[New-bugs-announce] [issue24014] Second pass of PyCode_Optimize

[Joe Jevnik]

New submission from Joe Jevnik:

There are a lot of optimizations that are being missed by only running a single pass of PyCode_Optimize. I originally started by trying to optimize for De Morgan's Laws in if tests; however, I realized that the issue actually went away if you run the optimizer twice. I imagine that this would provide a lot of other performance increases because some of the patterns don't show up until the optimizer has already run once. For example:

>>> def f(a, b):
...     if not a and not b:
...         return True
...     return False
... 

On default, this generates:
>>> dis(f)
  2           0 LOAD_FAST                0 (a)
              3 UNARY_NOT
              4 POP_JUMP_IF_FALSE       18
              7 LOAD_FAST                1 (b)
             10 UNARY_NOT
             11 POP_JUMP_IF_FALSE       18

  3          14 LOAD_CONST               1 (True)
             17 RETURN_VALUE

  4     >>   18 LOAD_CONST               2 (False)
             21 RETURN_VALUE


If we run the optimizer again, we can collapse some of the UNARY_NOT -> POP_JUMP_IF_FALSE back into POP_JUMP_IF_TRUE, like this:
>>> dis(f)
  2           0 LOAD_FAST                0 (a)
              3 POP_JUMP_IF_TRUE        16
              6 LOAD_FAST                1 (b)
              9 POP_JUMP_IF_TRUE        16

  3          12 LOAD_CONST               1 (True)
             15 RETURN_VALUE

  4     >>   16 LOAD_CONST               2 (False)
             19 RETURN_VALUE


Also, Python/importlib.h blew up in the diff; should this be included in the patch?

----------
components: Interpreter Core
files: secondpass.patch
keywords: patch
messages: 241626
nosy: llllllllll
priority: normal
severity: normal
status: open
title: Second pass of PyCode_Optimize
type: performance
versions: Python 3.5
Added file: http://bugs.python.org/file39144/secondpass.patch

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue24014>
_______________________________________