Add BOOL_FALSE guard to optimize empty container case (#95248)
There is a fast way to implement a guard for an empty dict, which is to check its bool() value.
However, we can't use this guard in general, since we can only safely apply it at runtime if the runtime value actually is a dict (or, another type that works with 'bool' in the same way). A counterexample is when a tensor is passed instead of a dict, and throws on bool() operator.
So we can put a type check in the guard, but that is slow enough it defeats the purpose.
Instead, we note that for the case of NNModuleVariables (which are specialized NNModules not unspecialized ones), we already have a hook in place to invalidate the guards if setattr is called. I am claiming that setattr is the only way that the type of a property on an NNModule could change. If I'm right, then it's safe to (a) only use this guard for NNModuleVariables, (b) not do a type check inside the guard.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/95248
Approved by: https://github.com/voznesenskym
