Patches item #1443159, was opened at 2006-03-04 13:52 Message generated for change (Settings changed) made by rhettinger You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=305470&aid=1443159&group_id=5470
Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. Category: Core (C code) Group: Python 2.5 >Status: Closed >Resolution: Invalid Priority: 5 Private: No Submitted By: Collin Winter (collinwinter) Assigned to: Raymond Hettinger (rhettinger) Summary: Remove bad PREDICT in ceval.c Initial Comment: The current FOR_ITER -> UNPACK_SEQUENCE prediction is only right 6.41% of the time (212 million opcodes analysed). This patch removes it. ---------------------------------------------------------------------- Comment By: Raymond Hettinger (rhettinger) Date: 2006-03-06 19:02 Message: Logged In: YES user_id=80475 Collin, you are welcome to write to me directly to discuss the results of your dynamic analysis. I suspect your results are almost certainly incorrect. The prediction was originally added after a detailed analysis of a great deal of Python code and checking the results of multiple pieces of benchmark code. Please do not arbitrarily start removing these unless you're damned certain the original study was erronenous. Also, I suspect that the given percentage does not reflect the conditional probability of the preceding PREDICT (STORE_FAST). The overwhelming majority of cases needing optimization involve "for x in iterable" where x is a fast local. If that prediction fails, then the next most common case is "for x,y in iterable". The latter is highly likely whenever we know the former has not occured. IOW, the unpack sequence may only come up 6% of the time, but its conditional probability rises above 90% when it follows the other prediction. Also, take some case with dynamic analysis. It is always tricky because it is very difficult to find truly representative code and to not have a single anomalous case run over and over again. ---------------------------------------------------------------------- Comment By: Neal Norwitz (nnorwitz) Date: 2006-03-06 18:42 Message: Logged In: YES user_id=33168 Raymond any comments? ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=305470&aid=1443159&group_id=5470 _______________________________________________ Patches mailing list Patches@python.org http://mail.python.org/mailman/listinfo/patches
