Optimise list.extend([...]) into list.extend((...)) since tuples are more efficient than lists.

Cython/Compiler/Optimize.py

@@ -2829,12 +2829,16 @@ class OptimizeBuiltinCalls(Visitor.NodeRefCleanupMixin,
         if len(args) != 2:
             return node
         obj, value = args
-        if not value.is_sequence_constructor or value.mult_factor is not None:
+        if not value.is_sequence_constructor:
             return node
         items = list(value.args)
-        if len(items) > 4:
-            # Appending wins for short sequences.
+        if value.mult_factor is not None or len(items) > 4:
+            # Appending wins for short sequences but might slow down for multiple resize operations.
             # Ignorantly assume that this a good enough limit that avoids repeated resizing.
+            if isinstance(value, ExprNodes.ListNode):
+                # At least avoid the list building and use a faster tuple instead.
+                tuple_node = args[1].as_tuple().analyse_types(self.current_env(), skip_children=True)
+                Visitor.recursively_replace_node(node, args[1], tuple_node)
             return node
         wrapped_obj = self._wrap_self_arg(obj, function, is_unbound_method, 'extend')
         if not items: