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Removed overhead from reshape() call if tensor doesn't need to be changed (#61466)

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Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61466

## Goal

Per #55126 the performance of `reshape` is worse than `alias` in cases where they are performing the same operation (i.e. where reshape is returning a view) because `reshape` delegates to `view` and duplicates some of the operations (specifically `infer_size_dv` and `computeStride`).

The goal of this pull-request is to reduce or remove the additional overhead that `reshape` has.

### Proposed Implementation

Instead of using `view` we implement a private/internal operator (`_reshape_alias`) that `reshape` dispatches to which skips the relevant checks. This is functionally equivalent to `as_strided` however it is a lot simpler because it's specialized to this use-case, and importantly the `backward` implementation is a lot faster.

Note that we have to dispatch (`reshape` is a composite operator) because `reshape` can return either a view or a copy of the Tensor depending on the parameters, and this complicates implementing a derivative/backward for `reshape`.

### Why not `as_strided`?

Using `as_strided` directly slows down autograd. If we use a custom function equivalent to `_reshape_alias` but with a simpler backward function then `view` has the same performance as `reshape`. If we delegate to `as_strided` it is about 56% slower (and this holds against our custom function).

This is also the reason we make an internal operator named `_reshape_alias` instead of exposing a new operator since this should only be used in the `reshape` case and it is effectively a more limited version of `view`, `alias`, and `as_strided`.

## Benchmarks
In a micro-benchmark for `backward` running:

```cpp
// Setup
at::Tensor x=torch::empty({2,2}, torch::requires_grad(true));

// Benchmark loop
// `reshape(-1)` replaced with a call to view(-1) for view baseline
x.pow(4).reshape(-1).mean().backward();
```

I also benchmarked simple operations without gradients using:

```cpp
// Setup
at::Tensor x=torch::empty({2,2}, torch::requires_grad(true));

// Benchmark loop
x.reshape(-1) // replaced with a call to view(-1) for view baseline
```

Baselined to `view`:

* Original `reshape`: `+3.3%` (without gradients `+20.8%`)
* Using `as_strided`: `+55.1%` (without gradients `+1.0%`)
* Using custom `_reshape_view`: `-1.0%` (without gradients `+6.2%`)

In absolute terms (note the percentages above were generated comparing between runs/tests rather than to a single baseline):

* Original `view`: `53.66 us` (without gradients `582.78 ns`)
* Original `reshape`: `55.46 us` (without gradients `704.24 ns`)
* Using `as_strided`: `83.24 us` (without gradients `576.49 ns`)
* Using custom `_reshape_view`: `53.13 us` (without gradients `536.01 ns`)

Note that these benchmarks perform a backwards operation as well. When compared without using gradient computation at all the performance differneces are more pronounced as this takes up more of the time.

