Optimize out __debug__ at the AST level

[serhiy-storchaka]

BPO	32372
Nosy	@rhettinger, @pitrou, @methane, @serhiy-storchaka
PRs	bpo-32372: Move __debug__ optimization to the AST level. #4925

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2017-12-25.10:48:57.560>
created_at = <Date 2017-12-19.14:11:45.504>
labels = ['interpreter-core', 'type-feature', '3.7']
title = 'Optimize out __debug__ at the AST level'
updated_at = <Date 2017-12-25.10:48:57.560>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2017-12-25.10:48:57.560>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2017-12-25.10:48:57.560>
closer = 'serhiy.storchaka'
components = ['Interpreter Core']
creation = <Date 2017-12-19.14:11:45.504>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 32372
keywords = ['patch']
message_count = 2.0
messages = ['308643', '309035']
nosy_count = 4.0
nosy_names = ['rhettinger', 'pitrou', 'methane', 'serhiy.storchaka']
pr_nums = ['4925']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue32372'
versions = ['Python 3.7']

[serhiy-storchaka]

__debug__ is substituted by the constant value at the code generation stage (see bpo-27169). This prevents it from participating in constant folding at the AST level. The proposed patch moves this optimization to the AST level. This will lead to optimizing "if not __debug__" and will allow to add more optimizations at the AST level (like optimizing expressions "a if __debug__ else b" and "__debug__ and a").

[serhiy-storchaka]

New changeset 3dfbaf5 by Serhiy Storchaka in branch 'master':
bpo-32372: Move __debug__ optimization to the AST level. (bpo-4925)
3dfbaf5