DynamicSlice
#include <popops/DynamicSlice.hpp>
Support for dynamic slices.

namespace poplar
Poplar classes and functions.

namespace popops
Common functions, such as elementwise and reductions.
Functions

poplar::Tensor createSliceableTensor(poplar::Graph &graph, const poplar::Type &type, const std::vector<size_t> &shape, const std::vector<size_t> &dims, const std::vector<size_t> &sizes, std::size_t minGrainSize = 0, const poplar::DebugContext &debugContext = {})
Create and map a tensor to be sliced/updated efficiently.
The returned tensor will be spread over as many tiles as possible while respecting the minimum number of elements per tile (
minGrainSize
) and still being in a form that can be sliced/updated efficiently. Parameters
graph – The Poplar graph.
type – The type of the elements.
shape – The shape of the tensor to be slice/updated.
dims – The dimensions of the tensor that will be slice/updated.
sizes – The size of the slice in each of the dimensions.
minGrainSize – The minimum elements per slice mapped to each tile
debugContext – Optional debug information.
 Returns
A tensor shape
shape
that is suitably mapped

poplar::Tensor createSliceableTensor(poplar::Graph &graph, const poplar::Type &type, const std::vector<size_t> &shape, const std::vector<size_t> &dims, const std::vector<size_t> &sizes, const SlicePlan &plan, const poplar::OptionFlags &options, const poplar::DebugContext &debugContext = {})
Create and map a tensor to be sliced/updated efficiently.
The returned tensor will be laid out according to the plan.
 Parameters
graph – The Poplar graph.
type – The type of the elements.
shape – The shape of the tensor to be slice/updated.
dims – The dimensions of the tensor that will be slice/updated.
sizes – The size of the slice in each of the dimensions.
plan – Plan describing how the slicing/updating operation will be implemented.
options – Flags controlling how the operation will be implemented.
debugContext – Optional debug information.
 Returns
A tensor shape
shape
that is suitably mapped.

poplar::Tensor createGroupedSliceableTensor(poplar::Graph &graph, const poplar::Type &type, const std::size_t groupSize, const std::vector<std::size_t> &shape, const std::vector<std::size_t> &dims, const std::vector<std::size_t> &sizes, const SlicePlan &plan, const poplar::OptionFlags &options, const poplar::DebugContext &debugContext = {})
Create and map a tensor with a group dimension to be sliced/updated efficiently.
Groups allow multiple independent slice/update operations of the same size to be done in parallel.
The
shape
,dims
, andsizes
parameters are defined as increateSliceableTensor()
and are used for every group.A valid plan must be provided. The returned tensor will be laid out according to the plan.
 Parameters
graph – The Poplar graph.
type – The type of the elements.
groupSize – The group size.
shape – The shape of the tensor to be slice/updated.
dims – The dimensions of the tensor that will be slice/updated.
sizes – The size of the slice in each of the dimensions.
plan – Plan describing how the slicing/updating operation will be implemented.
options – Flags controlling how the operation will be implemented.
debugContext – Optional debug information.
 Returns
A tensor suitably mapped with
groupSize
as the first dimension and the remaining dimensions as inshape
.

poplar::Tensor createSliceTensor(poplar::Graph &graph, const poplar::Tensor &t, const std::vector<size_t> &dims, const std::vector<size_t> &sizes, std::size_t numIndices, const poplar::DebugContext &debugContext = {})
Create and map a tensor that is used as a result of slicing, or as an input to an update.
Introspection on the tensor
t
is used to lay out the created tensor such that it can be used to efficiently updatet
. Parameters
graph – The Poplar graph.
t – The tensor to be updated.
dims – The dimensions of the tensor that will be sliced/updated.
sizes – The number of elements of each dimension in
dims
that will be sliced/updated.numIndices – The number of slices this tensor should contain.
plan – Plan describing how the slicing/updating operation will be implemented.
options – Flags controlling how the operation will be implemented.
debugContext – Optional debug information.
 Returns
A tensor with shape [numIndices, shape…] mapped appropriately to be sliced into/updated from.

