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GeezerVison is showing github.com — GH-132554: "Virtual" iterators by markshannon · Pull Request #132555 · python/cpython

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@markshannon

@markshannon markshannon commented Apr 15, 2025 •
edited by bedevere-app Bot
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Just a draft PR until I have performance numbers.

  • Issue: Use tagged ints for faster iteration #132554

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@bedevere-app bedevere-app Bot mentioned this pull request Apr 15, 2025
Use tagged ints for faster iteration #132554
Open
@markshannon
markshannon force-pushed the virtual-iterators branch from 417cd59 to 6c955e0 Compare April 16, 2025 09:26
@markshannon

markshannon commented Apr 16, 2025

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Performance is good. Nothing amazing, but a small speedup.

Stats show no significant changes
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markshannon added 7 commits April 29, 2025 18:22
@markshannon
FOR_ITER now pushes NULL as well as the iterator. Preparation for vir…
7476442 
…tual iterators
@markshannon
use tagged ints for indexes. Work in progress
38a429f
@markshannon
Remove debug code
2caf56f
@markshannon
Regenerate files
588943a
@markshannon
Tidy up list of non-escaping functions
aa62e39
@markshannon
Fix up list iteration for FT build
88562ec
@markshannon
Fix tier 2 FT build
025049d
@markshannon
markshannon force-pushed the virtual-iterators branch from a4b740d to 025049d Compare April 29, 2025 17:29
@markshannon markshannon added the skip news label Apr 29, 2025
markshannon added 5 commits April 30, 2025 10:11
@markshannon
Remove debugging code
35e389d
@markshannon
Merge branch 'main' into virtual-iterators
e8f4ce6
@markshannon
Rename function
ed89950
@markshannon
Restrict specialization in free-threaded build
ec8d797
@markshannon
Merge branch 'main' into virtual-iterators
cad1946
@markshannon
markshannon marked this pull request as ready for review April 30, 2025 11:38
@markshannon
markshannon requested review from Fidget-Spinner, ericsnowcurrently and iritkatriel as code owners April 30, 2025 11:38
@bedevere-app bedevere-app Bot added the awaiting core review label Apr 30, 2025
@markshannon
Add news
428735b
iritkatriel
iritkatriel reviewed Apr 30, 2025
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Comment thread Include/internal/pycore_stackref.h Resolved

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Comment thread Python/specialize.c Resolved

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Comment thread Python/stackrefs.c Resolved

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Comment thread Python/ceval.c Resolved

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Comment thread Python/ceval.c Resolved

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markshannon added 2 commits April 30, 2025 17:12
@markshannon
handle tagged ints when doing type checks
4c83848
@markshannon
Fix long check
f43ccc3
Fidget-Spinner
Fidget-Spinner reviewed Apr 30, 2025
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Comment thread Python/ceval.c Resolved

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markshannon added 2 commits April 30, 2025 20:05
@markshannon
Attempt to make _PyForIter_NextWithIndex thread safe.
3fd46c3
@markshannon
Add review comment
433282f
Fidget-Spinner
Fidget-Spinner reviewed May 1, 2025
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Comment thread Python/specialize.c Resolved

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markshannon added 3 commits May 8, 2025 10:55
@markshannon
Simplify list indexing code
e915a05
@markshannon
Merge branch 'main' into virtual-iterators
69a328d
@markshannon
GET_ITER may leave the iterable on the stack
6d1b93e
@markshannon markshannon mentioned this pull request May 8, 2025
LOAD_FAST_BORROW not being used even when safe to do so, if value is live at BB end. #133672
Open
@markshannon
Fix test_dis
37ca285
@ljfp ljfp mentioned this pull request May 8, 2025
gh-133672: Allow LOAD_FAST to be optimized to LOAD_FAST_BORROW #133721
Closed
@Fidget-Spinner

Fidget-Spinner commented May 11, 2025

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@markshannon I don't think it matters here, but you didn't update in https://github.com/python/cpython/pull/132545/files Py_TAG_BITS to 3. It's still 1. I know it "technically" doesn't matter because we use a bitshift to zero it out, but we should still update it to be consistent.
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@markshannon
Merge branch 'main' into virtual-iterators
f3b9074
@markshannon
markshannon force-pushed the virtual-iterators branch from efe465d to f3b9074 Compare May 19, 2025 13:42
markshannon added 3 commits May 20, 2025 16:49
@markshannon
Merge branch 'main' into virtual-iterators
0efab59
@markshannon
Merge branch 'main' into virtual-iterators
a0d814b
@markshannon
Merge branch 'main' into virtual-iterators
5cd55c4
@markshannon

markshannon commented May 22, 2025

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@markshannon I don't think it matters here, but you didn't update in https://github.com/python/cpython/pull/132545/files Py_TAG_BITS to 3. It's still 1. I know it "technically" doesn't matter because we use a bitshift to zero it out, but we should still update it to be consistent.

