[Pass] New Python ExprVisitor/ExprMutator! (#190)

Add decorators `visitor` and `mutator` to help users create `ExprVisitor` and `ExprMutator` in Python. Users can customize visit/rewrite/post-order-rewrite function in Python.  `PyExprVisitor` and `PyExprMutator` lists the functions users can customize.

python/tvm/meta_schedule/utils.py

@@ -75,14 +75,27 @@ def _extract(inst: type, name: str):
         def method(*args, **kwargs):
             return getattr(inst, name)(*args, **kwargs)
 
-        if getattr(base, name) is getattr(cls, name) and name != "__str__":
-            # for task scheduler return None means calling default function
-            # otherwise it will trigger a TVMError of method not implemented
-            # on the c++ side when you call the method, __str__ not required
-            return None
-        return method
+        for inherit_cls, base_cls in zip(cls.__mro__, cls.__mro__[1:]):
+            # extract functions that differ from the base class
+            if not hasattr(base_cls, name):
+                continue
+            if getattr(base_cls, name) is getattr(inherit_cls, name) and name != "__str__":
+                continue
+            return method
+
+        # for task scheduler return None means calling default function
+        # otherwise it will trigger a TVMError of method not implemented
+        # on the c++ side when you call the method, __str__ not required
+        return None
 
     assert isinstance(cls.__base__, type)
+    if hasattr(cls, "_type") and cls._type == "TVMDerivedObject":
+        raise TypeError(
+            (
+                f"Inheritance from a decorated object `{cls.__name__}` is not allowed. "
+                f"Please inherit from `{cls.__name__}._cls`."
+            )
+        )
     assert hasattr(
         cls, "_tvm_metadata"
     ), "Please use the user-facing method overriding class, i.e., PyRunner."
@@ -95,6 +108,9 @@ def method(*args, **kwargs):
     class TVMDerivedObject(metadata["cls"]):  # type: ignore
         """The derived object to avoid cyclic dependency."""
 
+        _cls = cls
+        _type = "TVMDerivedObject"
+
         def __init__(self, *args, **kwargs):
             """Constructor."""
             self.handle = None
@@ -111,12 +127,22 @@ def __init__(self, *args, **kwargs):
             # using weakref to avoid cyclic dependency
             self._inst._outer = weakref.ref(self)
 
-        def __getattr__(self, name: str):
-            """Bridge the attribute function."""
-            try:
-                return self._inst.__getattribute__(name)
-            except AttributeError:
-                return super(TVMDerivedObject, self).__getattr__(name)
+        def __getattr__(self, name):
+            # fall back to instance attribute if there is not any
+            # return self._inst.__getattribute__(name)
+            import inspect  # pylint: disable=import-outside-toplevel
+
+            result = self._inst.__getattribute__(name)
+            if inspect.ismethod(result):
+
+                def method(*args, **kwargs):
+                    return result(*args, **kwargs)
+
+                # set __own__ to aviod implicit deconstruction
+                setattr(method, "__own__", self)
+                return method
+
+            return result
 
         def __setattr__(self, name, value):
             if name not in ["_inst", "key", "handle"]:

python/tvm/relax/__init__.py

@@ -77,6 +77,5 @@
 
 # ExprFunctor
 ExprFunctor = expr_functor.ExprFunctor
-ExprVisitor = expr_functor.ExprVisitor
-ExprMutatorBase = expr_functor.ExprMutatorBase
-ExprMutator = expr_functor.ExprMutator
+PyExprVisitor = expr_functor.PyExprVisitor
+PyExprMutator = expr_functor.PyExprMutator