6. IPU supported operations

Below is a list of currently supported operations that can be executed on IPU hardware. This list will be expanded over time as we add more support. Some overloads and modes of operation for ops are not supported and we’ve tried to list all the caveats but some may have been missed.

6.1. Torch operations

6.1.1. Tensor operations

Many of the tensor operations will be executed before even reaching the IPU so we can consider them supported anyway. Some, like contiguous(), make no sense on a distributed memory system like the IPU so are ignored. There are no constraints on the memory format of how operations should be called other than the constraint that all graph inputs should be contiguous.

We will also create tensor views. However, the aliasing property of views with respect to in-place operations should not be relied on as we may have slightly different view behaviour.

Additionally, some PyTorch operations may be implemented by composition of the listed ops but may not be explicitly listed but are in fact supported.

Creation ops

• torch.arange

• tensor.fill

• torch.full

• torch.full_like

• torch.Tensor.new_ones

• torch.Tensor.new_zeros

• torch.ones

• torch.ones_like

• torch.zeros

• torch.zeros_like

Indexing, slicing, joining and mutating ops

In PyTorch, slicing a tensor is accessing a subset of the tensor by providing the start and end indices, such as tensor[1:5].

With a PopTorch model, you may take a slice of a tensor only if one of two conditions are met:

• The start and end are constants, or can be resolved to be constants (for example, a function of the shape of a tensor which does not change between runs).

• The start and end of the slice are related by a constant, for example tensor[x:x+5]. Please note that this will produce different results to PyTorch if the end value exceeds the length of the tensor: PyTorch will output a smaller size tensor but PopTorch will allow the slice to wrap round to the start of the relevant dimension.

PyTorch functions

• torch.cat

• torch.chunk

• torch.gather

• torch.index_select

• torch.index_reduce

• torch.reshape

• torch.roll

• torch.scatter

• torch.scatter_add

• torch.scatter_reduce

• torch.stack

• torch.split

• torch.squeeze

• torch.t

• torch.transpose

• torch.unbind

• torch.unsqueeze

• torch.where

Tensor methods

• tensor.expand

• tensor.expand_as

• tensor.masked_fill

• tensor.index_fill_

Random samplers

To set the random state, use poptorch.Options.randomSeed

• torch.bernoulli

• torch.distributions.Bernoulli

• torch.randn

• torch.normal

• torch.distributions.Normal

• torch.rand

• torch.uniform

• torch.distributions.Uniform

• torch.exponential

• torch.distributions.Exponential

6.1.2. Math operations

Pointwise ops

• torch.abs

• torch.acos

• torch.acosh

• torch.add

• torch.addcdiv

• torch.amax

• torch.amin

• torch.asin

• torch.asinh

• torch.atan

• torch.atanh

• torch.bitwise_and

• torch.bitwise_not

• torch.bitwise_or

• torch.bitwise_xor

• torch.ceil

• torch.clamp

• torch.clamp_max

• torch.clamp_min

• torch.cos

• torch.cosh

• torch.div

• torch.exp

• torch.expm1

• torch.floor

• torch.floor_divide

• torch.fmod

• torch.frac

• torch.log

• torch.log10

• torch.log1p

• torch.log2

• torch.logical_and

• torch.logical_or

• torch.mul

• torch.norm

• torch.neg

• torch.pow

• torch.reciprocal

• torch.remainder

• torch.round

• torch.rsqrt

• torch.sigmoid

• torch.sign

• torch.sin

• torch.sinh

• torch.sqrt

• torch.square

• torch.sub

• torch.tan

• torch.tanh

• torch.true_divide

• torch.trunc

Reduction ops

• torch.all

• torch.any

• torch.argmax

• torch.argmin

• torch.count_nonzero

• torch.mean

• torch.median

• torch.prod

• torch.logsumexp

• torch.std

• torch.std_mean

• torch.sum

• torch.var

• torch.var_mean

Comparison ops

• torch.eq

• torch.ge

• torch.gt

• torch.le

• torch.lt

• torch.max

• torch.min

• torch.ne

• torch.isnan

  torch.topk only supports sorted=True and largest=True arguments.

• torch.topk

• torch.argsort

• torch.randperm

torch.linalg ops

• torch.linalg.norm

  2-norm and nuclear norm are unsupported for matrices.

• torch.linalg.matrix_norm

  2-norm and nuclear norm are unsupported.

• torch.linalg.vector_norm

Other ops

• torch.cumsum

• torch.cross

• torch.meshgrid

• torch.cartesian_prod

• torch.tensordot

BLAS and LAPACK Operations

• torch.addmm

• torch.matmul

• torch.bmm

6.2. Torch.nn operations

6.2.1. Containers

torch.nn.Module and torch.nn.Sequential can be passed into our compiler wrappers and just work.

6.2.2. Convolution layers

Conv transpose operations do not yet support dilations.

• torch.nn.Conv1d

• torch.nn.Conv2d

• torch.nn.Conv3d

• torch.nn.ConvTranspose1d

• torch.nn.ConvTranspose2d

• torch.nn.ConvTranspose3d

6.2.3. Pooling layers

Currently the max pool layers do not return the indices so only the variants with return_indices=False are supported.

• torch.nn.MaxPool1d

• torch.nn.MaxPool2d

• torch.nn.MaxPool3d

• torch.nn.AvgPool1d

• torch.nn.AvgPool2d

• torch.nn.AvgPool3d

• torch.nn.AdaptiveAvgPool1d

• torch.nn.AdaptiveAvgPool2d

• torch.nn.AdaptiveAvgPool3d

6.2.4. Padding layers

All padding layers are supported.

