[SR] Scope exit guard for memory planner deallocation (#68795)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/68795
This change improves static runtime exception safety. Added a scope exit guard that invokes `MemoryPlanner::deallocate` in its destructor.
Caveat: we have to be really careful with the exception behavior of `MemoryPlanner::deallocate` and `MemoryPlanner`'s constructor, because they're now both potentially called in the destructor of the scope exit guard. Letting exceptions potentially escape destructors is playing with fire since 1) the destructor of `Deallocator` is (implicitly) `noexcept`, 2) even if it wasn't, `std::terminate` will be called if an exception escapes and the stack is already unwinding. To get around this, we wrap the deallocation stuff in a try/catch. If deallocation throws, then we simply reset all of the memory planner stuff and carry on.
There's a catch: the code path that we take when handling the deallocation exception can't throw. However, this code path is much simpler than memory planner construction/deallocation, so it's much easier to manually audit the correctness here.
Test Plan:
**New unit tests**
`buck test caffe2/benchmarks/static_runtime:static_runtime_cpptest`
Reviewed By: hlu1
Differential Revision: D32609915
fbshipit-source-id: 71fbe6994fd573ca6b7dd859b2e6fbd7eeabcd9e
