Class-decorator form of prim_func_pass broken with tvm-ffi >= 0.1.10 (__slots__ on Object)

[oraluben]

Summary

Starting with apache-tvm-ffi >= 0.1.10, the class-decorator form of tvm.tir.transform.prim_func_pass raises AttributeError: '...' object has no attribute '_inst'.

Reproducer

from tvm.tir.transform import prim_func_pass
from tvm.ir import IRModule
from tvm import tir

@prim_func_pass(opt_level=0, name="MyPass")
class MyPass:
    def transform_function(self, func: tir.PrimFunc, mod: IRModule, ctx) -> tir.PrimFunc:
        return func

p = MyPass()  # AttributeError: 'MyPass' object has no attribute '_inst'

Works with apache-tvm-ffi == 0.1.7, fails with >= 0.1.8.

Root Cause

In tvm/tir/transform/function_pass.py, _wrap_class_function_pass creates PyFunctionPass(PrimFuncPass) and sets self._inst = inst in __init__ (line 53).

With tvm-ffi < 0.1.8 (ctypes backend), Object has no __slots__, so __dict__ exists and arbitrary attributes can be set.

With tvm-ffi >= 0.1.8, tvm_ffi.core.Object and CObject define __slots__ = (). The entire MRO (Object → Pass → PrimFuncPass → PyFunctionPass) has empty __slots__ and no __dict__, so setting _inst raises AttributeError.

# tvm-ffi 0.1.7
Object.__slots__ → not set (has __dict__)

# tvm-ffi 0.1.10
Object.__slots__ = ()      # no __dict__
CObject.__slots__ = ()     # no __dict__

Impact

Any code using the class-decorator form of prim_func_pass:

@prim_func_pass(opt_level=0)
class MyPass:
    def transform_function(self, func, mod, ctx):
        ...

The function-decorator form is unaffected:

def my_pass(func, mod, ctx):
    ...
prim_func_pass(my_pass, opt_level=0)

This pattern is documented in TVM's own docstring (function_pass.py line 112-120) and works on tvm-ffi < 0.1.8.

Possible Fixes

1. Add __slots__ = ("_inst",) to PyFunctionPass in function_pass.py
2. Or ensure Object allows __dict__ in derived classes (e.g. by not setting __slots__ on Object, or by including __dict__ in the slots)

Workaround

Use the function-form instead of class-form:

def _my_pass(func, mod, ctx):
    ...

MyPass = prim_func_pass(_my_pass, opt_level=0, name="MyPass")

Environment

• apache-tvm-ffi 0.1.10
• Python 3.9 - 3.12
• Discovered via TileLang Metal GEMM

[junrushao]

I believe this issue has been reported in tilelang community in tile-ai/tilelang#2020, and the right fix is to cherrypick this commit: apache/tvm@44dbd13. Could you double check?

[oraluben]

@junrushao you're right. tilelang's tvm has been updated but submodule hasn't been updated. This issue is a duplicate with tile-ai/tilelang#2020