Use dict versioning in Py3.6+ to reduce the overhead of checking for the...

Use dict versioning in Py3.6+ to reduce the overhead of checking for the "C-line in tracebacks" runtime option.

Cython/Utility/Exceptions.c

@@ -611,7 +611,7 @@ static int __Pyx_CLineForTraceback(PyThreadState *tstate, int c_line);/*proto*/
 //@substitute: naming
 
 #ifndef CYTHON_CLINE_IN_TRACEBACK
-static int __Pyx_CLineForTraceback(CYTHON_UNUSED PyThreadState *tstate, int c_line) {
+static int __Pyx_CLineForTraceback(PyThreadState *tstate, int c_line) {
     PyObject *use_cline;
     PyObject *ptype, *pvalue, *ptraceback;
 #if CYTHON_COMPILING_IN_CPYTHON
@@ -622,7 +622,9 @@ static int __Pyx_CLineForTraceback(CYTHON_UNUSED PyThreadState *tstate, int c_li
 #if CYTHON_COMPILING_IN_CPYTHON
     cython_runtime_dict = _PyObject_GetDictPtr(${cython_runtime_cname});
     if (likely(cython_runtime_dict)) {
-      use_cline = __Pyx_PyDict_GetItemStr(*cython_runtime_dict, PYIDENT("cline_in_traceback"));
+        __PYX_PY_DICT_LOOKUP_IF_MODIFIED(
+        use_cline, *cython_runtime_dict,
+        __Pyx_PyDict_GetItemStr(*cython_runtime_dict, PYIDENT("cline_in_traceback")))
     } else
 #endif
     {
@@ -639,7 +641,7 @@ static int __Pyx_CLineForTraceback(CYTHON_UNUSED PyThreadState *tstate, int c_li
         c_line = 0;
         PyObject_SetAttr(${cython_runtime_cname}, PYIDENT("cline_in_traceback"), Py_False);
     }
-    else if (PyObject_Not(use_cline) != 0) {
+    else if (use_cline == Py_False || (use_cline != Py_True && PyObject_Not(use_cline) != 0)) {
         c_line = 0;
     }
     __Pyx_ErrRestoreInState(tstate, ptype, pvalue, ptraceback);

Cython/Utility/ModuleSetupCode.c

@@ -79,6 +79,8 @@
   #define CYTHON_PEP489_MULTI_PHASE_INIT 0
   #undef CYTHON_USE_TP_FINALIZE
   #define CYTHON_USE_TP_FINALIZE 0
+  #undef CYTHON_USE_DICT_VERSIONS
+  #define CYTHON_USE_DICT_VERSIONS 0
 
 #elif defined(PYSTON_VERSION)
   #define CYTHON_COMPILING_IN_PYPY 0
@@ -118,6 +120,8 @@
   #define CYTHON_PEP489_MULTI_PHASE_INIT 0
   #undef CYTHON_USE_TP_FINALIZE
   #define CYTHON_USE_TP_FINALIZE 0
+  #undef CYTHON_USE_DICT_VERSIONS
+  #define CYTHON_USE_DICT_VERSIONS 0
 
 #else
   #define CYTHON_COMPILING_IN_PYPY 0
@@ -181,6 +185,9 @@
   #ifndef CYTHON_USE_TP_FINALIZE
     #define CYTHON_USE_TP_FINALIZE (PY_VERSION_HEX >= 0x030400a1)
   #endif
+  #ifndef CYTHON_USE_DICT_VERSIONS
+    #define CYTHON_USE_DICT_VERSIONS (PY_VERSION_HEX >= 0x030600B1)
+  #endif
 #endif
 
 #if !defined(CYTHON_FAST_PYCCALL)
@@ -407,6 +414,23 @@ class __Pyx_FakeReference {
 #define __Pyx_PyFastCFunction_Check(func) 0
 #endif
 
+#if CYTHON_USE_DICT_VERSIONS
+#define __PYX_GET_DICT_VERSION(dict)  (((PyDictObject*)(dict))->ma_version_tag)
+#define __PYX_PY_DICT_LOOKUP_IF_MODIFIED(VAR, DICT, LOOKUP) { \
+        static PY_UINT64_T __pyx_dict_version = 0; \
+        static PyObject *__pyx_dict_cached_value = NULL; \
+        if (__PYX_GET_DICT_VERSION(DICT) == __pyx_dict_version) { \
+            (VAR) = __pyx_dict_cached_value; \
+        } else { \
+            (VAR) = __pyx_dict_cached_value = (LOOKUP); \
+            __pyx_dict_version = __PYX_GET_DICT_VERSION(DICT); \
+        } \
+    }
+#else
+#define __PYX_GET_DICT_VERSION(dict)  (0)
+#define __PYX_PY_DICT_LOOKUP_IF_MODIFIED(VAR, DICT, LOOKUP)  (VAR) = (LOOKUP);
+#endif
+
 #if CYTHON_COMPILING_IN_PYPY && !defined(PyObject_Malloc)
   #define PyObject_Malloc(s)   PyMem_Malloc(s)
   #define PyObject_Free(p)     PyMem_Free(p)