This is an experimental ML-based native size estimator, necessary for
computing partial rewards during -Oz inliner policy training. Data
extraction for model training will be provided in a separate patch.
RFC: http://lists.llvm.org/pipermail/llvm-dev/2020-April/140763.html
I would prefer to remove the TF prefix (in the generic code parts). Since we only have a single model evaluator class we could add using ModelEvaluator = TFModelEvaluator here. We then document it saying that new evaluators might be added in which case ModelEvaluator becomes an interface implemented by different classes.