.00% |
|x.index({"..."}) |12773015|12767015|-6000| 0.00% |
|x.index({Slice(None, None, None)}) |14837016|14907016|70000| 0.47% |
|x.index({None}) |15926015|15920015|-6000| 0.00% |
|x.index({false}) |36958000|37477000|519000| 1.40% |
|x.index({true}) |41971408|42426094|454686| 1.08% |
|x.index({"...", 0, true, Slice(1, None, 2), torch::tensor({1, 2})}) |168184392|164545682|-3638710| -2.16% |
Reviewed By: bhosmer
Differential Revision: D25454632
fbshipit-source-id: 28ab0cffbbdbdff1c40b4130ca62ee72f981b76d
Summary:
Clear static variable at the end of the test to ensure test passes after re-runs
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49581
Test Plan:
`./bin/test_api "--gtest_filter=CustomAutogradTest.ReentrantPriority" --gtest_repeat=50`
Before the change all subsequent runs of the test failed with
```
../test/cpp/api/autograd.cpp:681: Failure
Expected equality of these values:
order.size()
Which is: 310
10
```
Reviewed By: mrshenli
Differential Revision: D25632374
Pulled By: malfet
fbshipit-source-id: 4814d22b5dff15e1b38a0187e51070771fd58370
Summary:
Fixes https://github.com/pytorch/pytorch/issues/46213
I didn't yet update the documentation, will add those change soon. A few other things that I didn't do, but want to clarify if I maybe should.
1. I didn't expose projections in c++ API: torch/csrc/api/src/nn/modules/rnn.cpp. Let me know if this is desirable and I will add those changes.
2. I didn't expose projections in "lstm_cell" function and "_thnn_differentiable_lstm_cell_backward" functions from aten/src/ATen/native/RNN.cpp. As far as I understand, they are not needed for nn.LSTM CPU execution. For lstm_cell, projections don't bring any real benefit, since if cell is used separately, it can be easily added in Python. For "_thnn_differentiable_lstm_cell_backward", I'm actually not sure where exactly that function is used, so I also disabled projections there for now. Please let me know if I should change that.
3. I added check that projections are not supported for quantized LSTMs to quantized_lstm_<data/input> functions. But I didn't add any checks to LSTMCell code. It seems that since I disabled projections in "lstm_cell" function, they should also not be available for quantized models through any other API than quantized_lstm_<data/input>. Please let me know if I'm not correct and I will add checks to other places.
4. Projections are not supported for CuDNN versions < 7.1.2. Should I add the check for CuDNN version and disable projections in that case? If so, what will be the best way to do that?
5. Currently I added projection weight as the last weight, so the layout is "w_ih, w_hh, b_ih, b_hh, w_hr". This breaks the assumption that biases come after weights and thus I had to add additional if-s in various places. Alternative way would be to have "w_ih, w_hh, w_hr, b_ih, b_hh" layout, in which case the assumption will be true. But in that case I will need to split the loop in get_parameters function from aten/src/ATen/native/cudnn/RNN.cpp. And in some cases, I will still need to add an "undefined" tensor in the 3rd position, because we get all 5 weights from CuDNN most of the time. So I'm not sure which way is better. Let me know if you think I should change to the weights-then-biases layout.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47725
Reviewed By: zou3519
Differential Revision: D25449794
Pulled By: ngimel
fbshipit-source-id: fe6ce59e481d1f5fd861a8ff7fa13d1affcedb0c
Summary:
Ref https://github.com/pytorch/pytorch/issues/42175
This removes the 4 deprecated spectral functions: `torch.{fft,rfft,ifft,irfft}`. `torch.fft` is also now imported by by default.
