* fix -Wno-error=sign-compare warning in gcc8

test=develop

* fix warning in distributed codes

test=develop

* Optimize the elementwise op with CUDA kernels.
test=develop

* Support setting of attr in op config file.
test=develop

* Add the support the setting dtype and initializer in config.
test=develop

* Save workspace.

* Add initializer "zeros".
test=develop

* Fix compiling error.

* Support the use of existed file to initailize tensor in op_tester.

* Use eigen to optimize the elementwise_add/mul for the case that x and y have the same dims.
test=develop

- Support setting attr in config
- Support setting dtype and initializer for input in config
test=develop

- Support setting attr in config
- Support setting dtype and initializer for input in config
test=develop

Optimize the CUDA implementation of sequence_expand op by reduce the times of copying lod data from CPU to GPU. (#15493)

* Optimize the CUDA implementation of sequence_expand op by reduce the times of copying lod data from CPU to GPU.
test=develop

* Refine the op benchmark to support setting lod in config.
test=develop

* Initialize the benchmark tester for operator.
test=develop

* Rearrange the codes.
test=develop