Created on 2008-03-28 04:05 by belopolsky, last changed 2009-11-18 20:10 by rhettinger. This issue is now closed.
|fold-unary.diff||belopolsky, 2008-03-28 04:05||Patch against revision 61983|
|msg64613 - (view)||Author: Alexander Belopolsky (belopolsky) *||Date: 2008-03-28 04:05|
Before: >>> dis(lambda:+2) 1 0 LOAD_CONST 0 (2) 3 UNARY_POSITIVE 4 RETURN_VALUE >>> dis(lambda:not 2) 1 0 LOAD_CONST 0 (2) 3 UNARY_NOT 4 RETURN_VALUE After: >>> dis(lambda:+2) 1 0 LOAD_CONST 1 (2) 3 RETURN_VALUE >>> dis(lambda:not 2) 1 0 LOAD_CONST 1 (False) 3 RETURN_VALUE
|msg64618 - (view)||Author: Raymond Hettinger (rhettinger) *||Date: 2008-03-28 07:25|
It would be helpful if we talked before going further on build-outs to the peephole optimizer. IIRC, we chose to not do this one because it interfered with other more important optimizations. More importantly, we decided that the peepholer is the wrong place to do much of this work. Most of the peepholer is going to be migrated up the chain, after the AST is generated, but before the opcodes are generated. That is a faster, more reliable, and more general approach. The constant folding anti-duplication patch should also not be done for this same reason. That patch slows down compilation and makes it more fragile but does not add speed (just like the dead code elimination patches). When the peepholer is moved-up, the anti- duplication code won't be needed (as you won't need its attendant rescan/rewrite pass of the bytecode). You're writing these faster than I have time to review and likely reject them. Please show some moderation. The peepholer is intentionally very conservative.
|msg64638 - (view)||Author: Alexander Belopolsky (belopolsky) *||Date: 2008-03-28 13:27|
On Fri, Mar 28, 2008 at 3:25 AM, Raymond Hettinger <email@example.com> wrote: > > It would be helpful if we talked before going further on build-outs to > the peephole optimizer. Sure. > IIRC, we chose to not do this one because it > interfered with other more important optimizations. There are two optimization in my patch: one for +<const> and the other not <const>. I think you recall that not <const> optimization could interfere with not a is b --> a is not b and similar transformations. My patch, however does not affect those. With respect to unary +, I don't think it was intentionally omitted: I would think it is more common to use unary + on constants than `..`, but case UNARY_CONVERT is there in 2.x. Constant folding promotes more readable code: 24*60*60 is more obvious than 86400, prefixing positive numbers with + leads to better visual alignment, etc. Users should not be required to think twice about which constant expressions are folded and which are not. Here is another surprise with the current peepholer: 1 0 LOAD_CONST 0 (1) 3 LOAD_CONST 3 (6) 6 BINARY_ADD 7 RETURN_VALUE 1 0 LOAD_CONST 4 (7) 3 RETURN_VALUE I have a fix in the works, but I will wait for your further comments before submitting it. > > More importantly, we decided that the peepholer is the wrong place to > do much of this work. Most of the peepholer is going to be migrated > up the chain, after the AST is generated, but before the opcodes are > generated. That is a faster, more reliable, and more general > approach. > I agree. Constant folding, is an interesting case because peepholer has to duplicate a subset of eval logic. I wonder if the new approach could eliminate that. BTW, what is the rationale for leading +/- not being part of the number literal? Unary +/- optimization seems mostly useful for the simple +/-x case which could be handled by the tokenizer. What is the timeline for that project? Maybe a comment should be placed in peephole.c explaining that there is a plan to move uptimization logic up the compilation chain and announcing a moratorium on further peephole.c work. I am not the only one submitting peephole optimizer patches recently. > You're writing these faster than I have time to review and likely > reject them. Please show some moderation. ok :-) One more peephole optimizer related idea that I have in the pipeline is to implement an option to disable optimization altogether. Having such an option would help debugging/profiling the optimizer and will give users a simple check when they suspect that their code is improperly optimized. I would propose a patch already, but I could not think of a good command line option. Most compilers use -O0, but that would be confusingly similar to -OO. What do you think?
|msg94905 - (view)||Author: Antoine Pitrou (pitrou) *||Date: 2009-11-04 22:02|
Folding UNARY_POSITIVE was done by Raymond in r75601.
|msg95446 - (view)||Author: Raymond Hettinger (rhettinger) *||Date: 2009-11-18 20:10|
Closing this. The Unary Positive is already implemented and there are no known use cases for constant folding a Unary Not.
|2009-11-18 20:10:08||rhettinger||set||status: open -> closed|
resolution: out of date
messages: + msg95446
|2009-11-04 23:35:59||rhettinger||set||assignee: rhettinger|
messages: + msg94905
|2008-03-28 13:27:26||belopolsky||set||messages: + msg64638|
messages: + msg64618