The actual `at::native` functions are still used in `torch.stft` so can't be full removed yet. But will once https://github.com/pytorch/pytorch/issues/47601 has been merged.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48594
Reviewed By: heitorschueroff
Differential Revision: D25298929
Pulled By: mruberry
fbshipit-source-id: e36737fe8192fcd16f7e6310f8b49de478e63bf0
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47023
DeviceType pretty clearly only needs 1 byte. DeviceIndex only needs 1 byte given that machines don't have anywhere near 255 GPUs in them as far as I know.
ghstack-source-id: 116901430
Test Plan: Existing tests, added assertion to catch if my assumption about DeviceIndex is incorrect
Reviewed By: dzhulgakov
Differential Revision: D24605460
fbshipit-source-id: 7c9a89027fcf8eebd623b7cdbf6302162c981cd2
Summary:
`std::vector<bool>` can not return values by reference, since they are stored as bit fields
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47279
Reviewed By: glaringlee
Differential Revision: D24705188
Pulled By: malfet
fbshipit-source-id: 96e71cc4b9881f92af3b4a508d397deab6d68174
Summary:
This is a followup to the C++ anomaly detection mode, implementing the guard.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47164
Reviewed By: mruberry
Differential Revision: D24682574
Pulled By: albanD
fbshipit-source-id: b2224a56bf6eca0b90b8e10ec049cbcd5af9d108
Summary:
Fixes https://github.com/pytorch/pytorch/issues/46373
As noted in https://github.com/pytorch/pytorch/issues/46373, there needs to be a flag passed into the engine that indicates whether it was executed through the backward api or grad api. Tentatively named the flag `accumulate_grad` since functionally, backward api accumulates grad into .grad while grad api captures the grad and returns it.
Moving changes not necessary to the python api (cpp, torchscript) to a new PR.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46855
Reviewed By: ngimel
Differential Revision: D24649054
Pulled By: soulitzer
fbshipit-source-id: 6925d5a67d583eeb781fc7cfaec807c410e1fc65
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45377
This PR adds a C++ implementation of the TripletMarginWithDistanceLoss, for which the Python implementation was introduced in PR #43680. It's based on PR #44072, but I'm resubmitting this to unlink it from Phabricator.
Test Plan: Imported from OSS
Reviewed By: izdeby
Differential Revision: D24003973
fbshipit-source-id: 2d9ada7260a6f27425ff2fdbbf623dad0fb79405
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44433
Not entirely sure why, but changing the type of beta from `float` to `double in autocast_mode.cpp and FunctionsManual.h fixes my compiler errors, failing instead at link time
fixing some type errors, updated fn signature in a few more files
removing my usage of Scalar, making beta a double everywhere instead
Test Plan: Imported from OSS
Reviewed By: mrshenli
Differential Revision: D23636720
Pulled By: bdhirsh
fbshipit-source-id: caea2a1f8dd72b3b5fd1d72dd886b2fcd690af6d
Summary:
Fixes https://github.com/pytorch/pytorch/issues/43732.
Requires importing the fft namespace in the C++ API, just like the Python API does, to avoid clobbering torch::fft the function.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43749
Reviewed By: glaringlee
Differential Revision: D23391544
Pulled By: mruberry
fbshipit-source-id: d477d0b6d9a689d5c154ad6c31213a7d96fdf271
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43341
This is to remove the empty pretty_print() since it overrides the impl within Module base which is not as designed here.
Test Plan: Imported from OSS
Reviewed By: pbelevich
Differential Revision: D23244616
Pulled By: glaringlee
fbshipit-source-id: 94b8dfd3697dfc450f53b3b4eee6e9c13cafba7b
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43069
The transformer c++ impl need to put TransformerEncoderLayer/DecoderLayer and TransformerEncoder/TransformerDecoder in different header since TransformerEncoder/Decoder's options class need TransformerEncoderLayer/DecoderLayer as input parameter. Split header files to avoid cycle includsion.
Test Plan: Imported from OSS
Reviewed By: yf225
Differential Revision: D23139437
Pulled By: glaringlee
fbshipit-source-id: 3c752ed7702ba18a9742e4d47d049e62d2813de0
Summary:
Added a new option in AutogradContext to tell autograd to not materialize output grad tensors, that is, don't expand undefined/None tensors into tensors full of zeros before passing them as input to the backward function.
