Teach the peepholer to fold unary operations on constants.

Afterwards, -0.5 loads in a single step and no longer requires a runtime
UNARY_NEGATIVE operation.

1 files changed, 19 insertions, 0 deletions

diff --git a/Lib/test/test_peepholer.py b/Lib/test/test_peepholer.py
index 34bd99f2a4..4385a84c1f 100644
--- a/Lib/test/test_peepholer.py
+++ b/Lib/test/test_peepholer.py
@@ -133,6 +133,25 @@ class TestTranforms(unittest.TestCase):
         asm = dis_single('a="x"*1000')
         self.assert_('(1000)' in asm)
 
+    def test_folding_of_unaryops_on_constants(self):
+        for line, elem in (
+            ('`1`', "('1')"),                       # unary convert
+            ('-0.5', '(-0.5)'),                     # unary negative
+            ('~-2', '(1)'),                         # unary invert
+        ):
+            asm = dis_single(line)
+            self.assert_(elem in asm, asm)
+            self.assert_('UNARY_' not in asm)
+
+        # Verify that unfoldables are skipped
+        for line, elem in (
+            ('-"abc"', "('abc')"),                  # unary negative
+            ('~"abc"', "('abc')"),                  # unary invert
+        ):
+            asm = dis_single(line)
+            self.assert_(elem in asm, asm)
+            self.assert_('UNARY_' in asm)
+
     def test_elim_extra_return(self):
         # RETURN LOAD_CONST None RETURN  -->  RETURN
         def f(x):