_BUILD_TUPLE is preventing us from optimizing out_POP_CALL_TWO_LOAD_CONST_INLINE_BORROW.
The bytecode is basically:

LOAD_CONSTLOAD_CONST_BUILD_TUPLE_POP_CALL_TWO_LOAD_CONST_INLINE_BORROW

To optimize this, we'd need some special handling for_BUILD_TUPLE inremove_unneeded_uops.

I'm not sure about this define, maybe it's fine to duplicate this logic?

I'll let you choose. We should probably either duplicate it, or just make it a proper function inoptimizer_symbols.c.

We can't inferanything in this case, since the class could doanything in its__instancecheck__ or whatever, so it's no longer side-effect free. Need to bail on the whole optimization at this point.

So I don't think we needall_items_known, either. We can either:

• Break early on our firstTrue, like you do below, and inferTrue.
• Loop overeverything and inferFalse.
• Bail on an unknown thing and inferbool.

I guess we could still do something like this if we knowsym_get_type(item) == &PyType_Type, so it's guaranteed side-effect-free, we just don't know the result of the test. But that seems like a rare case (knowing something is atype, but not which type it actually is).

We can't infer anything in this case, since the class could do anything in itsinstancecheck or whatever, so it's no longer side-effect free. Need to bail on the whole optimization at this point.

Just to check if I understood this point: even if we have something likeisinstance(42, (unknown, int)) we can't inferTrue because ifunknown defines its own__instancecheck__, it would change the semantics of the program if we inferTrue. This is becauseunknown.__instancecheck__ would no longer be called, right?

So basically what you said, once we see an item with an unknown type, we must stop.

Basically, yeah. It's a bit more subtle, though: wecan infer the result to beTrue, but wecan't remove theisinstance call itself.

So we can set areplace_op = false flag or something to keep the inferred value but avoid theREPLACE_OP call. That would at least allow us to remove the following branch inif isinstance(42, (has_metaclass, int)): ..., even if theisinstance call itself remains.

Basically, yeah. It's a bit more subtle, though: we can infer the result to be True, but we can't remove the isinstance call itself.

Awesome, that was pretty much my understanding as well :)

I'll fix the PR hopefully this weekend.

I'll let you choose. We should probably either duplicate it, or just make it a proper function inoptimizer_symbols.c.