Patches item #1346238, was opened at 2005-11-02 10:49 Message generated for change (Comment added) made by nnorwitz You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=305470&aid=1346238&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: Performance >Group: Python 2.6 Status: Open Resolution: None >Priority: 6 Submitted By: Rune Holm (titanstar) Assigned to: Neal Norwitz (nnorwitz) Summary: A constant folding optimization pass for the AST Initial Comment: This patch adds the following: A visitor interface generalized from the existing ast pass code in order to make it easy to write ast passes that only care about specific node types. A constant folding pass that looks for operations involving number or string literals, and calculates these at compile time. Example code snippets that this pass will optimize: 3 + 4 + x => 7 + x 2 ** 2 ** 2 => 16 4 and 5 and x and 6 => x and 6 4 or 5 or x => 4 4 and 5 and ~6 => -7 When combined with patch 1346214, the compiler will also optimize statements like if 2**2**2 - 16: expensive_computation() => nothing The patch adds two new files: Include/optimize.h and Python.optimize.c. This was done because I anticipate adding more AST optimizations later using the same visitor interface, and Python/compile.c is already very crowded with byte code generation and bytecode optimization. If new files aren't desired, I could easily change the pass to add the extra code to compile.c This patch combined with patch 1346214 passes the unit tests on all the platforms I've tested it on, namely: macos 10.3/ppc linux/x86 linux/amd64 linux/ppc linux/ia64 valgrind on linux/x86 does not reveal any additional leaks or uninitialized accesses that aren't already in the svn head. ---------------------------------------------------------------------- >Comment By: Neal Norwitz (nnorwitz) Date: 2006-07-30 10:02 Message: Logged In: YES user_id=33168 Shoot. I missed this. Bumping priority so hopefully I will remember to take a look at this after 2.5 is out. We still need to split up compile.c along the lines of Jeremy's 2006 PyCon presentation (1-2 extra files). I think one extra file was for assembly. I don't remember the details now. ---------------------------------------------------------------------- Comment By: Georg Brandl (gbrandl) Date: 2006-05-17 08:54 Message: Logged In: YES user_id=849994 Candidate for Iceland? ---------------------------------------------------------------------- Comment By: Raymond Hettinger (rhettinger) Date: 2006-02-19 09:12 Message: Logged In: YES user_id=80475 I'm +1 on the idea, but won't have an opportunity to review the patch in detail (to check for possible semantic changes). Neal, what do you think? ---------------------------------------------------------------------- Comment By: Rune Holm (titanstar) Date: 2006-02-19 05:35 Message: Logged In: YES user_id=858364 It avoids generating constant objects with sizes above 20 (in a similar fashion as the bytecode peepholer), and checks whether the operand of unary minus is non-zero in order to avoid changing -0.0. As for the bytecode peephole optimizer, this AST constant folder performs quite similar optimizations, but optimizes partially constant and/or and comparative expressions in addition. This patch should however not be seen as a replacement for the bytecode constant folder, but rather as a complement. An optimizing compiler typically contains many forms of constant folding in the different phases of compilation, since many later optimizations benefit from constant folding (warranting early constant folding), and some optimizations might emit code that benefit from constant folding again (warranting late constant folding). For an example of the former, consider the statement if 1-1: some_code() both passes are able to transform this into if 0: some_code() but since the AST constant folder is run before the dead code eliminator at <http://python.org/sf/1346214>, these two together are able to optimize the if statement away altogether. Note that this patch probably won't apply cleanly anymore, since it was written three months ago and the AST code has undergone quite a few changes since then. But if there is interest in applying this patch, I'll gladly update it for the current trunk. ---------------------------------------------------------------------- Comment By: Raymond Hettinger (rhettinger) Date: 2006-02-19 02:09 Message: Logged In: YES user_id=80475 This should be compared to the constant folding already added to Py2.5 via the peepholer: dis.dis(compile('x=2+3', '', 'exec')) Also, make sure it doesn't go over the top consuming memory for the likes of: '-' * 100 (None,)*2000 Both of those should not be optimized away at compile-time. Also, be sure not optimize away -0.0. Thet is not the same as +0.0. The distinction is important for branch cuts in cmath. ---------------------------------------------------------------------- Comment By: Georg Brandl (birkenfeld) Date: 2006-02-19 01:41 Message: Logged In: YES user_id=1188172 Neal, what do you think of this? ---------------------------------------------------------------------- Comment By: Rune Holm (titanstar) Date: 2005-11-06 12:42 Message: Logged In: YES user_id=858364 Sorry, I'm new to the sourceforge patch tracker. The patch should be attached now. ---------------------------------------------------------------------- Comment By: Simon Dahlbacka (sdahlbac) Date: 2005-11-06 11:10 Message: Logged In: YES user_id=750513 the actual patch is missing... ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=305470&aid=1346238&group_id=5470 _______________________________________________ Patches mailing list Patches@python.org http://mail.python.org/mailman/listinfo/patches
