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Place dict (and values) pointers at a fixed (negative) offset from the base of the object. #90105

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markshannon opened this issue Dec 1, 2021 · 2 comments
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Place dict (and values) pointers at a fixed (negative) offset from the base of the object. #90105

markshannon opened this issue Dec 1, 2021 · 2 comments
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3.11 only security fixes interpreter-core (Objects, Python, Grammar, and Parser dirs) performance Performance or resource usage

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BPO 45947
Nosy @markshannon, @Fidget-Spinner
PRs
  • bpo-45947: Place dict and values pointer at fixed (negative) offset just before GC header. #29879
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    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/markshannon'
closed_at = <Date 2022-01-20.11:51:02.049>
created_at = <Date 2021-12-01.13:30:48.955>
labels = ['interpreter-core', '3.11', 'performance']
title = 'Place dict (and values) pointers at a fixed (negative) offset from the base of the object.'
updated_at = <Date 2022-01-20.11:51:02.049>
user = 'https://github.com/markshannon'

    bugs.python.org fields:

    activity = <Date 2022-01-20.11:51:02.049>
actor = 'Mark.Shannon'
assignee = 'Mark.Shannon'
closed = True
closed_date = <Date 2022-01-20.11:51:02.049>
closer = 'Mark.Shannon'
components = ['Interpreter Core']
creation = <Date 2021-12-01.13:30:48.955>
creator = 'Mark.Shannon'
dependencies = []
files = []
hgrepos = []
issue_num = 45947
keywords = ['patch']
message_count = 2.0
messages = ['407457', '407946']
nosy_count = 2.0
nosy_names = ['Mark.Shannon', 'kj']
pr_nums = ['29879']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue45947'
versions = ['Python 3.11']
    @markshannon
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    To get to the dict (or values array) of an object, we currently need 3 dependent loads.
    By placing the dict at a fixed offset, this can be reduced to one.

    What was obj[obj->type->dictoffset] becomes obj[FIXED_OFFSET]

    See faster-cpython/ideas#80, specifically
    faster-cpython/ideas#80 (comment) for more details.

    @markshannon markshannon added the 3.11 only security fixes label Dec 1, 2021
    @markshannon markshannon self-assigned this Dec 1, 2021
    @markshannon markshannon added 3.11 only security fixes interpreter-core (Objects, Python, Grammar, and Parser dirs) performance Performance or resource usage labels Dec 1, 2021
    @markshannon
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    New changeset 8319114 by Mark Shannon in branch 'main':
    bpo-45947: Place dict and values pointer at fixed (negative) offset just before GC header. (GH-29879)
    8319114

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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