Avoid some redundant thread state lookups.

Supply a general macro for fast exception setting without value (e.g. StopIteration).

Cython/Utility/Coroutine.c

@@ -725,14 +725,18 @@ static CYTHON_INLINE void __Pyx_Coroutine_ResetFrameBackpointer(__pyx_CoroutineO
 
 static CYTHON_INLINE
 PyObject *__Pyx_Coroutine_MethodReturn(CYTHON_UNUSED PyObject* gen, PyObject *retval) {
-    if (unlikely(!retval && !PyErr_Occurred())) {
-        // method call must not terminate with NULL without setting an exception
-        #ifdef __Pyx_AsyncGen_USED
-        if (__Pyx_AsyncGen_CheckExact(gen)) {
-            PyErr_SetNone(__Pyx_PyExc_StopAsyncIteration);
-        } else
-        #endif
-        PyErr_SetNone(PyExc_StopIteration);
+    if (unlikely(!retval)) {
+        __Pyx_PyThreadState_declare
+        __Pyx_PyThreadState_assign
+        if (!__Pyx_PyErr_Occurred()) {
+            // method call must not terminate with NULL without setting an exception
+            PyObject *exc = PyExc_StopIteration;
+            #ifdef __Pyx_AsyncGen_USED
+            if (__Pyx_AsyncGen_CheckExact(gen))
+                exc = __Pyx_PyExc_StopAsyncIteration;
+            #endif
+            __Pyx_PyErr_SetNone(exc);
+        }
     }
     return retval;
 }

Cython/Utility/Exceptions.c

@@ -79,8 +79,15 @@ static CYTHON_INLINE int __Pyx_PyErr_ExceptionMatchesInState(PyThreadState* tsta
 static CYTHON_INLINE void __Pyx_ErrRestoreInState(PyThreadState *tstate, PyObject *type, PyObject *value, PyObject *tb); /*proto*/
 static CYTHON_INLINE void __Pyx_ErrFetchInState(PyThreadState *tstate, PyObject **type, PyObject **value, PyObject **tb); /*proto*/
 
+#if CYTHON_COMPILING_IN_CPYTHON
+#define __Pyx_PyErr_SetNone(exc) (Py_INCREF(exc), __Pyx_ErrRestore((exc), NULL, NULL))
+#else
+#define __Pyx_PyErr_SetNone(exc) PyErr_SetNone(exc)
+#endif
+
 #else
 #define __Pyx_PyErr_Clear() PyErr_Clear()
+#define __Pyx_PyErr_SetNone(exc) PyErr_SetNone(exc)
 #define __Pyx_ErrRestoreWithState(type, value, tb)  PyErr_Restore(type, value, tb)
 #define __Pyx_ErrFetchWithState(type, value, tb)  PyErr_Fetch(type, value, tb)
 #define __Pyx_ErrRestore(type, value, tb)  PyErr_Restore(type, value, tb)

Cython/Utility/ObjectHandling.c

@@ -161,12 +161,7 @@ static PyObject *__Pyx_PyIter_Next2Default(PyObject* defval) {
         Py_INCREF(defval);
         return defval;
     }
-#if CYTHON_COMPILING_IN_CPYTHON
-    Py_INCREF(PyExc_StopIteration);
-    __Pyx_ErrRestore(PyExc_StopIteration, NULL, NULL);
-#else
-    PyErr_SetNone(PyExc_StopIteration);
-#endif
+    __Pyx_PyErr_SetNone(PyExc_StopIteration);
     return NULL;
 }