poplar::Tensor createSliceTensor(poplar::Graph &graph, const poplar::Type &type, const std::vector<std::size_t> &shape, const std::vector<std::size_t> &dims, const std::vector<std::size_t> &sizes, std::size_t numIndices, const SlicePlan &plan, const poplar::OptionFlags &options, const poplar::DebugContext &debugContext = {})
Create and map a tensor that is used as a result of slicing, or as an input to an update.
The returned tensor is laid out according to the plan for the slice/update operation.
 Parameters
graph – The Poplar graph.
type – The type of the elements.
shape – The shape of the tensor to be slice/updated.
dims – The dimensions of the tensor that will be sliced/updated.
sizes – The number of elements of each dimension in
dims
that will be sliced/updated.numIndices – The number of slices this tensor should contain.
plan – Plan describing how the slicing/updating operation will be implemented.
options – Flags controlling how the operation will be implemented.
debugContext – Optional debug information.
 Returns
A tensor with shape [numIndices, shape…]

poplar::Tensor createGroupedSliceTensor(poplar::Graph &graph, const poplar::Type &type, const std::size_t groupSize, const std::vector<std::size_t> &shape, const std::vector<std::size_t> &dims, const std::vector<std::size_t> &sizes, const std::size_t numIndices, const SlicePlan &plan, const poplar::OptionFlags &options, const poplar::DebugContext &debugContext = {})
Create and map a tensor with a group dimension that is used as a result of slicing, or as an input to an update.
The group dimension is the first dimension of the output tensor.
Groups allow multiple independent slice/update operations of the same size to be done in parallel.
The
shape
,dims
, andsizes
parameters are defined as increateGroupedSliceTensor
and are used for every group.The returned tensor is laid out according to the plan for the slice/update operation. It is an error to call this function without a valid plan.
 Parameters
graph – The Poplar graph.
type – The type of the elements.
groupSize – The group size
shape – The shape of the tensor to be slice/updated.
dims – The dimensions of the tensor that will be sliced/updated.
sizes – The number of elements of each dimension in
dims
that will be sliced/updated.numIndices – The number of slices this tensor should contain.
plan – Plan describing how the slicing/updating operation will be implemented.
options – Flags controlling how the operation will be implemented.
debugContext – Optional debug information.
 Returns
A tensor with shape [groupSize, numIndices, shape…]

poplar::Tensor createIndicesTensor(poplar::Graph &graph, const std::vector<std::size_t> &dims, std::size_t numIndices, const SlicePlan &plan, const poplar::OptionFlags &options, const poplar::DebugContext &debugContext = {})
Create and map a tensor to contain indices for slicing or updating a tensor efficiently.
 Parameters
graph – The Poplar graph.
dims – The dimensions of a tensor to be sliced/updated that will be sliced/updated using these indices.
numIndices – The number of indices this tensor should contain
plan – Plan describing how the slicing/updating operation will be implemented.
options – Flags controlling how the operation will be implemented.
debugContext – Optional debug information.
 Returns
A tensor of shape [numIndices, dims.size()] mapped appropriately to be used as the indices for a slice/update operation. Element type is always UNSIGNED_INT.

poplar::Tensor createGroupedIndicesTensor(poplar::Graph &graph, const std::size_t groupSize, const std::vector<std::size_t> &dims, const std::size_t numIndices, const SlicePlan &plan, const poplar::OptionFlags&, const poplar::DebugContext &debugContext = {})
Create and map a tensor with a group dimension to contain indices for slicing or updating a tensor efficiently.
Groups allow multiple independent slice/update operations of the same size to be done in parallel. Indices have the same bounds for every element in the group.
dims
is defined as in the nongrouped version. They do not include a group dimension.It is an error to call this function without a valid plan and
groupSize
must match the group size with which the operation is planned inplan
. Parameters
graph – The Poplar graph.
groupSize – The size of the group
dims – The dimensions of a tensor to be sliced/updated that will be sliced/updated using these indices.
numIndices – The number of indices this tensor should contain
plan – Plan describing how the slicing/updating operation will be implemented.
options – Flags controlling how the operation will be implemented.
debugContext – Optional debug information.
 Returns
A tensor of shape [groupSize, numIndices, dims.size()] mapped appropriately to be used as the indices for a slice/update operation. Element type is always UNSIGNED_INT.

