add substract of max and testcase (#63132)
Summary:
As discussed here https://github.com/pytorch/pytorch/pull/62897, in the path of BF16/non-last-dim Softmax, we miss the subtractions of max value which will cause the overflow in the `exp()` calculation when the value of input tensor is large, such as `1000.0`.
To avoid this issue, we add the subtractions of max value and the corresponding test cases in this PR.
Note w/o subtractions of max value(accidental reverts or changes), we will get the underlying error message of the test case
```
AssertionError: False is not true : Tensors failed to compare as equal!With rtol=0.05 and atol=0.05, found 103984 element(s) (out of 126720) whose difference(s) exceeded the margin of error (including 103984 nan comparisons). The greatest difference was nan (0.0 vs. nan), which occurred at index (0, 0, 0, 1).
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63132
Reviewed By: VitalyFedyunin
Differential Revision: D30280792
Pulled By: cpuhrsch
fbshipit-source-id: 722821debf983bbb4fec878975fa8a4da0d1d866
