optimize BFloat16 elemwise operators CPU: sigmoid, sigmoid_backward, tanh_backward, addcmul, addcdiv (#55221)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/55221
Test Plan: Imported from OSS
Reviewed By: bdhirsh
Differential Revision: D28836797
Pulled By: VitalyFedyunin
fbshipit-source-id: 6b79098c902ffe65d228668118ef36fb49bab800
