[IR] introduce slice support (#2302)

Author: Johansmm

onnxscript/ir/_linked_list.py

@@ -136,27 +136,12 @@ def __len__(self) -> int:
         )
         return self._length
 
-    def __getitem__(self, index: int) -> T:
+    def __getitem__(self, index: int | slice) -> T:
         """Get the node at the given index.
 
         Complexity is O(n).
         """
-        if index >= self._length or index < -self._length:
-            raise IndexError(
-                f"Index out of range: {index} not in range [-{self._length}, {self._length})"
-            )
-        if index < 0:
-            # Look up from the end of the list
-            iterator = reversed(self)
-            item = next(iterator)
-            for _ in range(-index - 1):
-                item = next(iterator)
-        else:
-            iterator = iter(self)  # type: ignore[assignment]
-            item = next(iterator)
-            for _ in range(index):
-                item = next(iterator)
-        return item
+        return tuple(self)[index]
 
     def _insert_one_after(
         self,

onnxscript/ir/_linked_list_test.py

@@ -60,6 +60,9 @@ def test_append_multiple_elements(self):
         self.assertEqual(linked_list[-3], elems[0])
         self.assertEqual(list(linked_list), elems)
         self.assertEqual(list(reversed(linked_list)), list(reversed(elems)))
+        self.assertEqual(list(linked_list[1:2]), elems[1:2])
+        self.assertEqual(list(linked_list[:2]), elems[:2])
+        self.assertEqual(list(linked_list[-2:]), elems[-2:])
 
     def test_extend(self):
         elems = [_TestElement(i) for i in range(3)]
@@ -73,6 +76,9 @@ def test_extend(self):
         self.assertEqual(linked_list[-3], elems[0])
         self.assertEqual(list(linked_list), elems)
         self.assertEqual(list(reversed(linked_list)), list(reversed(elems)))
+        self.assertEqual(list(linked_list[1:2]), elems[1:2])
+        self.assertEqual(list(linked_list[:2]), elems[:2])
+        self.assertEqual(list(linked_list[-2:]), elems[-2:])
 
     @parameterized.parameterized.expand(
         [