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size_t is an unsigned integer, with a conversion rank
 larger than int, therefore in the following expression
 the int value was promoted to size_t, making it a
 subtraction of unsigned values. The result of such
 a subtraction is also an unsigned value.

* expose peak gpu memory API to python test=develop

* add unittest for peak gpu memory monitoring test=develop

* add pybind change test=develop

* add mutex to gpu mem usage monitor test=develop

* update benchmark flag definition file test=develop

* tweak unittest for memory monitoring test=develop

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* use mat attr and refine test

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* add matmul jitcode

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* fix mac compile

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* Add INT8 calibration support in Paddle package; test=develop

* Enable pool2d operator for a ngraph engine
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* Update
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* Some improvements to support bert mixed precision training

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* Revert the cast in layer_norm

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* Refine beam_search_op to output an extra parent_idx tensor.
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* Fix the unittest test_beam_search_op.
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* Fix the merging mistake.
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