Issue #11244: Remove outdated peepholer check that was preventing the peepholer from folding -0 and -0.0. Thanks Eugene Toder for the patch.

Lib/test/test_peepholer.py

@@ -3,6 +3,7 @@ import re
 import sys
 from io import StringIO
 import unittest
+from math import copysign
 
 def disassemble(func):
     f = StringIO()
@@ -207,6 +208,9 @@ class TestTranforms(unittest.TestCase):
     def test_folding_of_unaryops_on_constants(self):
         for line, elem in (
             ('-0.5', '(-0.5)'),                     # unary negative
+            ('-0.0', '(-0.0)'),                     # -0.0
+            ('-(1.0-1.0)','(-0.0)'),                # -0.0 after folding
+            ('-0', '(0)'),                          # -0
             ('~-2', '(1)'),                         # unary invert
             ('+1', '(1)'),                          # unary positive
         ):
@@ -214,6 +218,13 @@ class TestTranforms(unittest.TestCase):
             self.assertIn(elem, asm, asm)
             self.assertNotIn('UNARY_', asm)
 
+        # Check that -0.0 works after marshaling
+        def negzero():
+            return -(1.0-1.0)
+
+        self.assertNotIn('UNARY_', disassemble(negzero))
+        self.assertTrue(copysign(1.0, negzero()) < 0)
+
         # Verify that unfoldables are skipped
         for line, elem in (
             ('-"abc"', "('abc')"),                  # unary negative

Misc/ACKS

@@ -867,6 +867,7 @@ Christian Tismer
 Frank J. Tobin
 R Lindsay Todd
 Bennett Todd
+Eugene Toder
 Matias Torchinsky
 Sandro Tosi
 Richard Townsend

Misc/NEWS

@@ -10,6 +10,9 @@ What's New in Python 3.3 Alpha 1?
 Core and Builtins
 -----------------
 
+- Issue #11244: Remove an unnecessary peepholer check that was preventing
+  negative zeros from being constant-folded properly.
+
 - Issue #11395: io.FileIO().write() clamps the data length to 32,767 bytes on
   Windows if the file is a TTY to workaround a Windows bug. The Windows console
   returns an error (12: not enough space error) on writing into stdout if

Python/peephole.c

@@ -238,7 +238,7 @@ fold_binops_on_constants(unsigned char *codestr, PyObject *consts, PyObject **ob
 static int
 fold_unaryops_on_constants(unsigned char *codestr, PyObject *consts, PyObject *v)
 {
-    PyObject *newconst=NULL/*, *v*/;
+    PyObject *newconst;
     Py_ssize_t len_consts;
     int opcode;
 
@@ -250,9 +250,7 @@ fold_unaryops_on_constants(unsigned char *codestr, PyObject *consts, PyObject *v
     opcode = codestr[3];
     switch (opcode) {
         case UNARY_NEGATIVE:
-            /* Preserve the sign of -0.0 */
-            if (PyObject_IsTrue(v) == 1)
-                newconst = PyNumber_Negative(v);
+            newconst = PyNumber_Negative(v);
             break;
         case UNARY_INVERT:
             newconst = PyNumber_Invert(v);