* Add fsp operator.
1 Add unitest.
2. Add python API.
3. Add layer test.

* Add quantization strategy.
1. Add API.
2. Add unitest.

* Add distillatoin strategy.

* Add unitest config file for quantization

* Fix Copyright
test=develop

* Fix setup.py

* Fix document of layers.py.
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* Fix unitest in python3.
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* Fix documents.
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* 1. refine fsp op by batched gemm
2. remove unused import
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* Fix test_dist_se_resnext.
1. disable test distillation.
2. reset framework.py
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* Enable unitest of distillation after fixing Block._clone_variable
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* Fix cdn issue.
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* fix cdn issue, test=develop

* fix cdn issue, test=develop

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* Add range op.
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* Add more unitests.
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* Fix API.spec
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* Fix API.spec
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* Fix API.spec
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* Enable INT8 Concat Kernel to improve the performance of MobileNet-SSD.
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* Optimize UT format.
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* Fix UT file address issue.
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* Refine the license year.
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* Optimize code for new API.
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* Restructure INT8 Concat kernel.
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* refine fused_all_reduce_op

* add unit test in test_parallel_executor_seresnext
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* add resnet nccl2 test=develop

* test dist train test=develop

* update test=develop

* increase timeout test=develop

* test on CI env test=develop

* Add softmax_with_cross_entropy_op test=develop

* simplify implementation test=develop

* fuse all_reduce
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* add fuse_parameter_groups_size
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* Polish code
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* Fix travis-ci
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* Add SetGroupAccordingToLayers and SetGroupAccordingToGroupSize
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* Add SetGroupAccordingToMemorySize
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* fix multi_devices_graph
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* reset params_grads
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* Polish code
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* wip allreduce in op

* wip

* wip

* wip

* wip adding test

* wip for conflict with mp mode

* fix tests test=develop

* fix cpu build test=develop

* fix travis clang format test=develop

* fix cpu build test=develop

* update api.spec test=develop

* delete comment test=develop

* fix cpplint test=develop

* fix test=develop

* follow comment test=develop

* add file test=develop

* fix build test=develop

* update test=develop

* to be compatible with sync_bn, and fix mp mode in develop test=develop

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* Enable INT8 transpose kernel for MobileNet-SSD improvement.
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* Refine the license year.
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* Delete redundant code.
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* Add axis check.
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* Add moving average absmax op in quantilize-aware training.

* Support Sync Batch Norm.
* Note, do not enable it in one device.

Usage:

build_strategy = fluid.BuildStrategy()
build_strategy.sync_batch_norm = True
binary = fluid.compiler.CompiledProgram(tp).with_data_parallel(
        loss_name=loss_mean.name,
        build_strategy=build_strategy)

* Impl fp16 compute kernel for slice_op

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* Use data() to replace mutable_data()

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* Remove Desc in Forward Pass

* Refactor VarBase

* Add dbg info

* Only check type in imperative mode

* Polish code and support optimizer

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* Fix stop gradient problem in PyLayer

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