• torch.nn.ReflectionPad1d

• torch.nn.ReflectionPad2d

• torch.nn.ReplicationPad1d

• torch.nn.ReplicationPad2d

• torch.nn.ReplicationPad3d

• torch.nn.ZeroPad2d

• torch.nn.ConstantPad1d

• torch.nn.ConstantPad2d

• torch.nn.ConstantPad3d

6.2.5. Activations

• torch.nn.ELU

• torch.nn.CELU

• torch.nn.GELU

• torch.nn.Hardshrink

• torch.nn.LeakyReLU

• torch.nn.LogSoftmax

• torch.nn.ReLU

• torch.nn.SELU

• torch.nn.SiLU

• torch.nn.Sigmoid

• torch.nn.Softmax

• torch.nn.Softplus

• torch.nn.Softsign

• torch.nn.Softshrink

• torch.nn.Tanh

• torch.nn.PReLU

• torch.nn.RReLU

• torch.nn.Hardtanh

• torch.nn.functional.glu

• torch.nn.Threshold

6.2.6. Normalization layers

Currently only affine=True is supported as a parameter. That is to say, only the variants with trainable parameters are supported.

• torch.nn.BatchNorm1d

• torch.nn.BatchNorm2d

• torch.nn.BatchNorm3d

• torch.nn.LayerNorm

• torch.nn.GroupNorm

• torch.nn.InstanceNorm1d

• torch.nn.InstanceNorm2d

• torch.nn.InstanceNorm3d

• torch.nn.utils.weight_norm

6.2.7. Recurrent layers

Bidirectional layers, non-zero dropout probabilities, and setting num_layers to a value greater than 1 are not currently supported for any recurrent layer. In addition, setting bias=False is currently only supported for torch.nn.GRU.

• torch.nn.RNN

• torch.nn.GRU

• torch.nn.LSTM

6.2.8. Linear layers

• torch.nn.Identity

• torch.nn.Linear

• torch.nn.Bilinear

6.2.9. Dropout

• torch.nn.dropout

6.2.10. Sparse layers

Embedding and EmbeddingBag are supported with the exception of the padding_idx parameter being unsupported.

• torch.nn.Embedding

• torch.nn.EmbeddingBag

• torch.nn.functional.one_hot

6.2.11. Loss functions

This version supports a limited subset of loss functions. However, we support identity_loss() which gives you the ability to implement any arbitrary loss function.

See also

identity_loss()

One caveat for the following loss functions is if they are used they will always be included in the back propagation and will always receive a gradient, which is a slight deviation from normal PyTorch operations, where they have to opt in to the gradient pass.

• torch.nn.L1Loss

• torch.nn.MSELoss

• torch.nn.CrossEntropyLoss

• torch.nn.NLLLoss

• torch.nn.BCELoss

• torch.nn.KLDivLoss

• torch.nn.PoissonNLLLoss

• torch.nn.HingeEmbeddingLoss

• torch.nn.BCEWithLogitsLoss

• torch.nn.SmoothL1Loss

• torch.nn.SoftMarginLoss

• torch.nn.CosineEmbeddingLoss

• torch.nn.MarginRankingLoss

• torch.nn.TripletMarginLoss

• torch.nn.CTCLoss

6.2.12. Vision Layers

Support nearest and bicubic mode.

• torch.nn.Upsample

PyTorch Scatter functions

• torch_scatter.scatter

• torch_scatter.composite.scatter_log_softmax

• torch_scatter.composite.scatter_softmax

• torch_scatter.composite.scatter_std

6.3. 16-bit float operations

Warning

Handling of float16 operations has been greatly simplified since PopTorch version 3.0. Please read this section carefully if you are used to the way this worked prior to version 3.0.

In PopTorch version 3.0 and later, float16 operations are handled straightforwardly by the dispatcher frontend. Tensors and models can be freely cast to and from float16, and normalization running statistics can also be retyped by simple casting.

If you have PopTorch code created with a previous version of PopTorch, see Section 6.4, 16-bit float migration.

6.4. 16-bit float migration

Legacy PopTorch code using float16 can be updated for the dispatcher frontend by considering the following points:

• Casts were not well supported by the tracing frontend. They are fully supported by the dispatcher frontend.

• opts.Precision.halfFloatCasting() was used to switch between ways of resolving ops with both float32 and float16 inputs (mixed-precision inputs), either by upcasting the inputs to float32, or by downcasting them to float16. This option is not supported under the dispatcher frontend: mixed precision ops are now always upcast to float32, in accordance with normal PyTorch behaviour. To recreate the effect of opts.Precision.halfFloatCasting(poptorch.HalfFloatCastingBehavior.FloatDowncastToHalf), which was the default behaviour with the tracing frontend, float32 inputs to mixed-precision ops should be explicitly cast to float16 before being passed to the op.

• opts.Precision.runningStatisticsAlwaysFloat() was used to cause the running mean and variance of certain normalization ops to be calculated in float32 precision, even though the normalization module itself had been cast to float16. This option is not supported in the dispatcher frontend, as the same effect can be achieved by simply casting the running statistic tensors back to float32 before running the model.

6.5. Gradient computation control

torch.no_grad is supported as a context manager as well as a decorator to suppress the computation of gradients locally.