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GeezerVison is showing github.com — gh-87729: improve hit rate of LOAD_SUPER_ATTR specialization by carljm · Pull Request #104270 · python/cpython

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@carljm

@carljm carljm commented May 7, 2023 •
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We observed that in stats collection on pyperformance (+ pyston macro-benchmarks), the hit rate of the LOAD_SUPER_ATTR specialization to LOAD_SUPER_ATTR_METHOD was not as good as expected. Investigation revealed a few causes for this.

  1. It is not uncommon to have super method calls that use argument unpacking (e.g. super().method(*args, **kwargs)) and so need to use e.g. CALL_FUNCTION_EX. This fails the checks for the load-method optimization in the compiler, so it emits a LOAD_SUPER_ATTR without the load-method optimization.

  2. Loading things that are not actually method descriptors via a call that looks like super().method() is also not uncommon. E.g. super().__new__() where the base class is e.g. builtin str.

  3. The type of self at a particular call-site of super() is commonly polymorphic, whenever the inheritance chain is longer than length 2. E.g. if C inherits B inherits A, then a call to super() in a method of B may commonly see self of type either B or C.

The fixes to (1) and (2) are simple enough: we should also specialize for LOAD_SUPER_ATTR_ATTR.

(3) is a much trickier problem, since it means we can't inline-cache the results of a super() lookup at all. The results of a super() lookup are dependent on the type of self, and we can't effectively specialize for the type of self (barring polymorphic inline caching, which we don't generally do and would make for a much large inline cache.)

This means that specialization of LOAD_SUPER_ATTR is just splitting out the "shadowed global super" case from the load-method and attr cases. This still preserves most of the performance improvement from LOAD_SUPER_ATTR, which always came from avoiding allocation of single-use super objects.

With this change, in my tests the hit rate of LOAD_SUPER_ATTR specialization in pyperformance is 100%. (Effectively this just means we don't have a case in pyperformance of shadowing the name super.)

  • Issue: Use dedicated opcodes to speed up calls/attribute lookups with super() as receiver #87729

