Title: AST-level Constant folding
Type: enhancement Stage: patch review
Components: Interpreter Core Versions: Python 3.7
Status: open Resolution:
Dependencies: 29463 Superseder:
Assigned To: Nosy List: benjamin.peterson, brett.cannon, georg.brandl, haypo, inada.naoki, ncoghlan, serhiy.storchaka, yselivanov
Priority: normal Keywords: patch

Created on 2017-02-07 04:02 by inada.naoki, last changed 2017-07-25 07:10 by inada.naoki.

File name Uploaded Description Edit
ast-constant-folding.patch inada.naoki, 2017-02-07 04:02 review
Pull Requests
URL Status Linked Edit
PR 2858 open inada.naoki, 2017-07-25 07:10
Messages (6)
msg287186 - (view) Author: INADA Naoki (inada.naoki) * (Python committer) Date: 2017-02-07 04:02
spin off of #11549.
This patch uses code generator to traverse AST.
msg287210 - (view) Author: STINNER Victor (haypo) * (Python committer) Date: 2017-02-07 08:55
I suggest you to look at my AST optimizer, especially the constant folding part:

And the unit tests, search for BaseConstantFoldingTests:

IHMO we must have a long test suite on this AST optimizer, because it's common that the AST changes in subtle ways, AST is complex and so we should prevent regressions. You may simply copy my unit tests.

My optimizer implements more optimization: just remove unit tests on cases which you don't want to optimize.
msg287214 - (view) Author: STINNER Victor (haypo) * (Python committer) Date: 2017-02-07 09:01
With this change, the Python compiler doesn't emit ast.Num nor ast.Str, right?

If we merge such change, we should prepare projects using AST. There is something like that in pip, but I failed to remind which one :-/ It should be easy: apply your patch, try to install something using pip and see the traceback ;-)
msg287227 - (view) Author: INADA Naoki (inada.naoki) * (Python committer) Date: 2017-02-07 11:32
Do you mean ?

This doesn't affect, maybe.
Constant folding is executed right before producing bytecode.
It doesn't affect to PyCF_ONLY_AST.

BTW, how do you feel

I feel it's too much only for constant folding, but it is too less for other advanced optimizations.
Actually, original patch in #11549 implements other optimizations
ported from peephole in compile.c.
And most tough part of updating this patch is resolve conflict with this commit.

I'll try to remove and ast_opt.ct in next version.
msg297596 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2017-07-03 14:26
In general the patch LGTM. I haven't found bugs.

I think that at this stage we can and ast_opt.ct and use just their result, ast_opt.c (maybe rename to optimize.c?) The grammar is not often changed, and in that case it would be not hard to modify the code manually. In any case compile.c should be modified manually. After removing no-op functions like astfold_operator() and inlining simple functions like astfold_arg() the code should be clearer.

Instead of converting all kinds of constants to Constant_kind, you could use is_const() and get_const_value() from compile.c.

I suggest to remove the parts of the peepholer that are superseeded by the AST optimizer.

As for preventing expensive calculations, there is a patch for the peepholer that does this. I wait on implementing the AST-level constant folding for adapting that patch for it.
msg297599 - (view) Author: STINNER Victor (haypo) * (Python committer) Date: 2017-07-03 14:39
Naoki: Can you please create a PR for your patch?
Date User Action Args
2017-07-25 07:10:59inada.naokisetpull_requests: + pull_request2909
2017-07-03 14:39:54hayposetmessages: + msg297599
2017-07-03 14:26:45serhiy.storchakasetmessages: + msg297596
2017-02-07 11:32:27inada.naokisetmessages: + msg287227
2017-02-07 09:10:57serhiy.storchakasetnosy: + brett.cannon, georg.brandl, ncoghlan, benjamin.peterson, serhiy.storchaka, yselivanov

type: enhancement
components: + Interpreter Core
stage: patch review
2017-02-07 09:01:57hayposetmessages: + msg287214
2017-02-07 08:55:31hayposetnosy: + haypo
messages: + msg287210
2017-02-07 04:02:52inada.naokisetdependencies: + Add `docstring` field to AST nodes
2017-02-07 04:02:38inada.naokicreate