poplar::Tensor createSliceableTensorFromSlice(poplar::Graph &graph, const poplar::Tensor &s, const std::vector<std::size_t> &dims, const std::vector<std::size_t> &numSlices, const poplar::DebugContext &debugContext = {})
Create and map a tensor to be sliced/updated.
The tensor is mapped in a way that can be efficiently sliced and updated to/from the given slice tensor. It will be distributed across as many tiles as the given slice and with the same contiguous regions on each tile. The tensor’s shape and mapping are derived from the reference slice tensor.
 Parameters
graph – The Poplar graph.
s – The reference slice.
dims – The dimensions of the returned tensor that will be sliced.
numSlices – The number of independent slices in each sliced dimension.
debugContext – Optional debug information.
 Returns
A tensor to be sliced/updated.

poplar::Tensor dynamicSlice(poplar::Graph &graph, const poplar::Tensor &t, const poplar::Tensor &offset, const std::vector<std::size_t> &dims, const std::vector<std::size_t> &sizes, poplar::program::Sequence &prog, const poplar::DebugContext &debugContext = {})
Slice a tensor based on offsets specified by a tensor.
dims
gives the dimensions to slice,sizes
defines the size of the slice in those dimensions andoffset
gives the base offsets on each execution.offset
[0],dims
andsizes
must have the same size.offset
may have a second dimension with an element per tile, which can eliminate exchange.Note
If the elements of a single slice cannot be well spread across available tiles (for example, because it has fewer elements than the available number of tiles) then the operation as a whole will also have poor tile balance and consequently poor tile memory balance.
 Parameters
graph – The Poplar graph.
t – The source tensor.
offset – A tensor of offsets at which the output is extracted.
dims – The dimensions of
t
to slice.sizes – The size of the slice in each of the dimensions in
dims
.prog – The program to be extended
debugContext – Optional debug information.
 Returns
The specified subtensor

void dynamicSliceWithOutput(poplar::Graph &graph, const poplar::Tensor &output, const poplar::Tensor &t, const poplar::Tensor &offset, const std::vector<std::size_t> &dims, const std::vector<std::size_t> &sizes, poplar::program::Sequence &prog, const poplar::DebugContext &debugContext = {})
Slice a tensor based on offsets specified by a tensor.
dims
gives the dimensions to slice,sizes
defines the size of the slice in those dimensions andoffset
gives the base offsets on each execution.offset
[0],dims
andsizes
must have the same size.offset
may have a second dimension with an element per tile, which can eliminate exchange. Parameters
graph – The Poplar graph.
output – The output tensor, This should ideally be created with
createSliceTensor
to maximise efficiency,t – The source tensor.
offset – A tensor of offsets at which the output is extracted.
dims – The dimensions of
t
to slice.sizes – The size of the slice in each of the dimensions in
dims
.prog – The program to be extended
debugContext – Optional debug information.

poplar::Graph::TileToTensorMapping getSliceMapping(poplar::Graph &graph, const poplar::Tensor &t, const std::vector<std::size_t> &dims, const std::vector<std::size_t> &sizes)
Get the tile mapping for a slice of a tensor.
dims
gives the dimensions to slice,sizes
defines the size of the slice in those dimensions. Parameters
graph – The Poplar graph.
t – The source tensor.
dims – The dimensions of
t
to slice.sizes – The size of the slice in each of the dimensions in
dims
.

void dynamicUpdate(poplar::Graph &graph, const poplar::Tensor &t, const poplar::Tensor &s, const poplar::Tensor &offset, const std::vector<std::size_t> &dims, const std::vector<std::size_t> &sizes, poplar::program::Sequence &prog, const poplar::DebugContext &debugContext = {})
Update a subtensor at offsets read from a tensor.
dims
gives the dimensions that are partially updated, bysizes
elements, at offsetsoffset
. Unspecified dimensions are copied in full with zero offset.offset
[0],dims
andsizes
must have the same size.offset
may have a second dimension with an element per tile, which can eliminate exchange. Parameters
graph – The Poplar graph.
t – The tensor to update.
s – The updates.
offset – The offset within
t
to be updated.dims – The dimensions to be dynamically updated.
sizes – The size of the update in each of the dimensions in
dims
.prog – The program to be extended.
debugContext – Optional debug information.

