How Modern CPUs Efficiently Predict Bytecode Interpreter Loops
2025-07-05
While investigating the performance of a new Python interpreter, the author discovered that modern CPUs can efficiently predict indirect jumps within bytecode interpreter loops. This is achieved through advanced branch predictors like TAGE and ITTAGE. These predictors map the program counter (PC) and its history to past execution behavior, using multiple tables with geometrically increasing history lengths to dynamically choose the best prediction. The author explores applying ITTAGE's principles to coverage-guided fuzzing and program state exploration, suggesting it could lead to better understanding and exploration of interpreters and similar programs.