### Original performance

<details>
  <summary>Benchmark results</summary>

```
[<torch.utils.benchmark.utils.common.Measurement object at 0x7f0e4d393160>
x.pow(4).view(-1).mean().backward();
setup: at::Tensor x=torch::empty({2,2}, torch::requires_grad(true));
  Median: 53.66 us
  IQR:    2.70 us (52.54 to 55.24)
  884 measurements, 100 runs per measurement, 1 thread]

[<torch.utils.benchmark.utils.common.Measurement object at 0x7f0e2ebd4fa0>
x.pow(4).reshape(-1).mean().backward();
setup: at::Tensor x=torch::empty({2,2}, torch::requires_grad(true));
  Median: 55.46 us
  IQR:    2.61 us (54.39 to 57.01)
  889 measurements, 100 runs per measurement, 1 thread]

2276116
2286256

<torch.utils.benchmark.utils.valgrind_wrapper.timer_interface.FunctionCounts object at 0x7f0e5b2e3e20>
   2640  ???:at::detail::computeStride(c10::ArrayRef<long>, c10::ArrayRef<long>, c10::SmallVector<long, 5u> const&)
   1920  ???:at::native::reshape(at::Tensor const&, c10::ArrayRef<long>)
   1520  ???:at::_ops::reshape::call(at::Tensor const&, c10::ArrayRef<long>)
   1040  ???:c10::SmallVectorImpl<long>::operator=(c10::SmallVectorImpl<long>&&)
    980  ???:void at::infer_size_impl<c10::SmallVector<long, 5u> >(c10::ArrayRef<long>, long, c10::SmallVector<long, 5u>&)
    720  ???:__tls_get_addr
    520  ???:at::shouldRunRecordFunction(bool*)
    520  ???:__memcpy_avx_unaligned_erms
    200  ???:c10::impl::wrap_kernel_functor_unboxed_<c10::impl::detail::WrapFunctionIntoFunctor_<c10:: ... g>)>::call(c10::OperatorKernel*, c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)
    100  ???:c10::TensorImpl::strides() const
    100  ???:c10::TensorImpl::sizes() const
    100  ???:at::(anonymous namespace)::manager()
     77  /tmp/benchmark_utils_jit_build__1626465284__8a34e7ff-cd37-4a82-be28-7f19e081e771/timer_cpp_7815557938202456331/timer_src.cpp:main
     40  ???:c10::TensorImpl::numel() const
    -77  /tmp/benchmark_utils_jit_build__1626465284__8a34e7ff-cd37-4a82-be28-7f19e081e771/timer_cpp_8055217880649990171/timer_src.cpp:main
   -260  ???:at::native::view(at::Tensor const&, c10::ArrayRef<long>)

Total: 10140
```

```
[<torch.utils.benchmark.utils.common.Measurement object at 0x7f850dd66c10>
x.view(-1);
setup: at::Tensor x=torch::empty({2,2});
  Median: 582.78 ns
  IQR:    33.80 ns (573.80 to 607.61)
  833 measurements, 10000 runs per measurement, 1 thread]

[<torch.utils.benchmark.utils.common.Measurement object at 0x7f850de31e20>
x.reshape(-1);
setup: at::Tensor x=torch::empty({2,2});
  Median: 704.24 ns
  IQR:    24.42 ns (697.20 to 721.62)
  679 measurements, 10000 runs per measurement, 1 thread]

56896
67036

<torch.utils.benchmark.utils.valgrind_wrapper.timer_interface.FunctionCounts object at 0x7f84e1930bb0>
   2640  ???:at::detail::computeStride(c10::ArrayRef<long>, c10::ArrayRef<long>, c10::SmallVector<long, 5u> const&)
   1920  ???:at::native::reshape(at::Tensor const&, c10::ArrayRef<long>)
   1520  ???:at::_ops::reshape::call(at::Tensor const&, c10::ArrayRef<long>)
   1040  ???:c10::SmallVectorImpl<long>::operator=(c10::SmallVectorImpl<long>&&)
    980  ???:void at::infer_size_impl<c10::SmallVector<long, 5u> >(c10::ArrayRef<long>, long, c10::SmallVector<long, 5u>&)
    720  ???:__tls_get_addr
    520  ???:at::shouldRunRecordFunction(bool*)
    520  ???:__memcpy_avx_unaligned_erms
    200  ???:c10::impl::wrap_kernel_functor_unboxed_<c10::impl::detail::WrapFunctionIntoFunctor_<c10:: ... g>)>::call(c10::OperatorKernel*, c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)
    100  ???:c10::TensorImpl::strides() const
    100  ???:c10::TensorImpl::sizes() const
    100  ???:at::(anonymous namespace)::manager()
     76  /tmp/benchmark_utils_jit_build__1626466038__15fbbac0-2072-4459-8f8e-08121a905b99/timer_cpp_547407365342278353/timer_src.cpp:main
     40  ???:c10::TensorImpl::numel() const
    -76  /tmp/benchmark_utils_jit_build__1626466038__15fbbac0-2072-4459-8f8e-08121a905b99/timer_cpp_3457873755756181226/timer_src.cpp:main
   -260  ???:at::native::view(at::Tensor const&, c10::ArrayRef<long>)

Total: 10140
```