poplar::Tensor multiSlice(poplar::Graph &graph, const poplar::Tensor &t, const poplar::Tensor &offsets, const std::vector<std::size_t> &dims, const std::vector<std::size_t> &sizes, poplar::program::Sequence &prog, const SlicePlan &plan, const poplar::OptionFlags &options, const poplar::DebugContext &debugContext = {})
Take multiple slices from a base tensor.
The returned tensor will have a rank one greater than
t
. Its outer dimension will beoffsets.dim(0)
. Note thatdims
refers to the dimensions oft
.t
can be created usingcreateSliceableTensor()
to ensure efficient mapping. Parameters
graph – The Poplar graph.
t – The tensor being sliced.
offsets – The offsets within
t
to be sliced.dims – The dimensions of
t
to be sliced.sizes – The size of the update in each of the dimensions in
dims
.prog – The program to be extended.
plan – Plan describing how the operation will be implemented.
options – Flags controlling how the operation will be implemented.
debugContext – Optional debug information.

poplar::Tensor groupedMultiSlice(poplar::Graph &graph, const poplar::Tensor &t, const poplar::Tensor &offsets, const std::vector<std::size_t> &dims, const std::vector<std::size_t> &sizes, poplar::program::Sequence &prog, const SlicePlan &plan, const poplar::OptionFlags &options, const poplar::DebugContext &debugContext = {})
Take multiple slices from a base tensor where the
base
tensor and theoffsets
tensor have the group dimension as the first dimension.The indices given in the
offsets
tensor should be in the range [0,base.dim(1)
]. Indices outside of this range are allowed but return undefined values.The returned tensor will have a rank one greater than
t
. Its outer dimension is the group size and the second dimension will beoffsets.dim(1)
.dims
indexes the dimensions of each group int
. This makes it consistent with grouped variants of functions to create tensors.t
can be created usingcreateGroupedSliceableTensor()
to ensure efficient mapping. Parameters
graph – The Poplar graph.
t – The tensor being sliced.
offsets – The offsets within
t
to be sliced.dims – The dimensions of
t
for each group.sizes – The size of the update in each of the dimensions in
dims
.prog – The program to be extended.
plan – Plan describing how the operation will be implemented.
options – Flags controlling how the operation will be implemented.
debugContext – Optional debug information.

poplar::Tensor multiSlice(poplar::Graph &graph, const poplar::Tensor &t, poplar::ArrayRef<unsigned> offsets, std::size_t dim, poplar::program::Sequence &prog, const poplar::DebugContext &debugContext = {})
Take multiple slices from a base tensor.
The returned tensor will have a rank one greater than
t
. Its outer dimension will beoffsets.size()
. Note thatdim
refers to a dimension oft
. Parameters
graph – The Poplar graph.
t – The tensor being sliced.
offsets – The offsets within
t
to be sliced.dims – The dimension of
t
to be sliced.prog – The program to be extended.
debugContext – Optional debug information.

void multiUpdate(poplar::Graph &graph, const poplar::Tensor &t, const poplar::Tensor &s, const poplar::Tensor &offsets, const std::vector<std::size_t> &dims, const std::vector<std::size_t> &sizes, poplar::program::Sequence &prog, const SlicePlan &plan, const poplar::OptionFlags &options, const poplar::DebugContext &debugContext = {})
Update multiple slices in a tensor.
 Parameters
graph – The Poplar graph.
t – The tensor being updated.
s – The slices to insert.
offsets – The offsets within
t
to be updated.dims – The dimensions of
t
to be updated.sizes – The size of the update in each of the dimensions in
dims
.prog – The program to be extended.
plan – Plan describing how the operation will be implemented.
options – Flags controlling how the operation will be implemented.
debugContext – Optional debug information.

void groupedMultiUpdate(poplar::Graph &graph, const poplar::Tensor &t, const poplar::Tensor &s, const poplar::Tensor &offsets, const std::vector<std::size_t> &dims, const std::vector<std::size_t> &sizes, poplar::program::Sequence &prog, const SlicePlan &plan, const poplar::OptionFlags &options, const poplar::DebugContext &debugContext = {})
Update multiple slices in a tensor with a group dimension.
The tensors
t
s
, andoffsets
have group dimension as the first dimension. Parameters
graph – The Poplar graph.
t – The tensor being updated.
s – The slices to insert.
offsets – The offsets within
t
to be updated.dims – The dimensions of each group of
t
to be updated.sizes – The size of the update in each of the dimensions in
dims
.prog – The program to be extended.
plan – Plan describing how the operation will be implemented.
options – Flags controlling how the operation will be implemented.
debugContext – Optional debug information.

