root module, so that the convolution structs can be deleted. This
     decreases model size without impacting numerics.

Add/ReLU fusion (blocklisting option
     mobile_optimizer.MobileOptimizerType.FUSE_ADD_RELU): This pass
     finds instances of "relu" ops that follow "add" ops and fuses
     them into a single "add_relu".

for Vulkan Backend, by default, if optimization blocklist is None or
empty, "optimize_for_mobile" will run the following optimization:
   * Automatic GPU Transfer (blocklisting option mobile_optimize
     r.MobileOptimizerType.VULKAN_AUTOMATIC_GPU_TRANSFER): This
     optimization pass rewrites the graph so that moving input and
     output data to and from the GPU becomes part of the model.
"optimize_for_mobile" will also invoke freeze_module pass which only
preserves "forward" method. If you have other method to that needed to
be preserved, add them into the preserved method list and pass into
the method.