Updated sum() logic to properly deal with bool tensor (#21421)
Summary:
`torch.tensor([True, False, True], dtype=torch.bool).sum()` should return **2** instead of **True** as it does now.
Tested via unit tests
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21421
Differential Revision: D15674203
Pulled By: izdeby
fbshipit-source-id: b00e3d0ca809c9b92b750adc05632522dad50c74
