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1b7f65437e
Enable Opset11 Sequence Ops on DirectML, and make the CPU
implementations agnostic to backend EP
Opset 11 introduced the following sequence related operators:
- SequenceAt
- SequenceConstruct
- SequenceEmpty
- SequenceLength
- SequenceErase
- SequenceInsert
- ConcatFromSequence
With the exception of ConcatFromSequence, all of the above operators
were implemented with CPU kernels that a) required all of the contained
tensors to also be on CPU, and b) would clone each tensor into a new
sequence as a side effect of each operator. The implementation of
sequences are backend agnostic, as they dont affect actual tensor layout
or manipulate the contents of the tensors. In addition, with the
exception of SequenceAt, the other operators need not make copies of the
underlying referenced tensors.
Consequently, this change does the following:
1) Sequence* operators (except SequenceAt) no longer copies the contents
of a sequence of tensors on every kernel execution.
2) SequenceAt uses the DataTransferManager to copy tensors agnostic to
backend.
3) The internal container implemented by TensorSeq has changed from
onnxruntime::Tensor to OrtValue. This is because onnxruntime::Tensor
does not support copy or assignment construction, so it must have a
singular owner. However, is same tensor participates in multiple
containers it would have multiple container "owners" and this would not
be possible.
4) Other code that accessed values from TensorSeq have associated
changes to extract Tensors from OrtValues now.
In addition, DirectML execution was very slow when the above Sequence
operators were added to a graph, as this caused MemcpyToHost and
MemcpyFromHost kernels to be inserted between the graph and the sequence
operators. To optimize DirectML,
1) The CPU implementations for the Sequence* ops were registered as DML
implementations. Since the above changes also includes making the CPU
kernel implementations EP agnostic, the CPU kernels can be added as is.
2) The ConcatFromSequence operator needed to be implemented on DirectML.
However, there was little DirectML EP operator framework support for
operators that accept/output sequences of tensors. This change has
modified the internal COM interfaces to include new apis to interrogate
for sequence shapes, and extract the needed tensors from TensorSeq.
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Co-authored-by: Patrice Vignola <vignola.patrice@gmail.com>
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