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@carljm
pythongh-87729: improve hit rate of LOAD_SUPER_ATTR specialization
5b64c58
@carljm
carljm requested review from brettcannon, encukou, ericsnowcurrently, markshannon, ncoghlan and warsaw as code owners May 7, 2023 17:24
@bedevere-bot bedevere-bot mentioned this pull request May 7, 2023
Use dedicated opcodes to speed up calls/attribute lookups with super() as receiver #87729
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@bedevere-bot bedevere-bot added the awaiting core review label May 7, 2023
@carljm
carljm removed request for brettcannon, encukou, ericsnowcurrently, ncoghlan and warsaw May 7, 2023 17:24
@carljm carljm added the skip news label May 7, 2023
carljm added 3 commits May 9, 2023 10:18
@carljm
Merge branch 'main' into fixloadsuperspec
cf11908 
* main: (35 commits)
  pythongh-97696 Add documentation for get_coro() behavior with eager tasks (python#104304)
  pythongh-97933: (PEP 709) inline list/dict/set comprehensions (python#101441)
  pythongh-99889: Fix directory traversal security flaw in uu.decode() (python#104096)
  pythongh-104184: fix building --with-pydebug --enable-pystats (python#104217)
  pythongh-104139: Add itms-services to uses_netloc urllib.parse. (python#104312)
  pythongh-104240: return code unit metadata from codegen (python#104300)
  pythongh-104276: Make `_struct.unpack_iterator` type use type flag instead of custom constructor (python#104277)
  pythongh-97696: Move around and update the whatsnew entry for asyncio eager task factory (python#104298)
  pythongh-103193: Fix refleaks in `test_inspect` and `test_typing` (python#104320)
  require-pr-label.yml: Add missing "permissions:" (python#104309)
  pythongh-90656: Add platform triplets for 64-bit LoongArch (LA64) (python#30939)
  pythongh-104180: Read SOCKS proxies from macOS System Configuration (python#104181)
  pythongh-97696 Remove unnecessary check for eager_start kwarg (python#104188)
  pythonGH-104308: socket.getnameinfo should release the GIL (python#104307)
  pythongh-104310: Add importlib.util.allowing_all_extensions() (pythongh-104311)
  pythongh-99113: A Per-Interpreter GIL! (pythongh-104210)
  pythonGH-104284: Fix documentation gettext build (python#104296)
  pythongh-89550: Buffer GzipFile.write to reduce execution time by ~15% (python#101251)
  pythongh-104223: Fix issues with inheriting from buffer classes (python#104227)
  pythongh-99108: fix typo in Modules/Setup (python#104293)
  ...
@carljm
Merge branch 'main' into fixloadsuperspec
5976df9 
* main:
  pythonGH-102181: Improve specialization stats for SEND (pythonGH-102182)
  pythongh-103000: Optimise `dataclasses.asdict` for the common case (python#104364)
  pythongh-103538: Remove unused TK_AQUA code (pythonGH-103539)
  pythonGH-87695: Fix OSError from `pathlib.Path.glob()` (pythonGH-104292)
  pythongh-104263: Rely on Py_NAN and introduce Py_INFINITY (pythonGH-104202)
  pythongh-104010: Separate and improve docs for `typing.get_origin` and `typing.get_args` (python#104013)
  pythongh-101819: Adapt _io._BufferedIOBase_Type methods to Argument Clinic (python#104355)
  pythongh-103960: Dark mode: invert image brightness (python#103983)
  pythongh-104252: Immortalize Py_EMPTY_KEYS (pythongh-104253)
  pythongh-101819: Clean up _io windows console io after pythongh-104197 (python#104354)
  pythongh-101819: Harden _io init (python#104352)
  pythongh-103247: clear the module cache in a test in test_importlib/extensions/test_loader.py (pythonGH-104226)
  pythongh-103848: Adds checks to ensure that bracketed hosts found by urlsplit are of IPv6 or IPvFuture format (python#103849)
  pythongh-74895: adjust tests to work on Solaris (python#104326)
  pythongh-101819: Refactor _io in preparation for module isolation (python#104334)
  pythongh-90953: Don't use deprecated AST nodes in clinic.py (python#104322)
  pythongh-102327: Extend docs for "url" and "headers" parameters to HTTPConnection.request()
  pythongh-104328: Fix typo in ``typing.Generic`` multiple inheritance error message (python#104335)
@carljm
Merge branch 'main' into fixloadsuperspec
4456dd6 
* main:
  pythongh-87849: fix SEND specialization family definition (pythonGH-104268)
  pythongh-101819: Adapt _io.IOBase.seek and _io.IOBase.truncate to Argument Clinic (python#104384)
  pythongh-101819: Adapt _io._Buffered* methods to Argument Clinic (python#104367)
  pythongh-101819: Refactor `_io` futher in preparation for module isolation (python#104369)
  pythongh-101819: Adapt _io.TextIOBase methods to Argument Clinic (python#104383)
  pythongh-101117: Improve accuracy of sqlite3.Cursor.rowcount docs (python#104287)
  pythonGH-92184: Convert os.altsep to '/' in filenames when creating ZipInfo objects (python#92185)
  pythongh-104357: fix inlined comprehensions that close over iteration var (python#104368)
  pythonGH-90208: Suppress OSError exceptions from `pathlib.Path.glob()` (pythonGH-104141)
@markshannon markshannon mentioned this pull request May 11, 2023
gh-103865: add monitoring support to LOAD_SUPER_ATTR #103866
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@markshannon

markshannon commented May 11, 2023

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I think this is fine for 3.12.

For 3.13 we will probably want something like we had before. With larger regions of optimization which handle polymorphism through code duplication prior to specialization, we will want the information about what the value of super().attr is.
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@carljm

carljm commented May 11, 2023

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Yes, I agree; once we have a reasonable way to handle specialization in polymorphic cases, we'll want to reintroduce this. But for now I don't think we can keep it; it results in too many failed specializations.
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markshannon
markshannon approved these changes May 11, 2023
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@bedevere-bot bedevere-bot added awaiting merge and removed awaiting core review labels May 11, 2023
@carljm
carljm merged commit 7726245 into python:main May 11, 2023
@bedevere-bot bedevere-bot removed the awaiting merge label May 11, 2023
@carljm
carljm deleted the fixloadsuperspec branch May 11, 2023 14:08
carljm added a commit to carljm/cpython that referenced this pull request May 11, 2023
@carljm
Merge branch 'main' into supermon
fb47955 
* main:
  pythongh-104057: Fix direct invocation of test_support (pythonGH-104069)
  pythongh-87729: improve hit rate of LOAD_SUPER_ATTR specialization (python#104270)
  pythongh-101819: Fix inverted debug preprocessor check in winconsoleio.c (python#104388)
@freakboy3742 freakboy3742 mentioned this pull request May 28, 2023
Incompatibility with Python 3.12.0b1 beeware/rubicon-objc#313
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@freakboy3742

freakboy3742 commented May 28, 2023

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@carljm FYI I've identified this commit as the source of a backwards incompatibility in Rubicon-Objc. I'm trying to narrow down a simpler reproduction case.
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@freakboy3742 freakboy3742 mentioned this pull request May 28, 2023
3.12.0b1 includes backwards incompatible change to operation of super() #105035
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