Micro-optimize TypeTraverserVisitor

Specialize for concrete sequence types (`list` and `tuple`) for faster
iteration, since the traversal code is very hot.

I used log tracing (#19457) to identify functions where
PyObject_GetIter was called frequently.

This is a aart of a set of micro-optimizations that improve self check
performance by ~5.5%.

Author: JukkaL

mypy/typetraverser.py

@@ -67,7 +67,7 @@ def visit_param_spec(self, t: ParamSpecType, /) -> None:
         t.default.accept(self)
 
     def visit_parameters(self, t: Parameters, /) -> None:
-        self.traverse_types(t.arg_types)
+        self.traverse_type_list(t.arg_types)
 
     def visit_type_var_tuple(self, t: TypeVarTupleType, /) -> None:
         t.default.accept(self)
@@ -78,11 +78,11 @@ def visit_literal_type(self, t: LiteralType, /) -> None:
     # Composite types
 
     def visit_instance(self, t: Instance, /) -> None:
-        self.traverse_types(t.args)
+        self.traverse_type_tuple(t.args)
 
     def visit_callable_type(self, t: CallableType, /) -> None:
         # FIX generics
-        self.traverse_types(t.arg_types)
+        self.traverse_type_list(t.arg_types)
         t.ret_type.accept(self)
         t.fallback.accept(self)
 
@@ -93,15 +93,15 @@ def visit_callable_type(self, t: CallableType, /) -> None:
             t.type_is.accept(self)
 
     def visit_tuple_type(self, t: TupleType, /) -> None:
-        self.traverse_types(t.items)
+        self.traverse_type_list(t.items)
         t.partial_fallback.accept(self)
 
     def visit_typeddict_type(self, t: TypedDictType, /) -> None:
         self.traverse_types(t.items.values())
         t.fallback.accept(self)
 
     def visit_union_type(self, t: UnionType, /) -> None:
-        self.traverse_types(t.items)
+        self.traverse_type_list(t.items)
 
     def visit_overloaded(self, t: Overloaded, /) -> None:
         self.traverse_types(t.items)
@@ -115,16 +115,16 @@ def visit_callable_argument(self, t: CallableArgument, /) -> None:
         t.typ.accept(self)
 
     def visit_unbound_type(self, t: UnboundType, /) -> None:
-        self.traverse_types(t.args)
+        self.traverse_type_tuple(t.args)
 
     def visit_type_list(self, t: TypeList, /) -> None:
-        self.traverse_types(t.items)
+        self.traverse_type_list(t.items)
 
     def visit_ellipsis_type(self, t: EllipsisType, /) -> None:
         pass
 
     def visit_placeholder_type(self, t: PlaceholderType, /) -> None:
-        self.traverse_types(t.args)
+        self.traverse_type_list(t.args)
 
     def visit_partial_type(self, t: PartialType, /) -> None:
         pass
@@ -136,7 +136,7 @@ def visit_type_alias_type(self, t: TypeAliasType, /) -> None:
         # TODO: sometimes we want to traverse target as well
         # We need to find a way to indicate explicitly the intent,
         # maybe make this method abstract (like for TypeTranslator)?
-        self.traverse_types(t.args)
+        self.traverse_type_list(t.args)
 
     def visit_unpack_type(self, t: UnpackType, /) -> None:
         t.type.accept(self)
@@ -146,3 +146,13 @@ def visit_unpack_type(self, t: UnpackType, /) -> None:
     def traverse_types(self, types: Iterable[Type], /) -> None:
         for typ in types:
             typ.accept(self)
+
+    def traverse_type_list(self, types: list[Type], /) -> None:
+        # Micro-optimization: Specialized for lists
+        for typ in types:
+            typ.accept(self)
+
+    def traverse_type_tuple(self, types: tuple[Type, ...], /) -> None:
+        # Micro-optimization: Specialized for tuples
+        for typ in types:
+            typ.accept(self)