The reason this change is here is to make the guard tstate->c_recursion_remaining <= 0 instead of tstate->c_recursion_remaining <= 1. Comparing to zero is generally faster.

It also seems more correct. If c_recursion_remaining is 1, that suggest that there is 1 remaining call, not 0.

The actual number we compare to doesn't really matter, as long as we are consistent.

The idea is that after DEOPT we will end up doing GOTO_ERROR in the original bytecode? (Is that what the comment is saying?)

The comment refers to our obligation to check the C recursion limit for almost all builtin function calls.

We can fulfil that obligation more cheaply this way.