</details>

### Using `as_strided`

<details>
  <summary>Benchmark results</summary>

```
[<torch.utils.benchmark.utils.common.Measurement object at 0x7f8b13bb5b50>
x.pow(4).view(-1).mean().backward();
setup: at::Tensor x=torch::empty({2,2}, torch::requires_grad(true));
  Median: 53.37 us
  IQR:    3.15 us (51.73 to 54.88)
  936 measurements, 100 runs per measurement, 1 thread]

[<torch.utils.benchmark.utils.common.Measurement object at 0x7f8af55f8490>
x.pow(4).reshape(-1).mean().backward();
setup: at::Tensor x=torch::empty({2,2}, torch::requires_grad(true));
  Median: 83.24 us
  IQR:    4.05 us (81.20 to 85.25)
  609 measurements, 100 runs per measurement, 1 thread]

2267916
2525061

<torch.utils.benchmark.utils.valgrind_wrapper.timer_interface.FunctionCounts object at 0x7f8af55f8e50>
   31930  ???:_int_free
   15940  ???:malloc
   11595  ???:_int_malloc
   10100  ???:torch::autograd::generated::details::as_strided_backward(at::Tensor, at::TensorGeometry, c10::ArrayRef<long>, c10::ArrayRef<long>, c10::optional<long>)
    9360  ???:__tls_get_addr
    8280  ???:free
    8100  ???:torch::autograd::VariableType::(anonymous namespace)::as_strided(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>, c10::optional<long>)
    4520  ???:c10::intrusive_ptr<c10::TensorImpl, c10::UndefinedTensorImpl>::reset_()
    4080  ???:operator new(unsigned long)
     ...
    -780  ???:at::_ops::view::redispatch(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)
    -920  ???:c10::SmallVectorImpl<long>::operator=(c10::SmallVectorImpl<long> const&)
   -1220  ???:torch::autograd::generated::ViewBackward::apply(std::vector<at::Tensor, std::allocator<at::Tensor> >&&)
   -1520  ???:at::_ops::view::call(at::Tensor const&, c10::ArrayRef<long>)
   -1580  ???:torch::ADInplaceOrView::(anonymous namespace)::view(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)
   -1680  ???:at::Tensor at::native::alias_with_sizes_and_strides<c10::SmallVector<long, 5u> >(at::Tensor const&, c10::SmallVector<long, 5u> const&, c10::SmallVector<long, 5u> const&)
   -2560  ???:at::detail::computeStride(c10::ArrayRef<long>, c10::ArrayRef<long>, c10::SmallVector<long, 5u> const&)
   -2640  ???:at::native::view(at::Tensor const&, c10::ArrayRef<long>)
   -4860  ???:torch::autograd::VariableType::(anonymous namespace)::view(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)

Total: 257145
```

```

[<torch.utils.benchmark.utils.common.Measurement object at 0x7f93176a0160>
x.view(-1);
setup: at::Tensor x=torch::empty({2,2});
  Median: 570.55 ns
  IQR:    32.69 ns (552.87 to 585.56)
  874 measurements, 10000 runs per measurement, 1 thread]

[<torch.utils.benchmark.utils.common.Measurement object at 0x7f92f8f29490>
x.reshape(-1);
setup: at::Tensor x=torch::empty({2,2});
  Median: 576.49 ns
  IQR:    37.95 ns (559.51 to 597.46)
  861 measurements, 10000 runs per measurement, 1 thread]

56896
58556

<torch.utils.benchmark.utils.valgrind_wrapper.timer_interface.FunctionCounts object at 0x7f932556ca60>
    2140  ???:at::native::reshape(at::Tensor const&, c10::ArrayRef<long>)
    1940  ???:torch::autograd::VariableType::(anonymous namespace)::as_strided(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>, c10::optional<long>)
    1880  ???:torch::ADInplaceOrView::(anonymous namespace)::as_strided(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>, c10::optional<long>)
    1720  ???:at::_ops::as_strided::call(at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>, c10::optional<long>)
    1520  ???:at::_ops::reshape::call(at::Tensor const&, c10::ArrayRef<long>)
    1400  ???:at::native::as_strided_tensorimpl(at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>, c10::optional<long>)
    1260  ???:at::_ops::as_strided::redispatch(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>, c10::optional<long>)'2
    1260  ???:at::_ops::as_strided::redispatch(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>, c10::optional<long>)
     980  ???:void at::infer_size_impl<c10::SmallVector<long, 5u> >(c10::ArrayRef<long>, long, c10::SmallVector<long, 5u>&)
     ...
    -620  ???:at::Tensor c10::Dispatcher::redispatch<at::Tensor, at::Tensor const&, c10::ArrayRef<long ... ::ArrayRef<long>)> const&, c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>) const
    -780  ???:at::_ops::view::redispatch(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)'2
    -780  ???:at::_ops::view::redispatch(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)
    -920  ???:c10::SmallVectorImpl<long>::operator=(c10::SmallVectorImpl<long> const&)
   -1520  ???:at::_ops::view::call(at::Tensor const&, c10::ArrayRef<long>)
   -1580  ???:torch::ADInplaceOrView::(anonymous namespace)::view(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)
   -1680  ???:at::Tensor at::native::alias_with_sizes_and_strides<c10::SmallVector<long, 5u> >(at::Tensor const&, c10::SmallVector<long, 5u> const&, c10::SmallVector<long, 5u> const&)
   -1740  ???:torch::autograd::VariableType::(anonymous namespace)::view(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)
   -2640  ???:at::native::view(at::Tensor const&, c10::ArrayRef<long>)

Total: 1660

