Optimize `x in set` using PySet_Contains()

Cython/Compiler/ExprNodes.py

@@ -12197,6 +12197,11 @@ class CmpNode(object):
                 self.special_bool_cmp_utility_code = UtilityCode.load_cached("PyDictContains", "ObjectHandling.c")
                 self.special_bool_cmp_function = "__Pyx_PyDict_ContainsTF"
                 return True
+            elif self.operand2.type is Builtin.set_type:
+                self.operand2 = self.operand2.as_none_safe_node("'NoneType' object is not iterable")
+                self.special_bool_cmp_utility_code = UtilityCode.load_cached("PySetContains", "ObjectHandling.c")
+                self.special_bool_cmp_function = "__Pyx_PySet_ContainsTF"
+                return True
             elif self.operand2.type is Builtin.unicode_type:
                 self.operand2 = self.operand2.as_none_safe_node("'NoneType' object is not iterable")
                 self.special_bool_cmp_utility_code = UtilityCode.load_cached("PyUnicodeContains", "StringTools.c")

Cython/Utility/ObjectHandling.c

@@ -1035,6 +1035,32 @@ static CYTHON_INLINE int __Pyx_PyDict_ContainsTF(PyObject* item, PyObject* dict,
     return unlikely(result < 0) ? result : (result == (eq == Py_EQ));
 }
 
+/////////////// PySetContains.proto ///////////////
+
+static int __Pyx_PySet_ContainsUnhashable(PyObject *set, PyObject *key) {
+    int result = -1;
+    if (PySet_Check(key) && PyErr_ExceptionMatches(PyExc_TypeError)) {
+        /* Convert key to frozenset */
+        PyObject *tmpkey;
+        PyErr_Clear();
+        tmpkey = PyFrozenSet_New(key);
+        if (tmpkey != NULL) {
+            result = PySet_Contains(set, tmpkey);
+            Py_DECREF(tmpkey);
+        }
+    }
+    return result;
+}
+
+static CYTHON_INLINE int __Pyx_PySet_ContainsTF(PyObject* key, PyObject* set, int eq) {
+    int result = PySet_Contains(set, key);
+
+    if (unlikely(result < 0)) {
+        result = __Pyx_PySet_ContainsUnhashable(set, key);
+    }
+    return unlikely(result < 0) ? result : (result == (eq == Py_EQ));
+}
+
 /////////////// PySequenceContains.proto ///////////////
 
 static CYTHON_INLINE int __Pyx_PySequence_ContainsTF(PyObject* item, PyObject* seq, int eq) {