void multiUpdateAdd(poplar::Graph &graph, const poplar::Tensor &t, const poplar::Tensor &s, const poplar::Tensor &offsets, const poplar::Tensor &scale, const std::vector<std::size_t> &dims, const std::vector<std::size_t> &sizes, poplar::program::Sequence &prog, const SlicePlan &plan, const poplar::OptionFlags &options, const poplar::DebugContext &debugContext = {})
Accumulate multiple slices in a tensor.
 Parameters
graph – The Poplar graph.
t – The tensor being updated (must be rank 2).
s – The slices to accumulate.
offsets – The offsets within
t
to be accumulated.scale – The scaling to apply to the update. The type of the tensor should be the same as that of
t
ands
except for the case whent
ands
are of type HALF. In which casescale
can be of type FLOAT or HALF.dims – The dimensions of
t
to be accumulated (must be rank 1).sizes – The size of the accumulate in each of the dimensions in
dims
.prog – The program to be extended.
plan – Plan describing how the operation will be implemented.
options – Flags controlling how the operation will be implemented.
debugContext – Optional debug information.

void groupedMultiUpdateAdd(poplar::Graph &graph, const poplar::Tensor &t, const poplar::Tensor &s, const poplar::Tensor &offsets, const poplar::Tensor &scale, const std::vector<std::size_t> &dims, const std::vector<std::size_t> &sizes, poplar::program::Sequence &prog, const SlicePlan &plan, const poplar::OptionFlags &options, const poplar::DebugContext &debugContext = {})
Accumulate multiple slices in a tensor where the first dimension of the tensors
t
,s
andoffsets
is the group dimension.t
,s
must be of the same type Parameters
graph – The Poplar graph.
t – The tensor being updated (must be rank 3).
s – The slices to accumulate.
offsets – The offsets within
t
to be accumulated.scale – The scaling to apply to the update. The type of the tensor should be the same as that of
t
ands
except for the case whent
ands
are of type HALF. In which casescale
can be of type FLOAT or HALF.dims – The dimensions of of each group to be accumulated.
sizes – The size of the accumulate in each of the dimensions in
dims
.prog – The program to be extended.
plan – Plan describing how the operation will be implemented.
options – Flags controlling how the operation will be implemented.
debugContext – Optional debug information.

void multiUpdateAdd(poplar::Graph &graph, const poplar::Tensor &t, const poplar::Tensor &s, poplar::ArrayRef<unsigned> offsets, const poplar::Tensor &scale, std::size_t dim, poplar::program::Sequence &prog, const poplar::DebugContext &debugContext = {})
Accumulate multiple slices in a tensor.
t
,s
must be of the same type Parameters
graph – The Poplar graph.
t – The tensor being updated.
s – The slices to accumulate.
offsets – The offsets within
t
to be accumulated.scale – The scaling to apply to the update. The type of the tensor should be the same as that of
t
ands
except for the case whent
ands
are of type HALF. In which casescale
can be of type FLOAT or HALF.dim – The dimension of
t
to be accumulated.prog – The program to be extended.
debugContext – Optional debug information.

void multiUpdateMax(poplar::Graph &graph, const poplar::Tensor &t, const poplar::Tensor &s, const poplar::Tensor &offsets, const std::vector<std::size_t> &dims, const std::vector<std::size_t> &sizes, poplar::program::Sequence &prog, const SlicePlan &plan, const poplar::OptionFlags &options, const poplar::DebugContext &debugContext = {})
Find maximum over multiple slices in a tensor.
t
,s
must have the same element type offsets[i] >= t.dim(0) are ignored. Parameters
graph – The Poplar graph.
t – The tensor being updated (must be rank 2).
s – The slices to find maximum over.
offsets – The offsets within
t
to find maximum over.dims – The dimensions of
t
to find maximum over (must be rank 1).sizes – The size of the update in each of the dimensions in
dims
.prog – The program to be extended.
plan – Plan describing how the operation will be implemented.
options – Flags controlling how the operation will be implemented.
debugContext – Optional debug information.