```

</details>

### Using custom function (`_reshape_alias`)

<details>
  <summary>Benchmark results</summary>

```
[<torch.utils.benchmark.utils.common.Measurement object at 0x7f16861d6b50>
x.pow(4).view(-1).mean().backward();
setup: at::Tensor x=torch::empty({2,2}, torch::requires_grad(true));
  Median: 53.50 us
  IQR:    2.64 us (52.32 to 54.96)
  906 measurements, 100 runs per measurement, 1 thread]

[<torch.utils.benchmark.utils.common.Measurement object at 0x7f1667b2ed60>
x.pow(4).reshape(-1).mean().backward();
setup: at::Tensor x=torch::empty({2,2}, torch::requires_grad(true));
  Median: 53.13 us
  IQR:    3.40 us (51.72 to 55.13)
  914 measurements, 100 runs per measurement, 1 thread]

2269736
2273236

<torch.utils.benchmark.utils.valgrind_wrapper.timer_interface.FunctionCounts object at 0x7f1693f8dc10>
    5060  ???:torch::autograd::VariableType::(anonymous namespace)::_reshape_alias(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>)
    2000  ???:at::native::reshape(at::Tensor const&, c10::ArrayRef<long>)
    1780  ???:torch::ADInplaceOrView::(anonymous namespace)::_reshape_alias(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>)
    1660  ???:at::_ops::_reshape_alias::call(at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>)
    1600  ???:at::Tensor at::native::alias_with_sizes_and_strides<c10::ArrayRef<long> >(at::Tensor const&, c10::ArrayRef<long> const&, c10::ArrayRef<long> const&)
    1520  ???:at::_ops::reshape::call(at::Tensor const&, c10::ArrayRef<long>)
    1240  ???:at::_ops::_reshape_alias::redispatch(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>)'2
    1240  ???:at::_ops::_reshape_alias::redispatch(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>)
    1220  ???:torch::autograd::generated::AliasToShapeBackward::apply(std::vector<at::Tensor, std::allocator<at::Tensor> >&&)
     ...
    -780  ???:at::_ops::view::redispatch(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)'2
    -780  ???:at::_ops::view::redispatch(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)
    -920  ???:c10::SmallVectorImpl<long>::operator=(c10::SmallVectorImpl<long> const&)
   -1220  ???:torch::autograd::generated::ViewBackward::apply(std::vector<at::Tensor, std::allocator<at::Tensor> >&&)
   -1520  ???:at::_ops::view::call(at::Tensor const&, c10::ArrayRef<long>)
   -1580  ???:torch::ADInplaceOrView::(anonymous namespace)::view(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)
   -1680  ???:at::Tensor at::native::alias_with_sizes_and_strides<c10::SmallVector<long, 5u> >(at::Tensor const&, c10::SmallVector<long, 5u> const&, c10::SmallVector<long, 5u> const&)
   -2640  ???:at::native::view(at::Tensor const&, c10::ArrayRef<long>)
   -4860  ???:torch::autograd::VariableType::(anonymous namespace)::view(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)

Total: 3500
```

```

[<torch.utils.benchmark.utils.common.Measurement object at 0x7f5287adfb20>
x.view(-1);
setup: at::Tensor x=torch::empty({2,2});
  Median: 505.10 ns
