make BUILD_MAP use it's argument

[mwhudson]

BPO	402227
Nosy	@mwhudson, @gvanrossum, @serhiy-storchaka
Files	None: None

^{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 = None
closed_at = <Date 2017-02-11.15:27:53.146>
created_at = <Date 2000-11-02.16:56:07.000>
labels = ['interpreter-core']
title = "make BUILD_MAP use it's argument"
updated_at = <Date 2017-02-11.15:27:53.146>
user = 'https://github.com/mwhudson'

bugs.python.org fields:

activity = <Date 2017-02-11.15:27:53.146>
actor = 'serhiy.storchaka'
assignee = 'jhylton'
closed = True
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2000-11-02.16:56:07.000>
creator = 'mwh'
dependencies = []
files = ['2909']
hgrepos = []
issue_num = 402227
keywords = ['patch']
message_count = 5.0
messages = ['34744', '34745', '34746', '34747', '287604']
nosy_count = 4.0
nosy_names = ['mwh', 'gvanrossum', 'jhylton', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'rejected'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue402227'
versions = []

[mwhudson]

No description provided.

[mwhudson]

This patch makes BUILD_MAP more like BUILD_LIST, and uses these newfound abilities to compile literal dictionaries into code more like that for lists and tuples.

No reason, really, beyong asthetics & the fact that this'll make some hacks I want to inflict on the function call mechanism easier...

[gvanrossum]

I'll give this to Jeremy for consideration, since he's working on a restructuring of the function call code anyway. I'll note thta this is really low priority.

[jhylton]

While this change make the generated code a lot simpler, it
also has a high cost in speed and memory. The stack for a code
object needs to be big enough to hold all the keys and values,
which can be costly. The pybench dict creation benchmark slows
down about 15%.

[serhiy-storchaka]

After all this change was implemented as a part of PEP-448 implementation (bpo-2292). But it was not documented and current documentation of the BUILD_MAP opcode doesn't match the implementation. See also bpo-26213.