diff -r a206f952668e Objects/sliceobject.c
--- a/Objects/sliceobject.c	Thu Aug 08 18:28:53 2013 +0100
+++ b/Objects/sliceobject.c	Thu Aug 22 23:04:23 2013 +0200
@@ -180,20 +180,23 @@
 
 int
 PySlice_GetIndicesEx(PyObject *_r, Py_ssize_t length,
-                     Py_ssize_t *start, Py_ssize_t *stop, Py_ssize_t *step,
-                     Py_ssize_t *slicelength)
+                     Py_ssize_t *_start, Py_ssize_t *_stop, Py_ssize_t *_step,
+                     Py_ssize_t *_slicelength)
 {
     PySliceObject *r = (PySliceObject*)_r;
     /* this is harder to get right than you might think */
 
     Py_ssize_t defstart, defstop;
 
+    /* work with locals so that optimization isn't hindered by aliasing concerns */
+    Py_ssize_t start, stop, step, astep, slicelength;
+
     if (r->step == Py_None) {
-        *step = 1;
+        step = 1;
     }
     else {
-        if (!_PyEval_SliceIndex(r->step, step)) return -1;
-        if (*step == 0) {
+        if (!_PyEval_SliceIndex(r->step, &step)) return -1;
+        if (step == 0) {
             PyErr_SetString(PyExc_ValueError,
                             "slice step cannot be zero");
             return -1;
@@ -203,46 +206,51 @@
          * guards against later undefined behaviour resulting from code that
          * does "step = -step" as part of a slice reversal.
          */
-        if (*step < -PY_SSIZE_T_MAX)
-            *step = -PY_SSIZE_T_MAX;
+        if (step < -PY_SSIZE_T_MAX)
+            step = -PY_SSIZE_T_MAX;
     }
 
-    defstart = *step < 0 ? length-1 : 0;
-    defstop = *step < 0 ? -1 : length;
+    defstart = step < 0 ? length-1 : 0;
+    defstop = step < 0 ? -1 : length;
 
     if (r->start == Py_None) {
-        *start = defstart;
+        start = defstart;
     }
     else {
-        if (!_PyEval_SliceIndex(r->start, start)) return -1;
-        if (*start < 0) *start += length;
-        if (*start < 0) *start = (*step < 0) ? -1 : 0;
-        if (*start >= length)
-            *start = (*step < 0) ? length - 1 : length;
+        if (!_PyEval_SliceIndex(r->start, &start)) return -1;
+        if (start < 0) start += length;
+        if (start < 0) start = (step < 0) ? -1 : 0;
+        if (start >= length)
+            start = (step < 0) ? length - 1 : length;
     }
 
     if (r->stop == Py_None) {
-        *stop = defstop;
+        stop = defstop;
     }
     else {
-        if (!_PyEval_SliceIndex(r->stop, stop)) return -1;
-        if (*stop < 0) *stop += length;
-        if (*stop < 0) *stop = (*step < 0) ? -1 : 0;
-        if (*stop >= length)
-            *stop = (*step < 0) ? length - 1 : length;
+        if (!_PyEval_SliceIndex(r->stop, &stop)) return -1;
+        if (stop < 0) stop += length;
+        if (stop < 0) stop = (step < 0) ? -1 : 0;
+        if (stop >= length)
+            stop = (step < 0) ? length - 1 : length;
     }
 
-    if ((*step < 0 && *stop >= *start)
-        || (*step > 0 && *start >= *stop)) {
-        *slicelength = 0;
+    if ((step < 0 && stop >= start)
+        || (step > 0 && start >= stop)) {
+        slicelength = 0;
     }
-    else if (*step < 0) {
-        *slicelength = (*stop-*start+1)/(*step)+1;
+    else if (step < 0) {
+        slicelength = (stop-start+1)/step+1;
     }
     else {
-        *slicelength = (*stop-*start-1)/(*step)+1;
+        slicelength = (stop-start-1)/step+1;
     }
 
+    *_start = start;
+    *_stop = stop;
+    *_step = step;
+    *_slicelength = slicelength;
+
     return 0;
 }