[Python-Dev] Suggest reverting today's checkin (recursive constant folding in the peephole optimizer) (original) (raw)
Cesare Di Mauro cesare.di.mauro at gmail.com
Sat Mar 12 06:44:08 CET 2011
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2011/3/12 Benjamin Peterson <benjamin at python.org>
2011/3/11 Raymond Hettinger <raymond.hettinger at gmail.com>: > Today, there was a significant check-in to the peephole optimizer that I > think should be reverted: > http://hg.python.org/cpython/rev/14205d0fee45/ > The peephole optimizer pre-dated the introduction of the abstract syntax > tree. Now that we have an AST, the preferred way to implement additional > optimizations is with AST manipulation, upstream from code generation. This > approach is faster and much more reliable than the more brittle approach > of disassembling, analyzing, and rewriting the bytecode created by the > compiler.
The problem is no such AST optimizer exists. It's one thing avoid changing old code because an improved version is in the works or available (say argparse in lieu of getopt) and quite another when no replacement code exists. At the moment, there is little reason not to accept progressive improvements (with sights on overall design as usual) to the code. IMO, Ast or not ast statically optimizing python in any meaningful way is a impossible task anyway. So, a better solution would be to just rip the thing out. -- Regards, Benjamin
It's not true. I already moved almost all peephole optimizations (introducing others, as well) from peephole.c to ast.c<http://code.google.com/p/wpython2/source/browse/Python/ast.c?repo=wpython11>and compiler.c<http://code.google.com/p/wpython2/source/browse/Python/compile.c?repo=wpython11>in WPython 1.1.
Take a look at pages 21-23 of this<http://wpython2.googlecode.com/files/Cleanup%20and%20new%20optimizations%20in%20WPython%201.1.pdf> .
Also, optimizations can be done not only for numbers, but even for tuples, lists, dictionaries, and... slices (pag. 22). See pages 21-24 of this<http://wpython2.googlecode.com/files/Beyond%20Bytecode%20-%20A%20Wordcode-based%20Python.pdf> .
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