Description

markshannon

opened on Apr 22, 2026

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Currently LOAD_COMMON_CONSTANT only loads 7 not-so-common constants and does so fairly inefficiently.

It could be improved in two ways:

• Add some more constants, especially None, but also "", True, False and -1
• Make the constants that it does load both statically allocated and immortal to avoid the pointer chasing and incref operation. Only any and all would need changing.

After some consideration, I think it best to leave the common constants table per interpreter, and not statically allocate them.

• The changes to any and all may be breaking.
• We also need to handle AssertionError and NotImplementedError will be tricky to make static

They should all be immortal though, and stored as _PyStackRefs not PyObject *s.

Linked PRs

• gh-148871: extend and improve LOAD_COMMON_CONSTANT #148971
• gh-148871: make LOAD_COMMON_CONSTANT use immortal stackref borrows #149625
• gh-148871: Add CONSTANT_EMPTY_TUPLE to LOAD_COMMON_CONSTANT #149688

Activity

1. markshannon

   added

   performancePerformance or resource usagePerformance or resource usage

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   on Apr 22, 2026
2. picnixz

   added

   type-featureA feature request or enhancementA feature request or enhancement

   on Apr 22, 2026
3. NekoAsakura

   added 5 commits that reference this issue on Apr 26, 2026

   Merge branch 'main' into pythongh-148871/load-common-constant

   22595cd

   Merge branch 'main' into pythongh-148871/load-common-constant

   ebd1c28

   Merge branch 'main' into pythongh-148871/load-common-constant

   558a5ac

   Merge branch 'main' into pythongh-148871/load-common-constant

   b017ae9

   Merge branch 'main' into pythongh-148871/load-common-constant

   cbd17a2
4. markshannon

   added a commit that references this issue on May 2, 2026

   gh-148871: extend and improve `LOAD_COMMON_CONSTANT` (GH-148971)

   7c9ad27
5. markshannon commented on May 2, 2026

   

   markshannon

   on May 2, 2026

   MemberAuthor

   More actions

   Now #148971 is merged, we need to make LOAD_COMMON_CONSTANT fast.

   Instead of storing an array of PyObject *s the array should contain _PyStackRefs and all objects should be made immortal.

   So, instead of

   interp->common_consts[CONSTANT_BUILTIN_ALL] = all;
   

   we should have

   _Py_SetImmortal(all);
   interp->common_consts[CONSTANT_BUILTIN_ALL] = _PyStackRef_FromPyObjectBorrow(all);
   

   most objects in the common constants set are already immortal.

   Then the code for LOAD_COMMON_CONSTANT becomes

           value = tstate->interp->common_consts[oparg];
   

   Without any need to handle refcounts.
6. eendebakpt

   added a commit that references this issue on May 11, 2026

   Add NEWS entry for pythongh-148871

   56d633a
7. NekoAsakura

   added a commit that references this issue on May 21, 2026

   Merge branch 'main' into pythongh-148871-immortal-stackref

   d81f9b6
8. markshannon

   added a commit that references this issue on May 21, 2026

   gh-148871: Add CONSTANT_EMPTY_TUPLE to LOAD_COMMON_CONSTANT (GH-149688)

   f2fa291
9. NekoAsakura

   added 2 commits that reference this issue on May 21, 2026

   Merge branch 'main' into pythongh-148871-immortal-stackref

   0cf0de2

   Merge branch 'main' into pythongh-148871-immortal-stackref

   9bbbb46
10. markshannon

    added a commit that references this issue on May 28, 2026

    gh-148871: make `LOAD_COMMON_CONSTANT` use immortal stackref borrows (G…

    39bd44f

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