  IQR:    20.04 ns (500.41 to 520.45)
  944 measurements, 10000 runs per measurement, 1 thread]

[<torch.utils.benchmark.utils.common.Measurement object at 0x7f526951b430>
x.reshape(-1);
setup: at::Tensor x=torch::empty({2,2});
  Median: 536.01 ns
  IQR:    17.81 ns (531.34 to 549.16)
  916 measurements, 10000 runs per measurement, 1 thread]

56896
60376

<torch.utils.benchmark.utils.valgrind_wrapper.timer_interface.FunctionCounts object at 0x7f5295896c10>
    2000  ???:at::native::reshape(at::Tensor const&, c10::ArrayRef<long>)
    1860  ???:torch::autograd::VariableType::(anonymous namespace)::_reshape_alias(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>)
    1780  ???:torch::ADInplaceOrView::(anonymous namespace)::_reshape_alias(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>)
    1660  ???:at::_ops::_reshape_alias::call(at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>)
    1600  ???:at::Tensor at::native::alias_with_sizes_and_strides<c10::ArrayRef<long> >(at::Tensor const&, c10::ArrayRef<long> const&, c10::ArrayRef<long> const&)
    1520  ???:at::_ops::reshape::call(at::Tensor const&, c10::ArrayRef<long>)
    1240  ???:at::_ops::_reshape_alias::redispatch(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>)'2
    1240  ???:at::_ops::_reshape_alias::redispatch(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>, c10::ArrayRef<long>)
     980  ???:void at::infer_size_impl<c10::SmallVector<long, 5u> >(c10::ArrayRef<long>, long, c10::SmallVector<long, 5u>&)
     ...
    -620  ???:at::Tensor c10::Dispatcher::redispatch<at::Tensor, at::Tensor const&, c10::ArrayRef<long ... ::ArrayRef<long>)> const&, c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>) const
    -780  ???:at::_ops::view::redispatch(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)'2
    -780  ???:at::_ops::view::redispatch(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)
    -920  ???:c10::SmallVectorImpl<long>::operator=(c10::SmallVectorImpl<long> const&)
   -1520  ???:at::_ops::view::call(at::Tensor const&, c10::ArrayRef<long>)
   -1580  ???:torch::ADInplaceOrView::(anonymous namespace)::view(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)
   -1680  ???:at::Tensor at::native::alias_with_sizes_and_strides<c10::SmallVector<long, 5u> >(at::Tensor const&, c10::SmallVector<long, 5u> const&, c10::SmallVector<long, 5u> const&)
   -1740  ???:torch::autograd::VariableType::(anonymous namespace)::view(c10::DispatchKeySet, at::Tensor const&, c10::ArrayRef<long>)
   -2640  ???:at::native::view(at::Tensor const&, c10::ArrayRef<long>)

Total: 3480

```

</details>

Test Plan: Imported from OSS

Reviewed By: ejguan

Differential Revision: D29792126

Pulled By: laurencer

fbshipit-source-id: f0519b45b65f868aa3e8651679354558bd761dfd
This commit is contained in:
Laurence Rouesnel 2021-07-21 14:04:03 -07:00 committed by Facebook GitHub Bot
parent a8d99a28d7
commit adb73d3dcf
8 changed files with 95 additions and 14 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

