cache the hash construction on Guard (#110464)
Summary:
X-link: https://github.com/pytorch/pytorch/pull/110464
Approved by: https://github.com/zou3519, https://github.com/voznesenskym
Reviewed By: PaliC
Differential Revision: D49921897
Pulled By: Chillee
fbshipit-source-id: 3bef469e24debf7880a8f2d2e929364f1dd6cd9b
