separate op for rowwise counter (#31612)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31612
Count the number recent update on rows. Exponential decay is applied on the counter with decay rate r, such that
r^{counter_halflife} = 0.5;
If counter_halflife is nonpositive, this operator is turned off.
Test Plan: added unittest
Reviewed By: chocjy
Differential Revision: D19217921
fbshipit-source-id: 96d850123e339212cc0e0ef352ea8a1b1bf61dfa
