[PyTorch][JIT] Use stack.pop_back() instead of pop(stack) for DROP (#69326)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/69326
Looks like this really is slightly cheaper (see assembly diff screenshot in internal test plan). The problem is that `pop()` returns the value, so we have to spend instructions moving it out of the stack and then destroying it via a local.
ghstack-source-id: 144641680
Test Plan:
{F684148304}
CI
Reviewed By: zhxchen17
Differential Revision: D32812841
fbshipit-source-id: e9e43458d3364842f67edd43e43575a1f72e3cb0
