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gh-131798: JIT: optimize _LOAD_COMMON_CONSTANT by trdthg · Pull Request #146104 · python/cpython · GitHub

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gh-131798: JIT: optimize _LOAD_COMMON_CONSTANT - #146104

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Fidget-Spinner merged 1 commit into
python:mainfrom
trdthg:trdthg/feature/jit-load-common-constant
Mar 19, 2026
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gh-131798: JIT: optimize _LOAD_COMMON_CONSTANT#146104
Fidget-Spinner merged 1 commit into
python:mainfrom
trdthg:trdthg/feature/jit-load-common-constant

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trdthg commented Mar 18, 2026 •
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Try to learn and make a small contribution :D

bedevere-app Bot commented Mar 18, 2026

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Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

python-cla-bot Bot commented Mar 18, 2026 •
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bedevere-app Bot mentioned this pull request Mar 18, 2026
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Fidget-Spinner approved these changes Mar 18, 2026
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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Thanks, this LGTM! Please remove the news entry, we don't need it as it's not a user facing code.

trdthg force-pushed the trdthg/feature/jit-load-common-constant branch from 068d2bb to 19fc90f Compare March 18, 2026 11:40

bedevere-app Bot commented Mar 18, 2026

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Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

Fidget-Spinner commented Mar 18, 2026

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_LOAD_COMMON_CONSTANT x86_64 dissasembly in jit_stencils-x86_64-unknown-linux-gnu.h:

    // 0000000000000000 <_JIT_ENTRY>:
    // 0: 49 8b 47 10                   movq    0x10(%r15), %rax
    // 4: 48 b9 00 00 00 00 00 00 00 00 movabsq $0x0, %rcx
    // 0000000000000006:  R_X86_64_64  _JIT_OPARG
    // e: 0f b7 c9                      movzwl  %cx, %ecx
    // 11: 48 8b bc c8 60 68 03 00       movq    0x36860(%rax,%rcx,8), %rdi
    // 19: 8b 07                         movl    (%rdi), %eax
    // 1b: 85 c0                         testl   %eax, %eax
    // 1d: 78 06                         js      0x25 <_JIT_ENTRY+0x25>
    // 1f: ff c0                         incl    %eax
    // 21: 89 07                         movl    %eax, (%rdi)
    // 23: eb 04                         jmp     0x29 <_JIT_ENTRY+0x29>
    // 25: 48 83 cf 01                   orq     $0x1, %rdi

I think this is prior to our CFG optimizations in the backend, so it's not 100% accurate, but pretty close.

_LOAD_CONST_INLINE_BORROW:

    // 
    // _LOAD_CONST_INLINE_BORROW_r01.o:       file format elf64-x86-64
    // 
    // Disassembly of section .text:
    // 
    // 0000000000000000 <_JIT_ENTRY>:
    // 0: 48 bf 00 00 00 00 00 00 00 00 movabsq $0x0, %rdi
    // 0000000000000002:  R_X86_64_64  _JIT_OPERAND0
    // a: 48 83 cf 01                   orq     $0x1, %rdi

This is a really nice reduction. Good job!

Fidget-Spinner reviewed Mar 18, 2026
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Comment thread Lib/test/test_capi/test_opt.py Outdated
trdthg force-pushed the trdthg/feature/jit-load-common-constant branch from 19fc90f to b37ec56 Compare March 18, 2026 12:30

Fidget-Spinner commented Mar 18, 2026

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We generally don't force push, because all PRs in CPython are squash-merged. So just push normal commits, thanks!

Fidget-Spinner approved these changes Mar 18, 2026
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Once again, LGTM. Thanks for this!

Fidget-Spinner merged commit 98977ca into python:main Mar 19, 2026
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pablogsal mentioned this pull request Apr 4, 2026
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ljfp pushed a commit to ljfp/cpython that referenced this pull request Apr 25, 2026
pythongh-131798: JIT: optimize _LOAD_COMMON_CONSTANT (pythonGH-146104)
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Fidget-Spinner Fidget-Spinner approved these changes
markshannon Awaiting requested review from markshannon markshannon is a code owner
tomasr8 Awaiting requested review from tomasr8 tomasr8 is a code owner
savannahostrowski Awaiting requested review from savannahostrowski

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