This PR is the second part that closes https://github.com/pytorch/pytorch/issues/41359. The first PR is https://github.com/pytorch/pytorch/pull/41490.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41821
Reviewed By: albanD
Differential Revision: D22693163
Pulled By: heitorschueroff
fbshipit-source-id: a8d060405a17ab1280a8506a06a2bbd85cb86461
Summary:
This PR creates a new namespace, torch.fft (torch::fft) and puts a single function, fft, in it. This function is analogous to is a simplified version of NumPy's [numpy.fft.fft](https://numpy.org/doc/1.18/reference/generated/numpy.fft.fft.html?highlight=fft#numpy.fft.fft) that accepts no optional arguments. It is intended to demonstrate how to add and document functions in the namespace, and is not intended to deprecate the existing torch.fft function.
Adding this namespace was complicated by the existence of the torch.fft function in Python. Creating a torch.fft Python module makes this name ambiguous: does it refer to a function or module? If the JIT didn't exist, a solution to this problem would have been to make torch.fft refer to a callable class that mimicked both the function and module. The JIT, however, cannot understand this pattern. As a workaround it's required to explicitly `import torch.fft` to access the torch.fft.fft function in Python:
```
import torch.fft
t = torch.randn(128, dtype=torch.cdouble)
torch.fft.fft(t)
```
See https://github.com/pytorch/pytorch/issues/42175 for future work. Another possible future PR is to get the JIT to understand torch.fft as a callable class so it need not be imported explicitly to be used.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41911
Reviewed By: glaringlee
Differential Revision: D22941894
Pulled By: mruberry
fbshipit-source-id: c8e0b44cbe90d21e998ca3832cf3a533f28dbe8d
Summary:
For CUDA >= 10.2, the `CUBLAS_WORKSPACE_CONFIG` environment variable must be set to either `:4096:8` or `:16:8` to ensure deterministic CUDA stream usage. This PR adds some logic inside `torch.set_deterministic()` to raise an error if this environment variable is not set properly and CUDA >= 10.2.
Issue https://github.com/pytorch/pytorch/issues/15359
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41377
Reviewed By: malfet
Differential Revision: D22758459
Pulled By: ezyang
fbshipit-source-id: 4b96f1e9abf85d94ba79140fd927bbd0c05c4522
Summary: function `cross_kernel_scalar` is not covered in `Aten/native/cpu/CrossKernel.cpp`, add tests to cover it
Test Plan:
1. Test locally to check new lines are covered
2. CI
https://pxl.cl/1fZjG
Reviewed By: malfet
Differential Revision: D22834122
fbshipit-source-id: 0d50f3a3e6aee52cb6fdee2b9f5883f542c7b6e2
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42266
function `lerp_kernel_scalar` and `lerp_kernel_tensor` are not covered in `Aten/native/cpu/LerpKernel.cpp`, add tests to cover them
Test Plan:
1. Test locally to check new lines are covered
2. CI
https://pxl.cl/1fXPd
Reviewed By: malfet
Differential Revision: D22832164
fbshipit-source-id: b1eaabbf8bfa08b4dedc1a468abfdfb619a50e3c
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42037
This is to fix#41951
Test Plan: Imported from OSS
Reviewed By: yf225
Differential Revision: D22764717
Pulled By: glaringlee
fbshipit-source-id: e6da0aeb05a2356f52446e6d5fad391f2cd1cf6f
Summary:
Leave undefined tensors / None returned from custom backward functions as undefined/None instead of creating a tensor full of zeros. This change improves performance in some cases.
**This is BC-Breaking:** Custom backward functions that return None will now see it potentially being propagated all the way up to AccumulateGrad nodes. Potential impact is that .grad field of leaf tensors as well as the result of autograd.grad may be undefined/None where it used to be a tensor full of zeros. Also, autograd.grad may raise an error, if so, consider using allow_unused=True ([see doc](https://pytorch.org/docs/stable/autograd.html?highlight=autograd%20grad#torch.autograd.grad)) if it applies to your case.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41490
Reviewed By: albanD
Differential Revision: D22578241
Pulled By: heitorschueroff
fbshipit-source-id: f4966f4cb520069294f8c5c1691eeea799cc0abe