Fixed in #134244
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@markshannon
Merge branch 'main' into virtual-iterators
867bd10
@markshannon markshannon mentioned this pull request May 27, 2025
[3.14] GH-128161: Remove redundant GET_ITER from list comprehension code #134778
Merged
iritkatriel
iritkatriel reviewed May 27, 2025
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Comment thread Include/internal/pycore_stackref.h Outdated
static inline _PyStackRef
PyStackRef_IncrementTaggedIntNoOverflow(_PyStackRef ref)
{
assert(ref.bits != (uintptr_t)-1); // Deosn't overflow

@iritkatriel iritkatriel May 27, 2025

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I don't understand why you use this condition. Should it not be assert(ref.bits + 4 > ref.bits) or something like that?

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markshannon added 2 commits May 27, 2025 12:15
@markshannon
Clarify assert
d9dc597
@markshannon
Checked for tagged ints
d60ef23
iritkatriel
iritkatriel reviewed May 27, 2025
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Comment thread Include/internal/pycore_stackref.h Outdated
return false;
}
return PyFunction_Check(PyStackRef_AsPyObjectBorrow(stackref));
}

@iritkatriel iritkatriel May 27, 2025

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Would it help to define these via a macro? Something like

#define STACKREF_CHECK_FUNC(T) \
    static inline bool \
    PyStackRef_ ## T ## Check(_PyStackRef stackref) \
        if (PyStackRef_IsTaggedInt(stackref)) { \
            return false; \
        } \
        return Py ## T ## _Check(PyStackRef_AsPyObjectBorrow(stackref)); \
    }

...
STACKREF_CHECK_FUNC(Exception);
STACKREF_CHECK_FUNC(Code);
STACKREF_CHECK_FUNC(Function);

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@Fidget-Spinner Fidget-Spinner May 27, 2025

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I think it might not work when want to define variants of Check and CheckExact, though we can always define two macros for that if we go down this route.

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Comment thread Lib/test/test_list.py
iterable doesn't prematurely free the iterable"""

def foo(x):
r = 0

@iritkatriel iritkatriel May 27, 2025

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I'd add this to make sure the test is testing what the comment is saying.
assert(sys.getrefcount(x) == 1)

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Comment thread Python/stackrefs.c Outdated
_PyStackRef
PyStackRef_IncrementTaggedIntNoOverflow(_PyStackRef ref)
{
assert(ref.index != (uintptr_t)-1); // Overflow

@iritkatriel iritkatriel May 27, 2025

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Do here same as in d9dc597 ?

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@markshannon
Address review comments
9a9d20d
iritkatriel
iritkatriel approved these changes May 27, 2025
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@bedevere-app bedevere-app Bot added awaiting merge and removed awaiting core review labels May 27, 2025
@markshannon
markshannon merged commit f6f4e8a into python:main May 27, 2025
@bedevere-app bedevere-app Bot removed the awaiting merge label May 27, 2025
@markshannon
markshannon deleted the virtual-iterators branch May 27, 2025 14:59
Pranjal095 pushed a commit to Pranjal095/cpython that referenced this pull request Jul 12, 2025
@markshannon @Pranjal095
pythonGH-132554: "Virtual" iterators (pythonGH-132555)
03f4000 
* FOR_ITER now pushes either the iterator and NULL or leaves the iterable and pushes tagged zero

* NEXT_ITER uses the tagged int as the index into the sequence or, if TOS is NULL, iterates as before.
taegyunkim pushed a commit to taegyunkim/cpython that referenced this pull request Aug 4, 2025
@markshannon @taegyunkim
pythonGH-132554: "Virtual" iterators (pythonGH-132555)
b3fb901 
* FOR_ITER now pushes either the iterator and NULL or leaves the iterable and pushes tagged zero

* NEXT_ITER uses the tagged int as the index into the sequence or, if TOS is NULL, iterates as before.
@ljfp ljfp mentioned this pull request Apr 25, 2026
gh-133672: Allow LOAD_FAST to be optimized to LOAD_FAST_BORROW #148999
Open
gostak-dd pushed a commit to gostak-dd/cpython that referenced this pull request Jun 2, 2026
@markshannon @gostak-dd
pythonGH-132554: "Virtual" iterators (pythonGH-132555)
88df9e9 
* FOR_ITER now pushes either the iterator and NULL or leaves the iterable and pushes tagged zero

* NEXT_ITER uses the tagged int as the index into the sequence or, if TOS is NULL, iterates as before.
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@Fidget-Spinner Fidget-Spinner Fidget-Spinner left review comments
@iritkatriel iritkatriel iritkatriel approved these changes
@ericsnowcurrently ericsnowcurrently Awaiting requested review from ericsnowcurrently ericsnowcurrently is a code owner

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@markshannon @Fidget-Spinner @iritkatriel
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