replace memset with value-initialization (#90048)
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* #89865
* #89852
* #89851
* __->__ #90048
replace memset with value-initialization
Summary:
This is equivalent to zero initialization for any members that are
scalar or have implicit default constructors.
Note that aside from the reset at the beginning, blockmask and
philox_args are not touched by this function.
Test Plan: Rely on CI.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90048
Approved by: https://github.com/drisspg, https://github.com/malfet
