[exyi]

It corresponds to a way more than one branch at instruction level. The branch prediction AFAIK does not care based on what are you branching, it just assumes branches will go in similar sequences as they did last time. If the Python 'if' is never taken, the instruction-level predictor will learn that after the comparison operation, there is an 'if' operation and then another array access operation. If the Python 'if' is unpredictable unpredictable, CPU predictor can't be sure which opcode are we processing after 'if', so there will be penalty.

[mardifoufs]

Is there any public documentation on modern branch prediction algorithms? I know branch prediction is very important to modern CPU so SOTA techniques are probably not public... But it's really amazing what it can do especially considering the "limited" cache sizes that branch predictors have .

[exyi]

I guess it depends on how deep you want to go, I think the real predictors are based on publicly known algorithms such as TAGE. This seems to be nice overview: https://comparch.net/2013/06/30/why-tage-is-the-best/ (it's 2013, so definitely not SOTA, but advanced enough for my taste :) )