SF Patch #1013667: Cleanup Peepholer Output

* Make a pass to eliminate NOPs.  Produce code that is more readable,
  more compact, and a tiny bit faster.  Makes the peepholer more flexible
  in the scope of allowable transformations.

* With Guido's okay, bumped up the magic number so that this patch gets
  widely exercised before the alpha goes out.

2 files changed, 104 insertions, 2 deletions

diff --git a/Lib/test/test_dis.py b/Lib/test/test_dis.py
index 6d5e054..985c878 100644
--- a/Lib/test/test_dis.py
+++ b/Lib/test/test_dis.py
@@ -18,8 +18,6 @@ dis_f = """\
 
  %-4d         5 LOAD_CONST               1 (1)
               8 RETURN_VALUE
-              9 LOAD_CONST               0 (None)
-             12 RETURN_VALUE
 """%(_f.func_code.co_firstlineno + 1,
      _f.func_code.co_firstlineno + 2)
 
diff --git a/Lib/test/test_peepholer.py b/Lib/test/test_peepholer.py
new file mode 100644
index 0000000..6c1900d
--- /dev/null
+++ b/Lib/test/test_peepholer.py
@@ -0,0 +1,104 @@
+import dis
+import sys
+from cStringIO import StringIO
+import unittest
+
+def disassemble(func):
+    f = StringIO()
+    tmp = sys.stdout
+    sys.stdout = f
+    dis.dis(func)
+    sys.stdout = tmp
+    result = f.getvalue()
+    f.close()
+    return result
+
+def dis_single(line):
+    return disassemble(compile(line, '', 'single'))
+
+class TestTranforms(unittest.TestCase):
+
+    def test_unot(self):
+        # UNARY_NOT JUMP_IF_FALSE POP_TOP  -->  JUMP_IF_TRUE POP_TOP'
+        def unot(x):
+            if not x == 2:
+                del x
+        asm = disassemble(unot)
+        for elem in ('UNARY_NOT', 'JUMP_IF_FALSE'):
+            self.assert_(elem not in asm)
+        for elem in ('JUMP_IF_TRUE', 'POP_TOP'):
+            self.assert_(elem in asm)
+
+    def test_elim_inversion_of_is_or_in(self):
+        for line, elem in (
+            ('not a is b', '(is not)',),
+            ('not a in b', '(not in)',),
+            ('not a is not b', '(is)',),
+            ('not a not in b', '(in)',),
+            ):
+            asm = dis_single(line)
+            self.assert_(elem in asm)
+
+    def test_none_as_constant(self):
+        # LOAD_GLOBAL None  -->  LOAD_CONST None
+        def f(x):
+                None
+                return x
+        asm = disassemble(f)
+        for elem in ('LOAD_GLOBAL',):
+            self.assert_(elem not in asm)
+        for elem in ('LOAD_CONST', '(None)'):
+            self.assert_(elem in asm)
+
+    def test_while_one(self):
+        # Skip over:  LOAD_CONST trueconst  JUMP_IF_FALSE xx  POP_TOP
+        def f():
+                while 1:
+                        pass
+                return list
+        asm = disassemble(f)
+        for elem in ('LOAD_CONST', 'JUMP_IF_FALSE'):
+            self.assert_(elem not in asm)
+        for elem in ('JUMP_ABSOLUTE',):
+            self.assert_(elem in asm)
+
+    def test_pack_unpack(self):
+        for line, elem in (
+            ('a, = 1,', 'LOAD_CONST',),
+            ('a, b = 1, 2', 'ROT_TWO',),
+            ('a, b, c = 1, 2, 3', 'ROT_THREE',),
+            ):
+            asm = dis_single(line)
+            self.assert_(elem in asm)
+            self.assert_('BUILD_TUPLE' not in asm)
+            self.assert_('UNPACK_TUPLE' not in asm)
+
+    def test_elim_extra_return(self):
+        # RETURN LOAD_CONST None RETURN  -->  RETURN
+        def f(x):
+            return x
+        asm = disassemble(f)
+        self.assert_('LOAD_CONST' not in asm)
+        self.assert_('(None)' not in asm)
+        self.assertEqual(asm.split().count('RETURN_VALUE'), 1)
+
+
+
+def test_main(verbose=None):
+    import sys
+    from test import test_support
+    test_classes = (TestTranforms,)
+    test_support.run_unittest(*test_classes)
+
+    # verify reference counting
+    if verbose and hasattr(sys, "gettotalrefcount"):
+        import gc
+        counts = [None] * 5
+        for i in xrange(len(counts)):
+            test_support.run_unittest(*test_classes)
+            gc.collect()
+            counts[i] = sys.gettotalrefcount()
+        print counts
+
+if __name__ == "__main__":
+    test_main(verbose=True)