avoid None check in __Pyx_PyDict_GetItem() when possible

Cython/Compiler/ExprNodes.py

@@ -2685,6 +2685,8 @@ class IndexNode(ExprNode):
                 elif is_slice and base_type in (bytes_type, str_type, unicode_type, list_type, tuple_type):
                     self.type = base_type
                 else:
+                    if base_type is dict_type:
+                        self.base = self.base.as_none_safe_node("'NoneType' object is unsubscriptable")
                     self.type = py_object_type
             else:
                 if base_type.is_ptr or base_type.is_array:

Cython/Utility/ObjectHandling.c

@@ -236,15 +236,10 @@ static CYTHON_INLINE int __Pyx_IterFinish(void) {
 }
 
 /////////////// DictGetItem.proto ///////////////
-//@requires: RaiseNoneIndexingError
 
 #if PY_MAJOR_VERSION >= 3
 static PyObject *__Pyx_PyDict_GetItem(PyObject *d, PyObject* key) {
     PyObject *value;
-    if (unlikely(d == Py_None)) {
-        __Pyx_RaiseNoneIndexingError();
-        return NULL;
-    }
     value = PyDict_GetItemWithError(d, key);
     if (unlikely(!value)) {
         if (!PyErr_Occurred())

tests/run/dict_getitem.pyx

+# mode: run
+# tag: dict, getitem
+
+cimport cython
+
 def test(dict d, index):
     """
     >>> d = { 1: 10 }
@@ -25,11 +30,6 @@ def test(dict d, index):
     """
     return d[index]
 
-cdef class Subscriptable:
-    def __getitem__(self, key):
-        return key
-
-
 def getitem_in_condition(dict d, key, expected_result):
     """
     >>> d = dict(a=1, b=2)
@@ -37,3 +37,20 @@ def getitem_in_condition(dict d, key, expected_result):
     True
     """
     return d[key] is expected_result or d[key] == expected_result
+
+@cython.test_fail_if_path_exists('//NoneCheckNode')
+def getitem_not_none(dict d not None, key):
+    """
+    >>> d = { 1: 10 }
+    >>> test(d, 1)
+    10
+
+    >>> test(d, 2)
+    Traceback (most recent call last):
+    KeyError: 2
+
+    >>> test(d, (1,2))
+    Traceback (most recent call last):
+    KeyError: (1, 2)
+    """
+    return d[key]