Note for possible future PR:

We could, at the cost of two bits in tp_flags avoid the version number and combine the ALWAYS_TRUE and NONE specializations.
We need a ALWAYS_TRUE_OR_FALSE and a IS_TRUE bit.
Classes that don't override __bool__ or __len__ and None would set the ALWAYS_TRUE_OR_FALSE bit. The IS_TRUE bit would be set to 0 for None, and to 1 for always true objects.

Rather than check the version number, check the ALWAYS_TRUE_OR_FALSE, then res = (tp_flags & IS_TRUE) ? Py_True : Py_False;

For abi4, we could add a per-object bit to handle immutable objects like ints and strings.

Merging is currently blocked on #106250.

Hey @brandtbucher, I have a question about this PR. In #106393 I had to change the code in POP_JUMP_IF_TRUE/FALSE from

JUMPBY(oparg * Py_IsFalse(cond));

to

if (Py_IsFalse(cond)) {
    JUMP_POP_DISPATCH(oparg, 1);  // Macro that wraps JUMPBY()
}

The reason is that the uop executor currently exits whenever it jumps, and your original code from this PR always jumps.

Did you (or @markshannon) have a reason to prefer the oparg * Py_IsFalse(cond) version over the conditional?

If there's no deep reason I'll keep it the way I coded it up; but if there is (maybe it came out faster in a micro-benchmark?) then I suppose I could fix it another way in the uop interpreter (e.g. only exiting if the jump offset is nonzero).

That the implementation of branches is itself branchless has a certain aesthetic appeal 🙂. TBH, that's the main reason.

The multiplication form will be quicker for unpredictable branches, and slower for predictable ones in the tier 1 interpreter.
I doubt it makes any difference in terms of overall performance, and will likely be irrelevant once the tier 2 interpreter does most of the work.