void groupedMultiUpdateMax(poplar::Graph &graph, const poplar::Tensor &t, const poplar::Tensor &s, const poplar::Tensor &offsets, const std::vector<std::size_t> &dims, const std::vector<std::size_t> &sizes, poplar::program::Sequence &prog, const SlicePlan &plan, const poplar::OptionFlags &options, const poplar::DebugContext &debugContext = {})
Find maximum over multiple slices in a tensor with a group dimension.
The tensors
t
,s
,offsets
have groups as their first dimension. Theoffsets
tensor contains indices per group which update elements of the corresponding group. Parameters
graph – The Poplar graph.
t – The tensor being updated (must be rank 2).
s – The slices to find maximum over.
offsets – The offsets within
t
to find maximum over.dims – The dimensions of each group of
t
to find maximum over (must be rank 1).sizes – The size of the update in each of the dimensions in
dims
.prog – The program to be extended.
plan – Plan describing how the operation will be implemented.
options – Flags controlling how the operation will be implemented.
debugContext – Optional debug information.

class SlicePlan
 #include <DynamicSlice.hpp>
An object representing a plan that describes how to implement a slice or update.
This can be used as a parameter to a function that will slice or update a tensor.

namespace embedding
Functions

SlicePlan plan(const poplar::Graph &graph, const poplar::Type &dataType, const std::size_t numEntries, const std::size_t outputSize, const std::vector<std::size_t> &numLookups, const poplar::OptionFlags &options)
Create a plan for implementing a set of operations on an embedding matrix.
** Embedding plan options **
usedForSlice
(true, false) [=true]If true, you intend to use this embedding plan for both a multiSlice operation. An error is thrown if set to false and
usedForUpdate
is set to false.usedForUpdate
(true, false) [=true]If true, you intend to use this embedding plan for both a multiUpdate operation. An error is thrown if set to false and
usedForSlice
is set to false.operationForUpdate
(“none”, “add”, “max”) [=”add”]Only applicable when
usedForUpdate
= true. Is the type of operation used in multiupdate. Set to “none” for multiUpdate “add” for multiUpdateAdd “max” for multiUpdateMaxavailableMemoryProportion
Decimal between 0 and 1 (inclusive) [=0.6]If set, gives the proportion of tile memory made available for temporary variables (variables that become live and die during the operation) for this operation. If not set, the operation has the freedom to use unlimited temporary memory.
See also
See also
Optimising Temporary Memory Usage for Convolutions and Matmuls on the IPU technical note for some practical examples of using
availableMemoryProportion
indicesDistribution
(uniform, onePoint) [=uniform]A description of the statistical distribution of the indices that will be sliced/updated over the input size (
numEntries
) of the operation. This is used to when estimating the runtime of the multiSlice and multiUpdate operation.uniform
Indices are assumed to be uniformly distributed over the input size of the embedding.onePoint
Indices are assumed to all be equal.
indicesAreSorted
(true, false) [=false]Plan assuming indices used in MultiUpdate/MultiUpdateOp are sorted in increasing order. The same option must then be used along with the plan when calling MultiUpdate with and without an operation.
validateIndices
(true, false) [=false]Check that all indices are valid at runtime. If any is invalid execution is aborted.
partialType
(half, float) If not provided, defaults to using the same as the data type. Partials type should always be the same or higher precision than the data type of the embedding matrix. Is applicable only for the case whereoperationForUpdate
isadd
. It is ignored for all other operations and multislice.
 Parameters
graph – The graph the operation will be added to.
dataType – The data type of the entries in the embedding matrix and the resulting lookups from the matrix.
numEntries – Input size of embedding matrix.
outputSize – Output size of embedding matrix lookup.
numLookups – Vector of numbers of indices which will be looked up in the embedding matrix.
options – Set of option flags controlling how the operation will be implemented.
 Returns
A plan which describes how the embedding matrix lookup/update operations should be implemented.

SlicePlan plan(const poplar::Graph &graph, const poplar::Type &dataType, const std::size_t numEntries, const std::size_t outputSize, const std::vector<std::size_t> &numLookups, const poplar::OptionFlags &options)

poplar::Tensor createSliceableTensor(poplar::Graph &graph, const poplar::Type &type, const std::vector<size_t> &shape, const std::vector<size_t> &dims, const std::vector<size_t> &sizes, std::size_t minGrainSize = 0, const poplar::DebugContext &debugContext = {})