Backport:

Tim found that once test_longexp has run, test_sort takes very much
longer to run than normal.  A profiler run showed that this was due to
PyFrame_New() taking up an unreasonable amount of time.  A little
thinking showed that this was due to the while loop clearing the space
available for the stack.  The solution is to only clear the local
variables (and cells and free variables), not the space available for
the stack, since anything beyond the stack top is considered to be
garbage anyway.  Also, use memset() instead of a while loop counting
backwards.  This should be a time savings for normal code too!  (By a
probably unmeasurable amount. :-)

diff --git a/Objects/frameobject.c b/Objects/frameobject.c
index b1aa156f81768c497df330b8432a0968e826ef15..8487bf2e75d0b5e0715ad18f5d3e999f481eb154 100644 (file)
--- a/Objects/frameobject.c
+++ b/Objects/frameobject.c
@@ -265,8 +265,6 @@ PyFrame_New(PyThreadState *tstate, PyCodeObject *code, PyObject *globals,
                        if (f == NULL)
                                return NULL;
                }
-               else
-                       extras = f->ob_size;
                _Py_NewReference((PyObject *)f);
        }
        if (builtins == NULL) {
@@ -317,10 +315,10 @@ PyFrame_New(PyThreadState *tstate, PyCodeObject *code, PyObject *globals,
        f->f_ncells = ncells;
        f->f_nfreevars = nfrees;
 
-       while (--extras >= 0)
-               f->f_localsplus[extras] = NULL;
+       extras = f->f_nlocals + ncells + nfrees;
+       memset(f->f_localsplus, 0, extras * sizeof(f->f_localsplus[0]));
 
-       f->f_valuestack = f->f_localsplus + (f->f_nlocals + ncells + nfrees);
+       f->f_valuestack = f->f_localsplus + extras;
        f->f_stacktop = f->f_valuestack;
        _PyObject_GC_TRACK(f);
        return f;