[PyTorch] Return raw ptr from ThreadLocalDebugInfo::get() (#47796)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47796
`ThreadLocalDebugInfo::get()` is a hot function. For example, it is called by `DefaultCPUAllocator::allocate()`. Most callers do not even bother to keep the returned `shared_ptr` around, proving that they have no lifetime issues currently. For the rest, it appears that the only way that the returned pointer could become invalid is if they then called a function that swapped out `ThreadLocalDebugInfo` using `ThreadLocalStateGuard`. There are very few such paths, and it doesn't look like any current callers of `ThreadLocalDebugInfo::get()` needed a `shared_ptr` at all.
ghstack-source-id: 116979577
Test Plan:
1) reviewers to double-check audit of safety
2) run framework overhead benchmarks
Reviewed By: dzhulgakov
Differential Revision: D24902978
fbshipit-source-id: d684737cc2568534cac7cd3fb8d623b971c2fd28
