Refactor create_type_object so that most of the code is monomorphic

In pyca/cryptography this function is the PyO3#1 source of lines of generated LLVM IR, because it is duplicated 42x (and growing!). By rewriting it so most of the logic is monomorphic, we reduce the generated LLVM IR for this function by 4x.

src/pyclass/create_type_object.rs

@@ -33,17 +33,34 @@ pub(crate) fn create_type_object<T>(py: Python<'_>) -> PyResult<PyClassTypeObjec
 where
     T: PyClass,
 {
-    unsafe {
+    // Written this way to monomorphize the majority of the logic.
+    #[allow(clippy::too_many_arguments)]
+    unsafe fn inner(
+        py: Python<'_>,
+        base: *mut ffi::PyTypeObject,
+        dealloc: unsafe extern "C" fn(*mut ffi::PyObject),
+        dealloc_with_gc: unsafe extern "C" fn(*mut ffi::PyObject),
+        is_mapping: bool,
+        is_sequence: bool,
+        doc: &'static CStr,
+        dict_offset: Option<ffi::Py_ssize_t>,
+        weaklist_offset: Option<ffi::Py_ssize_t>,
+        is_basetype: bool,
+        items_iter: PyClassItemsIter,
+        name: &'static str,
+        module: Option<&'static str>,
+        size_of: usize,
+    ) -> PyResult<PyClassTypeObject> {
         PyTypeBuilder {
             slots: Vec::new(),
             method_defs: Vec::new(),
             getset_builders: HashMap::new(),
             cleanup: Vec::new(),
-            tp_base: T::BaseType::type_object_raw(py),
-            tp_dealloc: tp_dealloc::<T>,
-            tp_dealloc_with_gc: tp_dealloc_with_gc::<T>,
-            is_mapping: T::IS_MAPPING,
-            is_sequence: T::IS_SEQUENCE,
+            tp_base: base,
+            tp_dealloc: dealloc,
+            tp_dealloc_with_gc: dealloc_with_gc,
+            is_mapping,
+            is_sequence,
             has_new: false,
             has_dealloc: false,
             has_getitem: false,
@@ -55,11 +72,30 @@ where
             #[cfg(all(not(Py_3_9), not(Py_LIMITED_API)))]
             buffer_procs: Default::default(),
         }
-        .type_doc(T::doc(py)?)
-        .offsets(T::dict_offset(), T::weaklist_offset())
-        .set_is_basetype(T::IS_BASETYPE)
-        .class_items(T::items_iter())
-        .build(py, T::NAME, T::MODULE, std::mem::size_of::<PyCell<T>>())
+        .type_doc(doc)
+        .offsets(dict_offset, weaklist_offset)
+        .set_is_basetype(is_basetype)
+        .class_items(items_iter)
+        .build(py, name, module, size_of)
+    }
+
+    unsafe {
+        inner(
+            py,
+            T::BaseType::type_object_raw(py),
+            tp_dealloc::<T>,
+            tp_dealloc_with_gc::<T>,
+            T::IS_MAPPING,
+            T::IS_SEQUENCE,
+            T::doc(py)?,
+            T::dict_offset(),
+            T::weaklist_offset(),
+            T::IS_BASETYPE,
+            T::items_iter(),
+            T::NAME,
+            T::MODULE,
+            std::mem::size_of::<PyCell<T>>(),
+        )
     }
 }