* support sparse gradients
test=develop

* feature/auto_growth_allocator, test=develop

* add unittest of AlignedAllocator, test=develop

* try to turn on auto_growth to test on CI, test=develop

* fix segmentation fault in mixed_vector.h, test=develop

* add unittests, test=develop

* remove async executor and add data_feed.proto to the deps of train demo

* feature/buffer_shared_inplace, test=develop

* refine code, test=develop

* fix elementwise_add op cpu inplace and sum inplace bug, test=develop

* add unittest and debug log, test=develop

* fix parallel_executor scope bug, polish code, test=develop

* fix sum op, activation op, single_in_place_inference bug, test=develop

* remove kLocalExecScopeName, test=develop

* fix unittest,test=develop

* fix out_var first version bug, test=develop

* follow comments,test=develop

* refine cuda place error msg, test=develop

* use LOG(ERROR)+exit(-1), test=develop

* update execution_strategy option default value
test=develop

* fix doc error
test=develop

* support avx and noavx core

* add catch and give some log

test=develop

* fix build

test=develop

* add missing package

test=develop

* fix pybind name

test=develop

* fix import error

test=develop

* conbime noavx core

test=develop

* add requirements

test=develop

* fix unkown message

test=develop

* fix api spec

test=develop

* refine and clean

test=develop

* update

* pass dist ut

* follow comments

test=develop

* refine scripts

test=develop

* fix the ParallelExecutor on Windows
test=develop
* restrict to use one GPU only under windows

* fix prepare context redundant code problem, optimize executor by caching create_varaiables
test=develop

* cache sub_scope, program, var when use_program_cache=True is set

* make fetch_list runable with variables, add more unittest for use_program_cache

* add __str__ method for tensor and lodtensor to support print test=develop

add Run Prepared Ctx, fix pybind problem

Python examples of fluid.layers.io.double_buffer and some BuildStrategy's methods.

* polish_executor_and_add_ctx_cache

* Revert "Revert "Fix allocator bug""

This reverts commit 174d0d0b.

* Revert "fix travis ci"

This reverts commit 5656fa9f.

test=develop

* add inlined_vector.h, test=develop

* add inlined_vector_test,test=develop

* fix distribute doc

Async exe support communicator

test=develop

* add var grad hook test=develop

* test=develop, add gradient sort backward strategy

* test=develop, fix test by add FLAGS_cudnn_deterministic on new tests

* test=develop, fix memory leak in dygraph mode

* test=develop, fix memory leak in dygraph mode

* test=develop, polish code

* test=develop, polish code

* test=develop, polish code

* make parallel_executor support FLAGS_use_mkldnn

test=develop

* add warning when set mkldnn_enabled_op_types_ in non-mkldnn env

test=develop

* test=develop, add gradient sort backward strategy

* test=develop, fix test by add FLAGS_cudnn_deterministic on new tests

* reset drop local scope counter
test=develop

Fix the following API examples:

paddle.fluid.scope_guard
paddle.fluid.backward.append_backward
paddle.fluid.cpu_places
paddle.fluid.cuda_pinned_places
paddle.fluid.cuda_places
paddle.fluid.in_dygraph_mode
paddle.fluid.CUDAPlace
paddle.fluid.CPUPlace
paddle.fluid.CUDAPinnedPlace

* move pass to ir

* polish code
test=develop

* fix dependency
test=develop

* fix mem leak when converting Tensor to numpy array
test=develop

* remove unused unittest,test=develop

* follow comments, test=develop

* fix dygraph bug,test=develop

implement dygraph.parallel.DataParallel to hook reduce op.

* add doc for memory_optimize, test=develop

* update doc, test=develop

* doc update, test=develop

test=develop

* Add an option to enable the cache of expected kernel in train phase.
test=develop

* Change the default value of cache_expected_kernel to true.

* test fuse all_reduce

* Try to enable the runtime_context_cache pass in train phase.

* Put the append of runtime_context_cache pass ahead of multi_dev passes.
test=develop

add NCCLParallelContext for parallel dygraph