Issue #15368: make bytecode generation deterministic.

meadori · meadori · commit 1f336adc8f21 · 2012-07-18T14:28:55.000-05:00
diff --git a/Misc/NEWS b/Misc/NEWS
@@ -10,6 +10,9 @@ What's New in Python 3.3.0 Beta 2?
 Core and Builtins
 -----------------
 
+- Issue #15368: An issue that caused bytecode generation to be
+  non-deterministic has been fixed.
+
 - Issue #15202: Consistently use the name "follow_symlinks" for
   new parameters in os and shutil functions.
 
diff --git a/Python/compile.c b/Python/compile.c
@@ -397,29 +397,48 @@ each key.
 static PyObject *
 dictbytype(PyObject *src, int scope_type, int flag, int offset)
 {
-    Py_ssize_t pos = 0, i = offset, scope;
+    Py_ssize_t pos = 0, i = offset, scope, num_keys, key_i;
     PyObject *k, *v, *dest = PyDict_New();
+    PyObject *sorted_keys;
 
     assert(offset >= 0);
     if (dest == NULL)
         return NULL;
 
-    while (PyDict_Next(src, &pos, &k, &v)) {
+    /* Sort the keys so that we have a deterministic order on the indexes
+       saved in the returned dictionary.  These indexes are used as indexes
+       into the free and cell var storage.  Therefore if they aren't
+       deterministic, then the generated bytecode is not deterministic.
+    */
+    sorted_keys = PyDict_Keys(src);
+    if (sorted_keys == NULL)
+        return NULL;
+    if (PyList_Sort(sorted_keys) != 0) {
+        Py_DECREF(sorted_keys);
+        return NULL;
+    }
+    num_keys = PyList_GET_SIZE(src);
+
+    for (key_i = 0; key_i < num_keys; key_i++) {
         /* XXX this should probably be a macro in symtable.h */
         long vi;
+        k = PyList_GET_ITEM(sorted_keys, key_i);
+        v = PyDict_GetItem(src, k);
         assert(PyLong_Check(v));
         vi = PyLong_AS_LONG(v);
         scope = (vi >> SCOPE_OFFSET) & SCOPE_MASK;
 
         if (scope == scope_type || vi & flag) {
             PyObject *tuple, *item = PyLong_FromLong(i);
             if (item == NULL) {
+                Py_DECREF(sorted_keys);
                 Py_DECREF(dest);
                 return NULL;
             }
             i++;
             tuple = PyTuple_Pack(2, k, k->ob_type);
             if (!tuple || PyDict_SetItem(dest, tuple, item) < 0) {
+                Py_DECREF(sorted_keys);
                 Py_DECREF(item);
                 Py_DECREF(dest);
                 Py_XDECREF(tuple);
@@ -429,6 +448,7 @@ dictbytype(PyObject *src, int scope_type, int flag, int offset)
             Py_DECREF(tuple);
         }
     }
+    Py_DECREF(sorted_keys);
     return dest;
 }
 
