Improve exception-matching speed

- Add a has_subclasscheck class slot
- Add a fast path for when the exception matches exactly (though
  we have to check that there isn't a metaclass involved first).

src/capi/abstract.cpp

@@ -797,8 +797,15 @@ extern "C" int PyObject_IsSubclass(PyObject* derived, PyObject* cls) noexcept {
         return r;
     }
     if (!(PyClass_Check(cls) || PyInstance_Check(cls))) {
-        PyObject* checker;
-        checker = _PyObject_LookupSpecial(cls, "__subclasscheck__", &name);
+        PyObject* checker = NULL;
+        if (cls->cls->has_subclasscheck) {
+            checker = _PyObject_LookupSpecial(cls, "__subclasscheck__", &name);
+            if (!checker && PyErr_Occurred())
+                return -1;
+
+            assert(checker);
+        }
+
         if (checker != NULL) {
             PyObject* res;
             int ok = -1;

src/capi/typeobject.cpp

@@ -1645,6 +1645,7 @@ static slotdef slotdefs[]
         TPSLOT("__del__", tp_del, slot_tp_del, NULL, ""),
         FLSLOT("__class__", has___class__, NULL, NULL, "", PyWrapperFlag_BOOL),
         FLSLOT("__instancecheck__", has_instancecheck, NULL, NULL, "", PyWrapperFlag_BOOL),
+        FLSLOT("__subclasscheck__", has_subclasscheck, NULL, NULL, "", PyWrapperFlag_BOOL),
         FLSLOT("__getattribute__", has_getattribute, NULL, NULL, "", PyWrapperFlag_BOOL),
         TPPSLOT("__hasnext__", tpp_hasnext, slotTppHasnext, wrapInquirypred, "hasnext"),
 

src/runtime/capi.cpp

@@ -984,6 +984,13 @@ extern "C" int PyErr_GivenExceptionMatches(PyObject* err, PyObject* exc) noexcep
         err = PyExceptionInstance_Class(err);
 
     if (PyExceptionClass_Check(err) && PyExceptionClass_Check(exc)) {
+        // Pyston addition: fast-path the check for if the exception exactly-matches the specifier.
+        // Note that we have to check that the exception specifier doesn't have a custom metaclass
+        // (ie it's cls is type_cls), since otherwise we would have to check for subclasscheck overloading.
+        // (TODO actually, that should be fast now)
+        if (exc->cls == type_cls && exc == err)
+            return 1;
+
         int res = 0, reclimit;
         PyObject* exception, *value, *tb;
         PyErr_Fetch(&exception, &value, &tb);

src/runtime/types.h

@@ -232,6 +232,7 @@ public:
 
     bool has___class__; // Has a custom __class__ attribute (ie different from object's __class__ descriptor)
     bool has_instancecheck;
+    bool has_subclasscheck;
     bool has_getattribute;
 
     typedef bool (*pyston_inquiry)(Box*);