Convolution derivatives in ATen (#4116)

* Convolution derivatives in ATen

This PR introduces ATen implementation of convolution, which dispatches to
THNN/CuDNN/nnpack based on input parameters. The general strategy is to compose
this function out of the various forward-backward pairs of specific
implementations, rather than write a monolithic function with backwards (which
is what we did before because the boilerplate of doing it otherwise would have
been very high.) The new API provides the following functions:

  - _convolution, which is a fully generic, native convolution implementation
    that dispatches to various other convolution implementations depending on
    input characteristics. This is prefixed with an underscore because it
    explicitly takes benchmark, deterministic and cudnn_enabled which are
    implementation details for CuDNN. The intent is to eventually provide a
    convolution that reads these parameters out of the context using #4104.
  - _convolution_nogroup is a convolution implementation for non-CuDNN
    algorithms which don't support group convolution natively.
  - _convolution_double_backward is the generic double-backwards implementation
    for convolution.

In more detail:

- Most functionality from torch/csrc/autograd/functions/convolution.cpp has been
  moved into aten/src/ATen/native/Convolution.cpp
- We continue to make use of ConvParams, but we now construct the parameters
  upon entry to a function from the function signature (which does not use
  ConvParams; having convolution take ConvParams directly would require teaching
  the code generator how to accept these as parameters, complicating ATen's API
  model) and destruct them when making subprocedure calls.
- I introduce a new idiom, input_r, which represents a const Tensor& reference,
  which will subsequently be assigned to a local Tensor input. This is helpful
  because a lot of the existing algorithms relied on being able to assign to
  locals, which is not permitted with a const reference.
- The native argument parser now supports std::array<bool,2> inputs (NB: there
  MUST NOT be a space; this is the same hack as is applied to derivatives.yaml)
- Native parser now supports Tensor? arguments, which indicates a nullable
  tensor. Previously this function was only used by NN methods.
- Documentation updates on THNN library
- I added an extra fgradInput argument to VolumetricConvolutionMM_updateOutput
  and VolumetricConvolutionMM_accGradParameters so that its buffer list lines up
  with the backward argument list. This makes it possible to write derivative
  for conv3d which previously was not supported (commented out in
  derivatives.yaml)
- Extra double_backward declarations for all convolution backwards functions was
  added.
- You can now use the syntax Tensor? in native_functions.yaml to indicate that a
  tensor argument is nullable.  There are adjustments to propagate this to the
  Python argument parser.
- NNPACK was ported to ATen, and ATen now builds and links against ATen if
  possible. New AT_NNPACK_ENABLED macro.  The nnpack functions are
  nnpack_spatial_convolution.
- Some modest CuDNN convolution refactoring to remove _forward from names.
- There's a new cudnn_convolution_backward function to deal with the fact that
  CuDNN convolution double backward requires you to have computed all gradients
  in one go.
- Variable set_flags now checks if the tensor is undefined, fixing a silent memory
  corruption.
- checkSameType updated to not raise an exception if called with Variable arguments
- "no ATen declaration found for" error message is improved to say what available declarations are
- make_variable now accepts undefined tensors, and returns an undefined tensor in this case.

1 files changed, 2 insertions, 0 deletions

diff --git a/torch/legacy/nn/VolumetricConvolution.py b/torch/legacy/nn/VolumetricConvolution.py
index 6b357fba37..0a3ace4b2e 100644
--- a/torch/legacy/nn/VolumetricConvolution.py
+++ b/torch/legacy/nn/VolumetricConvolution.py
@@ -95,6 +95,7 @@ class VolumetricConvolution(Module):
                 self.weight,
                 self.bias,
                 self.finput,
+                self.fgradInput,
                 self.kT, self.kW, self.kH,
                 self.dT, self.dW, self.dH,
                 self.padT, self.padW, self.padH
@@ -160,6 +161,7 @@ class VolumetricConvolution(Module):
                 self.gradWeight,
                 self.gradBias,
                 self.finput,
+                self.fgradInput,
                 self.kT, self.kW, self.kH,
                 self.dT, self.dW, self.dH,
                 self.padT, self.padW, self.padH,