50
aten/src/ATen/native/TensorShape.cpp
View file

@ -1040,21 +1040,43 @@ Tensor reshape(const Tensor& self, IntArrayRef proposed_shape) {
return at::_mkldnn_reshape(self, shape);
}
auto stride =
at::detail::computeStride(self.sizes(), self.strides(), shape);
// `computeStride` returns the proper strides to use if this
// `reshape` can be just a view.
//
// NB: Even though we have viewable geometry and the target strides here,
// we do not just call `as_strided` on `self` because the backward
// for `as_strided` is not as efficient as that of `view` (since the
// former is meant to handle general cases).
// `computeStride` returns the proper strides to use if this
// `reshape` can be just a view.
auto stride = at::detail::computeStride(self.sizes(), self.strides(), shape);
// NB: Even though we have viewable geometry and the target strides here,
// we do not just call `as_strided` on `self` because the backward
// for `as_strided` is not as efficient as that of `view` (since the
// former is meant to handle general cases).
//
// Similarly we don't call `view` because it duplicates some of the work
// we've already done, and instead call our internal/private operator
// `_reshape_alias` that essentially does the same thing as `view` and
// `as_strided` without any of the extra overhead.
if (stride.has_value()) {
return self.view(shape);
// Temporary check to revert to the old behavior/view in cases where the
// device is not supported (e.g. for XLA the operation is not supported
// so we use `view` instead).
//
// We need to do the checks here instead of in `native_functions.yaml`
// to preserve backwards compatibility.
if (! self.is_xla()) {
return self._reshape_alias(shape, stride.value());
} else {
return self.view(shape);
}
}
return at::_unsafe_view(self.clone(at::MemoryFormat::Contiguous), shape);
}
Tensor _reshape_alias(const Tensor& self, IntArrayRef sizes, IntArrayRef strides) {
// This is only used by `reshape` in cases where it would otherwise have dispatched
// to `view`. This removes the overhead of calling `view` which duplicates some of
// the work that's already been done (`infer_size_dv` and `computeStride`).
return alias_with_sizes_and_strides(self, sizes, strides);
}
Tensor reshape_as(const Tensor& self, const Tensor& other) {
return self.reshape(other.sizes());
}
@ -2152,11 +2174,13 @@ Tensor numpy_T(const Tensor &self) {
return self.permute(transpose_dims);
}
Tensor view(const Tensor& self, IntArrayRef size) {
Tensor view(const Tensor& self,
IntArrayRef size) {
at::DimVector inferred_size = at::infer_size_dv(size, self.numel());
auto stride = at::detail::computeStride(self.sizes(),
self.strides(),
inferred_size);
self.strides(),
inferred_size);
TORCH_CHECK(stride.has_value(), "view size is "
"not compatible with input tensor's size and stride (at least one dimension"
" spans across two contiguous subspaces). Use .reshape(...) instead.");

11
aten/src/ATen/native/native_functions.yaml
View file

@ -3443,6 +3443,17 @@
device_check: NoCheck
device_guard: False
# NOTE [ _reshape_alias ] is meant to be used in the implementation of reshape.
# They are not user-facing, hence the leading underscore. Please don't use it
# anywhere else.
- func: _reshape_alias(Tensor(a) self, int[] size, int[] stride) -> Tensor(a)
variants: function, method
device_check: NoCheck
device_guard: False
dispatch:
CPU, CUDA, Meta, QuantizedCPU, QuantizedCUDA: _reshape_alias
# We don't need to support mkldnn since this is handled explicitly by the reshape operator.
- func: _mkldnn_reshape(Tensor self, int[] shape) -> Tensor
device_check: NoCheck
device_guard: False

25
test/cpp/api/tensor.cpp
View file

@ -1117,3 +1117,28 @@ TEST(TensorTest, StdDimension) {
ASSERT_EQ(torch::std(x, 0, /*unbiased=*/true).numel(), 3);
ASSERT_EQ(std::get<0>(torch::std_mean(x, 0, /*unbiased=*/true)).numel(), 3);
}
// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
TEST(TensorTest, ReshapeAlias) {
// Tests the behavior of the _reshape_alias private operator so
// that it matches the behavior of as_strided and view.
auto x = torch::randn({3, 3});
ASSERT_TRUE(torch::equal(
torch::_reshape_alias(x, {2, 2}, {1, 2}),
torch::as_strided(x, {2, 2}, {1, 2})
));
ASSERT_TRUE(torch::equal(
torch::_reshape_alias(x, {9}, {1}),
x.view({-1})
));
// Test that the backward works fine.
auto y = torch::randn({3, 3}, torch::requires_grad(true));
auto z = torch::clone(y).detach().requires_grad_(true);
(y * y).view({-1}).mean().backward();
torch::_reshape_alias((z * z), {9}, {1}).mean().backward();
ASSERT_TRUE(torch::equal(
y.grad(),
z.grad()
));
}

