gh-144145: Add __slots__ object property tracking for the Tier 2 JIT optimizer

[cocolato]

This PR implements symbolic tracking for __slots__ object attributes in the Tier 2 JIT optimizer.

Currently, when the JIT optimizer encounters _LOAD_ATTR_SLOT, it creates a new unknown symbol (<!NULL>) even if the same slot was previously written in the same trace. This prevents the optimizer from:

1. Knowing the type of values loaded from slots
2. Eliminating redundant type guards
3. Performing further type-based optimizations

Before(set PYTHON_OPT_DEBUG=5):

51 abs: _LOAD_ATTR_SLOT (4, target=48, operand0=0x10, ...)
    stack=[..., <Point at 0x...440>]
52 abs: _POP_TOP
    stack=[..., <!NULL at 0x7fb981d874c0>, <Point at 0x...440>]
                ↑↑↑ NOT NULL TYPE

Now:

51 abs: _LOAD_ATTR_SLOT (4, target=48, operand0=0x10, ...)
    stack=[..., <Point slots[2] v131145 at 0x...440>]
52 abs: _POP_TOP
    stack=[..., <compact_int at 0x7f02ba1d6490>, <Point slots[2]>]
                ↑↑↑ we know the exact type

• Issue: Support track __slots__ object and its property in the Tier 2 optimizer #144145

[cocolato]

We might need to adjust this arena_size.

[markshannon]

This PR seems unrelated to the issue. It tracks the internal state of objects, not the uniqueness of references.
Please create a new issue.

Tracking the internal state of objects is tricky, as we need to keep track of where code might escape and invalidate any knowledge prior to the escape. So far, we have only tracked properties of stateless objects, so it isn't an issue.
There is value in tracking the state of objects, but it needs to be done carefully.

In future, I would also advise waiting to see if there is general support on the issue before spending time on the implementation.

[cocolato]

Thanks for reply!

This PR seems unrelated to the issue. It tracks the internal state of objects, not the uniqueness of references.
Please create a new issue.

Sorry, I'm linking to this issue because I discussed the implementation logic with @Fidget-Spinner in this issue, and I think this should be a pre-task for unique reference tracking (if I'm wrong, please point it out, thanks!). I'll create a new issue to link to this PR.

Tracking the internal state of objects is tricky, as we need to keep track of where code might escape and invalidate any knowledge prior to the escape. So far, we have only tracked properties of stateless objects, so it isn't an issue.
There is value in tracking the state of objects, but it needs to be done carefully.

Sorry again for overlooking object escape. I think may be Ken Jin's original requirement was just to add tracking for the Slots object(if I'm wrong, please point it out again, thanks!). Perhaps I should remove the optimization in the _LOAD_ATTR_SLOT section?

In future, I would also advise waiting to see if there is general support on the issue before spending time on the implementation.

Thanks for the reminder. I'll be more careful in the future.

[Fidget-Spinner]

Sorry again for overlooking object escape. I think may be Ken Jin's original requirement was just to add tracking for the Slots object(if I'm wrong, please point it out again, thanks!). Perhaps I should remove the optimization in the _LOAD_ATTR_SLOT section?

Yeah we need to track for escapes. I mentioned it here how to do it #143414 (comment). It got lost in the noise though, so no worries.

@markshannon

In future, I would also advise waiting to see if there is general support on the issue before spending time on the implementation.

I advised @cocolato to embark on this issue. I think there is value in doing it. They waited for me to give my go-ahead before doing it. So I think they didn't do anything wrong.

[cocolato]

Thanks! I will refactor this to also support #144141.

[cocolato]

@Fidget-Spinner Hi, one thing i want to know. Should this PR flag which property escape during escape handling UOPs (e.g. _CALL_*)? This would allow us to reset only those objects instead of resetting all __slot__ objects tracked in s_arena. However, this will made this PR more complex.

[Fidget-Spinner]

Sorry I'm busy for these 2 days. I'll try to review on Saturday. If Mark reviews it earlier, we can go with his ideas.