Remove unneeded dummy test from the set search loop (when the hashes match we...

Remove unneeded dummy test from the set search loop (when the hashes match we know the key is not a dummy).

Include/setobject.h

@@ -14,7 +14,10 @@ extern "C" {
 2. Active:  key != NULL and key != dummy
 3. Dummy:   key == dummy
 
-The hash field of Unused or Dummy slots have no meaning.
+The hash field of Unused slots have no meaning.
+The hash field of Dummny slots are set to -1
+meaning that dummy entries can be detected by
+either entry->key==dummy or by entry->hash==-1.
 */
 
 #define PySet_MINSIZE 8

Objects/setobject.c

@@ -65,8 +65,10 @@ set_lookkey(PySetObject *so, PyObject *key, Py_hash_t hash)
         return entry;
 
     while (1) {
-        if (entry->hash == hash && entry->key != dummy) {         /* dummy match unlikely */
+        if (entry->hash == hash) {
             PyObject *startkey = entry->key;
+            /* startkey cannot be a dummy because the dummy hash field is -1 */
+            assert(startkey != dummy);
             if (startkey == key)
                 return entry;
             if (PyUnicode_CheckExact(startkey)
@@ -83,15 +85,18 @@ set_lookkey(PySetObject *so, PyObject *key, Py_hash_t hash)
             if (cmp > 0)                                          /* likely */
                 return entry;
         }
-        if (entry->key == dummy && freeslot == NULL)
+        if (entry->hash == -1 && freeslot == NULL) {
+            assert(entry->key == dummy);
             freeslot = entry;
+        }
 
         for (j = 1 ; j <= LINEAR_PROBES ; j++) {
             entry = &table[(i + j) & mask];
             if (entry->key == NULL)
                 goto found_null;
-            if (entry->hash == hash && entry->key != dummy) {
+            if (entry->hash == hash) {
                 PyObject *startkey = entry->key;
+                assert(startkey != dummy);
                 if (startkey == key)
                     return entry;
                 if (PyUnicode_CheckExact(startkey)
@@ -108,8 +113,10 @@ set_lookkey(PySetObject *so, PyObject *key, Py_hash_t hash)
                 if (cmp > 0)
                     return entry;
             }
-            if (entry->key == dummy && freeslot == NULL)
+            if (entry->hash == -1 && freeslot == NULL) {
+                assert(entry->key == dummy);
                 freeslot = entry;
+            }
         }
 
         perturb >>= PERTURB_SHIFT;