16
test/test_view_ops.py
View file

@ -1355,6 +1355,22 @@ class TestOldViewOps(TestCase):
self.assertEqual(tensor.view(6, 2, 1), contig_tensor.view(6, 2, 1))
self.assertEqual(tensor.view(1, 6, 2, 1), contig_tensor.view(1, 6, 2, 1))
@dtypes(*torch.testing.get_all_dtypes())
def test_reshape_view_semantics(self, device, dtype):
tensor = make_tensor((15, 4), device, dtype)
target = (20, 3)
# Cases where the tensor can be returned as a view.
view_tensor = tensor.reshape(target)
self.assertEqual((view_tensor.size()), target)
self.assertEqual(tensor.storage().data_ptr(), view_tensor.storage().data_ptr())
# Cases where the tensor must be copied (transpose makes it non-contiguous forcing
# the copy).
copy_tensor = tensor.transpose(0, 1).reshape(target)
self.assertEqual(copy_tensor.size(), target)
self.assertNotEqual(tensor.storage().data_ptr(), copy_tensor.storage().data_ptr())
def test_contiguous(self, device):
x = torch.randn(1, 16, 5, 5, device=device)
self.assertTrue(x.is_contiguous())

3
tools/autograd/derivatives.yaml
View file

@ -1144,6 +1144,9 @@
# making it impossible (hard) to detect when it is actually a view.
# - name: reshape(Tensor self, IntArrayRef shape)
- name: _reshape_alias(Tensor(a) self, int[] size, int[] stride) -> Tensor(a)
self: grad.reshape(self.sizes())
- name: round(Tensor self) -> Tensor
self: zeros_like(grad)

1
tools/autograd/gen_inplace_or_view_type.py
View file

@ -58,6 +58,7 @@ VIEW_FUNCTIONS = {
# discrete anyways.
# FIXME: clone indices on construction.
'sparse_coo_tensor_with_dims_and_tensors': 'values',
'_reshape_alias': 'self',
}
for key in VIEW_FUNCTIONS_WITH_METADATA_CHANGE:

1
tools/autograd/gen_python_functions.py
View file

@ -92,6 +92,7 @@ _SKIP_PYTHON_BINDINGS = [
'data', 'is_leaf', 'output_nr', '_version', 'requires_grad_', 'retains_grad', 'set_',
'_fw_primal', 'fake_quantize_per_tensor_affine_cachemask',
'fake_quantize_per_channel_affine_cachemask',
'_reshape_alias',
]
SKIP_PYTHON_BINDINGS = list(map(lambda pattern: re.compile(rf'^{pattern}$'), _SKIP_PYTHON_BINDINGS))

2
tools/autograd/gen_variable_type.py
View file

@ -101,7 +101,7 @@ GRADIENT_IMPLEMENTED_FOR_COMPLEX = {
'diag', 'masked_scatter', 'masked_select', 'index_fill', 'trace', 'polar', 'cumsum', 'rsub',
'eig', 'lerp', 'linalg_vector_norm', 'cumprod', 'prod', 'index_copy', 'lu', 'unfold', 'unfold_backward',
'index', 'masked_fill', 'cross', 'lu_unpack', 'renorm', '_conj_physical',
'scatter', 'scatter_add', 'sigmoid', 'sigmoid_backward', 'trapezoid', 'conj_physical_', '_neg_view'
'scatter', 'scatter_add', 'sigmoid', 'sigmoid_backward', 'trapezoid', 'conj_physical_', '_neg_view', '_reshape_alias',
}
GRADIENT_IMPLEMENTED_FOR_SPARSE_COMPLEX = {